EPA-520/5-76-014
RADIATION DOSE ESTIMATES
TO PHOSPHATE INDUSTRY PERSONNEL
ENVIRONMENTAL PROTECTION AGENCY
Office of Radiation Program s
-------
EPA-520/5 76-014
RADIATION DOSE ESTIMATES
TO PHOSPHATE INDUSTRY PERSONNEL
Sam Windham
Jennings Partridge
Thomas Morton
Eastern Environmental Radiation Facility
P. 0. Box 3009
Montgomery, Alabama 36109
December 1976
\
o
U. S. ENVIRONMENTAL PROTECTION AGENCY
Office of Radiation Programs
Waterside Mall East
401 M Street, S. W.
Washington, DC 20460
-------
FOREWORD
The Office of Radiation Programs carries out a
national program designed to evaluate the exposure of man
to ionizing and nonionizing radiation, and to promote the
development of controls necessary to protect the public
health and safety and assure environmental quality.
Technical reports allow comprehensive and rapid
publishing of the results of Office of Radiation
Programs' intramural and contract projects. The reports
are distributed to State and local radiological health
offices, Office of Radiation Programs' technical and ad-
visory committees, universities, laboratories, schools,
the press, and other interested groups and individuals.
These reports are also included in the collections of the
Library of Congress and the National Technical
Information Service.
I encourage readers of these reports to inform the
Office of Radiation Programs of any omissions or errors.
Your additional comments or requests for further infor-
mation are also solicited.
W. D. Rowe, Ph.D.
Deputy Assistant Administrator
for Radiation Programs
-------
PREFACE
The Eastern Environmental Radiation Facility (EERF)
participates in the identification of solutions to prob-
lem areas as defined by the Office of Radiation Programs.
The Facility provides analytical capability for evalua-
tion and assessment of radiation sources through environ-
mental studies and surveillance and analysis. The EERF
provides technical assistance to the State and local
health departments in their radiological health programs
and provides special analytical support for Environmental
Protection Agency Regional Offices and other federal
government agencies as requested.
This study is one of several current projects which
the EERF is conducting to assess environmental radiation
contributions from the phosphate industry.
Charles R. Porter
Director
Eastern Environmental Radiation Facility
11
-------
CONTENTS
Page
FOREWORD . i
PREFACE i i
LIST OF TABLES AND FIGURES iii
ABSTRACT 1v
INTRODUCTION. / 1
GENERAL PHOSPHATE INDUSTRY AND OCCUPATION DESCRIPTIONS 1
RADIATION DOSE GUIDELINES 7
EXTERNAL RADIATION EXPOSURE 9
AIRBORNE RADIATION EXPOSURES 15
SUMMARY AND PROJECTED IMPACT 22
CONCLUSIONS 25
REFERENCES 27
TABLES
1. TLD measurements 13
2. PIC and scintillator measurements 14
3. Maximum external gamma doses 16
4. Comparison of MPC's for models used 19
5. Calculated lung doses, wet process plants. 20
6. Calculated lung doses, thermal process plants -.. 21
7. Summary of airborne and direct radiation doses, wet
process pi ants 23
8. Summary of airborne and direct radiation doses, thermal
process plants 24
FIGURES
1. Naturally occurring radionuclides and their daughters 2
2. Mining and benefication 3
3. Wet process phosphoric acid plant 6
4. Thermal process elemental phosphorus plant 8
iii
-------
ABSTRACT
Phosphate deposits throughout the world contain uranium and
thorium as a natural constituent of the ore. Mining and process-
ing of these ores redistributes much of this radioactive material
among the various products, by-products, and wastes. To determine
the radiological impact of the phosphate industry, the EPA Office
of Radiation Programs has been conducting an extensive study of
the redistribution of this radioactivity. One task of this overall
study was to evaluate the radiation exposure to phosphate industry
workers. This report describes the efforts undertaken to measure
the personnel exposures, describes the exposures encountered, and
relates these findings to existing federal guides regarding per-
sonnel exposures.
In determining the radiation dose equivalent received by
phosphate industry workers only two pathways were felt to .be po-
tentially significant, the external radiation exposure from gamma
radiation, and the dose received due to inhalation of airborne
radionuclides.
External gamma exposures to personnel were measured using
thermoluminescent dosimeters, pressurized ionization chambers, and
portable scintillation type survey instruments. High Volume air
samplers were used to collect airborne particulates on paper fil-
ters. These filters were analyzed to determine concentrations of
airborne particulates which were subsequently used to compute po-
tential radiation dose equivalents.
All measured direct gamma exposures were below the recom-
mended guideline of 0.5 rem per year for individual members of the
general population. All estimates of lung doses were below the
current guidance for radiation workers, and in most cases are
below the 1.5 rem per year guidance for an individual member of
the general population. This study was based on data collected at
several facilities located in Florida and North Carolina and may
not be completely applicable to other parts of the country.
IV
-------
URANIUM - 238 DECAY SERIES
THORIUM - 232 DECAY SERIES
ro
238
92°
4.5x1CPyr
!'
234
90™
24 da.
234
9, Pa
^
234
92^
2.5.10syr
4
230
90™
8 » Kr yr
218
84PD
3 min
'
V
214
82**
27 mn.
83Bi
19.7 mm
/,
214
84^
16.10* sec
^,lf"
u
'
"£*>
194 yr
-
63B
5 da
/"
210
84P°
138 da
^11-
y
.
82Pb
Stable
232
90™
(
228
68^
5.5 yr
228
89*
61 hr
X
228
90™
19 yr
4
224
ee"3
36 da
f
22O
86Rn
54 sec
?""
212
016 sec.
' ll'
212
82^
10.6 hr.
212
1 hr.
- /f\ lisl
0*'
i --
2O3
81T1
3.1 min.
212
84 *>
3 » 10 sec.
ijf
208
82^
Stable
,,
Figure 1. Naturally occurring radionuclides and their daughters.
-------
I. Introduction
Phosphate deposits throughout the world contain uranium
and thorium as a natural constituent of the ore. The phos-
phate ores mined in the United States contain up to 300 ppm
of uranium and 19 ppm of thorium. When these naturally oc-
curring radionuc.lides and their radioactive daughters (see
figure 1) are underground and covered by overburden, they
present no important impact on the biosphere except for
that which might arise from leaching into ground waters.
However, mining and processing of the phosphate deposits
removes this protective overburden and offers the oppor-
tunity for redistributing the radioactivity. Dispersal of
these materials throughout the environment could increase
radiation exposure to the public from these naturally oc-
curring radionuclides.
To determine the radiological impact of the phosphate
mining and milling industry, the EPA Office of Radiation
Programs has been conducting an extensive study of the redis-
tribution of this radioactivity. One task of this overall
study was to evaluate the radiation exposure to phosphate
industry workers. Although the potential exists for workers
in this industry to be occupationally exposed to radiation,
they have not been considered radiation workers in the con-
text of existing regulations. Therefore, the exposures to
these workers have not been routinely controlled or monitored.
This report describes the efforts undertaken to measure
the personnel exposures, describes the exposures encountered,
and relates these findings to existing federal guides regard-
ing personnel exposures.
II. General Phosphate Industry and Occupation Descriptions
This study of phosphate industry personnel exposures is
based entirely on data collected at several operations lo-
cated in Florida and North Carolina. Since mining and pro-
cessing in these locations is different from those in other
parts, of the country, the conclusions for this study may not
be completely applicable in all cases.
Mining and Benefication Operations
The mining and benefication operations as performed in
Florida and North Carolina are shown graphically in figure 2.
In the Florida and North Carolina phosphate field overburden
-------
Pit
Mine
Water
Ore1
Matrix
CO
Sluice
Pit
Screen
Slime
Flotation
Sand!
Tailings
Phosphate
Rock
Slime Storage
Pond
Sand Tailings
Storage
Figure 2. Mining and benefication.
-------
is stripped from above the phosphate ore using electric drag-
lines. The overburden varies in depths up to approximately
100 feet. These large quantities of overburden are put aside
for use in land reclamation projects. The ore is removed by
the same dragline and dropped into a sluice pit. In this
pit, high pressure water is used to produce a slurry which is
then pumped to the washer plant. The numbers of workers en-
gaged in the actual mining operations are small; only two
people are involved in the dragline operation and one person
operates the water nozzles at the sluice pit. Other support
people visit the mining site to provide services as required.
Mining operations are normally conducted 24 hours per day, 7
days per week, on three 8-hour shifts.
In the washing and benefication process, marketable rock
is separated from sand tailings and phosphatic clay slimes.
This is accomplished through a series of screening and flo-
tation steps. For each ton of marketable rock produced ap-
proximately one ton each of slime and sand tailings are pro-
duced. At the three benefication operations visited most
equipment was automatically controlled, thus not requiring
workers to be continuously present. As a result, most of
the normal operations were controlled and monitored from a
remote location. Due to the quantities of water involved,
approximately 10,000 gallons per ton of marketable rock,
airborne particulates were not observed to be an exposure
problem in the washing and screening plants.
From the washing process the marketable rock is trans-
ferred to the drying and storage area. Here the wet rock
is dried in large rotating drums. After drying the rock
is separated according to size and grade and stored for
later use. Most of this operation is also automated. High
concentrations of particulates were present in the environs
of plants which dried the beneficated rock.
Phosphate Rock Milling
Two types of plants are used to process the marketable
phosphate rock. At the "wet process" plants the rock is
combined with an acid, usually sulfuric, to produce phos-
phoric acid and waste gypsum. At "thermal process" plants
the rock is combined with coke and silica and electrically
smelted to produce elemental phosphorus, ferrophosphorus
and slag. Plants of each type have been studied to deter-
mine radiation exposures to the personnel.
-------
Wet Process Plants
The general operations performed at a wet process
phosphoric acid plant are shown in figure 3. In the
"wet process" plants studied, phosphate rock is usually
received in railroad cars. The rock was dropped from
car hoppers onto conveyor belts which moved the rock
to temporary storage. Car vibrators or shakers were
used to help dislodge rock packed in the railroad cars.
This resulted in extremely heavy dust in the immediate
vicinity of the unloading facility. Normally two to
four employees were present at the unloading facility
to operate the hopper doors, car shakers, and to move
railroad cars.
From storage, the rock is ground as necessary.
The crushed rock is then mixed with sulfuric acid in
the reactor vessel to make phosphoric acid. After
reaction, calcium sulfate (gypsum) is separated from
the phosphoric acid in pan filters and pumped as a
slurry to the waste gypsum pile. On the gypsum pile
the process water is decanted and returned to the plant
for reuse. The phosphoric acid is transferred to the
fertilizer plant to be treated in a number of ways de-
pending on the desired final product. As in the
washing/benefication operations, many of the activities
within the acid plant and fertilizer production facili-
ties are automatically controlled and monitored from
control rooms. Personnel are present to perform tasks
which arise; however, they do not "stand over" and ob-
serve each operation continuously. In the plants
studied, six to ten employees operated each acid plant
during each shift. The fertilizer production operation
was run by six to eight employees during each shift.
All facilities visited had granular fertilizer
stored in large warehouse buildings. The product is
deposited in the building via conveyor belts and from
there it was outloaded as required using front-end
loaders. When the product was being moved by front- ,
end loaders the airborne particulates were visibly
quite high. Loader operators in some cases were wear-
ing nose and mouth masks to remove particulates. Nor-
mally, only three to four employees were observed work-
ing in this operation.
Heavy equipment routinely operates on top of the
gypsum pile to maintain dikes and to direct the flow of
-------
Phosphate
Rock
Sulfuric
Acid
Gypsum
Pile
Drying
Grinding
Reactor
Vessel
Filter
Dry
Fertilizer
Product
Phosphoric
Acid
Fertilizer
Plant
Acid
Evaporator
-------
process water on the pile. Usually one to two people
work in this location, although during major dike modi-
fications it may require more workers.
In each facility surveyed the number of full time
personnel directly employed by the operator was rela-
tively small compared to the total number of persons
observed to be working. Generally a total of about
200-300 employees worked at the wet process plants
studied. Much of the routine maintenance and new
construction is performed by contract crews. These
crews were performing such tasks as painting, clean-
ing, and construction of new plant facilities and
maintaining dikes and ponds during the times of our
surveys.
Thermal Process Plants
In the "thermal process" plants surveyed, phos-
phate rock, coke, and siliceous material are electri-
cally smelted in a furnace (figure 4). Elemental
phosphorus is recovered by condensing vapors from the
furnace. The waste products, slag, and ferrophos-
phorus, are tapped from the furnace in molten form.
Rock unloading at the thermal plants surveyed
was similar to that observed at wet process plants.
At one plant rock was also hauled in using trucks.
Unloading and storage operations were usually carried
out by two to three people.
Although elemental phosphorus is'the principle
product at these facilities, ferrophosphorus and slag
are also loaded and sold for various uses. At each
plant approximately 25 to 35 personnel were required
to operate one furnace and supporting equipment.
III. Radiation Dose Guidelines
The Occupational Safety and Health Standards of the
Department of Labor as published in Federal Register, Vol.
37, No. 202, Section 1910.96 - October, 1972, basically
states that no individual in a "restricted area" should
receive a radiation dose equivalent of 5 rems per year
whole body or 15 rems per year to the lung. The "restricted
area" is defined in the same publication as an area whose
access is controlled for purposes of radiation protection.
-------
Coke Silica
00
Phosphate
Rock
Blending Sizing
Calcining
Electric
Furnace
Vapors
Phosphorus
Condenser
Ferrophosphorus
and Slag
Elemental
Phosphorus
Figure 4. Thermal process elemental phosphorus plant.
-------
The employees of the phosphate industry have gener-
ally not been working in "restricted areas" and the doses
encountered were much less than those noted above. There-
fore, these employees have not been considered subject to
federal or state radiation protection guidance. However,
for the purpose of comparison to the findings in this study
the radiation protection guidance provided by the former
Federal Radiation Council (FRC)1 (now a function of the EPA
Office of Radiation Programs); the National Council on
Radiation Protection (NCRP)2; and the International Commission
on Radiation Protection (ICRP)3 serve as a guideline for eval-
uating the estimated doses in this study.
•
The general guidance provided by these three groups for
an individual member of the general population (non-radiation
worker) is a whole body limit of 0.5 rem per year and the
annual dose equivalent limit to the lung of 1.5 rem. However,
this guidance applies to all radiation doses with the excep-
tion of medical exposures and normal background exposures.
Also, the general philosophy of these groups is that all radia-
tion exposures should be kept as low as practicable.
In determining the radiation dose equivalent received by
phosphate workers as a result of their occupation, only two
pathways were believed to be potentially significant: (1) the
external radiation exposure from gamma radiation and (2) the
dose received due to the inhalation of airborne radionuclides.
Therefore, the body organs of interest for this study were
the whole body and the lungs.
IV. External Radiation Exposure
To determine the direct exposure to persons working in
the phosphate industry, general surveys of several facilities
in central Florida and North Carolina were made. A detailed
survey of each facility was not attempted. However, an ef-
fort was made to survey general areas at several plants to
determine the approximate exposure to persons working in
these areas.
An examination of the decay series shown in figure 1
reveals a number of qamma emitters. These gamma emit-
ters when present in sufficient quantities can result in an
external radiation hazard. To determine if such an external
radiation hazard exists in the phosphate industry three
types of gamma radiation measuring devices were used in sur-
veys of the facilities. The three types of measuring devices
-------
used were: (1) thermoluminescent dosimeters (TLD); (2) pres-
surized ionization chambers (PIC); and (3) portable scintil-
lation type survey instruments. The TLD s were utilized for
long-term (longer than 1 month) integral exposure measure-
ments while PIC's and scintillation meters were used for in-
stantaneous measurements.
The TLD's used in this study were CaF2:Mn", glass bulb
type dosimeters. Previous studies have shown this type TLD
to be accurate to within ±7.5 percent at environmental ex-
posure levels of approximately 10 yR/hr*'5. Additional
studies have shown that results obtained with the TLD's and
PIC's to be in good agreement.6'7 The TLD's were annealed
in the field near the measurement site using the electronic
annealer developed at the Eastern Environmental Radiation
Facility (EERF)8. Following the exposure period, the dosim-
eters were returned to EERF for readout. Corrections were
made for any small exposures that were accrued during trans-
portation to EERF.
Commercially available PIC's similar to those described
by De Campo et al9 were used in this study to measure the
exposure levels in and around the various phosphate industry
facilities. The detector is a stainless steel chamber, 24
cm in diameter with a wall thickness of 0.3 cm. Previous
studies have demonstrated the ability of this instrument to
measure environmental radiation levels of approximately 10
yR/hr with an accuracy of better than ± 5 percent9.
The scintillation survey meter used has an internally
mounted 2.5 cm x 2.5 cm Nal (Tl) gamma scintillator as the
detector. This commercially available instrument has count-
ing ranges of 0-3 yR/hr with multiples of XI, X10, X100,
and XI000. This unit is portable, lightweight and conven-
ient for making quick surveys of large areas.
All instruments were calibrated at EERF for gamma ray
response using a standardized 226Ra source. In addition to
the EERF calibration, the scintillation survey meter was
calibrated against the PIC in the field. This was done to
correct the survey meter for any gamma energy response dif-
ferences between the 226Ra spectrum and natural background
spectra.
TLD Measurements
The results of the TLD measurements are shown in table
1. These results represent two monitoring periods, one of
10
-------
4-months duration and the other of 2-months duration.
Each value shown is the1mean of at least two dosimeters
positioned at each site. The exposure levels measured
at sites 1, 2, and 3 represent the typical undisturbed
natural background exposure levels for this region of
Florida.
Measurements at sites 4 and 5 were in the parking
lot and grounds surrounding the general office areas of
two plants. Site number 4 was near a road and this ex-
posure might be due in part to the use of radioactive
phosphate slag in paving material.
Sites 6 through 9 can generally be classified as the
ore unloading areas where large quantities of phosphate
ore are unloaded from railroad cars or large trucks.
Earlier studies10 have shown this ore to contain approxi-
mately 40 pCi/g of 226Ra.
The ball mill area, site number 10, is where the ore
is crushed into smaller sizes to be used in later plant
operations. Measurements were made near the area where
ore is fed into the ball mill. This measurement location
was adjacent to the control room for this operation where
personnel are working much of the time.
The phosphoric acid production facility is where the
phosphate rock is reacted with acid. Site number 11 was
located near the top of one of the large reactor vessels.
As a result of reacting the ore with acid, two products,
phosphoric acid and gypsum, are produced. Layers of the
gypsum are deposited on the inner surfaces of the reactor
vessel and associated components. This deposited material
or "scale" was analyzed and found to contain 210 pCi/g of
226Ra.
Site number 12 was located in the fertilizer produc-
tion building. This is the area where dry fertilizer
products are produced. Most of the processing takes place
inside large containers and these containers serve as
.shields which reduce the external gamma exposure rates.
Sites 13 and 14 were located in the areas where the
finished fertilizer products, diammonium phosphate (DAP)
and triple super phosphate (TSP), were stored. Several
tons of these materials were stored at these facilities.
11
-------
Previous studies10 have shown these products to contain
226Ra as high as 20 pCi/g.
Site .number 15 was located adjacent to the base of
the furnace in the thermal process plant. The measured
exposure rate of 65 yR/hr was due primarily to the 226Ra
and daughter products found in the slag which contained
20-60 pCi/g of radium.
Site number 16 was located at an ore drying facility
where the wet ore was dried, sized, graded, and stored for
later use. The TLD was located on an exterior office wall
near several large piles of rock.
PIC and Scintillation Measurements
The exposure rate measurements shown in table 2 were
made using a PIC and/or the portable scintillation survey
meter. These results are averages of several measurements
at different facilities. All measurements were made during
"walk through" surveys at the various plants. It should be
noted that these are only measurements at one particular
time and do not represent integrated exposures over long
periods of time as do the TLD measurements. As a result of
being instantaneous measurements, they are a function of the
quantity of material on hand at that particular time. How-
ever, there is no reason to believe that our survey wasn't
performed at a typical time and these results should be
representative of the normal operations. In most cases PIC
and scintillation measurements were not made simultaneously.
These results show exposure rates similar to those mea-
sured by the TLD's. The highest exposure levels were re-
corded in the areas associated with the ore handling/storage
facilities and the phosphoric acid facilities.
Of particular interest were the exposure levels inside
the reactor vessel during cleanout (500 yR/hr). This process
varies from plant to plant, but at two of the facilities sur-
veyed, each of the two reactors in the phosphoric acid plants
were cleaned out four to eight times per year, based on
quantity of scale buildup. Each cleanout operation reportedly
lasts from 5 to 7 days and involved 20 to 40 employees.
Measurements were taken on top of the gypsum piles at
each wet process facility surveyed. The exposure rates were
fairly uniform across the top of the piles. Earlier studies
have shown the gypsum to contain ~ 30 pCi/g of 226Ra10.
12
-------
Table 1
TLD measurements
Location
(1) Dundee, FL - Background
(2) Lake Wales, FL - Background
(3) Polk City, FL - Background
(4) Grounds - general office
(5) Parking lot - general office
(6) Ore unloading
(7) Ore unloading
(8) Ore unloading
(9) Ore unloading
(10) Ball mill area
(11) Phosphoric Acid Plant
(12) Fertilizer Plant
(13) Fertilizer Product Storage
(14) Fertilizer Product Storage
(15) Furnace Area - Thermal Process Plant
(16) Ore Drying and Storage
Average
Exposure iiR/hr
4
6
4
14
6
19
38
54
39
37
179
7
16
16
65
57
13
-------
Table 2
PIC and sdntillator measurements
PIC Scintillator
Area of Measurement yR/hr yR/hr
Washing and Benefication Facility No data 52
Ore Drying and Storage 90 105
Ore Unloading 100 115
Ball Mill Area 19 22
Phosphoric Acid Plant
General area around reactor 132 85
Inside reactor during cleanout -No data 500
Fertilizer Building 10 10
Product Storage Area
Dry Fertilizer Products 12 15
Slag and Ferrophosphorus No data- 150
Top of Gypsum Pile No data 30
General area around thermal No data 75
process plants
14
-------
The general area around two thermal process plants was
surveyed and exposure rates of approximately 50-150 uR/hr
were observed. It was noted that these grounds at both
facilities were covered with slag which typically contains
about 50 pCi/g of 226Ra.
To determine a maximum yearly dose to individuals in
different areas of the plants the results of survey measure-
ments shown in tables 1 and 2 were taken as typical expo-
sure levels. Since the TLD results were integral exposures
over a longer period of time, these results were used where
available. The PIC and scintillator measurements were only
used for those locations where no TLD measurements were made.
In locations where more than one TLD result was available the
exposures were averaged. The exposure rates for the respec-
tive areas were then multiplied by 40 hours per week and 50
- weeks per year to determine the maximum yearly exposure.
This yearly exposure is approximately equal to the yearly
dose equivalent. By assuming continuous occupancy during
work periods the doses to the personnel are overestimated.
The actual dose could be estimated more precisely by insert-
ing the actual occupancy factor for a particular locatiog.
Annual dose equivalent values are given in table 3..
The calculated dose inside the reactor vessel assumes a per-
son to be involved in eight cleanout operations per year,
each lasting 40 hours. This estimate assumes the typical
plant has two reactors, each being cleaned four times per
year,
V. Airborne Radiation Exposures
To compute potential doses due to airborne radioactive
particulates, radioisotopic air concentrations were needed.
These concentrations were obtained by collecting the particu-
lates on paper filters which were analyzed. Most of the fil-
ter samples were obtained by using high volume samplers with
a flow rate of 40 to 50 cubic feet per. minute (cfm). Some
additional data was generated by running samplers which sepa-
rate the particulates based on size. Two types' of particle
sizing samplers were utilized: .(1) High volume Cascade
Impactor with five fractional stages plus a backup stage and
(2) a Hi-Vol fractionating sampler with four-fractional stages
plus a backup filter. Both samplers were run at a flow rate
of 20 cfm. All filters were analyzed in the laboratory for
226Ra and the isotopes of uranium and thorium. Additionally,
a number of samples were analyzed for 210Po.
15
-------
Table 3
Maximum external gamma doses
Dose Equivalent Rate
Area of Plant rem/yr ._
Wet Process
Ore Drying and Storage Area .12
Ore Unloading Area .06
Ball Mill Area .07
Phosphoric Acid Building .04
Fertilizer Production Building .01
Product Storage and Shipment Area .03
Top of Gypsum Pile .06*
Inside Reactor (during cleanout) .16*
Thermal Process
Ore Unloading Area .11
Furnace Area .13
Ferrophosphorus and Slag Storage Area .30*
General Plant Area .10*
* Based on PIC or Scintillation survey meter measurements.
16
-------
Ambient air samples were collected at some locations and
analyzed for 22?Rn, a radioactive gas. The samples were col-
lected by drawing filtered air into an evacuated scintillation
counting cell (125 cc volume) which was counted directly on a
photomultiplier tube. Radon concentrations were calculated
based on the number of scintillations recorded by the counter.
Estimates of working level based on radon progeny concen-
trations were not made during this study due to lack of equip-
ment available. Because of the "open air" nature of most of
the areas in the plants there is little opportunity for the
buildup of radon progeny. However, certain locations such as
control rooms, offices, tunnels, etc., do exist where Buildup
may occur arid we plan to survey these areas on future visits
to the facilities.
Several different methods can be used to calculate poten-
tial lung doses due to inhalation of radioactive particulates
of uranium, thorium, and radium and radon gas and its daugh-
ters. One method is to use the International Commission on
Radiation Protection Report Number 2 (ICRP-2)3 recommendations
for calculating occupational lung doses. ICRP-2 includes maxi-
mum permissible concentrations (MPC's) based on a simplified
lung model where aerosol particle size is ignored and solu-
bility is lumped into the broad categories of being soluble or
insoluble.
Another calculational method is to utilize the dose con-
version factors recommended by the Environmental Protection
Agency in the Environmental Analysis of the Uranium Fuel Cycle
Part 1 - Fuel Supply11. This model takes the recommendations
of the ICRP Task Force12 report and assumes an aerosol parti-
cle size of ly AMAD (activity median aerodynamic diameter).
Furthermore, the EPA model assumes the radionuclides are re-
tained in the lung with a 500 day effective half-life (Class
Y - insoluble.)13'*1* and the lung mass is 480 grams15. Origi-
nally, a 1000 day.effective half-life was chosen11; therefore,
the dose conversion factors in reference 10 are reduced by a
factor of two to account for the reduction in the effective
half-life. The Class Y assumption may be valid for certain
chemical forms of uranium, thorium, and uranium daughters but
may not necessarily be true for radionrclides found in the
phosphate industry. The EPA model, therefore, predicts an
upper limit of potential exposure for insoluble particles.
17
-------
By applying both the ICRP-2 and the EPA models, a range
of potential lung doses to workers in the phosphate industry
was obtained. Table 4 lists the radionuclides considered
in each model along with the applicable MFC's for the radio-
nuclides. Dose contributions from 210Po and 222Rn were cal-
culated and included only where noted. Even though the EPA
model does not include doses from 210Po and thorium (except
230Th), it is expected that the dose fractions for these
radionuclides would be small compared to the total dose esti-
mates. The MPC for radon used in the EPA model is an average16
value which assumes a ventilation rate of one air change per
hour. Because of the nature of the phosphate plants, it could
not be determined if this is a realistic estimate of the venti-
lation rate. Both the ICRP-2 and EPA models tend to over-
estimate the lung dose due to radon and its daughters since
the MPC's in table 4 are for "ordinary air" and "clean air",
respectively.
Potential lung doses for the phosphate industry personnel
working in certain areas of the plants are listed in tables 5
and 6. These dose estimates are based on an assumed occupancy
factor of 40 hours per week, 50 weeks per year. It is rea-
lized that in many cases the actual occupancy in these areas
is much lower. In one location noted in table 5, it is not
possible to remain in the location for extended periods. The
"inside reactor during cleaning" location for wet process
plants can only be considered for periods during the cleaning
operation. This occurs four to eight times per year in each
of the two reactors at two of the plants surveyed. The doses
given for the cleanout operations have been reduced by 8/50th
of the annual dose to reflect this occupancy factor.
It is interesting to note the difference in potential
doses measured in the product storage and shipment areas A and
B in table 5. In the storage and shipment area A (average of
several plants) loading operations were taking place. Front-
end loaders were being used to remove fertilizer products from
the buildings. This resulted in high concentrations of air-
borne particulates and correspondingly higher lung doses. In
contrast, no loading operations were taking place in the "B"
locations and the airborne particulates and calculated lung
doses were considerably reduced.
The potential lung doses calculated for the top of the
gypsum pile are based on radon plus daughter concentrations
only. The EPA model assumes 50 percent daughter equilibrium.
Since this is an "open air" location, this percent equilibrium
18
-------
Table 4
Comparison of MFC's3 for models used
Radionuclide
2iopo
222Rn
226Ra
227Th
232
Th
235U
238y
ICRP-2
pCi/m3
200
30,000
50b
200
6
10
10
100
100
100
EPA
pCi/m3
-
11,000
8
.
-
8
-
9
9
9
a Occupational, 40 hours a week, lung (insoluble).
b NBS Handbook 69.
19
-------
Table 5
Calculated lung doses, wet process plants
(40 hr/wk, 50 wk/yr)
ICRP-2 EPA
Location rem/yra rem/yra
Ore Unloading Area 1.6 (.53-3.6) 5.5 (1.8-9)
Dryer Area .30 (.11- .66) 1.0 ( .33-2.2)
Ball Mill Area 1.1 (.94-1.4) 3.6 (3-4.7)
Fertilizer Production .90b (.32-2.1) 2.5 (.85-6)
Building
Product Storage and 1.0 (.16-1.9) 3.2 (.47-5.5)
Shipment Area A
Product Storage and .05 (.02- .09) .15 (.06-.27)
Shipment Area B
Top of Gypsum Pile 3.0 1.0C
(radon plus daughters only)
Inside Reactor during .24d (.24- .25) .70e (.66-.74)
Cleanout
a Average of two or more samples with the range of values in parentheses.
b Includes .011 rem for 210Po.
c Assumes 3 minute buildup of radon daughters with pure radon initially.17
d Includes .24 rem for radon and its daughters - assumes 8/50th of a
year occupancy.
e Includes .66 rem for radon and its daughters - assumes 8/50th of a
year occupancy.
20
-------
Table 6
Calculated lung doses,
thermal process plant
(40 hr/wk, 50 hr/wk)
ICRP-2 EPA
Location rem/yr rem/yr
Ore Unloading Area 2.3 6.0 (5.5-6.5)*
Beneath Ore Storage Bins .09 .28
Furnace Area .27 .85
* Average of two or more samples with the range of values in
parentheses.
21
-------
probably would not often be reached and thus the dose con-
tributed by the daughters would be correspondingly reduced;
therefore, a more realistic estimate was made corresponding
to an approximate 6 percent daughter equilibrium.17 Particu-
lates at this location were not measured due to the unavail-
ability of power to operate air samplers.
In general, good agreement was seen between doses calcu-
lated for the same operation at different plants. Potential
lung doses calculated were seen to be in direct proportion
to airborne particulates in a given area. Particle sizing of
a number of these samples showed that the majority of particu-
lates were greater than ly AMAD. Because of this, the doses
estimated using the EPA model are probably high since a ly
AMAD was assumed.
VI. Summary and Projected Impact
Tables 7 and 8 are summaries of the airborne and direct
doses calculated for wet and thermal process plants. The
doses and numbers of workers presented are typical for the
plants surveyed during the study. They are not intended to
describe any one plant. In each table the dose equivalent
to the lung from airborne particulates is greater than the
dose equivalent to the whole body from direct gamma expo-
sure. In all locations the annual whole body dose is less
than the applicable guidelines of 0.5 rem/yr.
Airborne lung doses calculated for some locations noted
in tables 7 and 8 are greater than the recommended guidance
of 1.5 rem per year to the lungs for an individual in the
general population but less than the limit of 15 rem/yr to
the lung for radiation workers.
The EPA model prediction of lung dose due to particu-
lates could be overestimated by a factor of 4 to 5 due to
assumptions made regarding lung mass and particle size as
discussed previously. Other factors which could reduce the
actual doses below the predicted or calculated doses include:
1. Lower than predicted occupancy at the location
2. Non-respirable characteristics of larger particles
3. Use of protective breathing devices
The extent to which these factors would reduce the
actual doses is difficult to estimate based on the limited
observations of our study. These factors would vary
22
-------
Table 7
Summary of airborne and direct radiation doses,
wet process plants
(assuming 40 hr/wk, 50 wks/yr)
Location
Ore Unloading Area
s.
Ball Mill Area
Fertilizer Production Building
Product Storage and Shipment Area
Top of Gypsum Pile (radon plus
daughters only)
Inside Reactor during Cleanout
(radon plus daughters included)
Direct
Airborne dose gamma dose
equivalent equivalent
rem/yr rem/yr
ICRP-2 .
1.6
1.0
0.9
1.0
3.0
EPA
5.5
3.6
2.5
3.2
1.0
.06
• 07
.01
.03
.06
0.2
.70
.16
* The reactor vessel is normally cleaned 4-8 times per year by 20-40
personnel, each cleaning lasts approximately 5-7 days. The doses
given are based on occupancy in the vessel for eight cleanouts each
lasting 40 hours during the year.
23
-------
Table 8
Summary of airborne and direct radiation doses
thermal process plants
(assuming 40 hr/wk, 50 wks/yr)
Location
Ore Unloading Area
Beneath Ore Storage Bins
Furnace Area
Ferrophosphorus and Slag
Storage Area
General Plant Area
Airborne dose
equivalent
rem/yr
ICRP-2 EPA
2.3 6.0
0.1 0.3
0.3 0.9
No data No data
Direct
gamma dose
equivalent
rem/yr
.11
No data
.13
.30
No data No data
.10
24
-------
considerably from plant to plant and even within a single
plant depending on an individual worker's habits.
In addition to the dose ranges for individuals, it is
necessary to estimate the total number of personnel working
in the various locations to determine the overall radio-
logical impact on phosphate industry workers. This is diffi-
cult due to differences between the plants and the general
lack of employment records for the industry. Estimates on
numbers of workers in this report are based on observations
made at plants in Florida and North Carolina. Records indi-
cate that there are now 35 wet process and 10 thermal pro-
cess plants in operation in the United States.
Generally three categories of employees were observed in
the plants surveyed. One category was comprised of part-time
personnel who performed maintenance and construction work on
the plant facilities. These personnel were not employed
directly by the phosphate plant, but by a contractor hired to
perform some specific task. A second category was comprised
of employees of the plant who do not routinely work in the
areas listed in tables 7 and 8. This group includes office
and clerical help, laboratory workers, maintenance workers,
etc. The third category of plant employees consists of the
personnel who routinely work in the areas listed in tables
7 and 8.
Extrapolation to the total industry from the plants sur-
veyed indicate there would be approximately 8000 total plant
employees in wet process plants, 2500 to 3500 of which rou-
tinely work in the areas listed in table 7. The thermal pro-
cess plants employ a total of approximately 3000 employees
with 400 to 700 routinely working in the areas listed in
table 8. The above estimates do not include the part-time •
(contract) maintenance and construction crews.
VII. Conclusions
The following general conclusions can be drawn from the
study described:
1. All measured direct gamma exposures, even assuming
continuous occupancy, are below the current Radiation
Protection Guides of 0.5 rem per year for individual
members of the general population.
25
-------
2. All estimates of lung doses are well below the cur-
rent occupational guidance for workers of 15 rems per
year and in most cases are below 1/10 of the guide.
3. In accordance with the additional Federal Guidance
that "every effort should be made to encourage the
maintenance of radiation doses as far below the (RPG's)
as practicable," the following suggestions to reduce
exposure warrant some consideration:
a. Reduction of dust concentrations in the work
place or by the use of protective respirators (non-
radiological health benefits would also be gained),
and
b. In new facilities, minimizing personnel expo-
sures by design and location of control rooms and
other routinely occupied work areas.
4. Additional data relative to particle size distribu-
tions, particle solubility, and occupancy factors could
be useful in more clearly defining the radiological im-
pact of the phosphate industry:
5. If specific situations exist at a facility that
could result in annual whole body exposures in excess
of 1.25 rem it would be necessary to provide personnel
monitoring devices for the workers exposed. This would
be in accordance with the present OSHA regulations.
26
-------
REFERENCES
1. FEDERAL RADIATION COUNCIL. Background Material for the
Development of Radiation Protection Standards, FRC Report
No. 1, DHEW, PHS, Washington, DC (May 1960).
2. NATIONAL COUNCIL ON RADIATION PROTECTION AND MEASUREMENTS
(NCRP). Basic Radiation Protection Criteria, NCRP - Report
No. 39, NCRP Publications, Washington, DC (January 1971).
3. INTERNATIONAL COMMISSION ON RADIOLOGICAL PROTECTION. Report
of Committee II on Permissible Dose for Internal Radiation,
ICRP Publication 2, Pergamon Press, New York (1959).
4. PARTRIDGE, J. E., S. T. WINDHAM, J. L. LOBDELL, and J. A.
OPPOLD. Suitability of Glass-Encapsulated CaF2:Mn TLD's
for Environmental Radiation Surveillance, ORP/EERF-73-1
(June 1973).
5. BURKE, Gail de P. Investigation of a CaF2:Mn TLD System
for Environmental Monitoring, HASL-252 (April 1972).
6. PARTRIDGE, J. E., J. C. LOCHAMY, J. C. EAKINS, and S. T.
WINDHAM. A Comparison of CaF2:Mn and LiF TLD's for
Environmental Radiation Surveillance, EPA 520/5-73-006.
7. PARTRIDGE, J. E., J. A. BROADWAY, S. T. WINDHAM, and C. R.
PHILLIPS. Low Uevel Population Exposure Measurements Using
TLD's, presented at Symposium on Population Exposures
CONF-741018 Proceedings of the Eighth Midyear Topical
Symposium of the Health Physics Society, Knoxville, TN
(October 1974).
8. WINDHAM, S. T., H. L. KELLEY, and T. K. PLANT. Portable
Annealer for TLD's, ORP/EERF-73-3 (June 1973).
9. DECAMPO, J. A., H. L. BECK, and P. D. RAFT. High Pressure
Argon lonization Chamber Systems for Measurement of
Environmental Radiation Exposure, HASL-260 (1972).
10. GUIMOND, R. J. and S. T. WINDHAM. Radioactivity Distribution
in Phosphate Products, By-Products, Effluents and Wastes,
ORP/CSD-75-3 (August 1975).
11. U. S. ENVIRONMENTAL PROTECTION AGENCY. Environmental Analysis
of the Uranium Fuel Cycle Part I - Fuel Supply, EPA-
520/9-73-003-B. Office of Radiation Programs, Field Operations
Division, Washington, DC (October 1973).
27
-------
12. MORROW, P. E. Deposition and Retention Models for Internal
Dosimetry of the Human Respiratory Tract. Health Physics
12:173-207 (1966).
13. U. S. ENVIRONMENTAL PROTECTION AGENCY. Environmental
Radiation Protection for Nuclear Power Operations,
Supplementary Information. Proposed Standards, 40CFR190
(January 1976).
14. INTERNATIONAL COMMISSION ON RADIOLOGICAL PROTECTION. The
Metabolism of Compounds of Plutonium and Other Actinides,
ICRP Publication 19, Pergamon Press, New York (1972).
15. MORGAN, K. Z. and TURNER, 0. E. Principles of Radiation
Protection, John Wiley & Sons, Inc. (1967).
16. JOHNSON, R. H., et al. Dose Conversion Factor for Radon-222
and Daughter Products, USEPA, OAB, EAD, ORP, Washington, DC
(April 1975 Draft).
28
------- |