Savannah River Site (SRS) Special Exposure 

Cohort Petition Evaluation Report

Addendum #3 – Thorium (post 1972)

Timothy D. Taulbee, Ph.D., CHP

Research Health Scientist

National Institute for Occupational Safety and Health

Division of Compensation Analysis and Support

December 2012

Knoxville, TN
Petition Overview

 November 2007: Petition received

 December 2008: Evaluation Report presented to 

the Advisory Board

 May 2010: Evaluation Report Addendum #1 –

Thorium presented to SRS Work Group

 January 2011: Work Group/Sanford Cohen & 

Associates comments received

• Significant Work Group finding: Potential thorium 

work in other areas not discussed in the Evaluation 

Report Addendum
Petition Overview—cont. 

 February 2011: SRS status update presented to 

the Advisory Board

 August 2011: In SRS Addendum #2, NIOSH 

recommended adding a class of thorium exposed 

workers in the 773-A and TNX to the SEC from 

January 1953 to October 1972 and proposed 

identifying the class based on dosimeter badge 

location

 August 2011: NIOSH indicated more research 

was needed for the post-Oct 1972 time period
Petition Overview—cont. 

 December 2011: Advisory Board partially 

concurred with NIOSH recommendation; 

however, recommended expansion of the class 

to include all workers at SRS

 March 2012: HHS Secretary added a class of all 

workers at SRS from January 1953 to October 

1972 to the SEC

 November 2012: NIOSH issued third addendum 

to the SEC petition evaluation report regarding 

thorium (to cover the time period October 1972 

through December 2007)
Recommendation to the Advisory Board

 NIOSH believes reconstruction of thorium 

exposures is feasible and that doses can be 

reconstructed with sufficient accuracy for 

compensation purposes from October 1972 

through December 2007

 How NIOSH reached this conclusion

• Very low inventory (source term)

• Minimal use in certain defined locations

• Knowledge of the processes

• Radiological controls

• Alternate bioassay data
Thorium Inventory 

(Presented in August 2011—Addendum #2)

Year

53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 

Thorium Inventory (kilograms)

0

20000

40000

60000

80000

100000

120000

140000
Additional SEC End Date Research

 Inventories indicate some small thorium work in 

later years

Year

73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 

Thorium in Production or Recieved

 (kilograms)

0

1000

2000

3000

4000

(Presented in August 2011—Addendum #2)
Additional NIOSH Research

 Reviewed

• Inventory reports (1972-2007)

• SRL and Works monthly technical reports

• Radiological surveys

• Evaluated

• Whole body count data

• Other bioassay methods

• Learned 

• Large spike of thorium work in 1977 that was 

reported in August 2011 was the receipt of spent 

thorium fuel in the receiving basin for offsite fuels 

(Receiving Basin for Offsite Fuels - RBOF)
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 
After Additional Review of Records

Year

1950 1955 

1960 

1965 

1970 

1975 

1980 

1985 

1990 

1995 

2000 

2005 

2010 

Thorium Inventory 

(kilograms)

0

20000

40000

60000

80000

100000

120000
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
Research vs. Waste and Storage

 Most of the thorium 

inventory was waste 

and storage

 Less than 1% of the 

thorium on site was 

available for 

potential exposure
Minimal Locations

Table 5-2: 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 154.01 ---2 0.03 --- 57.2 6.4 0.03 52.0 --- 66791

1974 104.0 --- --- --- --- --- --- 52.0 ---

1975 104.0 0.5 1.1 1.1 43.2 5.4 --- 52.0 --- 6757

1976 89.4 1.1 0.9 0.9 40.7 2.0 0.0 52.0 --- 6757

1977 85.4 1.1 0.9 0.9 25.4 2.0 0.0 52.0 --- 8329

1978 56.6 --- 4.0 4.0 25.2 2.1 0.0 52.0 --- 8729

1979 83.4 --- 4.0 4.0 31.1 2.1 0.0 52.0 --- 8729

1980 108.6 --- 4.5 4.5 31.1 --- 8.0 52.0 3.1 8726
Minimal Locations—cont. 

Year

1980 1990 

2000 

2010 

Thorium Inventory 

without stored spent fuel (kilograms)

0

200

400

600

800

1000

All non-storage areas

773-A
Thorium Nitrate

 Use of thorium nitrate is common in chemistry labs
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—cont. 

(Savannah River Laboratory 773A)

 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 (1995-2010)

• Thorium used as a surrogate for plutonium and other 

radionuclides to test methods for defense waste 

stabilization and immobilization 
Summary of Thorium Use

For more details please see Table 5-3

Year Operation Locations Average 

Inventory (kg)

Activity 

(millicuries)

1972- 1975 Storage, Surrogate 773A, M Area 

(storage) 158 15.8

1976 -1981 alternative fuels program, tritium 

studies, storage, surrogate

773A, 235-F, M 

Area (storage) 127 12.7

1982-1989 welding agent studies, storage, surrogate 773A, 235-F, M 

Area (storage) 38 3.8

1990-2003 defense waste research, storage, 

surrogate 773A, 235-F 224 22.4

2004-2007 defense waste research, storage, 

surrogate, D&D 773A 5 0.5
Radiological Controls (1972-1990)

 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

8. Internal radiation exposure control
 SRS implemented a new radiation control 

manual (WSRC-5Q) in 1991 to comply with DOE 

Order 5480.11, it was updated as follows to 

comply with:

• 1992 DOE Radiological Control Manual DOE N 5480.6

• 1994 DOE Radiological Control Manual DOE/EH-0256T

• 1995 Occupational Radiation Protection 10CFR835

Radiological Controls (1991-2007)
Other Radiological Information

 NIOSH has collected samples of contamination 

surveys in 773-A, M Area, 235-F, and TNX from 

1972 through 1988

 NIOSH has collected samples of air monitoring 

surveys from 773-A, 235F, and 244-F from 1972 

through 1988

 More contamination surveys and air sample 

results are available in electronic form 
Radionuclide Activities (1994)

Table 5-4: Radionuclide Activities

Isotope Inventory (g) SA (Ci/g) Activity (Ci)

Th-232 4.12E+07 1.10E-07 4.5

Np-237 6.90E+04 6.90E-04 47.6

U-233 1.34E+04 9.50E-03 126.8

Cf-252 2.50E-01 5.40E+02 135.1

Pu-239 5.13E+05 6.20E-02 31806.0

Am-241 7.23E+04 3.20E+00 231360.0

Cm-244 1.12E+04 8.20E+01 915940.0

Pu-238 1.49E+05 1.70E+01 2533000.0

Table includes waste that is not available for intake;

in 1994 only 0.0176 Ci were non-waste.
Alternate Bioassay Data

 A large number of workers in 773-A were 

monitored for Am, Cm, and Cf

 Review of the bioassay method during 

development of the co-worker model for Am, 

Cm, and Cf revealed that thorium would come 

through in the analysis and the alpha emissions 

would be counted as if it were Am, Cf, or 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.”
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 
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 does not contain plutonium, uranium, or 

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

and Bk
Alternate Bioassay Data—cont.

Year

1965 1970 1975 1980 1985 1990 1995 2000 2005

Alpha Activity Excretion (dpm/day)

0.0

0.2

0.4

0.6

0.8

1.0
Alternate Bioassay Data—cont. 

 How high are the doses (1972-1994)?

Estimated Organ Dose from Thorium (Intake: 1973-1994)

Material Type Lung Dose

(rem)

Bone Dose

(rem)

Type M 2.60 18.66

Type S 79.92 23.34
Whole Body Count Data

 In 1995, SRS started using Alpha Spectrometry 

(not gross alpha counts)

 Thorium was not one of the alpha energies 

evaluated

 Am, Cm, and Cf analysis only valid from 1972-

1994

 Must use Whole Body Count Data

• MDA for Th-232 = 0.15 nCi
Dose from Whole Body Count Data

Estimated Organ Dose from Thorium (1995-2007)

Material Type Lung Dose

(rem)

Bone Dose

(rem)

Type M 56.94 174.3

Type S 15.40 1.75

During the Radiological Controls from 10CFR835
Whole Body Count Data

 NIOSH has concluded that by this time period 

under 10 C.F.R. 835, people who should have 

been monitored were monitored

 NIOSH has also obtained lapel air sample data 

from 2004 when remediation work was 

conducted on a concrete pad that was 

contaminated with thorium
Summary

 Very low inventory (source-term)

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

and 1980s

• Most thorium on site was waste/storage

 Minimal use in certain defined locations

• Mostly 773-A (especially post-1983)

 Knowledge of the processes

• Mostly used as a surrogate

• Except for AFCT/TFCT (1977-1980)
Summary—cont.

 Radiological controls

• Procedures in place

• Routine monitoring of the workplace

• Survey data available

• Air monitoring data available

 Alternate bioassay data

• Am, Cm, and Cf bioassay was effectively gross alpha 

analysis that included thorium

• Doses are plausible
Feasibility Summary

Feasibility Findings for Savannah River Site 1972-2007

Source of Exposure

Dose Reconstruction 

Feasible

Dose Reconstruction NOT 

Feasible

Internal

 - Thorium X
Recommendation

 For the period October 1, 1972 through 

December 31, 2007, NIOSH finds that radiation 

dose from exposure to thorium can be 

reconstructed for compensation purposes

Class Feasibility Health Endangerment

October 1, 1972 –

December 31, 2007 Yes Yes