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Metals and Controls Corp. Thorium And 

Welding Exposure Model

White Paper

National Institute for Occupational 

Safety and Health

April 8, 2019

Pat McCloskey

Mutty Sharfi

Oak Ridge Associated Universities Team

Reviewed By: 

Christine Corwin

James W. Neton, Ph.D. CHP

Timothy D. Taulbee, Ph.D. 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. 
White Paper Metals and Controls Corp. Thorium and Welding

Exposure Model

April 8, 2019

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. 

INTRODUCTION

The National Institute for Occupational Safety and Health (NIOSH) presented the Evaluation 

Report (ER) for SEC-00236, Metals and Controls Corp. (M&C) to the Advisory Board on 

Radiation and Worker Health (Board) on August 24, 2017. At the conclusion of that 

presentation, a petitioner raised a concern about the adequacy of the ER in addressing 

maintenance type work. The petitioner stated that he “took great care to define the class of 

workers under evaluation in this petition as precisely and as narrowly as possible to coincide 

with workers for whom there is a high degree of confidence that they received elevated 

exposures to residual radioactive contamination.” 

In response to this concern, on September 5, 2017, NIOSH initiated strategies to continue M&C

research and further develop SEC-00236. These strategies included plans to review monitoring 

records in the Site Research Database (SRDB) and plans to search for former M&C workers so 

that NIOSH could conduct interviews with them. 

From October 24, 2017, through October 26, 2017, NIOSH, Oak Ridge Associated Universities 

(ORAU), and Sanford Cohen & Associates (SC&A) personnel interviewed 12 former M&C 

workers and individuals knowledgeable about maintenance work. Interviewers asked questions 

regarding the frequency and duration of work, including heating, ventilation, and air 

conditioning (HVAC), utility and drain line maintenance, and new equipment installations. 

In addition to the interviews, other notable actions included the following: 

• November 8, 2017 - The Metals and Controls Working Group (Working Group), SC&A,

Division of Compensation Analysis and Support (DCAS), and ORAU team members held a

teleconference to discuss technical issues associated with developing exposure models

regarding maintenance work.

• February 6, 2018 - NIOSH obtained additional monitoring data regarding remediation work

performed by Creative Pollutions Solutions (CPS) in 1992 and 1994 (CPS 1992-b; CPS

1994).

• February 13, 2018 - NIOSH received a report by SC&A titled Review of SEC Petition ER

SEC-00236 (Mauro, 2018).

• April 23, 2018 - NIOSH issued the Metals and Controls Corp. Subsurface Exposure Model

white paper (NIOSH, 2018-a) and made it available to SC&A and the Working Group.

• May 3, 2018 - During a Working Group meeting, SC&A presented their findings and

observations associated with the SEC-00236 ER. The petitioners also made a statement and

provided a letter with their concerns. After the meeting, an issues matrix was created.

• August 22, 2018 - During a full Board meeting, the Working Group presented their findings

and observations associated with the SEC-00236 ER and NIOSH provided an update. The

petitioners also made a statement and provided a letter with their concerns at the meeting.
White Paper Metals and Controls Corp. Thorium and Welding

Exposure Model

April 8, 2019

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. 

• November 20, 2018 - During a Working Group meeting, NIOSH presented the Metals and

Controls Corp. Maintenance Exposure Model white paper (NIOSH, 2018-b) that included

HVAC maintenance and Building 10 overhead exposure models. SC&A presented their

observations associated with the Metals and Controls Corp. Subsurface Exposure Model and

Metals and Controls Corp. Maintenance Exposure Model white papers (NIOSH, 2018-a;

NIOSH, 2018-b), and the petitioners also made a statement with their concerns.

• December 13, 2018 - During a full Board meeting, the Working Group presented an update.

The petitioners also made a statement and provided a letter with their concerns at the

meeting.

This white paper addresses two concerns recently raised by the petitioner; it provides an 

exposure model for exposures that occurred during welding activities and provides a method for 

bounding thorium exposures while working inside Building 10. 

INTERNAL EXPOSURES TO THORIUM

Background 

The SEC-00236 petitioner raised the following issue, which was designated as P5 in the M&C 

Issues Matrix (https://www.cdc.gov/niosh/ocas/pdfs/dps/dc-metcontimsec236-101218-508.pdf): 

The 1995 Drainage System Characterization Report (Weston 1996) included 15 grab samples of 

accumulated sediment or surrounding soils in discrete locations of the pipe where elevated 

direct measurements were observed. The grab sample analyses reported an isotopic analysis of 

uranium but no other radionuclides. In retrospect, we now know that thorium would have also 

been present, as it was historically processed on the same manufacturing equipment as uranium 

during the Atomic Weapons Employer (AWE) program. But given the limitation of the 1995 

survey measurements, we have no way of knowing how much thorium source term was present in 

the residual radioactivity to which the M&C maintenance workers were exposed (Elliott, 2018, 

PDF p. 7). 

NIOSH September 12, 2018, Response to Issue P5

NIOSH is aware that a small amount of thorium work was done on the same equipment in the 

same areas as the uranium work. NIOSH is also aware that the equipment was cleaned or 

shipped offsite and the areas cleaned (not decontamination and decommissioning [D&D]) when 

those operations ceased prior to the start of the residual period. NIOSH relies on the available 

data and models thorium exposures for those areas where we have thorium data. If the petitioner 

is aware of new information, NIOSH will consider it.

Thorium Operations 

During AWE operations, thorium-bearing component fabrication occurred (including reactor 

fuel, metallic alloys, and metallic foils). The only definitive information regarding the amount of 
White Paper Metals and Controls Corp. Thorium and Welding

Exposure Model

April 8, 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. 

thorium at M&C is from a 1962 nuclear safety analysis that listed the total quantity of thorium as 

244 kg. 

By comparison, during AWE operations, uranium-bearing component fabrication occurred 

(including reactor fuel, metallic alloys, and metallic foils). Inventory information for 1962 

indicated the presence of 7,097 kg uranium (ASTRA 1962, PDF p. 47). 

The uranium to thorium-232 ratio in the 1962 inventory data was dominated by uranium. There 

was approximately 29 times as much uranium as there was thorium-232 (assuming the mass of 

natural thorium consisted almost entirely of thorium-232), and the activity ratio was even more 

dominated by uranium where there was 188 times more uranium (assuming natural uranium and 

thorium-232). 

As M&C cleaned the areas used for AWE operations prior to 1968, they buried waste and 

materials in the area between Buildings 11 and 12. M&C personnel made the U.S. Nuclear 

Regulatory Commission (NRC) aware of this burial area in 1982 as part of their D&D effort. The 

NRC performed verification sampling of the burial area in 1984 and notified M&C personnel of 

the presence of contamination above release limits, including the presence of thorium. The M&C 

contractor, CPS, performed additional sampling of the burial area in 1992 and corroborated the 

presence of thorium in their report to M&C (CPS 1992-a). 

In addition, NIOSH determined the radioactivity ratio of uranium to thorium-232, using data 

from samples taken of waste and materials removed from the former AWE areas and placed in 

the burial area. There were 754 samples taken of the outside perimeter of Building 10 and the 

burial area that were analyzed for both uranium and thorium-232. NIOSH determined a paired 

activity ratio of uranium to thorium-232 for each of these samples and calculated a geometric 

mean ratio of uranium to thorium-232 as 9.88:1. 

New NIOSH Bounding Method (April 17, 2019) 

Although M&C only analyzed Building 10 subsurface samples for uranium in 1995, NIOSH can 

bound thorium exposures during maintenance work by assuming that the subsurface sediments 

contained equivalent amounts of natural uranium and thorium-232. 

NIOSH previously determined in the Metals and Controls Corp. Maintenance Exposure Model

white paper (NIOSH, 2018-b) that the 95th-percentile measured uranium activity in the 

sediment/sludge was 6,888 pCi/g, and since the specific activity of natural uranium is 7.1E+5 

pCi/g, this corresponds to a mass of 9.7 mg of natural uranium per gram of sludge or about 1% 

by weight.

If we assume that the subsurface was contaminated with equal amounts of thorium and uranium, 

then 1% of the sediment/sludge and the subsequent dust loading created from maintenance work 

would have resulted in a thorium air concentration of 2.2 μg/m3. Using the thorium-232 specific 

activity (0.11 μCi/g), the air concentration would have been 2.42 E-13 μCi/mL during the one 

month of subsurface maintenance each year. 
White Paper Metals and Controls Corp. Thorium and Welding

Exposure Model

April 8, 2019

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. 

To provide some perspective, using the largest ICRP 60 dose conversion factors (DCF) for 

thorium-232 and its progeny, this concentration would amount to an inhalation committed 

effective dose (CED) of 10.42 mrem/yr. If we also add ingestion this estimated dose becomes 

14.78 mrem/yr. 

NIOSH can use our calculated air concentration to bound internal thorium exposures that 

occurred while performing subsurface maintenance within Building 10. 

For those areas where gross alpha contamination surveys are available, NIOSH will continue to 

estimate worker doses using the most claimant-favorable isotope of thorium or uranium. 

For the burial area and Building 10 outside perimeter, NIOSH can use isotopic thorium-232 

results to model air concentrations breathed by maintenance workers as previously described in 

the Metals and Controls Corp. Maintenance Exposure Model white paper (NIOSH, 2018-b). 

INTERNAL EXPOSURES FROM WELDING

Welding Operations 

During the residual period, while performing maintenance work in the Building 10 overhead 

area, M&C workers were potentially exposed to contamination remaining from AWE operations. 

This work included installing pipe racks, welding supports to the trusses to fortify the roof, and

cutting and drilling up through the roof to make penetrations for running services to rooftop 

equipment, such as air-conditioning systems, recirculation water, chilled water supply and return 

and steam and condensate return, and installing equipment on the roof (ORAUT, 2017-a, 

October 24, 2017, PDF p. 4; ORAUT, 2017-b, October 25, 2017, PDF p. 7; NIOSH, 2018-c. 

A June 1981, NRC Inspection Report stated that Texas Instruments used a "Cutting and Welding 

Permit" program. This program required that a Cutting and Welding Permit was needed any time 

a cutting or welding job causing hot slag had to be done outside of a designated cutting and 

welding area.

The permit system used a card on which the necessary precautions required to be taken were 

listed. Authorization to perform the cutting and/or welding was shown by the signature of the 

"Fire Safety Supervisor." The card had a section that called for checking the work and all 

adjacent areas to which sparks and heat might have spread for a period of 30 minutes after the 

work was completed. The fact this check was done was shown by a signature (NRC 1981-1982, 

PDF p. 15). 

The 1964 M&C Safety Manual specified welding and flame-cutting precautions for fire safety, 

including pre-work cleaning of combustible debris, removal of deposits inside of ductwork, use 

of curtains and shields to protect personnel from glare and sparks, and use of “permit required” 

areas for sewers, pits, drains, ventilators, and ducts. The manual also stated that barricades were 

required for overhead work (M&C Nuclear, 1964, PDF pp. 10-12, 24). 
White Paper Metals and Controls Corp. Thorium and Welding

Exposure Model

April 8, 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. 

NIOSH obtained the following information during M&C worker interviews: 

Worker #1: When you’re cleaning beams so you can weld onto them... I would just go up 

on a high-lift and blow it all off with a compressed air tank. Then you would prep it with 

a wire brush, and then grind it to prep it for welding. For that period when you were 

doing that, you really made a heck of a mess. I used oxyacetylene all the time for brazing 

and silver soldering. 

Dr. Mauro: Did you use it for cutting steel pipe or for rebar and things like that? 

Worker #1: Yes, that job eventually became a job for the millwrights, but I did plenty of it 

because we had to make supports for my pipe racks and things like that. They were busy 

with their own stuff, so we did ours (Interview Worker #1, October 24, 2017, PDF p. 10). 

NIOSH Bounding Method

Interviews of M&C maintenance personnel indicated that welding in the dusty overhead area 

was only one of their many duties that also included subsurface and HVAC work. This bounding 

scenario applies to only those maintenance workers that performed welding tasks in the Building 

10 overhead area. 

NIOSH previously modeled maintenance work in the overhead area with an occupancy rate of 1 

month (168 hours) per year (NIOSH, 2018-b). Interviews conducted by NIOSH indicated that 

welding was one of the activities frequently performed while in the overhead area and that the 

amount of time spent was approximately 4 hours per month or 48 hours per year on average

(ORAUT, 2017-b, October 25, 2017). NIOSH will assume that welding tasks occupied this

amount of time per year.

NIOSH previously characterized the overhead work environment using the total surface activity

and assumed 10% of that activity was removable and available to generate airborne activity. 

NIOSH will continue to assign doses using this method for other work in the overhead area (e.g., 

light bulb replacements); however, for welding, NIOSH will assume 100% of the activity is 

resuspended. 

In addition, NIOSH modeled exposures for the entire overhead area uniformly using the 95thpercentile contamination level and a 10-4 resuspension factor. We are aware that good work 

practice requires clean bare metal prior to welding, which can include wire brushing and 

grinding as described by Worker #1 above. NIOSH believes this weld preparation work to be the 

portion of the welding task capable of generating the highest airborne concentration. In addition, 

NUREG-1400 (NRC, 1993) Section 1.2.3 indicates that a dispersibility factor of 10 should be 

used when modeling intakes that involve grinding operations. Therefore, NIOSH will increase 

the resuspension factor and apply a value of 10-3 to the 95th-percentile contamination level. 

In summary, the 95th-percentile gross-alpha contamination level was calculated as 89.94 

dpm/100 cm2 and the geometric standard deviation (GSD) at 3.61. NIOSH increased the 
White Paper Metals and Controls Corp. Thorium and Welding

Exposure Model

April 8, 2019

Page 7 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. 

resuspension factor to 10-3 because of the enhanced airborne generation caused by grinding, to 

determine an air concentration of 4.05E-12 μCi/mL during the 48 hours of welding each year. 

To provide some perspective, using the largest ICRP 60 DCF for uranium-234, this 

concentration would amount to an inhalation CED of 5.88 mrem/yr. The uranium ingestion dose 

associated with this estimate is negligible. In addition, using the largest ICRP 60 DCFs for 

thorium-232 and its progeny, this concentration would amount to an inhalation CED of 16.75 

mrem/yr. If we also add ingestion, this estimated dose becomes 16.77 mrem/yr. 

This air concentration would be assumed to be inhaled for the 48 hours of welding that occurred 

per year for M&C personnel that performed welding in the Building 10 overhead area and will 

be in addition to other assigned exposures. 

CONCLUSION

NIOSH has considered all of the information presented in this white paper and has used it to 

develop exposure models for Metals and Controls Corp. that account for the descriptions of work 

by former employees, pre-remediation sample data, and a realistic dust resuspension model. 

NIOSH believes that this model adequately bounds maintenance exposures experienced by M&C 

workers during the residual radiation period. 
White Paper Metals and Controls Corp. Thorium and Welding

Exposure Model

April 8, 2019

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. 

REFERENCES

ASTRA, 1962, Analysis of Possible Nuclear Material Losses and Possible Liabilities Associated 

with Present Fuel Manufacturing; ASTRA Inc.; March 12, 1962. [SRDB Ref ID: 13612] 

CPS (Creative Pollution Solutions, Inc.), 1992-a, Radiological Characterization of Texas 

Instruments, Incorporated-Attleboro Industrial Facility; 1992. [SRDB Ref ID: 164755] 

CPS (Creative Pollution Solutions, Inc.), 1992-b, Radiological Health and Safety Plan—

Appendix A, Health and Safety Activities During Remediation of the Texas Instruments 

Incorporated Attleboro Site; modified September 1, 1992. [SRDB Ref ID: 169474] 

CPS (Creative Pollution Solutions, Inc.), 1994, Radiological Health and Safety Plan—Appendix 

A, Health and Safety Activities During Remediation of the Texas Instruments Incorporated 

Attleboro Site; April 24, 1994. [SRDB Ref ID: 169475] 

Elliott, 2018, Special Exposure Cohort Petition SEC00236, correspondence to National Institute 

for Occupational Safety and Health; Michael J. Elliott; May 28, 2018. [SRDB Ref ID: 172717] 

Mauro, 2018, Review of SEC Petition Evaluation Report SEC-00236 Metals and Controls 

Corporation, SCA-TR-2018-SEC001, Revision 0; John Mauro, Robert Anigstein, Rose Gogliotti, 

and Nicole Briggs; February 2018. [SRDB Ref ID: 172715] 

M&C Nuclear, 1964, Health and Safety Manual; 1964. [SRDB Ref ID: 13642] 

NIOSH, 2018-a, Metals and Controls Corp. Subsurface Exposure Model; April 23, 2018. [SRDB 

Ref ID: 174132] 

NIOSH, 2018-b, Metals and Controls Corp. Maintenance Exposure Model; October 24, 2018. 

[SRDB Ref ID: 174357] 

NRC (Nuclear Regulatory Commission), 1981-1982, NRC Inspection Reports; various dates 

from 1981-1982. [SRDB Ref ID: 161187] 

NRC, 1993, NUREG-1400 Air Sampling in the Workplace; September 1993 [SRDB Ref ID: 

20129] 

ORAUT (Oak Ridge Associated Universities Team), 2017-a, Interview Worker #1; documented 

communication with former Metals and Controls Corporation worker; October 24, 2017. [SRDB 

Ref ID: 169918]

ORAUT (Oak Ridge Associated Universities Team), 2017-b, Interview Worker #7; documented 

communication with former Metals and Controls Corporation worker; October 25, 2017. [SRDB 

Ref ID: 169938] 
White Paper Metals and Controls Corp. Thorium and Welding

Exposure Model

April 8, 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. 

ORAUT (Oak Ridge Associated Universities Team), 2017-c, Interview Worker #5; documented 

communication with former Metals and Controls Corporation worker; October 25, 2017. [SRDB 

Ref ID: 169916] 

Weston, 1996, Texas Instruments Incorporated Attleboro Facility Building Interiors Remediation 

Drainage System Characterization; prepared by Roy F. Weston, Inc.; January 1996. [SRDB Ref 

ID: 165965]