De Soto Facility 

SEC Petition-00246 

Preliminary Review

Presented by: 

Bob Barton, SC&A, Inc.

Meeting of the Advisory Board on Radiation and Worker Health

Redondo Beach, CA 

December 12–13, 2018
Introduction and Background SEC Petition-00246

 SEC-00246 for the De Soto Facility was submitted on December 13, 

2017, with the following proposed definition: 

“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.” 

 The rationale provided in the original position read as follows:

“NIOSH has determined it cannot reconstruct radiation dose for 

americium, thorium, or associated progeny at SSFL Area IV, 

1965–1988. Based on shared contractor and operational history, 

shared data limitations between SSFL Area IV/De Soto Facility, 

and the established presence of americium, thorium and 

associated progeny at De Soto Facility until at least 1995, the 

following petition is submitted.”

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Introduction and Background SEC Petition-00246 (cont.)

 March 1, 2018: SEC Petition-00246 qualifies for 

evaluation (Note: the evaluated class remained 

essentially unchanged from the original petition 

submission)

 July 3, 2018: NIOSH Releases the SEC Petition 

Evaluation Report (SEC ER)

 August 23, 2018: NIOSH presents the results of the SEC 

ER to the Advisory Board at Meeting 124 in Providence, 

RI

 Following discussions at the August Advisory Board 

meeting, SC&A was tasked with reviewing the main 

conclusions of the NIOSH SEC ER

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Introduction and Background SEC Petition-00246 (cont.)

 NIOSH SEC Evaluation contained two central conclusions:

 Americium exposure potential and dose reconstruction: “neither the 

documents available to NIOSH nor interviews with former workers revealed 

any history of fabrication of americium sources, or work with uncontained 

americium at the De Soto Avenue Facility. Contrasting previous NIOSH 

evaluations of radiological work at Area IV of SSFL, NIOSH has found no 

indication that De Soto had sources of americium associated with work 

processes.”

 Thorium exposure potential and dose reconstruction: “NIOSH has 

identified detailed documentation of thorium work episodes in 1970 and 1979, 

providing source term, operational procedures, radiological protection 

protocols, names of individual operators, and dates of work. NIOSH has 

concluded that thorium-grinding operations in 1979 represent the bounding 

thorium internal exposures at the De Soto Avenue Facility during the 

operational period (January 1, 1965 through December 31, 1995). As 

presented in Section 7.2.3.1, NIOSH has sufficient personnel bioassay data 

(including per-work and post-work urinalysis), and job performance data, to 

allow it to develop a bounding dose estimate for workers with potential 

thorium exposures during the period from January 1, 1965 through 

December 31, 1995.”

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SC&A Review Approach

 Review of relevant available documentation contained in the 

Site Research Database (SRDB) as well as documents 

supplied by CORE Advocacy for Nuclear and Aerospace 

Workers

 Evaluation of documented interviews with former workers at the 

De Soto Facility and a signed affidavit supplied by a former 

Health Physicist at De Soto

 Examination of a substantial portion of the claimant population 

with job classifications with the likely potential for involvement 

in radiological operations. Review included:

 Review of computer-aided telephone interviews (CATIs)

 Review of statements in Department of Labor case files (as 

appropriate)

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Relevant Available Documentation

 In addition to retrospective historical documentation, 

SC&A’s review focused on four primary document types:

1. Health Physics Logbooks

2. Tagged Area Entry Permits

3. Routine Contamination Surveys

4. Area Air Sampling Results/Personnel Air Sampling 

Results (lapel air samplers)

 SC&A observed significant temporal gaps for the primary 

documentation during the period under evaluation (SC&A 

Finding 1)

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Relevant Available Documentation (cont.)

Health Physics Logbooks Available by Year

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Relevant Available Documentation (cont.)

Tagged Area Entry Permits by Year

8
Relevant Available Documentation (cont.)

Routine Contamination Survey Reports by Year

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Relevant Available Documentation (cont.)

Area Air Sampling Results by Year

(percentages do not include personnel lapel samplers)

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Americium Exposure Potential – Overview

 Potential sources of internal americium exposure:

 Handling and/or processing of decladded spent 

nuclear fuel

 Fabrication of sealed americium sources and/or loss of 

integrity of existing americium sources

 Involvement in Transuranic Management by 

Propartitioning-Separation (TRUMP-S) program 

activities that may have included americium as well as 

other transuranic material

 Loss of integrity of radioactive smoke detectors 

containing americium

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Americium Exposure Potential – Decladded Spent Fuel

 No identified evidence of decladding activities of spent nuclear fuel 

occurring at the De Soto site

 SC&A identified several examples of spent fuel arriving and being 

stored at the De Soto site; however, no direct evidence of handling or 

processing of decladded spent fuel

 SC&A did identify one example of a contaminated tray found in 

Building 4 (radiological laboratory building) that was indicated to have 

been used to clean sodium off of decladded fuel elements

 Not clear where the fuel had been decladded

 Assuming the decladded fuel element was irradiated, the 

contamination in the tray would be expected to contain transuranic 

material (including americium)

 This example is the subject of SC&A Finding 2

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Americium Exposure Potential – Am-241 Sources

 Encapsulated americium source material at De Soto is 

well documented

 Notice of Violation (NOV) in 1994 indicated that the required

6-month leak check was late by between 1 and 8 days

 1994 NOV was a repeat violation that was also noted in 1991

 No evidence identified of americium sources actually leaking 

during the period under evaluation

 SC&A did not identify evidence of the fabrication of new 

Am-241 sources occurring at De Soto, though the facility 

was licensed to perform such fabrication

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Americium Exposure Potential – TRUMP-S

 Documentation identified from 1989 of TRUMP-S material 

arriving at De Soto and potentially becoming “lost”

 TRUMP-S material was placed in a radiological storage locker 

upon arrival at De Soto; however, administrative paperwork failed 

to notify the proper health and safety staff

 Material was eventually located, and the packaging was intact 

with no external contamination

 Cited documents indicate the TRUMP-S material consisted of 

depleted uranium and plutonium (americium is not mentioned)

 SC&A did not identify evidence or documentation of the 

actual use of any TRUMP-S material at De Soto

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Americium Exposure Potential – Smoke Detectors

 Smoke detectors do not appear to have been in use at De Soto 

until April 1985 

 While preventative maintenance (such as general cleaning) 

was performed at the detector location, all actual repair work 

that may have exposed the source material was performed at 

the electrical shop at SSFL

 A radiological study of the exposure potential from preventative 

maintenance indicated little to no exposure potential

 All cleaning materials used were below the NRC levels for release 

to uncontrolled areas

 Workers involved in the preventative maintenance submitted 

bioassays that indicated no detectable activity

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Americium Exposure Potential – Other

 SC&A identified documentation describing a survey of the 

industrial waste drains in the Mass Spectrometry Lab 

(Building 4 at De Soto)

 The document appears to have been edited internally by 

site personnel (i.e., it contains red strikethrough marks 

and sentence additions/edits)

 Edits physically written on the document indicate that 

Am-241 was found in the industrial waste drains 

 Edits also note that no release of americium or plutonium 

occurred

 The source of the Am-241 allegedly detected in the drains 

is not currently known by SC&A (SC&A Finding 3)

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Americium Exposure Potential – Other (cont.)

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Excerpt from 1997 Radiological Survey
Americium Exposure Potential – Other (cont.)

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Magnified Portion Showing Edits Adding Am-241
Thorium Exposure Potential

 NIOSH SEC ER identified three distinct thorium operations:

1. Fabrication of thorium fuel simulant discs in June 1970

2. Post-test analysis of thorium capsules that had undergone 

destructive testing offsite occurring 6/15/1970–7/30/1970

3. Grinding of approximately 540 thorium plates 2/28/1979–

3/12/1979

 The 1979 grinding operation included pre- and post-operational 

bioassay sampling, which was used to develop a representative 

thorium intake for the operation

 NIOSH SEC ER concludes the calculated thorium intake from the 

grinding operation can be used to represent internal thorium 

exposures to workers at De Soto during the evaluation period

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Thorium Exposure Potential (cont.)

 Additional activities with thorium:

 Smear contamination surveys in support of a thorium source program that appears 

to have occurred in Buildings 4 and 5 in 1969

 Personnel air sampling results from thorium operations in Room 11H36 

(Building 1) in 1969

 Tagged area entry permit for the inspection of “Ca-Th-Mo” fuel simulant discs in 

March 1970

 Personnel air sampling result involving a ThO2 cutting operation in 1971

 Several references to Sodium Reactor Experiment (SRE) fuel and/or materials 

arriving at De Soto but no indication of intended future use other than storage

 Personnel air sampling results are provided in the units of μCi-hr/cm3; 

however, the actual time spent on the activity is not always indicated 

to allow for direct comparison to the thorium-grinding operation

 NIOSH should consider these additional activities to assure that the 

grinding operation is sufficiently bounding and provide guidance to 

assure that unmonitored intakes are appropriately assigned

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Documented Interviews Relevant to SEC-00246

 The NIOSH SEC ER documents interviews with just two 

individuals as part of the evaluation of SEC-00246 (SC&A 

Finding 4)

 One interviewee did not work at De Soto until the 1990s and gave 

information based on retrospective summary documentation

 The other worked in non-radiological areas at De Soto beginning in the 

late 1970s but likely had knowledge of radiological operations

 Seven additional interviews in the SRDB were performed prior 

to the submission of SEC Petition 246 and involved work at 

De Soto

 Three of the seven interviewees do not appear to have worked at 

De Soto during the period of interest

 Remaining four interviewees do not specifically discuss americium or 

thorium at De Soto

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Documented Interviews Relevant to SEC-00246 (cont.)

 DOE and EPA conducted interviews in 2010 and 2011 

with former SSFL workers (including those who spent 

time at De Soto)

 121 total interview summaries were cleared for release

 41 of the 121 interviews reported work during the De Soto 

SEC evaluation period

 13 of 121 interviews contained information relevant to 

SEC-00246

 Neither americium nor thorium exposure during the SEC period 

was specifically mentioned

 The 13 former workers (in particular those who discussed fuel 

fabrication) may represent suitable future interview candidates, if 

deemed necessary 

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Overview of the Claimant Population

 257 total claims with relevant covered employment at De Soto 

at the time of SC&A’s review

 SC&A examined the CATI files (and DOL case files as 

appropriate) for 187 of the 257 claims (~73%) (Note: only 165 

of the 187 reviewed claims had CATI reports completed)

 Reviewed claims selected based on job titles with a likely 

potential of involvement in radiological work

 Only a small fraction of the reviewed claimant population 

indicated exposure to thorium and/or americium. Six of these 

CATIs were conducted directly with the energy employee and 

may represent suitable future interview candidates, if deemed 

necessary.

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Petitioner-Supplied Documents

 CORE Advocacy for Nuclear and Aerospace Workers provided 

20 primary reference documents specific to De Soto, with 59 

individual items identified as relevant to SEC-00246 (Note: 

several documents provided were duplicates of documentation that 

had already been captured and included in the SRDB)

 Documents provided by CORE Advocacy included a signed 

affidavit from a former worker

 The affidavit did not provide direct indications of exposure 

potential to unencapsulated americium, decladded spent nuclear 

fuel, or additional thorium fuel fabrication operations.

 The worker was re-interviewed by SC&A and NIOSH on 

11/14/2018; the results have not yet been finalized.

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Petitioner-Supplied Documents

 SC&A reviewed each item presented by CORE Advocacy 

and the supporting reference documentation 

 SC&A did not identify evidence in the additional documentation of 

an internal exposure hazard to unencapsulated americium that 

occurred at De Soto

 Evidence of spent fuel arriving at De Soto in the additional 

documentation did not directly indicate processing of, and by 

extension an exposure potential to, decladded spent fuel elements 

containing transuranic material

 SC&A did not identify operations, such as direct processing of 

SRE fuel rods, or other thorium activities that would present a 

greater hazard than the thorium fuel plate-grinding operation in 

1979, which has been proposed for coworker assignment

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Summary of Findings

 Finding 1: SC&A noted significant temporal gaps in available primary 

documentation such as health physics logbooks, tagged area entry permits, 

contamination smear surveys, and general air sample reports. The 

disposition of additional primary documentation for De Soto is not known at 

this time.

 Finding 2: A health physics logbook entry involving a contaminated tray that 

had been used to clean decladded fuel was found in a De Soto hood in the 

fuel fabrication area. Contamination from decladded fuel (assuming 

irradiation) would contain Am-241 and potentially Th-232, depending on the 

original fuel composition.

 Finding 3: Internal editing of a 1997 document concerning the Mass 

Spectrometry Laboratory indicated that a 1988 survey detected Am-241 in 

the facility industrial waste drains. The source of the Am-241 is not currently 

known.

 Finding 4: Only two individuals were specifically interviewed about De Soto 

radiological conditions after the submission of Petition-00246 in December 

2017. SC&A has identified several potential future interview candidates, if 

deemed necessary.

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Preliminary Conclusion

Although SC&A did not find evidence of operational processes involving 

unencapsulated americium at De Soto, at least one incident of material 

potentially contaminated with the transuranic material associated with 

decladded fuel was identified. Furthermore, it appears that americium 

was detected in the Mass Spectrometry Lab drain samples in 1988 

whose provenance is unknown.

SC&A has not identified direct evidence of thorium operations occurring 

at De Soto during the period under evaluation that would not be bounded 

by the calculated intake rates derived from the 1979 grinding operation

that is being proposed for coworker application. 

However, SC&A also noted significant temporal deficiencies in the 

available primary documentation of health physics activities at De Soto. 

Furthermore, the available documented interviews directly associated 

with radiological conditions at De Soto under evaluation for SEC-00246 

are clearly limited at the current time.

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Work Group Recommendations and Path Forward

 Santa Susana Field Laboratory Work Group met by 

teleconference on December 3, 2018

 Work Group recommends pursuing further interviews with 

radiological workers at the De Soto Facility during the 

period of interest

 NIOSH to formally respond to the SC&A review of the 

SEC-00246 Evaluation Report

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Questions?

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