Savannah River Site Special Exposure 

Cohort Petition Evaluation Report 

Thorium at the Savannah River Site

(post 1972)

Timothy D. Taulbee, Ph.D., CHP

Research Health Scientist

National Institute for Occupational Safety and Health

Division of Compensation Analysis and Support

February 2014

Cincinnati, Ohio
Overview

 Thorium Inventory 

 Processes involving thorium

 Radiological Controls 1972-1990

 Alternate Bioassay

 Bioassay Control

 Am/Cm/Cf/Th Comparison

 Thorium 1990-2007
Thorium Inventory at SRS

Year

1950 

1955 

1960 

1965 

1970 

1975 

1980 

1985 

1990 

1995 

2000 

2005 

2010 

Thorium Inventory 

(kilograms)

0

20000

40000

60000

80000

100000

120000
Receiving Basin for Offsite Fuels (RBOF)

 Encapsulated spent nuclear fuels

 Fuels repackaged underwater

 Fuels stored underwater

Photos from WSRC-MS-99-00678 accessed via public internet at

http://sti.srs.gov/fulltext/ms9900678/ms9900678.html 

RBOF Building

Stored spent fuel

Repackaging basin 
Thorium inventory 

w/o water stored, encapsulated spent fuel

Year

1950 

1955 

1960 

1965 

1970 

1975 

1980 

1985 

1990 

1995 

2000 

2005 

2010 

Thorium Inventory 

without stored spent fuel (kilograms)

0

20000

40000

60000

80000

100000

120000
Expanded Scale of Previous Graph

 Inventories indicate very small thorium inventory 1972 - 2007

Year

1950 

1955 

1960 

1965 

1970 

1975 

1980 

1985 

1990 

1995 

2000 

2005 

2010 

Thorium Inventory (kilograms)

0

200

400

600

800

1000
Low Inventory @ Minimal Locations

SRS Thorium Inventory, 1972-2007 (kg) (partial)

Year 773A 723A 235-F 772-F 

Lab

M 

Area

777

M 

217-A 

Storage

100-K 

Basin

100-L 

Basin RBOF

1973 154 --- 0 --- 57 6 0 52 --- 6679

1974 104 --- --- --- --- --- --- 52 ---

1975 104 1 1 1 43 5 --- 52 --- 6757

1976 89 1 1 1 41 2 0 52 --- 6757

1977 85 1 1 1 25 2 0 52 --- 8329

1978 57 --- 4 4 25 2 0 52 --- 8729

1979 83 --- 4 4 31 2 0 52 --- 8729

1980 109 --- 5 5 31 --- 8.0 52 3 8726

1981 111 --- 4 4 23 --- 0 55 3 8726

1982 86 --- 4 4 23 --- 0 55 3 8726

1983 33 --- 4 2 --- 0 55 3 8726

1984 22 --- 4 1 2 --- --- 55 3 8726

1985 18 --- 4 1 2 --- --- 55 3 8726

1986 5 --- 4 1 2 --- --- 52 3 8726

1987 5 --- 4 1 2 --- --- 52 3 8726
Minimal Locations

Year

1980 

1990 

2000 

2010 

Thorium Inventory 

without stored spent fuel (kilograms)

0

200

400

600

800

1000

All non-storage areas

773-A
Process Knowledge

Savannah River Laboratory 773A

 1972 - Alpha Material Laboratory used thorium 

oxide as a surrogate for Pu-238 testing in glove 

boxes

 1973 – Gram quantities of thorium dioxide 

shards were used in 773A hot cells to test vapor 

deposition

 1977-1980 Alternate Fuel Cycle Technology 

Program (AFCT) and Thorium Fuel Cycle 

Technology Program (TFCT) – several research 

projects
Process Knowledge

Savannah River Laboratory 773A-cont.

 Multiple AFCT/TFCT studies

 Mechanical grinding of ThO2 in high level caves 

 Study on effects of heat treatment on thorium oxide

 Testing on conceptual THOREX flowsheets of Elk River 

fuel in high level caves

 Analysis of off gassing of spent thorium fuel (Elk River 

Fuel – high level caves)

 Hanford prepared (encapsulated) 30 fuel rods with 

80%ThO2 – 20%UO2 for irradiation at SRS. SRS 

received rods in 1979 and stored them in a cage in 

773A. The program was cancelled in May 1980 before 

they could be irradiated.
Process Knowledge - Other

 Pu-238 Fuel Form Facility (1980)

 Thorium used as a surrogate for some of the work 

performed in the hot cells of the PuFF. Also used as a 

doping agent of the iridium welding agents 

 Galileo Project (1987)

 Thorium used as a surrogate for plutonium during 

process testing

 Defense Waste Stabilization (1990-2010) 

 Thorium used as a surrogate for plutonium and other 

radionuclides to test methods for defense waste 

stabilization and immobilization 
Radiological Controls 1972-1989

 Special Hazards Bulletins and DPSOP-40 

Savannah River Plant Radiation and 

Contamination Control and DPST-RH Radiation 

Hazards Technical Standards covered:

1. Work in regulated areas

2. Investigating radiation and contamination incidents

3. Protective clothing

4. Injury in regulated areas

5. Disposal of contaminated waste

6. Fires in regulated areas

7. Radiation exposure control
Alternate Bioassay data

 A large number of workers in 773A were 

monitored for Am, Cm, Cf

 Review of the bioassay method during 

development of the co-worker model for Am, 

Cm, Cf revealed that thorium would come 

through in the analysis and the alpha emissions 

would be counted as if it were Am, Cf, Cm 
Alternate Bioassay data – cont.

FE Butler and RM Hall, Analytical Chemistry Vol 42, No 

9 pp. 1073-1076 (1970)

A procedure was developed for sequential extraction 

of plutonium, neptunium, and uranium with triisooctylamine (TIOA), followed by extraction of 

thorium, americium, curium, berkelium, californium, 

and einsteinium with bidentate. Compared with 

previous methods, the new procedure is simpler, 

requires less analysis time, and gives better recovery. 

The recovery of Am-Cm-Cf from 250 ml of urine or 20 

grams of feces was 90%. 
Alternate Bioassay data – cont.

All alpha emitting actinides from thorium through 

einsteinium extract, indicating an excellent gross alpha 

analytical procedure. The data show that in analysis of 

americium, curium, and californium any contaminating 

plutonium, neptunium, or uranium must be removed. 

At this laboratory, thorium, berkelium, and einsteinium 

are not present in biological samples in sufficient 

quantities to require separation or routine 

identification by alpha spectrometry.
Alternate Bioassay data

 No effort was made by the lab to remove the 

thorium contaminant from the urine sample

 Why?

 Activities were much lower

 Not viewed as a significant contaminant

 Thorium used as a surrogate because it was less 

hazardous than plutonium (i.e. safer to use)

 Effectively we have alpha urine bioassay sample 

that doesn’t contain plutonium, uranium, or 

neptunium, but does contain Th, Am, Cm, Cf, Es, Bk
Bioassay 

Control

 DPSOL 193-302 

 Rev. 5 (1971)
Bioassay Control - Construction

DPSOL 193-302 (Rev 5. 1971)
Bioassay Control Procedure Revision
Bioassay 

Control

 DPSOL 193-302 

 Rev. 8 (1978)

 DPSOL 193-302T 

 Rev. 0 (1985)

 DPSOL 193-211 

 Rev. 0 (1989)
Bioassay 

Control – 773A

 Minimum Potential – A 

 Analytical Chemistry, 

High Level Caves, 

Radiation Control, 

Building Services, 

Maintenance - CT

 Reactor Eng. - AEL 

 Clerical and Supervisory 

Personnel - B 

 Maximum Potential -

CFLU

DPSOL 193-302T (Rev 0 1985)
Bioassay Control - Construction

DPSOL 193-302T (Rev 0 1985)
Bioassay Control Summary

 Monitoring prescribed by work area

 Monitoring frequency is based on potential for 

exposure 

 Construction Workers covered under Job Plans
Dose Reconstruction Methodology

 NIOSH proposed to use the Am/Cm/Cf/Th

bioassay results to reconstruct thorium doses

 Given a particular cancer, NIOSH will use the 

radionuclide (Am, Cm, Cf, or Th) that results in 

the highest dose to the organ of interest
Example Dose Reconstruction

Radionuclide Bone Kidney Lung Prostate Skin

Am 18.960 0.146 0.814 0.021 0.021

Cm 15.240 0.132 0.971 0.016 0.016

Cf 36.580 0.005 3.688 0.009 0.002

Th M (total) 37.67 0.755 3.852 0.077 0.077

Th-228 3.071 0.080 1.390 0.008 0.008

Th-232 34.590 0.674 0.729 0.069 0.069

Th S (total) 37.944 0.279 16.390 0.034 0.033

Th-228 0.312* 0.009* 5.282* 0.001* 0.001*

Th-232 6.416* 0.147* 7.961* 0.015* 0.014*

Am 16.180 0.123* 0.695 0.018* 0.018*

Cm 13.000 0.111 0.823 0.014 0.014

Cf 31.22* 0.003 3.147* 0.007 0.002

Summary of Thorium and Trivalent Actinides Doses (1985–1989)

The table below outlines the doses for each organ of concern. The highest dose of the five 

(americium, curium, californium, thorium Type M, and thorium Type S) was used for dose 

assignment. Thorium M (including thorium-228 and thorium-232) resulted in the highest 

dose to the bone, kidney, prostate, and skin. Thorium S (including thorium-228, thorium-232, 

and californium-252) resulted in the highest dose to the lung.

Note: Bold characters indicate the dose used in the dose assignment (either Th M total or Th S total). 

*Indication of which options were used in the Th S dose total (highest dose of Am or Cm or Cf). 

Summary of Am/Cm/Cf/Th Dose
Am/Cm/Cf/Th Bioassay Comparison

 ORAUT-RPRT-0055: A Comparison of Exotic 

Trivalent Radionuclide Co-worker Models at the 

Savannah River Site

 Comparison is being reviewed by SEC Workgroup

 Three Co-worker Models Developed:

 Construction Trades Workers (CTW) Coworker Model

 Non-Construction Trades Workers (nCTW) Coworker 

Model

 Non-Construction Trades + unknowns (nCTW+unk) 

Co-worker Model
Am/Cm/Cf/Th Bioassay Results

Period AMW CTW nCTW nCTW +unk

Total OPOS Total OPOS Total OPOS Total OPOS

1970 1,955 567 328 124 1,593 451 1,627 461

1971 1,856 663 292 107 1,545 550 1,564 559

1972 1,565 650 208 109 1,312 525 1,357 541

1973 1,249 644 243 115 969 509 1,006 530

1974 1,067 456 162 86 876 357 905 371

1975 831 467 173 94 628 356 658 375

1976 695 450 148 90 523 346 547 360

1977 478 383 87 68 368 292 391 315

1978 306 228 66 49 232 171 240 179

1979 441 322 79 67 337 234 362 255

1980 253 230 44 42 198 178 209 188

1981 341 267

80 44 524 379 586 422

1982 325 307

1983 330 303 41 39 255 232 289 264

1984 347 275 63 20 234 210 284 255

1985 340 259 42 24 266 214 298 235

1986 399 273 101 26 253 219 298 247

1987 379 305

65 25 598 336 656 371

1988–1989 342 288
Worker and Bioassay Proportions

Year # nonCTW+unks # CTWs Population ratio Bioassay ratio 

1973 5,255 500 0.10 0.22 

1974 5,205 600 0.12 0.23 

1975 5,140 973 0.19 0.25 

1976 5,407 995 0.18 0.25 

1977 5,598 1,344 0.24 0.22 

1978 5,944 1,973 0.33 0.27 

1979 5,709 1,958 0.34 0.26 

1980 6,050 1,991 0.33 0.22 

1981 6,593 2,159 0.33 0.10
Am/Cm/Cf/Th - OPOS Test Results

Period CTW:nCTW CTW:nCTW+unknowns 

Peto-Prentice Holm cutoff Peto-Prentice Holm cutoff

1970 0.9815 0.05 0.8923 0.025 

1971 0.806 0.0125 0.813 0.0125 

1972 0.7692 0.01 0.7053 0.01 

1973 0.3314 0.005 0.3383 0.005 

1974 0.8536 0.0167 0.8684 0.0167 

1975 0.5771 0.0071 0.5465 0.0071 

1976 0.2562 0.0042 0.3021 0.0045 

1977 0.3587 0.0062 0.4499 0.0062 

1978 0.2401 0.0038 0.2186 0.0038 

1979 0.9295 0.025 0.9082 0.05 

1980 0.276 0.0045 0.2646 0.0042 

1981–1982 0.0243 0.0029 0.0315 0.0029 

1983 0.0129 0.0028 0.0074 0.0028 

1984 0.1263 0.0031 0.0930 0.0031 

1985 0.0006 0.0026 0.0005 0.0026 

1986 0.1268 0.0033 0.1782 0.0033 

1987–1989 0.6796 0.0083 0.6796 0.0083 

Significance p<0.05 and Peto-Prentice < Holm cutoff
Am/Cm/Cf/Th Coworker Model
Construction Trades Workers

 Am/Cm/Cf/Th Bioassay Samples (1972-1989) 

 Construction Trades Workers – 1602

 Non-Construction Trades Workers – 7573

 Unknown occupation – 422

 Recall construction trades workers were 

monitored based on Job Plans

 If Construction trades workers were never 

monitored then we would not have 1602 

bioassay samples
Thorium (1990-2007)

 Originally proposed use of Whole Body Counts to bound 

thorium Exposures

 Although bounding, the assignment of WBC missed dose 

would result in some significant doses in the modern era 

that we just don’t believe occurred given the radiological 

controls in place at the time

 NIOSH proposes using an air sample concentration of 

2e-13 uCi/cc as a maximum potential exposure 

 10% of the Plutonium DAC that was used as the cut point for 

respiratory protection
Thorium Inventory post - 1986

Year 773A 235-F 772-F M Area 100-K Basin 100-L Basin RBOF 

1987 5 4 1 2 52 3 8726 

1988 17 4 1 2 52 3 8726 

1989 42 4 1 2 52 3 8726 

1990 207 4 1 2 52 3 8726 

1991 208 4 1 2 52 3 8726 

1992 206 4 1 2 52 3 8726 

1993 167 5 1 --- 52 3 8727 

1994 170 5 1 --- 52 3 8727 

1995 170 5 --- --- 52 3 8730 

1996 170 5 --- --- 52 3 8730 

1997 171 4 --- --- 52 3 8730 

1998 175 4 --- --- 52 3 8730 

1999 175 --- --- --- 52 3 8730 

2000 286 --- --- --- 52 3 8730 

2001 286 --- --- --- 52 3 8730 

2002 399 --- --- --- 52 3 8730 

2003 299 --- --- --- 52 3 8730 

2004 8 --- --- --- 52 3 8730 

2005 7 --- --- --- 52 8785 ---

2006 4 --- --- --- --- 8968 ---

2007 4 --- --- --- --- 8968 ---

Kilograms of thorium
Thorium Volume and Activity

 Mass 

 200 kg = 20.0 mCi

 Small Volume

 200 kg = approximately ten 

2L bottles of ThO2 

 773-A is a fairly large 

building 

 Small volumetric source 

term 
Thorium (post 1990)

 Based on NIOSH’s review, the primary work 

involving thorium during the 1990s was defense 

waste processing research

 Thorium was used as a surrogate in place of 

plutonium and other actinides for vitrification 

research

Ramsey et al. (1994)
Research Examples (post 1990)
Research Examples (post 1990)
Research Examples (post 1990)
Thorium Handling Procedure
Radiological Control Program

 Three Components

 Radiation Survey Logsheets (RSL)

 Daily, Weekly, Monthly, Quarterly

 Air Sample Logsheets (ASL)

 Daily, Weekly

 <2% DAC

 <10% DAC

 Radiological Work Permit (RWP) System

ESH-HPT-2000-00064
773A Radiation Survey Logsheets 
773A - Contamination Surveys
773A Radiation Survey Logsheet
773A Radiation Survey Logsheets
773A Radiation Survey Logsheets
773A Air Monitoring (Weekly)

A somewhat illegible image of an SRS 

Filter Paper Analysis for Building 773A.
773A - Air Monitoring (Weekly)

 Sample Data

 Start: 7/5/1995 8:00

 Stop time: 7/11/95 9:25

 Average (cfm): 4.4

Sample Information Alpha Analysis 

Loc # 

Carrier 

No.

DAC 

Loc 

Location 

ID

Activity 

uCi/cc Flags

MDA

uCi/cc

Decay 

Hours

Cp 

uCi/cc DAC Completion TOD

A773F133 33 10% C-114 3.16E-13 8.71E-15 - - 0.158 7/11/95 13:59

A773F133 33 10% C-114 - 1.12E-14 19.0 1.96E-14 0.010 7/12/95 8:59

Initial

24 Hour

Initial

24 Hour
773A Lab 

C-114 

Evaluation
Radiological Work Permits (RWP)

 RWP Program implemented in 1991

 Official Use Only - (Personal Privacy Data)

 Section 1 – Requestor

 Task to be performed and location

 Section 2 - Radiological Control Operations

 Monitoring requirements

 Section 3 - Approvals 

 RWP Sign in sheets contain:

 RWP number, Name, SSN, Dept./Craft, Work 

location, Time in, Time out
RSL, ASL, RWPs Availability

 NIOSH has only collected a few examples

 RSL, ASL, and RWP are typically filed together through 

2003 time frame

 In EDWS two records sets have been identified

 QH Series - 2695 records/boxes

 QR Series - 7651 records/boxes

 Within QR series QR600 pertains to SRTC (773A)

 SRTC = 407 records/boxes

 Some records/boxes contain 200 pages (folder)

 Some records/boxes contain 2500 pages (box)
Example Dose Reconstruction

 Assign intakes based on 2E-13 uCi/cc air concentration if 

the worker was assigned to 773A

Description Thorium M Thorium S

Bone 5.617 0.395

Kidney 0.119 0.009

Lung 0.173 0.694

Prostate 0.010 0.001

Skin 0.010 0.001

Thorium Dose (1990-1997)

The thorium exposure and intake for this period were based on 10% of the 

plutonium derived air concentration (DAC) of 2.0 E-12 microcuries per cubic 

centimeter, a breathing rate of 1.2 cubic meters per hour and a 2000 hour work year. 

The resultant annual inhalation intake rate for thorium was 1070 dpm per year. In 

addition, ingestion intake rate of 22.2 dpm per year was considered in accordance 

with Technical Information Bulletin: Estimation of Ingestion Intakes. The thorium 

dose was based on the assumption of 100% Th-232 as the most claimant-favorable 

radionuclide.

Bold characters indicate the dose used in the dose assignment (either Th M total or Th S total).

Missed Thorium Dose (Based on 10% Pu DAC)
Summary

 Most thorium onsite was waste/storage (>95%)

 Encapsulated

 Very low unencapsulated inventory (source term) 

 More thorium inventory in 1990s and 2000s than 1970s 

and 1980s

 Minimal use in certain defined locations

 Mostly 773-A (especially post 1983)

 Knowledge of the processes

 AFCT/TFCT (1977-1980) - interviews gram quantities

 Mostly used as a surrogate in post 1990 for DWPF
Summary – cont.

 Radiological controls

 Procedures in place, Routine monitoring (Daily, Weekly) 

of the workplace

 Survey data and air monitoring data available 

electronically in pdf format

 1972-1989 Alternate bioassay data

 Am, Cm, Cf bioassay was effectively gross alpha analysis 

that included thorium

 Doses are reasonable

 1990-2007 Compliant Radiological Control Program

 Air controlled to <2.0 E-13 uCi/cc

 Doses are low