UniUjd States Office of EPA/520/1-75-001
Environmental Protection Radiation Programs December 1988
Agency Washington, D.C. 20460
Radiation
Manual of Protective
Action Guides and Protective
Actions for Nuclear Incidents
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MANUAL OF PROTECTIVE ACTION GUIDES AND PROTECTIVE ACTIONS
FOR NUCLEAR INCIDENTS
Office of Radiation Programs
United States Environmental Protection Agency
Washington, DC 20460
1989
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CONTENTS
Page
PREFACE vi
1. Overview 1-1
1.0 Introduction 1-1
1.1 Accident Phases and Protective Actions 1-3
1.2 Basis for Selecting PAG Values 1-5
1.3 Planning 1-6
1.4 Implementation of PAGs 1-7
References 1-9
2. Protective Action Guides for the Early Phase 2-1
2.1 Introduction 2-1
2.2 Exposure Pathways and the Population Affected 2-2
2.3 The Protective Action Guides 2-4
2.4 Dose Projection 2-8
2.5 Emergency Worker Limits 2-9
3. Protective Action Guides for the Intermediate Phase
(Food and Water) 3-1
4. Protective Action Guides for the Intermediate Phase
(Deposited Radioactive Materials) 4-1
4.1 Introduction 4-1
4.1.1 Exposure Pathways 4-3
4.1.2 The Population Affected 4-3
4.2 The Protective Action Guides for Deposited Radioactivity . . 4-4
4.2.1 Longer Term Objectives of the Protective Action Guides 4-5
4.2.2 Applying the Protective Action Guides for Relocation . 4-7
4.3 Exposure Limits for Persons Reentering the Restricted Zone . 4-8
References 4-9
5. Implementing the Protective Action Guides for the.Early Phase . . 5-1
5.1 Introduction 5-1
5.2 Initial Response and Sequence of Subsequent Actions 5-1
5.2.1 Notification 5-3
5.2.2 Immediate Protective Action 5-3
5.3 The Establishment of Exposure Patterns 5-5
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Page
5.4 Dose Projection 5-7
5.4.1 Duration of Exposure 5-7
5.4.2 Dose Conversion Factors 5-9
5.4.3 Relative Importance of Exposure Pathways 5-17
5.5 Protective Actions 5-19
5.5.1 Evacuation 5-21
5.5.2 Sheltering 5-22
5.5.3 Dual Protective Actions 5-26
5.5.4 General Guidance for Evacuation and Sheltering .... 5-27
References 5-30
6. Implementing the PAGs for the Intermediate Phase (Food and Water). 6-1
7. Implementing the Protective Action Guides for the Intermediate
Phase (Deposited Materials) 7-1
7.1 Introduction 7-1
7.1.1 Protective Actions 7-2
7.1.2 Areas Involved 7-2
7.1.3 Sequence of Events 7-4
7.2 Establishment of Isodose Rate Lines 7-7
7.3 Dose Projection 7-8
7.3.1 Projected External Gamma Dose 7-10
7.3.2 Inhalation Dose Projection 7-17
7.4 Priorities * 7-21
7.5 Reentry 7-21
7.6 Surface Contamination Control 7-22
7.6.1 Considerations and Constraints 7-22
7.6.2 Numerical Relationships 7-24
7.6.3 Recommended Surface Contamination Limits 7-24
References 7-28
8. Radiation Protection Guidance for Recovery 8-1
iii
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Page
TABLES
1-1 Exposure Pathways, Accident Phases, and Protective Actions . 1-4
2-1 PAGs for the Early Phase of a Nuclear Incident 2-5
2-2 Dose Limits for Emergency Workers 2-11
2-3 Acute Health Effects Associated with Whole-Body Absorbed
Doses 2-12
2-4 Average Cancer Risk to Emergency Workers Receiving 25 Rems
Whole-Body Dose 2-12
4-1 Protective Action Guides for Exposure to Deposited
Radioactivity During the Intermediate Phase of a Nuclear
Incident 4-4
4-2 Estimated Maximum Dose to Persons Not Relocated 4-6
5-1 Dose Conversion Factors (DCF) and Dose Response Levels (DRL)
for External Exposure due to Immersion in Contaminated Air . 5-10
5-2 Dose Conversion Factors (DCF) and Dose Response Levels (DRL)
for Doses due to Inhalation and from Material Deposited on
Skin and Clothing 5-12
5-3 Dose Conversion Factors (DCF) and Derived Response Levels
(DRL) for 4-Day Exposure to Gamma Radiation from Deposited
Radionuclides 5-14
5-4 Dose Conversion Factors (DCF) and Derived Response Levels
(DRL) for Combined Exposure Pathways during the Early Phase
5-5 Comparison of Projected Doses for Various Accident Scenarios 5-18
5-6 Representative Dose Reduction Factors for Direct Radiation . 5-23
5-7 Dose Reduction Factors for Inhalation 5-25
7-1 Initial gamma exposure rate and the effective dose equivalent
(corrected for radioactive decay and weathering) calculated
from an initial radioactive concentration of 1 pCi/m^ on
ground surface 7-11
7-2 Initial exposure rate and the effective dose equivalent
(corrected for radioactive decay) calculated from an initial
radionuclide concentration of 1 pCi/m^ on ground surface . 7-12
7-3 Example calculation of dose conversion factors for gamma
exposure rate measurements based on measured isotopic
concentrations 7-15
7-4 Dose conversion factors for inhalation 7-19
7-5 Skin beta dose conversion factors for exposure to deposited
radionuclides 7-20
7-6 Recommended surface contamination screening levels for persons
and other surfaces at monitoring stations in low background
radiation areas 7-26
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7-7 Recommended surface contamination screening levels for persons
and other surfaces at screening or monitoring stations in high
background radiation areas 7-27
FIGURES
7-1 Response areas 7-3
7-2 Time frame of response to a major nuclear reactor accident . 7-5
APPENDICES
A. Glossary A-l
B. (Reserved)
C. Protective Action Guides for the Early Phase:
Supporting Information C-l
D. (Reserved)
E. (Reserved)
F. Protective Action Guides for the Intermediate Phase:
(Deposited Materials): Supporting Information F-l
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PREFACE
Public officials are charged with the responsibility to protect the
health of the public during hazardous situations. The purpose of this
Manual is to assist these officials in establishing emergency response
plans, and in making decisions during a nuclear accident. It provides
radiological protection guidance for responding to nuclear incidents or
radiological emergencies and procedures for their implementation.
In conformance with regulations on radiological emergency planning
and preparedness issued by the Federal Emergency Management Agency
(47FR10758, March 11, 1982), the Environmental Protection Agency's
responsibilities include, among others, (1) to establish Protective Action
Guides (PAGs), (2) to prepare guidance on implementing PAGs, including
recommendations on protective actions, (3) to develop and promulgate
guidance to State and local governments on the preparation of emergency
response plans, and (4) to develop, implement, and present training
programs for State and local officials on PAGs and protective actions,
radiation dose assessment, and decision making. This document is intended
to respond to the first two of these responsibilities.
The Manual is organized to provide first, a general discussion of
Protective Action Guides (PAGs) and their use in planning for protective
actions to safeguard the public. The Manual then provides PAGs for
specific exposure pathways and associated time periods. This is followed
by guidance for their implementation. In addition, appendices describe
the rationale for the choice of the numerical values of the PAGs.
This revised Manual supercedes the 1980 edition. Previously issued
Appendix D "Technical Bases for Dose Projection Methods" has been deleted,
and the relevant portions have been incorporated into Chapter 5. PAGs for
ingestion of food and water and radiation protection guidance for recovery
will be incorporated at a later date. The chapters and appendices which
will address these are reserved. When they are completed, this Manual
will be reissued.
VI
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These PAGs are published on an interim basis in order to provide
timely guidance to officials who are charged with developing emergency
response plans. After some experience is gained in application of these
recommendations, they will be reexamined and final guidance issued. Users
of this Manual are encouraged to provide comments and suggestions for
improving its contents. Comments should be sent to Joe E. Logsdon, Guides
and Criteria Branch, Criteria and Standards Division, Office of Radiation
Programs, US Environmental Protection Agency, Washington, DC 20460.
Richard J. Guimond, Director Date
Office of Radiation Programs
VII
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CHAPTER 1
Overview
1.0 Introduction
Public officials are charged to protect the health of the public
during hazardous situations. In discharging this responsibility, they
will usually be faced with decisions that must be made in a short period
of time. A number of factors influencing the choice of protective actions
will exist, but the decision may be complex, and all of the information
needed to make the optimum choice will usually not be immediately
available. In situations where a public official must rapidly, make
decisions it is helpful if the complexity of the decisions needed can be
reduced during the accident response planning phase.
The Environmental Protection Agency has developed this Manual in
order to assist public officials in their decisionmaking process for
nuclear accidents. The Manual provides radiological protection criteria
for responding to nuclear incidents or radiological emergencies and
procedures for their implementation. These recommendations are for the
use of those at the national, State, and local government levels with
responsibility for emergency response planning. In the context of this
Manual, a nuclear incident is defined as an event or a series of events
leading to the release, or potential release, into the environment of
radioactive materials in sufficient quantity to warrant consideration of
protective actions. (The terms "incident" and "accident" have the same
meaning in the context of this Manual.) A radiological emergency may
result from an incident at a facility that is or is not part of the
nuclear fuel cycle, or from the transportation of radioactive materials.
This radiation protection guidance is intended to apply to all
radiological emergency response situations, other than nuclear war.
The decision to require members of the public to take an action to
protect themselves from radiation from a nuclear incident involves a
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complex judgment in which the risk avoided by the protective action must
be weighed against the risks and costs involved in taking the action.
Furthermore, the decision may have to be made under emergency conditions,
with little or no detailed information available. Therefore, considerable
planning is necessary to reduce to a manageable level the types of
decisions required to effectively protect the public.
The objective of emergency planning is to simplify the choice of
possible responses so that judgments are required only for viable
alternatives when an emergency occurs. During the planning process it is
possible to make some value judgments and determine which responses are
not required, which decisions can be made on the basis of prior judgments,
and which judgments must be made during an actual emergency. From this
exercise, it is then possible to devise operational plans which can be
used to respond to the spectrum of hazardous situations which may develop.
The main contribution to the protection of the public from abnormal
releases from a nuclear facility is provided by site selection, design,
quality assurance in construction, the engineered safety systems of the
installation, and the competence of staff in its safe operation and
maintenance. These measures can reduce both the probability of an
accident and the magnitude of potential consequences. Despite these
measures, the occurrence of accidents cannot be excluded. Accordingly,
emergency response planning to mitigate the consequences of an accident is
a necessary supplementary level of protection.
In an accident, the source of exposure is, by definition, not under
control and the exposure of members of the public can only be limited by
some form of intervention which will disrupt normal living. Such
intervention is termed protective action. A Protective Action Guide (PAG)
is the projected dose to standard man, or other defined individual, from
an accidental release of radioactive material at which a specific
protective action to reduce (or avoid) that dose is warranted. The
objective of this manual is to provide such PAGs for the principal
protective actions available to responsible public officials during a
nuclear accident, and to provide guidance for their use.
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1.1 Accident Phases and Protective Actions
It is convenient to identify three time phases which are generally
accepted as being common to all accident sequences; within each, different
considerations apply most to protective actions. These are termed the
early, intermediate and late phases. Although these phases cannot be
represented by precise periods and may overlap, they provide a useful
framework for the considerations involved in emergency response planning.
The early phase (also referred to as the emergency phase) is the
period at the beginning of a nuclear accident when immediate decisions for
effective use of protective actions are required and these must therefore
be based primarily on predictions of radiological conditions in the
environment from the condition of the source. This phase may last from
hours to days.
The intermediate phase is the period beginning after the the accident
source and releases have been brought under control and reliable
environmental measurements are available for use as a basis for decisions
on additional protective actions. It extends until these protective
actions are terminated. This phase may overlap the early and later phase
and may last from weeks to many months.
The late phase (also referred to as the recovery phase) is the period
beginning when recovery action designed to reduce radiation levels to
permanently acceptable levels are commenced, and ending when all recovery
actions have been completed. This period may extend from months to years.
The protective actions available to avoid or reduce radiation dose
can be categorized as a function of exposure pathway and accident phase,
as shown in Table 1-1. Sheltering (supplemented by bathing and changes of
clothing), administration of stable iodine and evacuation are the
principal protective actions for use during the early phase to protect the
public from exposure to direct radiation and inhalation from an airborne
plume. Some protective actions are not addressed by these PAGs. Although
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TABLE 1-1. EXPOSURE PATHWAYS, ACCIDENT PHASES,
AND PROTECTIVE ACTIONS.
POTENTIAL EXPOSURE PATHWAYS
AND ACCIDENT PHASES
PROTECTIVE
ACTIONS
1. External radiation from
facility
2. External radiation from plume
3. Inhalation of activity in
plume
4. Contamination of skin and
clothes
Early
5. External radiation from
ground deposition of activity
6. Inhalation of resuspended
activity
7. Ingestion of contaminated
food and water
Sheltering
Evacuation
Control of access
Sheltering
Evacuation
Control of access
Sheltering
Administration of stable iodine
Evacuation
Control of access
Sheltering
Evacuation
Decontamination of persons
Intermediate Evacuation
Late
Relocation
Decontamination of land
and property
Relocation
Decontamination of land
and property
Food and water controls
Note: The use of stored animal feed to limit the uptake of radionuclides by domestic
animals in the food chain can be applicable in any of the phases.
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the use of simple, ad hoc respiratory protection may be applicable for
supplementary protection In some circumstances, this protective action Is
primarily for use by emergency workers. The control of access to areas Is
also a protective action whose Introduction Is coupled to a decision to
Implement one of the early or Intermediate phase protective actions and is
not discussed separately.
Relocation and decontamination are the principal protective actions
for protection of the public from whole body external exposure due to
deposited material and from inhalation of any resuspended radioactive
particulate materials during the intermediate and late phases. It is
assumed that decisions will be made during the intermediate phase
concerning whether relocated areas will be decontaminated and reoccupied,
or condemned and the occupants permanently relocated. The second major
type of protective action during the intermediate phase encompasses
restrictions on the use of contaminated food and water. This protective
action, in particular, may overlap earlier and later phases.
It is necessary to distinguish between evacuation and relocation with
regard to accident phases. Evacuation is the urgent removal of people
from an area to avoid or reduce high-level, short-term exposure, usually
from the plume or deposited activity. Relocation, on the other hand, is
the removal or continued exclusion of people from contaminated areas to
avoid chronic radiation exposure. Conditions may develop in which some
groups who have been evacuated in an emergency may be allowed to return
based on the relocation PAGs, while others may be converted to relocation
status.
1.2 Basis for Selecting PAG Values
The PAGs in this manual incorporate the concepts and guidance
contained in Federal Radiation Council (FRC) Reports 5 and 7 (FR-64 and
FR-65). One of these is that the decision to implement protective actions
should be based on the projected dose that would be received if the
protective actions were not implemented. However, since these reports
were issued, considerable additional guidance as been developed on the
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subject of emergency response (IC-84, IA-89). EPA considered the
following four principles in establishing values for PAGs:
1. Acute effects on health (those that would be observable within a
short period of time and which have a dose threshold below which
they are not likely to occur) should be avoided.
2. The risk of delayed effects on health (primarily cancer and
genetic effects for which linear nonthreshold relationships to
dose are assumed) should not exceed upper bounds that are judged
to be adequately protective of public health under emergency
conditions, and are reasonable achievable.
3. PAGs should not be higher than justified on the basis of
optimization of cost and the collective risk of effects on
health. That is, any reduction of risk to public health
avoidable at acceptable cost should be carried out.
4. Regardless of the above principles, the risk to health from a
protective action should not itself exceed the risk to health
from the dose that would be avoided.
The above principles apply to the selection of any PAG. Similar
principles have been proposed for use by the international community
(IA-89). Appendices C and F demonstrate their application to the
selection of PAGs for evacuation and relocation. Although in establishing
PAGs it is necessary to consider a range of source terms to estimate the
variability of cost associated with their implementation, the PAGs are
chosen so as to be independent of the magnitude or type of accidental
release.
1.3 Planning
The planning elements for developing radiological emergency response
plans for accidents at nuclear power facilities are provided in NUREG-0654
(NU-80), which references the PAGs in this Manual as the basis for
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emergency response. NUREG-0396 (NU-78) provides guidance on time frames
for response, the types of releases to be considered, and emergency
planning zones (EPZ). The size and shape of the recommended EPZs were
only partially based on consideration of the numerical values of the
PAGs. A principle basis was that the planning zone for evacuation and
sheltering should be large enough to encompass all of rural areas and the
various organizations needed for emergency response. Experience gained in
exercises is then expected to provide an adequate basis for expanding
response to an actual incident to larger areas if needed. It was also
noted that the 10-mile radius EPZ for evacuation is large enough to avoid
exceeding the evacuation PAGs at its boundary for low-consequence,
core-melt accidents and to avoid early fatalities for high-consequence,
core-melt accidents. The 50-mile EPZ for ingestion pathways was selected
to account for the proportionately higher doses via ingestion compared to
inhalation and whole body external exposure pathways.
1.4 Implementation of PAGs
The sequence of events during the early phase includes notification
of responsible authorities, evaluation of potential offsite consequences,
recommendations for action, and protection of the public. In the early
phase of response, the time available to implement protective action will
probably be quite limited.
Immediately upon becoming aware that an incident has occurred that
may result in exposure of the offsite population, responsible authorities
will make a preliminary evaluation to determine the nature and potential
magnitude of the incident. This evaluation, if possible, will determine
potential exposure pathways, population at risk, and projected doses. At
this time, projected doses may be estimated from releases anticipated for
the particular circumstances types of the nuclear incident or from
monitoring data at the point of radionuclide release. The incident
evaluation and recommendations are then presented to emergency response
authorities for action. In the absence of recommendations from the
nuclear facility operator for protective actions in specific areas, the
emergency plan will provide for protective action in predesignated areas.
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Contrary to the situation during the early phase, dose projections
used to support protective action decisions during the intermediate and
late phases will be based on measurements of environmental radioactivity
and dose models. Following relocation of the public from affected areas
to protect them from exposure to deposited materials, it will also be
necessary to compile radiological and cost of decontamination data to form
the basis for radiation protection decisions for recovery.
The following chapters provide guidance on the projected doses at
which specific protective actions should be implemented and the
corresponding implementation procedures.
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REFERENCES
FE-85 FEDERAL EMERGENCY MANAGEMENT AGENCY. Federal Policy on
Distribution of Potassium Iodide around Nuclear Power Sites for
Use as a Thyroidal Blocking Agent. Federal Register 50-142, p.
30256, July 24, 1985.
FR-64 FEDERAL RADIATION COUNCIL. Radiation Protection Guidance for
Federal Agencies. Federal Register, Volume 29, pp. 12056-7,
August 22, 1965.
FR-65 FEDERAL RADIATION COUNCIL. Radiation Protection Guidance for
Federal Agencies. Federal Register, Volume 30, pp. 6953-5, May
22, 1965.
IA-89 INTERNATIONAL ATOMIC ENERGY AGENCY. Principles for Establishing
Intervention Levels for the Protection of the Public in the
Event of a Nuclear Accident or Radiological Emergency. Safety
Series No. 72, revision 1, in press. International Atomic
Energy Agency, Vienna, Austria.
IC-84 INTERNATIONAL COMMISSION ON RADIOLOGICAL PROTECTION. Protection
of the Public in the Event of Major Radiation Accidents:
Principles for Planning, ICRP Publication 40, Pergamon Press,
Oxford, England, 1984.
NU-78 NUCLEAR REGULATORY COMMISSION. Planning Basis for the
Development of State and Local Government Radiological Emergency
Response Plans in Support of Light Water Nuclear Power Plants.
(1978). U.S. Nuclear Regulatory Commission, Washington, D. C.
20555.
NU-80 NUCLEAR REGULATORY COMMISSION. Criteria for Preparation and
Evaluation of Radiological Emergency Response Plans and
Preparedness in Support of Nuclear Power Plants. (1980). U.S.
Nuclear Regulatory Commission, Washington, D. C. 20555.
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CHAPTER 2
Protective Action Guides for the Early Phase
2.1 Introduction
Rapid action may be needed to protect the public following an
accident involving a large release of radioactive material to the
atmosphere. This chapter identifies the levels of exposure to radiation
at which such prompt protective action should be initiated. These are set
forth as Protective Action Guides (PAGs) for the general population.
Limits for exposure of emergency workers during such an accident are also
provided. These guides and limits apply to any type of nuclear accident
or other incident that can result in exposure of the public to an airborne
plume of radioactive materials.
PAGs are expressed in terms of the projected doses above which
specified protective actions are warranted. In the case of an airborne
plume, the relevant protective actions are evacuation or sheltering.
These may be supplemented in special cases by washing and changing
clothing and by using stable iodine to block uptake by the thyroid.
The PAGs should be considered mandatory only for planning purposes:
for example, in developing radiological emergency response plans. Under
accident situations, because of unanticipated local conditions and
constraints, professional judgment will be required in their application.
Situations can be envisaged, for example, in which a nuclear accident
occurs at a time when other competing emergency conditions would make
evacuation impracticable. Conversely, under some conditions evacuation of
some areas may be quite practicable at projected doses below the PAGs.
These situations require judgments by those responsible for protective
action dec?''"is at the time of the accident. A discussion of the
implementation of these PAGs is provided in Chapter 5.
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The period addressed by this guidance is denoted the "early phase."
This is somewhat arbitrarily defined as the period from initiation of an
atmospheric release until four days after the event occurs, at which time
protective actions based on PAGs for relocation are assumed to be
implemented. Furthermore, after the initial emergency has passed, workers
are expected to be governed by the Federal guidance for normal work
situations. The PAGs for members of the public and limits for emergency
workers specified in this chapter, therefore, refer only to doses incurred
during the early phase. These may include whole-body external beta and
gamma dose from direct exposure to the airborne plume, exposure to beta
and gamma radiation from deposited materials, and the dose to internal
organs from direct inhalation of radioactive material from the plume.
Individuals exposed to a plume may also be exposed to deposited
material over longer periods of time via ingestion, direct external
exposure, and inhalation pathways. Because it is usually not practicable,
at the time of an accident, to project the long-term doses that might
occur after plume passage, and because different protective actions may be
appropriate, these are not included in the dose specified in these PAGs.
The former Federal Radiation Council (FRC), in a series of
recommendations issued in the 1960's, introduced the concept of PAGs and
issued guides for avoidance of exposure due to ingestion of strontium-89,
strontium-90, cesium-137, and iodine-131. These guides were developed for
the case of worldwide atmospheric fallout from weapons testing, and were
appropriate for application to food products that were contaminated as a
result of such atmospheric releases. That is, they were not developed for
application to protective actions relevant to prompt exposure to a plume
from a nuclear accident. The guidance in this chapter thus does not
supersede this previous FRC guidance, but provides new guidance for
different exposure pathways and situations.
2.2 Exposure Pathways and the Population Affected
The most immediate exposure pathway from an accidental airborne
release of radioactive material is direct exposure to an overhead plume of
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radioactive material carried by prevailing winds. The detailed content of
such a plume will depend on the source involved and conditions of the
accident. In the case of an accident at a nuclear power reactor, it will
most commonly contain radioactive noble gases, radioiodines, and
radioactive particulate materials. These materials emit gamma radiation,
which is not significantly absorbed by air and can expose people nearby as
the plume passes.
An additional exposure pathway occurs when people are directly
immersed in the radioactive plume, in which case radioactivity is inhaled
and the skin and clothes become contaminated. When this occurs, internal
body organs as well as the skin will be exposed through proximity to
radioactive materials. Although beta radiation from materials deposited
on the skin and clothing could be significant, generally it will be less
important than radioactive material taken into the body through
inhalation. This is especially true if early protective actions include
washing exposed skin and changing clothing. Inhaled radioactive
particulate materials, depending on their solubility in body fluids, will
remain in the lungs or move via the bloodstream to other organs. Some
radionuclides, once in the bloodstream, are concentrated in a single body
organ, with only small amounts going to other organs. For example, if
radioiodines are inhaled into the lungs, they move rapidly through the
bloodstream to the thyroid gland, where most of the dose is delivered.
As the passage of a typical radioactive plume progresses, some
radioiodines and radioactive particulate materials will settle out onto
the ground and other surfaces. People present after the plume has passed
will receive whole-body exposure from beta and gamma radiation emitted
from these deposited materials. If the proportion of radioiodines or
particulate materials contained in a release is large compared to the
noble gases, this exposure pathway can be more significant than direct
exposure to gamma radiation from the passing plume.
These PAGs are intended for general use to protect all of the
individuals in an exposed population. However, there are some population
groups that are at markedly different levels of risk from some protective
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actions—particularly evacuation. To avoid social and family disruption
and the complexity of implementing different PAGs for different groups in
a population under emergency conditions, the PAGs are intended to be
applied equally to most members of the population. Optional, higher
values are, however, appropriate for a few groups for whom the risk
associated with evacuation is exceptionally high (e.g., infirm persons).
These higher levels are provided to assure that the risk associated with
evacuation of these groups will not exceed the radiation risk avoided by
evacuation.
Prisoners are a special group who are not at higher risk from
evacuation, but due to the potential for escapes during or following their
evacuation, the population may be at greater risk. States may wish to
consider extra security to eliminate this risk as well as the protection
factor from sheltering in prisons.
It should also be recognized that the risk from evacuation could be
higher than normal if carried out under hazardous environmental
conditions. Examples of these conditions are: severe weather, flood,
earthquake, or the existence of a competing disaster. Higher dose levels
may be justified for continued sheltering under these conditions.
2.3 The Protective Action Guides
The PAGs for the early phase are summarized in Table 2-1 . They
are expressed in terms of effective dose, with supplementary guides for
dose to the thyroid and skin. The basis for these values is given in
detail in Appendix C. In summary, these analyses indicate that evacuation
of the public is not justified unless the projected dose to individuals
receiving the largest exposure at the outer edge of the evacuation zone is
at least one rem. This conclusion is based primarily on consideration of
This more complete guidance updates and replaces previous values,
expressed in terms of whole-body dose equivalent from external gamma
exposure and thyroid dose equivalent from inhalation of radioactive
iodines, that were recommended in the 1980 edition of this document.
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Table 2-1 PAGs for the Early Phase of a Nuclear Incident
Protective Action
PAG
(projected dose)a
Comments
Shelter; wash and
change clothes, if
immersed in plume.
rem
Evacuate the general
population.0
Evacuate special
groups.0
1 rem
5 rems
There is no dose below which these
protective actions are not recom-
mended. Local planners and
decision makers must consider other
factors, such as boundaries of
designated planning areas, the need
for rapid communication with the
public, risks associated with
sheltering, and the extent of local
contamination from the plume.
Special groups'
sheltered.
may remain
Higher doses may be permissible
under some circumstances.^
a The PAGs are expressed in terms of the projected committed effective
dose equivalent from exposure to the plume and deposited materials during
the first 4 days. Projected committed dose equivalents to the thyroid and
to the skin may be 5 and 50 times larger, respectively. In cases where
sheltering and/or evacuation will not prevent thyroid doses from exceeding
25 rems, stable iodine may be used (subject to approval by State medical
officials) to block the uptake of radioiodines by the thyroid.
b Special groups (e.g., infirm persons) are those for which evacuation
creates a higher than normal risk.
0 Under hazardous weather conditions or in the event of a competing
disaster, the general population may remain sheltered at projected doses
up to 5 rems, and special groups up to 10 rems. Evacuation should not be
carried out in any special circumstance for which the health risk from the
action would exceed the health risk to be avoided.
d PAGs for evacuation are based in part on the assumption that sheltering
will reduce dose from the plume by approximately a factor of two. The
emergency planning process may identify structures with significantly
different dose reduction factors, which would justify their use for
sheltering at higher or lower projected doses.
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the magnitudes of the risks of cancer and of effects on the unborn from
the radiation dose that is avoided by such evacuation. The analyses also
show that, at this radiation dose, the ratio of the cost of evacuation to
the risk avoided falls within the range of values commonly placed on
avoiding risk to public health. Because of the higher risk associated
with evacuation of some groups in the population (e.g. infirm persons and
prisoners), projected doses up to 5 rems were judged permissible in order
to provide reasonable assurance that the risk associated with their
evacuation would be justified. Under unusually hazardous environmental
conditions, or in the event of a competing disaster, projected doses of up
to 5 rems to the general population and up to 10 rems to special groups
are judged to be justified. (At these levels, attendants for special
groups would still not exceed acceptable levels for emergency workers.)
Effective dose considers only the risk of fatal cancer from
irradiation of organs within the body, and does not include dose to skin.
Since the thyroid is at disproportionately high risk for induction of
nonfatal cancers and nodules by radiation compared to other internal
organs, supplementary guides are provided to limit dose to the thyroid to
five times the PAG for effective dose to reduce the risk of these effects.
Supplementary guidance is also provided to limit dose to skin to 50 times
the numerical value of the PAG for effective dose to protect against the
risk of skin cancer, which is -not accounted for by effective dose.
Low-risk, low-cost protective actions such as sheltering, washing, and
changing clothes are recommended at projected dose levels below 1 rem, the
PAG for evacuating most members of the public under normal environmental
conditions. Because of the unknown, but assumed very low, cost and risk
associated with short duration (a few hours) sheltering, and because of
the associated enhanced capability for response officials to communicate
with sheltered populations, no PAG is established below which sheltering
is not recommended. The choice of the lower bound of projected dose at
which to order sheltering is left to the judgment of planners and
implementers of emergency response, based on conditions at the location
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and time of an accident. Normally, this choice will be strongly
influenced by the principle that exposure to radiation should be
maintained as low as reasonably achievable. As a reference level for a
lower bound, it may be useful to note that most planned releases of
radioactive materials from individual sources are limited in the United
States in such a manner as to assure that annual doses greater than 25
mrem will not occur. Further, international recommendations limit chronic
annual dose from all sources combined to 0.1 rem. Temporary sheltering
may also be indicated as a minimum response for projected doses higher
than the evacuation PAG for situations where evacuation cannot be carried
out prior to plume arrival, if the dose during evacuation is projected to
exceed that under sheltering.
Washing and changing of clothing is recommended primarily to provide
protection from beta radiation from materials deposited on the skin or
clothing. Calculations indicate that dose to skin should not be a
controlling pathway if these actions take place within 12 hours after
exposure. However, it is good radiation protection practice to recommend
these actions to all persons exposed to the plume as soon as practical.
Evacuation of most individuals is recommended, under normal
environmental conditions, at a projected dose of 1 rem. In the case of
special population groups for -which the risk associated with evacuation is
higher than normal (e.g., infirm persons or prison populations),
evacuation is not recommended until the projected dose is 5 rems.
However, if environmental conditions are severe, so that the risk of
evacuation is much higher than normal, evacuation of the general
population may be deferred until the projected dose is as high as 5 rems.
Since special groups also experience additional risk from evacuation
during hazardous environmental conditions, their evacuation may be
deferred until the projected dose is as high as 10 rems. However, in
situations where it is impracticable to apply the different PAG for
persons at high risk, a 1 rem PAG for evacuation under normal
environmental conditions, or up to 5 rems under hazardous environmental
conditions, may be applied to the entire population.
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The PAGs governing evacuation are based in part on the assumption
that short-term sheltering (two hours or less) will usually reduce dose
from a plume by a factor of about two. Evacuation from specific
structures (or types of structures) for which the dose reduction factor
for sheltering is different may be appropriate at higher or lower
projected doses. For example, large institutional structures, such as
hospitals and prisons, are typically expected to provide a protection
factor of about four. Sheltering in such facilities for protection from
short duration plumes would be justified at projected doses up to 10 rems
under normal environmental conditions and up to 20 rems under hazardous
environmental conditions.
The use of stable iodine to protect against uptake of inhaled
radioiodine by the thyroid is recognized as an effective alternative to
evacuation for situations involving radioiodine releases where evacuation
cannot be implemented. If the administration of stable iodine is included
in an emergency response plan, its use should be considered for any
radioiodine exposure situation in which the committed thyroid dose is
projected to be 25 rems or greater.
The PAGs do not imply an acceptable level of risk for normal
(nonetnergency) conditions. Furthermore, under emergency conditions, in
addition to the protective actions specifically identified for application
of the PAGs, any other reasonable measures available should be taken to
minimize radiation exposure of the general public and of emergency
workers. These PAGs are also not intended for use as criteria for the
ingestion of contaminated food or water, or for return to an area
contaminated by radioactivity. Separate guidance is provided for these
situations in Chapters 3 and 4.
2.4 Dose Projection
The PAGs are expressed in terms of projected dose. However, in the
early phase of an accident, parameters other than projected dose may
frequently provide a more appropriate basis for decisions to implement
protective actions. In a rapidly unfolding accident situation it will
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usually be impractical to directly estimate the projected dose soon
enough. For such cases, provision should be made for decisions to be made
on the basis of specific conditions at the source of a possible release
that are relatable to anticipated offsite doses. Nuclear power plant
emergency response plans should therefore include Emergency Action Levels
(EALs) which indicate in-plant conditions that will trigger notification
of and recommendations to offsite officials to implement prompt sheltering
or evacuation in specified areas in the absence of information on actual
releases or environmental measurements. Later, when these data become
available, dose projections based on measurements may be used as a basis
for implementing further action based on the PAGs.
The projected dose should include only contributions from exposures
and intakes during the early phase of an emergency. Doses incurred prior
to the protective action under consideration should not normally be
included. However, in those rare cases where individuals might exceed 50
rems (the assumed threshold for acute effects) these doses should be
included, to the extent that they can be projected. Similarly, doses that
might be received following the early phase should not be included for
decisions on whether or not to evacuate or shelter. Such doses, which may
occur from food pathways, long-term radiation exposure to deposited
radioactive materials, or long-term inhalation of resuspended materials,
are chronic exposures for which neither emergency evacuation nor
sheltering are appropriate protective actions. Separate PAGs relate the
appropriate protective action decisions to those exposure pathways.
In practical applications, dose projection will usually begin at the
time the condition on which the projection is based occurs. For rare
situations where significant time will elapse before the earliest possible
implementation of protective actions, the projected dose for comparison to
the PAG should be that beginning at the earliest time that protective
actions could be implemented.
2.5 Emergency Worker Limits
The PAGs for protection of the general population and dose limits for
emergency workers are derived under different assumptions. PAGs consider
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primarily the risk to individuals from exposure to radiation and the risk
and costs associated with the protective actions themselves. On the other
hand, emergency workers may receive exposure in order to assure protection
of the population and of valuable property. These exposures will be
justified if the individual risks are acceptability low, and the risks or
costs avoided by their actions outweigh the risks to which they are
subjected. Examples of emergency worker occupations are law enforcement,
fire fighting, civil defense, traffic control, health services,
environmental monitoring, transportation services, and animal care.
Similarly, some workers at utility, industrial, and institutional
facilities, and at farms, must control releases and/or protect property,
as well as protect employees and others during an emergency.
Dose limits for emergency workers are summarized in Table 2-2.
Radiation exposure of emergency workers should normally be limited by the
Federal Radiation Protection Guidance for occupational exposure. This
guidance provides an upper bound of five rems committed effective dose
equivalent per year. In addition, in order to satisfy the provisions of
this guidance for protection of minors and the unborn, emergency work
during nuclear accidents should be limited to nonpregnant adults.
There are some emergency situations, however, for which higher
exposures may be justified. Justification of any such exposure must
include the presence of conditions that prevent the rotation of workers or
other commonly-used dose reduction methods. The dose resulting from such
emergency exposures should be limited to 10 rems for protecting property,
and to 25 rems for life saving activities and the prevention of high risks
to populations. In the context of this guidance, high risks to
populations means situations in which the collective dose avoided by the
emergency operation is significantly larger than that incurred by the
emergency workers involved.
Situations may also rarely occur in which a dose in excess of 25 rems
for emergency exposure would be unavoidable in order to carry out a
lifesaving operation or to avoid large risks to populations. It is not
possible to prejudge the risk that one should be allowed to take to
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Table 2-2 Dose Limits for Emergency Workers
Dose limit3
5 rems
Activity
all activities
Condition
Use rotation of workers
or other common radiation
protection methods to
maintain doses as low as
practicable.
10 rems
protecting property
Lower dose not practicable.
25 rems
>25 rems
life saving or
preventing high risk
to populations
lifesaving or
preventing high risk
to populations
Lower dose not practicable.
Only on a voluntary basis
to persons fully aware of
the risks involved.
3 Committed effective dose equivalent to nonpregnant adults from exposure
during an emergency situation. In addition to the limitation on effective
dose equivalent, emergency workers should not exceed 15 rems to the lens
of the eye, or 50 rems to any other organ, tissue (including the skin), or
extremity of the body.
save the lives of others. However, persons undertaking any emergency
operation in which the dose will exceed 25 rems to the whole body should do so
only on a voluntary basis and with full awareness of the risks involved,
including the numerical levels of dose at which acute effects of radiation
will be incurred and numerical estimates of the risk of delayed effects.
Tables 2-3 and 2-4 provide some general information that may be useful in
advising emergency workers of risks of acute and delayed health effects
associated with large doses of radiation. Table 2-3 presents the estimated
risks of fatalities and moderately severe prodromal (forewarning) effects that
are likely to occur shortly after exposure to a wide range of whole-body
radiation doses. Estimated average cancer mortality risks for emergency
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Table 2-3 Acute Health Effects Associated with Whole-Body Absorbed Doses
(see Appendix C)
Absorbed dose
(rem)
<140
140
200
300
400
460
Fatalities
(percent)
a
5
15
50
85
95
Absorbed dose
(rads)
<50
50
100
150
200
250
Prodromal effects
(percent affected)
a
2
15
50
85
98
a The risK of fatality Delow 140 rems ana of prodromal effects
below 50 rems is indeterminate.
Table 2-4 Average Cancer Risk to Emergency Workers Receiving 25 Rems
Whole-Body Dose (see Appendix C)
Age of the
emergency
worker
(years)
20 to 30
30 to 40
40 to 50
50 to 60
Approximate risk
of premature death
(deaths per 1 ,000
persons exposed)
9.1
7.2
5.3
3.5
Average years of
life lost if premature
death occurs
(years)
24
19
15
11
workers corresponding to a whole-body dose of 25 rems are given in
Table 2-4, as a function of age at the time of exposure. To approxi-
mately estimate average cancer mortality for lifesaving missions at
higher doses (up to a few hundred rems), the values in Table 2-4 may
be increased linearly. For example, if the dose is increased
three-fold to 75 rems, the projected incidence of fatal cancer over
the ensuing lifetimes of workers exposed at age 25 would be about 27
per 1000 persons exposed. These values were calculated using a life
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table analysis that assumes the period of risk continues for the
duration of the worker's lifetime. Somewhat smaller risks of serious
genetic effects (if gonadal tissue is exposed) and of nonfatal cancer
would also be incurred.
Many emergency workers will have little or no health physics
training, so dose minimization through use of protective equipment
cannot always be assumed. However, the use of respiratory protective
equipment can reduce dose from inhalation, and clothing can reduce
beta dose. Stable iodine may also be appropriate for blocking thyroid
uptake of radioiodine in personnel involved in emergency actions where
atmospheric releases include radioiodine. The issuance of stable
iodine must be carried out in accordance with State medical procedures,
and planning is required to ensure its availability and proper use.
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CHAPTER 3
Protective Action Guides for the Intermediate Phase
(Food and Water)
(reserved)
-------
CHAPTER 4
Protective Action Guides for the Intermediate Phase
(Deposited Radioactive Materials)
4.1 Introduction
Following a nuclear accident it may be necessary to temporarily
relocate the public from areas where extensive deposition of radioactive
materials has occurred until decontamination has taken place. This chapter
identifies the levels of radiation exposure which indicate when relocation
from contaminated property is warranted.
The period addressed by this guidance is denoted as the "intermediate
phase." This is arbitrarily defined as the period beginning after the
accident source and releases have been brought under control and
environmental measurements are available for use as a basis for decisions on
protective actions and extending until these protective actions are
terminated. This phase may overlap the early phase and may last from weeks
to many months. For the purpose of dose projection, it is assumed to last
for one year. Prior to this period protective actions will have been taken
based upon the PAGs for the early phase (Chapter 2). It is assumed that
decisions will be made during the intermediate phase concerning whether
particular areas or properties from which persons have been relocated will
be decontaminated and reoccupied, or condemned and the occupants permanently
relocated. These actions will be carried out during the late or "recovery"
phase.
Although these Protective Action Guides (PAGs) were developed based on
expected releases of radioactive materials characteristic of reactor
accidents, they may be applied to any type of nuclear accident or other
incident that can result in long-term exposure of the public to deposited
radioactivity.
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PAGs are expressed in terms of the projected doses above which specified
protective actions are warranted. In the case of deposited radioactivity, the
major relevant protective action is relocation. Persons not relocated (from
less contaminated areas) may reduce their dose through the application of
simple decontamination techniques and by spending more time than usual in low
exposure rate areas (e.g., indoors).
The PAGs should be considered mandatory only for planning purposes: for
example, in developing radiological emergency response plans. Under accident
situations, because of unanticipated local conditions and constraints,
professional judgment by responsible officials will be required in their
application. Situations can be envisaged, where contamination from a nuclear
accident occurs at a site or time in which relocation of the public, based on
the recommended PAGs, would be impracticable. Conversely, under some
conditions, relocation may be quite practicable at projected doses below the
PAGs. These situations require judgments by those responsible for protective
action decisions at the time of the accident. A discussion of the
implementation of these PAGs is provided in Chapter 7.
The PAGs for relocation specified in this chapter refer only to estimates
of doses due to exposure during the intermediate phase. These may include
external exposure to radiation from deposited radioactivity and inhalation of
resuspended radioactive materials. Protective Action Guides for ingestion
exposure pathways, which also apply during the intermediate phase, are
discussed separately in Chapter 3.
Individuals who live in areas contaminated by materials deposited from an
airborne plume may be exposed to radiation from these materials over the
entire time that they live in the area. This would be the case for those who
are not relocated as well as for persons who return following relocation.
Because it is usually not practicable, at the time of a decision to relocate,
to calculate the doses that might be incurred from exposure beyond one year,
and because different protective actions may be appropriate over such longer
periods of time, these doses are not included in the dose specified in the
PAGs for relocation.
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4.1.1 Exposure Pathways
The principal pathways for exposure of the public occupying locations
contaminated by deposited radioactivity are expected to be exposure of the
whole body to external gamma radiation from deposited radioactive materials
(groundshine) and internal exposure from the inhalation of resuspended
materials. For reactor accidents, external gamma radiation is expected to be
the dominant source.
In most cases relocation decisions will be based on doses from the above
pathways. However, in rare cases where withdrawal of contaminated food or
drinking water from public consumption would itself create a risk to health,
dose from the ingestion pathway should also be included. In this case, the
projected committed effective dose from ingestion of food and water should be
added to the dose from the above exposure pathways in making relocation
decisions. (PAGs related specifically to the withdrawal of contaminated food
and water from use are discussed in Chapter 3).
Other potentially significant exposure pathways include exposure to beta
radiation from surface contamination and direct ingestion of contaminated
soil. These pathways are not expected to be controlling for reactor accidents
(EP-88).
4.1.2 The Population Affected
The PAGs for relocation are intended for use in establishing the boundary
of a restricted zone within an area that has been subjected to deposition of
radioactive materials. During their development, consideration was given to
the higher risk of effects on health to children and fetuses from radiation
dose and the higher risk to some other population groups from relocation. To
avoid the complexity of implementing separate PAGs for individual members of
the population, the relocation PAG is established at a level that will provide
adequate protection for all relocated individuals.
Persons residing in contaminated areas outside the restricted zone will
be at some risk from radiation dose. Therefore, guidance on the reduction of
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dose during the first year to residents outside this zone is also provided.
Due to the high cost of relocation, it is more practical to reduce dose in
this population group by the early application of simple, low-impact,
protective actions other than by relocation.
4.2 The Protective Action Guides for Deposited Radioactivity
PAGs for protection from deposited radioactivity during the
intermediate phase are summarized in Table 4-1. The basis for these values
is presented in detail in Appendix F. In summary, relocation is warranted
when the projected sum of dose from external gamma radiation and the
committed effective dose from inhalation of resuspended radionuclides
exceeds 2 rems in the first year. Relocation to avoid exposure of the skin
to beta radiation is warranted at 50 times the numerical value of the
relocation PAG for effective dose.
Persons who are not relocated, i.e., those in areas that received
relatively small amounts of deposited radioactive material, should reduce
their exposure by the application of other measures. Possible dose
reduction techniques range from the simple processes of scrubbing and/or
flushing surfaces, soaking or plowing of soil, removal and disposal of small
spots of soil found to be highly contaminated (e.g., from settlement of
water), and spending more time than usual in lower exposure rate areas
(e.g., indoors), to the difficult and time-consuming processes of removal,
disposal, and replacement of contaminated surfaces. It is anticipated that
simple processes will be most appropriate for early application. Many can
be carried out by residents themselves with support from response officials
for assessment of the levels of contamination, guidance on appropriate
actions, and disposal of contaminated materials. Due to the relatively low
cost and risk associated with these protective actions, no dose level is
established below which they are not recommended. It is, however,
recommended that response officials concentrate their initial efforts in
areas where the projected dose from the first year of exposure exceeds 0.5
rems. In addition, first priority should be given to residences of pregnant
women.
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Table 4-1 Protective Action Guides for Exposure to Deposited Radioactivity
during the Intermediate Phase of a Nuclear Incident
Protective
Action
PAG (projected
dose)a
Comments
Apply simple dose
reduction techniques.
Relocate the general
population.0
<2 rems There is no dose below which
these protective actions are
not recommended. Early efforts
should reduce the highest
exposure rates, with priority
given to residences of pregnant
women.
>2 rems Beta dose to skin may be up to
50 times higher.
a Dose refers to the projected sum of effective dose equivalent from
the external gamma radiation and the committed effective dose
equivalent from inhalation of resuspended materials, during the first
year. Projected dose means the dose that would be received in the
absence of shielding from structures or the application of dose
reduction techniques.
b Simple dose reduction techniques include scrubbing and/or flushing
hard surfaces, soaking or plowing soil, minor removal of soil from
spots where radioactive materials have concentrated, and spending
more time than usual indoors or in other low exposure rate areas.
c Persons previously evacuated from areas outside the relocation zone
defined by this PAG may return to occupy their residences. Cases
involving relocation of persons at high risk from such action (e.g.,
patients under intensive care), should be evaluated individually
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4.2.1 Longer Term Objectives of the Protective Action Guides
It is an objective of these PAGs to assure that 1) doses in any single
year after the first will not exceed 0.5 rems, and 2) the cumulative dose
over the next 50 years will not exceed 5 rems. For reactor accidents, the
above PAG of 2 rems projected dose in the first year is expected to meet
both of those objectives. Decontamination of areas outside the restricted
area may be required during the first year to meet these objectives for
other types of accidents. For situations where it is impractical to meet
these objectives though decontamination, consideration should be given to
relocation at a lower projected first year dose than that specified by the
relocation PAG.
After the population has been protected in accordance with the PAGs for
relocation, return for occupancy of previously restricted areas should be
governed on the basis of Recovery Criteria as presented in Chapter 8.
Projected dose considers exposure rate reduction from radioactive decay
and, generally, weathering. When one also considers the anticipated effects
of shielding from partial occupancy in homes and other structures, persons
who are not relocated should receive a dose substantially less than the
projected dose. For commonly assumed reactor source terms, we estimate that
2 rems projected dose in the first year will be reduced to about 1.2 rems by
these factors as shown in Table 4-2. The application of simple
decontamination techniques shortly after the accident can be assumed to
provide a further 30 percent or more reduction, so that the maximum first
year dose to persons who are not relocated is expected to be less than one
rem. Taking account of decay rates assumed to be associated with releases
from nuclear power plant accidents (SN-82) and shielding from partial
occupancy and weathering, a projected dose of 2 rems in the first year is
likely to amount to 0.5 rems or less in the second year and 5 rems or less
in 50 years. The application of simple dose reduction techniques would
reduce these doses further. Results of calculations supporting these
projections are summarized in Table 4-2.
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Table 4-2 Estimated maximum dose to persons not relocated
Accident
Category
SST-1
SST-2
SST-3
No appl
Year 1
1.2
1.2
1.2
led dose
Year 2
0.5
0.34
0.20
Dose
reduction15
50 years
5.0
3.9
3.3
(rem)
Early
Year
0.9
0.9
0.9
simple dose
1 Year 2
0.35
0.24
0.14
reduction0
50 years
3.5
2.7
2.3
aApplies to fuel-melt reactor accidents.
^Based on relocation at a projected dose of 2 rems in the first
year and 40 percent dose reduction to nonrelocated persons from normal,
partial occupancy in structures. No dose reduction is assumed from
decontamination, shielding, or special limitations on time spent in high
exposure rate areas.
cThe projected dose is assumed to be reduced 30 percent by the
application of simple dose reduction techniques during the first month.
If these techniques are completed later in the first year, the first year
dose will be greater.
4.2.2 Applying the Protective Action Guides for Relocation
Establishing the boundary of a restricted zone may result in three
different types of actions:
a. Persons who, based on the PAGs for the early phase of a nuclear
accident (Chapter 2), have already been evacuated from an area
which is now designated as a restricted zone must be converted to
relocation status.
b. Persons not previously evacuated who reside inside the restricted
zone must relocate.
c. Persons who normally reside outside the restricted zone, but were
previously evacuated, may return. A gradual return is
recommended, as discussed in Chapter 7.
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Small adjustments in the boundary of the restricted zone from that given
by the PAG may be justified on the basis of difficulty or ease of
implementation. For example, the use of a convenient natural boundary could
be justification for adjustment of the restricted zone. However, such
decisions should be supported by demonstration that exposure rates to persons
not relocated can be promptly reduced by methods other than relocation to meet
the PAG, as well as the longer term dose objectives addressed in Section 4.1.1.
Reactor accidents involving releases of major portions of the core
inventory under adverse atmospheric conditions can be postulated for which
large areas would have to be restricted under these PAGs. As the affected
land area increases, they will become more difficult and costly to implement,
especially in densely populated areas. For situations where implementation
becomes impracticable or impossible, informed judgment must be exercised to
assure priority of protection for individuals in areas having the highest
exposure rates. In such situations, the first priority for any area should be
to reduce dose to pregnant women.
4.3 Exposure Limits for Persons Reentering the Restricted Zone
Individuals who are permitted to reenter a restricted zone to work, or
for other justified reasons, will require protection from radiation. Such
individuals should enter the restricted zone under controlled conditions in
accordance with dose limitations and other procedures for control of
occupationally-exposed workers (EP-87). Ongoing doses received by these
individuals from living in a contaminated area outside the restricted zone
should be included as part of the dose limitation applicable to workers.
However, dose received previously from the plume and associated groundshine,
during the early phase of the nuclear incident, need not be considered unless
it is significant with respect to the higher occupational dose limits for
health effects other than cancer and genetic effects (i.e., the limits for
nonstochastic effects).
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REFERENCES
EP-87 U.S. ENVIRONMENTAL PROTECTION AGENCY. Radiation Protection
Guidance to Federal Agencies for Occupational Exposure. Federal
Register. Vol. 52, No. 17, Page 2822, U.S. Government Printing
Office, Washington, DC 20402, January 1987.
EP-88 AABERG, ROSANNE, Battelle Northwest Laboratories. Evaluation of
Skin and Ingestion Exposure Pathways. U.S. Environmental Protection
Agency/Office of Radiation Programs, Washington, D.C. 20460 (1988
Draft).
SN-82 SANDIA NATIONAL LABORATORY. Technical Guidance for Siting Criteria
Development. NUREG/CR-2239. U.S. Nuclear Regulatory Commission,
Washington, DC 20555, 1982.
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CHAPTER 5
Implementing the Protective Action Guides
for the Early Phase
5.1 Introduction
This chapter provides guidance for implementing the Protective
Action Guides (PAGs) set forth in Chapter 2. The main objectives are
to provide guidance for estimating doses from exposure to an airborne
plume, and for choosing and implementing protective actions.
Due to the wide variety of types of nuclear facilities and releases
that could occur, it is not practical to provide general implementing
guidance for all situations. The guidance in this chapter applies
primarily to accidents at nuclear power plants. In some situations it
may also be applied to accidental releases from other nuclear
facilities. In most cases, however, specific implementation procedures
for incidents at nuclear facilities other than nuclear power plants will
have to be developed by planners on a case-by-case basis.
Following an incident which has the potential for an atmospheric
release of radioactive material, the responsible authorities (State
and/or local) will need to decide whether protective actions are needed
and, if so, where and when they should be implemented. These decisions
will be based primarily on (a) the potential for releases, and (b)
projected doses as a function of time at various locations in the
environment.
5.2 Initial Response and Sequence of Subsequent Actions
In the case of an atmospheric release, the protective actions which
may be required are those which protect the population from inhalation of
radioactive materials in the plume, from exposure to gamma radiation from
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the plume, and from short-term exposure to radioactive materials
deposited on the ground. It may also be necessary to consider protective
action to avoid doses from deposition of radioactive material on the skin
and clothing.
The time of exposure to a plume can be divided into two periods:
(a) the period immediately following the incident, when little or no
environmental data are available to confirm the magnitude of releases,
and (b) the subsequent period, when environmental levels are known.
During the first period, speed in completing such actions as
sheltering, evacuating, and control of access may be critical to minimize
exposure. Environmental measurements made during this period may have
little meaning because of uncertainty concerning the location of the
plume when the measurements are made or uncertainty about changes in the
releases from the facility, due to changes in pressure and radionuclide
concentrations within the structures from which the plume is being
released. Therefore, it is advisable to initiate early protective
actions in a predetermined manner that is related to plant conditions.
This will normally be carried out through recommendations provided by the
facility operator. During the second period, when environmental levels
are known, these actions can be adjusted as necessary.
For incidents involving release to the atmosphere, the following
sequence of actions is suggested:
1. Notification of State and/or local authorities by the facility
operator that an incident has occurred with the potential to
cause offsite doses that exceed normal limits. This should be
provided as soon as possible, following the incident, and prior
to the release, if possible. (NRC regulations require such
notification within 15 minutes of declaring an emergency.)
2. Immediate evacuation (and/or sheltering) of populations in
predesignated areas without waiting for release rate or
environmental measurements.
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3. Monitoring of release rates, plant conditions, environmental
concentrations, and exposure rates.
4. Calculation of the plume center!ine dose rates and projected
doses at various distances downwind from the release point.
5. Implementation of protective actions in additional areas if
indicated. (Withdrawal of protective actions from areas where
they have already been implemented is usually not advisable
during the early phase because of the potential for changing
conditions.)
6. Continuation of adjustments as more data become available.
5.2.1 Notification
The first indication that a nuclear incident has occurred should
come to State and/or local authorities from the facility operator.
Notification by a nuclear power facility of State and local response
organizations should include recommendations, based on plant conditions,
for early evacuation and sheltering in predesignated areas. An early
estimate of the projected dose to the population at the site boundary and
at more distant locations, along with estimated time frames, should be
made as soon as release data become available. Emergency response
planners should make arrangements with the facility operator to assure
that this information will be made available on a timely basis and that
dose projections will be provided in units that can be directly compared
to the PAGs.
5.2.2 Immediate Protective Action
The Planning Basis for the Development of State and Local Government
Radiological Emergency Response Plans (NR-78) recommends that States
designate an emergency planning zone (EPZ) for protective action for
plume exposure out to about 10 miles from a nuclear power facility.
Within this zone, areas should be predesignated for immediate response,
5-3
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based on specified plant conditions, prior to the availability of
information on quantities of radioactive materials released. These
should consist of a circular (or, depending on local topography, other
appropriately shaped) area centered on the facility and extending outward
for 2 to 3 miles, with additional areas, in the downwind direction at the
time of the incident, to distances determined by the potential magnitude
of the release, and of an angular spread determined by meteorological
conditions. An angular spread of 90 degrees (4 sectors) will usually be
adequate for this immediate response. The remaining area within the EPZ
should be placed on alert, pending more information.
The predesignated areas for immediate protective action may be
reserved for use only in situations where the facility operator cannot
provide an immediate reliable estimate of projected dose based on actual
releases. If the facility operator is able to provide reliable and
prompt offsite dose projections, then these may be used to determine the
area for immediate protective action, in lieu of using a predesignated
area.
This will be possible when the facility operator can estimate the
potential offsite dose based on information in the control room, using
relationships developed during planning that relate abnormal plant
conditions and meteorological conditions to potential offsite doses.
After the release starts and the release rate is measurable and/or when
plant conditions or measurements can be used to estimate the
characteristics of the release and the release rate as a function of
time, then these factors, along with meteorological stability conditions,
windspeed, and wind direction, can be used to estimate integrated
concentrations of radioactive contamination as a function of location
downwind. Although such projections are useful for initiating protective
action, the accuracy of these methods for estimating projected dose is
necessarily poor because of unknown factors and uncertainty related to
input data. For this reason, follow-up measurements in the environment
will almost always be required.
5-4
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When further information or forecasts on wind direction and
meteorology become available, decisions for protective action in
additional areas can be made. With dependable and stable meteorological
and wind direction information, it may be possible to reduce the angular
spread of the area in which additional protective action is taken.
However, if the wind direction is variable or uncertain, the start of the
release is delayed, the release is large, the duration is long, or the
atmosphere is very unstable, the angular spread of the evacuated area may
have to be increased, and possibly extended to a complete circle. The
importance of current information on and forecasts of wind direction
cannot be overemphasized.
5.3 The Establishment of Exposure Patterns
During and immediately following the early response to protect the
population close to a facility, detailed environmental measurements are
not possible, and calculations based on minimal measurements must be used
to project doses. These projections are needed to determine whether
protective action should be implemented in additional areas during the
early phase. Because of the short time frame involved (4 days), if lower
concentrations or exposure rates are projected than were initially
predicted (usually on the basis of plant conditions alone), existing
protective action should not be terminated. Such decisions should be
based on the PAGs for relocation (Chapter 4).
Exposure rates or concentrations measured in the plume at a few
selected locations may be used to estimate the pattern of the exposed
area in a variety of ways. A simple, but crude, method is to measure the
plume centerline exposure rate at ground level at a known distance
downwind of the release point and then to calculate exposure rates at
other downwind locations by assuming that the plume centerline exposure
1 The centerline exposure rate can be determined by traversing the
plume at a point sufficiently far downwind that it has stabilized
(usually more than one mile from the site) while taking continuous
exposure rate measurements, preferably from a helicopter or other small
aircraft.
5-5
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rate is a known function of the inverse of the distance from the release
2
point.
The following relationship can be used for this calculation:
D2 = DX [Rj_ /R2]x,
where D, = exposure rate at distance R,,
D2 = exposure rate at distance R2> and
x = a constant, which depends on the stability class.
For average meteorological conditions, this relationship can be used
to develop a pattern of estimated exposure rates by assuming that x = 1.5
and that the exposure rate calculated for the plume center!ine would exist
at all points equidistant from the source in the general downwind
direction. To use this method, one must be sure that the exposure rate
measurement is taken at or near the plume centerline. Another method
useful for estimating exposure rate patterns for flat terrain is to use a
series of previously-prepared isopleths for standard meteorological
4
conditions which are calculated using more sophisticated models.
Computer modeling is now extensively used to estimate exposure rate
patterns. A variety of computer software has been developed which will
yield real-time isodose lines from projected (or actual) releases as well
as from offsite measurements. This is the preferred method for
estimating exposure patterns, because of the ease of performing
2 This may not always be a valid assumption. In the case of an
elevated plume, for example, the ground level exposure rate at a near
point may be less than at a location farther downwind.
3 This value applies to meteorological stability classes C and D. If
the meteorological stability condition is known, more accuracy can be
achieved by using the values x = 2 for stability classes A and B;
and x = 1 for classes E and F.
4 Since meteorological stability class and the windspeed at the time of
the release affect the shape of such isopleths, several sets of curves
are needed in association with a corresponding map. By the application
of simple multipliers, these isopleths may be used to estimate exposure
rates over a wide area based on measurements at specific locations.
5-6
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sophisticated calculations, as well as the ability to rapidly process
large amounts of data and to simulate results for a wide variety of
release and meteorological scenarios.
5.4 Dose Projection
The PAGs set forth in Chapter 2 are specified in terms of the
effective dose equivalent. This dose includes that due to external gamma
exposure of the whole body, as well as the committed effective dose
equivalent from inhaled radionuclides. Guidance is also provided for the
thyroid and skin in terms of the dose equivalent to these organs.
Methods for estimating projected doses in each of these units, based on
the exposure pattern, are discussed below. These require knowledge of or
assumptions for the duration of exposure and the relation, for each
radioisotope, between exposure and dose.
5.4.1 Duration of Exposure
The projected dose (or projected committed dose in the case of
inhaled radionuclides) for comparison to the PAGs is calculated for
exposure during the early phase of an emergency, normally defined as the
first four days following the start of a release. In the case of a short
duration release, this will encompass the entire period of exposure to
the plume and exposure to deposited material for the first four days
(deposition on skin and clothing is limited to 12 hours).
Doses that are incurred before the start of the release for which
protective action is being considered should not normally be included in
evaluating the need for protective action. Likewise, radiation doses
that may be incurred at later times should not be included. These doses,
which may occur through ingestion pathways or long-term exposure to
deposited radioactive materials, take place over a different, longer time
period. Protective action for such exposure is based on guidance
addressed in other chapters.
The projected dose from a plume is proportional to the
time-integrated concentration of radioactivity in the plume at each
5-7
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location. This concentration will depend on both the rate of release and
meteorological conditions. Release rates will vary with time, and this
time-dependence cannot usually be predicted accurately. In the absence
of more specific information, the release rate is therefore usually
assumed to be constant.
The only remaining factor is then the duration of the plume at a
particular location. Plume exposure will start at a particular location
when the plume arrives and end when the plume is no longer present, due
either to an end to the release, or a change in wind direction.
Prediction of time frames for releases is difficult because of the
wide range associated with the potential spectrum of accidents.
Therefore, planners should consider the possible time periods between an
initiating event and arrival of a plume and the duration of releases in
relation to the time needed to implement protective actions. Analyses
(NR-75) have shown that some reactor incidents may take several days to
develop to the point of a release, while others may begin as early as
one-half hour after an initiating event. Furthermore, the duration of a
release may range from less than one hour to several days, with the major
portion of the release usually occurring within the first day. In
addition, significant plume travel times are associated with the most
adverse meteorological conditions (low windspeeds and stable atmospheric
conditions), which may result in large exposures far from the site. For
example, under such adverse conditions, two hours or more might be
required for a plume to travel five miles. For equivalent release
characteristics, higher windspeeds (which produce shorter travel times
and provide more dispersion) result in individual exposures less than
those under lower windspeeds. Planning information on time frames for
releases from nuclear power facilities may be found in Reference NR-78.
Since a change in wind direction will also affect the duration of
exposure, it is very important that arrangements be made for the State or
local weather forecast center to provide information on current
meteorological and wind conditions and predicted wind direction
persistence during an incident, in addition to information received from
5-8
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the facility operator. If neither a wind change nor the time to the end
of the release can be predicted, the period of exposure should be
conservatively assumed to be equal to the 99 percent probable maximum
duration of wind direction persistence at the site. Historical data on
wind direction persistence as a function of atmospheric stability class
for nuclear power plant sites are available in the Final Safety Analysis
Reports prepared by facility operators.
5.4.2 Dose Conversion Factors
This section provides dose conversion factors (DCFs) and derived
response levels (DRLs) for those radionuclides important for accidents at
nuclear power plants. These are supplemented by an example to
demonstrate their application. The DCFs are useful where multiple
radionuclides are involved, because the total dose from a single exposure
pathway will be the sum of the doses calculated for each radionuclide.
The DRLs are useful for releases consisting primarily of a single
nuclide, in which case the DRL can be compared directly to the measured
or calculated concentration. (DRLs can be used for multiple
radionuclides by summing the ratios of the environmental concentration of
each nuclide to its respective DRL. To meet the PAG, this sum must be
equal to or less than unity.)
Table 5-1 provides DCFs and DRLs for external exposure to gamma and
beta radiation due to immersion in contaminated air. The values for
gamma radiation will provide conservative estimates for exposure to an
overhead plume under most realistic conditions. They are derived under
the assumption that the plume is correctly approximated by a
semi-infinite source.
The beta dose to skin from immersion is considered only for the
noble gases. For other radionuclides, the beta skin dose is
5 The exposure from gamma radiation in air is not numerically equal to
effective dose equivalent, because of attenuation of gamma radiation in
the body. An approximation, valid for radionuclides from typical reactor
accidents, is that the numerical value of the effective dose equivalent
is about 0.7 times the numerical value of the exposure in air. Dose
conversion factors in this section take these differences into account.
5-9
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Table 5-1 Dose Conversion Factors (DCF) and Derived Response Levels (DRL) for External Exposure
due to Immersion in Contaminated Air
I
I—'
o
Radionuclide3
Kr-85
Kr-85m
Kr-87
Kr-88
Zr-95
Ru-103
Ru/Rh-106
Te/ 1-132
1-131
1-132
1-133
1-135
Xe-133
Xe-135
Cs-134
Cs/Ba-137
Ba-140
Ce-144
Np-239
Whole
DCFb
rem
pCi-h/cm3
1.2E 0
8.4E+1
4.8E+2
1.2E+3
4.1E+2
2.6E+2
2.4E-1
1.1 1+2
2.0E+2
1.3E+3
3.3E+2
9.0E+2
1.8E+1
1.3E+2
8.6E+2
7.1E-1
l.OE+2
9.2E 0
8.6E+1
body gamma dose
DRLC
yCi-h/cm3
8.3E-1
1.2E-2
2.1E-3
8.3E-4
2.4E-3
3.9E-3
4. IE 0
8.9E-3
5.0E-3
7.9E-4
3.1E-3
1.1E-3
5.6E-2
7.7E-3
1.2E-3
1.4E 0
l.OE-2
1.1E-1
1.2E-2
Beta
DCFd
rem
uCi-h/cm3
1.7E+2
1.8E+2
1.2E+3
2.8E+2
3.5E+1
2.3E+2
dose to skin
DRLe
uCi-h/cm3
2.9E-1
2.8E-1
4.2E-2
1.8E-1
1.4E 0
2.2E-1
a Data from NUREG/CR-1918, Kocher (KO-81), pp. 163-205,
b Effective dose equivalent per unit exposure.
c Assumes a PAG of 1 rem.
d Dose equivalent per unit exposure.
e Assumes a PAG of 50 rems.
-------
insignificant in comparison to the committed effective dose from
inhalation. Even though the beta dose exceeds the gamma dose in the case
of the noble gases, it is usually not controlling, because the guide for
dose to skin is 50 times the PAG for exposure of the whole body. Kr-85
is an exception, because the beta dose exceeds the gamma dose by a factor
of about 140. This radionuclide is not dominant for reactor accidents,
however, because the inventory of Kr-85m normally exceeds that of Kr-85
by a factor of about 40.
Table 5-2 provides DCFs and DRLs for dose due to inhalation and for
dose to skin from radionuclides deposited on skin and clothing. DCFs and
DRLs are also provided for dose to the thyroid due to inhalation of
radioiodines. For protective action decisions, it is necessary to
consider the effective dose (to the whole body) and dose to thyroid and
skin individually.
The effect of varying dose per unit intake and breathing rate with
respect to age were analyzed, and the dose conversion factors tabulated
in Table 5-2 are those that yield the greatest dose per unit
concentration in air. These dose conversion factors are based on the
assumption that the radionuclides are in oxide form (class Y), except for
iodine (elemental), and that the particle size is one micron. For other
chemical forms of practical interest the doses will differ, but in
general only by a small factor (IA-86). If the solubility class or
particle size is known or can be predicted, the inhalation dose
conversion factors should be adjusted as appropriate.
It is not practical to determine dose to skin by measurement of the
beta exposure rate near the skin surface. Such doses are determined more
practically through calculations based on time-integrated air
concentration, an assumed deposition velocity, and an assumed time period
between deposition and skin decontamination. For purposes of calculating
the DRLs, a deposition velocity of 1 cm/sec and an exposure time before
decontamination of 12 hours were assumed. If other values are more
appropriate, the tabulated DRLs can be scaled accordingly.
5-11
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Table 5-2 Dose Conversion Factors (DCF) and Derived Response Levels (DRL) for Doses due to Inhalation
and from Material Deposited on Skin and Clothing
I
(-•
ro
Radionuclide3
Sr-89
Sr-90
Zr-95
Ru-103
Ru/Rh-106
Te/I-132
1-131
1-132
1-133
1-135
Cs-134
Cs/Ba-137
Ba-140
Ce-144
Np-239
Pu-238
Pu-239
Pu-240
Pu-241
Am-241
Cm-242
Cm-244
Effective
DCF
rem
uCi-h/cm3
9.1E+3
2.2E+5
2.6E+4
1.1E+4
6.0E+5
1.3E+4
5.1E+4
4.9E+2
8.5E+3
1.7E+3
4.3E+4
2.6E+4
4.3E+3
4.3E+5
3.3E+3
2.6E+8
2.6E+8
2.6E+8
4.3E+6
4.3E+8
2.2E+7
2.2E+8
Inhalation
dose
DRLC
uCi-h/cm3
1.1E-4
4.5E-6
3.8E-5
9.1E-5
1.7E-6
7.7E-5
2.0E-5
2.0E-3
1.2E-4
5.9E-4
2.3E-5
3.8E-5
2.3E-4
2.3E-6
3.0E-4
3.8E-9
3.8E-9
3.8E-9
2.3E-7
2.3E-9
4.5E-8
4.5E-9
dosesb
Thyroid
DCF DRLd
rem «
r. u i ~\ uCi-h/cm3
ui/i -n/cmj
3.3E+5 1.5E-5
1.7E+6 3.0E-6
9.1E+3 5.5E-4
2.6E+5 1.9E-5
4.3E+4 1.2E-4
Beta
Ski
DCF
rem
uCi-h/cm3
1.9E+5
1.9E+5
1.5E+5
1.2E+5
1.9E+5
2.0E+5
5.5E+5
1.6E+5
5.1E+5
3.3E+5
1.2E+5
2.4E+5
1.9E+5
2.9E+5
1.3E+5
dose
n
DRLe
uCi-h/cm3
2.6E-4
2.6E-4
3.3E-4
4.2E-4
2.6E-4
2.5E-4
9.1E-5
3.1E-4
9.8E-5
1.5E-4
4.2E-4
2.1E-4
2.6E-4
1.7E-4
3.8E-4
a Data for all elements except I and Te are from Table XX, IAEA Safety Series 81 (IA-86). The data for I
and Te are from NRPB R-162 (GR-85).
b The DCFs and DRLs are based on the age groups that would receive the greatest dose.
c Assumes a PAG of 1 rem.
d Assumes a PAG of 5 rems.
e Assumes a PAG of 50 rems, a deposition velocity of 0.01 m/s, and an exposure period of 12 hours after
deposition. Data are from IAEA Safety Series 81 Table XII (IA-86).
-------
DCFs and DRLs for beta dose to skin are not provided in Table 5-2
for the transuranic alpha emitters because skin dose from these
radionuclides is insignificant compared to from inhalation, and thus
would not affect decisions on evacuation. It should be noted that, even
in situations where the beta skin dose might exceed 50 rems, evacuation
would not usually be the appropriate protective action, because skin
decontamination and clothing changes are easily available and effective
protective actions.
Table 5-3 provides DCFs and DRLs for 4-day exposure to gamma
radiation from selected radionuclides following deposition on the ground
from a plume. The deposition velocity (assumed to be 1 cm/s) could vary
widely, depending on meteorological (primarily precipitation)
conditions. Decision makers are cautioned to pay particular attention to
actual measurements of gamma exposure from deposited materials in
situations where precipitation occurs during plume passage. The
tabulated values include consideration of the dose contributed by
short-lived daughters over the assumed 4-day period of exposure.
The above tables provide DCFs and DRLs for individual exposure
pathways. Since these quantities are all expressed in terms of the
integrated air concentration, they can be conveniently summed over the
three major exposure pathways (plume gamma, plume inhalation, and gamma
exposure to deposited materials) for the early phase to obtain a
composite DRL for each radionuclide. These are tabulated in Table 5-4.
(Since, in the case of exposure of the skin and thyroid, only one pathway
is significant for each, the DCFs and DRLs for these organs are identical
to those in Tables 5-1 and 5-2 for the thyroid and skin.) Table 5.4
summarizes all the factors necessary to evaluate the significance of
environmental concentrations during the early phase of an accident.
To apply the data in Table 5-4, one may use either the DCFs or
DRLs. The DCFs are used by calculating the projected composite dose for
each radionuclide, summing these doses, and comparing them to the PAG.
The DRLs may be used by summing the ratios of the concentration of each
5-13
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I
!-•
JS
Table 5-3 Dose Conversion Factors (DCF) and Derived Response Levels (DRL)
for 4-Day Exposure to Gamma Radiation from Deposited Radionuclides
Radionuclidea
Zr-95
Nb-95
Ru-103
Ru/Rh-106
Te/I-132
1-131
1-132
1-133
1-135
Cs-134
Cs/Ba-137
Ba-140
Ce-144
Np-239
DCFb
rem
uCi-h/cm3
2.8E+4
2.7E+4
1.8E+4
7.6E+3
7.6E+3
1.4E+4
2.9E+3
7.1E+3
5.1E+3
5.9E+4
2.1E+4
5.1E+4
2.1E+3
3.8E3
DRL^.C
uCi-h/cm3
3.5E-5
3.7E-5
5.7E-5
1.3E-4
1.3E-4
7.1E-5
3.4E-4
1.4E-4
2.0E-4
1.7E-5
4.7E-5
2.0E-5
4.9E-4
2.6E-4
a Data are from Table IX, page 56, IAEA Safety Series 81 (IA-86).
b Assumes a deposition velocity of 1 cm/sec, and that all
activity is deposited at approximately the time of the incident.
c Assumes a PAG of 1 rem.
-------
-------
radionuclide to its corresponding DRL. If the sum of the ratios exceeds
unity, the appropriate protective action should be initiated.
The following example demonstrates the use of the data in Table 5-4
for a simple analysis involving three radionuclides.
EXAMPLE:
Based on source term and meteorological considerations, it is
assumed that the worst probable accident at an industrial facility is a
fire that could disperse radioactive material into the atmosphere,
yielding a time-integrated concentration of radionuclides at a nearby
populated area, as follows:
Radionuclide uCi-h/cm
Zr-95 2E-6
Cs-134 4E-8
1-131 1.2E-5
We examine whether evacuation is warranted at these levels, based on
PAGs of 1 rem for effective dose to the whole body, 5 rems for dose to
the thyroid, and 50 rems for dose to skin. We use the DCFs in Table 5-4
and the following equation:
HE - E on
where HF = effective dose (rem),
D = DCF x C ; where, for radionuclide n,
DCF = dose conversion factor, and
C = environmental concentration.
For effective dose:
(2 E-6 x 5.4E+4) + (4E-8 x 1.0 E+5) + (1.2E-5 x 6.5E+4) = 0.89 rem.
For dose to the thyroid:
1.2E-5 x 1.7E+6 = 20.4 rems.
For dose to the skin:
(2E-6 x 1.5E+5) + (4E-8 x 1.2E+5) + (1.2E-5 x 5.5E+5) = 6.9 rems.
5-16
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The results of these calculations show that, at the location for
which these time-integrated concentrations are specified, the
committed dose equivalent to the thyroid from inhalation would be
about four times the PAG for dose to thyroid, thus justifying
evacuation. Using meteorological dilution factors, one could
calculate the additional distance to which evacuation would be
justified to avoid exceeding the PAG for thyroid dose.
The process for using the DRLs from Table 5-4 is as follows:
DRL
where DRLn is the derived response level for radionuclide n, and Cn
is defined above.
For effective dose:
2 E-6 4E-8 1.2 E-5
1.9 E-5 1 E-5 1.5 E-5
For the dose to thyroid:
1.2 E-5
3.0 E-6 " 4
For the dose to skin:
2 E-6 4 E-8 1.2 E-5
3.3 E-4 4.2 E-4 9.1 E-5
. „_„
It is apparent that these calculations yield the same conclusions.
5.4.3 Relative Importance of Exposure Pathways
Many emergency response plans have already been developed using
previously-recommended PAGs that apply to the dose equivalent to the
whole body from direct (gamma) radiation from the plume and to the
thyroid from inhalation of radioiodines. Those PAGs were 1 to 5 rems to
the whole body and 5 to 25 rems to the thyroid. For response to nuclear
5-17
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power plant accidents, they provide public protection comparable to that
provided by the PAGs based on effective dose equivalent and dose
equivalent to the thyroid and skin now recommended. This is demonstrated
in Table 5-5, which shows comparative doses for nuclear power plant
fuel-melt accident sequences having a wide range of magnitudes.
Thyroid dose, skin dose, and effective dose to the whole body from
the three major plume exposure pathways were calculated for radionuclide
mixes postulated for three nuclear power plant accident sequences, using
the dose conversion factors in Table 5-4. The doses were then normalized
for each accident so that they represent a location in the environment
where the controlling dose (effective, thyroid, or skin) would be equal
to the corresponding current PAG. The calculated direct radioactive dose
from external gamma radiation from the plume, based on data in Table 5-1,
is shown in the last column.
Table 5-5 Comparison of Projected Doses for Various Accident Scenarios
Accident Effective dose Skin dose Thyroid dose Direct radiation
category3 equivalent'' equivalent equivalent dose equivalent
(rem) (rem) (rem) (rem)
SST-1
SST-2
SST-3
0.6
0.8
0.4
6 5C
3 5C
7 5C
0.03
0.33
0.03
a See NUREG/CR-2239(SM-82) for a description of these accident scenarios.
D The dose is the the sum of doses from 4-day exposure to direct
radiation from and inhalation of the plume, and from deposited materials,
c Doses are normalized so that the relevant projected dose is equal
to the limiting PAG.
5-18
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Based on the results shown in Table 5-5, the following conclusions
are apparent for the accident sequences analyzed:
1. The current PAG for thyroid dose is controlling for all three
accident categories. For the SST-2 category, effective dose
approaches being controlling.
2. Application of the full range of the previous PAG (5-25 rems) for
thyroid would provide the same or less protection, depending on
the choice of level within the range.
3. Skin doses will not be controlling for any of the accident
sequences (if bathing and change of clothing is completed within
12 hours of plume passage, as assumed).
4. Gamma dose from direct exposure to the plume is small compared to
the effective dose from the three major exposure pathways
combined.
5.5 Protective Actions
This section provides guidance for implementing the principal
protective actions available for protection against an airborne plume,
sheltering and evacuation. Sheltering means the use of the closest
available structure which will provide protection from exposure to an
airborne plume, and evacuation means the transfer of individuals away
from the path of the plume.
Sheltering and evacuation provide different levels of dose reduction
for the principal exposure pathways (inhalation of radioactive material,
and direct gamma exposure from the plume on from material deposited on
surfaces.) The effectiveness of evacuation depends primarily on how
rapidly it can be implemented in relation to the arrival of radioactive
material at a given location. Sheltering, which in most cases should be
almost immediately implementable, varies in usefulness depending upon the
type of shelter available and the duration of the plume passage.
5-19
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Studies have been conducted to evaluate shelter (EP-78a) and
evacuation (HA-75) as protective actions. Reference EP-78b suggests one
method for evaluating and comparing the benefits of these two actions.
This requires collecting planning information before and data following
an incident, and using calculations and graphical means to evaluate
whether evacuation, sheltering, or a combination of sheltering followed
by evacuation should be recommended at different locations. Because of
the many interacting variables, the user is forced to choose between
making decisions during the planning phase, based on assumed data that
may be grossly inaccurate, or using a time-consuming more comprehensive
process after the incident when data may be available. In the former
situation, the decision may not have a sound basis, whereas in the
latter, the decision may come too late to be useful.
The recommended approach is to use planning information for making
early decisions. The planned response should then be modified following
the incident only if timely detailed information is available to support
such modifications.
The planner should first compile the necessary information about the
emergency planning zone (EPZ) around the facility. This should include
identifying the population distribution, the sheltering effectiveness of
residences and other structures, institutions containing population
groups that require special consideration, evacuation routes, logical
boundaries for evacuation zones, transportation systems, communications
systems, and special problem areas. In addition, the planner should
identify the information that may be available following an incident,
such as environmental monitoring data, meteorological conditions, and
plant conditions. The planner should identify key data or information
that would justify specific protective actions. The evaluation and
planning should also include the selection of institutions where persons
should be provided with stable iodine for thyroid protection in
situations where radioiodine inhalation is projected.
The following sections discuss key factors which affect the choice
between evacuation and sheltering.
5-20
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5.5.1 Evacuation
The primary objective of evacuation is to avoid exposure to airborne
or deposited radioactive material by moving individuals away from the
path of the plume. Accordingly, evacuation, if accomplished soon enough,
can be 100 percent effective in avoiding exposure. If, however,
evacuation coincides with or follows plume passage, the reduction of
exposure will be only partial. Since, in the absence of evacuation,
sheltering will be implemented at any location where significant exposure
is possible, the maximum dose avoided by evacuation will be the dose not
avoidable by sheltering. Accordingly, if an evacuation is carried out
improperly and direct exposure to the plume occurs during evacuation
itself, the dose could be greater than if sheltering were continued.
Some general conclusions regarding evacuation (HA-75) which may be
useful for planning purposes are summarized below:
1. Advanced planning is essential to identify potential problems
that may occur in an evacuation.
2. Most evacuees use their own personal transportation.
3. Most evacuees assume the responsibility of acquiring food and
shelter for themselves.
4. Evacuation costs are highly location-dependent and usually will
not be a deterrent to carrying out an evacuation.
5. Neither panic nor hysteria has been observed when evacuation of
large areas is managed by public officials.
6. Large or small population groups can be evacuated effectively
with minimal risk of injury or death.
7. The risk of injury or death to individual evacuees does not
change as a function of the number of persons evacuated, and can
5-21
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be conservatively estimated using National Highway Safety Council
statistics for motor vehicle accidents (subjective information suggests
that the risks will be lower).
Evacuation of the elderly, the handicapped, and inhabitants of
medical and penal institutions presents special problems. When
sheltering can provide adequate protection, this will often be the
protective action of choice. However, if the general public is evacuated
and those in institutions are sheltered, there is a risk that attendants
at these institutions may leave and make later evacuation of
institutionalized persons difficult because of a lack of attendants.
Conversely, if evacuation of institutions is attempted during evacuation
of the public, traffic conditions may cause unacceptable delays. If
evacuation of institutions is attempted before evacuating the public,
increased risk to the public from a delayed evacuation could occur,
unless the incident is very slow in developing to the point of an
atmospheric release. The potential risk to society of evacuating
dangerous criminals from prison at relatively low projected doses should
also be considered.
Because of the above difficulties, medical and penal institutions
located within the EPZ should be evaluated to determine whether there are
any logical categories of persons that should be evacuated after the
public (or, when time permits, before).
5.5.2 Sheltering
Sheltering refers here to the use of readily available nearby
structures for protection from exposure to an airborne plume.
As with evacuation, delay in taking shelter during plume passage
will reduce the protection from exposure to radiation. The degree of
protection provided by structures is governed by attenuation of radiation
by structural components (the mass of walls, ceilings, etc.) and by
outside/inside air-exchange rates. These two protective characteristics
are considered separately.
5-22
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The protection factor may be characterized by a dose reduction
factor (DRF), defined as:
DRF =
dose with protective action
dose without protective action*
The shielding characteristics of most structures for gamma radiation can
be categorized based on whether they are "small" or "large." Small
structures are primarily single-family dwellings, and large structures
include office, apartment, industrial, and commercial buildings. The
typical attenuation factors given in Table 5-6 show the importance of the
type of structure for protection from direct radiation (EP-78a). If the
structure is a wood frame house without a basement, then sheltering from
gamma radiation would provide a DRF of 0.9; i.e., only 10 percent of the
dose would be avoided. The DRFs shown in Table 5-6 are initial values
prior to infiltration and therefore apply to short duration plumes. The
values will increase with increasing time of exposure to a plume because
of the increasing importance of inside-outside air exchange. However,
this reduction in efficiency is not dramatic for gamma radiation because
most of the dose arises from outside, not from the small volume of
contaminated air inside a shelter. Therefore, most shelters will retain
their efficiency as shields against gamma radiation, even if the
concentration inside equals the concentration outside.
Table 5-6 Representative Dose Reduction Factors for Direct
Radiation
Structure
Wood frame house (first floor)
Wood frame house (basement)
Masonry house
Large office or industrial building
DRF
0.9
0.6
0.6
0.2 or less
Effectiveness
(percent)
10
40
40
80 or better
5-23
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The second factor contributing to the degree of protection
(primarily against exposure by inhalation) is the inside/outside air
exchange rate. This is expressed as the number of air exchanges per
hour, L (h~ ), or the volume of fresh air flowing into and out of the
structure per hour divided by the volume of the structure. Virtually any
structure that can be used for sheltering has some degree of outside/
inside air exchange due to natural ventilation, forced ventilation, or
uncontrollable outside forces, primarily wind.
Assuming constant atmospheric and source conditions and no effects
from filtration, deposition, or radioactive decay, the following model
can be used to estimate the buildup of indoor concentration of
radioactivity from a given outdoor concentration as a function of time,
after appearance of the plume, and of ventilation rate:
Ci = C0(l - e-Lt),
where C. = concentration inside,
C = concentration outside,
1
L = ventilation rate (h ), and
t = elapsed time (h).
Typical values for ventilation rates range from 0.2 to several air
exchanges per hour. In the absence of measurements, an air exchange rate
of 1.0/h may be assumed for structures with no special preparation except
for closing the doors and windows. An air exchange rate of 0.3/h is
appropriate for relatively air-tight structures, such as well-sealed
residences, interior rooms with doors chinked and no windows, or large
structures with ventilation shut off. Using the above model to calculate
indoor concentrations relative to outdoor concentrations after one, two,
and four complete air exchanges, the indoor concentrations would be about
64 percent, 87 percent, and 98 percent of the outside concentrations,
respectively. It is apparent that staying in a shelter for more time
than that required for one or two complete air exchanges is not very
effective for reducing inhalation exposure.
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The inhalation DRF is equal to the ratio of the average
inside-to-outside air concentrations over the period of sheltering.
Studies have been conducted of typical ventilation rates for dwellings
(EP-78a) and for large commercial structures (GR-86). In each case the
rate varies according to the air tightness of the structure, windspeed,
and the indoor-to-outdoor temperature difference. It is not practical,
however, to adjust the implementation of the PAGs for these variables, so
average ventilation rates were chosen for the two types of structures
that are of greatest interest for decisions on evacuation and
sheltering. Table 5-7 shows calculated dose reduction factors for
inhalation exposure as a function of plume duration, assuming average
ventilation rates for these structures.
A potential problem with sheltering is that persons may not leave
the shelter as soon as the plume passes and, as a result, will receive
exposure from radioactive gases trapped inside. The values for DRFs
tabulated in Table 5-7 ignore this potential contribution. This effect
Table 5-7 Dose Reduction Factors for Inhalation
Ventilation rate
(air changes/h)
0.3a
1.0b
Duration of
plume exposure
0.5
1
2
4
6
0.5
1
2
4
6
DRF
0.07
0.14
0.25
0.41
0.54
0.21
0.36
0.56
0.75
0.83
a Applicable to relatively "airtight" structures
such as well-sealed residences, interior rooms
with chinked doors and no windows, or large
structures with outside ventilation shut off.
b Applicable to structures with no special
preparation except for closing of doors and
windows.
5-25
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is minor for gamma dose (generally less than a 10 percent increase in the
dose received during plume passage, (EP-78b)), but can be greater for
inhalation dose.
Dose reduction factors for sheltering can be improved in several
ways, including reducing air exchange rates by sealing cracks and
openings with cloth or weather stripping, tape, etc. and filtering the
inhaled air with common items like wet towels and handkerchiefs.
5.5.3 Dual Protective Actions
A combination of sheltering followed by evacuation may be effective
for situations where the plume is projected to arrive too soon to permit
effective evacuation or if there are longer than expected periods of
exposure.
Another evacuation/shelter protective action combination that may be
effective occurs when it is desirable to evacuate people in a high-dose
area, but shelter those in areas farther downwind where sheltering could
provide an adequate level of protection and thus reduce the possibility
of overloading evacuation routes.
There may also be situations where sheltering in large structures
will give adequate protection, but it is desirable to evacuate
individuals from less effective shelters. This sort of "shelter-
availability" split may be appropriate if timely evacuation is difficult
in areas where large structures are more prevalent than small structures.
Situations may also occur in which sheltering is appropriate
initially because of a prediction of a short duration plume, and, because
the duration is more extended than anticipated, it becomes necessary to
reduce the dose by evacuation.
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5.5.4 General Guidance for Evacuation and Sheltering
The process of evaluating, recommending, and implementing evacuation
or shelter for the public is far from an exact science, particularly in
view of time constraints that prevent thorough analysis at the time of an
incident. Its effectiveness, however, can be improved considerably by
planning and testing. Early decisions should be based on information
collected from the emergency planning zone during the planning phase and
on information regarding conditions at the nuclear facility at the time
of the incident. Generally, it is to be expected that evacuation will be
appropriate initially near the point of release, with sheltering being
preferred (at least temporarily until more information is available) at
greater distances in the downwind direction.
The following should be helpful in making more detailed decisions:
1. Evacuation will provide total protection from any airborne
release if it is completed before arrival of the plume.
2. Sheltering may be appropriate because:
a. It is faster than evacuation,
b. It may provide adequate protection,
c. A majority of the public is already sheltered, or
d. It is less expensive and disruptive.
3. Sheltering is usually not appropriate for significant exposure
lasting longer than two complete air exchanges (2 to 6 hours
for most structures).
4. Because sheltering may be implemented in less time than
evacuation, it may be the protective action of choice if rapid
evacuation is impeded, e.g.:
a. Short time avail able—high wind velocity, location close to
source;
b. Severe environmental conditions—weather, flood;
c. Health constraints—hospitals, nursing homes;
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d. Public safety considerations—prisoners, emergency workers;
and
e. Long mobilization times—certain industries, farms.
5. The longer the projected duration of exposure, the less
attractive sheltering becomes, particularly in small
structures. Effectiveness of shelters can be improved by
turning off ventilation systems, closing cracks and other
penetrations, and filtering inhaled air, Turning off
ventilation systems could pose a severe hazard in some
facilities, thus reducing their appropriateness as a shelter.
6. If the plume is expected to arrive during mobilization for
evacuation, it may be appropriate to shelter first, then
evaluate the desirability of subsequent evacuation.
7. The use of large structures, such as shopping centers, schools,
churches, and commercial buildings, as collection points during
evacuation mobilization will generally provide greater
protection than use of small structures.
8. If a major release of radioiodine or particulate materials
occurs, inhalation dose may be the controlling criterion. In
this case:
a. Ventilation control is essential for effective sheltering.
b. Simple filtering of breath using common household items
(i.e., folded wet handkerchiefs or towels) is of
significant help.
c. Following plume passage, people should exit shelters to
avoid airborne activity trapped inside, and they should
leave high exposure areas as soon as possible after cloud
passage to avoid exposure to deposited radioactive material
d. Consideration should be given to the prophylactic
administration of potassium iodide (KI) as a
thyroid-blocking agent to emergency workers, prisoners,
workers in critical industries, and others for whom State
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and local plans may not include evacuation as a
predetermined protective action.
9. If whole body dose is the controlling criterion, shelter
construction and size are the most important considerations;
ventilation control and filtering are less important. The main
factors which reduce whole body exposure are:
a. Wall thickness and size of structure,
b. Number of stories overhead, and
c. Central location within the structure.
6 Each State has the responsibility for formulating guidance to define
when (and if) the public should be given potassium iodine and
instructions on how to use it to reduce the thyroid uptake of
radioiodine. Planning for its use should include the considerations in
"Potassium Iodide as a Thyroid-blocking Agent in a Radiation Emergency:
Final Recommendations on Use" (FD-82).
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REFERENCES
EP-78a U.S. ENVIRONMENTAL PROTECTION AGENCY. Protective Action
Evaluation Part I - The Effectiveness of Sheltering as a
Protective Action Against Nuclear Accidents Involving Gaseous
Releases, EPA 520/1-78-001A. National Technical Information
Service, 5285 Port Royal Road, Springfield, VA 22161 (PB-215
428), 1978.
EP-78b U.S. ENVIRONMENTAL PROTECTION AGENCY. Protective Action
Evaluation Part II - Evacuation and Sheltering as Protective
Actions Against Nuclear Accidents Involving Gaseous Releases, EPA
520/1-78-001B. National Technical Information Service, 5285 Port
Royal Road, Springfield, VA 22161 (PB-215 451), 1978.
FD-82 FOOD AND DRUG ADMINISTRATION (HHS). Potassium Iodide as a
Thyroid-Blocking Agent in a Radiation Emergency: Final
Recommendations on Use, 47 FR 28158, Food and Drug Administration
(HHS), Washington, DC, June 29, 1982.
GR-85 GREENHALGH, J.R. et al. Doses from Intakes of Radionuclides by
Adults and Young People. NRPB-R162. National Radiological
Protection Board, Oxfordshire, England, OX110RQ, 1985.
GR-86 GROT, RICHARD A. AND ANDREW K. PERSILY. Measured Air
Infiltration Rates in Eight Large Office Buildings. Special
Technical Publication 904. 1986. American Society for Testing
and Materials. 1916 Race Street, Philadelphia, PA 19103.
HA-75 HANS, J.M., JR. AND SELL, T.C. Evacuation Risks - An Evaluation,
EPA-520/6-74-002. National Technical Information Service, 5285
Port Royal Road, Springfield, VA 22161 (PB-235 334/AS), 1975.
IA-86 INTERNATIONAL ATOMIC ENERGY AGENCY. Derived Intervention Levels
for Application in Controlling Radiation Doses to the Public in
the Event of a Nuclear Accident or Radiological Emergency. IAEA
Safety Series No. 81. International Atomic Energy Agency,
Vienna, Austria, 1986.
KO-81 KOCHER, D.C. Dose Rate Conversion Factors for External Exposure
to Photons and Electrons, NUREG/CR-1918. U.S. Nuclear Regulatory
Commission, Washington, DC 20555, 1981.
NR-75 U.S. NUCLEAR REGULATORY COMMISSION. An Assessment of Accident
Risks in U.S. Commercial Nuclear Power Plants. (WASH-1400), U.S.
Nuclear Regulatory Commission, Washington, DC 20555, 1975.
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NR-78 U.S. NUCLEAR REGULATORY COMMISSION and U.S. ENVIRONMENTAL
PROTECTION AGENCY. Task Force Report. Planning Basis for the
Development of State and Local Government Radiological
Emergency Response Plans in Support of Light Water Nuclear
Power Plants, NUREG-0396 or EPA-520/1-78-016, U.S.
Environmental Protection Agency, Office of Radiation Programs,
Washington, DC 20460, 1978.
SN-82 SANDIA NATIONAL LABORATORY. Technical Guidance for Siting
Criteria Development. NUREG/CR-2239. U.S. Nuclear Regulatory
Commission, Washington, DC 20555, 1982.
5-31
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CHAPTER 6
Implementing the PAGs for the Intermediate Phase
(Food and Water)
(reserved)
-------
CHAPTER 7
Implementation Guidance for Protective Actions
During the Intermediate Phase
(Exposure to Deposited Materials)
7.1 Introduction
This chapter provides guidance for implementing the PAGs set forth in
Chapter 4. This guidance is for use by State and local officials in
developing their radiological emergency response plans to protect the
public from exposure to radiation from deposited radioactive materials.
See Appendix A for definitions and Appendix F for the rationale on which
these PAGs are based.
Contrary to the situation during the early phase of a nuclear
incident, when decisions usually must be made and implemented quickly by
State and local officials before Federal assistance is available, many
decisions and actions during the intermediate phase can be delayed until
Federal resources are present, as described in the Federal Radiological
Monitoring and Assistance Plan (FE-84). Because of the reduced level of
urgency for immediate implementation of these protective actions, somewhat
less detail may be needed in State radiological emergency response plans
than is required for the early phase.
At the time of decisions on relocation and early decontamination,
some sheltering and evacuation may have already been completed to protect
the public from exposure to the airborne plume. These protective actions
may have been implemented prior to verification of the path of the plume
and therefore some persons may have been unnecessarily evacuated from
areas where actual dose is much lower than projected. Others who were in
the path of the plume may have been sheltered or not protected at all.
During the intermediate phase of the response persons must be relocated
from areas where the projected dose exceeds the PAG for relocation, and
other actions taken to reduce dose to persons who are not relocated.
7-1
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7.1.1 Protective Actions
The main protective actions for protection of the public from
exposure to deposited radioactivity are relocation, decontamination,
shielding, time limits on exposure, and control of the spread of surface
contamination. Relocation is the most effective, and, usually, the most
costly and disruptive. It is therefore only applied when the dose is
sufficiently high to warrant such. The others are generally applied to
reduce exposure of persons who are not relocated, and apply to areas that
receive lower levels of deposited radioactivity. This chapter provides
guidance for translating radiological conditions in the environment to
projected dose, to provide the basis for decisions on the appropriate
protective actions.
7.1.2 Areas Involved
Figure 7-1 provides a generalized example of the different areas and
population groups to be dealt with. The path of the plume is assumed to
be represented by area 1. In reality, variations in meteorological
conditions would almost certainly produce a more complicated shape, but
the same principles would apply.
Because of plant conditions and other considerations prior to or
after the release, persons will already have been evacuated from area 2
and sheltered in area 3. Persons who have been evacuated from or
sheltered in areas 2 and 3, respectively, as precautionary actions for
protection from the plume, but whose homes are outside the plume
deposition area (area 1), may return to their homes or discontinue
shelter as soon as environmental monitoring verifies the boundary of the
area that received deposition (area 1).
Area 4 is designated a restricted zone and is defined as the area
where projected doses are equal to or greater than the relocation PAG.
Persons residing just outside the boundary of the restricted zone may
receive a dose near the PAG for relocation if decontamination or other
dose reduction efforts are not implemented.
7-2
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LO
ARBITRARY SCALE
PLUME TRAVEL
DIRECTION
LEGEND
| | 1. PLUME DEPOSITION AREA.
L-J
2. AREA FROM WHICH POPULATION IS EVACUATED.
3. AREA IN WHICH POPULATION IS SHELTERED.
4. AREA FROM WHICH POPULATION IS RELOCATED (RESTRICTED ZONE).
FIGURE 7-1. RESPONSE AREAS.
-------
Area 1, with the exception of the restricted zone, represents the
area of contamination that may continue to be occupied by the general
public. Nevertheless, there will be contamination levels in this area
that will require continued monitoring and dose reduction efforts other
than relocation.
The relative positions of the boundaries shown in Figure 7-1 depend
on areas evacuated and sheltered, and the radiological characteristics of
the release. For example, area 4 (the restricted zone) could fall
entirely inside area 2 (area evacuated), so that the only persons to be
relocated would be those residing in area 4 who were missed in the
evacuation process.
At the time the restricted zone is established, a temporary buffer
zone (not shown in Figure 7-1) may be needed outside portions of the
restricted zone in which occupants will not be allowed to return until
monitoring confirms the stability of deposited contamination. Such zones
would be near highly contaminated areas in the restricted zone where
deposited radionuclides might be resuspended and then redeposited outside
the restricted zone. This could be especially important at locations
close to the accident site where the radioactivity levels are high and
the restricted zone may be narrow. The extent of the buffer zone will
depend on local conditions. Similarly, a buffer zone encompassing the
«
most highly contaminated areas in which persons are allowed to reside may
be needed. This area should be monitored routinely to assure
acceptability for continued occupancy.
7.1.3 Sequence of Events
Following passage of the airborne plume, several tasks, as shown in
Figure 7-2, must be accomplished simultaneously to provide for timely
protection of the public. The decisions on the early task of relocating
persons from high exposure rate areas must be based on exposure rate
measurements and dose analyses. It is expected that monitoring and dose
assessment will be an on-going process, with priority given to the areas
7-4
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I I I I Hill I I I I Mill I I I I Mill I I I I Mill
w
oc
3
U
o
o
UJ
PERIOD OF
RELEASE,
DISPERSION,
DEPOSITION,
SHELTERING
AND EVACUATION.
(NO TIME SCALE)
CONDUCT AERIAL AND GROUND SURVEYS. DRAW ISODOSE RATE LINES.
IDENTIFY HIGH DOSE RATE AREAS. CHARACTERIZE CONTAMINATION.
RELOCATE POPULATION FROM HIGH DOSE RATE AREAS.
ALLOW IMMEDIATE RETURN OF EVACUEES TO NONCONTAMINATED AREAS.
ESTABLISH RESTRICTED ZONE BOUNDARY AND CONTROLS.
RELOCATE REMAINING POPULATION FROM WITHIN RESTRICTED ZONE.
GRADUALLY RETURN EVACUEES UP TO RESTRICTED ZONE BOUNDARY
CONDUCT D-CON AND SHIELDING EXPERIMENTS AND ESTABLISH PROCEDURES
FOR REDUCING EXPOSURE OF PERSONS WHO ARE NOT RELOCATED.
PERFORM DETAILED ENVIRONMENTAL MONITORING.
PROJECT DOSE BASED ON DATA
DECONTAMINATE ESSENTIAL FACILITIES AND THEIR ACCESS ROUTES.
RETRIEVE VALUABLE AND ESSENTIAL RECORDS AND POSSESSIONS.
REESTABLISH OPERATION OF VITAL SERVICES.
BEGIN RECOVERY ACTIVITIES.
CONTINUE RECOVERY.
MONITOR AND APPLY A LARA FOR EXPOSED GROUPS.
I I I I II
I I I I I
I I I I Hill
0.1
1.0 10 100
TIME AFTER DEPOSITION (DAYS)
1,000
FIGURE 7-2. TIME FRAME OF RESPONSE TO A MAJOR NUCLEAR REACTOR ACCIDENT (ASSUMED).
-------
with the highest exposure rate. The general sequence of events is
itemized below, but the time frames will overlap, as demonstrated in
Figure 7-2.
A. Based on environmental data, determine the areas where the
projected one-year dose will exceed 2 rems and relocate persons from
those areas, with priority given persons in the highest exposure
rate areas.
B. Allow persons who were evacuated to return immediately to their
residences if they are in areas where field gamma measurements
indicate that exposure rates are near normal background levels (not
in excess of twice the normal background in the area before the
accident). If, however, areas of high deposition are found to be
near areas with low deposition such that resuspended activity could
drift into the occupied areas, a buffer zone should be established
to restrict occupancy until the situation is analyzed and dose
projections are confirmed.
C. Conduct experiments to determine the dose reduction effectiveness
of simple decontamination techniques and of sheltering due to
partial occupancy of-residences and workplaces. Results of these
experiments may influence recommendations for reducing exposure
rates for persons who are not relocated from areas near, but
outside, the restricted zone.
D. Determine the location of the isodose line corresponding to the
relocation PAG, establish the boundary of the restricted zone, and
relocate any persons who still reside within the zone. Also,
convert any evacuees who reside within the restricted zone to
relocation status. Evacuated persons whose residence is in the area
between the boundary of the plume deposition and the boundary to the
restricted zone may return gradually as confidence is gained
regarding the projected dose in the area.
7-6
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E. Establish a mechanism for controlling access to and egress from
the restricted zone. Typically this would be accomplished through
control points at roadway accesses to the restricted zone.
F. Establish monitoring and decontamination stations.
G. Implement simple decontamination techniques in occupied areas,
with priorities for areas with higher exposure rates and for
residences of pregnant women. This includes institutions such as
hospitals.
H. Collect data needed to establish long-term radiation protection
criteria for recovery and data to determine the effectiveness of
various decontamination or other recovery techniques.
I. Begin operations to recover contaminated property in the
restricted zone.
7.2 Establishment of Isodose Rate Lines
As soon as Federal or other assistance is available for aerial and
ground monitoring, a concentrated effort should begin to establish
isodose-rate lines on maps and the identification of boundaries to the
restricted zone. Planning for this effort should include the development of
standard gridded maps that can be used by all of the involved monitoring and
dose assessment organizations to record monitoring data.
Aerial monitoring (e.g., the Department of Energy Aerial Monitoring
Service) can be used to collect data for establishing general patterns of
radiation exposure rates from deposited radioactive material. These data,
after translation to readings at 1 meter above ground, may form the primary
basis for the development of isodose lines out to a distance where aerial
monitoring shows no radiation above twice natural background levels. Air
sample measurements will also be needed to verify the contribution to dose
from this pathway.
7-7
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Gamma exposure rates measured at 1 meter will no doubt vary as a
function of the location of the measurement within a very small area. This
could be caused by different deposition rates for different types of
surfaces (e.g., smooth surfaces versus heavy vegetation). Rinsing or
precipitation could also reduce levels in some areas and raise levels in
others where runoff settles. In general, where exposure rates vary within
designated areas, the higher values should be used for dose projection for
persons within these areas unless judgment can be used to estimate an
appropriate average exposure rate.
Measurements made at 1 meter to project whole body dose from gamma
radiation should be made with instruments of the "closed window" type so as
to avoid the detection of beta radiation. Although beta exposure will
contribute to skin dose, its contribution to the overall risk of health
effects from the radionuclides expected to be associated with reactor
accidents should be minor in comparison to the whole body gamma dose
(AB-88). Special beta dose analyses should be made when time permits to
determine its contribution to skin dose. Since beta dose rate measurements
require sophisticated equipment that is generally not available for field
use, beta dose to the skin should generally be calculated based on
concentrations of radionuclides per unit area. These data will already be
available for use in gamma dose projections.
7.3 Dose Projection
The primary dose of interest for reactor accidents is the sum of the
effective gamma dose equivalent from external exposure and the committed
effective dose equivalent from inhalation. Skin dose from exposure to beta
radiation may also be significant in some cases and should be evaluated.
The exposure periods of interest are first year, second year, and up to 50
years after the accident.
Calculation of the projected gamma dose from measurements will require
knowledge of the principal radionuclides contributing to exposure and their
relative abundances. Information on these radiological characteristics can
7-8
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be compiled either through the use of portable gamma spectrometers or by
radionuclide analysis of environmental samples. Several measurement
locations may be required to determine whether any selective radionuclide
deposition occurred as a function of weather, surface type, or distance from
the point of release. As part of the Federal Radiological Monitoring and
Assessment Plan (FE-84), the U. S. Department of Energy and the U. S.
Environmental Protection Agency have equipment and procedures to assist
State officials in performing environmental measurements, including
determination of the radiological characteristics of deposited materials.
The gamma exposure rate may decrease rapidly if deposited material
includes a significant fraction of short-lived radionuclides. Therefore,
the relationship between instantaneous exposure rate and projected first-
and second-year annual or the 50-year doses will change as a function of
time, and these relationships must be established for the particular mix of
deposited radioactive materials present at the time of the gamma exposure
rate measurement.
For accidents involving releases from nuclear power plants, gamma
radiation from deposited radioactive materials is expected to be the
principal exposure pathway, as noted above. Other pathways should also be
evaluated, and their contributions added, if significant. These may include
inhalation of resuspended material and beta dose to the skin. Exposure from
ingestion of food and water is normally limited independently of decisions
for relocation and decontamination (see Chapters 3 and 6). In some
instances, however, where withdrawal of food and/or water from use would, in
itself, create a health risk, relocation may be an appropriate protective
action for protection from exposure via ingestion. In this case, the
committed effective dose equivalent from ingestion should be added to the
projected dose from other exposure pathways for decisions on relocation.
The following sections provide methods for evaluating the projected
dose from whole body external exposure and from inhalation of resuspended
particulate material, based on environmental information.
7-9
-------
7.3.1 Projected External Gamma Dose
Projected whole body external gamma doses at 1 meter in height at
particular locations during the first year, second year, and over the
50-year period after the accident are the parameters of interest. The
environmental information available for calculating these doses is expected
to be the instantaneous gamma exposure rate at 1 meter in height and the
relative abundance of each radionuclide contributing significantly to that
exposure rate. Calculational models are available for predicting exposure
rate as a function of time due to radioactive decay and weathering (NR-75),
and information is available for relating surface concentrations to a gamma
exposure rate at 1 meter (KO-81).
Following the accident, experiments should be conducted to determine
the dose reduction factors associated with part-time occupancy of dwellings
and workplaces, and with simple, rapid, decontamination techniques, so that
these factors can also be applied to the calculation of dose to persons who
are not relocated. However, these factors should not be included in the
calculation of projected dose for decisions on relocation.
Relocation decisions can generally be made on the basis of the first
year projected dose. However, projected doses during the second year and
over 50 years are needed for decisions on the need for other protective
actions for persons who are not relocated. Dose conversion factors are
therefore needed for converting environmental measurements to projected dose
during the first year, second year, and over 50 years following the
accident. Of the two types of environmental measurements that can be made
to project whole body external gamma dose, gamma exposure rate in air is the
easiest to make and is the most directly linked to gamma dose rate.
However, a few measurements of the second type (radionuclide concentrations
on surfaces) will also be needed to properly project decreasing dose rates.
Tables 7-1 and 7-2 provide information to simplify the development of
dose conversion factors through the use of data on the radionuclide mix, as
determined from environmental measurements. These tables list the deposited
radionuclides most likely to be the major contributors to dose from
7-10
-------
Table 7-1 Initial Gamma Exposure Rate and the Effective Dose Equivalent (Corrected for Radioactive Decay and
Radlonucl
Zr-95
Nb-95
Ru-103
Ru-106
Te-132
1-131
1-132
1-133
1-135
Cs-134
Cs-137
Ba-140
La-140
Weathering) Calculated
Half-Hfe
1de hours
1.54E+03
8.41E+02
9.44E+02
8.84E+03
7.82E+01
1.93E+02
2.30E+00
2.08E+01
6.61E+00
1.81E+04
2.65E+05
3.07E+02
4.02E+01
from an Initial Radlonucl Ide
Initial exposure3
rate at 1 m
(mR/h
per pC1/m2)
1.4E-08
1.5E-08
9.8E-09
4.1E-09
5.3E-09
7.9E-09
4.4E-08
1.2E-08
2.7E-08
3.0E-08
1.2E-08
4.1E-09
4.0E-08
2
Concentration of 1 pC1/m on Ground Surface
year 1
(mrem per
pC1/m2)
3.3E-05
(b)
7.1E-06
2.1E-05
3.4E-06
1.3E-06
(b)
2.3E-07
1.6E-07
l.OE-04
4.7E-05
1.2E-05
(b)
Integrated dose
(weathering factor Included)**
year 2
(mrem per
pC1/m2)
4.0E-07
(b)
0
6.7E-06
0
0
(b)
0
0
4.8E-05
3.0E-05
0
(b)
0-50 year
(mrem per
pC1/m2)
3.4E-05
(b)
7.1E-06
3.3E-05
3.4E-06
1.3E-06
(b)
2.3E-07
1.6E-07
2.4E-04
6.4E-04
1.2E-05
(b)
aBody surface exposure rate at 1 meter above contaminated ground surface. Based on data from Kocher (KO-81).
bRadionuc!1des that have short-lived daughters (Zr/Nb-95, Te/I-132, Ru/Rh-106, Cs-137/Ba-137m, Ba/La-140) are
assumed to quickly reach equilibrium. The Integrated dose factors listed are the effective whole body gamma
dose due to the parent and the daughter. Based on data from Kocher (KO-83).
-------
Table 7-2 Initial Exposure Rate and the Effective Dose Equivalent (Corrected for Radioactive Decay) Calculated
I
(-"
tsJ
from an
Rad1onuc11de
Zr-95
Nb-95
Ru-103
Ru-106
Te-132
1-131
1-132
1-133
1-135
Cs-134
Cs-137
Ba-140
La-140
Initial Rad1onucl1de
Half-Hfe
hours
1.54E+03
8.41E+02
9.44E+02
8.84E+03
7.82E-I-01
1.93E+02
2.30E+00
2.08E+01
6.61E+00
1.81E+04
2.65E+05
3.07E+02
4.02E+01
aBody surface exposure rate at 1 meter
bRad1onucl1des that
assumed to quickly
Concentration of
Initial exposure3
rate at 1 m
(mR/h
per pC1/m2)
1.4E-08
1.5E-08
9.8E-09
4.1E-09
5.3E-09
7.9E-09
4.4E-08
1.2E-08
2.7E-08
3.0E-08
1.2E-08
4.1E-09
4.0E-08
above contaminated
have short-lived daughters (Zr/Nb-95,
reach equilibrium.
2
1 pCI/m on Ground
Surface
Integrated dose
(weathering factor not
year 1
(mrem per
pC1/m2)
3.8E-05
(b)
7.9E-06
2.7E-05
3.4E-06
1.3E-06
(b)
2.3E-07
1.6E-07
1.4E-04
6.3E-05
1.2E-05
(b)
ground surface.
year 2
(mrem per
pC1/m2)
7.0E-07
(b)
0
1.4E-05
0
0
(b)
0
0
9.8E-05
6.2E-05
0
(b)
Based on data from
Ru/Rh-106, Te/I-132, Cs-137/Ba-137m,
The Integrated dose factors listed
Included)15
0-50 year
(mrem per
pC1/m2)
3.9E-05
(b)
7.9E-06
5.4E-05
3.4E-06
1.3E-06
(b)
2.3E-07
1.6E-07
4.8E-04
1.9E-03
1.2E-05
(b)
Kocher (KO-81).
Ba/La-140) are
are the effective whole body gamma
dose due to the parent and the daughter. Based on data from Kocher (KO-83).
-------
accidents at nuclear power facilities. In addition to providing integrated,
effective doses per unit of surface concentration, they provide, in column
three, the exposure rate (mR/h) in air per unit of surface contamination.
All exposure rate values are based on those given by Kocher (KO-81), and the
integrated effective doses are based on dose conversion factors also given
by Kocher (KO-83). Table 7-1 takes into account both radioactive decay and
weathering, whereas the values in Table 7-2 include only radioactive decay.
The effect of weathering is uncertain and will vary depending of the type of
weather, type of surface, and the chemical form of the radionucTides. The
user may choose either table depending on the confidence accorded the
assumed weathering factors.
The following steps can be used to develop dose conversion factors to
calculate projected external whole body gamma dose from gamma exposure rate
measurements for specific mixes of radionuclides:
A. By gamma spectral analysis of environmental samples of deposited
radioactivity, determine the relative abundance of the principal gamma
emitting radionuclides. Analyses of samples from several different
locations may be necessary to determine whether the relative
concentrations of radionuclides are constant. The results should be
expressed as the activity (pCi) for each radionuclide in the sample.
B. Multiply the concentrations from step A by the corresponding values
in column 3 of Table 7-1 or Table 7-2 (depending on whether or not
weathering is to be considered) to determine the (relative)
contributions to the gamma exposure rate (mR/h) at the 1-meter height
for each radionuclide. (The total activity represented by the sample
cancels in step E, thus removing the effect of sample size.)
C. Similarly, multiply the activities from step A by the corresponding
values in columns 4, 5, and 6 to determine the 1-year, 2-year, and
50-year relative integrated doses contributed by each radionuclide.
Radionuclides listed in Tables 7-1 and 7-2 that have short-lived
daughters (Zr/Nb-95, Te/I-132, Ru/Rh-106, Cs-137/Ba-137m, Ba/La-140)
7-13
-------
are assumed to be in equilibrium with their daughters when calculating
the integrated dose, so that the values for the parents include the
total dose from the parent and the daughter. (In the cases of
Cs-137/Ba-137m, and Ru-106/Rh-106, the parents are not gamma emitters
so the listed exposure rates and doses are actually those from the
daughters alone.)
D. Sum the results of step B to determine a total (relative) exposure
•
rate "X" (mR/h) at 1 meter for the sample being considered. Likewise,
for the total first year, second year, and 50-year (relative) doses
•
"H." (mrem), sum the respective results of step C.
E. Using the results from step D, calculate the ratios
DCFi = Hi(mrem)/X (mR/h)
for the first, second, and 50-year doses. (Since the absolute activities
represented in the numerator and denominator are identical, the effect of
the size of the sample cancels.) The result is dose conversion factors
DCF. (mrem per mR/h) for any gamma exposure rate measurement for which
the relative concentrations of radionuclides are the same as in the
sample that was analyzed.
The following example demonstrates the use of the above procedures. For
purposes of the example it is assumed that environmental measurements revealed
a mix of radionuclides as shown in column 3 of Table 7-3. The (relative)
exposure rate conversion factors in column 4 of Table 7-3 are taken from
column 3 of Table 7-1. The (relative) exposure rates in column 5 are the
products of columns 3 and 4. The (relative) doses for individual
radionuclides in columns 6, 7, and 8 were calculated by multiplying the
concentrations in column 3 by the dose conversion factors in columns 4, 5, and
6 of Table 7-1, respectively. (Columns 4, 5, and 6 of Table 7-2, which do not
include weathering, could have been used instead of those in Table 7-1.)
7-14
-------
Table 7-3 Example9 Calculation of Dose Conversion Factors for Gamma Exposure Rate Measurements Based on
Measured Isotoplc Concentrations
Rad1onucl1de
Iod1ne-I3l
Tellurlum-132
1-132
Ruthen1um-I03
Rhodium- 106?
Ces1um-l34
£ Bar1um-I37mf
Total s
Half-life
(hours)
193
78
2.3
944
8,840
18,100
265,000
Measured
concentration
(pC1 /sampled)
2.6E+2
3.6E+3
3.6E+3
2.2E+2
5.0E+1
6.8E+1 •
4.2E+1
mR/hc
2
pCI/m
7.9E-9
5.3E-9
4.4E-8
9.8E-9
4.1E-9
3.0E-8
1.2E-8
Calculated
Exposure rate
at 1 m (mR/hr)
2.0E-6
1.9E-5
1.6E-4
2.1E-6
2.0E-7
2.0E-6
4.9E-7
2.2E-4
Calculated
year 1
(mrem)
3.3E-4
1.2E-2
(e)
1.6E-3
l.OE-3
7.0E-3
2.0E-3
2.4E-2
effective dose
year 2
(mrem)
0
0
(e)
0
3.4E-4
3.3E-3
1.2E-3
4.5E-3
at 1 meter
50 year
(mrem)
3.3E-4
1.2E-2
(e)
1.6E-3
1.6E-3
1.6E-2
2.7E-2
5.8E-2
aThe data In this table are only examples to demonstrate a calculatlonal process. The results should not be
used 1n the prediction of relationships that would exist following a nuclear Incident.
^Calculations are based on data 1n Table 7-1, which Includes consideration of both radioactive decay and
weathering.
cExternal exposure rate factors at 1 meter above ground for a person standing on contaminated ground, based
on data In Table 7-1.
size of the sample Is not Important for this analysis because only the relative concentrations are needed
to calculate the ratio of Integrated dose to exposure rate.
eThe Integrated dose from 1-132 1s not calculated because It Is a short-lived daughter of Te-132, and the
values for Integrated doses 1n Tables 7-1 and 7-2 Include the equilibrium doses from short-lived daughters 1n
the values for the parents.
^Th1s 1s a short lived daughter of a parent that has no gamma emissions and the halfHfe given Is that of the
parent.
-------
For this example, the conversion factor for dose in the first year was
obtained for the assumed radionuclide mix from the totals of columns 5 and
6 of Table 7-3, which indicate that a calculated dose of 0.024 mrem in one
year corresponds to an initial exposure rate of 2.2E-4 mR/h. Therefore,
the first year dose conversion factor (DCF.) for this example is 109 mrem
per mR/h.
This DCF may be multiplied by any gamma exposure rate measurement to
estimate the dose in the first year for locations where the exposure rate
is produced by a radionuclide mix the same as assumed for calculating the
DCF,and where weathering affects the exposure rate as assumed. For
example, if a gamma exposure rate measurement were taken at the location
where the contamination sample in Table 7-3 was taken, this exposure rate
could be multiplied by the DCF calculated in the above example to obtain
the projected first year dose at that point. Based on the example analysis
and a relocation PAG of 2 rems, for this case the exposure rate at the
boundary of the restricted zone should be no greater than
2 rem = 18 mR/h,
109 mrem/mR/h
if the contribution to effective dose from inhalation of resuspended
radioactive materials is zero (See Section 7.3.2). The example DCF for the
second year and 50 years are obtained by a similar process, yielding DCFs
of 20 and 263 mrem per mR/h, respectively.-
The ratio of the second year to first year dose is 20/109 = 0.18. If
this is the case, persons not relocated on the basis of a 2 rem PAG should,
for this example, receive no more than 0.18 x 2 = 0.36 rems in year 2.
Similarly, the dose in fifty years should be no more than 4.8 rems. Actual
doses should be less than these values to the extent that exposure rates
are reduced by shielding from structures and by decontamination.
Prior to reaching conclusions regarding the gamma exposure rate that
would correspond to the relocation PAG, one would need to verify by
multiple sampling the consistency of the relative abundance of specific
radionuclides as well as the relative importance of the inhalation pathway.
7-16
-------
Dose conversion factors will change as a function of the
radiological makeup of the deposited material. Therefore, dose
conversion factors must be calculated based on the best current
information following the accident. Since the relative concentrations
will change as a function of time due to different decay rates, dose
conversion factors must be calculated for specific measurement times of
interest. By calculating the decay of the original sample(s), a plot of
dose conversion factors (mrem per mR/h) as a function of time after the
accident can be developed. As weathering changes the radionuclide mix,
and as more is learned about other dose reduction mechanisms, such
predictions of dose conversion factors may require adjustment.
7.3.2 Inhalation Dose Projection
It can be shown, for the mixture of radionuclides assumed to be
deposited from postulated reactor accidents, and an assumed average
-5 1
resuspension factor of 10 m , that the effective dose from
inhalation is small compared to the corresponding effective dose from
external exposure to gamma radiation. However, air sample analyses
should be performed for specific situations (e.g., areas of average and
high dynamic activity) to determine the magnitude of possible inhalation
exposure. The committed effective dose equivalent (HrQ) resulting from
the inhalation of resuspended airborne radioactive materials is
calculated as follows:
H5Q = I (DCF) (1)
where,
I = The total intake (uCi), and
DCF = effective dose per unit intake (rem/uCi).
It is assumed that tlie intake rate will decrease with time due to
radioactive decay and weathering. No model is available to calculate the
effect of weathering on resuspension of deposited materials, so the model
developed for calculating its effect on gamma exposure rate (MR-75) is
assumed to be valid- This should provide conservative results. The
total intake (I) from inhalation over time t may be calculated for each
radionuclide, using the following equation:
7-17
-------
I =BCQ
0 63
U-PJ
-Ui+X?)t n -(x+Ajt
• *• J
1 -p ) + 11 P ^
X1+X2 X1+X3
(2)
** ^* 1 »* ^ /*1/XO
where
8 = average breathing rate for adults
= 8 E+3 m3/a (IC-75),
C = initial measured concentration of the resuspended radionuclide
3
in air (pCi/m ),
t = time during which radionuclides are inhaled (a),
x, = radioactive decay constant (a~ ),
\2 = assumed weathering decay constant for 63 percent of the
^ i
deposited activity, and is taken as 1.13 a (NR-75), and
x., = assumed weathering decay constant for 37 percent of the
-1
deposited activity, and is taken as 7.48 E-3 a (NR-75).
Table 7-4 tabulates results calculated using the above assumptions
for weathering. The table contains factors relating the committed
effective dose from exposure during the first and second years after the
accident to an initial air concentration of 1 pCi/m for each of the
principal radionuclides expected to be of concern from reactor
accidents. The dose conversion factors are taken from ICRP-30 (IC-78).
Parent radionuclides and their short lived daughters are grouped together
because these dose conversion factors are based on the assumption that
both parents and daughters will occur in equal concentrations and will
decay with the half life of the parent. Therefore, measured
concentrations of the short lived daughters should be ignored and only
the parent concentrations should be used in calculating long term
projected doses.
Table 7-4 lists factors which include the effects of both weathering
and radioactive decay, as well as those that include only the effects of
-------
Table 7-4 Dose Conversion Factors for Inhalation
I
t—•
v£>
Committed effective dose equivalent from specified exposure periods based on
an initial concentration of one pCi/m^ in air (with and without weathering)
Committed dose
considering radioactive
decay and weathering
(mrem per
Committed dose
considering radioactive
decay only
(mrem per
Radionuclide3
Sr-90/Y-90
Z-95/Nb-95
Ru-103
Ru-106/Rh-106
Te-132/ 1-132
1-131
Cs-134
Cs-137/Ba-137m
Ba-140/La-140
Ce-144/Pr-144
year 1
1.3EO
3.0E-2
3.4E-3
2.5E-1
7.1E-4
8.1E-3
2.4E-1
1.8E-1
2.8E-3
8.3E-1
year 2
7.7E-1
0
0
9.0E-2
l.OE-5
0
1.1E-1
1.1E-1
0
1.7E-1
year 1
1.9E 0
3.5E-2
3.8E-3
3.3E-1
7.2E-4
8.3E-3
3.1E-1
2.2E-1
2.9E-3
1.1EO
year 2
1.4E 0
0
0
1.7E-1
l.OE-5
0
2.3E-1
2.3E-1
0
4.0E-1
aShort lived daughters are not listed separately because the entries include the dose from both the
daughter and the parent. These factors are based on the concentration of the parent only, at the
beginning of the exposure period.
-------
radioactive decay. Users of these data should decide which factors to use
based on their confidence on the applicability of the weathering models used
(NR-75) to their environment.
The committed effective dose equivalent is calculated by multiplying
the measured initial air concentration (pCi/m ) for each radionuclide of
concern by the appropriate factor from the table and summing the results.
This sum may then be added to the corresponding external whole body gamma
dose to yield the total committed effective dose equivalent from these two
pathways.
The PAGs include a guide for dose to skin 50 times the magnitude of the
PAG for effective dose. Analyses indicate (EP-88) that this guide is not
likely to be controlling for radionuclide mixes expected to be associated
with nuclear power plant accidents. Dose conversion factors are provided in
Table 7-5 for use in case of accidents where the source term consists
primarily of pure beta emitters. The skin dose from each radionuclide may
be calculated using the corresponding dose conversion factor.
Table 7-5 Skin Beta Dose Conversion Factors for Exposure to Deposited
Radionuclides
Dose conversion factors3
Radionuclides
Sr/Y-90
Zr/Nb-95
Ru-103
Ru/Rh-106
Te/ 1-132
1-131
Cs-134
Cs-137/Ba-137m
Ba/La-140
Ce/Pr-144
(mrem per
Radioactive decay
plus weathering
6.8E-4
3.5E-7
1.3E-7
6.8E-4
3.8E-6
1.3E-7
5.4E-6
3.0E-5
5.0E-5
5.5E-4
pCi/m2)
Radioactive
decay only
l.OE-3
4.0E-7
1.4E-7
8.8E-4
3.9E-6
1.4E-7
7.1E-6
3.7E-5
5.1E-5
7.2E-4
aDose equivalent integrated for a one-year exposure
7-20
-------
7.4 Priorities
In most cases protective actions during the intermediate phase will
be carried out over a period of many days. It is therefore useful to
consider what priorities are appropriate. Further, for situations where
the affected area is so large that it is impractical to relocate all of
the public, especially from areas exceeding the PAGs by only a small
amount, priorities are needed for protective actions. The following
priorities are appropriate:
1. As a first priority, assure that all persons are protected from
doses that could cause acute health effects from all exposure
pathways, including previous exposure to the plume.
2. Recommend the application of simple decontamination techniques
and that persons remain indoors as much as possible to reduce
exposure rates.
3. Establish priorities for relocation with emphasis on high
exposure rate areas and pregnant women (especially those in the
8th to 15th week of pregnancy).
7.5 Reentry
After the restricted zone is established, persons will need to
reenter for a variety of reasons, including recovery activities, retrieval
of property, security patrol, operation of vital services, and, in some
cases, care and feeding of farm animals. It may be possible to quickly
decontaminate access ways to vital institutions and businesses in certain
areas so that they can be occupied by adults either for living (e.g.,
institutions such as nursing homes, prisons, and hospitals) or for
employment. Clearance of these areas for such occupancy will require dose
reduction to comply with occupational exposure limits (EP-87). Dose
projections for individuals should take into account the maximum expected
duration of exposure.
7-21
-------
Persons residing or working in areas inside the restricted zone
should operate under the controlled conditions normally established for
occupational exposure.
7.6 Surface Contamination Control
Areas under the plume can be expected to contain deposited
radioactive materials if aerosols or particulate materials were released
during the accident. In extreme cases, individuals and equipment may be
highly contaminated, and screening stations will be required for emergency
monitoring and decontamination of individuals and to evaluate the need for
medical evaluation. Equipment should be checked at this point and
decontaminated as necessary to avoid the spread of contamination to other
locations. This screening service would be required for only a few days
following plume passage until all such persons have been evacuated or
relocated.
After the restricted zone is established, based on the PAGs for
relocation, adults may reenter the restricted zone under controlled
conditions in accordance with occupational exposure standards. Monitoring
stations will be required along roadways to control surface contamination
at exits from the restricted zone. Because of the possibly high
background radiation levels at control points near exits, significant
levels of surface contamination on persons and equipment may be
undetectable at these locations. Therefore, additional monitoring and
decontamination stations may be needed at nearby low background
locations. Decontamination and other measurements should be implemented
to maintain low exposure rates at monitoring stations.
7.6.1 Considerations and Constraints
Surface contamination limits recommended to control routine
operations at nuclear facilities and to transport radioactive material are
generally at set levels lower than are practical for accident situations
involving high-level, widespread contamination of the environment.
7-22
-------
The principal exposure pathways for loose surface contamination on
persons, clothing, and equipment are (a) internal doses from ingestion by
direct transfer, (b) internal doses from inhalation of resuspended
materials, (c) skin dose from contaminated skin or clothing, and (d) whole
body dose from external gamma radiation.
Because of the difficulties in predicting the destiny of uncontrolled
surface contamination, a contaminated individual or item should not be
released to an unrestricted area unless contamination levels are low
enough that they produce only a small dose (e.g., less than 10 percent),
compared to the whole body gamma dose in the area that is unrestricted.
On the other hand, a level of contamination comparable to that existing on
surfaces immediately outside the restricted zone may be acceptable on
materials leaving the restricted zone. Otherwise, persons and equipment
occupying areas immediately outside the restricted zone would not meet the
surface contamination limits. These two constraints can be used to set
permissible surface contamination values.
The contamination limit should be influenced by the potential for the
contamination to be ingested, inhaled, or transferred to other locations.
Therefore, it is reasonable to have lower limits for surfaces where
contamination is loose than on surfaces where the contamination is fixed.
For routine (nonaccident) situations, measurement of gross beta-gamma
surface contamination levels is commonly performed with a thin-window
geiger counter or ionization chamber. In accident situations where gamma
exposure rates are high enough to be measured with such equipment, the
corresponding beta readings would not be predictable or interpretable in
terms of dose, but they would yield much higher instrument readings than
the gamma component. Therefore, it is recommended in these cases that
surface contamination measurements be performed using gamma exposure rate
measurements with the beta shield closed. In low background areas, thin
2
window (approximately 30 mg/cm ) measurements would be appropriate to
improve detectability.
7-23
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7.6.2 Numerical Relationships
As discussed in Section 7.3.1, a relationship can be established
between projected first year doses and instantaneous gamma exposure rates
from properly characterized surface contamination. Based on assumed
radiological characteristics of releases from fuel melt accidents, gamma
exposure rates in areas where the projected dose is equal to the
relocation PAG of 2 rems in the first year will be in the range of 2 to 5
mR/h during the first few days following the deposition from an SST-2
accident. (This relationship must be determined for each specific release
mixture.) Based on relationships in NURE6 CR-1918 (KO-81) and a mixture
of radionuclides expected to be typical of an SST-2 type accident, surface
7 2
contamination levels of 8x10 pCi/m would correspond approximately to
a gamma exposure rate of 1 mR/h at 1 meter height.
7.6.3 Recommended Surface Contamination Limits
Surface contamination must be controlled both before and after
relocation PAGs are implemented. Therefore, this section deals with the
control of surface contamination on persons and equipment being protected
during both the early and intermediate phases of a nuclear accident.
For emergency situations, the following general guidance regarding
surface contamination is recommended:
A. Do not delay urgent medical care for decontamination efforts or
for time-consuming protection of attendants.
B. Do not waste effort trying to contain contaminated wash water.
C. Do not allow monitoring and decontamination to delay evacuation
from high or potentially high exposure rate areas.
D. Establish monitoring and personnel decontamination (bathing)
facilities at evacuation centers. Encourage evacuated persons who
did not go to an evacuation center but who were in specified
7-24
-------
areas at specified times (based on the location of the airborne
plume) to bathe, change clothes, wash clothes, and wash other
exposed surfaces such as cars and trucks and their contents and then
report to these evacuation centers for monitoring. Table 7-6
provides recommended surface contamination screening levels for use
at these centers.
E. After plume passage, establish contamination screening stations
in areas reading less than 5 mR/h gamma exposure rate. These
screening stations should be used to monitor persons emerging from
possible high exposure areas, provide simple (rapid) decontamination
if needed, and make decisions on whether to send them for medical
care or to a monitoring and decontamination station in a lower
background area. Table 7-7 provides recommended surface
contamination screening levels for use at these stations.
F. After the restricted zone is established, set up monitoring and
decontamination stations at exits from the restricted zone. Because
of the probably high background radiation levels at these locations,
low levels of contamination may be undetectable. If contamination
levels are undetectable, then they probably do not exceed those in
some unrestricted areas occupied by the exposed population and no
decontamination is required. Nevertheless, these individuals should
be advised to bathe and change clothes at their first opportunity
and certainly within the next 24 hours. If, after decontamination
at the boundary of the restricted zone station, persons still exceed
the limits for this station, they should be sent for further
decontamination or for medical or other special attention. As an
alternative to decontamination, contamination on other than persons
or animals may be retained in the restricted zone for radioactive
decay.
G. Establish auxiliary monitoring and decontamination stations in
low background areas (background less than 0.1 mR/h). These
stations should be used to achieve ALARA surface contamination
levels. Table 7-6 provides surface contamination screening levels
for use at those stations.
7-25
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Table 7-6 Recommended Surface Contamination Screening Levels for Persons
and Other Surfaces at Monitoring Stations in Low Background
Radiation Areas (<0.1 mR/h Gamma Exposure Rate)
Condition
Before decontamination
After simple
decontamination
effort
After full0
decontamination
effort
Geiger counter
thin window3 reading
<2X bkgd
>2X bkgd
<2X bkgd
>2X bkgd
<2X bkgd
>2X bkgd
<0.5 mR/hd
Recommended action
Unconditional
release
Decontaminate
Unconditional
release
Full
decontamination
Unconditional
release
Continue to d-con
persons
Release animals
and equipment
After additional
full decontamination
effort
>2X bkgd
>0.5 mR/hd
Send persons for
medical or other
special evaluation
Use informed
judgment for
control of animals
and equipment
aWindow thickness of approximately 30mg/cm2 -js considered
acceptable.
^Vacuuming and flushing with water are examples of simple
decontamination efforts.
cWashing with soap or solvent followed by flushing is an example of a
full decontamination effort.
dClosed shield reading including background.
7-26
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Table 7-7 Recommended Surface Contamination Screening Levels for
Persons and Other Surfaces at Screening or Monitoring
Stations in High Background Radiation Areas (0.1 mR/h to
5 mR/h Gamma Exposure)
Condition
Geiger counter-shielded
window reading
Recommended action
Before decontamination
<2X bkgd and <0.5 mR/h
above background
>2X bkgd or >0.5 mR/h
above background
Unconditional
release
Decontaminate.
Equipment may be
stored or disposed
of as appropriate.
After decontamination
<2X bkgd and <0.5 mR/h
above background
>2X bkgd or >0.5 mR/h
above background
Unconditional
release
Continue to
decontaminate or
refer to low back-
ground monitoring
and d-con station.
Equipment may also
be stored for
decay or disposed
of as appropriate.
7-27
-------
REFERENCES
EP-83 U.S. ENVIRONMENTAL PROTECTION AGENCY. Guidelines for Performing
Regulatory Impact Analyses. EPA 230-01-84-003. U.S. Environmental
Protection Agency, Washington, DC 20460, December 1983.
EP-87 U.S. ENVIRONMENTAL PROTECTION AGENCY. Radiation Protection Guidance to
Federal Agencies for Occupational Exposure. Federal Register. Vol.
52, No. 17, Page 2822, U.S. Government Printing Office, Washington, DC
20402, January 1987.
EP-88 AABERG, RESANNE, Battelle Northwest Laboratories. Evaluation of Skin
and Ingestion Exposure Pathways. U.S. Environmental Protection
Agency/Office of Radiation Programs, Washington, D.C. 20460 (1988
Draft).
FE-84 FEDERAL EMERGENCY MANAGEMENT AGENCY. Federal Radiation Monitoring and
Assessment Plan. Federal Register Vol. 49, No. 19, U.S. Government
Printing Office, Washington, DC 2*0402, January 27, 1984.
FR-61 FEDERAL RADIATION COUNCIL. Radiation Protection Guidance for Federal
Agencies. Federal Register, U.S. Government Printing Office,
Washington,~DC20~402, September 26, 1961.
IC-75 INTERNATIONAL COMMISSION ON RADIATION PROTECTION. ICRP Publication
23. Report of the Task Group on Reference Man. Pergamon Press.
Oxford, 1975.
IC-78 INTERNATIONAL COMMISSION ON RADIATION PROTECTION. ICRP Publication 30,
Radiation Protection. Pergamon Press, Oxford, 1978.
KO-81 KOCHER, D.C. Dose Rate Conversion Factors for External Exposure to
Photons and Electrons. . NUREG/CR-1918. U.S. Nuclear Regulatory
Commission, Washington,' DC 20555, August 1981.
KO-83 KOCHER, D.C. Dose Rate Conversion Factors for External Exposure to
Photons and Electrons. Health Physics. Vol. 45, No. 3 (September)
pp. 665-686, 1983.
NR-75 U. S. NUCLEAR REGULATORY COMMISSION. Reactor Safety Study. An
Assessment of Accident Risks in U. S. Commercial Nuclear Power Plants.
WASH-1400. NUREG-75/014. U.S. Nuclear Regulatory Commission,
Washington, DC 20555, October 1975.
RI-82 RISO. Weathering and Decontamination of Radioactivity Deposited on
Asphalt Surfaces. RISO National Laboratory, DK 4000, Roskilde,
Denmark, December 1982.
SN-82 SANDIA NATIONAL LABORATORIES. Technical Guidance for Siting Criteria
Development. NUREG-CR 2239. U.S. Nuclear Regulatory Commission,
Washington, DC 20555, December 1982.
7-28
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CHAPTER 8
Radiation Protection Guidance for Recovery
(reserved)
-------
APPENDIX A
Glossary
-------
APPENDIX A
Glossary
The following definitions apply specifically to terms used in this manual.
Accident phase: This guidance distinguishes three phases of an incident
(or accident): (a) early phase, (b) intermediate phase, and (c) late phase.
(a) Early phase: The period at the beginning of a nuclear accident
when immediate decisions for protective actions are required,
and must be based primarily on predictions of radiological
conditions in the environment. This phase may last from hours
to days. For the purpose of dose projection, it is assumed to
last for four days.
(b) Intermediate phase: The period beginning after the accident
source and releases have been brought under control and
environmental measurements are available for use as a basis for
decisions on protective actions and extending until these
protective actions are terminated. This phase may overlap the
early phase and may-last from weeks to many months. For the
purpose of dose projection, it is assumed to last for one year.
(c) Late phase: The period beginning when radiation levels have
been reduced so that previously implemented protective actions
can be withdrawn, and ending when all recovery actions have been
completed. This period may extend from months to years (also
referred to as the recovery phase).
Acute health effects: Prompt radiation effects for which a threshold
exists above which the severity of the effect varies with the dose.
Buffer zone: An area selected for temporary radiation protection controls
until the stability of radioactivity levels in the area is confirmed.
A-l
-------
Committed dose: The total dose due to radionuclides in the body over a 50
year period following their inhalation or ingestion.
Delayed health effects: Radiation effects which are manifested long after
the relevant exposure. The vast majority are stochastic, that is, the
severity is independent of dose and the probability is assumed to be
proportional to the dose, without threshold.
Derived response level (DRL): A level of radioactivity in an
environmental medium that would be expected to produce a dose equal to its
corresponding Protective Action Guide.
Dose equivalent: The product of the absorbed dose in rads, a quality
factor related to the biological effectiveness of the radiation involved
and any other modifying factors.
Effective dose equivalent: The sum of the products of the dose equivalent
to each organ and a weighting factor, where the weighting factor is the
ratio of the risk of mortality from delayed health effects arising from
irradiation of a particular organ or tissue to the total risk of mortality
from delayed health effects when the whole body is irradiated uniformly to
the same dose.
Evacuation: The urgent removal of people from an area to avoid or reduce
exposure, usually from the plume or from high levels of deposited
activity.
Groundshine: Gamma radiation from radioactive materials deposited on the
ground.
Nuclear incident (nuclear accident): An event or series of events leading
to the release, or potential release, of radioactive materials into the
environment of sufficient quantity to warrant consideration of protective
actions.
A-2
-------
Projected dose; Future dose calculated on the basis of estimated or
measured initial concentrations of radionuclides or exposure rates.
Protective action; An activity conducted in response to an accident or
potential accident to avoid or reduce radiation dose to members of the
public (sometimes called a protective measure).
Protective Action Guide (PAG): The projected dose to standard man, or
other defined individual, from an accidental release of radioactive
material at which a specific protective action to reduce or avoid that
dose is warranted.
Recovery: The process of reducing radiation exposure rates and
concentrations in the environment to acceptable levels for unconditional
occupancy or use.
Reentry: Temporary entry into a restricted zone under controlled
conditions.
Relocation: The removal or continued exclusion of people from
contaminated areas to avoid chronic radiation exposure.
Restricted zone: An area with controlled access from which the population
has been relocated.
Return: The reoccupation of areas cleared for unrestricted residence or
use.
Sheltering: The use of a structure for radiation protection from an
airborne plume and/or deposited radioactive materials.
A-3
-------
APPENDIX B
(reserved)
-------
APPENDIX C
Protective Action Guides for the Early Phase:
Supporting Information
-------
Contents
Page
C.I Introduction . . C-l
C.I.I Existing Federal Guidance C-l
C.I.2 Principle Exposure Pathways C-2
C.I.3 Units of Dose C-3
C.I.4 Principles for Establishing Protective Action Guides . C-4
C.2 Acute Effect.s C-5
C.2.1 Review of Acute Effects C-6
C.2.1.1 The Median Dose for Lethality C-7
C.2.1.2 Variation of Response for Lethality C-8
C.2.1.3 Estimated Lethality vs Dose for Man .... C-ll
C.2.1.4 Threshold Dose Levels for Acute Effects . . C-15
C.2.1.5 Acute Effects in the Thyroid C-18
C.2.1.6 Acute Effects in the Skin C-19
C.2.1.7 Clinical Pathophysiological Effects .... C-19
C.2.2 Summary and Conclusions Regarding Acute Effects . . . C-24
C.3 Mental Retardation C-25
C.4 Delayed Health Effects C-26
C.4.1 Cancer C-26
C.4.1.1 Thyroid C-29
C.4.1.2 Skin C-30
C.4.1.3 Fetus C-30
C.4.1.4 Age Dependence of Doses C-31
C.4.2 Genetic Risk C-32
C.4.3 Summary of Risks of Delayed Effects C-33
C.4.4 Risks Associated with Other Radiation Standards . . . C-33
11
-------
Contents (continued)
Page
C.5 Practicality of Implementation C-35
C.5.1 Cost of Evacuation C-36
C.5.1.1 Assumptions C-36
C.5.1.2 Analysis C-39
C.5.1.3 Results C-43
C.5.2 Risk of Evacuation C-44
C.5.3 Thyroid Blocking C-47
C.6 Recommended PAGs for Exposure to a Plume C-48
C.7 Avoided Dose vs. Projected Dose C-52
C.8 Dose Limits for Emergency Workers C-53
References C-57
Figures
C-l Acute Health Effects as a Function of Whole Body Dose .... C-13
C-2 Evacuation Model C-38
Tables
C-l Radiation Doses Causing Acute Injury to Organs C-20
C-2 Acute Radiation Exposure as a Function of Rad
Equivalent Therapy Units (rets) C-22
C-3 Radiation Exposure to Organs Estimated to Cause Clinical
Pathophysiological Effects Within 5 Years to 0.1 Percent
of the Exposed Population C-23
i i i
-------
Tables (continued)
Page
C-4 Average Risk of Delayed Health Effects in a Population .... C-33
C-5 Costs for Implementing Various PAGs for an SST-2 Type
Accident (Stability Class A) C-40
C-6 Costs for Implementing Various PAGs for an SST-2 Type
Accident (Stability Class C) C-41
C-7 Costs for Implementing Various PAGs for an SST-2 Type
Accident (Stability Class F) C-42
C-8 Upper Bounds on Dose for Evacuation, Based on the Cost of
Avoiding Statistical Fatalities C-44
C-9 Average Dose Avoided per Evacuated Individual for
Incremental Evacuation Levels C-46
C-10 Summary of Considerations in Selecting Evacuation PAGs .... C-49
C-ll Cancer Risk to Emergency Workers Receiving 25 Rems Whole
Body/Dose C-55
IV
-------
APPENDIX C
Protective Action Guides for the Early Phase:
Supporting Information
C.I Introduction
This appendix describes the basis for the choice of Protective
Action Guides (PAGs) for the early phase of the response to a nuclear
incident, following an accidental release of airborne radioactive
material, as well as the choice of exposure limits for emergency workers.
These guides and limits are set forth in Chapter 2.
Response to a radiological emergency will normally be carried out in
three phases, as discussed in Chapter 1. Decisions during the first
(early) phase will be based primarily on predicted or potential
radiological conditions in the environment, rather than on actual
measurements. The principal protective action is evacuation, with
sheltering serving as a suitable alternative under some conditions. This
appendix therefore examines in some detail the potential magnitudes and
consequences of predicted exposures of populations during the early phase,
for selected accident scenarios, in relation to the benefits and other
consequences of evacuation and sheltering. Supplementary protective
actions, such as washing and change of clothing to reduce exposure of the
skin and use of stable iodine to block uptake of radioiodine to the
thyroid, are also considered, but in less detail.
C.I.I Existing Federal Guidance
In the 1960's, the Federal Radiation Council (FRC) defined PAGs and
established limiting guides for ingestion of strontium-89, strontium-90,
cesium-137, and iodine-131 (FR-64; FR-65). That guidance applied to
restricting the use of food products that had become contaminated as the
result of release of radioactivity to the stratosphere from weapons
C-l
-------
testing. During the period immediately following an incident at a
domestic nuclear facility, v/hen the critical source of exposure is
expected to be a nearby airborne plume, the principal protective actions
are evacuation or sheltering. The PAGs developed here thus do not
supersede previous guidance, but provide additional guidance for prompt
exposure pathways specific to a domestic nuclear incident.
C.I.2 Principal Exposure Pathways
The immediate exposure pathway from a sub-stratospheric airborne
release of radioactive materials is direct exposure from the cloud of
radioactive material carried by prevailing winds. Such a radioactive
plume can contain noble gases, iodines, and/or particulate materials,
depending on the source involved and conditions of the accident. These
materials emit gamma rays, which are not significantly absorbed by air,
and will expose the entire bodies of nearby individuals.
Another exposure pathway occurs when people are submerged in the
radioactive cloud. In this case radioactivity is inhaled, and the skin
and clothes are contaminated. Inhaled radioactive materials, depending on
their solubility in body fluids, may either remain in the lungs or move
via the blood to other organs. Many radionuclides which enter the
bloodstream tend to be predominantly concentrated in a single organ. For
example, if radioiodines are inhaled, they will tend to move rapidly from
the lungs through the bloodstream to the thyroid gland, where most of the
dose will be delivered. Although beta exposure from materials deposited
on the skin and clothing could be significant, it will be less important
than exposure from inhalation if early protective actions include washing
of exposed skin and changes of clothing.
As the plume passes over an area, radioactive materials may settle
onto the ground and other surfaces. People remaining in the area will
then continue to be exposed through ingestion and direct radiation, and
through inhalation of resuspended materials. Doses from such deposited
materials may be more significant than those due to direct exposure to the
plume, because the length of exposure can be much longer. However, since
C-2
-------
the protective actions considered here (evacuation and/or sheltering) may
not be appropriate or may not apply to the same individuals for this
longer term exposure, doses from these exposures are not included in the
dose considered in the PAGs for the early phase. It is assumed that,
within four days after an incident, the population will be protected from
these subsequent doses on the basis of the PAGs for relocation and for
contaminated food and water. (See Chapters 3 and 4.)
Based on the foregoing considerations, the PAGs for the early phase
are expressed in terms of estimated doses from exposure due to direct
radiation, inhalation, and contamination of the skin during the first four
days, only, following an incident.
C.I.3 Units of Dose
The objective of protective action is to reduce the risk to health
from exposure to radiation. Ideally, one would like to assure the
same level of protection for each member of the population. However,
protective actions cannot take into account individual variations in
radiosensitivity, since these are not known. Therefore, these PAGs are
based on assumed average values of risk. We further assume that these
risks are proportional to the dose, for any level of dose below the
threshold for acute effects (see Section C.2.).
The dose from exposure to radioactive materials may be delivered
during the period of environmental exposure only (e.g., external gamma
radiation), or over a longer period (e.g., inhaled radionuclides which
deposit in body organs). In the latter case, dose is delivered not only
during intake from the environment, but continues until all of the
radioactive material has decayed or is eliminated from the body. Because
of the variable time over which such doses may be delivered, the PAGs are
expressed in terms of a quantity called the "committed dose." Committed
dose is conceptually the dose delivered over an individual's remaining
lifetime following an intake of radioactive material. However, due to
differences in physiology and remaining years of life, the committed dose
C-3
-------
to a child from internal radioactivity may differ from that to an adult.
For simplicity, adult physiology and a remaining lifetime of 50 years are
assumed for the purpose of calculating committed dose, unless the
differences are large.
Another important consideration is that different parts of the body
are at different risk from the same dose. Since the objective of
protective actions is the reduction of health risk, it is appropriate to
use a quantity called "effective dose." Effective dose is the sum of the
products of the dose to each organ or tissue of the body and a weighting
factor for risk. These weighting factors are chosen as the ratio of
mortality (from delayed health effects) from irradiation of particular
organs or tissues to the total risk of mortality when the whole body is
irradiated uniformly at the same dose.
Finally, doses from different types of radiation (e.g. alpha, beta,
gamma, and neutron radiations) have different biological effectiveness.
These differences are customarily accounted for, for purposes of radiation
protection, by multiplicative modifying factors. A dose modified by these
factors is designated the "dose equivalent." The PAGs are therefore
expressed in terms of committed effective dose equivalent.
PAGs are intended to apply to all individuals in a population other
than emergency workers. However, there may be identifiable groups that
have different average sensitivity to radiation or, because of their
living situation, will receive higher or lower doses. In addition, some
groups may be at greater risk from taking a given protective action.
These factors are separately considered below, when it is appropriate, in
establishing values for the PAGs.
C.I.4 Principles for Establishing Protective Action Guides
The following four principles provide the basis for establishing
values for Protective Action Guides:
C-4
-------
1. Acute effects on health (those that would be observable within a
short period of time and which have a dose threshold below which
they are not likely to occur) should be avoided.
2. The risk of delayed effects on health (primarily cancer and
genetic effects, for which linear nonthreshold relationships to
dose are assumed) should not exceed upper bounds that are judged
to be adequately protective of public health, under emergency
conditions, and are reasonably achievable.
3. PAGs should not be higher than justified on the basis of
optimization of cost and the collective risk of effects on
health. That is, any reduction of risk to public health
avoidable at acceptable cost should be carried out.
4. Regardless of the above principles, the risk to health from a
protective action should not itself exceed the risk to health
from the dose that would be avoided.
With the exception of the second, these principles are similar to
those set forth by the International Commission on Radiological Protection
(IC-84) as the basis for establishing intervention levels for nuclear
accidents.
C.2 Acute Effects
This section provides information relevant to the first principle:
avoidance of acute effects on health from radiation.
Acute radiation health effects are those clinically observable
effects on health which are manifested within two or three months after
exposure. Their severity depends on the amount of radiation dose that is
received. Acute effects do not occur unless the dose is relatively large,
and there is generally a level of dose (i.e., threshold) below which an
effect is not expected to occur. Acute effects may be classified as
severe or nonsevere clinical pathophysiological effects. Severe
C-5
-------
pathophysiological effects are those which have clinically observable
symptoms and may lead to serious disease and death. Other patho-
physiological effects, such as hematologic deficiencies, temporary
infertility, and chromosome changes, are not considered to be severe,
but may be detrimental in varying degrees. Some pathophysiological
effects, such as erythema, nonmalignant skin damage, loss of appetite,
nausea, fatigue, and diarrhea, when associated with whole body gamma
or neutron exposure, are prodromal (forewarning of more serious
pathophysiological effects, including death).
C.2.1 Review of Acute Effects
This section summarizes the results of a literature survey of reports
of acute effects from short-term (a few days) radiation exposure in some
detail. Many reports of observed effects at lower doses differ, and some
are contradictory; however, most have been included for the sake of
completeness. The results of the detailed review described in this
Section are summarized in Section C.2.2.
The biological response to the rapid delivery of large radiation
doses to man has been studied since the end of World War II. Dose-
response relationships for prodromal (forewarning) symptoms (ED ) and
X
for death within 60 days (LDx/50)> where x is the probability (in
percent) of response, have-been developed from data on the Japanese A-bomb
survivors, Marshall Island natives exposed to fallout, and patients
undergoing radiotherapy. This work has been supplemented by a number of
animal studies under controlled conditions.
The animal studies, usually using lethality as the end point, show
that many factors can influence the degree of response. The rate at which
the dose is delivered can affect the median lethal dose C-D5Q) in many
species, particularly at dose rates less than 5 R/min (PA-68a; BA-68).
However, in primates there is less than a 50 percent increase in the
LD5Q as dose rates are decreased from 50 R/min to about O.OlR/min
(PA-68a). There is good evidence of species specificity (PA-68a; 80-69).
The ID™ ranges from about 100 rads for burros to over 1000 rads for
lagomorphs (e.g., rabbits). Response is modulated by: age (CA-68), extent
C-6
-------
of shielding (partial body irradiation) (BO-65), radiation quality
(PA-68a; 80-69), diet, and state of health (CA-68).
While animal studies provide support and supplemental information,
they cannot be used to infer the response for man. This lack of
comparability of man and animals had already been noted by a review
committee for the National Academy of. Sciences as early as 1956, in
considering the length of time over which acute effects might be
expressed (NA-56): "Thus, an LDj-0, 30-day consideration is inadequate
to characterize the acute lethal dose response of man, and an LD5n,
60 days would be preferable."
Several estimates of the levels at which acute effects of radiation
occur in man have been published. For example, an early estimate of the
dose-response curves for prodromal (forewarning) symptoms and for
lethality was made in the first edition of "The Effects of Nuclear
Weapons" (1957) (GL-57), and a more recent and well documented estimate is
given in a NASA publication, "Radiobiological Factors in Manned Space
Flight" (LA-67).
C.2.1.1 The Median Dose for Lethality
The radiation dose that would cause 50 percent mortality in 60 days
was estimated as 450 Roentgens in early reports (NA-56; GL-57; RD-51).The
NCRP calculated that this would correspond to a midline absorbed dose of
315 rads (NC-74). The ratio of 315 rads to 450 Roentgens is 0.70, which
is about the estimated ratio of the active marrow dose, in rads, to the
tissue kerma in air, in rads (KE-80). The BEAR Committee noted that the
customary reference to LDr0 in animal studies, as if it were a specific
property, independent of age, was not justifiable (NA-56): "...it is
evident, now, that the susceptibility of a whole population is not
committee (known as the BEAR Committee) also noted "The reservation
must be made here that the exposed Japanese population was heterogeneous
with respect to age, sex, phys'ical condition and degree of added trauma
from burns or blast. The extent to which these factors affected the
survival time has not been determined. In studies on laboratory animals
the converse is true—homogeneous populations are studied" (NA-56, p.1-6)
C-7
-------
describable by a single LDgQ. The published values are usually obtained
for young adults and are therefore maximal or nearly maximal for the
strain. In attempts to estimate LD™ in man, this age dependence should
be taken into consideration" (NA-56, pp.4-5). They observed that the
LDg0 approximately doubled as rats went from neonates to young adults
and then decreased as the animals aged further. Finally, the BEAR
Committee concluded: "The situation is complex, and it became evident that
it is not possible to extrapolate with confidence from one condition of
radiation exposure to another, or from animal data to man"
(NA-56, p.1-8). Nevertheless, results from animal studies can aid in
interpreting the human data that are available.
The NCRP suggested the LD5Q,g0 might be 10 to 20 percent lower for
the old, very young, or sick, and somewhat greater for healthy adults of
intermediate age (RD-51). Other estimates of adult LD,-0/60 have ranged
from about 300 rads to 243 + 22 rads. These lower estimates are
apparently based on a ratio of air to tissue dose similar to those
calculated for midline organs in the body; 0.54 to 0.66 (KE-80; OB-76;
KO-81).
A NASA panel examined all patient and accident studies, tried to
remove confounding factors, and concluded, "On this basis, it may be
assumed that the LD5Q value of 286 rads obtained by a normal fit to the
patient data is the preferred value for healthy man" (LA-67).
An ID™,,... of 286 + 25 rads (standard deviation) midline absorbed
oU/oU —
dose and an absorbed dose/air dose ratio of 0.66, suggested by MAS
(LA-67), is probably a reasonable value for healthy males. In the absence
of more complete information, we assume that a value of 300 rads _+ 30 rads
is a reasonable reflection of current uncertainties for average members of
the population.
C.Z.I.2 Variation of Response for Lethality
Uncertainty in the dose-response function for acute effects has been
expressed in various ways. The slope of the estimated dose-response
C-3
-------
function has most commonly been estimated on the basis of the percent
difference in the LD5Q and the LD.g g or LDg. . (one standard
deviation from the LDcn). as was done by NASA (GL-57). These and other
parameters derived in a similar manner describe the uncertainty in the
central risk estimate for the dose-response function.
Another means is to use an estimate of upper and lower bounds for the
central risk estimate, e.g., the 95 percent fiducial limits. At any given
response point on the dose-response function, for example, the LD.Q, the
dose causing that response has a 95 percent probability of lying between
the lower and upper bounds of the 95 percent fiducial limit for that
point. To estimate this value, probit analyses were run for each species
using data in published reports (KO-81; TA-71). This provided estimates
for each species for comparability analyses. The 95 percent fiducial
limits at the LD5Q response for LDgQ/30 studies averaged +9 percent
(range -9 to +26 percent) and for LD5Q.,Q studies +17 percent (range -20
to +45 percent). At the LD,g response, values were +_16 percent (range
-12 to +50 percent) for LD15/30 data and +26 percent (range -20 to +65
percent) for LD.,-,g0 data. For the LDg5 response, values were +17
percent (range -36 to +36 percent) for the LD85,~_ data and +24 percent
(range -46 to +31 percent) for LDocc data.
The differences in the magnitude of the fiducial limits are a
function of the differences in age, sex, radiation quality, degree of
homogeneity of the experimental animals, husbandry, and other factors.
The estimates show that the fiducial limits, expressed as a percent of the
dose at any response, get greater the farther from the LDr0 the estimate
is made. For the purpose of estimating fiducial limits for humans, the 95
percent fiducial limits will be considered to be LD-5 +_15 percent,
LD50 1*° Percent, and LD35 ±15 percent. Beyond these response levels,
the fiducial limits are too uncertain and should not be used.
If the median lethal dose, LD5Q/60' 1S taken as 30° I30 rads
midline absorbed dose, the response to higher and lower doses depends on
the degree of biological variation in the exposed population. The NASA
panel decided the wide variation in the sensitivity of patients was a
C-9
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reflection of the heterogeneity of the sample; and that the variation in
sensitivity, the slope of the central estimate of the response function,
would be stated in the form of one standard deviation calculated as
58 percent of the LD5Q. They further decided the deviation in the
patients (58 percent) was too great, and the standard deviation for
"normal" man should be closer to that of dogs and monkeys (18 percent)
(LA-67). (The rationale for selecting these species was not given.)
Jones attempted to evaluate the hematologic syndrome from mammalian
lethality studies using the ratio of dose to ID™ dose as an indicator
of the steepness of the slope of the dose-response function (JO-81).
However, he evaluated LD5_ studies only of species having a rather steep
slope, i.e., dogs, monkeys, mice, and swine. He also looked at several
different statistical models for dose-response functions and pointed out
the problems caused by different models and assumptions, particularly in
evaluating the tails of the dose-response function (less than LD.Q and
greater than LDg_). Jones recommended using a log-log model, which he
felt provided a better fit at low doses (JO-81).
Scott and Hahn also evaluated acute effects from mammalian lethality,
but suggested using a Weibull model (SC-80). One of the advantages of the
Weibull model is that in addition to developing the dose-response
function, it can also be used to develop hazard functions. These hazard
functions, if developed using the same model, can be summed to find the
joint hazard of several different types of exposure (SC-83). This would
allow estimation of the total hazard from multiple organ exposures to
different types of radiation.
As mentioned earlier, the human median lethal dose is commonly
reported in terms of the ^cn/cr\- Most laboratory animal median lethal
doses are reported in terms of the LD5Q/3Q- In those cases where
estimates of both LD.^ and LD50/60 are available' i-e-» the burro
(ST-69), the variation (that is, the slope of the dose-rssponse curve) is
greater in the LDcn/so study than in the LD 59/30 study. Both the dog
and the monkey data are for LDcQ/30, and so are not appropriate for
direct comparison to man.
C-10
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If an estimate of the deviation is made for data from other studies
and species, those where .most of the fatalities occur within 30 days (like
dogs and monkeys) have standard deviations of from around 20 percent
(swine (x-ray) (ST-69), dogs (NA-66), hamsters (AI-65), primates (Macaca)
(DA-65)] to 30 percent [swine (60- ) (HO-68)). Those in which most
deaths occur in 60 days, like man, have deviations from around 20 percent
(sheep (CH-64)) to 40 percent (goats (PA-68b), burros (TA-71)). Nachtwey,
^t al_. (NA-66) suggested the steepness of the slope of the exposure
response curve depends on the inherent variability of the subjects exposed
and any variation induced by uncontrolled factors, e.g., temperature,
diurnal rhythm, and state of stimulation or arousal. So, while the slope
of the response curve for the patients studied by the NASA panel may be
unrealistically shallow for normal human populations, there is no reason
to think it should be as steep as those for dogs and monkeys.
The average deviation for those species (burros, sheep, and goats)
for which the standard deviation of the LD,.,.,,,,, is available has been
bU/oO
used as an estimator for man. The mean value is 34 +_ 13 percent. This is
only slightly greater than the average value for all physically large
animals (swine, burros, sheep, and goats), 32 +_ 12 percent.
C.2.1.3 Estimated Lethality vs Dose for Man
As noted in Section C.2.1.1, dose-response estimates vary for a
number of reasons. Some factors affecting estimates for humans are:
1. Age:
Casarett has published studies on rats which indicate the LD^Q
is minimal for perinatal exposure, rises to maximum around
puberty, and then decreases again with increasing age (CA-68).
The perinatal LD$Q is about one-third of that for the healthy
young adult rats; that for the geriatric rat is about one-half of
that for the young adult rat.
2. Sex:
Females are slightly more sensitive than males in most species
(CA-68).
C-ll
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3. Health:
Animals in poor health are usually more sensitive than healthy
animals (CA-68), unless elevated hematopoietic activity is
occurring in healthy animals (SU-69).
While these and other factors will affect the LDc0/gQ and the
response curve for man, there are no numerical data available.
The variation in response at a given dose level increases as the
population at risk becomes more heterogeneous and as the length of time
over which mortality is expressed increases. In general, larger species
show greater variance and longer periods of expression than do small
mammals, e.g., rodents. It is likely that the human population would show
at least the same amount of variation as do the larger animals, i.e., a
coefficient of variation of about one-third.
The degree of variation exhibited in animal studies follows a
Gaussian distribution as well as or better than a log normal distribution
over that range of mortality where there are reasonable statistics. We
have assumed here that the functional form of human response is
Gaussian. Generally, sample sizes for extreme values (the upper and
lower tails of the distribution) are too small to give meaningful
results. Therefore, we have not projected risks for doses more than 2
standard deviations from the ^cg/go' We recognize that estimates of
acute effects may not be reliable even beyond one standard deviation for a
population containing persons of all ages and states of health. However,
in spite of these uncertainties, previous estimates have been made of the
acute effects caused by total body exposure to ionizing radiation as a
function of the magnitude of the exposure (NC-71; LU-68; FA-73; MA-73).
Given the large uncertainties in the available data, a median lethal
dose value of about 300 rads at the midline, with a standard deviation of
100 rads, may be assumed for planning purposes. Such risk estimates
should be assumed to apply only in the interval from 5 percent to 95
percent fatality, as shown in Figure C-l. (See also the discussion at
C.2.1.4.)
C-12
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100
100
FIGURE C-1.
200 300 400 500
MIDLINE ABSORBED DOSE (rem)
ACUTE HEALTH EFFECTS AS A FUNCTION
OF WHOLE BODY DOSE.
600
C-13
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Figure C-l is based on the following values:
Dose (rads) Percent fatalities
<140 none2
140 5
200 15
300 50
400 85
460 95
For moderately severe prodromal (forewarning) effects, we
believe the dose at which the same percentage of exposed would show
effects would be approximately half of that causing fatality. This
yields the following results (see also Figure C-l):
Dose (rads) Percent affected
50 <2
100 15
150 50
200 35
250 98
Although some incidence of prodromal effects has been observed at
doses in the range of 15 to 20 rads in patients (LU-68) and in the 0 to
10 rads range of dose in Japanese A-bomb survivors (SU-80a; GI-84), there
is great uncertainty in interpreting the data. Patients may be abnormally
sensitive, so that the dose-response function in patients may represent
the lower bound of doses that would show a response in a healthy
population (LU-67). The response of Japanese survivors in the low dose
ranges is complicated by the blast and thermal exposure that occurred at
the same time (SU-80b). For these reasons, care should be taken in
applying estimates of prodromal effects. The prodomal dose-response
function listed above is more likely to overestimate the proportion of
persons affected than to underestimate it.
These estimated ranges and effects are in agreement with estimates
made for manned space flights (LA-67; LU-67), which included consideration
2The risk of fatality below 140 rads is not necessarily zero; rather, it
is indeterminate and likely to remain so. This also applies to prodromal
effects below 50 rads.
C-14
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of the effect of abnormal physiology or sickness in the patients to which
the data apply. Uncertainty in estimates of the biological effects of
radiation exposure is great. It is probably due in part to variation in
the health of individuals in exposed populations. These estimates assume
a healthy young adult population and may not be a conservative estimate of
risk for other population groups, such as children or the elderly.
Lushbaugh, et a]_. (LU-68) found that prodromal effects probably occur in
both healthy and ill persons in about the same dose range. However,
Lushbaugh, et a]_. (LU-68) and NATO (NA-73) suggest that acute mortality in
a population which is ill, injured, or in other ways debilitated will
occur in 50 percent of that population at doses of 200-250 rads in about
60 days C-D^J ln contrast to an LD5Q/60 fr0m doses °^ 220-310
rads for a healthy young adult population. Thus, the ill or injured are
assumed to have an increased risk of acute mortality at high doses.
The above estimates for LD50/60 are also based on the assumption of
minimal medical care following exposure. Although the threshold for some
specific acute effects would undoubtedly be higher in the presence of more
intense medical care, no data are available to quantify the effects of
increased medical care and no such quantification is attempted here.
C.2.1.4 Threshold Dose Levels for Acute Effects
This section summarizes information available in the literature
regarding thresholds for health effects. It also reviews actions that
have been taken as a result of radiation exposure to provide insight on
dose levels at which actions to avoid dose may be appropriate.
Some acute effects, such as cellular changes, may occur at low doses
with no dose threshold. Most such effects have a minimum threshold of
detectability; for example, five rems is about the lower limit of whole
body dose which causes a cellular effect detectable by chromosome or other
special analyses (NC-71; FA-73). This value is recommended by UNSCEAR as
the starting point for biological dosimetry (UN-69). Purrott, ^t aj_. have
reported a lower limit of detection of chromosome aberrations of 4 rads
for x-rays and 10 rads for gamma rays (PU-75).
C-15
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More recent advanced chromosome banding techniques permit detection
of increased incidence of chromosome abnormalities from continuous
exposure to systematically deposited radioisotopes or radioisotopes
deposited in the lung at very low levels, e.g., body burdens of 100 to
1200 pCi of plutonium-239 (BR-77). While the exact dose associated with
such burdens is not known, it is probably on the order of ten to one
hundred millirems per year. Lymphocytes exposed to 5 rems in vitro show
severe metabolic dysfunction and interphase cell death (ST-64). The
extent to which similar effects occur after in vivo exposure is unknown.
While chromosome abnormalities in circulating lymphocytes are reported to
persist for long periods (UN-69), the significance of such abnormalities
is not known (BR-77).
Hug has suggested 5 rems as the lower limit of exposure which might
produce acute effects (WH-65). Five rems is also in the low dose,
short-term exposure range defined by Cronkite and Haley, and is below the
10 rads which they thought would cause only a slight detectable
physiological effect of unknown clinical significance (CR-71).
Although the ICRP has suggested that annual doses of 15 rems would
not impair the fertility of normal fertile men (IC-59), an acute dose of
15 rads causes "moderate" oligospermia (approximately 70 percent reduction
in sperm count) which lasts for some months (LA-67). Popescu and
Lancranjan reported alterations of spermatogenesis and impaired fertility
in men exposed to from 500 millirems to 3 rems per year for periods
varying from 2 to 22 years (PO-75). The shortest exposure period in which
abnormal spermatogenesis was reported was 31 to 41 months (PO-75); at the
highest dose rate reported (3 rems/a), this is a cumulative dose of 8 to
10 rems. While more study is required, these results suggest the need to
restrict acute doses to below 10 rems to avoid this effect, because a
given acute dose is anticipated to be more effective than the same
cumulative dose given over a longer period of time (NA-56; UN-58).
Many observations have indicated that doses of 10 rems or more to the
pregnant woman are hazardous to the fetus. Mental retardation due to
exposure of- the fetus is discussed in Section C.3; this discussion is
C-1S
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restricted to acute effects. The World Health Organization (WHO)
indicates that there is no evidence of teratogenic effects from short term
exposure of the fetus to a dose less than ten rems during the early phase
of gestation, the period when the fetus is most sensitive to these
effects(WH-84).
Hammer-Jacobsen recommended that exposures of 10 Roentgens or higher
be considered an indication for induced abortion (HA-59). Brent and
Gorson also suggest that at doses of 10 rads or more, it is appropriate to
investigate the merits of terminating the pregnancy (BR-72). The Swedish
Government Committee on Urban Siting of Nuclear Power Stations stated the
situation more succinctly: "What we have called unconditional indication
of abortion involves the exposure of pregnant women where radiation dose
to the fetus is higher than 10 rads. When such doses are received in
connection with medical treatment, it has hitherto been assumed that the
probability of damage to the fetus is so high that an abortion is
recommended. The probability for such injury is still moderate compared
with the normal frequency of similar fetal injuries, and the probability
is particularly reduced when the dose is received late in the
pregnancy" (NA-74).
Hammer-Jacobsen stated that although there may be a question of
whether or not therapeutic abortion should be considered in the case of
exposures of 1 to 10 R, there is no need for therapeutic abortion for
exposures of 1 R or less (HA-59). Although Brent and Gorson suggest that
10 rads is a "practical" threshold for induction of fetal abnormalities,
they do extend their discussion to counseling a pregnant women who have
received 1 to 2 rads (BR-72). The general suggestion is that the
possibility of acute effects in the fetus is avoided as long as the fetal
dose does not exceed 1 rad.
Devick examined in detail the Scandinavian countries' basis for
recommending induced abortion following radiation exposure (DE-70).
Their basis seemed to be a risk of greater than 1 in 10 of radiation-
induced fetal injury. Sweden, Denmark, and Finland recommended
termination of the pregnancy in cases of prenatal radiation exposure if
C-17
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the exposure exceeded 10 Roentgens. If the exposure was under 1 Roentgen
(Sweden and Denmark) or under 2 Roentgens (Finland), the irradiation was
not considered to cause significant damage. For exposures between these
limits, termination of pregnancy was a subject of judgment (DE-70).
In the German Democratic Republic, also, termination of pregnancy is
recommended in cases of exposure to 10 Roentgens or more (NE-76).
Federal Radiation Protection Guidance, adopted in 1987, recommends
that dose to occupationally exposed pregnant women be controlled to keep
the fetal dose below 0.5 rem over the entire term of pregnancy, and that
no dose be delivered at more than the uniform monthly rate that would
satisfy this limit (i.e., approximately 50-60 mrems/month)(EP-87). The
NCRP has, for many years, recommended a limit of 0.5 rem (NC-71). ICRP
recommends controlling exposure of the fetus to less than 0.5 rem in the
first 2 months to provide appropriate protection during the essential
period of organogenesis (IC-77).
C.2.1.5 Acute Effects in the Thyroid
Acute effects are produced in the thyroid by doses from radioiodine
on the order of 3000 to 100,000 rads. Ablation of the thyroid requires
doses of 100,000 rads (BE-68). The thyroid can be rendered hypothyroid by
doses of about 3000 to 10,000 rads (IC-71). A thyroid dose from
radioiodines of 1000 rads in adults and 400 rads in children implies an
associated whole body dose of about 1 rem due to radioiodines circulating
in the blood. Following inhalation of I, the committed thyroid dose
131
is about one rad/wCi intake of I in adults. In the developing fetus,
131
the thyroid dose ranges from 1 to 6 rads per uCi of I entering the
mother's body (IL-74).
Although acute clinical effects are only observed at high doses,
subclinical acute thyroid radiation effects may occur at lower doses
(DO-72). Impaired thyroid capability may occur above a threshold of about
200 rads (DO-72).
C-18
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Effects of radiation exposure of the thyroid have been shown in
animal experiments. Walinder and Sjoden found that doses in excess of
3,000 rads from I caused noticeable depression of fetal and juvenile
mouse thyroid development (WA-69). Moore and Calvin, working with the
Chinese hamster, showed that an exposure as low as 10 Roentgens (x-rays)
would give rise to 3 percent aberrant cells when the thyroid was cultured
(MO-68). While the direct relationship of these results to human effects
is not certain, mammalian thyroid cells can be injured at exposures as low
as 10 Roentgens.
C.2.1.6 Acute Effects in the Skin
The first stage of skin reaction to radiation exposure is erythema
(reddening) with a threshold of from 300 to 800 rads. Acute exudative
radiodermatitis results from doses of 1200 to 2000 rads (WH-84).
C.2.1.7 Clinical Pathophysiological Effects
A large amount of anecdotal information is available on the injury of
organ tissues by high doses of radiation. Acute injury to tissue includes
swelling and vacuolation of the cells which make up the blood vessels,
increased permeability of vessels to fluids so that exudates form,
formation of fibrin clots and thrombi, fibrinoid thickening in the walls
of blood vessels, and swelling and vacuolization of parenchymal cells.
In summary, there is an initial exudative reaction followed in time by
fibrosis and sclerosis (WH-76, CA-76).
Estimates of radiation doses necessary to cause severe tissue
response in various organs are given in Table C-l. These tissue dose
estimates are based on response to radiotherapy treatment, which is
normally given on a fractionated dose basis, but also may be given as a
continuous exposure. Therefore, these estimates must be adjusted to the
equivalent single radiation dose for use in the present analysis. The
formalism of Kirk, et £]_. (KI-71) is used to estimate the equivalent dose
for a single acute exposure in rad-equivalent therapy units (rets: the
dose calculated from the fractionated exposure which is equivalent to a
C-19
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Table C-l Radiation Doses Causing Acute Injury to Organs (RU-72, RU-73)
Organ
Bone marrow
Liver
Stomach
Intestine
Lung
Kidney
Brain
Spinal cord
Heart
Skin
Fetus
Lens of eye
Ovary
Testes
Volume or
area of
exposure3
whole
segment
whole
100 cm2
400 cm2
100 cm2
whole
100 cm2
whole
whole
10 cm
60 percent
—
whole
whole
whole
whole
Risk of injury
5 percent
(rad)
250
3000
2500
4500
4500
5000
1500
3000
2000
6000
4500
4500
5500
200
500
200-300
500-1500
in five years
50 percent
(rad)
450
4000
4000
5500
5500
6500
2500
3500
2500
7000
5500
5500
7000
400
1200
625-1200
2000
Type of injury
aplasia and
pancytopenia
acute and chronic
hepatitis
ulcer, perforation,
hemorrhage
ulcer, perforation,
hemorrhage
acute and chronic
pneumonitis
acute and chronic
nephrosclerosis
infarction,
necrosi s
infarction,
necrosis
pericarditis and
pancarditis
ulcers, fibrosis
death
cataracts
permanent
steri lization
permanent
steri lization
aDose delivered in 200-rad fractions, 5 fractions/week.
— Unspecified.
C-20
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single acute exposure for a specific biological endpoint.) Table C-2
lists acute exposure equivalents in rets for various organs.
With the exception of bone marrow, the exposures required to cause
5 percent injury within 5 years (TD 5/5) in internal organs are in the
range of 1000 to 5000 rads. Since, with this type of injury, the dose
response is nonlinear and has a threshold (i.e., is nonstochastic), there
is an exposure below which injury is not expected. If the shape of the
injury dose-response curve is the same for all internal organs as it is
for the lung, plotting the two acute exposure equivalents (TD 50/5 and
5/5) for each organ on log probability paper allows a crude estimation of
the number of clinical pathophysiological effects per 1000 persons exposed
as a function of dose level. If one acute effect per 1000 persons within
5 years (TD 0.1/5) is taken as the threshold for the initiation of
clinical pathophysiological effects in organs other than thyroid, the
equivalent dose level for most organs is 550 rets or more; testes 440 _^
150 rets, ovary 170 + 70 rets, and bone marrow 165 rets.
The radiation exposure to organs in rad units that will cause
clinical pathophysiological effects within 5 years to 0.1 percent of the
exposed population as a function of the duration of a continuous level of
exposure can then be estimated by using Goitein's modification of the Kirk
methodology (GO-76). This relationship is shown in Table C-3.
Bone marrow is an organ of particular concern because radionuclides
known to concentrate in this organ system occur in nuclear accidents. The
acute lethality due to the hematologic syndrome (LA-67) is estimated to
occur in the range of 200 to 1,000 rads, so that the difference is small
between exposure levels that might cause acute lethality and exposure
levels that might cause only "severe clinical pathophysiology," as derived
from radiotherapy data.
In summary, organ systems are not expected to show symptoms of severe
clinical pathophysiology for projected short-term exposure doses less than
a few hundred rads. Projected doses to bone marrow at this high
C-21
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Table C-2 Acute Radiation Exposure as a Function of Rad Equivalent
Therapy Units (Rets)
Organ
Bone marrow
Liver
Stomach
Intestine
Lung
Kidney
Brain
Spinal cord
Heart
Skin
Fetus
Lens of eye
Ovary
Testes
Volume or
area of
exposure
whole
segment
whole
100 cm2
400 cm2
100 cm2
whole
100 cm2
75 percent
whole
whole
10 cm
60 percent
—
whole
whole
whole
whole
(steri lization)
Risk of injury
5 percent
(rets)
230
1135
1000
1465
1465
1570
720
1135
770b
875
1770
1465
1465
1665
200
355
200-430*
340-7203
in five years
50 percent
(rets)
340
1360
1360
1665
1665
1855
1000
1245
1000
1950
1665
1665
1950
315
620
410-8753
410-875a
aFor a 200-rad/treatment, 5 treatments/week schedule (LU-76)
bReference WA-73.
— Unspecified.
C-22
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Table C-3 Radiation Exposure to Organs Estimated to Cause Clinical
Pathophysiological Effects within 5 Years to 0.1 percent
of the Exposed Population (GO-76)
Duration of
exposure
(days)
(acute)
1
2
4
7
30
365b
Ovary
(rad)
(170 rets)a
315
390
470
550
840
1740
Bone marrow
(rad)
(165 rets)
300
380
450
540
820
1690
Testes
(rad)
(440 rets)
810
1010
1210
1430
2190
4510
Other organs
(rad)
(550 rets)
1020
1260
1510
1790
2740
5640
aThe dose in rets is numerically equal to the dose in rads.
bAssuming tissue recovery can continue at the same rate as observed
during 30- to 60-day therapeutic exposure courses.
level are relatively more serious and more likely to result in injury than
doses to other organ systems.
Even if severe clinical pathophysiological effects can be avoided,
there is still a possibility of clinical pathophysiological effects of a
less severe or transitory nature. The 1982 UNSCEAR report (ilN-82)
reviewed much of the data on animals and man. In the animal studies,
there were reports of: changes in stomach acid secretion and stomach
emptying at 50 to 130 rads; stunting in growing animals at the rate of
3 to 5 percent per 100 rads; degeneration of some cells or functions in
the brain at 100 rads, particularly in growing animals; temporary changes
in weight of hematopoietic tissues at 40 rads; and more damage in ovaries
and testes caused by fractionated doses rather than acute doses. Some of
the effects are transitory, others "are long-lasting, but with only minor
reductions in functional capacity.
Human data are limited and are reported primarily in the radiotherapy
literature. The data suggest most tissues in man are more radiation
resistant than those in animals. However, the human hematopoietic system
shows a transient response, reflected by decreased circulating white cells
C-23
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and platelets, at about 50 rads. Temporary sterility has been observed
after doses of 150 rads to the ovaries and 10 rads to the testes, when
given as fractionated doses.
There is not sufficient data to determine dose-response functions,
nor to describe the duration and severity of dysfunction expected.
C.2.2 Summary and Conclusions Regarding Acute Effects
Based on the foregoing review of acute health effects and other
biological effects, the following whole body doses from acute exposures
provide useful reference levels for decisionmaking:
50 rems - Less than 2 percent of the exposed population would be
expected to exhibit prodromal (forewarning) symptoms.
25 rems - Below the dose where prodromal symptoms have been observed.
10 rems - The bottom of a range of doses above which most members of
the medical profession have recommended abortion. This is
also the dose level below which a fetus would not be
expected to suffer teratogenesis (but see Section C.3,
Mental Retardation.).
5 rems - The approximate minimum level of detectability for acute
cellular effects using the most sensitive methods.
Although these are not severe pathophysiplogical effects,
they may be detrimental.
1 rem - The dose below which abortion has not been considered
necessary by the medical profession.
Based on the first principle to be satisfied by PAGs (paragraph
C.I.6), which calls for avoiding acute health effects, values of 50 rems
for adults and 10 rems for fetuses appear to represent upper bounds. The
effects of the other three principles are considered in the sections that
follow.
C-24
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C.3 Mental Retardation
Brain damage to the unborn is a class of injury reported in atomic
bomb survivors which does not fall into either an acute or delayed effect
category, but exhibits elements of both. What has been observed is a
significant, dose-related increase in the incidence and severity of mental
retardation, microencephaly (small head size), and microcephaly (small
brain size) in Japanese exposed to radiation in utero during the 8th to
15th week after conception (BL-73; MI-76). While the actual injury may be
acute, it is not identified until some time after birth.
In an early study Mole (MO-82) suggested that, although radiation
may not be the sole cause of these conditions, it is prudent to treat the
phenomenon as radiation related. More recently, Otake and Schull (OT-83)
have concluded: (1) there is no risk to live-born due to doses delivered
up to 8 weeks after conception, (2) most damage occurs at the time when
rapid proliferation of neuronal elements occurs, i.e., 8 to 15 weeks of
gestational age, (3) the dose-response function for incidence during this
period appears to fit a linear model, (4) the risk of occurrence is about
five times greater during the period 8-15 weeks of gestation than in
subsequent weeks, and (5) in later stages of gestation, e.g., after the
15th week, a threshold for damage may exist.
In their published reports, Otake and Schull (OT-83) evaluated the
incidence of severe mental retardation using the T-65 dosimetry and the
dosimetry estimates developed in the ongoing dose reassessment program for
the atomic bomb survivors, and using two tissue dose models. Their
estimated ranges of risk were:
8 to 15 weeks after gestation: 3-4xlO~3 cases/rad;
16 or more weeks after gestation: 5-7xlO~4 cases/rad.
The higher values are based on the T-65 dosimetry and the Oak Ridge
National Laboratory estimate of tissue dose. The lower values are based
on Oak Ridge National Laboratory dosimetry and the Japanese National
C-25
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Institute of Radiological Sciences estimates of tissue dose. Later
estimates based on the dose reasessment completed in 1986 are consistent
with these published results (SC-87).
In view of the foregoing, the risk of mental retardation from
exposure of a fetus in the 8th to 15th week of pregnancy is taken to be
about 4x10" per rem. Because of this relatively high risk, special
consideration should be given to protection of the fetus during this
period. The risk to a fetus exposed after the 15th week is taken as
-4
6x10 per rem. For the cases studied (OT-84), no increased incidence
of mental retardation was observed for exposure during the 1st to the 7th
week of pregnancy. In order to prevent the risk of mental retardation
from exceeding the risk of fatal cancer for the general population (see
section C.4) it would appear necessary that the dose to fetuses of
gestational age 8 to 15 weeks not exceed about one tenth the dose to
members of the general population.
C.4 Delayed Health Effects
This section addresses information relevant to the second principle
(paragraph C.I.5) for establishing PAGs, the risk of delayed health
effects in exposed individuals. The following subsections summarize the
estimated risks of cancer and genetic effects, the two types of delayed
effects caused by exposure to radiation.
C.4.1 Cancer
Because the effects of radiation on human health have been more
extensively studied than the effects of many other environmental
pollutants, it is possible to make numerical estimates of the risk as
a result of a particular dose of radiation. Such estimates, may, however,
give an unwarranted aura of certainty to estimated radiation risks.
Compared to the baseline incidence of cancer and genetic defects,
radiogenic cancer and genetic defects do not occur very frequently. Even
in heavily irradiated populations, the number of cancers and genetic
defects resulting from radiation is known with only limited accuracy. In
C-26
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addition, all members of existing exposed populations have not been
followed for their full lifetimes, so data on the ultimate numbers of
effects is not yet available. Moreover, when considered in light of
information gained from experiments with animals and from various theories
of carcinogenesis and mutagenesis, the observed data on the effects of
human exposure are subject to a number of interpretations. This, in turn,
leads to differing estimates of radiation risks by individual scientists
and expert groups. In summary, the estimation of radiation risks is not a
fully mature science and the evaluation of radiation hazards will continue
to change as additional information becomes available.
Most of the observations of radiation-induced carcinogenesis in
humans are on groups exposed to low-LET radiations. These groups include
the Japanese A-bomb survivors and medical patients treated with X-rays for
ankylosing spondylitis in England from 1935 to 1954 (SM-78). The National
Academy of Science Committee on the Biological Effects of Ionizing
Radiations (BEIR) (NA-80) and UNSCEAR (UN-77) have provided knowledgeable
and exhaustive reviews of these and other data on the carcinogenic effects
of human exposures. The most recent of the BEIR studies was published in
1980 and is here designated BEIR-3 to distinguish it from previous reports
of the BEIR committee.
The most important epidemiological data on radiogenic cancer is that
from the A-bomb survivors. The Japanese A-bomb survivors have been
studied for more than 40 years, and most of them have been followed in a
major, carefully planned and monitored epidemiological survey, the Life
Span Study Sample, since 1950 (KA-82, WA-83). They were exposed to a wide
range of doses and are the largest group that has been studied. They are
virtually the only group providing extensive information on the response
pattern at various levels of exposure to low-LET radiation.
The estimated cancer risk from low-LET, whole body, lifetime exposure
presented here is based on a life table analysis using a linear response
model. We use the arithmetic-average of relative and absolute risk
projections (the BEIR-3 L-L model) for solid cancers, and an absolute risk
projection for leukemia and bone cancer (the BEIR-3 L-L model). For whole
C-27
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body dose, this yields an estimated 280 (with a possible range of 120 to
1200) fatalities per million person-rem for a population cohort
representative of the U.S. population. (The rounded value, 3x10"
fatalities per person-rem, has been selected for this analysis.)
Whole body dose means a uniform dose to every organ in the body. In
practice, such exposure situations seldom occur, particularly for ingested
or inhaled radioactivity. Inhaled radioactive particulate materials may
be either soluble or insoluble. Soluble particulate materials deposited
in the lung will be rapidly absorbed, and the radionucl ides associated
with them distributed throughout the body by the bloodstream. As these
radionuclides are transported in the blood, they irradiate the entire
body. Usually, they then redeposit in one or more organs, causing
increased irradiation of that organ. Insoluble particulate materials, on
the other hand, are only partially absorbed into body fluids. (This
fraction is typically assumed to be about 8 percent.) This absorption
occurs over a period of years, with a portion entering the bloodstream and
another retained in the pulmonary lymph nodes. The balance (92 percent)
of inhaled insoluble particulate materials are removed from the lung
within a few days by passing up the air passages to the pharynx where they
are swallowed. Inhaled insoluble particulate materials thus irradiate
both the lung and the gastrointestinal tract, with a small fraction being
eventually absorbed into the bloodstream (TG-66). These nonuniform
distributions of dose (and therefore risk) are taken into account through
use of the weighting factors for calculating effective dose.
There is a latent period associated with the onset of radiation-
induced cancers, so the increased risk is not immediately apparent. The
increased risk is assumed to commence 2 to 10 years after the time of
exposure and continue the remainder of the exposed individual's lifespan
(NA-80; EL-84).
^Preliminary reviews of new results from studies of populations exposed
at Hiroshima and Magasaki indicate that these risk estimates may be
revised upwards significantly' in the near future, particularly for acute
exposure situations. EPA will publish revised risk estimates to reflect
new results following appropriate review.
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For uniform exposure of the whole body, about 50 percent of
radiation-induced cancers in women and about 65 percent in men are fatal
(NA-80). Therefore, 1 rem of low-LET radiation would be expected to cause
a total of about 500 cancer cases if delivered to a population of one
million. (In the case of thyroid and skin, the ratio of nonfatal to fatal
cancers are much higher. These are addressed separately below.) This
corresponds to an average annual individual probability of developing
cancer of about 7x10" per year. For perspective, the average annual
risk of dying of cancer from all causes in the United States, in 1982, was
1.9xlO"3.
C.4.1.1 Cancer Risk Due to Radiation Exposure of the Thyroid
Exposure of the thyroid to extremely high levels of radiation may
cause it to degenerate. At moderate levels of exposure some loss of
thyroid function will occur. At lower levels of exposure, there are
delayed health effects, which take the form of both thyroid nodules and
thyroid malignancies (NA-72; NA-80). Doses-as low as 14 rads to the
thyroid have been associated with thyroid malignancy in the Marshall
Islanders (CO-70). The increased risk of radiation-induced cancer is
assumed to commence about 10 years after initial exposure and to continue
for the remaining lifespan of an exposed individual.
The true nature of thyroid nodules cannot be established until they
are surgically removed and examined histologically, and those that are
malignant can lead to death if not surgically removed (SA-68; DE-73;
PA-74). Although thyroid malignancies are not necessarily fatal, effects
requiring surgical removal of the thyroid cannot be considered benign. In
this analysis, all thyroid cancers, both fatal and nonfatal, are counted
for the purpose of estimating the severity of thyroid exposures.
Based on findings in BEIR-3, we estimate that 1 rem of thyroid
-4
exposure carries a risk of producing a thyroid cancer of 3.6x10 , of
which a small fraction (on the order of 1 in 10) will be fatal (NA-80).
Since the calculation of effective dose equivalent does not include
consideration of nonfatal thyroid cancers and the severity of the medical
C-29
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procedures for their cure, it is appropriate to limit the dose to the
thyroid by an additional factor beyond that provided by the PAG expressed
in terms of effective dose equivalent. Protective action to limit dose to
thyroid is therefore recommended at a thyroid dose 5 times the numerical
value of the PAG for effective dose.
C.4.1.2 Cancer Risk Due to Exposure of the Skin
The risk of fatal skin cancer is estimated to be on the order of one
percent of the total risk of fatal cancer for uniform irradiation of the
entire body (IC-78). However, since the weighting scheme for calculating
effective dose equivalent does not include skin, the PAG expressed in
terms of effective dose does not provide protection against radionuclides
which primarily expose skin. As in the case of the thyroid, the ratio of
nonfatal to fatal cancers from irradiation of the skin is high (on the
order of 100 to 1). It would not be appropriate to ignore this high
incidence of nonfatal skin cancers by allowing 100 times as much dose to
the skin as to the whole body. For this reason, evacuation is recommended
at a skin dose 50 times the numerical value of the PAG for effective dose
to the entire body. (Bathing and change of clothing are also effective
protective actions for radionuclides deposited on skin and clothing.
Since these are low-cost, low-risk actions, no dose level is specified
below which they are not recommended.)
C.4.1.3 Cancer Risk Due to Radiation Exposure of the Fetus
The fetus is estimated to be 5 to 10 times as sensitive to radio-
genic cancer as an adult (FA-73; WH-65). Stewart reports increased
relative incidence of childhood cancers following prenatal x-ray doses as
low as 0.20 to 0.25 rem and doubling of childhood cancers between 1-4 rems
(ST-73). She concluded that the fetus is about equally sensitive to
cancer induction in each trimester. Her findings are supported by similar
results reported by MacMahon and Hutchinson (MA-64), Kaplan (KA-58),
Polhemus and Kock (PO-59), MacMahon (MA-63), Ford, et aj_. (FO-59), Stewart
and Kneale (ST-70b), and an AEC report (AE-61). MacMahon reported that
although there were both positive and negative findings, the combination
C-30
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of weighted data indicates a 40 percent increase in childhood cancer
mortality after in vivo exposure to diagnostic X rays (1.0 to 5.0 rads):
about 1 cancer per 2,000 exposed children in the first 10 years after
birth (MA-63). He concluded that although the range of dose within which
these effects are observed is wide, effects will be fewer at 1 rem than at
5 rems.
Graham, et al., investigating diagnostic x-ray exposure, found a
significantly increased relative risk of leukemia in children: by a
factor of 1.6 following preconception irradiation of mothers or in utero
exposure of the fetus; by a factor of 2 following postnatal irradiation of
the children; and by a factor of 2 following preconception irradiation of
the mother and in utero exposure of the child (GR-66).
C.4.1.4 Age Dependence of Doses
Almost all dose models are based on ICRP "Reference Man," which
adopts the characteristics of male and female adults of working age.
ICRP-30 dosimetric models, which use "Reference Man" as a basis, are
therefore appropriate for only adult workers and do not take into account
differences in dose resulting from the differences in physiological
parameters between children and adults, e.g., intake rates, metabolism,
and organ size. Although it is difficult to generalize for all
radionuclides, in some cases these differences tend to counterbalance
each other. For example, the ratio of volume of air breathed per unit
time to lung mass is relatively constant with age, so that the ICRP adult
model for inhaled materials provides a reasonably good estimate of the
dose from a given air concentration of radioactive material throughout
life.
The thyroid is an exception because the very young have a relatively
high uptake of radioiodine into a gland that is much smaller than the
adult thyroid (see Section C.4.2.2.). This results in a larger childhood
dose and an increased risk which persists throughout life. Since this is
a worst case situation, we have examined it with some care, using the
age-specific risk coefficients for thyroid cancer in Table V-14 of the
C-31
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BEIR-3 report (NA-80) and an age-dependent dose model (OR-84). The
analysis indicates that, for iodine-131 ingestion, the estimated lifetime
risk is increased by a factor of 1.6, due to a 30 percent increase in
lifetime dose over that obtained for an adult by the same model. Results
are the same for inhalation of iodine-131, that is, the estimated lifetime
risk of fatal thyroid cancer is increased by a factor of 1.6.
C.4.2 Genetic Risk
An average parental dose of 1 rem before conception has been
estimated to produce 5 to 75 significant genetically-related disorders per
million liveborn offspring (NA-80). For this analysis we use the
geometric mean of this range, i.e. 1.9x10" . This estimate applies to
effects in the first generation only, as a result of dose to parents of
liveborn offspring. The sum of effects over all generations is estimated
-4
to be approximately twelve times greater; that is, 2.3x10 . In
addition, since any radiation dose delivered after a parent's last
conception has no genetic effect, and not all members of the population
become parents, less than half of the entire dose in an average population
is of genetic significance. Taking the above factors into account, we
estimate that the risk of genetically-related disorders in all generations
-4
is 1x10 per person-rem to a typical population.
Although the overall severity of the genetic effects included as
"significant" in the above estimates is not well known, rough judgements
can be made. The 1980 BEIR report referred to " disorders and traits
that cause a serious handicap at some time during lifetime" (NA-80). From
the types of defects reported by Stevenson (ST-59), it can be estimated
that, of all radiation-induced genetic effects, 50 percent lead to minor
to moderate medical problems (i.e., hair or ear anomalies, polydactyly,
strabismus, etc.), 25 percent lead to severe medical problems (i.e.,
congenital cataracts, diabetes insipidus, deaf mutism, etc.), 23 percent
would require extended hospitalization (i.e., mongolism, pernicious
anemia, manic-depressive psychoses, etc.), and 2 percent would die before
age 20 (i.e., anencephalus, hydrocephalus, pancreatic fibrocytic disease,
etc.).
C-32
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C.4.3 Summary of Risks of Delayed Effects
Table C-4 summarizes average lifetime risks of delayed health effects
based on results from the above discussion. Because of the nature of the
dose-effect relationships assumed for delayed health effects from
radiation (linear, nonthreshold), there is no dose value below which no
risk can be assumed to exist.
Table C-4 Average Risk of Delayed Health Effects in a Population
Fatal cancers
Nonfatal cancers
Genetic disorders
(all generations)
Effects
Whole Body
2.8E-4b
2.4E-4b
l.OE-4
per person-rem
Thyroid0
3.6E-5
3.2E-4
Skin
3.0E-6
3.0E-4
a We assume a population with the same age distribution as that of the
U.S. population in 1970.
b Risk to the fetus is estimated to be 5 to 10 times higher..
c Risk to young children is estimated to be about 1.6 times higher
C.4.4 Risks Associated with Other Radiation Standards
A review of radiation standards for protection of members of the
general population from radiation shows a range of values spanning several
orders of magnitude. This occurs because of the variety of bases (risk,
cost, practicability of implementation, and the situations to which they
apply) that influenced the choice of these standards. Some source-
specific standards are relatively protective, e.g., the standard limiting
exposure of the public from nuclear power operations (25 mrem/y)
corresponds to a risk (for cancer death) of 5xlO~ for lifetime
exposure. Others permit much higher risks. For example, the level at
C-33
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which the Environmental Protection Agency recommends action to reduce
exposure to indoor radon (0.02 working levels) corresponds to a risk of
_2
about 2x10 (for fatal lung cancer) for lifetime exposure. All of
these standards apply to non-emergency situations and were based on
considerations beyond a simple judgement of acceptable risk. The more
protective standards provide some guidance on lower bounds for the use of
sheltering. However, none of these source-specific standards for
non-emergency situations provide a useful basis for decisions on PAGs for
evacuation during the early phase of an accident.
Federal Radiation Protection Guidance for non-emergency situations
recommends that the dose from all sources combined (except from exposure
to medical and natural background radiation) to individuals in the
population not exceed 0.5 rem in a single year (FR-60) and that the dose
to the fetus of occupationally-exposed mothers not exceed 0.5 rem during
the 9-month gestation period (EP-87). These doses correspond to a
lifetime risk of fatal cancer to members of the general population of
-4
about 1.4x10 and, for exposure of fetuses, a 5 to 10 times greater
risk. If exposure of the fetus is limited to one ninth of 0.5 rems per
month over the entire gestation period, as recommended, the risk of severe
-4
mental retardation in liveborn is limited to about 7x10
The International Commission on Radiation Protection recommends that
the dose to members of the public not exceed 0.5 rems per year due to
non-recurring exposure to radiation from other than natural sources or
beneficial medical uses of radiation (IC-77). They also recommend a
limiting dose to members of the public of 0.1 rems per year from all such
sources combined for chronic (i.e., planned) exposure (IC-84).
Environmental Protection Agency regulations limit the dose due to the
combined emissions of radionuclides to air from routine operation of all
facilities combined to the same values; that is, to 0.5 rem per year for
non-recurring releases, and to 0.1 rem per year for chronic releases.
(These values are upper bounds for the combined exposure from multiple
sources under variance provisions; lower values normally apply to most
single sources.)
C-34
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These upper bounds may be taken as representative of acceptable
values for the situations to which they apply. That is, these are levels
of individual risk that are acceptable for the sum of all sources and
exposure pathways, for circumstances that are justified on the basis of
public benefit, and when actual doses from individual sources are "as low
as reasonably achievable" (ALARA) within these upper bounds. Although
these levels were not developed for the emergency situations governed by
these PAGs, they do provide useful precedents for acceptable levels of
involuntary risk in nonemergency situations. As such, the values for
nonrecurring exposure may reasonably be assumed to provide guidance on the
acceptability of risks in emergency situations (subject to the usual
caveats regarding use of lower levels if justified by cost-risk
(optimization) considerations.) The values for chronic exposure may also
be useful guidance for decisions involving exposures originating from an
accident that are avoidable in a nonemergency context, such as local
exposure over the long term and the export (or import) of foodstuffs to
locations remote from a nuclear accident.
C.5 Practicality of Implementation
Whereas Sections C.3 and C.4 dealt with the risk associated with the
projected dose that could be avoided by protective actions, this section
addresses the costs and risks associated with the protective actions
themselves. These analyses" of practicality relate to principles 3 and 4,
as set forth in Section C.I.6.
The principal relevant protective actions during the early phase are,
as noted earlier, evacuation and sheltering. In some cases, washing and
changing of clothing, or thyroid blocking may also be appropriate
actions. The costs, risks, and degrees of protection associated with
evacuation are generally higher than those for sheltering. Although there
may be some costs and risks associated with the other protective actions
they are small and not readily quantifiable. Therefore, only the costs
and risks associated with evacuation will be evaluated here. These
factors are evaluated to determine whether the costs are low enough to
justify lower PAGs than would be required to satisfy upper bounds of
acceptable risk under principle 2.
C-35
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C.5.1 Cost of Evacuation
Costs incurred to reduce the radiation risk from nuclear accidents
can be considered to fall into several major categories. A first category
includes the design, construction, and operation of nuclear facilities in
such a manner as to minimize the probability and consequences of
radiological accidents. It is recognized that the probability and
consequences of such accidents cannot be reduced to zero. Therefore, a
second category is necessary: the development of emergency response plans
to invoke actions which would reduce exposure of potentially exposed
populations, and consequently their risks, if a major nuclear accident
should occur.
Both of the above categories of cost are properly attributed to the
cost of design and operation of a nuclear facility. A third category of
costs involves actual protective actions which are implemented only as a
result of an accident. The choice of levels for PAGs affects only this
category of costs. Conversely, all costs in the first two categories are
unaffected by decisions on the levels of PAGs (unless the PAGs were to be
set so high as to never require protective action, in which case response
plans would be unnecessary). Therefore, the costs associated with
implementing the PAGs are evaluated only in terms of the actual cost of
response. In a similar manner, the risk incurred by protective actions is
compared only to the risk associated with the radiation dose that would be
avoided by the action, and is unaffected by any other measures taken to
reduce risk that fall in the first two categories of cost identified above.
C.5.1.1 Cost Assumptions
The cost analyses in this section are based on an evaluation of the
costs of evacuation and the population doses that would be received in the
absence of protective actions for nuclear power plant accidents. These
were calculated as a function of offsite location, meteorological
condition, and accident type (TA-87). Cost and dose data are based on the
following assumptions:
C-36
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a. Airborne releases are those associated with fuel melt accidents
followed by containment failure.
b. Meteorological conditions range from stable to unstable, and
windspeeds are those typical of the stability class.
c. Plume dispersion follows a Gaussian distribution, with a 0.01 m/s
'dry deposition velocity for iodine and particulate materials.
d. Doses are those incurred during the first four days due to whole
body gamma radiation from the plume, inhalation of radioactive
material in the plume, and direct and inhalation exposure to
deposited radioactive material.
e. Population distributions are the average values observed around
111 nuclear reactor plants, based on 1970 data.
f. The cost of evacuation is 2185 per person for a 4-day evacuation
and a 100-mile round trip, with an average of 3 persons per
household. These evacuation costs include wages and salaries of
personnel directing the evacuation, transportation costs of
evacuees to and from the staging location, food and lodging for
the evacuees during the evacuation period, loss of personal and
corporate income during the evacuation period, and the costs of
any special supplies.
The estimated costs and doses avoided are based on the following
evacuation area model (see Figure C.2.):
a. All people within a 2-mile radius of the accident are evacuated
for all scenarios.
b. People are also evacuated from a downwind area bounded by a ray
on either side of the- center line of the plume defining the
angular spread of the area evacuated and by an arc at the
distance beyond which the evacuation dose would not be exceeded
on the plume center line.
C-37
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2 MILE RADIUS
AREA WHERE PLUME
PAGs ARE EXCEEDED
AREA EVACUATED
i
FIGURE C-2. EVACUATION MODEL.
C-38
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Figure C-2 shows the relationship between the area in which the
evacuation dose would be exceeded and the larger area that might be
evacuated. As shown in the Figure, although the calculation assumes that
the plume will be centered in the evacuation arc, in real cases this will
generally not occur.
C.5.1.2 Analysis
Evaluation of costs for evacuation and doses to populations as a
function of the area evacuated depends on a variety of assumptions. Three
fuel-melt accident categories, six meteorological stability classes, and
three evacuation area models were examined. Detailed assumptions and data
are reported elsewhere (TA-87). Selected data, including the cost per
unit of collective dose to the population (person-rem) avoided, are
presented in Tables C-5, C-6, and C-7, for three stability classes, for
the median nuclear accident category examined (SST-2).
The data are presented for both the total area and the incremental
area evacuated for each change in dose level examined. When evaluating
the cost per person-rem avoided for a specific set of circumstances, it is
appropriate to assess the ratio of the total cost to the total dose
avoided to calculate the average cost per person-rein avoided. However,
when one is comparing the cost versus dose avoided to make a judgment
between a variety of different limiting dose values, it is appropriate
to compare the dose savings and costs at the margin, since the cost of
evacuating the additional area is incurred to avoid the incremental
collective dose. Therefore, the appropriate quantities are the cost and
risk for the additional area evacuated. Results of analyses on both a
total and incremental basis are presented in Tables C-5, C-6, and C-7 for
accident category SST-2. This is the smallest category of fuel melt
accident yielding effective dose equivalents during the first 4 days
of exposure that are greater than 0.5 rems outside the assumed 2-mile
evacuation circle for all stability classes. Data on costs verus dose
saved for all three accident categories are summarized in Table C-8 in
the next section.
C-39
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Table C-5 Costs for Implementing Various PAGs for an SST-2 Type Accident (Stability Class A)
n
Evacuation
angle
(degrees)
70
90
180
PAG
value
(rem)
0.5
1
2
5
10
0.5
1
2
5
10
0.5
1
2
5
10
Cost
(dollars)
2.83E+7
6.68E+6
1.49E+6
2.99E+5
(\
a)
3.63E+7
8.54E+6
1.86E+6
3.26E+5
(a)
7.16E+7
1.67E+7
3.48E+6
4.48E+5
(a)
Total Area
Dose
avoided
(person-rem)
8.97E+4
4.06E+4
1.73E+4
5.22E+3
(\
a)
9.29E+4
4.24E+4
1.82E+4
5.41E+3
(a)
9.33E+4
4.27E+4
1.84E+4
5.46E+3
(a)
Dollars/
person-rem
avoided
315
164
88
57
(\
a)
391
201
102
60
(a)
767
391
190
82
(a)
ACost
(dollars)
2.16E+7
5.19E+6
1.19E+6
9.70E+4
2.78E+7
6.68E+6
1.54E+6
1.25E+5
5.49E+7
1.32E+7
3.04E+6
2.47E+5
Marginal Area
ADose
avoided
(person-rem)
4.91E+4
2.33E+4
1.21E+4
2.44E+3
5.05E+4
2.42E+4
1.28E+4
2.63E+3
5.06E+4
2.43E+4
1.29E+4
2.68E+3
ADollars/
Aperson-rem
avoided
440
223
98
40
550
276
120
47
1080
543
235
92
a The 4-day dose does not exceed the PAG outside the 2-mile radius of the accident site.
The total cost of evacuation within this radius is 2.02E+5 dollars; the total dose avoided
is 2.78E+3 person-rems; and the total cost per person-rem avoided is $73.
-------
Table C-6 Costs for Implementing Various PAGs for an SST-2 Type Accident (Stability Class C)
o
Evacuation
angle
(degrees)
70
90
180
PAG
value
(rem)
0.5
1
2
5
10
20
50
0.5
1
2
5
10
20
50
0.5
1
2
5
10
20
50
Cost
(dollars)
4.95E+7
1.23E+7
2.46E+6
7.82E+5
3.93E+5
2.60E+5
(a)
6.35E+7
1.58E+7
3.11E+6
9.48E+5
4.47E+5
2.77E+5
a)
1.25E+8
3.10E+7
5.95E+6
1.68E+6
6.87E+5
3.51E+5
(-* \
a)
Total Area
Dose
avoided
(person-rem)
1.13E+5
6.31E+4
3.73E+4
2.71E+4
2.10E+4
1.62E+4
(a)
1.13E+5
6.32E+4
3.74E+4
2.72E+4
2.10E+4
1.63E+4
(\
a)
1.13E+5
6.32E+4
3.74E+4
2.72E+4
2.10E+4
1.63E+4
(\
a)
Dollars/
person-rem
avoided
439
195
66
29
19
16
(a)
564
250
83
35
21
17
a)
1110
491
159
62
33
22
(\
a)
ACost
(dollars)
3.71E+7
9.87E+6
1.68E+6
3.89E+5
1.32E+5
3.40E+4
4.77E+7
1.27E+7
2.16E+6
5.00E+5
1.70E+5
3.40E+4
9.44E+7
2.51E+7
4.28E+6
9.90E+5
3.36E+5
6.70E+4
Marginal Area
ADose
avoided
(person-rem)
4.95E+4
2.58E+4
1.02E+4
6.15E+3
4.75E+3
2.50E+3
4.95E+4
2.58E+4
1.02E+4
6.16E+3
4.76E+3
2.50E+3
4.95E+4
2.58E+4
1.02E+4
6.16E+3
4.77E+3
2.50E+3
^Dollars/
Aperson-rem
avoided
750
382
165
63
28
10
964
491
212
81
36
14
1910
971
419
161
70
27
a The 4-day dose does not exceed the PAG outside the 2-mile radius of the accident site.
The total cost of evacuation within this radius is 2.02E+5 dollars; the total dose avoided
is 2.78E+3 person-rems; and the total cost per person-rem avoided is $73.
-------
Table C-7 Costs for Implementing Various PAGs for an SST-2 Type Accident (Stability Class F)
o
-t>
N)
Evacuation
angle
(degrees)
70
90
180
PAG
value
(rem)
0.5
1
2
5
10
20
50
0.5
1
2
5
10
20
50
05
1
2
5
10
20
50
Cost
(dollars)
8.95E+7
4.95E+7
2.83E+7
1.23E+7
6.68E+6
3.65E+6
1.49E+6
1.15E+8
6.35E+7
3.63E+7
1.58E+7
8.54E+6
4.64E+6
1.86E+6
2.27E+8
1.25E+8
7.16E+7
3.10E+7
1.67E+7
8.98E+6
3.51E+6
Total Area
Dose
avoided
(person-rem)
4.61E+5
4.41E+5
4.19E+5
3.83E+5
3.53E+5
3.22E+5
2.68E+5
4.61E+5
4.41E+5
4.19E+5
3.83E+5
3.53E+5
3.22E+5
2.68E+5
4.61E+5
4.41E+5
4.19E+5
3.83E+5
3.53E+5
3.22E+5
2.68E+5
Dollars/
person-rem
avoided
194
112
67
32
19
11
5.6
250
144
87
41
24
14
6.9
493
285
171
81
47
28
13
ACost
(dollars)
4.01E+7
2.12E+7
1.59E+7
5.65E+6
3.03E+6
9.70E+5
5.15E+7
2.72E+7
2.05E+7
7.26E+6
3.90E+6
1.30E+6
1.02E+8
5.39E+7
4.05E+7
1.44E+7
7.71E+6
2.40E+6
Marginal Area
ADose
avoided
(person-rem)
1.98E+4
2.17E+4
3.66E+4
2.93E+4
3.18E+4
3.10E+4
1.98E+4
2.17E+4
3.66E+4
2.93E+4
3.18E+4
3.10E+4
1.99E+4
2.17E+4
3.66E+4
2.92E+4
3.18E+4
3.10E+4
ADollars/
Aperson-rem
avoided
2020
977
436
193
95
32
2600
1260
560
248
123
41
5120
2480
1110
492
242
80
-------
Changes in population density would not affect the above results,
since both cost and collective dose are proportional to the size of
the population affected. Factors that could affect these results are
different assumptions for cost of evacuation, accident scenarios, and
evacuation models. The results will be directly proportional to different
assumptions for the cost of evacuation. Some data on the variation with
accident scenario are presented in the next section. In situations where
different widths of evacuation are assumed, the change in cost per unit
dose avoided will be approximately proportional to the change in width in
degrees. This approximation is more accurate for the higher stability
classes (E and F). Evacuation within a 2 mile radius circle and a 90
degree sector in the downwind direction is generally considered to be
adequate for release durations not exceeding a few hours and where
reliable wind direction forecasts are available.
C.5.1.3 Results of the Cost Analysis
As shown in Tables C-5, C-6, and C-7 for an SST-2 accident, the cost
per unit dose avoided is greatest for wide angle evacuation and for the
lowest stability class (F). Although some emergency plans call for
evacuation over wider angles (up to 360 degrees), the model shown in
Figure C-2 with a 90 degree angle is most common.
To estimate an upper bound on dose for evacuation based on cost, we
first consider common values placed on avoiding risk. As one input into
its risk management decisions, EPA has used a range of $400,000 to
$7,000,000 as an acceptable range of costs for avoiding a statistical
-4
death from pollutants other than radiation. For a risk of 3x10 cancer
deaths per person-rem, these dollar values are equivalent to a range of
from about $120 to $2,000 per person-rem avoided. These values can be
compared to the marginal cost-effectiveness (dollars per person-rem) of
evacuation over an angle of 90 degrees. The resulting ranges of upper
bounds on dose are shown in Table C-8 for SST-1, SST-2, and SST-3 accident
scenarios. The maximum upper bounds (based on minimum costs for avoiding
risk) range from 1 to 10 rems, with most values being approximately 5
rems. The minimum upper bounds (based on maximum costs for avoiding risk)
C-43
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Table C-8 Upper Sounds on Dose for Evacuation, Based on the
Cost of Avoiding Statistical Fatalities3
Accident
Category
SST-1
SST-2
SST-3
Atmospheric
Stability Classb
A
C
F
A
C
F
A
C
F
Dose
Maximum
(rem)
5
5
10
1
3.5
10
(d)
(d)
5
Upper Bounds0
Minimum
(rem)
0.4
0.4
0.8
0.15
0.25
0.7
(d)
(d)
0.45
a Based on data from TA-87.
b Windspeeds typical of each stability class were chosen.
c Based on an assumed range of 5400,000 to $7,000,000 per
statistical life saved.
d For stability classes A and C, the dose from an SST-3 accident
is not predicted to exceed 0.5 rem outside a 2-mile radius. It
is assumed that evacuation inside this radius would be carried out
based on the emergency condition on the site. No differential
evacuation costs were calculated within this area.
range from 0.15 to 0.8 rem, with 0.5 rem being representative of most
situations. From these data we conclude that, based on the cost of
evacuation, a PAG larger than the range of values 0.5 to 5 rems would be
incompatible with principle three, Section C.I.4., for average members of
the population.
C.5.2 Risk of Evacuation
Principle four requires that the risk of the protective action not
exceed the risk associated with the dose that will be avoided. Risk from
evacuation can come from several sources, including (1) transportation
C-44
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accidents for both pedestrians and vehicle passengers, (2) exposure to
severe weather conditions or a competing disaster, and (3), in the case of
the infirm, anxiety, unusual activity, and separation from medical care or
services. The first source, transportation accidents, is the only category
for which the risk has been quantified. An EPA report (HA-75) evaluated
the risk of transportation fatalities associated with emergency evacuations
that have actually occurred and concluded that the risk of death per mile
traveled is about the same as that for routine automobile travel. Using
-8
this as a basis, the risk of death from travel is about 9x10" deaths per
person-mile, or 9xlO~ deaths per person for the 100-mile round trip
assumed for evacuation. Assuming a risk of fatal cancer from radiation of
-4
approximately 3x10 per person-rem, such an evacuation risk is
equivalent to a dose of about 0.03 rems.
In comparing this risk (or, more exactly, its equivalent in dose) to
the risk avoided by evacuation, it is important to note that protective
action must be implemented over a larger population than will actually be
exposed at the level of the PAG. Because of uncertainty or unpredictable
changes in wind direction, the exact location of the plume will not be
precisely known. Dose projections are made for the maximum exposed
individuals - those at the assumed location of the plume center!ine. To
assure that these individuals will be protected it is necessary that others
on either side take protective action at exposures that are less than at
the plume centerline, and, in some cases, are zero. Thus, the entire
evacuated population might incur, on the average, a risk from the
protective action which exceeds the risk of the radiation dose avoided.
We examined the average dose avoided for various choices of evacuation
levels. Table C-9 presents the results, which are derived from the data in
Tables C-5, C-6, and C-7. For the levels analyzed, the average dose
avoided is always significantly greater than 0.03 rems. We conclude,
therefore, that the choice of PAGs will not be influenced by the fourth
principle, for persons in the general population whose risk from evacuation
is primarily the normal risk of transportation, if the centerline dose
avoided is at or above 0.5 rems.
C-45
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Table C-9 Average Dose Avoided per Evacuated Individual for Incremental
Evacuation Levels
., . ,. . Average dose avoided (rem per individual)
Center-line dose by stabi 11 ty class
U emy
0.5 to 1
1 to 2
2 to 5
5 to 10
A
0.34
0.67
C
0.19
0.38
0.87
F
0.07
0.15
0.33
0.75
As previously discussed, hazardous environmental conditions (e.g.,
severe weather or a competing disaster) could create transportation risks
from evacuation that would be higher than normal. It is therefore
appropriate to make an exception to allow higher projected doses for
evacuation decisions under these conditions. In the absence of any
definitive information on these higher risks from evacuation itself, we
have arbitrarily assumed that it would be appropriate to increase the
projected dose for decisions to evacuate the general population under
hazardous environmental conditions up to a factor of 5 higher than under
normal environmental conditions.
It is also recognized that infirm persons are at higher risk from
evacuation than are average members of the population. It would be
appropriate to adopt higher PAGs for evacuation of individuals who would
be at greater risk from evacuation itself than for the typically healthy
members of the population who are at low risk from evacuation. In the
absence of definitive information on the higher risk associated with the
evacuation of this group, we have arbitrarily assumed that it is
appropriate to adopt PAGs a factor of five higher for evacuation of high
risk groups under normal environmental conditions. If both conditions
exist, (high risk groups and hazardous environmental conditions) projected
doses up to 10 times higher than the PAGs for evacuation of the general
population under normal conditions may be justified.
C-46
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Evacuation the general population at a projected dose of five rems
under hazardous environmental conditions, and 10 rems for special high
risk groups, is expected to result in actual doses avoided by evacuation
of one half (or more) of these values, depending on the effectiveness of
sheltering as discussed in Section C.7. These doses are expected to
satisfy Principle 4 without violating the other three principles.
C.5.3 Thyroid Blocking
The ingestion of stable potassium iodide (KI) to block the uptake of
radioiodine by the thyroid has been identified as an effective protective
action. The Food and Drug Administration (FDA) analyzed available
information on dose-response for radioiodine-induced thyroid cancers and
the incidence and severity of side effects from potassium iodide (FD 82).
They concluded "...risks from the short-term use of relatively low doses
of potassium iodide for thyroid olocking in a radiation emergency are
outweighed by the risks of radioiodine-induced thyroid nodules or cancer
at a projected dose to the thyroid gland of 25 rem. FDA recommends that
potassium iodide in doses of 130 milligrams (mg) per day for adults and
children above 1 year and 65 mg per day for children below 1 year of age
be considered for thyroid blocking in radiation emergencies in those
persons who are likely to receive a projected radiation dose of 25 rem or
greater to the thyroid gland from radioiodines released into the
environment. To have the greatest effect in decreasing the accumulation
of radioiodine in the thyroid gland, these doses of potassium iodide
should be administered immediately before or after exposure. If a person
is exposed to radioiodine when circumstances do not permit the immediate
administration of potassium iodide, the initial administration will still
have substantial benefit even if it is taken 3 or 4 hours after acute
exposure". Evacuation and sheltering are, however, preferred alternatives
for most situations because they provide protection for the whole body and
avoid the risk of misapplication of potassium iodide.
The Federal Emergency Management Agency has published a Federal
policy developed by the Federal Radiological Preparedness Coordinating
Committee regarding the use of KI as a protective action (FE-85). In
C-47
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summary, the policy recommends the stockpiling of KI and distribution
during emergencies to emergency workers and institutionalized persons, but
does not recommend requiring stockpiling or distribution to the general
public. The policy recognizes, however, that options on the distribution
and use of KI rests with the States and, hence, the policy statement
permits State and local governments, within the limits of their authority,
to take measures beyond those recommended or required nationally.
C.6. Recommended PAGs for Exposure to a Plume
Previous sections have reviewed data, standards, and other
information relevant to the principles set forth in section C.I.4. for
establishing PAGs. The results of these reviews are summarized in Table
C-10.
Based on principles 1 (avoidance of acute risk) and 3 (cost/risk
considerations) 5 rems is an upper bound on the dose at which evacuation
of the general population is justified. Principle 4 (risk of the
protective action itself) supplies a lower bound of 0.03 rems for
evacuation of most members of the public. However, under Principle 3
(cost/risk considerations) only values equal to or greater than 0.5 rems
are justified. This will be limiting unless lower values are required for
purely health-based reasons (Principle 2). This is not the case. The
single lower purely health-based value, 0.1 rems, is only valid as a
health-based criterion for chronic exposure. We have selected the value
0.5 rems as the dose which justifies evacuation, because 1) it satisfies
the criterion for acceptable risk from nonrecurring doses to the general
public, 2) it satisfies the criterion for acceptable risk to the fetus of
occupationally exposed mothers (as well as falling well below dose values
at which abortion is recommended), and 3) it falls within the range of
acceptable costs for the risks avoided.
As noted in Section C.7, we assume that the dose avoidable by
evacuation is one half of the projected dose. The value of the PAG for
evacuation of the general public is therefore chosen as one rem projected
committed effective dose equivalent.
C-48
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Table C-10. Summary of Considerations for Selecting the Evacuation PAGs.
Dose3
(rem) Consideration Principle Section
50 Assumed threshold for acute health
effects in adults. 1 C.2.1.1
10 Assumed threshold for acute health
effects in the fetus. 1 C.2.1.4
5 Maximum acceptable dose for normal
occupational exposure of adults. 2 C.4.4
5 Maximum dose justified to average
members of the population, based
on the cost of evacuation. 3 C.5.1.3
1 Dose above which abortion may be
recommended. 1,2 C.2.1.4
0.5 Maximum acceptable dose to the
general population from all
sources from nonrecurring, non-
accidental exposure. 2 C.4.4
0.5 Minimum dose justified to average
members of the population, based
on the cost of evacuation. 3 C.5.1.3
0.5 Maximum acceptable dose'' to
the fetus from occupational
exposure of the mother. 2 C.4.4
0.1 Maximum acceptable dose to the
general population from all
sources from routine (chronic),
nonaccidental exposure. 2 C.4.4
0.03 Dose that carries a risk assumed
to be equal to or less than that
from evacuation. 4 C.5.2
a These values are expressed in terms of avoided dose, whereas PAGs
are expressed in terms of projected total dose. See Section C.6.1.
b This is also the dose to the 8- to 15-week-old fetus at which the risk
of mental retardation is assumed to be equal to the risk of fatal cancer
to adults from a dose of 5 rems.
C-49
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These considerations apply to evacuation of typical members of the
population and are based on effective dose equivalent. As discussed in
previous sections, it may be appropriate to further limit dose to the
thyroid and skin and to adjust the value for special groups of the
population at unusually high risk from from evacuation. Different values
may also apply for protective actions other than evacuation.
In the case of exposure of the thyroid to radioiodine, action based
solely on effective dose would not occur until a thyroid dose about 33
times higher than the corresponding whole body dose. As noted in Section
C.4.1.1, because the weighting factor for thyroid used to calculate
effective dose does not reflect the high ratio of curable to fatal thyroid
cancers, protective action to limit dose to the thyroid is recommended at
a thyroid dose 5 times the numerical value of the PAG for effective dose.
Similarly, since effective dose does not include dose to the skin,
and for other reasons discussed in Section C.4.1.1, protective action to
limit dose to skin is recommended at a skin dose 50 times the numerical
value of the PAG for effective dose. As in the case of the thyroid, this
includes consideration of the risk of both curable and noncurable cancers.
Special risk groups include fetuses, and infirm persons. As noted in
Sections C.3 and C.4.1.3, we assume that the risk of radiation-induced
cancer is about 5 to 10 times higher for fetuses than for adults and that
the risk of mental retardation in fetuses exposed during the 8th to 15th
weeks of gestation is about 10 times higher than the risk of fatal cancer
in equivalently exposed adults. However, due to the difficulty of rapidly
evacuating only pregnant women in a population, and the assumed
higher-than-average risk associated with their evacuation, it is not
considered appropriate to establish separate PAGs for pregnant women. In
part for this reason, the PAG is chosen sufficiently low to satisfy
Federal guidance for limiting exposure of the fetus in pregnant workers.
Higher PAGs for situations involving higher risks from evacuation
were discussed in section C.5.2. Under normal, low-risk, environmental
conditions, PAGs for evacuation of groups who present higher than average
C-50
-------
risks from evacuation (e.g., infirm persons) are recommended at projected
doses up to 5 rems. Evacuation of the general population under high-risk
environmental conditions is also recommended at projected doses up to 5
rems. If evacuation of high risk groups under hazardous environmental
conditions is being considered, projected doses up to 10 rems may be
justified.
Short-term sheltering is recognized as a low-cost, low-risk,
protective action primarily suited for protection from exposure to an
airborne plume. Sheltering is clearly justified to avoid any doses above
0.5 rems on the basis of avoidance of health risks alone. However, data
are not available to establish the dose below 0.5 rems at which sheltering
is no longer justified because of its cost or its risk from
implementation. If such data were available, they would be likely to
justify dose levels much lower than 0.5 rems. Because of this, and
because sheltering has other benefits related to emergency communication
with members of the public, no dose level is established below which
sheltering is not recommended. It should always be carried out in
situations where 0.5 rem or greater would be avoided, and sheltering will
almost invariably still be appropriate if any appreciable dose is
projected. However, for some specific situations (e.g. poor ventilation
or high temperatures) when risks from sheltering can be identified, it may
be appropriate to establish a dose value below which sheltering should not
be implemented.
Bathing and changing of clothing are effective for reducing beta dose
to the skin of persons exposed to an airborne plume of radioactive
materials. Since these are also low-cost, low-risk actions, no PAG is
recommended for initiating their implementation. It is expected that any
persons sheltered in or evacuated from contaminated areas, or persons
otherwise believed to have been exposed to an airborne plume, will be
routinely advised by emergency response officials to take these actions
within 12 hours after exposure.
The use of stable iodine to protect against uptake of inhaled
radioiodine by the thyroid is recognized as an effective alternative to
C-51
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evacuation for situations involving radioiodine releases where evacuation
cannot be implemented. Use of stable iodine should be considered for any
such situation in which evacuation or sheltering will not be effective in
preventing thyroid doses of 25 rems.
C.7 Avoided Dose vs. Projected Dose
A further consideration in the selection of PAGs is whether to
express them in terms of projected dose or avoided dose. The analysis for
selecting the PAG for evacuation is carried out in terms of avoided dose.
However, PAGs have commonly been expressed in terms of projected dose,
which is more easily used during an emergency. Therefore, it is necessary
to consider the relation between avoided and projected dose.
One factor that affects the dose avoided is whether evacuation can be
completed before plume arrival. It is not possible to predict this.
Emergency plans are, however, expected to include procedures for early
notification and evacuation of populations in potentially high exposure
areas. For these reasons, no difference in avoided and projected dose is
assumed on the basis of delayed evacuation.
Another factor affecting the dose avoided by evacuation is the dose
reduction by sheltering (where sheltering is assumed to mean staying
inside a structure with doors and windows closed and exterior ventilation
systems shut off). Since sheltering is a low-cost, low-impact protective
action, it is assumed that sheltering will be implemented at any location
where evacuation is considered. In this case, the dose avoidable by
evacuation is the difference between the projected dose and the dose
avoided by sheltering.
The effectiveness of sheltering as a protective action is discussed
in Chapter 5, Section 5.5.2. Tables 5-6 and 5-7 summarize dose reduction
factors as a function of type of structure, plume duration, and structure
tightness. Dose reduction factors for gamma radiation range from 0.2 for
large buildings to 0.9 for frame construction with no basement. For
inhalation exposure in structures with no special measures except closing
C-52
-------
doors and windows, the dose reduction factor is estimated as 0.6 or less
for plume durations of up to 2 hours. For tight structures, the
corresponding dose reduction factor is 0.3 or less.
Based on these data, dose reduction factors for sheltering are
assumed to be about 0.5 for normal housing and about 0.25 for specially
prepared or large structures with exterior ventilation ducts closed.
Therefore the PAG for evacuating the general population is specified as
1 rem projected dose. For situations involving population groups at high
risk from evacuation (for which the PAG is 5 rems) who are sheltered in
specially prepared or large structures that would provide better than
average radiation protection, the PAG is twice the projected dose for
normal structures, or 10 rems. Other projected doses may be justified for
shelters with confirmed dose reduction factors that are different from
those assumed here.
C.8 Dose Limits for Emergency Workers
The dose limits for emergency workers are based on avoiding acute
health effects and limiting the risk of delayed health effects in the
context of the need to assure protection of the population and of valuable
properties. It is assumed that most emergency workers are accustomed to
accepting an element of risk as a condition of their employment. Examples
of emergency worker occupations include law enforcement, firefighting,
civil defense, traffic control, health services, environmental monitoring,
animal care, and transportation services. Similarly, utility, industrial,
and institutional facilities normally designate employees who are
responsible for controlling releases and/or protecting property, as well
as for protecting employees and others in the facility during an
emergency. Persons involved in the emergency shutdown of facilities,
including farms, may also be considered as emergency workers.
Radiation exposure of emergency workers should normally be governed
by the Federal Radiation Protection Guidance for Occupational Exposure
(EP-87). This guidance specifies an upper bound of five rems committed
effective dose equivalent per year for most workers. (Pregnant women,
C-53
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who, under this guidance should not normally engage in work situations
that involve more than approximately 50 mrem/month, would normally be
evacuated as part of the general population.) The guidance also specifies
that doses should be maintained as low as reasonably achievable; that
doses shoulckbe monitored; and that workers should be informed of the
risks involved and of basic principles for radiation protection.
There are some emergency situations, however, for which higher doses
may be justified. These include lifesaving operations and the protection
of valuable property. International guidance (IC-77) recognizes two
additional dose levels for workers under specially justified
circumstances: two times the annual limit for any single event, and five
times the annual limit in a lifetime. The dose limits recommended here
adopt the former value (10 reins) for operations limited to the protection
of property. The latter value (25 rems) may be permitted for situations
involving lifesaving operations or activities that are essential to
preventing substantial risks to populations. In this context "substantial
risks" means collective doses that are significantly larger than those
incurred through the protective activities engaged in by emergency
workers. Emergency workers should not operate under dose limits higher
than five rems unless the following conditions are satisfied:
1. Lower doses through the rotation of workers or other
commonly-used dose reduction methods are not possible, and
2. Instrumentation is available to measure the dose.
Thyroid and skin doses to workers are normally limited to 50 rems.
This level is sufficient to avoid acute effects, and it is expected that
emergency plans will provide for special protection of emergency workers
exposed to airborne radioiodine and beta radiation so that these limits
for thyroid and skin can be satisfied.
Situations may occur in which a dose in excess of 25 rems would be
required for lifesaving operations. It is not possible to prejudge the
risk that one person should be allowed to take to save the life of
' C-54
-------
another. However, persons undertaking an emergency mission in which the
dose would exceed 25 rems to the whole body should do so only on a
voluntary basis and with full awareness of the risks involved, including
the numerical levels of dose at which acute effects of radiation will be
incurred and numerical estimates of the risk of delayed effects.
The risk of acute health effects is discussed in section C.2. Table
C-ll presents estimated cancer mortality rates for a dose of 25 rems, as a
function of age at the time of exposure. The risk of cancer from
moderately higher doses will increase proportionately. These values were
calculated using risk estimates from BEIR-3 (NA-80) as discussed in
Section C.4.1, and life table analyses that assume the period of cancer
risk lasts for the worker's lifetime (BU-81). The risk was calculated for
the midpoint of each age range. Roughly equivalent risks of nonfatal
cancers and serious genetic effects (if gonadal tissue is exposed) will
also be incurred.
Table C-ll Cancer Risk to Emergency Workers Receiving 25 Rems Whole
Body Dose
Age of the
emergency
worker at time
of exposure
(Years)
Approximate risk3
of premature death
(deaths per 1,000 persons exposed)
Average years of
life lost if premature
death occurs
(Years)
20 to 30
30 to 40
40 to 50
50 to 60
9.1
7.2
5.3
3.5
24
19
15
11
aLife Plateau: Period following the latent cancer period and extending to
death.
C-55
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The dose limits of 75 rems previously recommended by EPA and 100 rems
that has been recommended by NCRP (GL-57) for lifesaving action represents a
very high level of risk of acute and delayed health effects. A dose of 100
rems is expected to result in an approximately 15 percent risk of temporary
incapacity from nonlethal acute effects and an indeterminate, but less than 5
percent, chance of death within 60 days. This is in addition to a risk of
about 1 in 30 of incurring fatal cancer. Such high risk levels can only be
accepted by a recipient who has been made aware of the risks involved;
therefore, no absolute dose limit for lifesaving activities is offered.
C-56
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U.S. AEC Report TID-2373, U.S. Nuclear Regulatory Commission,
Washington, DC 20555, 1961.
AI-65 AINSWORTH, E.J., et al. Comparative Lethality Responses of Neutron and
X-Irradiated Dogs: Influence of Dose Rate and Exposure Aspect. Rad.
Research 26:32-43, 1965.
BA-68 BATEMAN, J.L. A Relation of Irradiation Dose-Rate Effects in Mammals
and in Mammalian Cells, in Dose Rate Mammalian Radiation Biology, pp.
23.1-23.19, CONF 680401, U.S. Atomic Energy Commission, Oak Ridge, TN,
1968.
BE-68 BEIERWALTER, W.H. and WAGNER, H.N., JR. Therapy of Thyroid Diseases
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:-65
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APPENDIX 0
(reserved)
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APPENDIX E
(reserved)
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APPENDIX F
Protective Action Guides for the Intermediate Phase
(Deposited Radioactive Materials):
Supporting Information
-------
CONTENTS
Page
F.I Introduction F-l
F.I.I Response Duration F-l
F.I.2 Source Term F-2
F.I.3 Exposure Pathways F-4
F.I.4 Response Scenario F-5
F.2 Considerations for Establishing PAGs for the Intermediate Phase.. F-7
F.2.1 Principles F-9
F.2.1.1 Cost/Risk Considerations F-10
F.2.1.2 Protection of Special Groups F-12
F.2.2 Federal Radiation Protection Guides F-14
F.3 Dose from Reactor Accidents F-15
F.4 Alternatives to Relocation F-17
F.5 Risk Comparisons F-18
F.6 Relocation PAG Recommendations F-21
F.7 Criteria for Reentry into the Restricted Zone F-24
References F-25
Figures
F-l Response Areas F-6
F-2 Time Frame of Response to a Major Nuclear Reactor Accident F-10
F-3 Cost of Avoiding Statistical Fatalities and Exposure
Rates Corresponding to Various Total First Year Doses F-13
F-4 Average Lifetime Risk of Death from Whole Body Radiation Dose
Compared to the Average Risk of Accidental Death from Lifetime
(47 years) Occupation in Various Industries F-19
Tables
F-l Brief Descriptions Characterizing Nuclear Power Plant Accident
Types (SN-82) F-3
F-2 Release Quantities for Postulated Nuclear Reactor Accidents F-3
F-3 Annual Doses Corresponding to 5 Rems in 50 Years F-15
F-4 Measure of Lifetime Risk of Mortality from a Variety of Causes... F-20
F-5 Summary of Considerations for Selecting PAGs for Relocation F-22
F-6 Estimated Maximum Doses to Nonrelocated Persons F-23
-------
Protective Action Guides for the Intermediate Phase
(Deposited Radioactive Materials):
Supporting Information
F.I Introduction
The purpose of this Appendix is to provide background information
and a rationale for the choice of Protective Action Guides (PAGs) for
relocation and other protective actions during the intermediate phase of
the response to a nuclear accident. The resulting PAGs and associated
implementing guidance are provided in Chapters 4 and 7, respectively.
This rationale is based on the assumption that an airborne plume of
radioactive material has already passed over an area and left a deposit
of radioactive material behind, and that the public has been either
sheltered or evacuated, as necessary, on the basis of PAGs for the early
phase of a nuclear accident, as discussed in Chapters 2 and 5. PAGs for
subsequent relocation of the public and other protective actions, as well
as dose limits for persons reentering the area from which the public is
relocated, are addressed in this Appendix.
We first set forth the assumptions used to derive information
pertinent to choosing the dose level at which relocation of the public is
appropriate. This is followed by an examination of information relevant
to this decision, and selection of the PAG for relocation. The Appendix
concludes with a brief discussion of the basis for dose limits for
persons temporarily re-entering areas from which the public has been
relocated.
F.I.I Response Duration
In order to decide whether to initiate relocation of the public from
specific areas it is necessary to predict the dose that would be
avoided. One factor in this prediction is the duration of the exposure
to be avoided. Relocation can begin as soon as patterns of exposure from
deposited radioactivity permit restricted areas to be identified. For
the purpose of this analysis, relocation of persons who have not already
F-l
-------
been evacuated from the restricted zone is assumed to take place on the
fourth day after the accident. Return of evacuated persons to their
residences outside the restricted zone and transition to relocation
status of persons already evacuated is assumed to occur over a period of
a week or more.
The period of exposure avoided by relocation ends when the relocated
person either returns to his property or is permanently resettled in a
new location. At the time of relocation decisions, it will usually not
be possible to predict when either of these actions will occur.
Therefore, for convenience of dose projection, it is assumed that the
period of exposure avoided is one year and that any extension beyond'this
period will be determined on the basis of recovery criteria. This
assumption corresponds to emergency response planning guidance by ICRP
(IC-84) and IAEA (IA-85).
F.I.2 Source Term
The "source term" for this analysis is comprised of the quantities
and types of particulate radioactive material found in the environment
following an accidental release. Nuclear accidents can be postulated
with a wide range of release characteristics. The characteristics of the
source terms assumed for the development of these PAGs are those
postulated for releases from various types of fuel-melt accidents at
nuclear power plants (SN-82). Table F-l provides brief descriptions of
these accident types. Radionuclide releases have been estimated for the
three most severe accident types (SST-1, SST-2, SST-3) based on
postulated core inventories and release fractions (Table F-2). The other
types (SST-4 and SST-5) would generally not produce offsite doses from
exposure to deposited material sufficient to warrant consideration of
relocation.
If the release from an accident includes a large proportion of
long-lived radionuclides, doses will continue to be delivered over a long
period of time and, if no remedial actions are taken, the dose delivered
in the first year may represent only a small portion of the total dose
F-2
-------
Table F-l Brief Descriptions Characterizing Various Nuclear Power Plant
Accident Types (SN-82)
Type
Description
SST-1
SST-2
SST-3
SST-4
SST-5
Severe core damage. Essentially involves loss of all installed
safety features. Severe direct breach of containment.
Severe core damage. Containment fails to isolate. Fission
product release mitigating systems (e.g., sprays, suppression
pool, fan coolers) operate to reduce release.
Severe core damage. Containment fails by base-mat melt-
through. All other release mitigation systems function as
designed.
Modest core damage.
mode.
Containment systems operate in a degraded
Limited core damage. No failures of engineered safety features
beyond those postulated by the various design basis accidents.
The most severe accident in this group assumes that the
containment functions as designed following a substantial core
melt.
Table F-2 Release Quantities for Postulated Nuclear Reactor Accidents
Principal
radionuclides
contributing
to dose from
deposited
materials
Zr-95
Nb-95
Ru-103
Ru-106
Te-132
1-131
CS-134
CS-137
Ba-140
la-140
Half-life
(days)
6.52E+1
3.50E+1
3.95E+1
3.66E+2
3.25
8.05
7.50E+2
1.10E+4
1.28E+1
1.67
Estimated
SST-1
1.4E+6
1.3E+6
6.0E+6
1.5E+6
8.3E+7
3.9E+7
8.7E+6
4.4E+6
1.2E+7
1.5E+6
quantity released3
(Curies)
SST-2
4.5E+4
4.2E+4
2.4E+5
5.8E+4
3.9E+6
2.6E+5
1.2E+5
5.9E+4
1.7E+5
5.1E+4
SST-3
1.5E+2
1.4E+2
2.4E+2
5.8E+1
2.6E+3
1.7E+4
1.3E+2
6.5E+1
1.7E+2
1.7E+2
a Based on the product of reactor inventories of radionuclides and
estimated fractions released for three accident categories (SN-82).
F-3
-------
delivered over a lifetime. On the other hand, if the release consists
primarily of short-lived radionuclides, almost the entire dose may be
delivered within the first year.
From the data in Table F-2, it is apparent that, for the groups of
accidents listed, both long and short lived radionuclides would be
released. Consequently, doses due to deposited materials from such
accidents would be relatively high during the first year followed by long
term exposures at lower rates.
F.I.3 Exposure Pathways
The principal exposure pathway to members of the public occupying
land contaminated by deposits of radioactive materials from reactor
accidents is expected to be exposure of the whole body to external gamma
radiation. Although it is normally expected to be of only minor
importance, the inhalation pathway would contribute additional doses to
internal organs. The health risks from other pathways, such as beta dose
to the skin and direct ingestion of dirt, are also expected to be minor
in comparison to the risks due to external gamma radiation (EP-88). Skin
and inhalation dose would, however, be important exposure pathways for
source terms with significant fractions of pure beta emitters, and
inhalation dose would be important for source terms with significant
fractions of alpha emitters.
Since relocation, in most cases, would not be an appropriate action
to prevent radiation exposure from ingestion of food and water, these
exposure pathways have not been included in this analysis. They are
•addressed in Chapters 3 and 6. In some instances, however, where
withdrawal of food and/or water from use would, in itself, create a
health risk, relocation may be an appropriate alternative protective
action. In this case, the committed effective dose equivalent from
ingestion should be added to the projected dose from deposited
radionuclides via other pathways, for decisions on relocation.
F-4
-------
F.I.4 Response Scenario
This section defines the response zones, population groups, and the
activities assumed for implementation of protective actions during the
intermediate phase.
After passage of the radioactive plume, the results of environmental
monitoring will become available for use in making decisions to protect
the public. Sheltering, evacuation, and other actions taken to protect
the public from the plume will have already been implemented. The tasks
immediately ahead will be to (1) define the extent and characteristics of
deposited radioactive material and identify a restricted zone in
accordance with the PAG for relocation, (2) relocate persons from and
control access to the restricted zone, (3) allow persons to return to
areas outside the restricted zone, (4) control the spread of and exposure
to surface contamination, and (5) apply simple decontamination and other
low-cost, low-risk techniques to reduce the dose to persons who are not
relocated.
Because of the various source term characteristics and the different
protective actions involved (evacuation, sheltering, relocation,
decontamination, and other actions to reduce doses to "as low as
reasonably achievable" levels), the response areas for different
protective actions may be complex and may vary in size with respect to
each other. Figure F-l shows a generic example of some of the principle
areas involved. The area covered by the plume is assumed to be
represented by area 1. In reality, variations in meteorological
conditions would almost certainly produce a more complicated shape.
Based on plant conditions and other considerations prior to or after
the release, members of the public are assumed to have already been
evacuated from area 2 and sheltered in area 3. Persons who were
evacuated or sheltered as a precautionary action for protection from the
plume but whose homes are outside the plume deposition area (area 1) are
F-5
-------
ARBITRARY SCALE
LEGEND
| | 1. PLUME DEPOSITION AREA.
1.-J
PLUME TRAVEL
DIRECTION
2. AREA FROM WHICH POPULATION IS EVACUATED.
3. AREA IN WHICH POPULATION IS SHELTERED.
4. AREA FROM WHICH POPULATION IS RELOCATED (RESTRICTED ZONE).
FIGURE F-1. RESPONSE AREAS.
-------
assumed to return to their homes or discontinue sheltering when
environmental monitoring verifies the outer boundary of area 1.
Area 4 is the restricted zone and is defined as the area where
projected doses are equal to or greater than the relocation PAG. The
portion of area 1 outside of area 4 is designated as a study zone and is
assumed to be occupied by the public. However, contamination levels may
exist here that would be of concern for continued monitoring and
decontamination to maintain radiation doses "as low as reasonably
achievable" (ALARA).
The relative positions of the boundaries shown in Figure F-l are
dependent on areas evacuated and sheltered. For example, area 4 could
fall entirely inside area 2 (the area evacuated) so that relocation of
persons from additional areas would not be required. In this case
relocation PAG would be used only to determine areas to which evacuees
could return.
Figure F-2 provides, for perspective, a schematic representation of
the response activities expected to be in progress in association with
implementation of the PAGs during the intermediate phase of the response
to a nuclear accident.
F.2 Considerations for Establishing PAGs for the Intermediate Phase
The major considerations in selecting values for these PAGs for
relocation and other actions during the intermediate phase are the four
principles that form the basis for selecting all PAGs. Those are
discussed in Section F.2.1. Other considerations (Federal radiation
protection guidance and risks commonly confronting the public) are
discussed in Sections F.2.2 and F.4.
In addition, a planning group consisting of State, Federal, and
industry officials provided recommendations in 1982 which EPA considered
in the development of the format, nature, and applicability of PAGs for
relocation. Abbreviated versions of these recommendations are as follows:
F-7
-------
tn
oc
3
U
u
o
i-rt UI
I O
oo jj
u
"I I I I Mill I I I I UNI I 1 I I Illll I I I I Mill
PERIOD OF
RELEASE,
DISPERSION,
DEPOSITION,
SHELTERING
o
ui
ui
_i
a.
Z
O
U
AND EVACUATION. 5;
O
a.
u
O
(NO TIME SCALE)
0.1
CONDUCT AERIAL AND GROUND SURVEYS. DRAW ISODOSE RATE LINES.
IDENTIFY HIGH DOSE RATE AREAS. CHARACTERIZE CONTAMINATION.
RELOCATE POPULATION FROM HIGH DOSE RATE AREAS.
ALLOW IMMEDIATE RETURN OF EVACUEES TO NONCONTAMINATEO AREAS.
ESTABLISH RESTRICTED ZONE BOUNDARY AND CONTROLS.
RELOCATE REMAINING POPULATION FROM WITHIN RESTRICTED ZONE.
GRADUALLY RETURN EVACUEES UP TO RESTRICTED ZONE BOUNDARY
CONDUCT D-CON AND SHIELDING EXPERIMENTS AND ESTABLISH PROCEDURES
FOR REDUCING EXPOSURE OF PERSONS WHO ARE NOT RELOCATED.
PERFORM DETAILED ENVIRONMENTAL MONITORING.
PROJECT DOSE BASED ON DATA
DECONTAMINATE ESSENTIAL FACILITIES AND THEIR ACCESS ROUTES.
RETRIEVE VALUABLE AND ESSENTIAL RECORDS AND POSSESSIONS.
REESTABLISH OPERATION OF VITAL SERVICES.
BEGIN RECOVERY ACTIVITIES.
CONTINUE RECOVERY.
§§? MONITOR AND APPLY ALARA FOR EXPOSED GROUPS.
I I I I Illll I I I I Hill III! Illll I I I I Illll
1.0 10 100
TIME AFTER DEPOSITION (DAYS)
1,000
FIGURE F-2. TIME FRAME OF RESPONSE TO AJ/IAJOR NUCLEAR REACTOR ACCIDENT (ASSUM
-------
a. The PAGs should apply to commercial, light-water power reactors.
b. The PAGs should be based primarily on health effects.
c. Consideration should be given to establishing a range of PAG
values.
d. The PAGs should be established as high as justifiable because at
the time of the response, it would be possible to lower them, if
justified, but it probably would not be possible to increase
them.
e. Only two zones (restricted and unrestricted) should be
established to simplify implementation of the PAGs.
f. The PAGs should not include past exposures.
g. Separate PAGs should be used for ingestion pathways.
h. PAGs should apply only to exposure during the first year after
an accident.
Although these PAGS may be applied to any nuclear accident, they
were derived primarily for the case of commercial U.S. reactors. In
general, we have found it possible to accommodate most of the above
recommendations.
F.2.1 Principles
In selecting values for these PAGs, EPA has been guided by the same
principles that were applied in the selection of PAGs for the early phase
of a nuclear accident (Appendix C). They are repeated here for
convenience:
1. Acute effects on health (those that would be observable within a
short period of time and which have a dose threshold below which
they are not likely to occur) should be avoided.
F-9
-------
2. The risk of delayed effects on health (primarily cancer and
genetic effects, for which linear nonthreshold relationships to
dose are assumed) should not exceed upper bounds that are judged
to be adequately protective of public health, under emergency
conditions, and are reasonably achievable.
3. PAGs should not be higher than justified on the basis of
optimization of cost and the collective risk of effects on
health. That is, any reduction of risk to public health
avoidable at acceptable cost should be carried out.
4. Regardless of the above principles, the risk to health from a
protective action should not itself exceed the risk to health
from the dose that would be avoided.
These four principles were discussed in detail in Appendix C as they
relate to the PAGs derived there. The portions of Appendix C that
analyzed the risks of health effects as a function of dose (Principles 1
and 2) also apply to doses associated with these PAGs. Considerations
for selection of PAGs for the intermediate phase of a nuclear accident
differ from those for selection of PAGs for the early phase primarily
with regard to implementation factors (i.e., Principles 3 and 4).
Specifically, they differ with regard to cost of avoiding dose, the
practicability of leaving infirm persons and prisoners in the restricted
zone, and avoiding dose to fetuses. Although sheltering is not generally
a suitable alternative to relocation, other alternatives (e.g.,
decontamination and shielding) are suitable. These considerations are
reviewed in the sections that follow.
F.2.1.1 Cost/Risk Considerations
The Environmental Protection Agency has issued guidelines for
internal use in for performing regulatory impact analyses (EP-83). These
include consideration of the appropriate range of costs for avoiding a
statistical death. The values are inferred from the additional
compensation associated with employment carrying a higher than normal
F-10
-------
risk of mortality, and is expressed as a range of $0.4 to %1 million per
statistical death avoided. The following discussion compares these
values to the cost of avoiding radiation-induced fatal cancers through
relocation.
A report by Bunger (BU-88) is used as a basis for estimating the
costs for relocation. The estimated incremental costs per day per person
relocated are shown below to be approximately 227.00. Moving and loss of
inventory costs are averaged over one year.
Moving $1.60
Loss of use of residence 2.80
Maintain and secure vacated property 0.90
Extra living costs 1.20
Lost business and inventories 14.00
Extra travel costs 4.10
Idle government facilities - 2.30
Total
The quantity of interest is the dose at which the value of the risk
avoided is equal to the cost of relocation. Since the above costs are
expressed in dollars/person-day, it is convenient to calculate the dose
that must be avoided per-person day. The equation for this is:
D =-
U VR
where:
D = dose (rem/day)
C = cost of relocation (dollars/day).
V = value of avoiding a statistical death (dollars/death)
R = statistical risk of death from radiation dose (deaths/rem)
Using the values cited above, and a value for R of 3xlO~ deaths/rem
(See Appendix C), one obtains a range of doses of about 0.01 to 0.2
rems/day. Thus, over a period of one year the total dose that should be
avoided to justify the cost of relocation would be about 4 to 70 rems.
F-ll
-------
These doses are based on exposure accumulated over a period of one
year. However, exposure rates decrease with time due to radioactive decay
and weathering. Thus, for any given cumulative dose in the first year, the
daily exposure rate continually decreases, so that a relocated person will
avoid dose more rapidly in the first part of the year than later. Figure
F-3 shows the effect of changing exposure rate on the relationship between
the cost of avoiding a statistical death and the time after an SST-2
accident (See Table F-l) for several assumed cumulative annual doses. The
points on the curves represent the cost per day divided by the dose avoided
per day, at time t, for the annual dose under consideration, where t is the
number of days after the accident. The right ordinate shows the gamma
exposure rate (mR/h) as a function of time for the postulated radionuclide
mix at one meter height.
The convex downward curvature results from the rapid decay of
short-lived radionuclides during the first few weeks following the
accident. Since the cost per day for relocation is assumed to be constant
and the dose avoided per day decreases, the cost effectiveness of relocation
decreases with time. For this reason it is cost effective to quickly
recover areas where the population has been relocated at projected doses
only marginally greater than the PAG.
Only trends and general relationships can be inferred from Figure F-3
because it applies to a specific mix of radionucl ides. However, for this
radionuclide mix, cost analysis supports relocation at doses as low as one
rem for the first week and two rems for up to 25 days after an accident.
F.2.1.2 Protection of Special Groups
Contrary to the situation for evacuation during the early phase of an
accident, it is generally not practical to leave a few persons behind when
most members of the general population have been relocated from a specified
area for extended periods of time. Further, no data are available on
differing risks of relocation for different population groups. In the
absence of such data, we have assumed that these risks will be similar to
those from evacuation. Those risks were taken as equivalent to the health
F-12
-------
0)
JS
"5
•o
o
o
_l
LU
oc
m
o
LU
Q
O
u»
I
CO
g
CO
oc
UJ
Q.
CO
o
o
10 15 20
TIME AFTER ACCIDENT (days)
25
30
FIGURE F-3. COST OF AVOIDING STATISTICAL FATALITIES AND
EXPOSURE RATES CORRESPONDING TO VARIOUS
TOTAL FIRST YEAR DOSES (ASSUMES AN SST-2
ACCIDENT AND A $27 PER PERSON-DAY COST OF
RELOCATION).
0.2
0.3
0.4
0.5
0.6
0.8 u
CO
1.0 §
o
z
5
O
Q.
OT
4 uj
oc
oc
5 °
0 o
6
b=
8
10
20
30
40
F-13
-------
risk from doses of 30 mrems for members of the general population and of 150
mrems for persons at high risk from evacuation (see Appendix C). Therefore,
to satisfy Principle 4 for population groups at high risk, the PAG for
relocation should not be lower than 150 millirems. Given the arbitrary
nature of this derivation, it is fortunate that this value is much lower than
the PAG selected, and is therefore not an important factor in its choice.
Fetuses are a special group at greater risk of health effects from
radiation dose than is the general population, but not at significantly
greater risk from relocation itself. The risk of mental retardation from
fetal exposure (see Appendix C) is significant. It is affected by the stage
of pregnancy relative to the assumed one-year exposure, because the 8 - week
critical period during which the risk is greatest, must be considered in
relation to the rapidly changing dose rate. Taking these factors into
account, it can be postulated that the risk of mental retardation due to
exposure of the fetus during the intermediate phase will range from one to
five times the cancer risk of an average member of the public, depending upon
when conception occurs relative to the time of the accident. The elevated
risk of radiation-induced cancer from exposure of fetuses is less
significant, as discussed in Appendix C.
It will usually be practicable to reduce these risks by establishing a
high priority for efforts other than relocation to reduce the dose in cases
where they reside near the boundary of the restricted zone. However, women
who are less than seven months pregnant should relocate for the balance of
their pregnancy if the projected dose during pregnancy cannot be reduced
below 0.5 rem.
F.2.2 Federal Radiation Protection Guides
The choice of a PAG at which relocation should be implemented does not
mean that persons outside the boundary of the restricted zone should not be
the subject of other protective actions to reduce dose. Such actions are
justified on the basis of existing Federal radiation protection guidance
(FR-65) for protecting the public, including implementation of the principle
of maintaining doses "as low as reasonably achievable" (ALARA).
F-14
-------
The intended actions to protect the public from radiation doses on the
basis of RPGs are those related to source control. Although it is reasonable
for members of the public to receive higher exposure rates prior to the
accident source term being brought under control, the establishment of
acceptable values for relocation PAGs must include consideration of the total
dose over the average remaining lifetime of exposed individuals (usually
taken as 50 years).
The nationally and internationally recommended upper bound for dose in a
single year from man-made sources excluding medical radiation, is 500 mrem
per year to the whole body of individuals in the general population (IC-77,
FR-65). These recommendations were not developed for accidents. They are
also not appropriate for chronic exposure. The ICRP recommends an upper
bound of 100 mrem per year, from all sources combined, for chronic exposure
(IC-77). The corresponding 50-year dose at 100 mrem/yr is 5 rems. We have
chosen to limit the projected first year dose to individuals from an accident
to the Relocation PAG, the projected second year dose to 500 mrem, and the
dose projected over a fifty year period to 5 rems. Due to the extended
duration of exposures and the short halflife of important radioiodines, no
special limits for thyroid dose are needed.
F.3. Dose from Reactor Accidents
Doses from an environmental source will be reduced through the natural
processes of weathering and radioactive decay, and from the shielding
associated with part time occupancy in homes and other structures. Results
of dose calculations based on the radiological characteristics of releases
from three categories of postulated, fuel-melt, reactor accidents (SST-1,
SST-2, and SST-3) (SN-82) and a weathering model from WASH-1400 (NR-75) are
shown in Table F-3. This table shows the relationship between annual doses
for the case where the sum, over fifty years, of the effective dose
equivalent from gamma radiation and the committed effective dose equivalent
from inhalation of resuspended materials, is 5 rems. Radioactive decay and
weathering reduces the second year dose from reactor accidents to 20 to 40
percent of the first year dose, depending on the radionuclide mix in the
release.
F-15
-------
Table F-3 Annual Doses Corresponding to 5 Rems in 50 Years3
Dose According to Accident Category
i cai
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
SST-l(rem)
1.25
0.52
0.33
0.24
0.18
0.14
0.12
0.10
0.085
0.080
0.070
0.060
0.060
0.055
0.055
0.050
SST-2(rem)
1.60
0.44
0.28
0.20
0.16
0.12
0.11
0.085
0.075
0.070
0.060
0.055
0.055
0.050
0.045
0.045
SST-3(rem)
1.91
0.38
0.24
0.17
0.13
0.11
0.090
0.070
0.065
0.060
0.050
0.050
0.045
0.040
0.040
0.040
aWhole body dose equivalent from gamma radiation plus committed
effective dose equivalent from inhalation assuming a resuspension factor
of 10"6 nr1. Weathering according to the WASH-1400 model (NR-75)
and radioactive decay are assumed.
bRadionuclide abundance ratios are based on reactor inventories from
WASH-1400 (NR-75) and release fractions for accident categories SST-1,
SST-2 and SST-3 are as described in reference SN-82. Initial
concentrations are assumed to have decayed for 4 days after reactor
shutdown.
cAnnual doses after 16 years would be less than 0.05 rems.
Based on studies reported in WASH-1400 (NR-75), the most conservative
dose reduction factor for structures (frame structures) is about 0.4 (dose
inside divided by dose outside) and the average fraction of time spent in a
home is about 0.7. Combining these factors yields a net dose reduction factor
of about 0.6. In most cases, therefore, structural shielding v/ould be
expected to reduce the dose to persons who are not relocated to 60 percent (or
less) of the values shown in Table F-3 before the application of
decontamination.
F-16
-------
F.4 Alternatives to Relocation
Persons who are not relocated, in addition to dose reduction provided by
partial occupancy in homes and other structures, can reduce their dose by the
application of various techniques. Dose reduction efforts can range from the
simple processes of scrubbing and/or flushing surfaces, soaking or plowing of
soil, removal and disposal of small spots of soil found to be highly
contaminated {e.g., from settlement of water), and spending more time than
usual in lower exposure rate areas (e.g., indoors), to the difficult and time
consuming processes of removal, disposal, and replacement of contaminated
surfaces. It is anticipated that simple processes would be most appropriate
to reduce exposure rates for persons living in contaminated areas outside the
restricted zone. Many of these can be carried out by the residents with
support from officials for monitoring, guidance on appropriate actions, and
disposal. The more difficult processes will usually be appropriate for
recovery of areas from which the population is relocated.
Decontamination experiments involving radioactive fallout from nuclear
weapons tests have shown reduction factors for simple decontamination methods
in the vicinity of 0.1 (i.e., exposure rate reduced to 10 percent of original
values). However, recent experiments at the Riso National Laboratory in
Denmark (WA-82, WA-84), using firehoses to flush asphalt and concrete surfaces
contaminated with radioactive material of the type that might be deposited
from reactor accidents, show decontamination factors for radionuclides
chemically similar to cesium that are in the range of 0.5 to 0.95, depending
on the delay time after deposition before flushing is applied. The factor for
ruthenium on asphalt was about 0.7 and was independent of the delay of
flushing. The results of these experiments indicate that decontamination of
the important reactor fission products from asphalt or concrete surfaces may
be much more difficult than decontamination of nuclear weapons fallout. Other
simple dose reduction methods listed above would be effective to varying
degrees. The average dose reduction factor for gamma radiation from
combinations of simple decontamination methods is estimated to be at least
0.7. Combining this with the-40 percent reduction estimated above for
structural shielding indicates that the doses listed in Table F-3 may be more
than twice as high as those which v/ould actually be received by persons who
are not relocated.
F-17
-------
F.5 Risk Comparisons
Many hazardous conditions and their associated risks are routinely
faced by the public. A lingering radiation dose will add to those risks,
as opposed to substituting one risk for another, and, therefore, radiation
protection criteria cannot be justified on the basis of the existence of
other risks. It is, however, useful to review those risks to provide
perspective. This section compares the risks associated with radiation
doses to those associated with several other risks to which the public is
commonly exposed.
Figure F-4 compares recent statistics for the average lifetime risk
of accidental death in various occupations to the estimated lifetime risk
of fatal cancer for members of the general population exposed to radiation
doses ranging up to 25 rems. Non-radiation risk values are derived from
information in reference (EP-81) and radiation risk values are from
Appendix C. These comparisons show, for example, that the lifetime cancer
risk associated with a dose of 5 rems is comparable to the lifetime risk
of accidental death in some of the safest occupations, and is well below
the average lifetime risk of accidental death for all industry.
Risks of health effects associated with radiation dose can also be
compared to other risks facing individuals in the general population. The
risks listed in Table F-4 are expressed as the number of premature deaths
and the average reduction of life-span due to these deaths within a group
of 100,000 persons. For purposes of comparison, a dose of 5 rems to each
member of a population group of 100,000 persons representative of the
average U.S. population carries an estimated lifetime risk of about 150
fatal cancers (see Appendix C). The number of deaths resulting from the
various causes listed in Table F-4 is based on data from mortality
records.
In Summary, the risk of premature death normally confronting the
public from specific types of'accidents ranges from about 2 to 1000 per
100,000 population. The estimated radiation doses required to produce a
similar risk of death from radiation-induced cancer range from about 0.07
to 33 rems.
F-18
-------
10
-2
UJ
a
UJ
cc
at
cc
a
10-3
CC
UJ
UJ
u.
UJ
O
cc
UJ
10-4
CONSTRUCTION & MINING
AGRICULTURE
•TRANSPORTATION & PUBLIC UTILITIES
AVERAGE FOR ALL UTILITIES
•GOVERNMENT
.SERVICE
MANUFACTURING
• RETAIL &
WHOLESALE
TRADE
25 rem
5 rem
1 rem
0.5 rem
I
I
I
I
I
6 8 1012 14 16 18
rem (effective dose equivalent)
20 22 24 26
FIGURE F-4. AVERAGE LIFETIME RISK OF DEATH FROM WHOLE BODY RADIATION DOSE
COMPARED TO THE AVERAGE RISK OF ACCIDENTAL DEATH FROM LIFETIME
(47 YEARS) OCCUPATION IN VARIOUS INDUSTRIES.
F-19
-------
Table F-4 Measure of Lifetime Risk of Mortality from a Variety of Causes3
(Cohort Size = 100,000)
Aggregate years Reduction of Average years
Nature of Premature of life lost life expectancy of life lost to
accident deaths to cohort at birth (years) premature deaths
Falls
Fires
Drowning
Poisoning
1,000
300
190
69
12,000
7,600
8,700
2,500
0.12
0.076
0.087
0.025
11
26
45
37
by drugs and
medicaments
Cataclysm13 17 490 0.005 30
Bites and 8 220 0.002 27
stingsc
Electric 8 290 0.003 37
current
in homesd
aAl1 mortality effects shown are calculated as changes from the U.S. Life
Tables for 1970 to life tables with the cause of death under investigation
removed. These effects also can be interpreted as changes in the opposite
direction, from life tables with the cause of death removed to the 1970
Life Table. Therefore, the premature deaths and years of life lost are
those that would be experienced in changing from an environment where the
indicated cause of death is not present to one where it is present. All
values are rounded to no more than two significant figures.
^Cataclysm is defined to include cloudburst, cyclone, earthquake, flood,
hurricane, tidal waves, tornado, torrential rain, and volcanic eruption.
cAccidents by bite and sting of venomous animals and insects include bites
by centipedes, venomous sea animals, snakes, and spiders; stings of bees,
insects, scorpions, and wasps; and other venomous bites and stings. Other
accidents caused by animals include bites by any animal and nonvenomous
insect; fallen on by horse or other animal; gored; kicked or stepped on by
animal; ant bites; and run over by horse or other animal. It'excludes
transport accidents involving ridden animals; and tripping, falling over an
animal. Rabies is also excluded.
^Accidents caused by electric current from home wiring and appliances
include burn by electric current, electric shock or electrocution from
exposed wires, faulty appliances, high voltage cable, live rail, and open
socket. It excludes burn by heat from electrical appliances and lighting.
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F.6 Relocation PAG Recommendations
Previous sections have reviewed data, standards, and other information
relevant to establishing PAGs for relocation. The results are summarized in
Table F-5, in relation to the principles set forth in Section F.2.1.
Based on the avoidance of acute effects alone (Principle 1) 50 rems and
10 rems are upper bounds on the dose at which relocation of the general
population and fetuses, respectively, is justified. However, on the basis of
control of chronic risks (Principle 2) a lower upper bound is appropriate.
Five rems is taken as an upper bound on acceptable risk for controllable
1ifetime exposure to radiation, including avoidable exposure to accidentally
deposited radioactive materials. This corresponds to an average of 100 mrem
per year for fifty years, a value commonly accepted as an upper bound for
chronic annual exposure of members of the public from all sources of exposure
combined, other than natural background and medical radiation (IC-77). In the
case of projected doses from nuclear reactor accidents, a five rem lifetime
dose corresponds to about 1.25 to 2 rems from exposure during the first year
and 0.4 to 0.5 rems from exposure during the second year.
Analyses based on Principle 3 (cost/risk) indicate that considering cost
alone would not drive the PAG to values less than 5 rems. Analyses in support
of Principle 4 (risk of the protective action itself) provide a lower bound
for relocation PAGs of 0.15 rems.
Based on the above, 2 rems projected committed effective dose equivalent
from exposure in the first year is selected as the PAG for relocation.
Implementation of relocation at this value will provide reasonable assurance
that, for a reactor accident, a person relocated from the outer margin of the
relocation zone will, by such action, avoid an exposure rate which, if
continued over a period of one year, would result in a dose of about 1.2
rems. This assumes that 0.8 rems would be avoided without relocation through
normal partial occupancy of homes and other structures. This PAG will provide
reasonable assurance that persons outside the relocation zone, following a
reactor accident, will not exceed 1.2 rems in the first year, 0.5 rems in the
second year, and 5 rems in 50 years. The implementation of simple dose
F-21
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Table F.5 Summary of Considerations for Selecting PAGs for Relocation
Dose
(rem)
50
10
6
5
5
3
3
2
Consideration
Assumed threshold for acute health effects in adults.
Assumed threshold for acute health effects in the
fetus.
Maximum projected dose in first year to meet 0.5 rems
in the second yeara.
Maximum acceptable annual dose for normal
occupational exposure of adults.
Minimum dose that must be avoided by
one year relocation based on cost.
Minimum projected first-year dose corresponding
to 5 rems in 50 years3.
Minimum projected first-year dose corresponding
to 0.5 rems in the second yeara.
Maximum dose in first year corresponding to
Principle
1
1
2
2
3
2
2
5 rems in 50 years from a reactor accident,
based on radioactive decay and weathering only. 2
1.25 Minimum dose in first year corresponding to 5 rems
in 50 years from a reactor accident based on
radioactive decay and weathering only. 2
0.5 Maximum acceptable single-year dose to the
general population from all sources from
non-recurring, non-accident exposure. 2
0.5 Maximum acceptable dose to the fetus from
occupational exposure of the mother. 2
0.1 Maximum acceptable annual dose to the general
population from all sources due to routine (chronic),
non-accident, exposure. 2
0.03 Dose that carries a risk assumed to be equal to
or less than that from relocation. 4
aAssumes the source term is from a reactor accident and that simple
dose reduction methods are applied during the first month after the
accident to reduce the dose to persons not relocated from contaminated
areas.
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reduction techniques, as discussed in section F-4, will further reduce dose
to persons who are not relocated from contaminated areas. Table F-6
summarizes the estimated maximum dose that would be received by these
persons for various reactor accident categories with and without the
application of simple dose reduction techniques.
Since effective dose does not include dose to the skin (and for other
reasons discussed in Appendix C) protective action to limit dose to skin is
recommended at a skin dose 50 times the numerical value of the PAG for
effective dose. This includes consideration of the risk of both curable and
fatal cancers.
Table F-6 Estimated Maximum Doses to Nonrelocated Persons'
Accident
Category
SST-1
SST-2
SST-3
No add
Year 1
1.2
1.2
1.2
itional dose
Year 2
0.5
0.34
0.20
Dose
reduction
50 years
5.0
3.9
3.3
(rem)
Early
Year 1
0.9
0.9
0.9
simple dose
Year 2
0.35
0.24
0.14
reduction^
50 years
3.5
2.7
2.3
aBased on relocation at a projected dose of 2 rems in the first
year and 40 percent dose reduction from normal, partial occupancy in
structures. No dose reduction from applied decontamination, shielding,
or time controls are assumed.
bThe projected dose is assumed to be reduced 30 percent by the
application of simple dose reduction techniques during the first month.
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F.7 Criteria for Reentry into the Restricted Zone
Persons may need to reenter the restricted zone for a variety of
reasons, including radiation monitoring, recovery work, animal care,
property maintenance, and factory or utility operation. Some persons
outside the restricted zone, by nature of their employment or habits, may
also receive higher than average radiation doses. Tasks that could cause
such exposures include, 1) changing of filters on air handling equipment
(including vehicles), 2) handling and disposal of contaminated vegetation
(e.g., grass and leaves) and, 3) operation of control points for the
restricted zone.
Individuals who reenter the restricted zone or who perform tasks
involving exposure rates that would cause their radiation dose to exceed
that permitted by the PAGs should do so in accordance with existing Federal
radiation protection guidance for occupationally exposed workers (EP-87).
The basis for that guidance has been provided elsewhere (EP-87)
F-24
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REFERENCES
BU-88 BUNGER, BYRON M., Cost of Relocation. U.S. Environmental
Protection Agency/Office of Radiation Programs.
Washington, D.C. 20460. 1989 (draft).
EP-81 U.S. ENVIRONMENTAL PROTECTION AGENCY. Background Report.
Proposed Federal Radiation Protection Guidance for
Occupational Exposure. EPA 520/4-81-003. U.S. Environmental
Protection Agency/Office of Radiation Programs. Washington,
D.C. 20460. January, 1981.
EP-83 U.S. ENVIRONMENTAL PROTECTION AGENCY, Office of Policy
Analysis. Guidelines for Performing Regulatory Impact
Analysis, EPA-23-01-84-003. U.S. Environmental Protection
Agency, Washington, DC 20460. December 1983.
EP-87 U.S. ENVIRONMENTAL PROTECTION AGENCY. Radiation Protection
Guidance to Federal Agencies for Occupational Exposure.
Federal Register. Vol. 52, No. 17, p. 2822, U.S.
Government Printing Office, Washington, DC 20402..January
27, 1987.
EP-88 AABERG, ROSANNE, Battelle Northwest Laboratories.
Evaluation of Skin and Ingestion Exposure Pathways. U.S.
Environmental Protection Agency/Office of Radiation
Programs, Washington, D.C. 20460 (1988 Draft).
FR-65 FEDERAL RADIATION COUNCIL. Radiation Protection Guidance
for Federal Agencies. Federal Register, Volume 30, pp.
6953-6955, U.S. Government Printing Office, Washington, DC
20402, May 22, 1965.
IA-85 INTERNATIONAL ATOMIC ENERGY AGENCY. Principles for
Establishing Intervention Levels for Protection of the
Public in the Event of a Nuclear Accident or Radiological
Emergency, Safety Series No.72, International Atomic Energy
Agency, Vienna, 1985.
IC-77 INTERNATIONAL COMMISSION ON RADIOLOGICAL PROTECTION.
Radiological Protection. ICRP Publication 26, Pergamon
Press, Oxford, England, January 1977.
IC-84 INTERNATIONAL COMMISSION ON RADIOLOGICAL PROTECTION.
Protection of the Public in the Event of Major Radiation
Accidents: Principles for Planning, ICRP Publication 40,
Pergamon Press, New York, 1984.
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NR-75 U.S. NUCLEAR REGULATORY COMMISSION. Calculations of
Reactor Accident Consequences, WASH-1400, U.S. Nuclear
Regulatory Commission, Washington, DC 20555, October 1975.
SN-82 SANDIA NATIONAL LABORATORIES. Technical Guidance for
Siting Criteria Development, NUREG/CR-2239, U.S. Nuclear
Regulatory Commission, Washington, DC 20555, December 1982.
TA-85 TAWIL, J.J. Cost/Risk Components for Analyses to Support
Development of Long-Term Reentry and Recovery Radiation
Protection Criteria (draft report), Pacific Northwest
Laboratory, Richland, WA 99352, 1985.
WA-82 WARMING, L. Weathering and Decontamination of
Radioactivity Deposited on Asphalt Surfaces, Riso-M-2273,
Riso National Laboratory, DK 4000 Roskilde, Denmark,
December 1982.
WA-84 WARMING, L. Weathering and Decontamination of Radioactivity
Deposited on Concrete Surfaces. RISO-M-2473. Riso National
Laboratory, DK-4000 Roskilde, Denmark. December 1984.
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