Department of Health and Human Services

Centers for Disease Control and Prevention

National Institute for Occupational Safety and Health

De Soto Avenue Facility

SEC-00246

Lara Hughes, PhD, CHP

Health Physicist

Division of Compensation Analysis and Support

Advisory Board on Radiation and Worker Health, 124th meeting

Providence, RI

August 23, 2018
Department of Health and Human Services

Centers for Disease Control and Prevention

National Institute for Occupational Safety and Health

Previous related SEC classes

Petition NIOSH recommended SEC class

SEC-00093 All covered employees, all areas of Area IV SSFL, Jan. 1, 1955 - Dec. 31, 1958

- based on lack of internal monitoring pre-1959

SEC-00156 All covered employees, all areas of Area IV SSFL, Jan. 1, 1959 – Dec. 31, 1964

- based incomplete bioassay data available to NIOSH pre-1965

SEC-00168

All covered employees, all areas of the DeSoto Avenue Facility from January 1, 1959 through 

December 31, 1964

- Based on incomplete bioassay data available to NIOSH pre-1964

SEC-00234 All covered employees, all areas of Area IV, SSFL, Jan. 1, 1965 – Dec. 31, 1988

- based on insufficient data to assess intakes from thorium and americium

SEC-00235 None (NIOSH evaluated Area IV, 1992-1994 for SSFL Area IV)

SEC-00246 None (Current De Soto evaluation)
Department of Health and Human Services

Centers for Disease Control and Prevention

National Institute for Occupational Safety and Health

SEC-00246 Petition

• Petition received December 13, 2017

• Additional supporting documents received February 27 and March 29, 2018

• Requested class: All workers who worked at the De Soto Avenue Facility in 

Los Angeles County, CA during the period from January 1, 1965 through 

December 31, 1995.

• Petition qualified on March 1, 2018

• No modification to petitioner requested class

• Evaluation Report sent to ABRWH: July 5, 2018 (within 180 day 

timeframe)

• NIOSH recommended class to be added to SEC: None
Department of Health and Human Services

Centers for Disease Control and Prevention

National Institute for Occupational Safety and Health

De Soto Facility - Petition Concerns

• SEC-00234: Th and Am exposures cannot be reconstructed at Area IV

• Area IV and De Soto Avenue operated under the same H&S oversight

• Petition states americium and thorium were used at De Soto 

• SRE

• TRUMP-S

• SNAP

• Thorium fabrication work 

• Controls for Environmental Pollution bioassay contractor (1992-1994)
Department of Health and Human Services

Centers for Disease Control and Prevention

National Institute for Occupational Safety and Health

De Soto Facility Claims, July 2018

Total Number of claims submitted for DR 292

Total number of claims for workers who worked during the period 

from January 1, 1965 through December 31, 1995

255

Number of DRs completed for the evaluated period (submitted to 

DOL)

210

Number of claims with internal dosimetry records for the 

evaluated period

64

Number of claims with external dosimetry records for the 

evaluated period

104
Department of Health and Human Services

Centers for Disease Control and Prevention

National Institute for Occupational Safety and Health

De Soto Facility - Site Description

• Located at 8900 De Soto 

Avenue, Canoga Park, CA

• Covered Period 

• DOE 1959-1995

• Remediation 1998

• Two buildings involved in 

radiological work.

• Bldg. 001 - Fuel fabrication

• Bldg. 004 – R&D 

• Gamma Irradiation Facility (GIF)

• Helium Mass Spectrometry Lab

DeSoto

SSFL
Department of Health and Human Services

Centers for Disease Control and Prevention

National Institute for Occupational Safety and Health

Bldg. 

004

Bldg. 001

Bldg. 005

Bldg. 003

Bldg. 

002

De Soto Facility - Site Description – cont’d
Department of Health and Human Services

Centers for Disease Control and Prevention

National Institute for Occupational Safety and Health

De Soto Facility - Site History

• Facility constructed in 1959

• Headquarters of Atomics International (AI)

• DOE operations 1959-1995

• Engineering design and construction

• Nuclear fuel fabrication 1959 – 1983

• L-77 research reactor 1959 – October 1974 (fuel removed 1976)

• Gamma Irradiation Facility (operated 1966 – 1994)

• Helium Mass Spectrometer Lab

• Radiochemistry Support

• Space Nuclear Auxiliary Power (SNAP) program R&D 1955 - 1973
Department of Health and Human Services

Centers for Disease Control and Prevention

National Institute for Occupational Safety and Health

De Soto - End of Operations Timeline

• 1983 – Nuclear activities terminated except GIF and Mass Spec 

• 1984 – Nuclear areas decontaminated and released for 

unrestricted use (except GIF and Mass Spec Lab)

• 1994 – GIF ceases operations

• 1995 – Mass Spec Lab operations end in May

• 1998 – DOE remediation period, D&D of Mass Spec Lab and GIF
Department of Health and Human Services

Centers for Disease Control and Prevention

National Institute for Occupational Safety and Health

De Soto Facility-Information Resources

• Site Profile, Site Coworker Studies (Internal and External), and 

Procedures

• NIOSH Site Research Data Base: ~ 3143 documents for all 

SSFL/AI related sites

• Existing claimant files

• Data base entered from worker radiological file images

• Documentation provided by petitioner

• Interviews with former De Soto Avenue/SSFL employees
Department of Health and Human Services

Centers for Disease Control and Prevention

National Institute for Occupational Safety and Health

De Soto Facility - Americium

• Some instances of Am storage/shipping from vault

• Licensed for source fabrication

• No indication of americium fabrication or operational use

• Interviews confirmed no operational use of Am

• No occupational exposure data for Am

• Only Am use in commercial products (i.e. smoke detectors)
Department of Health and Human Services

Centers for Disease Control and Prevention

National Institute for Occupational Safety and Health

De Soto Facility - Thorium

• Fabrication ThO2 fuel simulant discs for transit capsule testing, May 

1970

• Post-test analysis transit capsule testing – Bldg. 001 Hot Shop, June 

1970

• Application for Thorium Oxide Material Users Permit (3/11/71)

• Aerospace Corporation (non-covered, off-site work)

• Machining thorium metal plates, Feb. 1979

• Bioassay and air data available for both operations

• Small scale process, names of involved personnel available
Department of Health and Human Services

Centers for Disease Control and Prevention

National Institute for Occupational Safety and Health

De Soto Facility - Petition Concerns

• SRE: only Th fuel for SRE was fabricated and stored at Area IV

• SNAP: De Soto did reactor/fuel R&D before reactor operations at Area IV, 

no used fuel handling

• TRUMP-S: no indication program was ever operational, received material 

in storage until shipped off site

• CEP primary vendor for urine sample analysis in 1992-1994

• Nuclear facilities D&D complete except GIF and Mass Spec Lab

• SEC-00235, for Area IV, found no impact on feasibility of DR due to 

discarding CEP associated data 
Department of Health and Human Services

Centers for Disease Control and Prevention

National Institute for Occupational Safety and Health

De Soto Facility - Internal Exposure

• Inhalation and Ingestion of radioactive contamination from unsealed 

materials from fuel production and radiochemistry operations

• De Soto internal exposure potential different from Area IV 

• Mostly uranium from fuel production 

• Uranium-Aluminide (UAlx) fuel production for ATR 

• Special DR methodology developed for UAlx workers

• Well documented exposure issue

• Thorium from episodic work in 1970 and 1979

• No indication of Americium exposure potential
Department of Health and Human Services

Centers for Disease Control and Prevention

National Institute for Occupational Safety and Health

Internal Monitoring Data

• Radiation workers in high contamination areas 

• Workers handling unencapsulated radiological materials 

• Special samples triggered by air sample results

• In vitro and in vivo routine monitoring of rad workers by job 

assignment

• De Soto Avenue had radiation protection procedures and the 

Rocketdyne Radiological Controls Manual

• Event/condition driven special sampling program
Department of Health and Human Services

Centers for Disease Control and Prevention

National Institute for Occupational Safety and Health

Thorium Dose Reconstruction

• 1970: production and post test analysis of simulated Th fuel disks 

• 1979: machining of Th metal discs (dose bounding operation)

• Limited containment and larger quantity

• 8 day operation

• Operational details and worker rosters available

• Baseline and post-work analyses for main operator (<MDA)

• Lapel air sample results

• Intakes can be calculated based on 8 day chronic intake for natural 

thorium using <0.99 μg/d urine sample result for machining operator

• Doses can be assigned for natural Thorium based on calculated intakes 

and solubility assumptions
Department of Health and Human Services

Centers for Disease Control and Prevention

National Institute for Occupational Safety and Health

De Soto - Feasibility Conclusion

• Fuel fabrication operations present no dose reconstruction 

infeasibility 

• Bioassay is generally available after 1965

• ORAUT-OTIB-0080 coworker available for potential 

unmonitored internal exposures

• No operational americium exposures identified

• Thorium campaigns in 1970 and 1979 have thorium-specific 

personnel and workplace monitoring and doses can be 

bounded

• Lack of CEP data does not affect NIOSH’s ability to perform 

sufficiently accurate internal dose reconstructions
Department of Health and Human Services

Centers for Disease Control and Prevention

National Institute for Occupational Safety and Health

De Soto Facility - Summary

Feasibility Findings for De Soto SEC-00246 after January 1, 1965

Source of Exposure Dose Reconstruction

Feasible

Internal

- all radionuclides X

External 

-Beta-Gamma X

- Neutron X

- Occupational Medical X-ray X