Savannah River Site

Special Exposure Cohort 

Petition Evaluation Report

Addendum #2 – Thorium

Timothy D. Taulbee, Ph.D., CHP

Research Health Scientist

National Institute for Occupational Safety and Health

Division of Compensation Analysis and Support

August 2011

Richland, WA
Petition Overview

 November 2007: Petition received

 December 2008: Evaluation Report presented to 

the Advisory Board

 May 2010: Evaluation Report Addendum –

Thorium presented to SRS Work Group

 January 2011: Work Group/SCA 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

 SRS update on priority issues—thorium 

• Discussed the isotope development and production 

process

 Laboratory research

 Semi-works

 Fuel target fabrication

 Reactor irradiation

 Chemical separations
Recommendation to the Advisory Board

 A class be added to the Special Exposure Cohort 

based on internal thorium exposures in 773A 

and the TNX facilities 

 Class definition based on external monitoring

• Workers likely exposed

• Workers who may have been exposed

• Workers who were not exposed 
Thorium Research and Development

 Lab work (700A)

 Semi-works (CMX/TNX)

 Fuel and target 

fabrication (300)

 Reactor irradiation (100)

 Chemical separations 

(200)

 Heavy water production 

(400)
Thorium Work at SRS

 Dose reconstruction methods for 300 area

• Potential for internal exposure, but dose 

reconstruction method can bound the dose

 Encapsulated = no internal exposure potential

 Unencapsulated = potential for internal exposure
Year

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

100 Area - Reactors

235F - Support facility

200H - Canyon

300M - Target Fabrication

400D - Heavy Water

700A - Savannah River Laboratory

CMX - Reactor Semi-works

TNX - Separations Semi-works

777M - Physics Lab 

Central Shops (CS)

B Area - HWCTR

Thorium Dose Reconstruction

Dose Reconstruction Method

Encapsulated thorium

Unencapsulated thorium L M H

Thorium not present

Thorium not present, however, construction trades could have worked in any area
Additional Research Conducted

 Reviewed

• Inventory reports

• Monthly technical reports

• Health Physics Logbooks (773A & CMX/TNX)

 Conducted interviews

 Other areas

• Savannah River Laboratory (773A)

• Semi-works plants (CMX/TNX)

• Burial grounds

• Separations area (200H)
Savannah River Laboratory 773A

 Generally research in SRL 

was with small quantities 

of thorium

 A report indicating center 

sections cut from 12 

irradiated slugs using an 

underwater saw.

• Sections dissolved and two 

8 mL samples were 

analyzed 

Dry box for the electrolysis of thorium 

compounds (DPST-55-388, SRDB: 70791)

(DPST-55-412, SRDB: 94565)
Savannah River Laboratory 773A—cont.

 Exception was the metal fabrication lab

• D wing or Part III of SRL

 Intense research activities 1953 into 1957 and 

then, they appear to stop

• Neptunium research began using thorium as a 

surrogate starting in 1959

 Research picked back up in the mid 1960s and 

continued until 1971
Savannah River Laboratory 773A—cont.
Savannah River Laboratory 773A—cont.

 Active radiological protection program

• Routine surveys of corridors

—Most indicated “no contamination detected”

• Documented “spills” and incidents

—One spill indicated 37cpm highest smearable

—Others spills several thousand cpm

• Routine surveys of special work and materials leaving 

the building

 Researchers conduct of operations

• Sometimes less than formal and documented by 

Radiation Control Technicians
Savannah River Laboratory 773A—cont.

 Bioassay data

• 1956 only

• 225 samples for 175 workers

• Indication in logbook of beginning to compile list of 

workers who ever worked with thorium

 Air sampling

• Not breathing zone representative (interviews)

• Could not locate significant air sample data

—Apparently different recording practice for the technical area as 

opposed to production areas
Savannah River Laboratory 773A—cont.

 Smear data

• Data available in Health Physics logbooks

• Tremendous effort to locate all logbooks, code all of the 

data to develop an exposure model

• Not clear where routine samples were taken within the 

labs—some samples indicate edge of hood, but others 

do not indicate location 

• Most (not all) routine data stated as “no contamination 

detected” with no further information

• After the analysis, still not sure exposure model would 

be reasonable
Savannah River Laboratory 773A—cont.

 Source-term (modeling)

• Different chemical and physical forms in every 

laboratory and within laboratory

• Constant movement of material between laboratories

• Cannot place people in specific laboratories (especially 

construction workers)
Semi-Works (TNX)

Swanson, 2006
Semi-Works (TNX)—cont.

 Scaled up dissolving experiments from lab scale 

to semi-production scale

 Inventories indicate intermittent work with 

thorium 

• August 1954 – December 1956

• September 1964 – December 1969

 Inventories indicate significant quantities of 

thorium (few tons)

• Some information about quantity of material in 

dissolvers (few tons)
Semi-Works (TNX)—cont.

 Internal radiation monitoring data

• No bioassay although some of the workers moved 

between 773A and TNX

• No air sample data located for TNX

• Health Physics logbooks similar to 773A

—Surveys note levels but not exact locations 

• Source-term data

—Similar issues to 773A but not as complex
Burial Grounds

 Material going to burial grounds was surveyed 

for contamination

 300 area radiation survey log sheets

 773A Health Physics logbooks

 TNX Health Physics logbooks

 High level cave waste was encapsulated in 

concrete and sent to burial ground
200H Separations

 Uranium-233 was the product

 Due to extremely high photon dose rate (R/hr), 

minimal potential for internal exposure

 Wet process dissolving irradiated thorium in canyons

 Transfer from hold-up tank to railroad cars

 Rail cars equipped with filters to prevent particulate 

contamination during filling and thermal expansion

 Due to high photon dose rate, rail cars were roped 

off and inspected via binoculars for leaks
NIOSH Proposed Class

All externally monitored employees of the Department of Energy, its 

predecessor agencies, and their contractors and subcontractors who 

worked at the Savannah River Site from January 1, 1953 through 

December 31, 1957, and whose records have dosimetry codes A, G, 

CMX, or TNX; and all externally monitored employees of the 

Department of Energy, its predecessor agencies, and their contractors 

and subcontractors who worked at the Savannah River Site from 

January 1, 1958 through September 30, 1972, and whose records have 

dosimetry codes 5A, 5C, 6B through 6Z, 12D through 12H, or 12J 

through 12Z for a number of work days aggregating at least 250 work 

days, occurring either solely under this employment or in combination 

with work days within the parameters established for one or more 

other classes of employees included in the Special Exposure Cohort.
Thorium Feasibility Summary 53-57

Function Area 

Designation

HP Area 

Code

Unencapsulated 

Thorium

Encapsulated 

Thorium

Inclusion 

in SEC

Separations 200F F No No No

200H H No No No

Manufacturing 300M M Yes Yes No

Heavy Water 400D D No No No

Laboratory 773A A Yes Yes Yes

Physics Lab 777M M Yes Yes No

Semi-works CMX/TNX A,G,CNX,TNX Yes Yes Yes

A Area support A Yes

Reactors 100R R No Yes No

100P P No Yes No

100L L No Yes No

100K K No Yes No

100C C No Yes No

Central Shops CS G Yes
Thorium Feasibility Summary 58-72

Function Area 

Designation

HP Area 

Code

Unencapsulated 

Thorium

Encapsulated 

Thorium

Inclusion in 

SEC

Separations 200F 1A No Yes No

200H 2A Yes Yes No

Manufacturing 300M 3A Yes Yes No

Heavy Water 400D 4A No No No

Laboratory 773A 5A Yes Yes Yes

Physics Lab 777M 5B Yes Yes No

Semi-works CMX/TNX 5C Yes Yes Yes

A Area support 6B-6Z Yes

Reactors 100R 7A No Yes No

100P 8A No Yes No

100L 9A No Yes No

100K 10A No Yes No

100C 11A No Yes No

Central Shops CS 12D-12H

12J-12Z

Yes
Recommendation to the Board

 All workers had to wear a dosimeter to enter a 

regulated area (radiation area)

 Class definition based on external monitoring

• Workers likely exposed

1953-1957 Dosimeter Codes = A, CMX, TNX

1958-Sept. 1972 Dosimeter Codes = 5A, 5C

• Workers who may have been exposed

1953-1957 Dosimeter Codes = G

1958-Sept. 1972 Dosimeter Codes = 6B-6Z, 12D-12H, 12J-12Z

• Workers who were not exposed 

All other dosimeter codes 
SEC End-Date Determination

 Major drop in thorium inventory

• 773A less than 225 kilograms

• TNX no inventory after June 1969

 End-date coincides with D&D of 300M area 

thorium oxide room signifying end of production 

and effectively research

 Whole body count information more readily 

available after 1971
Thorium Inventory

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
Whole Body Count Data

Year

1960 1965 1970 1975 1980 1985

# of Whole Body Counts in NOCTS

0

20

40

60

80

100

120

140
Feasibility Summary

Feasibility Findings for SEC-00103 (Thorium)

Source of Exposure

Dose 

Reconstruction 

Feasible

Dose Reconstruction 

NOT Feasible

Internal

- Thorium

(1953 – 1957) A,G,TNX,CMX

(1958 – Sept 1972) 5A, 5C

6B-6Z & 12C-12H & 12J-12Z 

X

External

- Beta-Gamma X

- Neutron X

- Occupational Medical 

X-ray

X
Health Endangerment

 The evidence reviewed in this evaluation 

indicates that some workers in the class may 

have accumulated chronic radiation exposures 

through intakes of thorium.

 Consequently, NIOSH is specifying that health 

may have been endangered for those workers 

covered by this evaluation who were employed 

for a number of work days aggregating at least 

250 work days within the parameters 

established for this class or in combination with 

work days within the parameters established for 

one or more other classes of employees in the 

SEC.
Recommendation

 For the period January 1, 1953 through 

September 30, 1972, NIOSH finds that radiation 

dose from exposure to thorium in 773A and TNX 

facilities cannot be reconstructed for 

compensation purposes

Class Feasibility Health 

Endangerment

January 1, 1953 –

September 30, 1972 No Yes