Savannah River Site (SRS) 

Special Exposure Cohort (SEC)

Update on Priority Issues

Timothy D. Taulbee, PhD, CHP

Research Health Scientist 

National Institute for Occupational Safety and Health

Division of Compensation Analysis and Support

May 2011

St. Louis, MO
SRS Priority Issues

 Issue 1: Thorium 1953 – 1965: metal

 Issue 2: Thorium 1965 – 1971: oxide

 Exotic Radionuclides

• Issue 4: Trivalent (Am, Cm, Cf)

• Issue 5: Neptunium

• Issue 6: Mixed Fission Products

• Issue 7: Cobalt-60

• Issue 11: Other exotics (Po, Tm, Tl)
SRS Isotope Production

 Three step process:

1. Target manufacture 

• 300 Area or M area

2. Target irradiation

• 100 Area – reactors

3. Target chemical separation

• 200 Area – canyons
Target Manufacture

 Material

• Th metal pre 1965

• Th oxide post 1965

 Material Canning

• Onsite pre 1955

• Offsite 55-64 - Sylvania

• Onsite post 1964

 Target Inspection

• Pressure tests

• Radiography

• Smears
Target Irradiation

 Assembly

• Encapsulated thorium 

slugs loaded into 

assemblies

 Reactor

• Encapsulated thorium 

slugs irradiated for 

specified period

 Disassembly

• Encapsulated thorium 

slugs unloaded and 

allowed to cool in pool
Target Chemical Separation 

(pre 1964)

 Offsite – Oak Ridge

• Pre 1964: the 

encapsulated thorium 

slugs that had been 

irradiated were sent to 

ORNL

 Onsite – 700 area

• Some samples sent for 

lab analysis
Target Chemical Separation 

(post 1964)

 Onsite – 200 H Canyon

• First campaign (1964): 

Th treated as a waste 

product and slurry with 

mixed fission products 

sent to tank farms. 

• Later campaigns: Th 

recovered as ThNO3 and 

sent to Fernald
Target Chemical Separation—cont.

(post 1964)

 H Canyon

• Separate U-233 from 

thorium and mixed 

fission products

• U-233 ,which was the 

product, was sent to 

the B-Line

• Mixed Fission Products 

(MFP) sent to waste 

tanks (tank farms)

• Th recovered as ThNO3

and sent to Fernald
SEC Evaluation – Th Addendum

 Of the three steps in the U-233 production 

campaigns, NIOSH originally felt the exposures 

in the 300M Area were of greatest concern

• 300M Area – unencapsulated material

• 100 Areas – encapsulated material

• 200 Area

– Material not present until 1964

– After 1964, wet process and ThNO3 sent to 

Fernald for processing back to metal
Thorium Metal Dose Reconstruction 

Methodology for 300M Area

 Thorium canning AlSi

dipping method

 Other components of 

canning process

 Lathing

 Dipping

 Welding

 Inspection

Interior of canning building illustrating dip canning process, 

(SRS Archives 1956, SRDB 27540)
Thorium Metal Dose Reconstruction 

Methodology for 300M Area—cont. 

 Thorium canning process similar to uranium 

canning process

 After 1956, thorium was canned at Sylvania 

and finished/inspected in the 300M area

 Uranium bioassay available

 Since U-Th canning processes were similar

• Used uranium bioassay to determine the mass

intake of uranium

• Assumed equal mass intake of thorium and 

calculated dose
Thorium Slug Production

Year Number of 

Uranium Targets

Number of 

Thorium Targets

Thorium 

Fraction 

1953 200,000 321 0.0016

1954 500,000 1,726 0.0036

1955 1,200,000 26,618 0.0222

1956 2,700,000 0 0

1957 751,000 5,200 0.0069

1958 840,000 0 0

1959 1,600,000 0 0

1960 1,106,500 0 0

1961 725,100 417 0.0006

1962 955,000 14,000 0.0147

1963 404,825 16,500 0.0408

1964 286,900 9,600 0.0335
Thorium Oxide Dose Reconstruction 

Methodology for 300M Area 

 Powder form of thorium required vibration and 

compaction

 Different than metal process thus uranium 

bioassay was not useful

 Due to powder form, glovebox was used to can 

the thorium
Thorium Oxide Dose Reconstruction 

Methodology for 300M Area—cont. 

Worker at thorium 

glovebox containment 

(SRS Archives)

Thorium oxide glovebox containment 

structure (SRS Archives)
Thorium Oxide Dose Reconstruction 

Methodology for 300M Area—cont. 

Thorium oxide containment 

ventilation system HEPA filtration of thorium oxide 

containment
Thorium Oxide Dose Reconstruction 

Methodology for 300M Area—cont.
Thorium Oxide Dose Reconstruction 

Methodology for 300M Area—cont.

 Obtained air sample data in the room of 

thorium oxide manufacturing line (glovebox) 

 Confirmed through interviews with 

Radiological Control Technician that the air 

samples outside glovebox was breathing zone 

equivalent

 Based on air samples we calculated intakes and 

doses
Thorium Work in Other SRS Areas

 300M Area – predominant exposure potential

 Interviews with workers knowledgeable of the 

thorium operations indicated that Research and 

Development work was minor using only bench 

top type quantities

 SC&A finding (January 2011)

• NIOSH did not address thorium exposures in other 

areas
Thorium Work in Other SRS Areas—cont. 

 Data review at SRS in March 2011

• Material Accountability Ledgers (inventories)

 Found significant quantities of unencapsulated

thorium in the following areas

• 700A Area

• TNX Area
Thorium Research and Development 

(R&D)

 Apparently three 

steps to new 

processes:

1. Lab work (700)

2. Semi-works or 

pilot plant scaled 

up from Lab but 

below production

3. Full scale 

production
Thorium R&D in 700A Area

 700A Area – Savannah River Laboratory

• Memos discussing bench top thorium work in B-wing 

room 131 appears often

• Some Hanford irradiated thorium work in High Level 

Caves

• Metallurgical R&D Laboratory

– Known to have capability to manufacture full scale 

fuel and target assemblies

– Current belief that most thorium work in 700A area 

was conducted in this Lab
Thorium R&D in TNX Area

 TNX Area – Separations Semi-works

• Ledgers indicate intermittent work

– 1954-1956, and 1964-1968 timeframes

• 1964 -1968: work involves dissolving un-irradiated 

(normal) thorium slugs to test designs of separations 

process for the canyons

• Thorium separations building built in 1956 (677-G)

– Building was never put into operation

– Project was cancelled in 1956
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

Thorium not present

Thorium not present, however, construction trades could have worked in any area
Thorium Timeline

 Anticipate revised evaluation report addendum or 

83.14 for the Advisory Board’s consideration 

during August meeting

 NIOSH has conducted additional interviews with 

individuals knowledgeable about thorium 

research 

 Early to mid-June, data review to follow last 

thread on thorium at SRS
Thorium R&D Radiological Records

 700A Area – Savannah River Laboratory

• Identified a box of records labeled as follows

A Pu results Pu control Thorium Log 54-58

A A Area 

Pu results Plutonium bioassay results for A area 

Pu control Plutonium spikes and blanks for the A Area 

results 

Thorium Log A thorium bioassay logbook or air samples???

54-58 The data in the box covers 1954 through 1958
Exotic Radionuclides

 Recall: Construction Trades-based SEC Evaluation

 Generally there is less bioassay for construction 

trades workers compared to operations workers

 Concern has been raised as to whether co-worker 

models are applicable to construction trades 

workers due to difference in the nature of the 

work

• Potential for higher intensity

• Less frequent exposure
Exotic Radionuclides—cont.

 Use co-worker models to estimate dose to 

unmonitored workers

 Analysis Process (co-worker models)

• Develop All Monitored Workers (AMW) model

• Develop Construction Trades Worker (CTW) model

• Hypothesis test to compare the two models

– Tritium comparison completed in December 2010
Exotic Radionuclides—cont.

 Bioassay samples for Co-worker models for exotic 

radionuclides

• Am, Cm, Cf

– 13,189 urinalysis samples (1964 – 1980)

• Neptunium

– 3,012 urinalysis samples (1961-1980)

– + NOCTS Whole Body Counts

• Mixed Fission Products

– 49,061 urinalysis samples (1955-1980)

– + NOCTS Whole Body Counts
Exotic Radionuclides Concerns

 Insufficient data when only using NOCTS

 Resulted in the coding of all of the Am, Cm, Cf data

 All neptunium urinalysis data has been coded along 

with whole body count data from NOCTS to 

supplement

 Mixed Fission Product (MFP) evaluation underway 

 Coding work history information

 Initially used self report from NOCTS

 Currently using SRS work history cards
Issue #11 Timeline (Other Exotics)

 March 2011: Extracted exotic information from 

Savannah River Laboratory (SRL) monthly reports

 Selected excerpts from SRL monthly reports

• Currently undergoing classification review
Questions