United States
Environmental Protection
Agency
Office of
Radiation Programs
Washington DC 20460
EPA 520/1-89-019
August 1989
Radiation
svEPA
A Review and Evaluation
of Principles Used in the
Estimation of Radiation
Doses Associated with
Deep sea Disposal of
Low-Level Radioactive
Waste
Printed on Recycled Paper
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EPA 520/1-89-019
A REVIEW AND EVALUATION OF PRINCIPLES USED
IN THE ESTIMATION OF RADIATION DOSES
ASSOCIATED WITH
DEEPSEA DISPOSAL OF LOW-LEVEL RADIOACTIVE WASTE
D. A. Baker
W. L. Templeton
J. K. Soldat
Battelle-Pacific Northwest Laboratory
Richland, Washington 99352
Prepared Under
Interagency Agreement DE-ACO6-76RLO 1830
Project Officer
Robert S. Dyer
Office of Radiation Programs
U.S. Environmental Protection Agency
Washington, DC 20460
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FOREWORD
In 1972 the Congress enacted Public Law 92-532, the Marine
Protection, Research and Sanctuaries Act (MPRSA), which authorized
the Environmental Protection Agency (EPA) to regulate any future
ocean disposal of waste materials, including low-level radioactive
waste (LLW). In response, the EPA Office of Radiation Programs
(ORP) initiated studies at ocean sites previously used for disposal
of LLW.
These studies were initiated: (1) to determine the condition
of LLW containers after disposal and prolonged exposure to the
marine environment; (2) to assess whether previous ocean disposals
of LLW were adversely affecting human health or the marine
environment; and (3) to obtain data to develop and support criteria
for regulating any future ocean disposal of LLW.
In 1983 the Congress enacted Public Law 97-424, the Surface
Transportation Assistance Act. Section 424 of that Act pertains
to ocean dumping and amends the MPRSA to require a Radioactive
Materials Disposal Impact Assessment (RMDIA) as part of a disposal
permit application. The RMDIA must include consideration of any
potential adverse environmental effects from ocean disposal of LLW.
Thus, the ORP, as part of an interagency agreement with the
Department of Energy (DOE), tasked the DOE's Battelle-Pacific
Northwest Laboratory to review and evaluate the principles used to
estimate radiation doses from deep ocean disposal of LLW.
This report summarizes dose limitation data, as recommended
by various national and international radiation protection
organizations. It also discusses available pathway dose models and
identifies problems in assessing ocean disposal as a waste
management option for LLW.
The Agency invites all readers of this report to send comments
or suggestions to Mr. David E. Janes, Director, Analysis and
Support Division (ANR-461), Office of Radiation Programs,
Environmental Protection Agency, Washington, DC 20460.
Richard JyT/Guamond, Director
Office ofURadiation Programs
iii
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SUMMARY
This report presents information obtained from reviewing
relevant guidance for estimating radiation doses applicable to
deepsea disposal of low-level radioactive wastes (LLW) . The review
was requested by the Environmental Protection Agency's (EPA) Office
of Radiation Programs (ORP) via an interagency agreement with the
Department of Energy's (DOE) Battelle-Pacific Northwest Laboratory
(B-PNL) to determine whether a specific, acceptable methodology
exists for assessing risks from ocean disposal of LLW.
The report includes discussions of: (1) dose categories and
recommended dose limits; (2) the radiation protection philosophy
of the International Commission on Radiological Protection (ICRP);
(3) physical and biological pathways by which radiation from
disposals of LLW in the marine environment could also reach man;
(4) three types of existing pathway models that can be used to
estimate dose to man; (5) oceanographic and radiological components
of existing assessment models; (6) proposed models; and, (7)
problems related to assessing risk from ocean disposal of LLW.
The report concludes that existing models, if improved as
additional environmental and risk assessment data becomes
available, should provide adequate information for regulatory
determination of risk from any future ocean disposals of LLW. The
existing models identified in this report should be able to
indicate whether maximum individual exposure limits are likely to
be exceeded.
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ACKNOWLEDGMENTS
We wish to express our gratitude to Robert S. Dyer, Office of
Radiation Programs, Environmental Protection Agency, for his ideas,
support, discussion, and assistance in this work.
We also wish to thank John E. Till for his pertinent and
helpful advice.
vii
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TABLE OF CONTENTS
Page
FOREWORD iii
SUMMARY v
ACKNOWLEDGMENTS vii
LIST OF FIGURES AND TABLES xi
1 INTRODUCTION 1
DOSE LIMITATIONS RECOMMENDED
BY VARIOUS ORGANIZATIONS 2
2.1 DOSE CATEGORIES 2
2.2 INTERNATIONAL COUNCIL ON RADIATION
PROTECTION (ICRP) 3
2.3 NATIONAL COUNCIL ON RADIATION PROTECTION
AND MEASUREMENTS (NCRP) 4
2.4 WORLD HEALTH ORGANIZATION (WHO) 5
2.5 U.S. GOVERNMENT 5
2.5.1 Federal Radiation Council (FRC) 5
2.5.2 Environmental Protection Agency (EPA) 6
ICRP RADIATION PROTECTION PHILOSOPHY 6
3.1 JUSTIFICATION 6
3.2 OPTIMIZATION 7
PATHWAY DOSE MODELING 9
4.1 STEADY-STATE MODELING 10
4.2 TRANSIENT MODELING 12
4.3 SPECIFIC ACTIVITY MODELING 15
4.4 MODELING CONSIDERATIONS 15
4.5 SELECTION AND IDENTIFICATION OF PARAMETER VALUES 16
4.5.1 Nature of the Released Radioactivity 17
4.5.2 Concentration Factors 17
4.5.3 Consumption Rates and Occupancy Factors 18
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TABLE OF CONTENTS (Continued)
Page
THE BASIS FOR DEEP OCEAN DISPOSAL 18
5.1 LONDON DUMPING CONVENTION (LDC) RECOMMENDATIONS 18
5.2 RADIOLOGICAL EVALUATION OF OCEAN DISPOSAL
PRACTICES 20
5.2.1 Need for Modeling 20
5.2.2 Need for Research 21
5.3 NUCLEAR ENERGY AGENCY (NBA) MODEL 21
5.3.1 Release Model 22
5.3.2 Marine Model 22
5.3.3 Pathway Model 22
5.4 INTERNATIONAL ATOMIC ENERGY AGENCY (IAEA) MODEL 23
5.4.1 Oceanographic Component 23
5.4.2 Radiological Component 27
PROBLEMS IN THE ASSESSMENT OF OCEAN DISPOSAL
OF LOW-LEVEL RADIOACTIVE WASTE (LLW) 31
6.1 COLLECTIVE DOSE 31
6.2 CHOICE OF A RADIOLOGICAL PROTECTION SYSTEM 32
CONCLUSIONS 36
8 REFERENCES 37
9 GLOSSARY 42
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LIST OF FIGURES AND TABLES
Page
FIGURE 1 Theoretical Relationships Between Costs and
Collective Dose Showing Optimum Collective
Dose, S0/ at Optimum Cost, C0
8
FIGURE 2 Simple Compartment Model
14
TABLE 1 Current NCRP Dose Limits for Members of
the Public or Occasionally Exposed Individuals
TABLE 2 Pathways and Mode of Exposure in the
IAEA Radiological Component
28
TABLE 3 Pathways and Usages Proposed by the IAEA
30
TABLE 4 Comparison of Allowable Intake by
Individual Members of the Public
for Selected Radionuclides
34
XI
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1. INTRODUCTION
The selection of a specific methodology for the assessment of
the risks of ocean disposal of other than high-level radioactive
waste (OTHLW) must be preceeded by an examination of the need for
this mode of waste disposal. Assuming that such disposal would be
permitted and licensed by a governmental agency, some limitation
must be placed on the quantities to be disposed, the location of
the disposal site, the waste matrix material, the kinds of
monitoring to be performed, and the types of containers. In the
United States, the agency assigned the responsibility for
developing such limitations and guidance is the Environmental
Protection Agency (EPA). However, any regulations and criteria the
EPA promulgates should be at least as restrictive as the
recommendations of international bodies such as the International
Atomic Energy Agency (IAEA) and the Nuclear Energy Agency (NEA).
They should also be in accord with provisions contained in the
London Dumping Convention (LDC) that cover the practice of ocean
disposal of wastes, including those that are radioactive.
The U.S. guidance must address the sea disposal of wastes by
any commercial or governmental entity within the U.S. territorial
waters and Exclusive Economic Zone (out to 200 miles from the coast
line) to ensure protection of the U.S. population and of the
contiguous marine environment. In addition, the U.S. guidance must
cover disposal by U.S. entities in international waters, since the
United States is a signatory to the LDC.
In this report we discuss the radiological protection
considerations necessary for the disposal of low-level radioactive
waste (LLW) that could detrimentally affect populations worldwide.
The applicable dose limitations, recommended for various disposal
practices by the International Commission on Radiological
Protection (ICRP), the National Council on Radiation Protection and
Measurements (NCRP), and the EPA are identified. Some recent
conclusions from the World Health Organization (WHO) concerning
waste disposal are summarized.
This report primarily considers the current ICRP-IAEA
philosophy concerning dose assessment, and the modeling of dose
pathways to individuals and populations, from any release of
LLW in the deep ocean. The present IAEA release rate limits for
ocean disposal of LLW are discussed, as are the models proposed by
NEA and IAEA. Finally, some of the inadequacies of the recent ICRP
methodology for calculating dose are presented.
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2. DOSE LIMITATIONS AS RECOMMENDED BY VARIOUS ORGANIZATIONS
This section provides a summary of dose categories and
presents pertinent radiation guidance developed by various national
and international bodies. it concentrates primarily on the
radiation standards set for the general population; standards for
radiation workers are not covered.
2.1 DOSE CATEGORIES
Radiation doses (a) can be calculated for individuals in a
"critical group" and for populations. In order to assess the dose
received by an exposed population in dose equivalent terms, use is
made of the collective dose equivalent. This collective dose can
be obtained by integration of the ranges of dose rates within the
population or the population group. In actual practice, this
collective dose is usually derived by multiplying the average or
per capita dose equivalent by the number of subgroup individuals
in the population. In some instances, assessment of collective
dose can be simplified, often avoiding the need to identify and
assess the separate individual doses. For example, in a food-chain
pathway it is sufficient to know only the total collective
consumption of marine organisms - not the individual consumption
rates. However, in a geographically extensive pathway, such as
fish consumption, it will be necessary to group the total catches
and to weight them according to their concentrations of
radioactivity. The latter will generally vary with distance from
the point of release.
The collective dose rate will vary as a function of time. The
total collective dose equivalent commitment from a particular
source can be obtained by integrating the collective dose
equivalent rate. This collective dose equivalent commitment is
required for the justification or optimization of different choices
of waste management practices. The collective quantities are
frequently expressed as man-rem (or man-Sv) to distinguish them
from individual doses.
The term "dose" in this report should be interpreted to mean
the sum of the internal and external dose equivalents unless
otherwise indicated.
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2.2 INTERNATIONAL COUNCIL ON RADIATION PROTECTION (ICRP)
The ICRP has recommended radiation protection standards for
consideration by its member countries. The first standard, issued
in 1959 [ICRP 1959], as well as a later one issued in 1965 [ICRP
1965], set the dose-rate limit to the whole body of a member of the
public at 0.5 rem/yr (5 mSv/yr) . This same limit was also
stipulated for gonads and red bone marrow. A dose-rate limit of
3 rem/yr (30 mSv/yr) was stipulated for skin, bone and the thryoid.
However, the limit was set at 1.5 rem/yr (15 mSv/yr) for thryroids
in children up to age 16. Later, in 1977, the ICRP revised their
dose recommendations on the basis of a new concept of (weighted)
effective whole-body dose [ICRP 1977].
Recommendations were made for "stochastic" and "nonstochastic"
effects. Stochastic effects were defined as those for which the
probability of an effect occurring, rather than its severity, is
regarded as a function of dose without threshold. On the other
hand, nonstochastic effects were defined as those for which the
severity of the effect varies with -dose and for which a threshold
may occur.
The ICRP regards hereditary effects and somatic effects,
primarily cancer, as stochastic. Nonstochastic effects are
specific to particular tissues, such as lens cataracts,
nonmalignant skin damage, depletion of bone marrow, and gonadal
cell damage, which may cause infertility.
In their 1977 recommendations, the ICRP went on to define two
types of members of the general population: critical groups and
average members of the population. A typical member of the
critical group would closely resemble the "maximum individual" as
used in the United States. The average member of the population
would correspond to the U.S. nomenclature "average individual," or
the European term "per caput." The 1977 ICRP whole-body dose
recommendations (pp. 23-25) are as follows:
Stochastic:
Critical groups 0.5 rem/yr (5 roSv/yr)
Nonstochastic:
Any member of public 5 rem/yr (50 mSv/yr)
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The stochastic limit of 0.5 rem/yr (5 mSv/yr) to individual
members of the public is likely to result in average dose
equivalents of less than 50 mrem/yr (0.5 mSv/yr) provided that
disposal practices exposing the public are few and cause little
exposure outside of the critical group.
2.3 NATIONAL COUNCIL ON RADIATION PROTECTION AND MEASUREMENTS
(NCRP)
In 1975, the NCRP issued limits for maximum radiological dose
in the United States. Their recommended annual dose limit for an
occasionally exposed individual member of the general public was
set at 0.5 rem/yr (5 mSv/yr) . The NCRP established an average
annual dose limit of 0.17 rem/yr (1.7 mSv/yr) for the general
public. This limit applied to both genetic and somatic doses.
TABLE l
Current NCRP dose limits for members of the public
or occasionally exposed individuals [NCRP 1975, p.34]
Individual Dose Limits
Occasionally Exposed Public 0.5
Students 0.1
Population Dose Limits
Emergency (Lifesaving) Dose Limits
Individual (over age 45,
if possible) 100
Hands and Forearms 200
Emergency (Less Urgent) Dose Limits
Individual 25
Hands and Forearms 10o
Family of Radioactive Patients
Individual (under age 45) o.5
Individual (over age 45) 5
rem in any one year
rem in any one year
0.17 rem average per year
rem
additional rem
(300 rem total)
rem
rem total
rem in any one year
rem in any one year
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2.4 WORLD HEALTH ORGANIZATION (WHO)
Historically, the WHO has accepted the ICRP dose limits and
philosophy, A 1978 WHO working group agreed that the basic
principle to be used in formulating radiation protection
regulations is the ICRP recommendation that all radiation exposures
should be kept as low as readily [sic] achievable, with economic
and social considerations taken into account. With regard to the
dumping of wastes into the oceans, the working group recognized
that current dumping levels represent only a minute fraction of the
maximum amounts permitted by the IAEA [IAEA 1975]. Accordingly,
the WHO working group recommended that studies of sea disposal, as
well as other waste disposal methods, be continued; and they called
upon the IAEA to accelerate the acceptance by member states of the
IAEA recommendations and procedures, as specified in the LDC [WHO
1978, p. 33]. The WHO working group also stressed that attention
should be given to the various exposure routes to humans rather
than to possible effects on aquatic populations. Although they
observed no evidence that previous releases into the sea have been
harmful to anyone, the group cautioned that prudence dictates that
the exposure paths leading to man and to accumulation in marine
organisms should be closely monitored [WHO 1978, p. 34].
2.5 UNITED STATES GOVERNMENT
2.5.1 Federal Radiation Council (FRC)
The FRC was established in 1960 to provide guidance to
the President in radiation matters. It established and promulgated
radiation standards that were not to be exceeded (without formal
justification) by Federal Agencies. In its first report, the
Council set limits for external exposure of the total body; viz.,
0.5 rem/yr (5 mSv/yr) to the individual and 5 rem (50 mSv) per 30
year (equal to 0.17 rem/yr or 1.7 msv/yr) to the average individual
of suitable sample of the exposed population [FRC i960]. In its
second report, the Council recommended that exposure of bone and
thyroid from internally deposited radionuclides should be limited
to 1.5 rem/yr (15 mSv/yr) for the individual and 0.5 rem/yr (5
mSv/yr) for a suitable sample of the population [FRC 1961].
By authority of the President, FRC authority -was
transferred in 1970 to the newly-formed EPA.
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2.5.2 Environmental Protection Agency (EPA)
The EPA has promulgated dose limits for any member of the
general public from the uranium fuel cycle, as given in 40 CFR 190,
and from geologic disposal of high-level radioactive wastes (HLW),
as stated in 40 CFR 191.
EPA states that the total annual dose to the whole body
from all aspects of the uranium fuel cycle shall not be greater
than 25 mrem (0.25 mSv), and that the annual dose to the thyroid
and any other body organ shall not exceed 75 mrem (0,75 mSv) and
25 mrem (0.25 mSv), respectively.
It should be noted that doses received from mining
operations, waste disposal and associated transportation to support
mining and disposal activities, are not included when determining
compliance to the EPA dose limits. Doses from Radon daughter
nuclides are not included in the above limits, but are to be
addressed separately.
3 ICRP RADIATION PROTECTION PHILOSOPHY
The ICRP radiation protection philosophy is based upon three
primary guiding principles (justification, optimization, and
compliance) which together, constitute its dose-limitation system
[ICRP 1973 and 1977].
3.1 JUSTIFICATION
This principle states that no practice or operation (i.e,
nuclear power production, military or civilian isotopic research,
development or manufacturing activities) shall be adopted unless
a positive net benefit to society is produced.
The ICRP does not consider this principle to be amenable to
formal analysis since many broad issues must be considered and
assessed to determine whether "net benefit(s)" are produced from
a particular practice/operation. The issues are likely to include
economic, social, military, scientific and political factors.
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3.2 OPTIMIZATION
This prinicple states that all exposures shall be kept as low
as reasonably achievable (ALARA), upon consideration of economic
and social factors.
The ICRP recommendation that all exposures be kept "as low as
practicable" or "as low as reasonably achievable" is also supported
in the U.S. by the NCRP, the EPA and the Nuclear Regulatory
Commission (NRC).
The ICRP first addressed the practical implications of this
recommendation in 1973. In 1977, the ICRP further stated that
optimization would be achieved when the level of exposure is such
that any increase in the cost of protection per unit dose
equivalent is balanced by a reduction of detriment per unit dose
equivalent. The ICRP methodology that can be used to assist in
determining optimization is given by the following equations.
B = V - (P + X + Y) (1)
where V = gross benefit of operation or practice
P = basic production costs
X = cost of achieving a selected level of
protection
Y = cost of the detriment involved in the operation
or practice
Thus, optimization is achieved when the net benefit is
maximized with respect to the costs associated with the level of
radiation protection. Let X and Y be functions of the collective
dose, S, and assume that the gross benefit, V, and production
costs, P, are independent of S. Then on differentiating Equation
(1) with respect to S, we arrive -at
(dX/dS)s + (dY/dS)s =0 (2)
o o
where S0 = optimum level of collective dose (dB/dS0 = 0). Figure
1 shows this relationship.
Since it .is not usually practical to consider infinitesimal
changes in costs and collective doses, Equation (2) may be written
in terms of finite increments.
(AX/AS)S + (AY/AS)S = 0 (3)
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Then by cancelling the
(3), we can write:
A X
AY
AS in the denominators of Equation
(4)
The result can be obtained by a simple inspection of tables
of cost values, but with discrete options it is very unlikely that
the incremental costs can be exactly matched. The optimum control
option will be defined when AX + Ay is closest to zero for a set
of options. It should be emphasized that while it is relatively
easy to mathematically specify a procedure for optimization, it is
exceedingly difficult to apply this formalism in practice. One may
find examples of applying these equations in IAEA Proceedings
1979b.
Cost S
FIGURE 1.
Theoretical relationship between costs and
collective dose showing optimum collective dose, S
at optimum cost, C0
o/
8
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4 PATHWAY DOSE MODELING
To determine the appropriate release limit to set for a
specific practice or operation, you must analyze the various
pathways leading to man in order to determine those that could lead
to doses exceeding the limit or that lead to the highest exposure.
These are often referred to as critical pathways and the group of
persons so exposed are called critical groups. As used here,
"critical" denotes the sense of importance relative to other
•pathways and groups and identifies the pathway(s) that will have
to be limited to control the dose.
For any given site, only one or a few pathways will prove to
be limiting. If the total dose to the public via these limiting
pathways is kept below the ICRP recommended dose limits, then the
total dose from all pathways combined may be less than the
recommended limit. In addition, although a large number of
radionuclides may be released, only a few may contribute
significantly to the total dose.
Webb (1980) listed the items to consider in the analysis of
a general pathway model for ocean dumping of radioactive waste, as
follows:
• release of radionuclides from the package (container and
waste form)
• local mixing with water and adsorption onto sediments
• local biological uptake processes
• physical transport of dissolved or resuspended
radionuclides via the water column
• biological transport of radionuclides
• sediment transport
• reconcentration of dissolved radionuclides by biota after
transport in water to location of harvest
• exposure of man via ingestion, inhalation, and direct
irradiation
The estimation of dose to man from ocean disposal of
radioactive waste may be carried out using mathematical models
describing either transient or steady-state conditions. A third
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method based upon specific activity is the simplest; however, it
can only be applied to those radionuclides having stable analogs.
The steady-state or concentration-factor approach is only slightly
more complex, but it necessitates that the user assume the system
is at equilibrium. On the other hand, the transient or
compartmental model methodology, which describes a transient
condition produced from a variable source function, is usually more
complex and time consuming. Also a knowledge of a great many
transfer rates between the various compartments making up the model
is required. In most instances the concentration-factor models are
used unless the dynamics or time variations of radionuclides in
various compartments is important [ICRP I980b] .
4.1 STEADY-STATE MODELING
The steady-state or concentration factor (CF) model contains
multiplicative parameters called transfer or concentration factors,
FIJ, defined as:
FIJ = Mj(t)/M,(t)
where F(J = the factor relating concentrations in media , and j
M,(t) = activity concentration in compartment , at time t
Mj(t) = activity concentration in compartment j at time t
The factors, FIJ, are expressed in tenr.s of the units of the
M, and M,. For example, the concentration factor in SI units that
relates fish concentration to that of its surrounding water is in
units of Bq/kg per Bq/m3 or m3/kg.
For equilibrium conditions, the concentrations attain constant
values so that we can write:
Ml,« - M ,,. F u
where the M,,. and M,,. are equilibrium concentrations.
be roeasured directly because it is lower
or h~ ^h bac!c?round' Accordingly, the limits are often set
for either the radioactive discharge of the practice or the
genrat°nS ln air °r wa*er- These limits are called
the limits are Placed °n discharge rate,
™od«l na hn S °S6 llttts Usin9 ™* °* ***
modeling techniques and the full critical path. When the limits
10
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are placed on environmental concentrations, multiple pathways need
not be considered because they were considered in the setting of
the concentration standards.
As mentioned above, for systems that have come to equilibrium
or for dynamic systems that may be approximated by a steady-state
approach the use of the concentration-factor model is usually
justified. An example of this methodology is presented for
calculating the dose, H, (either annual or committed) from the
consumption of seafood harvested in waters containing a
radionuclide that has been transported from a waste container
Leaking at a constant rate:
H = R P B U DF rem (Sv) (7)
where H = annual dose, or committed dose over 50 years rem (Sv}
R• = leak rate (Ci/yr) or (Bq/yr) of a radionuclide from
the waste container
P = hydrospheric dispersion factor (Ci/m )/(Ci/yr) or
(Bq/m3)/( Bq/yr) 3
B = bioaccumulation factor for seafood (Ci/kg)/(Ci/ra ) or
(Bq/kg)/(Bq/m3)
U = consumption rate of seafood (kg/yr)
DF = dose factor (rem/Ci) or Sv/Bq.
The calculated dose, H, may be either an annual dose or a
committed dose over a 50 year period. The annual dose is
calculated in determining compliance with the ICRP dose limits.
The dose factor, DF, is dependent upon the radionuclide involved
and the age of the consumer. The collective dose is usually
calculated by assuming the population is made up entirely of
average adults. This is probably satisfactory for calculating
collective dose from seafood consumpiton since, in most countries,
infants and younger Children do not consume as much seafood as
adults.
in selectina a disposal site, it is necessary to determine the
maximum r^lease^ rate of radionuclides that would not lead to
?adiat?on exposures in excess of the ICRP limits Equation (7) may
be rearranged to give a release rate, R*, that should not be
exceeded, as follows:
R* = H* (8)
P B U DF
where H* = the relevant dose limit.
11
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In application, R is usually kept much smaller than R* for any
particular nuclide or practice so that the dose limit, H*, will not
be exceeded if the individual is subject to exposure from
radionuclides resulting from practices or operations other than
ocean disposal.
4.2 TRANSIENT MODELING
A system that is not in equilibrium may, with appropriate
approximation, be modeled using concentration factors; however, a
more rigorous method is to use a multicompartmental model coupled
together by linear first-order equations. This technique,
sometimes called the system analysis (SA) method, has been used for
the analysis of tracer kinetics in living organisms [Whicker and
Schultz, 1982 and Finkelstein and Carson, 1979]. It can be
extended to dynamically simulate the movement of radionuclides
through various environmental media. These compartments are then
connected by various rate constants which determine the relative
movement of a radionuclide throughout the system.
The compartments may be highly conceptual, such as the world's
surface water or vegetation, or they may be specific subunits, such
as the portion of the sea in a small geographic location. The
quantity (activity) of a radionuclide is calculated for each
compartment at a certain time, and then the whole set of equations
governing the system is incremented in units of time (e.g. day,
week, month or year) , depending on the rates in that system. Thus,
the activity in each compartment will change with each time
increment. It is assumed in this type of analysis that, after each
iteration, the activity in each compartment is homogenously and
instantaneously distributed through the compartment such that its
concentration is constant throughout the compartment. This
assumption becomes more uncertain or questionable as the size -of
the compartment is increased and the time increment is decreased.
A great many calculations must be made, depending on the number of
compartments and time iterations involved.
The general formula for the set of differential equations
describing a system of connected compartments with radiological
decay is given by:
n
v, +
, - 1
i " j
n
K,, +A,
I - 1
I - I
(9)
12
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where j = compartment of reference
i - all other compartments
K |j and K ji - transfer coefficients between compartments
having activity inventories of Y| and Yj.
The first two terms after the equal sign in Equation (9)
represent all the activity entering compartment j from all other
compartments | and from outside the system Pj. The terms in
brackets represent all the activity leaving compartment j and going
to all other compartments , (Kj,) and being removed from the system
entirely { A j) • The Pj includes the source term and ingrowth of
daughter radionuclides. The ^ j includes the radioactive decay
constant along with any other removal of concern.
As an example, consider an idealized three-compartment
system of a fish existing in a body of water in which radioactive
wastes are being released (see Figure 2) . It is required to
estimate the activity in the fish when activity is being released
into the sediment and surrounding water from the waste container
at the rates indicated. Here (Figure 2), Yt represents activity
levels in the * compartment and K,j is the constant fractional rate
of activity flow in units of reciprocal time from compartment | to
compartment j. The following set of system equations may then be
written for this example:
Compartment 1. Water
dY,/dt = K21Y2 + K3,Y3 + P1 - Y,(Kt2 + K13 + A ,) (10)
Compartment 2 . Sediment
dYa/dt - K12Y, + K^Yg + P2 - Y^K* + K^ + 3 r)
Compartment 3. Fish
= K13Y, + K^Ya - Y3 (Ksi + K» + * r)
Here, PI and P2 represent the release rate from the waste
containers to the water and sediment, respectively. The term for
removal from the system is the radiological decay term ^ r) .
This set of equations (10, 11 and 12) may be solved
analytically [Whicker and Schultz, 1982 J; however, for more than
about four equations, numerical methods must be used. By
converting these equations to difference equations so that a finite
change in t will produce a finite change in Yt such that by adding
each AYj to each Y( and then repeating this process for all the
equations, the system may be iterated through time until
equilibrium is reached (dY,/dt = 0) .
13
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The resulting compartment activities-, Y,, may be divided by
their respective volumes or masses to determine the concentration
of activity in each compartment after any given time period. By
decreasing the time increments, At, any degree of precision may be
achieved, but only at the cost of increased computational time.
However, the degree of numerical precision of the results should
never be more than that of the input parameters.
Discussions of compartmental modeling are given in many
publications. Good discussions with examples are presented in
ICRP Publication 29 [1980b] and in a 1980 Organization for Economic
Cooperation and Development (OECD)/ Nuclear Energy Agecy (NEA)
publication. Methods for solving these models are summarized in
a publication for microcomputer users [HicJcs, 1981].
FIGURE 2. Simple Compartment Model
14
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4.3 SPECIFIC ACTIVITY MODELING
Whereas the previous two modeling methods are concerned with
various pathways, especially the critical pathway, the specific-
activity approach is independent of any pathway. The basic
assumption in this method is that the specific activity (the ratio
of the concentration of a radioactive isotope to its stable analog)
remains constant throughout all environmental media. Thus, by
limiting the release of various radionuclides, the specific
activity of a recipient medium (e.g. sea water) is kept below a
fixed value. Thus, the specific activity cannot be exceeded at any
point in the food chain or in a critical organ in humans (NAS/NRC,
1962; IAEA, 1978a; and, Foster, Ophel and Preston, 1971). The
advantage to this approach is that the requirement for various
dilution factors, concentration factors, transfer coefficients,
etc. is eliminated. The disadvantages are: some of the
radionuclides (e.g. americium and curium) do not have stable
analogs; the chemical form of a released radionuclide may differ
from its stable analog; and, calculating Gl-tract dose is not
applicable since exposure is produced by food passing through the
gut rather than from tissue deposition. However, this approach is
useful for some radionuclides (e.g. carbon-14, tritium, iodine-131,
and strontium-90). It should be noted, however, that this approach
is not compatible with the methodology in ICRP Publication 26
[ICRP, 1977], since the ICRP equations and parameters are based on
the intake of the radionuclides irrespective of stable element
intake.
4.4 MODELING CONSIDERATIONS
Following the stage of dilution into the immediate receiving
water mass, allowances must be made for factors that influence the
amount of a radionuclide actual'ly transferred through successive
model compartments. It is important, for example, to consider are
distribution coefficients (KdS) between the water and seabed or
between the water and sedimentary materials in suspension, as
sediment »contaminated' by water-borne radionuclides may be a
direct pathway of exposure to man via occupational exposure from
the use of bottom-fishing equipment or via recreational exposure
on beaches. Radionuclide transport from sediment to water is also
important to consider for any disposal of radioactive wastes under
the surface of the seabed.
Modeling of food-chain pathways results in calculated
concentrations of radionuclides in food products that are consumed
by humans. One these concentrations are predicted, the intake of
radionuclides can be determined from the consumption rates of the
food products.
15
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The inverse ratio of the dose (calculated using such models)
to the appropriate annual limits of intake (ALI) and external
exposure rates recommended by ICRP gives an estimate of the maximum
permissible daily discharge rate. The major difference between
this method and the "specific activity" approach is that estimates
are required for the degree of contamination of environmental
materials, and for detailed information about eating, working, and
leisure habits of local and distant populations subject to
exposure.
Determining equilibrium concentrations in environmental media
and marine organims, using the above pathway approaches, provides
the starting point for calculating dose according to methods given
in IAEA publications [IAEA, 1976 and 1979a].
To ensure that no member of the general public is exposed
beyond the recommended dose limit, individuals or individual groups
having exceptional habits that could lead to such exposure must be
identified. Estimated average exposures for these critical
individuals/groups provides a basis for ultimately determining
permissible release rates.
4.5 SELECTION AND IDENTIFICATION OF PARAMETER VALUES
The availability of parameter values (data) that support
models used to predict transfer of radionuclides along
environmental pathways is an important factor in determining the
complexity or realism that can be represented by pathway models.
It is also a major factor in deciding whether to apply the more
fundamentally rigorous transient (systems analysis) method, or the
more simplified steady state (concentration factor) method.
For the transient method, transfer functions are required
between compartments that are both time and spatially dependent.
For the steady state method, only the ratio of concentrations (or
the time concentration integral) is needed between interacting
compartments (e.g. fish and seawater) since it is assumed that
equilibrium conditions exist. Although the nature of the parameter
values used in each modeling method are different, the data needs
in the final stage of converting an intake rate of a food-chain
material (with a calculated concentration or measured dose rate
associated with a nonfood-chain pathway) to dose are similar. For
strict application of the transient method, time dependence should
be built in. Alternatively, time-averaged values are generally
adopted over a one-year period to be consistent with the ICRP dose
limits time base.
16
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Values chosen will depend on the type of dose calculation
(individual or collective) and, for individual dose, will generally
characterize those people most likely to be highly exposed through
the pathway under analysis. IAEA Safety Series publication number
45 addresses this topic in detail [IAEA, 1978a] .
4.5.1 Nature of the Released Radioactivity
To assess the affects of radioactivity released into the
environment, it is important to know daily or annual quantities
released, the radionuclide(s) , and the physical and chemical forms
of that radionuclide at the time of release. The behavior of
Plutonium, for example, differs according to chemical state or
isotopio number [Befsley and Fowler, 19761. Additionally, the
discharge of some radionuclides in combination with certain
nonradioactive wastes may result in complexation or adsorption
before mixing with seawater - which could affect subsequent
transport or availability to biological systems. It is .also
inmoT-t-ant to know the proposed method of release (e.g. continuous,
pSlsS or * ^binatfon of both) since the method could help to
determine whether the steady state or transient modeling approach
for dose estimation is more appropriate.
4.5.2 concentration Factors
When calculating dose, it is obvious that concentration
»? or ratios ~ and are subject to continuous revision.
the waste is tawm ir
-------
4.5.3 Consumption Rates and Occupancy Factors
In applying the ICRP and national dose limits, it is
necessary to definitely establish that the dose to the most highly
exposed individuals be within those dose limits. In this case,
identification of the working, eating and recreational habits of
the local population and, in certain instances, a population at
some distance from the site may be essential. For example, this
might include estimates of seafood ingested and the area from which
it came, hours spent on the beach at work or in recreation, and
hours spent handling fishing gear on the beach or at sea.
Consumption rates and occupancy factors, derived from surveys of
the habits of the identified critical group, will be extremely
variable. ICRP considers that these sources of variability may
appropriately be dealt with by the consideration of dose limits to
individuals in this group rather than of an overall dose to the
whole group (population dose).
When important pathways cannot be fully identified,
potential pathways suspected to be most important, such as
consumption of any marine fish species or occupancy of the beach
at low tide, should be selected. Following the start of disposal
operations, radioactive materials in these assumed pathways should
be monitored to provide the basis for their control.
5 THE BASIS FOR DEEP-OCEAN DISPOSAL
5.1 LONDON DUMPING CONVENTION RECOMMENDATIONS
In contrast to the disposal of liquid wastes to coastal
waters, which is under national control, the dumping of packaged
radioactive wastes in the deep ocean is specifically governed by
the 1970 International Convention on the Prevention of Marine
Pollution by Dumping of Wastes and Other Matter, known as the
London Dumping Convention [IAEA, 1974]. This Convention, which
embraces all types of wastes, divides radioactive wastes into two
categories: high-level (Annex I) wastes (HLW), which are considered
unsuitable for dumping in the oceans; and other radioactive wastes
(Annex II), which may be dumped under a national permit.
The Convention requires the IAEA to define radioactive
material that is unsuitable for dumping and to make recommendations
that should be considered when issuing national permits. The IAEA
has prepared a provisional definition for Annex I waste, and has
issued recommendations for disposal of Annex II wastes [IAEA,
1975]. This document was subsequently reviewed, revised, and
adopted [IAEA, 1978d]. IAEA also has issued two key supporting
documents - "The Oceanographic Basis" [I978b] and "The Radiological
Basis" [1978c],
18
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The IAEA definition of HLW took the form of specific
activities, which were in turn based on release rate limits; i.e.,
upper values of release rates for various radionuclides, which,
under a series of generally pessimistic pathway parameter values,
might give rise to critical group exposure at the I CRP recommended
dose limit to the public of 5 mSv (500 mrem) . From these studies
a revised definition was adopted [IAEA, I978d) , which states:
For the purpose of Annex I to the Convention, high-level
radioactive wastes or other high-level radioactive matter
unsuitable for dumping at sea means any waste or other
matter with an activity per unit gross mass (in tonnes)
exceeding :
(a) 1 Curie (Ci)/tonne (t) for alpha-emiiters but
limited to 10"* Ci/t for 2Z8Ra and supported ^"Po;
(b) 102 Ci/t for beta/gamma-emitters with half-
lives of at least 0.5 years (excluding tritium) and
beta/gamma-emitters of unknown half -lives; and,
(c) 10* Ci/t for tritium and beta/gamma-emitters
with half-lives of less than 0.5 years.
The above activity concentrations shall be averaged over
a gross mass not exceeding 1000 tonnes.
In a footnote, the IAEA further defines the upper limits to
ocean disposal. The definition is based on:
(1) An assumed upper limit to the mass dumping rate of
100,000 t/year (yr) at a single dumping site: and,
(2) Calculated upper limits to activity release rates
from all (other than natural) sources of
(a) 10s Ci/yr for alpha-emitters but
limited to 10* Ci/yr for 2asRa and
supported
(b) 10T Ci/yr for beta/gamma-emitters with
half-lives of at least 0.5 years (excluding
tritium) and beta/gamma-emitters of unknown
half -lives, and
(c) 1011 ci/yr for tritium and beta/gamma-
emitters with half -lives of less than 0.5
years
at a single dumping site and also, for alpha-
emitters, when released to an ocean basin of not
less than 1017ms.
19
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In 1985 the IAEA proposed a new definition of HLW that
includes the irradiated reactor fuel and the liquid wastes from
chemical porcessing of such fuel through the first solvent
extraction cycle. The new definition also included other wastes
having activity levels, per unit mass, exceeding:
5 x 10~s Tera-Becquerels (TBq)/kilogram (kg) (1 x 10"3
Ci/kg) for alpha-emitters
2 x 10"2 TBq/kg (0.5 Ci/kg) for beta/gamma-emitters with
half-lives greater than 1 year (excluding tritium); and,
3 TBq/kg (80 Ci/kg) for tritium and beta/gamma-eraitters
with half-lives of 1 year or less.
It is assumed in the definition that the following conditions
are satisfied: activity concentrations specified shall be
averaged over a gross mass not greater than 1000 tonnes;
disposal takes place in an ocean-basin volume of 1017m5;
average water depth of a site is 4000m; rate of disposal is
10* kg/yr; disposal continues for 1000 years; and, annual dose
to critical group members shall not exceed 1 mSv (100 mrem).
When the activity levels per unit mass given in the proposed
definition are multiplied by the 108 kg/yr disposal rate, there is
only about a 40 percent increase in the alpha-emitters allowed for
disposal within a year. Also, there is no special reduction for
radium-226 and polonium-210. The allowable limit for beta/gamma-
emitters has increased 5-fold for those having a long half-life,
excluding tritium, and decreased 10-fold for those with a short
half-life, including tritium. The cut-off point between short and
long half-life has been increased from 1/2 year to 1 year. Thus,
in general, the basis for the revised (1985) definition of HLW is
less restrictive than it was previously.
5.2 RADIOLOGICAL EVALUATION OF OCEAN DISPOSAL PRACTICES
5.2.1 Need for Modeling
The application of the basic IAEA site selection criteria
[IAEA, 1978d] effectively minimizes the interaction of the
radionuclides from the disposal material with man's activities.
This poses a problem for both predicting the potential exposure of
populations before the disposal operation and for confirming the
estimated exposure following initiation of disposal operations.
Additionally, the quantity of radionuclides relative to the size
of the receiving environment, together with such factors as the
degree of containment and the time scales involved in transport
from the deep ocean, will most likely result in lower
concentrations of potentially critical materials than can be
measured.
20
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If site-specific radiological assessments are required
either before the operation is authorized or at intervals
thereafter, the lack of confirming data makes validation of the
dose exposure estimate from deep ocean disposal exceeding
difficult. This is in contrast to coastal discharges, where
validation of quite simple models can be conducted almost
immediately following the initiation of the disposal operations,
For the reasons given above, the assessment of deep ocean disposal
will have to rely heavily on mathematical modeling techniques.
Thus, the use of models is central to the assessment of
radiation doses from ocean disposal operations. Models provide the
primary means of integrating and interpreting the information
gained from other investigations.
5.2.2 Need for Research
To apply models, additional deep ocean scientific
research and monitoring will be required to provide realistic
parameters that correctly represent the major oceanographic and
biological processes of the area in question. However, in view of
the ICRP requirement for optimization of radiological protection,
which involves considerations of costs and benefits, the research
requirements must focus on the needs of the pathway analysis rather
than on acquiring a detailed understanding of all the pysical and
biological transport processes involved within the system.
It should be noted that the term "site specific" does not
mean that all investigations must be undertaken at and in the
vicinity of a proposed site. It is possible that the released
radionuclides will be transported away from the site, especially
the long-lived radionuclides whose half-lives exceed the residence
times in the oceans. It is therefore necessary to obtain data on
basin-wide circulations, as well as on mixing within the ocean
basin. In addition, there is a need to examine those processes
that occur on the margins of basins, which have the potential to
mix or conduct water from the deep ocean into biologically
productive zones.
Four distinct areas of research are required for a
coordinated effort: physical transport processes, geochemistry,
biological pathways anlysis, and model development,
5,3 NEA MODEL
The conceptual framework proposed by OECD/NEA in 1981 for
evaluation of ocean disposal of radioactive wastes may be
represented by a general model that we will call the "NEA Model."
21
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The general form of the model is designed to aid in focusing
research work and to assist in incorporating the results of
research directly relevant to the preparation of a site-specific
assessment of doses resulting from deep ocean disposal.
The general model envisaged for overall assessment purposes
may be divided into three essentially distinct parts: release,
marine, and pathway.
5.3.1 Release Model
This model describes the release of radionuclides from
waste packages; its input is the rate of disposal of wastes, and
its output is the release rate of various radionuclides from the
packages to sea water or the sediments.
Past assessments have assumed that disposal of all
radionuclides in the ocean are released instantaneously . This is
probably a reasonable assumption (except for radionuclides with
very short half-lives, e.g., those less than 10 years), and only
a small elaboration of this part of the model would be appropriate.
A suitable next step might be to use a single compartment model
with a flushing time that depends on leach rate from the package,
the radionuclide involved and its chemical form.
5.3.2 Marine Model
This model describes the dispersion and reconcentration
of radionuclides throughout the marine environment. Its inputs are
the release rates of the various radionuclides; its outputs are the
time-dependent concentrations of the various radionuclides
throughout the water column, in the sediments and in marine biota.
The model includes both geochemical (e.g., sediment/water
interactions) and biological (e.g., scavenging and bioturbation)
processes that can significantly affect the mass transport of
radionuclides and, therefore, their overall concentrations in the
marine environment. The calculated concentrations may be long-term
averages, or they may include short-term fluctuations.
5.3.3 Pathway Model
This model describes the transport of radioactivity
through food chains and other direct pathways to man (e.g. external
exposure from sediments). Its input is the concentrations of
radionuclides in edible marine organsims or other materials; its
output is dose to man derived from the marine biota and other data.
The transports may be very small in mass transport terms
(i.e., they do not significantly perturb the overall concentrations
22
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of radioactivity) , but they are crucial because they lead directly
to man. The food chains may contain several links and may begin
with the sedentary biota in either deep or shallow water. The
concentrations ofradionuclides in marine biota are calculated as
part of the marine and pathway models and, thus, may be used to
evaluate doses to both the organisms themselves and to man.
5.4 IAEA MODEL
The model developed by IAEA contains two parts:
(a) an oceanoaraphic component that predicts the relationship
between water concentration and release rate at a given
ocean location, appropriate to potential or existing
pathways [IAEA, 1987b]; and,
(b) a radiolocrical component that uses the oceanographic
component prediction results and combines that data with
data on (assumed) environmental exposure pathways, and
ICRP data, to relate human radionuclide intake rates to
dose (IAEA, 1978c].
Since the IAEA model was first proposed, work has been carried
out by an international Group of Experts on the scientific Aspects
of Marine Pollution (GESAMP) to provide advice for more suitable
modeling techniques. GESAMP, comprised of representatives from
IMO, FAO, UNESCO, WMO, WHO, IAEA, UN, and UNEP, studied various
models which were thought to reasonably estimate doses to humans
and biota from ocean disposal of radioactive waste riAEA, 1983].
Based upon the GESAMP study, the IAEA summarized the models and
parameter values thought to provide an approach to the definition
of wastes that are unsuitable for disposal at sea, but that would
not exceed recommended limits [IAEA, 1984]. The following sections
discuss the original IAEA oceanographic and radiological components
and modifications recommended in 1983 and 1984 by GESAKP and IAEA.
5.4.1 oceanographic Component
5.4.1.1 Original Model
The model adopted by IAEA in 1978 was a hybrid of several
fairly simple calculations. It was based partly on conclusions
from previous (1976) work by Shepherd, but it also included
considerations of possible effects from short-term processes and
unusual events. These are particularly important insofar as they
may "short-circuit" the steady and progressive deep ocean
dispersion allowed for in Shepherd's model.
23
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The Shephered model was developed to calculate
theoretical equilibrium concentrations in the ocean, both at the
surface and in vertical profile, from a continuous release of
material on the bottom of the deep ocean. Application of the model
showed that, except under rather extreme conditions, the given
surface concentrations would not exceed the long-term average value
that would arise if all the activity released were eventually
distributed over the whole ocean. To overcome the possibility that
some biological pathways might short-circuit the most obvious
pathway to man (via dispersion of activity in the water mass and
then via the consumption by man of fish from the surface layer of
the continental shelf fishing grounds), the IAEA based its
radiological assessment on bottom concentrations as if the
(normally higher) bottom concentrations were present in the surface
waters. A considerably slower vertical diffusivity (1 cm2/s) was
used, corresponding to a 4000-year vertical mixing time in the
Shepherd model. It was also assumed that release would continue
for a period of 40,000 years, which is comparable with the mean
lifetime of plutonium-239.
These results provided concentrations applicable to an
ocean volume of 10 m (which is slightly smaller than the volume of
the North Atlantic), irrespective of whether a single site or
multiple sites are used for disposal. While Shepherd's model
provided concentrations that could arise from long-term, large-
scale dispersions from a disposal site, it did not include the
possibility of physical, chemical or biological processes which,
on time-scales of decades or less, might result in high
concentrations in pathways leading to man. The IAEA oceanographic
basis included estimates of such processes that could short-circuit
long-term dispersion processes. These were based on the
possibility of an advective, year-long plume reaching a fishing
zone in deep water (e.g., a long-line fishery operation) and deep
convective mixing of the type that has been observed down to about
2000 m in the Mediterranean Sea and in the polar deep-water
formation regions. Calculations for these areas indicated that the
short-term concentrations in a single site might be on the order
of 10 Ci/m3 per Ci/s released, and this value was therefore used
as a more restrictive limit for single sites, except for the
longer-lived nuclides, where the whole ocean limit becomes more
restrictive.
The oceanographic model also describes disposal of waste
in an area where the depths are normally greater than 4000 m. The
assumption is usually made that radionuclides are continuously
released as soon as the waste container reaches the ocean floor.
However, any delay in the release of activity from the container
once it has reached bottom, would actually reduce the activity that
24
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could be released later because of the radioactive decay process,
but that factor is not included in the model. The model also
assumes a transit time of 3 years between any release from the
container and arrival at the nearest possible place of interaction
with man, and it also assumes that continuous release rates
prevail.
The oceanographic basis, therefore, depends on fairly
elementary calculations and makes use of several rather sweeping
simplifications, principally that: (1) the concentrations
appropriate for input to food chains in the surface waters are the
(higher) concentrations of deep ocean waters; (2) although
sediments are assumed to come to equilibrium with concentrations
in water, no activity is actually depleted from the water column
onto/into the sediments; and (3) there is an appreciable chance
that fluctuations will dominate concentrations in a critical
pathway.
These simplifying assumptions are intended to err on the
side of conservatism (tending to overestimate dose). They are in
general particularly pessimistic for short-lived radionuclides.
For long-lived alpha-emitting wastes (such as plutonium-239), which
are of particular concern, the degree of conservatism is not large,
perhaps one or, at most, two orders of magnitude. The IAEA
advisory group, who drew up the revised definition, attempted to
estimate the possible degree of conservatism and it was stated when
the radiological basis was published [IAEA, 1978c].
5.4.1.2 Revised Models
The newer, GESAMP, models are somewhat more sophisticated
than the older Shepherd model. The philosophy, however, is still
that the sophistication level of models should match what is
actually known about natural processes. The following processes
were considered by IAEA in 1984:
(a) movement and mixing of water within an ocean basin;
(b) radioactive decay or chemical degradation of
contaminants;
(c) interaction of contaminats with particles of various
types, both within the water column and on the sea
bottom; and,
fd) mixing and diffusion, including that due to
bioturbation, in and out of surface sediments.
The GESAMP stressed that the interactions of contaminants
with inorganic and organic particles was important in the resulting
activity contributed to water.
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Three distance ranges from a source were considerd for
calculation of activity concentrations: an extreme near-field, an
intermediate near-field, and a far-field (see the Glossary section
for definitions of these terms). The IAEA subsequently chose to
use the models discussed in Appendices VI and VII of the GESAMP
report [IAEA, 1983].
Model VII is a simple three-dimensional, ocean-diffusion
model modified for finite source size and scavenging, whereas model
VI is a one-dimensional model. Model VII should be used for most
near-field distance ranges, unless it gives a smaller concentration
than model VI. in such instances, model VI should be used. For
the extreme near-field ranges, model VII should be used.
The Appendix VII (near-field and extreme near-field)
model is summarized below. The radionuclide activity concentration
(C) is given by:
r. KHKV (13)
where Q = the rate of release,
r» •» the radius of the source,
KV = the horizontal and vertical eddy diffusivity in the
water column, respectively,
C* - three complex functions of parameters which depend
on the distance from the source.
Although the above model is intended primarily for near-
field and extreme near-field calculations, it may also be used for
some far-field calculations.
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The Appendix VI model (far-field) is a simplified
equilibrium version of a more complex model found in Appendix IX
of the GESAMP report. This one-dimensional model includes
diffusion, boundary and interior scavenging, and up/down water
movement. The formula for radionuclide activity concentration (C)
is given by:
r,z r2z
C - ae + be (14)
where z = the vertical distance from the ocean bottom,
ri, r2 = the roots of a quadratic equation with coefficients
being functions of various oceanographic parameters,
a,b = involved functions determined by the surface and
bottom boundary conditions.
This model should be used for far-field calculations, and
for near^field calculations when the results obtained are higher
than the Appendix VII model.
5.4.2 Radiological Component
5.4.2.1 Original Model
For the radiological component, the IAEA [1978c]
considered doses to critical groups via 12 pathways (see Table 2).
Release-rate limits were derived by first calculating the dose to
man in each pathway arising from a unit release rate. The method
used for this calculation was conventional, combining an estimate
of water concentration (from the oceanographic basis), a
concentration factor, a consumption or occupancy rate, and the
appropriate maximum permissible annual intake for ingestion or
inhalant pathways (see Equation (7) for an example). The release
rate which would lead to the ICRP dose limit was then derived.
Additivity due to the possibility of exposure via more than one
pathway was admitted in appropriate cases. The lowest of the
release-rate limits for the different critical groups was then
adopted as the overall release-rate limit for each radionuclide.
Some of the pathway parameter values adopted (e.g.,
seaweed consumption rate) were unreal1stically high. Because of
these maximizing assumptions and others in both the oceanographic
and radiological components, the doses that would result from
release rates at the limits calculated would, in practice, probably
be very much less than the dose limit (e.g., 5 mSv (500 mrem)) for
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TABLE 2
Pathways and mode of exposure in
the IAEA radiological component [IAEA, 1978c]
Pathway
Fish consumption
Crustacea consumption
Mollusc consumption
Seaweed consumption
Plankton consumption
Exposure from shore
sediments
Exposure from fishing
equipment
Suspension of sediments
Evaporation of sea water
Desalinated water
consumption
Sea salt consumption
Swimming
Mode of
Exposure
Ingestion
Ingestion
Ingestion
Ingestion
Ingestion
External
irradiation
External
irradiation
Inhalation
Inhalation
Inaestion Rates fka/vrl
or
Occupancy Rates fhr/vrl
220
37
37
110
11
100O
300
Continuous
Continuous
Ingestion 730
Ingestion i
External irradiation 300
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the whole body. This is confirmed in the case of radium-226, for
example. The release-rate limit for radium-226 is of the same
order as the natural production rate, while the natural dose rates
from marine radium-226 are known to be much less than the ICRP dose
limit [Mitchell and Shepherd, 1981].
It should be recognized that the mathematical modeling
from which the current IAEA definition was derived is generic in
nature. As such, it provides a means by which upper limit dose
values may be estimated. It thus is more likely to lead to
overestimates of dose than is one tailored to a specific location
or set of conditions.
5.4.2.2 Revised Model
The primary changes to the radiological component of the
original model were a reduction of the disposal period from 400,000
to 1,000 years, and changes in pathways and usage rates [IAEA,
1984].
The disposal period was changed to 1,000 years because
it more nearly represents a fraction of well-recorded political and
social history but only a minute fraction of geological history.
Thus, it was thought that no major social or geological changes
would have taken place over this time period to invalidate the
pathway and usage assumptions.
The new pathway and usage assumptions (see Table 3)
reflect concerns for future ocean activities, thus additional
pathways (e.g., deep ocean mining activities, consumption of deep
ocean fish, plankton consumption) were incorporated. The IAEA
cautioned, however, that the latter two examples were hypothetical
and should not be included in the calculation of disposal-rate
limits with "careful consideration."
Release-rate limits were then derived, as previously,
using the appropriate annual limit of intake and dose limit for
internal and external exposures, respectively.
Except for mid-depth fishing and deep ocean mining
activities surface-water concentrations should be used for pathway
calculations. A depth of 100 m was recommended for mid-depth
fishing calculations. In addition, a sensitivity analysis should
be performed to ascertain the importance of the various parameters
and assumptions.
Dose to marine organisms should be calculated separately,
including both internal and external doses from the spatial
distribution of activity predicted by the models - including that
from sediments. An assessment of the combination of effects from
these doses on the ecological populations should then be made.
29
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TABLE 3
Pathways and usages proposed by the IAEA in 1934
Pathway Usage
ACTUAL
Inaestion
Surface fish 300 g/d
Mid-depth fish 300 g/d
Crustacean 100 g/d
Mollusc 100 g/d
Salt 3 g/d
Desalinated sea water 2 kg/d
Inhalation
Suspended airborne sediments 23 mVd
Marine aerosols 23 m /d
External irradiation
Boating 5000 hr/yr
Swimming 30o hr/yr
Beach sediments 2000 hr/yr
Deep-sea mining w 500 hr/yr
HYPOTHETICAL
Inaestion
Deep-sea fish 60 g/d
Plankton 3
also inhalation at 23 ma/d
30
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6 PROBLEMS IN THE ASSESSMENT OF OCEAN DISPOSAL FOR LLW
6.1 COLLECTIVE DOSE
In principle, the acceptable risk level associated with a
practice such as ocean disposal should be examined through a
cost/benefit analysis, based on the principle of optimization
(ALARA). The detriments from the use of nuclear energy are best
expressed a collective dose equivalent in order to permit a
meaningful cost/benefit analysis to be performed. An optimization
derived from a cost/benefit analysis should be translatable to
guidance on allowable disposal rates, although resulting
regulations may or may not define limitations on the collective
committed dose.
At present, there are not specific U.S. regulations that
address quantitative limitations on collective dose. Regulations
to establish limitations for populations near light-water reactors
were previously considered by the former Atomic Energy Commission
(AEC), but never issued. The EPA regulations for geologic disposal
of HLW (40 CFR 191} do contain limits on releases of radionuclides
from a repository to the "accessible environment" that were
derived from a consideration of the potential health effects to the
population exposed to such a release. These health effects were
considered to be proportional to collective dose in the EPA. system
of radiological assessment, which uses a linear, nonthreshold
assumption approach.
Regardless of whether the best approach is to define the basic
limits in terms of collective dose or nuclide releases, limits must
be translated usable terms such as: allowable quantities of
radionuclides per waste container, allowable annual quantity to be
disposed, and/or total allowable quantity for disposal per site.
Granted that the calculation of some type of collective dose
is warranted, the question remains as to what type should be
calculated. It is possible to evaluate a "collective committed
dose," wherein an acute or chronic external exposure and
radionuclide intake are used to derive a total dose accrued over
some time longer than the standard IAEA exposure period of 50
years.
It is also possible to evaluate the "collective dose
commitment,11 accrued by one or several generations of people,
resulting from long-term exposure to radionuclides in the
environment, due to ocean disposals, over the entire exposure
period. This is preferred because it provides an indication of the
total potential detriment from disposal practices; not just the
detriment possible from a single release or an annual release.
31
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The collective dose commitment was used by the EPA in the
calculation of its "environmental dose" and potential health
effects from nuclear power facilities [EPA, 1974], A further
decision is needed on the length of time over which the population
detriment should be evaluated: hundreds, thousands, or tens of
thousands of years.
6.2 CHOICE OF A RADIOLOGICAL PROTECTION SYSTEM
Because a potential detriment to the U.S. (or to the world)
population could arise from wastes disposed by more than one
national authority, the systems of radiological assessment used by
each nation should be compatible. Compatibility would allow for
a common basis in summarizing and comparing potential effects from
ocean disposals.
Several radiological guidance systems are available for
calculating dose. The U.S., for example, previously used the
equations in ICRP Publication #2 (1959) to first calculate organ
or whole-body dose, and then to apply that data to a population
group. The ICRP has developed improvements to its equations over
the years, including multiple exponential radionuclide retention
in the body and in individual organs (1968) and the task group lung
model (1972).
The advantages of the system described in ICRP Publication 2
include simplicity of the dosimetry equations, as compared to those
in ICRP Publication 26 (1977), and familiarity of those in the
health physics profession with its application and interpretation.
In addition, the maximum permissible concentrations (MPC) in air
and water, derived within this system, were incorporated into U.S.
regulations (10 CFR 20), and those of several other countries.
This may be a disadvantage, however, as changes and improvements
to metabolic parameter data that enter into dose calculations are
not usually reflected in a convenient and timely manner in the
above MPC values.
Collective doses can also be calculated using the radiological
protection system defined in ICRP Publication #26 (1977), wherein
an "effective" (weighted) whole-body dose is calculated. This
system is based on a desire to limit total risk from a health
detriment to all exposed body organs. It attempts to arrive at a
single weighted value for an "effective" whole-body dose. One
advantage of this system is that it obviates the need to compound
potential health effects in each of several organs after the
individual doses are calculated.
Considerable discussions have occurred on the problems of
implementing the "ICRP-26" system. Those problems may not be
apparent to those not readily familiar with internal dosimetry
calculations and the metabolic parameters needed to use the
"effective" whole-body dose concept [Thompson, 1979].
32
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A principal problem is that uptake and elimination parameters
for most radionuclides are available for only a few of the organs
for which ICRP has assigned weighting fraction (WT) values. In
addition, such data are generally only available for those organs
that tend to have the highest concentrations and for the whole
body. Thus, it was to simply assume that those radionuclides not
having deposition parameters are uniformly distributed throughout
the remainder of the body mass. The mass, in this case, is the
difference between 70 kg and the mass of those organs having a
known deposition. This approach was considered to be the most
feasible to use since the only other alternative seemed to be
delaying implemention of "the system for years until the data needed
was identified and obtained.
Another disadvantage of the method in ICRP-26, at least in
theory, is that the correct intake limits, which are based on a
"weighted" whole-body dose for each nuclide, should not be
calculated independently of the other nuclides present in a
mixture. Since the formula involves terms for summing dose to the
"next five highest" exposed organs, the sum of dose to all organs
from all nuclides present should be calculated before it is
determined which five organs receive the highest exposure.
In addition, the technigue of spreading the "remaining" body
activitv over the "remaining" body mass tends to create effective
dose factors that are heavily dependent on the few "known" organs
for is some cases a single critical organ;. Thus, the major
d?ffer^ncrbetweSen radionuclide intake limits in ICRP-2JW59) and
ICRP-26 (1977) often result from revisions to metabolic parameters.
Potential differences from using different radiation
protection systems to derive guidance for ocean disposal of
radioactive wastes were compared for nine radionuclides of
interest The comparisons were actually made between maximum
permissible rates of intake (MPRI) by ingestion, based on the
methodology in ICRP-2 and variations thereof, and the annual limit
of intake fALI) methodology, derived from ICRP-26, as described in
ICRP Publication 30 and supplements [1979a, 1979b, 1980af 1981a,
1981b 1982a, and 1982b]. The calculated MPRI and ALI values were
expressed as' those assumed to be appropriate for an individual
adult member of the general public (i.e., one-tenth of the values
for persons occupationally exposed for 168 hours/week). The
results of this comparison are given in Table 4.
33
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TABLE 4
Comparison of allowable intake by individual
members of the public for selected radionuclides
MPRI tBa/vr)
Ratio ALI/MPRI
(Ba/vrl
FRC Dose
ICRP-2(a) 10CRF20(a) Limits(b) ICRP-30 ICRP-2 10CRF20 FRC
3H
"CO
"Sr
106Ru
129-j-
I37CS
144Ce
^Ra
239pu
3E8
1.5E6
9E3
3E5
2E3(e)
6E5
3E5
9E2
2E5
3E8
1.4E6
6E3
3E5
8E3
3E5
3E5
8E1
7E4(f)
lE5(h)
3E8
7E5
1E5
7E5
2E4
4E5
8E5
7E3
2E4
1
0.5
10
2
2
0.7
3
20
0.1
3
0.5
10
2
10
0.7
3
8
0.1
(0.2)
1
0.5
20
2
3
1
3
80
0.3
(b)
(c)
(d)
(e)
W
(0)
(h)
0)
Calculated by multiplying most restrictive 168 hr MPCW (public)
by annual water intake
Calculated by dividing the FRC dose limits for individual organs
by the corresponding values of dose per unit intake [Hoenes
and Soldat, 1977] with metabolic parameters from ICRP-19
Calculated for whole body and Q = 1.0
Based on body water and Q = 1.7
MPC values for I in 10CFR20, based on a 2 g thryroid, 1 L/d
fluid intake and 1.5 rem/yr (15 mSv/yr) annual dose limit
Based on parameters in ICRP-2, with bone as critical organ
Based on parameters in ICRP-19, with liver as critical organ
Based on parameters in ICRP-19, with bone as critical organ
Values listed are 1/10 of the most restrictive occupational ALI
for the corresponding nuclide
34
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As evidenced by the many footnotes in Table 4, the comparisons
are not completely straightforward in all cases. Besides changing
the basis for deriving values for ALI, as compared to former MPRI
(MFC) values, there have been several changes in metabolic models
and parameters, and in values for quality factors (Q) . The results
of those changes can be seen in the ALI/MPRI ratios that are the
furthest from a value of l.
The metabolic model for ^Sr, for example, has changed since
ICRP-2 from a single to a multiple exponential and then to a
combination of a multiple exponential and a power function. In the
process, the value of parameter (ft), for uptake from the GI-LLI to
blood, has been changed and the value of the biological half-life
recommended for the single exponential model has also been changed.
The ratio of ALI to the FRC's MPRI is 20, rather than 10, because
the FRC dose limit is 1.5 rem/yr (15 mSv/yr) to bone - as opposed
to a 3.0 rem/yr (30 mSv/yr) dose limit recommended in ICRP-2, and
used as the basis for the MPC values in 10CFR20.
The ratios for 239Pu are complicated by the change in the value
of Q for alpha emitters from 10 in ICRP-2 to 20 in ICRP-30. In
addition, the introduction of new values for distribution of Pu in
the body (ICRP-19) changed the critical organ from bone to liver.
For the ICRP-2 corrected values (see footnote (8>, Table 4} , this
also meant a shift from a dose limit of 3 rem/yr (30 mSv/yr) to
bone, to a dose limit of 1.5 rem/yr (15 raSv/Yr) to liver. The net
result was that no significant difference Appeared in the MPRI
calculations via ICRP-2 methodology, whether based on the ICRP-2
parameters for bone or the ICRP-19 parameters for liver. The
values listed for FRC dose limits for Pu are lower than ICRP-2
and 10CFR20 because of the lower FRC bone limit of 1.5 rem/yr (15
mSv/yr).
The purpose of this discussion is to illustrate both the
extreme complexity involved in the different systems of radiation
protection, and the problems involved in comparing calculated doses
or ALI in one system to those calculated in another system.
35
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7 CONCLUSIONS
Until essential data on key oceanographic and biological
processes are available, assessing the impact of ocean disposals
will be based on applying simplistic and intentionally conservative
assumptions. Accordingly, such assessments will provide upper-
limit or pessimistic values instead of more realistic dose
calculations. It will not be possible to determine more realistic
values for radiation doses until the concentrations of
radionuclides in critical pathways are determined. Nevertheless,
existing models, which should continue to be improved as more data
becomes available, are adequate for regulators to use in deciding
whether disposals should be authorized because they can indicate
whether maximum individual (critical group) exposure limits are
likely to be exceeded.
To implement the ICRP optimization principle, the collective
dose commitment (total dose to an exposed population) must be
estimated. The method usually involves a step-by-step summation
of a series of calculated committed doses. For long-lived
radionuclides, the assumption of a well-mixed ocean requires that
all or some of the global population be considered the exposed
population. It is then relatively straightforward, given the total
annual production of foods from all or portions of the oceans, to
estimate the collective amount of activity ingested and to estimate
dose. For shorter-lived nuclides, the oceanographic dispersion
models do not presently provide sufficient spatial resolution to
identify the geographical radionuclide distributions needed to
successfuly identify an exposed population. Because any values
derived are likely to be over-estimates, perhaps by several orders
of magnitude, the models can only provide a less than precise
assessment of collective dose commitments. Optimization will,
therefore, still be qualitative, based on value judgements.
Newer models and information, however, are continuouly being
developed by the international community to assess and compare land
and ocean disposal of radioactive wastes, in general and on a site-
specific basis. It is apparent that future site characterizations,
for both land and ocean, will employ modeling techniques. Thus,
the newly developed models must include data to define exposure
pathways and calculate conservative, yet realistic, dose scenarios.
36
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8 REFERENCES
Beasley, T.M. and Fowler, S.W.
Plutonium and Americium Uptake from Sediment bv Polvchaete
Worms IAEA-187, IAEA, Monaco, 1976.
Finkelstein, L. and Carson, E.R.
Mathematical Modeling of Dynamic Biological Systems
Research Studies Press, Forrest Grove, OR, 1979.
Foster, R.F., et al. . .
"Evaluation of Human Radiation Exposure" in Radioactivity in
the Marine Environment
National Academy of Sciences, Washington, DC, 1971.
Hicks, R.E. .
"Mathematical Modeling: A BASIC Program to Simulate Real World
Systems" in BYTE, vol. 6, no. 6
McGraw Hill, Peterborough, NH, June 1981.
Hoenes, G.R. and Soldat, J.K.
Aae-Specific Radiation Dose Commitment Factors for a One-Year
Chronic Intake NUREG-0172
US Nuclear Regulatory Commission, Washington, DC, 1977
International Atomic Energy Agency (IAEA)
convention on the Prevention of Marine Pollution by
Dumping of Wastes and Other Matter
INFCIRC/205, IAEA, Vienna, 1974
Convention on the Prevention of Marine Pollution bv Dumping
of Wastes and Other Matter. The Definition Reguired bv Annex
I. Paragraph 6r to the Convention, and the Recommendations
Required bv Annex II. Section D
INFCIRC/205/Add 1, IAEA, Vienna, 1975
Effects of Ionizing Radiation on Aquatic Organisms and
Ecosystems
Technical Report Series No. 172, IAEA, Vienna, 1976
Principles for Establishing Limits for the Release of
Radioactive Materials into the Environment
Safety Series No. 45, IAEA, Vienna, 1978a
37
-------
REFERENCES (Continued)
The oceanoaraphic Basis of the IAEA Revised Definition and
Recommendations Concerning Hiah-Level Radioactive Waste
unsuitable for Dumping at Sea
IAEA-TECDOC-210, IAEA, Vienna, 1978b
The Radiological Basis of the IAEA Revised Definition and
Recommendations Concerning Hiqh-Level Radioactive Waste
Unsuitable for Dumping at Sea
IAEA-TECDOC-211, IAEA, Vienna, 1978c
Convention on the Prevention of Marine Pollution by Dumping
of Wastes and Other Matter. The Definition Required by Annex
If Paragraph 6. to the Convention, and the Recommendations
Required by Annex II. Section D
INFCIRC/205/Add I/Rev 1, IAEA, Vienna, 1978d
Methodology for Assessing Impacts of Radioactivity on Aquatic
Ecosystems
Technical Report Series No. 190, IAEA, Vienna, 1979a
Application of the Dose Limitation System for Radiation
Protection. Practical Implications
Proceedings Series, IAEA, Vienna, 1979b
An Oceanographic Model for the Dispersion of Wastes Disposed
of in the Deepsea IMO/FAO/UNESCO/WMO/WHO/IAEA/UN/UNEP Joint
Group of Experts on the Scientific Aspects of Marine
Pollution-GESAMP
Reports and Studies No. 19, IAEA, Vienna, 1983
The Oceanographic and Radiological Basis for the Definition
of Hiah-Level Wastes Unsuitable for Dumping at Sea
Safety Series No. 66, IAEA, Vienna, 1984
The Definition Required bv Annex I. Paragraph 6 to the
Convention. and the Recommendations Required bv Annex II.
Section D Final Draft
INFCIRC/205/Add I/Rev 2, IAEA, Vienna, 1985
International Commission on Radiological Protection (ICRP)
Recommendations of the International Commission on
Radiological Protection
ICRP Publication 2, Pergamon Press, Oxford, 1959
38
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8 REFERENCES (Continued)
Recommendations of the International Commission on
Radiological Protection
ICRP Publication 9, Pergamon Press, Oxford, 1965
Evaluation of Radiation Doses to Body Tissues from Internal
Contamination due to Occupational Exposure
ICRP Publication 10, Pergamon Press, Oxford, 1968
The Metabolism of Compounds of Plutonium and Other Actinides
ICRP Publication 19, Pergamon Press, Oxford, 1972
Implications of Commission Recommendations that Doses be Kept
as Low as Readily Achievable
ICRP Publication 22, Pergamon Press, Oxford, 1973
Recommendations of the International Commission on
Radiological Protection
ICRP Publication 26, Pergamon Press, Oxford, 1977
Limits for Intakes of Radionuclides bv Workers
ICRP Publication 30, Part I, Pergamon Press, NY, 1979a
Limits for Intakes of Radionuclides bv Workers
ICRP Publication 30, Supplement to Part I, Pergamon
Press, New York, 1979b
Limits for Intakes of Radionuclides bv Workers
ICRP Publication 30, Part 2, Pergamon Press, NY, 1980a
Radionuclide Release into the Environment: Assessment of Doses
to Man
ICRP Publication 29, Pergamon Press, New York, 1980b
Limits for Intakes of Radionuclides bv Workers
ICRP Publication 30, Supplement to Part 2, Pergamon
Press, New York, 198la
s for intakes of Radionuclides bv Workers
ICRP Publication 30, Part 3 - including addendum to Parts
1 and 2, Pergamon Press, New York, 1981b
s for intakes of Radionuclides bv Workers
ICRP Publication 30, Supplement A to Part 3, Pergamon
Press, New York, 1982a
T.Imits for Intakes of Radionuclides bv Workers
ICRP Publication 30, Supplement B to Part 3 - including
addendum to the supplements of Parts 1 and 2, Pergamon
Press, New York, 1982b
39
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8 REFERENCES (Continued)
Mitchell, N.T. and Shepherd, J.G.
"The UK Disposal of Solid Radioactive Waste into the Atlantic
Ocean and its Environmental Impact" in Environmental Impact
of Nuclear Power
British Nuclear Society, London, 1981
National Academy of Sciences/National Research Council (NAS/NRC)
Disposal of Low-Level Radioactive Waste into Pacific Coastal
Waters
Publication 985, NAS/NRC, Washington, DC, 1962
National Council on Radiological Protection and Measurements (NCRP)
Review of the Current State of Radiation Protection Philosophy
Report No. 43, NCRP, Washington, DC, 1975
Organization for Economic Cooperation and Development/Nuclear
Energy Agency (OECD/NEA)
Review of the Continued Suitability of the Dumping Site for
Radioactive Waste in the North-East Atlantic
OECD/NEA, Paris, 1980
Aaencv Research and Environmental Surveillance Program Related
to Sea Disposal of Radioactive Waste
OECD/NEA, Paris, 1981
Shepherd, J.G.
"A Simple Model for the Dispersion of Radioactive Wastes
Dumped on the Deep Seabed" in Fish. Res. Tech. Report No. 29
Ministry of Agriculture, Food and Fisheries, UK, 1976
Thompson, R.C.
"A Consideration of the Wider Impact of Present Trends in
Radiation Protection Systems" in Proceedings of a Topical
Seminar on the Practical Limitations of the ICRP
TtecQimnendations (1977^ and the Revised IAEA Basic Standards
for Radiation Protection. PP. 629-637
IAEA, Vienna, March 5-9, 1979
US Code of Federal Regulations (CFR)
Title 10, Part 20 "Standards for Protection Against
Radiation"
Title 40, Part 190 "Environmental Radiation Standards for
Nuclear Power Operation"
40
-------
8 REFERENCES (Continued)
Title 40, Part 191 "Environmental Standards for the
Management and Disposal of Spent Nuclea Fuel, High-Level and
Transuranic Radioactive Wastes"
US Environmental Protection Agency (EPA)
Environmental Radiation Dose Commitment: An Application to the
Nuclear Power Industry
Report No. 520/4-73-002, EPA, Washington, DC, 1974
US Federal Radiation Council (FRC)
Background Material for the Development of Radiation
Protection Standards
Staff Report No. 1, Washington, DC, 1960
Background Material for the Development of Radiation
Protection Standards
Staff Report No. 2, Washington, DC, 1961
Webb, G.A.M.
"The Interaction Between Radiological Assessments and Research
Requirements Related to Waste Disposal in the Deepsea" in
Proceedings of the Third NBA Seminar on Marine Radioecology
NBA, Paris, 1980
Whicker, F.W. and Schultz, V.
Radioecoloavt Nuclear Energy and the Environment. Volume II
CRC Press, Inc., Boca Raton, FL, 1982
World Health Organization (WHO)
Health Implications of Nuclear Power Production
WHO Regional Publications, European Series No. 3,
Copenhagen, 1978
41
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9 GLOSSARY
This list provides some understanding of a selection of
specialized terms used in this report.
Absorbed dose The amount of energy in the form of ionizing
radiation absorbed in a unit mass of matter. The unit is the gray
(Gy) = 1 joule/kg = 100 rad.
Activity A measure of the rate at which a material is emitting
nuclear radiations; radioactivity usually given in terms of the
number of nuclear disintegrations occurring in a given quantity of
water over a period of time. The unit is the becquerel (Bq) = l
disintegration per second =27 picocuries.
Acute Pertains to short duration, intense effects. An acute
dose would be that delivered over a short time period.
Adsorption The process of attachment onto particle surfaces.
Aloha radiation An emission of particles (helium nuclei) from
a material undergoing nuclear transformation (decay) ; the particles
have a mass number of 4 and a charge of +2.
Annual limit of intake fALIl The limiting intake, in Bq, that a
radiation worker might ingest without exceeding the effective dose
limit of 50 mSv/yr (5 rem/yr).
Average individual An individual of the general public whose
habits are average for the general population.
Becouerel (Eg} The international system (SI) unit of acitivity (1
Bq = 1 disintegration/second = 27 picocuries).
Benthic Pertains to biota living on or in the sea-bed.
Beta radiation Charged particles (electrons and positrons) emitted
from the nucleus of atoms undergoing nuclear transformation
(decay).
Bioaenic Pertains to material originating from biological
processes.
Biota Plant and animal life; the living things of a region.
Bioturbation Mixing of surface sediments by animal activity.
Chronic Pertains to long duration effects. A chronic dose would
be that which is delivered over a long time period.
42
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9 GLOSSARY (Continued)
Collective dose equivalent The summation of the radiation dose
(rem or Sv units) received by all individuals in a population
group. It is principally applied to whole-body dose (units of man-
rein, person-rem, or man-Sv. (Often referred to as "collective
dose" or "population dose."
Committed dose equivalent The dose equivalent that will be
accumulated over a 50 year period, representing a working lifetime,
following intake of radioactive material.
Complexation The formation of a complex compound that is a type
of compound in which a part of the molecular binding is of the
coordinate type.
Concentration Factor Ratio of concentration of an element or
radionuclide in an aquatic plant or animal to that of the
surrounding water at equilibrium.
critical group For a given source or group of sources, the group
of members of the public whose exposure is reasonably homogenous
and is typical of individuals receiving the highest dose.
Critical pathway fsl The pathway (s) through which the critical group
receives their radiation dose. Those paths by which an individual
or population receives the highest dose.
curie fCil Unit of activity defined as the amount of ja
radioactive material that has an activity of 3.7 x 10
disintegrations/second. Replaced by the new SI standard unit
"becquerel" = 1 disintegration/second = 27 picocuries.
Decay chain The sequence of radioactive disintegrations in
succession from one nuclide to another until a stable daughter is
reached.
Detriment The mathematical expectation of harm-which is^determined
by taking into account the severity of an effect and the
probability of its occurrence.
noM nomTnitment The integrated dose that results from external
ex^osSre to, or an intake of, radioactive material when dose is
evaluated from the beginning of exposure, or intake, to a later
time (usually 50 years). Also used for the long-term integrated
dosS to which people are considered committed because radioactive
material has been released to the environment.
43
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9 GLOSSARY (Continued)
Dose equivalent The product of absorbed dose, quality factors,
dose distribution factor, and other necessary modifying factors.
The unit is the sievert (Sv) = 100 rem.
Dose factor A number which relates a dose to an intake of a
radionuclide over a time period, usually a year (e.g. rem/Ci).
Disposal The planned release or placement of waste in a manner
that precludes recovery; dumping (as used by the IAEA and related
international organizations).
Effective dose equivalent The sum of the product of mean dose
equivalents for an organ (tissue) and their respective weighting
factors as defined in ICRP-26.
Exposure The condition of being made subject to the action of
radiation or agents (i.e. chemical exposure).
Extreme near-field That part of the benthic boundary layer in
the vicinity of a release. It is essentially the region where
the model for predicting near-field concentration breaks down due
to the differences between the mixing rates in the benthic
boundary layer and in the over-lying water. In practice, this
region could be on the order of 100m thick and, perhaps, 30km in
radius.
Far-field The remaining ocean, outside the near-field (IAEA,
1984) .
Food chain A number of organisms forming a feeding series
through which energy is passed.
Gamma radiation Electromagnetic energy emitted in the process
of a nuclear transition.
General population Group or population not employed in
occupations dealing with radioactive materials.
Generic Pertains to the general characteristics of a number of
sites.
Gray (Gy) The international system (SI) unit for absorbed dose (1
Gy - 1 J/kg = 100 rad).
Half-life The time required for the activity of a radionuclide to
decay to half its value; used as a measure of persistance of
radioactive materials.
44
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9 GLOSSARY (Continued)
Hiah- Level radioactive waste fKLVH In general, that nuclear
waste that is made up of fission products and actinides resulting
from reprocessing spent fuel from nuclear reactors. For purposes
of ocean disposal, the definition of the London Dumping Convention
(see page 19) applies.
Hydrospheric dispersion factor The ratio of the concentration
of a material in water at a location to the release rate of the
material into the water at the point of origin. This factor is
usually derived from oceanographic models. Analogous to the
atmospeheric dispersion factor (x/g) for estimating concentrations
of a material in air downwind from its release point.
Individual member of the public Individual member of the general
population; not a worker in a radiation industry.
Justification A concept of the ICRP in which no practice shall be
adopted unless its introduction produces a positive net benefit.
It is concerned with the original practice that generated waste
(i.e. nuclear power, weapons, medical isotopes, etc.), but not the
disposal of that waste.
Life-saving dose Dose from radioactive material judged to be
acceptable to an individual involved in saving the lives of others.
Maximum individual (maximally exposed individual) An individual
of the general public whose locations and habits tend to maximize
his/her radiation dose, resulting in a dose higher than that
received by other individuals in the general population (see
.critical group) .
permissible concentration (MFC) The average
concentration of a radionuclide in air (HPCa) or water (MPCw) to
which a worker or member of the general population may be exposed
continuously without exceeding an established standard of radiation
dose limitation.
Maximum permissible- rates of intake fMPRIl of a radionuclide The
product Of" MFC and the annual consumption rate.
Model f mathematical^ Representation of a physical, chemical, or
biological system by mathematical expressions designed to aid in
predicting the behavior of that system under specified conditions.
Wear-field The region in the vicinity of the release in which
the concentration is significantly greater than the ocean basin
average. Its size is variable, but it is usually less than 10 per
cent of the volume of the ocean basin, and may be very much less
for very long-lived contaminants (IAEA, 1984).
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9 GLOSSARY (Continued)
Nonstochastic effects Those effects for which the severity of
the effect varies with the dose.
Nuclide A specie of atom having a specific mass, atomic number
and nuclear energy state.
Optimization A concept of the ICRP in which all exposures shall
be kept as low as reasonably achievable (ALARA) , economic and
social factors being considered.
Other than high-level [radioactive waste] (OTHL) Nuclear waste
that is not defined as high-level by the London Dumping Convention.
Quality factor (Q) The factor by which the absorbed dose (rad
or Gy) is multiplied to obtain a quantity that expresses the
effectiveness of the absorbed dose on a common scale for all
ionizing radiation. In practice, Q is taken as unity for x-rays,
gamma rays and beta particles (see Dose Equivalent).
Radiation (ionizing) Particles and electromagnetic energy
emitted by nuclear transformations that are capable of producing
ions when interacting with matter; gamma rays and alpha/beta
particles are examples.
Radioactivity See Activity.
Radionuclide Any nuclide that is radioactive.
Radon daughters The members of the decay chain of radon-222,
polonium-218, lead-214, bismuth-214, polonium-214, lead-2lo)
bismuth-210, polonium-210 and lead-206 (stable).
Radwaste Waste that contains radioactive materials.
Release limit Number against which the concentration of
radioactive material released to the environment from a facility
or practice is controlled; usually derived from a dose limit for
persons in the environment by considering the environmental
behavior of the released material and habits of -persons considered
to be at risk.
A unit of dose equivalent. The absorbed dose of ionizing
radiation modified by the quality factor and, sometimes, other
factors that result in the same biological effect as one rad of
radiation; 1 rem = 1 rad for X or gamma radiation. It is the
standard unit of dose equivalent in U.S. government regulations.
Residence time A time characteristic of the length of time spent
by a substance in an oceanic system.
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GLOSSARY (Continued)
Scavenging The removal of chemical elements from the ocean by
their incorporation into, or attachment onto, surfaces of
particles; or by their ingestion by living organisms.
Sediment A solid material that is not in solution and is either
distributed throughout the liquid (suspended) or has settled out
of the liquid.
Sievert fSvl The international system (SI) unit of dose
equivalent (1 Sv = 100 rem) . The standard unit for dose equivalent
in European literature and regulations.
Site specific Pertains to the characteristics of one particular
site.
Somatic effects Those effects of radiation that are expressed
during the lifetime of an individual/ but are not passed on to
future generations.
Specific activity As used in this report, the ratio of
concentration of an isotope in a media to the concentration of its
stable analog in that same media. It is also the activity of an
isotope per unit mass of compound, element or radionuclide. As
used in the IAEA definition of HLW, it is the ratio of the activity
of a material disposed into the sea to that of its mass in Bq/kg.
Stochastic effects Those effects for which the probability of
occurrence, rather than severity, are regarded as a function of
dose.
Terabecquerels fTBcr) Equal to 1012 Bq.
Tonne ft) A metric ton (1 t = 1 megagram = 1000 kilograms).
Transuranic Pertains to elements having atomic numbers greater
than that of uranium (# 92); all are radioactive and members of the
actinide group.
Tritium Isotope of hydrogen with atomic mass number 3.
Weighted whole-body dose Effective dose equivalent to the body as
a whole.
Weighting factor fW-rl A weighting factor representing the
proportion of the stochastic risk resulting from tissue (T) to the
total risk, when the whole-body is irradiated uniformly (ICRP-26).
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