National Institute for Occupational Safety and Health

Y-12 SEC-00250 Petition Evaluation Report

Addendum

Lara Hughes, PhD CHP

Health Physicist

Advisory Board on Radiation and Worker Health, 141st Meeting

August 18, 2021
Y-12 SEC History

Petition Status Basis of Class added to SEC

SEC-00250 

Addendum Reserved period (1987-1994) None recommended

SEC-00250 Class added to SEC for 1977-07/1979

(No class rec. for 8/1979-1986)

Infeasibility to reconstruct doses from Thorium (Th), 

period from 1987-1994 reserved

SEC-00251 Class added to SEC for 1958 - 1976 Infeasibility to reconstruct doses from Thorium (Th), 

and plutonium-241 

SEC-00186 Class added to SEC for 1948 - 1957 Infeasibility to reconstruct doses from Th and 

cyclotron radionuclides

SEC-00098 Class added to SEC for 1943 - 1947 Infeasibility to reconstruct internal doses from 

calutron operations

SEC-00028 1948-1957 Initial limited class 

SEC-00018 1943-1947 Initial limited class
Y-12 SEC-00250 Petition Evaluation

 Received November 1, 2018 with proposed class:

– All workers who worked in any area of Y-12 where Uranium (U) was 

fabricated or processed from January 1, 1980 to December 31, 2000

 NIOSH-evaluated class:

– All employees who worked at the Y-12 Plant in Oak Ridge, TN that may 

have incurred Th exposures during the period January 1, 1977 through 

December 31, 1994

– Y-12 plant was placed in stand down mode in Sep. 1994 – end of routine 

processing operations, thus NIOSH ended the qualified period then
Y-12 SEC-00250 Petition Evaluation History (cont.)

 Period not recommended to be added to the SEC:

– August 1, 1979 through December 31, 1986: Th doses can be 

reconstructed with available data

 SEC-00250 ER Addendum:

– January 1, 1987 through December 31, 1994: Th doses can be 

reconstructed with available data
Y-12 Claim Numbers (as of January 2021)

6,869 Total number of claims submitted for dose reconstruction (DR)

2,763 Workers who worked from January 1, 1987 through December 31, 

1994 

806 Workers who started employment during the evaluation period 

2,616 DRs completed during the reserved evaluation period

1,341 With internal dosimetry records for evaluation period 

2,363 With external dosimetry records for evaluation period 
Sources of Available Information

 Data collected from Y-12

 DOE operations center 

Germantown

 Site Profile and Technical 

Information Bulletins and 

Procedures

 NIOSH Site Research Database 

(SRDB): >10,000 documents related 

to Y-12

 Coworker studies

 Electronic databases

 23 Interviews with former Y12 employees

 Scientific publications

 Existing claimant files 
Y-12 History

 811-acre site

 0.67 by 3.2 miles

 Peak employment: 22,000 

workers, down to ~5700 by 

1998

 Covered period: 1942 - present
Y-12 Site History

 First Era (until 1946) – U isotope separation

– Calutrons for U enrichment

 Second Era (until ~ 1994) – Cold War nuclear weapons components 

manufacturing

– Produce and test key components of nuclear weapons

• Stockpiling HEU

• Technology development for new weapons designs

 Third Era (after ~ 1994) – Multiple new missions

– Storing HEU

– Environmental and waste management

– Continued weapons part production on smaller scale
Y-12 History – Th Parts Production

 Production of Th metal parts using arc melting started in 1959

 Th pellets pressed into electrodes and arc-melted into ingots

 Ingots from meltings pressed, rolled and machined, scrap recycled 

 Radium and other Th progeny volatilized during arc melting

 Major Th processing ended in mid-1970s, all Th arc melting ended in 1994
Y-12 History – Th Parts Production (cont.)

 Th parts refurbishment and small-scale special projects continued until

1999

 Entire Y-12 Plant was in stand-down in 1994 through 1998

 All special projects ended in 1999 after a DU incident with the arc melter

 Process Buildings: 9202, 9766, 9215, 9201-5, 9204-4, 9201-1, 9206

 Storage Buildings: 9202, 9995
Y-12 History – Th Inventory 

Year Th inventory (kg)

1986 5437

1987 4101

1988 4171

1989 4185

1990 4180

1991 4166

1992 4888

1993 4885

1994 5499

1995 18,066

• Inventory relatively consistent 

over evaluation period (1987-

1994)

• Increase in 1995 is due to 

“weapons awaiting disassembly” 

i.e. storage operations
Th Exposure Potential

 Th is the beginning of a decay series which contains multiple radionuclides

 Number of separations of the Th affects total dose potential

 Nuclides of particular dosimetric concern: Th-232, Th-228, Ra-228

 Arc melting is the Th process of most concern due to airborne 

contamination generation and disruption of the Th decay chain 

 Radium contained in the metal is vaporized and released into the air 

 Ingot from arc melting has radium enriched outer layer
Internal Th Dose Data Availability

 Th lung counts exist for 1959-1994 

 Th results available in units of mass (mg) for 1959 – July 31, 1979

 Th results containing progeny activity available from 8/1979 – 1994

 NIOSH has obtained useable Th in vivo count data for 1987-1994 from 3 

systems: 

– NaI detector at Y-12 in vivo facility (1/2/1987-12/10/1991)

– LEGe detector at K-25 (1/13/1992 – 1/6/1994)

– LEGe detector at Y-12 (5/14/1992 – 12/29/1994)
Y-12 Th Records 1979-1986 (SEC-00250 ER)

Year Number Individuals Number of Ac/Pb 

Measurements

1979 43 55

1980 110 128

1981 142 208

1982 83 179

1983 130 166

1984 87 89

1985 83 84

1986 95 98

Total 512 1,007
Y-12 Th Records 1987-1994 (SEC-00250 Addendum)

Year Y-12 NaI Lung 

Counts

K-25 LEGe Lung 

Counts

Y-12 LEGe Lung 

Counts

1987 240

1988 547

1989 665

1990 825

1991 1182

1992 174 460

1993 4 886

1994 850

Total 3459 198 2196
Data Pedigree

 Standard process of SEC evaluations

 Data stored in two separate data repositories for evaluation period (1987-

1994)

– Delta View Imaging System, scans of “raw” data reports

– Electronic Record System (ERS), tabulated records summary

 Some discrepancies were found when comparing the two sources

– Delta View but not in ERS: 838 records

– Mostly from 7000 and 9000 series departments

 Clarification requested from Y-12
Data Pedigree (cont.)

 Y-12 provided updated ERS file, based on updated search criteria

– 568 were provided by Y-12 in the update file

– 132 declared invalid measurements

– 128 not in ERS because of a data migration error (Delta View is copy of

record)

 Pedigree issues were satisfactorily resolved

 Data are of sufficient quality to be used in bounding Th dose
General Approach for Th Dose Reconstruction

 Th doses can be bounded using the gamma spectral data from the in vivo

count for Ac-228 and Pb-212, nuclides in the Th decay chain

 NIOSH developed OTIB-0076, Guiding Reconstruction of Intakes of Th

Resulting from Nuclear Weapons Programs to assign Th doses

 Pb-212 results are used to estimate intakes of Th-232 and Th-228

 Ac-228 results are used to estimate intakes of Ra-228

 Intakes are used to assign internal doses from Th
Specifics for Th Dose Reconstruction for Y-12

 Th results from Y 12 NaI in vivo facility (1987-1991): doses can be bounded

using established procedures

 Th results from K-25 facility (Jan-May 1992) cannot be used (no Ac-228 or

Pb-212 reported)

 Th results from Y-12 LEGe in vivo facility (June 1992-Dec.1994): Ac-228

results only: doses can be bounded using available chest wall thickness

(CWT) data as outlined in DCAS-RPRT-008
DCAS RPRT-008

 Lung counts from June 1992- Dec. 1994 records only have Ac-228

measurement, but no Pb-212 measurement

 In-vivo spectral data was used to estimate the Pb-212 detection efficiency

and background in the Pb-212 energy region

 A function was developed to derive the Pb-212 MDA using the chest wall

thickness measurement (CWT)

 MDA can be used as an upper bound in lieu of critical level

 Applied as a triangular distribution
Internal Dose Bounding Summary 

 Available monitoring records are sufficient to complete internal Thorium

dose reconstruction for the proposed class of employees from January 1,

1987 through December 31, 1994

– 1/1/1987 – 12/31/1991: using available Ac-228 and Pb-212 data to

bound the dose using methods described in OTIB-0076

– 6/1/1992 – 12/31/1994: using available Ac-228 data and CWT

information outlined in DCAS-RPRT-008

– Data from K-25 in vivo counter 5/1992-12/1994 is not used
Feasibility Findings for Y-12 (SEC00250)

Source of Exposure Dose Reconstruction Feasible

Internal - Th Yes
Questions/Discussion