National Institute for Occupational Safety and Health

Area IV – SSFL Follow up on SEC-00235 on Am/Th and 

Air Data

Lara Hughes, PhD CHP

Division of Compensation Analysis and Support

Advisory Board on Radiation and Worker Health, 126th Meeting

Redondo Beach, CA

December 12, 2018
Area IV SSFL 

 290 Acres, Ventura County, 

30 miles NW of Los 

Angeles

 Covered period (DOE):

– 1955-1988

– 1988-present 

(remediation)
SEC Classes for Area IV SSFL

Petition 

Number NIOSHrecommended 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-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 – class evaluated: Aug. 1, 1991 through June 30, 1993
BACKGROUND

 SEC-00235 petition for Area IV SSFL for period after 1988 (remediation 

period)

 Qualified for evaluation for Aug. 1, 1991 – June 30, 1993, CEP period

 NIOSH evaluation to Board in August 2017, no class recommended

 Evaluation discussed with Area IV SSFL Work Group on Dec. 4, 2017

 WG requested additional work on two issues:

– Status of Thorium and Americium operations post-1988 (in light of 

SEC-00234)

– Evaluate available air sample data during the CEP period (when in 

vitro bioassay data are invalid)

 2 White Papers issued by NIOSH in November 2018
Area IV SSFL status after 1988

 Three facilities are main focus from exposure standpoint

– Hot Lab (Building 20)

– RMDF

– SNAP reactor facility

 Main radionuclides of concern during D&D are

– Fission Products, mostly Cs-137 and Sr-90

– Residual alpha activity in Hot Lab is Pu-239

– Activation Product in SNAP reactor facility is Co-60
Status of Operations with Th and Am after 1988 

 All reactor operations ended by 1980

 Nuclear support operations ended by 1988 

 Thorium source term pre-1988:

– Reactor fuel component of SRE and ATR

– Nuclear support operations of this fuel

 Americium source term pre-1988:

– Transuranic in all used reactor fuel

– Sealed sources
Thorium 

 SRE Core II in operation 1960-1964 – Th-232 and EU alloy 

– Core II fuel assembled in Engineering Test Building

– SRE Core II fuel stored in RMDF after removal from Reactor, 1964

– Core II fuel disassembled in Hot Lab starting in 1974

– Shipped off site in 1977

– Engineering Test Building released for unrestricted use in 1985

 AETR operated from 1960-1974, fuel fabricated at reactor building in 

1959

– AETR building released for unrestricted use in 1980

 No incidents involving Th listed 
Americium

 All reactor fuel was removed from site by 1988

 Transuranic Management by Pyropartitioning Separation program used 

Americium and other isotopes, but program never started, materials 

were in storage only

 Incidents mentioning Am only before 1988

 Hot Lab and RMDF have potential for some residual contamination from 

transuranics

 Review of decommissioning and quarterly review reports do not 

indicate any evidence that Am or Th were encountered at the 

operational facilities
Conclusion on Th and Am status

 The major source term for Am and Th had been removed from site by 

1988 (nuclear reactor fuel)

 Detailed review of facilities during the remediation period do not 

indicate a sustained radiation exposure similar to operational period

 D&D could produce unpredictable exposures, but site had an internal 

exposure monitoring program driven by air sampling

 NIOSH does not find that the exposure potential from the operational 

period continued into the remediation period
Air Sampling Background

 General Air sampling (GA): fixed location sampling, weekly results 

averaged over quarter (13 weekly results)

 Breathing Zone air sampling (BZ): worn by worker during jobs 

 Results compared to max permitted air concentration (MPC) for 

radionuclides of concern:

– Sr-90 (beta): 1E-09 μCi/mL

– Pu-239 (alpha): 2E-12 μCi/mL

 BZ compared to MPC-hr limit of 2000/yr or 520/quarter

 Full face and air line respirators in use

 Until 1992 air sampling was the primary exposure assessment method, 

bioassay was backup
Operations and Data Summary – SNAP (T-059)

 Air data available for 1991 (4 quarters)

 Facility is undergoing D&D, Co-60 is main contaminant

 Structural steel and irradiated concrete are reduced in size and sent to 

RMDF for interim storage until shipped off-site

 Airborne radionuclides observed during removal of old NaK lines

 Workers wore BZ samplers during operations causing airborne 

contamination

 No GA samplers in SNAP area
Operations and Data Summary – Hot Lab

 Air data available for 1990-1993 (15 quarters)

 28 GA samplers recorded air data every quarter

 Workers with potential for intakes wore BZ and respirators if needed

 Facility with largest amount of BZ data available

 D&D operations mainly removal of cell liners and drain pipes

 Some incident reports indicate small events of contamination

 Period in 1993 showed some elevated GA data points

 Any potential intakes could be assessed
Operations and Data Summary – RMDF

 Air data available for 1990-1991, one quarter missing

 Seven fixed GA air samples

 BZ data for up to 10 workers available

 Only facility that was not in D&D mode

 Receiving material from other areas at Area IV

 Size reduction, packaging, storing and shipment of materials off-site
Hot Lab Beta GA Max. Average - Operational Period

1.E-15

1.E-14

1.E-13

1.E-12

1.E-11

1.E-10

1.E-09

1.E-08

1.E-07

1.E-06

1.E-05

1974 1976 1978 1980 1982 1984 1986 1988 1990

GA beta annual average air concentration, 

μCi/mL

Year

GA

MPC
GA Max Quarterly Averages – Remediation Period
Max BZ per Quarter– Remediation Period
Hot Lab Elevated Data

 Quarters 1 – 3 had elevated quarterly results in three locations

– Service Gallery: staging area behind hot cells

– Basement: not generally occupied, except when work is done, such 

as removal of contaminated drain lines

 Worker BZ data remained below regulation level

 Workers’ WBC data was reviewed, some had small readings of Cs-137 

 New bioassay contractor available starting third quarter 1993, would 

have picked up potential worker intakes 
Air Data Conclusion

 GA and BZ data are available, but some quarters and some facilities are 

not currently available to NIOSH

 Raw data/logbooks potentially available

 It is not clear if this data is available and how easily it could be collected

 Hot Lab data set is most complete and believed to be bounding

 Elevated samples are unusually high, but elevated samples in general 

would be in line with disruptive operations during D&D

 Despite these type of operations, no significant worker intakes observed

 NIOSH believes that the available information is sufficient to bound doses 

from D&D operations during the CEP period
For more information, contact CDC

1-800-CDC-INFO (232-4636)

TTY: 1-888-232-6348 www.cdc.gov

The findings and conclusions in this report are those of the authors and do not necessarily represent the 

official position of the Centers for Disease Control and Prevention.