Savannah River Site Special Exposure 

Cohort Petition Evaluation 

Status Update

Timothy D. Taulbee, Ph.D., CHP

Research Health Scientist

NIOSH 

Division of Compensation Analysis and Support

April 29, 2014

Augusta, GA
Overview

 Key Issues being addressed

 Thorium: Oct 1972 - 2007

 Neptunium: 1972 – 1989

 Construction Worker 

Subcontractors monitoring data
Unencapsulated Thorium inventory 

not in basins (i.e Receiving Basin for Offsite Fuels (RBOF)

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
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
Process Knowledge

Savannah River Laboratory 773A

 Thorium used as a surrogate for multiple 

research efforts such as testing glove boxes, 

plutonium heat sources, and for waste 

vitrification studies.

 1977-1980 Alternate Fuel Cycle Technology 

Program (AFCT) and Thorium Fuel Cycle 

Technology Program (TFCT) – multiple research 

projects

 SC&A conducted interviews with workers in August 

2013 confirmed small quantities (gram) of thorium 

used
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 thorium 

were Am, Cf, Cm

 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

 Monitoring 

based on 

potential for 

exposure 

 DPSOL 193-302 

 Rev. 5 (1971)
Bioassay Control - Construction

DPSOL 193-302 (Rev 5. 1971)
Dose Reconstruction Methodology

1972-1989

 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
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
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 amongst 898 CTW workers
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 

which don’t seem possible given the radiological controls 

in place at the time nor the work being conducted

 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 Summary

 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 research
Summary – cont.

 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

 Radiological controls

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

of the workplace

 Survey data and air monitoring data available 

electronically in pdf format
Thorium – Status Update

 NIOSH is addressing SRS Workgroup concerns:

1. Use of 10% of Derived air concentration for 

1990-2007 time period

2. Compare bioassay of workers known to have 

worked with thorium to the co-worker model

3. Explain high variability observed in some 

Am/Cm/Cf/Th bioassay 

• Most are DTPA related and/or low sample volume 

due to known intake of another radionuclide (i.e. 

Plutonium)

4. Develop thoron exposure model
Neptunium Exposures at SRS

 Overall Goal was the production of Pu-238 

Np-237 (n, γ) Np-238  Pu-238

 Production: 

 1961 through July 1984

 Main Processes involving Np

• Manufacture Np-Al targets (200 and 300 area)

• Irradiate targets in reactors (100 area)

• Chemical Separation of 238Pu from Np (200 area)
Basic Neptunium Flow Diagram

Neptunium Nitrate

(221H – Canyon Frames)

Conversion to Np Oxide 

NpO2 (HB Line)

Np Oxide loaded into 

aluminum billets (235F)

Np-Al Billets Extruded 

into target tubes (321M)

Np-Al tubes irradiated in 

reactors (R, P, K, L, C)

Irradiated Np-Al tubes 

disolved & 238Pu and Np 

seperated in Canyons 

Frames (221H)
HB-Line Np Process

 Mission: Conversion of Np nitrate to Np oxide

 SRS Workgroup toured HB-Line in 2010

 Two main sources of Np nitrate (97%)*

• HM Process from enriched uranium (EU)

‒ Approx. 3-4 kg / month (23% of total)*

‒ Low plutonium contamination

• Frames – dissolving irradiated Mk-53 targets

‒ Approx. 8-10 kg / month (74% of total)*

‒ Significant plutonium contamination

 * ESH-HPT-96-117
Neptunium Billet Fabrication 235F
Neptunium Billet Glovebox Line

DPSPF 30200-6 (1980) 
Neptunium Billet Glovebox Line

Maintenance side of glovebox line

DPSPF 20355-1 (1976) DPSPF 30200-24 (1980)
235F Summary / Observations

 Relatively small glovebox line 

• (10s of workers not 100s)

 Regulated radiation area

• Supervisors – White Lab coat shoe covers

• Operators – White regulated clothing and neutron 

dosimeters

 Shadow shields due to high gamma dose rate

 Billets are bagged for transfer to 321M
235F Routine Air Monitoring
Radiological Controls - 235F

 Neptunium billets surveyed before transfer

• High gamma dose rate

• Neutron component is about 1%
321M Np Billet Extrusion

 Billet Extrusion Process

1. Bagged Billets are received

2. Billets are surveyed

3. Billets are helium leak checked

4. Billets are outgassed

5. Billets are preheated

6. Billets extruded into long thin tubes

7. Tubes are surveyed for shipment to reactors
321M Np Billet Survey - Example
321M Np Billet Extrusion

Bebbington (1990) History of DuPont at the Savannah River Plant
321M Np Billet Extrusion

Bebbington (1990) History of DuPont at the Savannah River Plant
321M Np Tube Survey - Example
Personnel Monitoring

 Dosimeters

• Must wear dosimeter in regulated areas

‒ Gamma dose rate was significant on Np Billet line and 321M

‒ Interviews indicate workforce swap-out

‒ Operators were required to wear neutron dosimeters

 Bioassay 

 DPSOL 193-302 Rev 7, 1976

 Np analysis are performed on samples from personnel 

designated by area Health Physics when Pu analysis are 

positive 

 DPSOL 193-302 Rev 8, 1978

• Np urinalysis routine for workers in 235F
Pu contamination in NpO2 

Report # NpO2 

(kg)

Minimum 

Pu wt%

Average 

Pu wt%

Maximum 

Pu wt%

# Billets 

made (235F)

# Tubes Extruded 

(321M)

SRDB #

DPSP-74-1-1 21.80 <0.05 0.16 0.60 5 12 72893

DPSP-74-1-2 4.84 0.18 0.36 0.53 7 12 72894

DPSP-74-1-3 12.65 0.02 0.18 0.42 5 0 72895

DPSP-74-1-4 5.25 0.01 0.03 0.06 4 14 72896

DPSP-74-1-5 2.25 0.25 0.28 0.32 0 0 72897
Why is Pu contamination important?

 Specific Activity

(alpha activity)

• Pu-238 = 17.1 Ci/g

• Np-237 = 0.00069 Ci/g

 NpO2 - Plutonium is the main hazard

 Requires ultra pure Np for it to dominate 

exposure 

Np wt% Pu wt% Pu : Np 

alpha ratio

99.5 0.5 125 : 1

99.9 0.1 25 : 1

99.95 0.05 12 : 1

99.99 0.01 2.5 : 1

99.995 0.005 1.2 : 1

99.999 0.001 0.25 : 1
Bioassay 

Control

 DPSOL 193-302 

• Rev. 5 (1971)
Bioassay Control Summary

 Monitoring prescribed by work area based on 

potential for exposure

 Monitoring frequency is based on potential for 

exposure 

 Post 1978 - Neptunium urine bioassay for 

highest exposure potential area 

 Neptunium billet line in 235F working with oxide
Neptunium Monitoring Data

Year Number of Samples by Area

 235-F HB Line 321M 773/772-F other

1972 20 

1973 16 1 

1974 17 1 

1975 

1976 

1977 

1978 

1979 1 

1980 36 8 3 2 

1981 3 2 9 3 2 

1982 36 32 6 3 1 

1983 12 4 7 2 

1984 23 5 16 4 

1985 7 2 3 2 

1986 

1987 

1988 5 5 16 4 

1989 3 9 2 

Total 178 50 41 49 15

 333 Np urine 

samples 

 Area frequency 

based on exposure 

potential

 Most samples are 

from 235F
Np Dose Reconstruction Methods

 At least four methods that NIOSH could use to 

develop a co-worker model in order to estimate 

Np exposures in the 1970 to 1990 timeframe: 

1. Use the limited bioassay (333 samples)

2. Ratio Np from the Pu bioassay given that the Pu 

activity is between 2-10 times greater than Np 

activity (best estimate for an epidemiology studies)

3. Interpolate between urine bioassay points between 

1969 and 1990 

4. Use whole body count data to develop co-worker 

model (most claimant favorable)
Np Co-worker Model and Bioassay
NIOSH Co-worker Model

 NIOSH chose to use whole body count 

information because:

• At the time NIOSH didn’t have complete information 

on the actual Pu:Np ratio (data has now been 

obtained)

• NIOSH has confirmed that workers in Np areas were 

required to have whole body counts

‒ Shift employees - 2/year

‒ Day employees - 1/year

• Np doses calculated using WBC (Whole Body Count) 

are claimant favorable upper bounds but not 

unreasonably high as to be insufficiently accurate 
NIOSH Co-worker Model

 50 year equivalent doses

Organ 50-Year Equivalent Dose (rem)

Urinary Bladder 0.352

Breast 0.352

Kidneys 0.958

Liver 4.280

Red Bone Marrow 10.300

Bone Surface 268.000

Stomach 0.352

Lung 6.920

Even the 268 rem / 50 years = approximately 5 rem / year
Np Co-worker Review Status

 Comparing workers with Np urinalysis and WBC 

to co-worker model

 Calculating the Np dose using Pu contamination 

in Np and compare to current Np co-worker 

model

 Researching potential construction trades 

worker exposures during new construction of 

the Plutonium Fuel Fabrication Facility (PuFF) in 

the mid 1970s
Np Co-worker Model Comparision

 34 workers both Np urinalysis and WBC data

Worker Cancer Number of Samples Dose (rem)

Urinalysis WBC Urinalysis WBC Co-worker

A Lung 24 9 0.374 3.383 7.099 

B Skin 8 24 0.005 0.080 0.197 

C Bladder 4 3 0.001 0.027 0.007 

D Skin 3 15 0.008 0.105 0.266 

E Prostate 5 27 0.009 0.209 0.235 
Subcontractor Records Status

 Reviewing NOCTS to identify Construction Trades 

Workers that worked for subcontractors (i.e. not 

DuPont Construction) to evaluate dosimetry 

record completeness

 This review also involves comparing electronic 

datasets HPAREA, FAYERWET, SRPABSTR, and 

SRSABSTRNIOSH to the original dosimetry printouts.
Questions?