Page 1 of 9

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. 

Status of Operations Involving Thorium 

and Americium at Area IV SSFL During 

the Remediation Period (1988 - Present)

White Paper

National Institute for Occupational 

Safety and Health

November 6, 2018

Lara Hughes 

Division of Compensation Analysis and Support
White Paper Status of Operations Involving Thorium and Americium at 

Area IV SSFL During the Remediation Period (1988 - Present)

November 6, 2018

Page 2 of 9

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. 

BACKGROUND

In May, 2017, NIOSH issued an evaluation report for petition SEC-00235 for Area IV of the 

Santa Susana Field Laboratory (SSFL) from August 1, 1991 to June 30, 1993 (NIOSH, 2017). 

NIOSH found that there was no dose reconstruction infeasibility for the evaluated period and did 

not recommend that a class be added to the SEC. During the ABRWH work group discussion on 

this evaluation on December 04, 2017, the work group pointed out the lack of discussion on the 

thorium and americium source term after the end of the operational period in 1988 (Transcript, 

2017). The previous SEC evaluation (SEC-00234) for Area IV of the SSFL was added to the 

SEC because NIOSH found an infeasibility to reconstruct internal doses from thorium and 

americium radionuclides (NIOSH, 2016). The recommended period of the SEC class for SEC00234 was 1965 through 1988. The work group has requested that NIOSH provide more detail 

and relevant references on the nature of the source term for thorium and americium after 1988 at 

Area IV SSFL. The following is a more detailed workup of the operations and facilities that 

were identified as having handled Am and Th at Area IV, and what their status was in the post1988 period. 

STATUS OF THORIUM AND AMERICIUM SOURCE TERMS AT AREA IV SSFL

AFTER 1988

All reactor facilities ended operations by 1980, and all nuclear support operations were 

terminated by 1988, with the exception of operations that supported closure and cleanup 

activities (hence the DOE determined end of the EEOICPA operational period). Figure 1 

provides a timeline of reactor operations at Area IV SSFL. Americium at Area IV was produced 

as a transuranic element in the reactor cores during reactor operation. It was also present in form 

of sealed sources. Thorium was a component of the reactor fuel for two reactors, the Advanced 

Epithermal Thorium Reactor (AETR) and Core II of the Sodium Reactor Experiment (SRE). 

Transuranic and activation radionuclide contamination from the fuel within the reactors could 

have contributed to radiological exposures at the reactor buildings in Area IV. The majority of 

the transuranic activity would have been from plutonium-238, plutonium-239, plutonium-240, 

plutonium-241, americium-241, and curium-244. Research activities on the spent fuel, including 

decladding operations in hot cells, could have potentially been a path of exposure for employees. 

Workers who subsequently performed decommissioning and decontamination (D&D) procedures 

on the hot cells could potentially be exposed to residual amounts of these radionuclides. Based 

on a review of available health physics documentation during the remediation period (Moore, 

1992; Quarterly Reviews, 1991-1993), the major transuranic radionuclide of concern was Pu239, which was present in small residual amounts at the Hot Lab facility. During the D&D 

period, radiological surveillance documents report the major radionuclides of concern at Area IV 

SSFL to be fission products (Cs-137 and Sr-90) and the activation products Co-60 (Documented 

Communication 2017a; Documented Communication 2017b; Moore, 1992). 

The main facilities involved in thorium operations were the SRE complex and the AETR, along 

with their reactor and fuel handling support facilities. The main facilities that had potential 

americium exposure were reactor facilities where irradiated fuel was handled (there was no fuel 

reprocessing at Area IV, SSFL, but there was some fuel decladding and other experimental 
White Paper Status of Operations Involving Thorium and Americium at 

Area IV SSFL During the Remediation Period (1988 - Present)

November 6, 2018

Page 3 of 9

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. 

handling and analyses of irradiated fuel). Fuel decladding operations were done in the Hot Lab 

(Building 20). 
White Paper Status of Operations Involving Thorium and Americium at

Area IV SSFL During the Remediation Period (1988 - Present)

November 6, 2018

Page 4 of 9

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. 

Figure 1. Facility Operations Timeline, Area IV SSFL (Sapere and Boeing, 2005)
White Paper Status of Operations Involving Thorium and Americium at 

Area IV SSFL During the Remediation Period (1988 - Present)

November 6, 2018

Page 5 of 9

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 SRE was a sodium cooled, graphite moderated, thermal reactor that used uranium-thorium 

metal alloy fuel in its Core II, that was in operation between 1960 and 1964 (Ureda, 1975). The 

fuel for Core II was assembled by loading the fuel slugs into metal tubes in the Engineering Test 

Building (Building 4003) to create the fuel rods (meaning the actual fuel slugs were not 

produced on-site) (Rucker, 2009). The Core II fuel consisted of Th-232 and enriched uranium 

(EU) alloy. The fuel from Core II was stored in the fuel storage vault at the Radioactive 

Materials Disposal Facility (RMDF) after it was removed from the SRE in 1964 (Dennison, 

1977). 

In 1974, the SRE Core II fuel was disassembled at the Hot Lab so that the fuel could be shipped 

off-site to the Savannah River Site where it would be reprocessed. The fuel disassembly at the 

Hot Lab consisted of the removal of the fuel from storage casks, removing the fuel from the 

cladding material and removing the sodium-potassium (NaK) around the fuel slugs. Cladding 

and wires and washing solvent were disposed as high level waste. The slugs were further cleaned 

with a hot alcohol bath and then packaged into a SRE shipping can, which was welded shut and 

leak tested before being transferred to the RMDF for storage and, eventually, shipping. 

Documentation indicates that approximately 1,972 kg of thorium were shipped to Savannah 

River as declad fuel over nine shipments (Dennison, 1977). The last shipment of Core II left 

Area IV at 2-19-1977. There is no documentation that indicated that any of the fuel slugs were 

damaged or ruptured during disassembly of Core II, but there was a potential of some 

contamination of the inside of the hot cells where the Core II fuel was handled. The 

documentation of the fuel handling indicates that the hot cell was cleaned up after Core II was 

processed (Dennison, 1977). The packaged fuel was stored in a sealed container at the RMDF 

until shipment in 1977. Based on this information, it is unlikely that there was a significant

internal exposure potential from Th at the RMDF during the post-1988 period, which is over a 

decade after the Th containing canisters were removed. Annual reports and quarterly 

surveillance reports for the D&D of the Hot Lab are available (Annual Reports, 1992-1994, 

Quarterly Reviews 1991-1993), but there are no indications of thorium contamination being 

encountered. 

The SRE Core II fuel was assembled in the Engineering test building before 1960. Later on, this 

building was used for analysis of SNAP fuel burn up analyses and evaluation of irradiation 

experiments. Some research on reprocessing of used nuclear fuel was done in the Hot Cave of 

the Engineering Test Building. These research-related experiments used quantities of up to 1 kg 

of uranium and thorium (Oldenkamp, 1990) and up to 100 g quantities of highly irradiated 

materials. The remediation of this building ended in 1975, after the Hot Cave was dismantled 

and the main process infrastructure was removed (fume hoods, rad waste sinks, drain lines etc.). 

Some drain line contamination was found later and removed. Suspected contaminated sewer 

lines were removed in 1982. The building was released for unrestricted use in 1985 (Sapere and 

Boeing, 2005) and was used for non-radioactive storage after that. The building was demolished 

in 1999. There seems no likely exposure scenario to thorium or americium from the Engineering 

Test Building after 1988.
White Paper Status of Operations Involving Thorium and Americium at 

Area IV SSFL During the Remediation Period (1988 - Present)

November 6, 2018

Page 6 of 9

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 AETR (Building 4100) which operated from 1960–1974, also used thorium-containing fuel. 

The AETR’s first nine core configurations (through 1965) contained various amounts of U-233 

and Th-232, and were driven by 93% enriched uranium fuel. For both the SRE and AETR, the 

thorium isotopes present in the fuel would have consisted mainly of Th-232 and its decay 

progeny, Th-228, in partial equilibrium. Eggen and Morewitz, 1959, indicate that the AETR fuel 

was fabricated at the fuel fabrication area in the AETR lab, which had an 1100 square feet area 

for that purpose. The work was done in a series of glove boxes. The thorium fertile material was 

in the form of 2 by 2 inch metal plates of varying thicknesses. The AETR reactor program was 

terminated in 1974 and the NRC released the building for unrestricted use in 1980. After that, it 

housed other operations, including a Computer Aided Tomography facility and a radioactive 

sample counting lab (Sapere and Boeing, 2005). There seems no plausible exposure to thorium 

after the building was released for unrestricted use. 

The Transuranic Management by Pyropartitioning-Separation (TRUMP-S) program, a joint 

project between the United States and Japan, intended to use small quantities of plutonium, 

neptunium, and americium. The materials for the TRUMP-S testing included 4 g of americium, 

which was stored in the Fuel Storage Facility, Building 4064. The project was transferred to the 

University of Missouri Research Reactor sometime after 1990. There is no evidence that the 

program work was ever started and there was no use of the materials other than storage at Area 

IV SSFL. The Fuel Storage Facility was only used for storage of non-irradiated reactor fuels, but 

all fissionable material was removed by the mid-1980s and was used for storage of 

miscellaneous materials afterwards. There is no indication of a release of materials from the 

TRUMP-S program (Sapere and Boeing, 2005).

The SSFL incident report data base was reviewed for incidents involving americium or thorium. 

There are some indications of incident reports that list americium among other contaminants 

before 1988. Incidents, 1970, page 184, has a listing of Pu and Am particle contamination of 

T055 glovebox maintenance that resulted in some airborne in June, 1979. Incidents, 1980, page 

154, lists personal contamination of Am-241 in 1986, resulting from a smoke detector source. 

There are no listings of incidents involving thorium or americium during the post -1988 period, 

but not all incidents list the nuclide of concern (SSFL 2007, Incidents 1980; Incidents 1990). 

Facilities with potential for thorium and americium residual contamination after 1988 were the 

Hot Lab and the RMDF. Some residual material containing thorium and americium could be 

present at the Hot Lab, based on the operations outlined above for SRE core II and other fuel 

handling operations. During the post-1988 period, the hot lab was being decommissioned and 

decontaminated. A review of the incident report data base indicates a number of small scale 

incidents in the hot lab in the post-1988 period, resulting from D&D operations. None if the 

incident reports list thorium or americium as a radionuclide of concern. The RMDF (Buildings 

4021/4022) consists of several buildings that were used for processing radioactive wastes from 

on-site processes for packaging and disposal. During operation, the facility was guarded and 

fenced to prevent unauthorized access. It was used for storage of wastes through the 

decontamination period. The materials handled had changed from reactor fuels and supporting 

materials to storage of wastes from the decommissioning operations. There is no indication that 
White Paper Status of Operations Involving Thorium and Americium at 

Area IV SSFL During the Remediation Period (1988 - Present)

November 6, 2018

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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 remaining wastes contained significant levels of thorium or americium, because all fuel 

materials had been removed from the site. A review of activity reports on D&D operations for 

the Hot Lab and a review of quarterly surveillance reports for the Hot Lab and the RMDF during 

the 1991-1993 period do not contain any reference to thorium. There is no evidence that there 

was a significant exposure potential to americium or thorium radionuclides at the Hot Lab or the 

RMDF during the post-1988 period. 

CONCLUSION

The major sources of radioactivity at the SSFL came from the reactor facilities, the nuclear fuel 

manufacturing operations and the operations in the Hot Lab. By the end of the operational 

period, all of the highly radioactive fuel had been removed from the site. Thus, two of the most 

important types of radioactivity, the fission products and the transuranics in the reactor fuel had 

all been removed from SSFL by 1988. A detailed review of the operational facilities during the 

remediation period for Area IV SSFL does not indicate a sustained radiation exposure potential 

similar to the operational period. The remaining radionuclides of concern at Area IV in 1992 

were Cs-137, Sr-90, Co-60 and Pu-239. Only Cs-137 and Sr-90 were present in sufficient 

quantity to be readily dispersed for inhalation by workers, and Cs-137 was considered the most 

important radionuclide of concern during this period in operational history (Moore, 1992). 

Although the D&D of remaining facilities may result in unpredictable exposures to residual 

contamination, it is believed that the facility had at that point a state-of-the-art radiation 

protection program that was capable of detecting relevant radionuclides, and that those data are 

available for dose reconstruction under EEOICPA. NIOSH, therefore, does not believe that the 

exposure potential outlined in the SEC-00234 evaluation report continued into the remediation 

period (post-1988). 

REFERENCES

Annual Report, 1992, Annual Report Rockwell International Hot Laboratory Decommissioning, 

GFY 1992, E. M. Larson, Rockwell International, July 02, 1993. [SRDB Ref ID: 072050] 

Annual Report, 1993, Annual Report Rockwell International Hot Laboratory Decommissioning, 

GFY 1993, L. D. Felton, Rockwell International, April 26, 1995. [SRDB Ref ID: 072025] 

Annual Report, 1994, Annual Report Rockwell International Hot Laboratory Decommissioning, 

GFY 1994, L. D. Felton, Rockwell International, April 26, 1995. [SRDB Ref ID: 072026] 

Dennison, 1977, Final Report – SRE Fuel Decladding, W. F. Dennison, February 22, 1977. 

[SRDB Ref ID: 158246] 

Documented Communication, 2017a, Documented Communication with Former Area IV of the 

SSFL Employee, Email communication by ORAU Team and NIOSH, May 10, 2017. 

[SRDB Ref ID: 166848] 
White Paper Status of Operations Involving Thorium and Americium at 

Area IV SSFL During the Remediation Period (1988 - Present)

November 6, 2018

Page 8 of 9

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.

Documented Communication, 2017b, Personal Communication with Former Area IV of the 

SSFL Employee, Interview by ORAU Team and NIOSH, April 18, 2017. [SRDB Ref ID: 

166847]

Eggen and Morewitz, 1959, Epithermal Critical Experiments Hazards Summary Advanced 

Epithermal Thorium Reactor (AETR), D. T. Eggen, H. A. Morewitz, August 1, 1959.

[SRDB Ref ID: 077447]

Incidents, 1980, Radiological Incidents in 1980’s, Compilation of Incident Reports. [SRDB Ref 

ID: 169468]

Incidents, 1990, Radiological Incidents in 1990’s, Compilation of Incident Reports. [SRDB Ref 

ID: 169476]

Moore, 1992, Internal Dose Assessment Program Procedures, Operating Procedure, J. D. 

Moore, Rockwell International, December 16, 1992. [SRDB Ref ID: 073474]

NIOSH, 2016, SEC Petition Evaluation Report for Petition SEC-00234, Area IV of the Santa 

Susana Field Laboratory, National Institute for Occupational Safety and Health 

(NIOSH), October 11, 2016. [SRDB Ref ID: 166405]

NIOSH, 2017, SEC Petition Evaluation Report for Petition SEC-00235, Area IV of the Santa 

Susana Field Laboratory, National Institute for Occupational Safety and Health 

(NIOSH), May 11, 2017. [SRDB Ref ID: 174360]

Oldenkamp, 1990, Nuclear Operations at Rockwell’s Santa Susana Field Laboratory – a Factual 

Perspective, R. D. Oldenkamp and J. C. Mills, January 1990. [SRDB Ref ID: 75029]

Quarterly Reviews, 1991–1993, Compilation of Quarterly ALARA and Surveillance Reports 

(1991–1993), correspondence; various authors, Rockwell International; various dates 

through 1991–1993. [SRDB Ref ID: 166444]

Rucker, 2009, Radionuclides Related to Historical Operations at the Santa Susana Field 

Laboratory Area IV, Thomas L. Rucker, March 2009. [SRDB Ref ID: 132139]

Sapere and Boeing, 2005, Historical Site Assessment of Area IV Santa Susana Field Laboratory, 

Ventura County, California; Sapere Consulting, Inc. and Boeing Company, May, 2005, 

[SRDB Ref ID: 20531]

SSFL 2007, SSFL File Locator and Incident Report Access Databases, provided by Phil 

Rutherford to ORAU TEAM Dose Reconstruction Project for NIOSH on 12/31/2007. 

[SRDB Ref ID: 37588]

Transcript, 2017, U.S. Department of Health and Human Services Centers for Disease Control 

National Institute for Occupational Safety and Health, Advisory Board on Radiation and 
White Paper Status of Operations Involving Thorium and Americium at 

Area IV SSFL During the Remediation Period (1988 - Present)

November 6, 2018

Page 9 of 9

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.

Worker Health, Area IV of the Santa Susana Field Laboratory Work Group, Transcript, 

Monday, December 4, 2017. [SRDB Ref ID: 174359]

Ureda, 1975, Facilities Dismantling Plan for SRE, B. Ureda and W. Heine; June 24, 1975.

[SRDB Ref ID: 158214]