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NIOSH Response to SC&A Review of 

SEC-00246 De Soto Avenue Facility 

Evaluation Report

Response to Findings and Observations

National Institute for Occupational 

Safety and Health

May 13, 2019

Prepared by: Monica Harrison-Maples 

Oak Ridge Associated Universities Team

Reviewed by: Lara Hughes, PhD, CHP 

Division of Compensation Analysis and Support

This is a working document prepared by NIOSH’s Division of Compensation Analysis and Support (DCAS) or its contractor for use in discussions 

with the ABRWH or its Working Groups or Subcommittees. Draft, preliminary, interim, and White Paper documents are not final NIOSH or 

ABRWH (or their technical support and review contractors) positions unless specifically marked as such. This document represents preliminary 

positions taken on technical issues prepared by NIOSH or its contractor. NOTICE: This report has been reviewed to identify and redact any 

information that is protected by the Privacy Act 5 USC §552a and has been cleared for distribution. 
Response Paper NIOSH Response to SC&A Review of SEC-00246 05/13/2019

De Soto Avenue Facility Evaluation Report

Page 2 of 11

This is a working document prepared by NIOSH’s Division of Compensation Analysis and Support (DCAS) or its contractor for use in discussions 

with the ABRWH or its Working Groups or Subcommittees. Draft, preliminary, interim, and White Paper documents are not final NIOSH or 

ABRWH (or their technical support and review contractors) positions unless specifically marked as such. This document represents preliminary 

positions taken on technical issues prepared by NIOSH or its contractor. NOTICE: This report has been reviewed to identify and redact any 

information that is protected by the Privacy Act 5 USC §552a and has been cleared for distribution.

INTRODUCTION

In December 2018, Sanford Cohen and Associates, the Technical Support Contractor to the 

Advisory Board on Radiation and Worker Health (SC&A) delivered a draft report, Review of the 

NIOSH Evaluation Report for SEC-00246 at the De Soto Facility (SCA-TR-2018-SEC006, 

Rev.0), presenting four findings and six observations related to the NIOSH SEC evaluation 

report of the SEC-00246 petition. The evaluation reviewed the feasibility of reconstruction of 

potential internal exposures to americium and thorium at the De Soto facility from 1965 through 

the end of 1995. This reports contains the first set of NIOSH responses to the SC&A findings. 

FINDING 1: GAPS IN DOCUMENTATION

SC&A identified significant temporal gaps in four key types of documents available in the 

SRDB: health physics logbooks, tagged area entry permits, routine smear surveys, and general 

air sampling reports. The disposition of additional documents of this type is not known at this 

time.

NIOSH Response (Finding 1):

NIOSH uses a documented hierarchy of data to reconstruct internal (and external) dose. 

That hierarchy proceeds from individual dosimetry data to workplace monitoring data 

and finally to source term data for the facility [OCAS-IG-002 Rev 00]. Individual 

dosimetry data can generally be categorized as bioassay data, personal monitoring data 

collected in the workplace, in that order of primacy. The four document types listed by 

SC&A are defined as primary records for data pedigree purposes because of the 

background, history, and origin of the documents. 

For SEC evaluations, NIOSH typically focuses on the capture of high-level documents, 

such as annual reports, annual summaries, and operational histories to supplement 

bioassay data and develop a full understanding of exposure scenario conditions. The highlevel documents captured and the data contained within them was assessed for value in 

developing dose reconstructions during the De Soto SEC evaluation. NIOSH has not 

attempted to search out all logbooks, Tagged Area Entry Permits (TAEPs), routine smear 

surveys and general air sampling reports, but rather, have collected such information as it 

is identified. NIOSH did not identify a specific concern during the evaluation that is likely 

to be resolved through a review of additional logbooks. While logbooks and access 

records, such as TAEPs, are generally supportive documentation, they are not required 

documentation for dose reconstruction. A review of the SRDB holdings shows no 

indication that operations occurred that would allow internal exposures to americium and 

no indication that operations occurred which would have had a thorium exposure concern 

beyond the bounding thorium approach presented in the SEC-00246 evaluation report.

NIOSH agrees that these gaps in supplemental documentation identified by SC&A are 

valuable areas for targeted data capture in the event of a specific concern and will consider 

a focus on such documents for any future data capture efforts.
Response Paper NIOSH Response to SC&A Review of SEC-00246 05/13/2019

De Soto Avenue Facility Evaluation Report

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This is a working document prepared by NIOSH’s Division of Compensation Analysis and Support (DCAS) or its contractor for use in discussions 

with the ABRWH or its Working Groups or Subcommittees. Draft, preliminary, interim, and White Paper documents are not final NIOSH or 

ABRWH (or their technical support and review contractors) positions unless specifically marked as such. This document represents preliminary 

positions taken on technical issues prepared by NIOSH or its contractor. NOTICE: This report has been reviewed to identify and redact any 

information that is protected by the Privacy Act 5 USC §552a and has been cleared for distribution.

FINDING 2: CONTAMINATED CONTAINER

SC&A did not identify any activities involving the handling of decladded spent nuclear fuel that 

may have presented an internal exposure potential to Am-241. However, at least one reference 

indicates that a contaminated container used to clean sodium from decladded fuel had been 

discovered in a hood area in Building 1 at De Soto. Unless the decladded fuel was fresh fuel 

undergoing decladding, the fuel would be expected to have been irradiated, and thus would likely 

contain americium.

NIOSH Response (Finding 2):

The finding relates to a log book entry from 3/11/1965 [Entry 1030, 1965]. The entry reads:

“Smear survey of hood in the NW corner of 1110-80 indicated a maximum of 1.8 x 103 dpm/100 

cm2 alpha and 6 x 103 dpm/100 cm2 beta in a long thin tray used to clean Na from decladded 

fuel. The nomenclature identifying the room appears to be in Building 001 (other entries from 

the same day refer to room 1110-65 and Room 1110-62 which is the Powder Room). At Area IV, 

SSFL, reactors such as the SRE, the SNAP 8 Experimental Reactor (S8ER), and the SNAP 8 

Development Reactor (S8DR) used an alloy of sodium (Na) and potassium (K) coolant (NaK). 

The report Metallurgical Aspects of SRE Fuel Element Damage Episode [Ballif, 1961] briefly 

describes examinations and two special tests made with both damaged and undamaged fuel 

elements from the SRE, performed in hot cells, to determine causative factors of the fuel 

damage. NIOSH reviewed references showing that the SRE had specially designed hot cells to 

clean fuel assemblies, and to examine the fuel using cameras. Inert atmosphere conditions were 

required when working in containment with NaK to prevent fires. Sodium is pyrophoric at or 

below 130° F and is highly reactive when exposed to water or dry air [Handbook V3, 1978]. 

NaK will spontaneously ignite in air much more easily than sodium and is considered somewhat 

more hazardous than sodium [Handbook V3, 1978]. The SRE-engineered safety controls were a 

designed part of the reactor facility because of the hazardous nature of sodium-bearing materials. 

The logbook entry specifies sodium (Na) as the material cleaned from the decladded fuel in the 

tray, rather than NaK. This makes it unlikely that the fuel referenced in the logbook entry came 

from one of the sodium-cooled reactors at SSFL. While there is no direct evidence that reactor 

fuel material was or was not cleaned in the hood, the pyrophoric nature of sodium makes it 

unlikely that this type of fuel material was cleaned of sodium in a hood which is not a contained 

area with a controlled atmosphere. This indicates the cleaning likely occurred elsewhere.

As noted in the finding, if the fuel had been irradiated, it is likely it would have contained 

americium from the decay of plutonium produced by activation during reactor operation. It 

seems unlikely that the radiation hazard associated with irradiated fuel from any reactor would 

be unknown or not handled with the care associated with highly radioactive material. A tray used 

during the cleaning of irradiated fuel would be considered potentially contaminated, and would 

not likely be removed from a shielded, contained condition to a hood area. It is therefore more 

likely that the fuel that was cleaned was unirradiated fuel. That would be more consistent with 

the level of contamination reported as well. 
Response Paper NIOSH Response to SC&A Review of SEC-00246 05/13/2019

De Soto Avenue Facility Evaluation Report

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This is a working document prepared by NIOSH’s Division of Compensation Analysis and Support (DCAS) or its contractor for use in discussions 

with the ABRWH or its Working Groups or Subcommittees. Draft, preliminary, interim, and White Paper documents are not final NIOSH or 

ABRWH (or their technical support and review contractors) positions unless specifically marked as such. This document represents preliminary 

positions taken on technical issues prepared by NIOSH or its contractor. NOTICE: This report has been reviewed to identify and redact any 

information that is protected by the Privacy Act 5 USC §552a and has been cleared for distribution.

NIOSH’s research suggests a possible source of unirradiated reactor fuel requiring removal of 

sodium. Following a fuel damaging incident in the SRE in 1959, Atomics International 

investigated reactor fuel cladding failure. Multiple experiments were conducted to investigate the 

mode of failure, including experiments performed on unirradiated reactor fuel [Daniel, 1959]. In 

summary, the log book notation describes a contaminated container, found in a hood. The 

purpose of the container is described as: “to clean Na from decladded fuel.” The entry makes no 

mention of decladding operations occurring in the hood area and gives no information about 

where the decladding operation took place. The entry gives no indication if it was fuel in the 

form of an element/assembly or a sample of fuel material, although the description of the tray as 

long and thin implies the former. The entry describes sodium rather than NaK, so the fuel 

material seems to have come from an operation or experiment other than one of the reactors that 

used NaK as a coolant material. This would include scenarios such as testing the response of 

cladding to physical stress conditions to determine a possible cause of cladding failure. If the 

nuclear fuel material cleaned in the tray was not irradiated prior to cleaning, there would be no 

reason to assume americium fission product as a component of the fuel material or part of the 

contamination. The amount of contamination and the location of the contaminated tray in a hood 

implies the fuel material was unirradiated fuel. 

NIOSH has researched the incident database provided by Boeing and has been unsuccessful in 

finding further documentation to corroborate or provide more detailed information about this 

event in the Building 104 hood.

FINDING 3: MASS SPEC LAB DRAIN CONTAMINATION

While SC&A did not observe any documentation directly indicating the handling of 

unencapsulated americium source material, evidence from at least one document suggests that a 

1988 survey of floor drains in the laboratory area identified Am-241 contamination. Such 

contamination would not be expected unless unencapsulated americium was used at some point 

during laboratory activities.

NIOSH Response (Finding 3):

Building 104 at the De Soto facility was home to a number of analytical laboratories that 

supported nuclear-related activities and conducted radiochemistry analyses. One of the facilities 

was the Mass Spec laboratory, which used a high precision helium mass spectrometer to analyze 

milligram sized metallic specimens, irradiated in test reactors across the nation, to study the 

effects of helium embrittlement and neutron dosimetry. According to the document "Final Report 

for Decontamination & Decommissioning of the De Soto 104 Helium Mass Spectrometer 

Laboratory" [Stelman, 1999] specimens were vaporized and the amount of helium present in the 

effluent gas was analyzed. In the process, the mass spectrometer, the associated vacuum system, 

and the HEPA exhaust system were contaminated with small amounts of activation products 

from the irradiated specimens (typically Co-60 and Mn-54 from neutron activated steel). Some 

contamination of laboratory fume hoods and machine tools likely occurred during the handling 

and preparation of samples. The Mass Spec Lab was connected to the Building 104 industrial 

radioactive water drain system. During remediation of the other radiological laboratories in Bldg. 
Response Paper NIOSH Response to SC&A Review of SEC-00246 05/13/2019

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This is a working document prepared by NIOSH’s Division of Compensation Analysis and Support (DCAS) or its contractor for use in discussions 

with the ABRWH or its Working Groups or Subcommittees. Draft, preliminary, interim, and White Paper documents are not final NIOSH or 

ABRWH (or their technical support and review contractors) positions unless specifically marked as such. This document represents preliminary 

positions taken on technical issues prepared by NIOSH or its contractor. NOTICE: This report has been reviewed to identify and redact any 

information that is protected by the Privacy Act 5 USC §552a and has been cleared for distribution. 

104 during the 1980s, the radioactive drain system was removed back to the Mass Spec Lab 

perimeter. The radioactive drains within the perimeter of the Mass Spec Lab were sealed and 

isolated to prevent further use [Stelman, 1999]. 

Hand-written editorial notes referenced in the finding read: “The presence of 49 pCi Am-241 

was in 49 gm of soil drain sample”. The notes indicate there was no recorded release of 

plutonium or americium. The notes are edits to an unknown report and are included in a NIOSH 

available file with survey maps and routine radiation survey reports [Surveys, 1997]. There are 

no markings to indicate the source of the original document or the author of the handwritten 

edits. NIOSH researched facility environmental reports, annual reviews of radiological controls, 

survey reports, licensing documentation, occurrence reports, and activity reports in an effort to 

verify the hand-written notes, and found no additional information that could be used to 

definitively identify the 1988 survey reference or any other associated references. NIOSH was 

able to identify a document (Boeing, 2003) which includes a citation in the list of references that 

is likely the 1988 survey. That document states, “The presence of Am-241 in drain sample IW25 is unexplained. There was no recorded release of plutonium or americium in the labs in 

DS104. The sample showed approximately 400 pCi in 49 grams of scale scraped from the drain 

[emphasis added]” [Rocketdyne, 1988]. The 1988 survey date, the similarity of the wording and 

the reference to the drain sample indicate this document is the likely source for the edit notes, 

though the activity of the americium is significantly more than what was indicated in the 

handwritten notes cited in the finding. These samples were analyzed by gamma spectroscopy. 

The 1988 survey supported the decontamination and demolition of the ground floor of Building 

104, including removal of most of the drain-lines that served the radioactive labs, to permit 

renovation of the area [Tuttle, 1989]. The concentration of Am-241 was listed as 400 pCi in 49 

grams of scale, which corresponds to 8.2 pCi/gram of scale scraped from the Building 104 

industrial waste return drains.

Am-241 was also detected in a drain trench soil sample in 1998. The document: “Draft Docket 

for the Release of Mass Spectroscopy Laboratory (Building 104)” [Stelman, 1999] includes a 

description of trench sampling and a summary of the analysis results. A single result in the 

quantitative soil measurements of piping trenches [Liddy, 1998] was 0.03 pCi/gm Am-241. The 

minimum detectable activity (MDA) was 0.061 pCi/gm and the soil guideline release limit for 

Am-241 was 5.44 pCi/gm [Liddy, 1998]. 

In trying to identify a possible source of Am-241 contamination in the drain lines, NIOSH 

reviewed the Boeing incident report files. Several incident reports were identified for that time 

period, but none indicated Am-241 as the relevant radionuclide. 

In summary, Am-241 was detected at low levels in the scale scraped from the industrial waste 

drain line in 1988. The amount detected was well below the EPA soil decontamination limit of 

30 pCi/g. In 1998, the non-functional remnants of the industrial drain and cooling water return 

line under the Mass Spec Lab were excavated and a soil sample from the excavation indicated 

Am-241 but at a level less than the MDA. NIOSH reviewed radiological surveys, environmental 

reports, and incident reports but found no record of an americium release into the waste drains. 
Response Paper NIOSH Response to SC&A Review of SEC-00246 05/13/2019

De Soto Avenue Facility Evaluation Report

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This is a working document prepared by NIOSH’s Division of Compensation Analysis and Support (DCAS) or its contractor for use in discussions 

with the ABRWH or its Working Groups or Subcommittees. Draft, preliminary, interim, and White Paper documents are not final NIOSH or 

ABRWH (or their technical support and review contractors) positions unless specifically marked as such. This document represents preliminary 

positions taken on technical issues prepared by NIOSH or its contractor. NOTICE: This report has been reviewed to identify and redact any 

information that is protected by the Privacy Act 5 USC §552a and has been cleared for distribution.

At this point, the source of the sample is unknown, but it is plausible that it is a result of an 

analytical sample spill of some sort. Building 104 housed radiochemistry labs, which performed 

analysis on radioactive samples which could have included fission products and transuranics. 

Radiochemical analysis involves samples large enough to provide statistically accurate analyses. 

Analytical sample quantities are not usually available in sufficient quantity to be readily 

dispersed for inhalation by workers, especially in light of hood enclosures, ventilation controls, 

and administrative controls. The low levels of americium detected and the complete lack of 

operational history referring to americium in Building 104 do support the conclusion that 

americium was not a radionuclide of concern during the 1965-1995 period at De Soto Building 

104 and did not pose a potential internal exposure hazard to workers.

FINDING 4: FORMER WORKER INTERVIEWS

Only two interviews are documented in the SRDB as a result of NIOSH’s SEC-00246 

evaluation, and only one of those two interviews involves a worker at De Soto prior to 1991. A 

third interview occurred in November 2018 after NIOSH issued its evaluation of SEC-00246 and 

was performed by SC&A in conjunction with NIOSH and CORE Advocacy. This interview has 

not yet been finalized.

NIOSH Response (Finding 4):

NIOSH has contacted its contractor, ATL, to follow up with the suggested NOCTS interviewees 

suggested in SC&A’s report. A notice was sent to DOE, who contacted the contractor who did 

the DOE interviews in the 2010/2011 timeframe. A letter was sent by DOE, attempting to 

contact the selected persons and asking if they are willing to be interviewed. Additional 

interviewees were identified by ATL and five additional interviews were completed in May, 

2019. Interview transcripts will be available in the SRDB once they have been finalized.

ABRWH IDENTIFIED FINDING: ENVIRONMENTALSTACK RELEASES

The ABRWH asked for clarification on the assertion from the petitioner that the mention of Am 

and Th in the stack analyses reported at De Soto in the 1990s confirms that De Soto processed 

Am and Th.

NIOSH Response (ABRWH Finding):

The environmental TBD for Area IV/De Soto discusses radionuclide-specific gross alpha and 

gross beta stack emissions only for 1988-1999. For the De Soto facility, the only stack emission 

data available is for Building 004, Hot Analytical Chemistry, a facility related to operations of 

the Mass Spectroscopy Laboratory, which analyzed small samples of activated materials. It 

ceased operations in 1995. Table 4-1 in the TBD indicates that Americium and Thorium were 

analyzed in the effluents during this period. The exhaust through the stacks was filtered through 

HEPA filters, before being discharged to the atmosphere. Exhaust air samples were counted for 

gross alpha and beta activity on a weekly basis until 1990, when Rocketdyne began sending 

airborne effluent samples for radionuclide specific analysis as a result of concern expressed by 
Response Paper NIOSH Response to SC&A Review of SEC-00246 05/13/2019

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This is a working document prepared by NIOSH’s Division of Compensation Analysis and Support (DCAS) or its contractor for use in discussions 

with the ABRWH or its Working Groups or Subcommittees. Draft, preliminary, interim, and White Paper documents are not final NIOSH or 

ABRWH (or their technical support and review contractors) positions unless specifically marked as such. This document represents preliminary 

positions taken on technical issues prepared by NIOSH or its contractor. NOTICE: This report has been reviewed to identify and redact any 

information that is protected by the Privacy Act 5 USC §552a and has been cleared for distribution.

the public and the media. The annual environmental reports contain analysis results for a 

consistent set of radioisotopes reported for the RMHF, the Hot Lab and De Soto 104, indicating 

that the samples were sent for analysis to a vendor under one contract. 

Americium measurement results were reported in 1990, 1991, 1995, and 1996, but only in 1995 

was the reported activity greater than the analysis LLD. In 1995, the analysis LLD was 0.430 pCi 

and the activity detected result was 0.452 pCi. The concentrations in the effluent at the exhaust 

stack were below the maximum permitted concentrations (MPCs) of State of California, 

California Code of Regulations (CCR) Title 17, Section 30253 for exposure of the public. The 

stack monitoring results for 1992, 1993, 1994, 1996, 1997 and 1998 all reported thorium content 

as non-detectable. In 1995, all thorium results were below the analysis LLD. Based on NIOSH’s 

review of the document holdings, the results of the effluent monitoring demonstrate americium 

was not a release concern and americium was not released to the environment by the De Soto 

facility. The monitoring program included americium and thorium as part of a non-specific suite 

of radionuclides encompassing concerns from Area IV and De Soto, in response to community 

concerns. There was only one reported Am-241 result that exceeded what could confidently be 

called radioactive and none exceeded the release LLD. The isotopic analysis results do not 

indicate evidence of unencapsulated work with americium or thorium at the De Soto Building 

004 facility.

OBSERVATION 1: AM-241 SOURCES

SC&A found examples of Am-241 source material being transferred to different locations at the 

De Soto site; however, no evidence of the fabrication of new Am-241 sources, as allowed by 

Radioactive Material License 0015-59, was identified.

NIOSH Response (Observation 1):

No NIOSH response required.

OBSERVATION 2 (TRUMP-S):

Documentation confirms that TRUMP-S material was shipped to the De Soto site. However,

SC&A did not find any indication of TRUMP-S operations occurring at the site that could have 

involved unencapsulated Am-241.

NIOSH Response (Observation 2):

No NIOSH response required.

OBSERVATION 3 (AM-241 IN SMOKE DETECTORS):

Smoke detectors containing Am-241 were in use at De Soto beginning in 1985; however, 

radiological exposure characterization of routine preventative maintenance of the detectors 

indicated little to no internal exposure potential. Actual repair of the radioactive smoke detectors, 

which may involve exposing the Am-241 source material, occurred at SSFL and not De Soto.
Response Paper NIOSH Response to SC&A Review of SEC-00246 05/13/2019

De Soto Avenue Facility Evaluation Report

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This is a working document prepared by NIOSH’s Division of Compensation Analysis and Support (DCAS) or its contractor for use in discussions 

with the ABRWH or its Working Groups or Subcommittees. Draft, preliminary, interim, and White Paper documents are not final NIOSH or 

ABRWH (or their technical support and review contractors) positions unless specifically marked as such. This document represents preliminary 

positions taken on technical issues prepared by NIOSH or its contractor. NOTICE: This report has been reviewed to identify and redact any 

information that is protected by the Privacy Act 5 USC §552a and has been cleared for distribution.

NIOSH Response (Observation 3):

No NIOSH response required.

OBSERVATION 4 (URANIUM ISOTOPE INFORMATION):

A 1977 licensing document states that the handling of unencapsulated material at the De Soto 

facility only involves isotopes of uranium.

NIOSH Response (Observation 4):

NIOSH reviewed process descriptions, radiological surveys, and environmental reports and 

performed keyword searches to identify any reference to reprocessed fuel, or spent fuel. 

NIOSH found no reference to, or evidence of, the handling of U-236 containing material at De 

Soto. A keyword search of the available documents found reference to U-236 in two documents 

other than the cited licensing document; a 2012 Final Field Sampling Plan for Soil Sampling 

Area IV Radiological Study [EPA, 2012] and an internal letter [Tschaeche, 1968] on updated 

isotopic data for the ATR/ETR Fuel receipt giving the isotopic composition of fuel received 

between June 1966 and October 1967. This fuel was to be used in the “Powder Room” in 

Building 101 and generally contained approximately 0.3 Wt. % U-236. This does not constitute a 

“significant quantity” and does not seem to indicate the fuel was reprocessed. The field sampling 

plan lists U-236 in a table of radionuclides of interest for soil sample analysis, selected by a 

National Environmental Laboratory Accreditation Program (NVLAP) certified laboratory rather 

than a site-specific listing. NIOSH found no indications the fuel material had been irradiated or 

that americium was a component of the fuel.

OBSERVATION 5 (THORIUM INTAKE ASSIGNMENT):

The NIOSH SEC ER provides calculated intake rates for thorium based on bioassay data related 

to the 1979 grinding operation. NIOSH notes that such intakes can be assigned to De Soto 

workers “as appropriate,” although it does not indicate what criteria would need to be satisfied 

for an unmonitored worker to be assigned the derived coworker intake rate. However, it must be 

noted that establishing policies concerning coworker application are generally considered site 

profile issues rather than SEC issues.

NIOSH Response (Observation 5):

NIOSH assigns calculated intake rates based on individual claim information and site 

knowledge. An overarching policy on the criteria for assigning a derived coworker intake rate is 

not considered feasible given the variations in operations and conditions from site to site. As 

noted by SC&A, policies concerning coworker application are handled as site profile issues,

taking into account available site data and information. Such policy determinations are beyond 

the scope of SEC evaluation.
Response Paper NIOSH Response to SC&A Review of SEC-00246 05/13/2019

De Soto Avenue Facility Evaluation Report

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This is a working document prepared by NIOSH’s Division of Compensation Analysis and Support (DCAS) or its contractor for use in discussions 

with the ABRWH or its Working Groups or Subcommittees. Draft, preliminary, interim, and White Paper documents are not final NIOSH or 

ABRWH (or their technical support and review contractors) positions unless specifically marked as such. This document represents preliminary 

positions taken on technical issues prepared by NIOSH or its contractor. NOTICE: This report has been reviewed to identify and redact any 

information that is protected by the Privacy Act 5 USC §552a and has been cleared for distribution.

OBSERVATION 6: THORIUM

SC&A identified evidence in SRDB documentation indicating spraying, cutting, and laboratoryspecific operations involving thorium that were not identified or discussed in the NIOSH SEC 

ER. However, SC&A did not identify evidence associated with these operations/processes to 

suggest they would not be bounded by the grinding operation in 1979 for which NIOSH has 

developed coworker intake rates of thorium. NIOSH should consider these additional operations 

when assigning unmonitored thorium intakes to workers at the De Soto facility. 

NIOSH Response (Observation 6):

NIOSH is aware of transit capsule testing programmatic work using ThO2 powder containing 

natural thorium. While authorizations for parts of this campaign have been cited in the evaluation 

report (Authorization No. 13, Authorization No. 21) as examples, NIOSH does not believe these 

examples describe the entire campaign. Citation of these authorization documents within the 

evaluation report was not intended to restrict the scope of this work to June and July of 1970, and 

NIOSH will continue to pursue and consider any documentation associated with this project that 

expands the understanding of the scope. 

NIOSH reviewed personnel radiation dosimetry files, personnel air sampling data sheets and 

TAEPs for information on thorium work as part of the evaluation. As stated in the evaluation 

report, the site frequently relied on the experience of the same individuals to perform work 

involving thorium. One individual is associated with the work indicated in the SC&A Review 

document as Th-6, Th-12, and Th-13. This same individual is also identified as working on the 

1979 thorium grinding operation. This individual’s radiation exposure monitoring data was 

significant to the development of the conclusion that the other identified thorium operations at 

De Soto would be bounded by the 1979 grinding operation. 

The reference to “ThO2 machining” in room 11H-28 cited by SC&A (Th-13) is not an activity 

description that was seen elsewhere in the process documentation. The evaluation report did 

mention analysis of the thoria-molybdenum cermet fuel simulant was performed by operators for 

whom NIOSH has dosimetry records. An internal letter [Meyer, 1970] describes the transit 

capsule post-test analyses. The analysis was to have been performed in 11H-28, the Hot Machine 

shop in Building 101, and was to have consisted of leak testing, dye-penetrant inspection, and 

volumetric measurement. The capsule was to be disassembled through machining, and the 

simulant fuel removed, sealed in packages and ultimately shipped to LASL. The planning did not 

include machining of the ThO2 containing fuel simulant discs.

NIOSH has reviewed Table 2. Description of Thorium Related Information Contained in the Site 

Research Database provided in SC&A’s review and performed a targeted assessment of the 

available data. Additional data capture does not seem indicated at this time. Any future data 

capture opportunities will include an effort to further support the logbook entries and other 

documentation.
Response Paper NIOSH Response to SC&A Review of SEC-00246 05/13/2019

De Soto Avenue Facility Evaluation Report

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This is a working document prepared by NIOSH’s Division of Compensation Analysis and Support (DCAS) or its contractor for use in discussions 

with the ABRWH or its Working Groups or Subcommittees. Draft, preliminary, interim, and White Paper documents are not final NIOSH or 

ABRWH (or their technical support and review contractors) positions unless specifically marked as such. This document represents preliminary 

positions taken on technical issues prepared by NIOSH or its contractor. NOTICE: This report has been reviewed to identify and redact any 

information that is protected by the Privacy Act 5 USC §552a and has been cleared for distribution.

OBSERVATION 6: FORMER WORKER INTERVIEWS

SC&A identified 13 individuals among over 120 interviews conducted by DOE/EPA related to 

the SSFL site who may have relevant information regarding De Soto. If available, these 

individuals may represent suitable interview candidates in the future, as required.

NIOSH Response (Former Worker Interviews):

An attempt was made with help of DOE to contact the former workers who participated in the 

DOE interviews from 2010. One worker was willing to be interviewed, but scheduling and health 

issues of the interviewee are ongoing, and it is unclear if the interview will proceed as of this 

writing.

REFERENCES

Ballif, 1961; Metallurgical Aspects of SRE Fuel Element Damage Episode [SRDB Ref ID 

175533] 

Boeing, 1999; Draft Docket for the Release of Mass Spectroscopy Laboratory (Building 104) at 

the Rocketdyne (Boeing North American) De Soto Facility Operated by Former Energy 

Technology Engineering Center September 1999 [SRDB Ref ID: 170434]

Boeing, 2003; Rocketdyne Propulsion and Power Appendix B: Radiological Operations and 

Cleanup at the De Soto Facility [SRDB 19145]

Entry 1030, 1965; Log Book De Soto 1964-1965 [SRDB Ref ID 169514] 

EPA, 2012; Final Field Sampling Plan for Soil Sampling Area IV Radiological Study Santa 

Susana Field Laboratory Ventura County, California [SRDB Ref ID 158004]

Surveys, 1997, Collection of survey maps and reports from De Soto Mass Spec Lab, Building 

004 in 1997 [SRDB Ref ID 170416]

Handbook V3, 1978; Sodium-NaK Engineering Handbook Volume III 1978 [SRDB Ref ID 

175535]

Daniel, 1959; Investigation of Releases from Santa Susana Sodium Reactor Experiment in July, 

1959 [SRDB Ref ID: 142171]

Liddy, 1998; De Soto 104 Mass Spectroscopy Laboratory Final Status Survey Report [SRDB 

Ref ID: 170434]

Meyer, 1970; SSC Fuel Simulant Disc Fabrication Program, June 8-12 [SRDB Ref ID: 170466] 

OCAS-IG-002 Rev 00, Aug 2002; Internal Dose Reconstruction Implementation Guideline 

[SRDB Ref ID: 22402]
Response Paper NIOSH Response to SC&A Review of SEC-00246 05/13/2019

De Soto Avenue Facility Evaluation Report

Page 11 of 11

This is a working document prepared by NIOSH’s Division of Compensation Analysis and Support (DCAS) or its contractor for use in discussions 

with the ABRWH or its Working Groups or Subcommittees. Draft, preliminary, interim, and White Paper documents are not final NIOSH or 

ABRWH (or their technical support and review contractors) positions unless specifically marked as such. This document represents preliminary 

positions taken on technical issues prepared by NIOSH or its contractor. NOTICE: This report has been reviewed to identify and redact any 

information that is protected by the Privacy Act 5 USC §552a and has been cleared for distribution. 

NRC, 1981; Decontamination Limits for Americium-241; https://www.nrc.gov/aboutnrc/radiation/protects-you/hppos/hppos183.html [SRDB Ref ID 175532] 

Rocketdyne, 1988; Rockwell International, 1988. Radiation Survey for Release for Unrestricted 

Use of De Soto Facility, 1st Floor, Building 104. N001SRR140103 dated Aug 17, 1988 [SRDB 

Ref ID 170451] 

Stelman, 1999; Final Report for Decontamination & Decommissioning of the De Soto 104 

Helium Mass Spectrometer Laboratory [SRDB Ref ID: 170434] 

Tuttle, 1989; Annual Review of Radiological Controls – 1988 [SRDB Ref ID: 19139] 

Tschaeche, 1968; Updated Isotopic Data for ATR/ETR Fuel Receipts [SRDB 171859]