National Institute for Occupational Safety and Health

Y-12 SEC-00250 Petition Evaluation Report

Lara Hughes, PhD CHP

Health Physicist

Advisory Board on Radiation and Worker Health, 130th Meeting

Oak Ridge, TN | August 21, 2019
Y-12 SEC History

Petition Status Basis

SEC-00250 Current petition Pending Board Action

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

 Reserved period:

– January 1, 1987 through December 31, 1994: awaiting release of Th 

data from Y-12
Proposed Class Definition (Initial)

 All employees of the Department of Energy, its predecessor agencies, and 

their contractors and subcontractors who worked at the Y-12 Plant in Oak 

Ridge, Tennessee, during the period January 1, 1977 through July 31, 1979 

for a number of work days aggregating at least 250 work days, occurring 

either solely under this employment or in combination with work days 

within the parameters established for one or more other classes of 

employees in the Special Exposure Cohort.
Y-12 Claim Numbers (as of May 2019)

6,525 Total number of claims submitted for dose reconstruction (DR)

3,615 Workers who worked from January 1, 1977 - December 31, 1994 

1,825 Workers who started employment during the evaluated period 

3,211 DRs completed for the evaluated period

1,688 With internal dosimetry records for evaluation period 

3,267 With external dosimetry records for evaluation period 
Sources of Available Information

 Site Profile and Technical 

Information Bulletins and 

Procedures

 NIOSH Site Research Database 

(SRDB): >10,000 documents related 

to Y-12

 Existing claimant files 

 Coworker studies

 Electronic databases

 Interviews with former Y-12 

employees

 Scientific publications
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 highly enriched U (HEU)

• Technology development for new weapons designs

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

– Storing HEU

– Continued weapons part production on smaller scale D&D

– Environmental and waste management
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 depleted U (DU) incident with 

the arc melter

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

 Storage Buildings: 9202, 9995
Y-12 History – U Processes

 U processed to produce weapons components using a variety of 

compounds and enrichments

 Larger scale process compared to Th operations

 U enrichment production started in 1943
Y-12 History – U Processes (cont.)

 U operations shifted to recovery and recycling mostly normal and 

depleted U after WW II

 U production processes also included arc melting 

 Machined components sent through finishing operations that included 

drilling, welding, brazing, polishing, and final specification checks 
Y-12 History – Isotopes Production Group

 ORNL Isotopes Group used Y-12 (and ORNL) facilities for isotope 

production, separation and purification

 Y-12 facility, but main operations staffed by ORNL workers

 Production of radioactive and stable materials

 Addressed in a previous NIOSH report (RPRT-0090) to address exotics at 

ORNL
Y-12 History – Isotopes Production Group (cont.)

 Calutrons in Building 9204-3: U and Plutonium (Pu) production

 86-inch cyclotron (9201-2): medical isotope production, operated 1950-

1983

 Conversion Lab: Radiochemistry facility that handled the radioisotopes 

from the calutron and cyclotron operations
U and Other Isotopes Exposure Potential

 Inhalation of airborne particulate radioisotopes was the main concern for 

internal exposure to U and other isotopes 

 U was the principal source of internal exposure at Y-12 due to the large 

scale of the operations

 Trace quantities of Pu, Np and Tc from recycled U
U and Other Isotopes Exposure Potential (cont.)

 Radionuclides handled by the ORNL Isotopes group at Y-12 and ORNL 

included 213 different isotopes

 Materials are detailed in ORAUT-RPRT-0090, which is currently being 

reviewed and discussed under the NIOSH ORNL effort

 Available data for U and other isotopes are sufficient to bound doses to 

these nuclides
Th Exposure Potential

 Th is part of a decay chain

 Number of separations of the Th affects dose

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

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

potential of airborne contamination 
Th Exposure Potential (cont.)

 Arc melting process disrupts the Th decay chain

 Large quantities of the radium contained in the metal is vaporized and 

released into the air 

 Ingot from arc melting has radium enriched outer layer

 Ra-224 and its sub-series quickly return to equilibrium
Internal Th Dose Data Availability

 Th lung counts exist for 1977-1994 

 Change in recording procedure in August 1979

 Th results are reported in units of mg for 1977 – July 31, 1979

 NIOSH has received useable Th lung count data for 1979-1986

 Post-1987 available according to Y-12, but there are accessibility issues
Internal Th Dose Data Availability (cont.)

 From Y-12 in-vivo facility using NaI or Ge detector system 

 Th results can be associated with Ac-228 (Actinium) and Pb-212 (Lead) 

measurements recorded for August, 1979 – December 31, 1986 lung 

counting 

 Th chain disequilibrium is an issue 

 No measurement data for Ra-228
Y-12 Th Records 1979-1986

Year Number Individuals Number of Ac/Pb 

Measurements

1979 46 55

1980 137 128

1981 146 208

1982 84 179

1983 130 166

1984 87 89

1985 83 84

1986 95 98

Total 808 1,007
Approach for Th Dose Reconstruction

 Th doses can be bounded using OTIB-0076, Guiding Reconstruction of 

Intakes of Th Resulting from Nuclear Weapons Programs:

 Th results have to be associated with in-vivo Ac-228 and Pb-212 

measurements recorded for August, 1979 – December 31, 1986

 The separation history of the material has to be known or assumed (triple 

separated will be used for Y-12 Th approach)
Approach for Th Dose Reconstruction (cont’d)

 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 estimate doses to organs
Internal Dose Bounding Summary 

 Th internal dose reconstruction infeasibility January 1977 – July 1979 

(SEC class recommendation)

 August 1979 – December 1986: analysis of Th worker Ac/Pb data can be 

used to bound exposure to all Th workers

 January 1987 – Dec. 1994: Evaluation Report section reserved – data 

expected to be obtained from Y-12, needs to be evaluated for suitability 

to be used in Th dose reconstruction

 Internal doses to U and exotic isotopes can be bounded using available 

methods discussed in Technical Basis Document and Report 90
External Dose Data

 A dosimetry (film)/security badge was adopted for use at all Y-12 facilities in 

the pre-SEC-00250 time period. 

 Issued to all personnel at Y-12 Plant because it was part of the security 

badge 

 Badges provided routine and accident-related monitoring 

 In 1980, the film badges were replaced by Thermoluminescent Dosimeters 

(TLD) 

 OTIB-0064 contains coworker data from 1952 – 1979

 External doses assigned based on available data and methods
Feasibility Findings for Y-12 (SEC00250)

Source of Exposure Dose Reconstruction Feasible

Internal - Th 

No (1/1/77 – 7/31/79)

Yes (8/1/79-12/31/86)

Reserved (1/1/1987 – 12/31/1994)

Internal - U Yes (1/1/1977 – 12/31/1994)

Internal – Exotics Yes (1/1/1977 – 12/31/1994)

External – Beta-Gamma Yes (1/1/1977 – 12/31/1994)

External – Neutron Yes (1/1/1977 – 12/31/1994)

External – Occup. Medical X-ray Yes (1/1/1977 – 12/31/1994)
Class definition recommended

 All employees of the Department of Energy, its predecessor agencies, and 

their contractors and subcontractors who worked at the Y-12 Plant in Oak 

Ridge, Tennessee, during the period January 1, 1977 through July 31, 1979 

for a number of work days aggregating at least 250 work days, occurring 

either solely under this employment or in combination with work days 

within the parameters established for one or more other classes of 

employees in the Special Exposure Cohort.