Draft 

Advisory Board on Radiation and Worker Health

National Institute for Occupational Safety and Health

SC&A’s Review of NIOSH’s White Paper, “Internal Dosimetry 

Coworker Intake and Exposure Model for the W. R. Grace 

Company, Erwin, Tennessee” 

Contract No. 75D30119C04183

Document No. SCA-TR-2019-SP001, Revision 0

Prepared by

Ron Buchanan, PhD, CHP

SC&A, Inc.

2200 Wilson Boulevard, Suite 300

Arlington, VA 22201-3324

August 30, 2019

DISCLAIMER

This is a working document provided by the Centers for Disease Control and Prevention (CDC) 

technical support contractor, SC&A for use in discussions with the National Institute for 

Occupational Safety and Health (NIOSH) and the Advisory Board on Radiation and Worker 

Health (ABRWH), including its Working Groups or Subcommittees. Documents produced by 

SC&A, such as memorandum, white paper, draft or working documents are not final NIOSH or 

ABRWH products or positions, unless specifically marked as such. This document prepared by 

SC&A represents its preliminary evaluation on technical issues.

NOTICE: This document has been reviewed to identify and redact any information that is 

protected by the Privacy Act 5 U.S.C. § 552a and has been cleared for distribution.
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SC&A, Inc. Technical Support for the Advisory Board on Radiation and Worker Health’s Review 

of NIOSH Dose Reconstruction Program

Document Title SC&A’s Review of NIOSH’s White Paper, “Internal Dosimetry Coworker 

Intake and Exposure Model for the W. R. Grace Company, Erwin, 

Tennessee”

Document Number SCA-TR-2019-SP001

Revision Number 0 (Draft)

Supersedes N/A

Effective Date August 30, 2019

Task Manager Ron Buchanan, PhD, CHP

Project Manager John Stiver, MS, CHP (signature on file)

Document Reviewer(s) John Stiver, MS, CHP

Record of Revisions

Revision Number Effective Date Description of Revision

0 (Draft) 8/30/2019 Initial Issue
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Table of Contents

Abbreviations and Acronyms........................................................................................... 4

1 Introduction and Background ................................................................................... 5

2 Outline of White Paper............................................................................................. 5

2.1 Plutonium activities and characteristics at WRG................................................ 5

2.2 Bioassay data 1967–1973.................................................................................. 5

2.3 Air measurement data 1976–1993..................................................................... 6

2.4 The 1974–1975 period without recorded data.................................................... 6

3 White Paper’s Use of Coworker Guidelines ............................................................. 6

4 SC&A’s Evaluation of White Paper .......................................................................... 7

4.1 Bioassay data 1967–1973.................................................................................. 7

4.2 Air measurement data 1976–1993..................................................................... 8

4.3 The 1974–1975 period without recorded data.................................................... 9

4.4 Decontamination and decommissioning period 1990–1993............................... 9

5 Summary and Conclusions ...................................................................................... 9

6 References............................................................................................................. 11
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Abbreviations and Acronyms

ABRWH, Board Advisory Board on Radiation and Worker Health 

AWE Atomic Weapons Employer 

CW coworker 

D&D decontamination and decommissioning 

DOE U.S. Department of Energy 

dpm/d disintegrations per minute per day 

DR dose reconstruction 

IMBA Integrated Modules for Bioassay Analysis

m3 cubic meter

MPC maximum permissible concentration

μCi/mL microcurie per milliliter

NFS Nuclear Fuel Services

NIOSH National Institute for Occupational Safety and Health

NOCTS NIOSH OCAS Claims Tracking System

ORAUT Oak Ridge Associated Universities Team

OTIB ORAUT technical information bulletin

SEC Special Exposure Cohort 

WRG W. R. Grace
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1 Introduction and Background

W. R. Grace Company (WRG) was an Atomic Weapons Employer (AWE) facility from 1958 

through 1970 with an AWE residual contamination period from 1971 through March 1, 2011.

The National Institute for Occupational Safety and Health (NIOSH) issued on March 1, 2019, the

white paper Internal Dosimetry Coworker Intake and Exposure Model for the W. R. Grace 

Company, Erwin, Tennessee (NIOSH, 2019; hereafter referred to as the “white paper”). The 

purpose of the white paper was to develop plutonium intake data from recorded coworker (CW) 

bioassay data and air concentration measurements to assign intake values to workers with gaps in 

their plutonium bioassay data or for workers that should have been monitored for plutonium.

NIOSH used recorded bioassay plutonium data from the period of 1967–1973 and gross-alpha 

air concentration measurements from the period of 1976–1993 to predict the potential intakes of 

plutonium (as Pu-239), solubility Types M and S, for the plant production period (1965–1973) 

and plant residual period (1974–2011) at WRG. SC&A was tasked on March 20, 2019, to review 

the white paper.

2 Outline of White Paper

2.1 Plutonium activities and characteristics at WRG

• Table 1, page 7, of the white paper provides a timeline and summary of the plutonium 

activities at WRG (1964–2009).

• Tables 2 and 3, page 8, of the white paper provide a summary of the quantities and types 

of plutonium processed at WRG.

• Table 4, page 10, of the white paper provides a summary of the radionuclide assumptions 

used to develop the CW model.

2.2 Bioassay data 1967–1973

• Source of plutonium bioassay data – Because no electronic database for plutonium 

bioassays existed at WRG, NIOSH used the plutonium bioassay data from claims in the 

NIOSH OCAS Claims Tracking System (NOCTS) to perform a CW intake analysis for 

the 1967 to 1973 period of WRG’s plutonium production. The derived intake rates for 

1967 were extended back to include the period of plutonium operation of January 1, 

1965, through 1966. 

• Analyses of plutonium bioassay data – Attachment B of the white paper provides 

instructions for how to organize and sort the bioassay data from NOCTS to determine the 

annual excretion rates. The recorded data were obtained from gross alpha counting of 

urine samples; it was assumed the radioactive material was plutonium for dose 

reconstruction (DR) purposes. Attachment A of the white paper develops the analyses of 

the plutonium bioassay data from NOCTS. Table A-1, page 18, summarizes the urinary 

excretion rates, in disintegrations per minute per day (dpm/d), obtained from the analyses 

of the bioassay data for the period 1967–1973.
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• Projection of potential plutonium intakes using urinalyses data – Figures A-2 through 

A-16 in attachment A provide results obtained using the Integrated Modules for Bioassay 

Analysis (IMBA) program to project the potential intake values if using the bioassay 

results from table A-1. The resulting intake values are summarized in tables A-2 and A-3, 

page 19, and reproduced in tables 5 and 6, page 11, including a back extrapolation to 

1965–1966.

2.3 Air measurement data 1976–1993

• Source of air concentration measures – There were gross alpha air concentration data

taken in the plutonium areas at WRG and recorded in terms of percent of maximum 

permissible concentration (MPC) for the period 1976–1993. 

• Analyses of air measurement data – Attachment C of the white paper presents an 

outline of the analyses of the MPC data. Table C-2, page 32, summarizes the annual air 

concentration data.

• Intake modeling – Attachment C briefly discusses the lognormal distribution fit of the 

air concentration data necessary to obtain the plutonium intake rates, which are 

summarized in table C-3, page 33, and reproduced in table 7, page 12, including a

forward extrapolation to the period 1994–2011.

2.4 The 1974–1975 period without recorded data

There were not significant bioassay or air monitoring data during the period 1974–1975 to create 

a CW model for plutonium intakes at WRG. Therefore, NIOSH used an exponential decay curve 

fit between the intake rate for 1973 (from bioassay data) and the intake rate for 1976 (from 

measured air concentrations) to create intake rates for the years 1973 and 1974, according to 

methods recommended in ORAUT-OTIB-0070, Dose Reconstruction During Residual 

Radioactivity Periods at Atomic Weapons Employer Facilities, revision 01 (NIOSH, 2012). 

Table 8, page 13, in the white paper lists these intake rates for Type M plutonium and table 9, 

page 13, for Type S plutonium.

3 White Paper’s Use of Coworker Guidelines

The Draft Criteria for the Evaluation and Use of Coworker Datasets, revision 4 (NIOSH, 2015)

outlines NIOSH’s CW data guidelines (hereafter referred to as the “Guide”). The four major 

criteria are (1) data adequacy, (2) data completeness, (3) review and analysis of monitoring 

program data, and (4) evaluation of stratification.

The white paper was evaluated for compliance with these general guidelines as outlined below.

1. Section 2.1 of Guide: Data adequacy – The bioassay data were specifically analyzed for 

plutonium. The air monitoring data gross alpha counting was assumed to be all 

plutonium. These data provided for adequate information to project potential plutonium 

intakes.
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2. Section 2.2 of Guide: Data completeness – Most of the years of concern had some 

monitoring data. While the number of annual bioassays listed in table A-1, page 18, and 

the number of air samples listed in table C-2, page 32, are small compared to some U.S. 

Department of Energy (DOE) sites, they are useful for developing CW data for small 

AWE sites such as WRG, where a relatively small number of workers were potentially

exposed to plutonium processed in limited and known areas (a minimum of 15 to 30 data 

points per time interval, or less for smaller operations, is recommended in NIOSH, 2015, 

page 7). 

3. Section 3.0 of Guide: Review and analysis of monitoring program data – Attachment 

B of the white paper provides a record of instruction concerning the manipulation of the 

recorded data used to develop the CW data.

• Section 3.1 of Guide: Application of monitoring data to unmonitored workers –

Attachment D of the white paper discusses the plutonium bioassay program and its 

application to unmonitored workers for production and post-production periods and 

the decontamination and decommissioning (D&D) period.

• Section 3.2 of Guide: Analysis and application to the unmonitored population –

Attachment A of the white paper discusses the analyses of the recorded data and the 

derivation and application of the CW excretion and intake data. According to page 17

of the whitepaper “After extraction, these data were subjected to a 100% review for 

transcription errors and corrected as necessary.”

• Section 3.3 of Guide: Time interval of the modeled data – The gaps (1965–1966 

and 1974–1975) in the available data are relatively small for plutonium compared to 

the years that data are available, as discussed in section 3.3.4 (pages 24–25) of 

ORAUT-OTIB-0060, revision 02, Internal Dose Reconstruction (NIOSH, 2018) and 

did not exceed 3 years as recommended in section 3.3 (page 10) of NIOSH (2015).

4. Section 4.0 of Guide: Evaluation of stratification – According to page 19 of the white 

paper, statistical analysis of the plutonium gross alpha bioassay data was performed in 

accordance with ORAUT-RPRT-0053, revision 02, Analysis of Stratified Coworker 

Datasets (NIOSH, 2014). However, considering the limited number of workers and work 

areas involved in the handling of plutonium at the WRG facility, the most likely exposed 

workers were monitored, and stratification is not indicated, or practical, as discussed in 

section 4.0, page 10, of NIOSH (2015).

4 SC&A’s Evaluation of White Paper

The following summarizes SC&A’s review of the white paper.

4.1 Bioassay data 1967–1973

SC&A reviewed the spreadsheets containing the plutonium bioassay data, which were derived 

from the NOCTS claim files that NIOSH used to perform excretion analysis for the period of 

plutonium production at WRG from 1967 to 1973. SC&A evaluated the methods, analyses, and 

IMBA runs used in attachment A of the white paper to derive the excretion rates (table A-1) and
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the intake values (tables A-2 and A-3) and did not identify any errors or inappropriate 

assumptions. Tables 5 and 6, page 11, of the white paper summarize the derived intake rates. The 

intake values for 1967 were extended back to include the period of plutonium operations, 

January 1, 1965, through December 31, 1966, when no plutonium bioassay data were available. 

Therefore, SC&A had the following observation: 

Observation 1: Extension of 1967 data to include 1965 and 1967

NIOSH stated on page 36 of the white paper, “The coworker intake rates for the 1967 through 

1968 period should be used for 1965 and 1966 because no other data are available for that 

period.” The absence of data does not provide very strong support for back-extending the 1967 

data to cover the earlier period, especially since this was not a gap, but instead a beginning of 

operations with no intake data. A more detailed analysis addressing this issue and explaining 

why the earlier potential exposures were similar to, or no greater than, the 1967 exposures would 

have added support to this assumption. The importance of this issue is somewhat mitigated by 

the fact that an existing WRG Special Exposure Cohort (SEC) class for that period extends 

through 1970. That SEC class, however, was not based on the inability to recreate plutonium 

intake. 

4.2 Air measurement data 1976–1993

SC&A evaluated the gross alpha air concentration data and the methods, analyses, and 

assumptions used by the white paper in attachment C to derive potential intakes. SC&A analyses 

did not identify any errors or inappropriate assumptions. Table C-2 (page 32) of the white paper 

summarizes the derived annual air concentration data, and table C-3 (page 33) lists the 50th and 

95th percentile intake values. However, SC&A did have the following observation: 

Observation 2: Use of 30 percent and 3.9 percent factor unclear

NIOSH states on page 37 of the white paper: 

The intakes from the 1976-1987 period were based on a concentration of 

6.0 × 10-13 μCi/mL [microcurie per milliliter], or 30% of the MPC of plutonium, 

while the intakes for the 1988-1993 period were based on a concentration of 

7.8 × 10-14 μCi/mL, or 3.9% of the MPC. The site was using an MPC of 

2 × 10-12 μCi/mL.

It appears that the value of 30 percent was obtained from the 95th percentile value of 

0.2994 MPC listed in figure C-1, page 34, and that the value of 3.9 percent was obtained from 

the 95th percentile value of 0.03877 MPC listed in figure C-2, page 35, of the white paper. 

However, the white paper does not explain why the 95th percentile inhalation intake value of 

8.741 dpm/d (instead of 0.30 × 4.44 dpm/m3 (cubic meter) × 1.2 m3 per day × 8 hour per day = 

12.79 dpm/d) is listed in table 7, page 12, and table C-3, page 33, for 1976–1987. Likewise, why 

is the 95th percentile inhalation intake value of 1.132 dpm/d (instead of 0.039 × 4.44 dpm/m3 × 

1.2 m3

 per day × 8 hours per day = 1.66 dpm/d) listed in table 7, page 12, and table C-3, page 33, 

for 1988–1993? One possible explanation is that NIOSH adjusted the intake values of 12.79 

dpm/d from figure C-1 and 1.132 dpm/d from figure C-2 by an exposure factor of 

(250 day)/(365 day), which would have resulted in the values of 8.74 dpm/d and 1.13 dpm/d as 

listed in tables 7 and C-3. However, this is not stated in the white paper. 
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4.3 The 1974–1975 period without recorded data

SC&A evaluated the 1973 bioassay and 1976 gross alpha air concentration data and the methods, 

analyses, and assumptions used by the white paper on pages 13 and 14 to derive potential 

plutonium intake rates for the 1974–1975 data gap. SC&A analyses did not identify any errors or 

inappropriate assumptions. NIOSH analyses were performed correctly according to ORAUTOTIB-0070 (NIOSH, 2012), using Equation 4-1, page 15, and recommendations in table 5-1, 

page 16. Table 8, page 13, of the white paper lists the derived 95th percentile intake values for 

Type M plutonium, and table 9, page 13, for Type S plutonium. SC&A did not identify any 

findings or observations in this section. 

4.4 Decontamination and decommissioning period 1990–1993

The white paper does not address the D&D period in detail, except to mention on page 6 that 

individual bioassay data are presumed sufficient for all workers exposed to plutonium during the 

D&D period, and to provide a short discussion concerning radiological monitoring during the 

D&D period in attachment D, page 40. SC&A reviewed the bioassay data for the D&D period 

and found that approximately 16 workers submitted approximately 200 urine bioassay samples, 

which were analyzed for Pu-239 and total plutonium. A review of the urinalyses indicated that 

they were conducted on approximately quarterly bases. SC&A did not locate any in vivo lung 

count data in NIOSH’s bioassay files for the D&D period. SC&A had the following observation: 

Observation 3: Were in vivo bioassays required or performed for D&D workers? 

SC&A reviewed the referenced Nuclear Fuel Services, Plutonium Facilities, Decommissioning 

Project Plan, Condition Addendum (NFS, 1989, PDF page 170), that states: 

Bioassay frequencies, at a minimum, will be quarterly for urine/fecal samples and 

annually for invivo lung counting. 

It is not completely clear from this statement if the bioassay method could be urine/fecal 

sampling performed quarterly or in vivo lung counts performed annually, or if both were 

required. 

5 Summary and Conclusions

SC&A’s review of the white paper found that NIOSH used the recommended methods, per 

approved appropriate procedural documents, to derive reasonable CW data from the available 

recorded bioassay and air monitoring data. SC&A did not identify any findings, but did have 

three observations:

• Observation 1: Extension of 1967 data to include 1965 and 1967 – NIOSH stated on 

page 36 of the white paper, “The coworker intake rates for the 1967 through 1968 period 

should be used for 1965 and 1966 because no other data are available for that period.” 

The absence of data does not provide very strong support for back-extending the 1967 

data to cover the earlier period, especially since this was not a gap, but instead a 

beginning of operations with no intake data. A more detailed analysis addressing this 

issue and explaining why the earlier potential exposures were similar to, or no greater 

than, the 1967 exposures would have added support to this assumption. The importance 
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of this issue is somewhat mitigated by the fact that an existing WRG SEC class for that 

period extends through 1970. That SEC class, however, was not based on the inability to 

recreate plutonium intake.

• Observation 2: Use of 30 percent and 3.9 percent factor unclear – NIOSH states on 

page 37 of the white paper: 

The intakes from the 1976-1987 period were based on a concentration of 

6.0 × 10-13 μCi/mL, or 30% of the MPC of plutonium, while the intakes 

for the 1988-1993 period were based on a concentration of 7.8 × 10-14

μCi/mL, or 3.9% of the MPC. The site was using an MPC of 2 × 10-12

μCi/mL.

It appears that the value of 30 percent was obtained from the 95th percentile value of 

0.2994 MPC listed in figure C-1, page 34, and that the value of 3.9 percent was obtained 

from the 95th percentile value of 0.03877 MPC listed in figure C-2, page 35, of the white 

paper. However, the white paper does not explain why the 95th percentile inhalation 

intake value of 8.741 dpm/d (instead of 0.30 × 4.44 dpm/m3 × 1.2 m3 per day × 8 hour 

per day = 12.79 dpm/d) is listed in table 7, page 12, and table C-3, page 33, for 1976–

1987. Likewise, why is the 95th percentile inhalation intake value of 1.132 dpm/d 

(instead of 0.039 × 4.44 dpm/m3 × 1.2 m3 per day × 8 hours per day = 1.66 dpm/d) listed 

in table 7, page 12, and table C-3, page 33, for 1988–1993? One possible explanation is 

that NIOSH adjusted the intake values of 12.79 dpm/d from figure C-1 and 1.132 dpm/d 

from figure C-2 by an exposure factor of (250 day)/(365 day), which would have resulted 

in the values of 8.74 dpm/d and 1.13 dpm/d as listed in tables 7 and C-3. However, this is 

not stated in the white paper.

• Observation 3: Were in vivo bioassays required or performed for D&D workers? – 

SC&A reviewed the referenced Nuclear Fuel Services, Plutonium Facilities, 

Decommissioning Project Plan, Condition Addendum (NFS, 1989, PDF page 170), that 

states:

Bioassay frequencies, at a minimum, will be quarterly for urine/fecal 

samples and annually for invivo lung counting. 

It is not completely clear from this statement if the bioassay method could be urine/fecal 

sampling performed quarterly or in vivo lung counts performed annually, or if both were 

required. 

SC&A performed a focused review of the white paper to evaluate if the appropriate methods and 

procedures were used to analyze the available data and to derive internal CW intake values for 

WRG workers potentially exposed to plutonium during the period 1965–2011. This review did 

not include evaluating the numerous related NIOSH documents used in CW data development, 

as this would be beyond the tasking of this review.
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6 References

National Institute for Occupational Safety and Health (NIOSH). (2012). Dose reconstruction 

during residual radioactivity periods at atomic weapons employer facilities (ORAUT-OTIB0070, rev. 01). Retrieved from https://www.cdc.gov/niosh/ocas/pdfs/tibs/or-t70-r1.pdf 

National Institute for Occupational Safety and Health (NIOSH). (2014). Analysis of stratified 

coworker datasets (ORAUT-RPRT-0053, rev. 02). Retrieved from 

https://www.cdc.gov/niosh/ocas/pdfs/orau/oraurpts/or-rprt-53-r2.pdf 

National Institute for Occupational Safety and Health (NIOSH). (2015). Draft criteria for the 

evaluation and use of coworker datasets (rev. 4). Retrieved from 

https://www.cdc.gov/niosh/ocas/pdfs/dps/dc-cwds-r4.pdf 

National Institute for Occupational Safety and Health (NIOSH). (2018). Internal dose 

reconstruction (ORAUT-OTIB-0060, rev. 02). Retrieved from

https://www.cdc.gov/niosh/ocas/pdfs/tibs/or-t60-r2-508.pdf 

National Institute for Occupational Safety and Health (NIOSH). (2019). Internal dosimetry 

coworker intake and exposure model for the W. R. Grace Company, Erwin, Tennessee [White 

paper]. Retrieved from SRDB Ref. ID 175523 

Nuclear Fuel Services (NFS). (1989). Plutonium facilities, decommissioning project plan, 

condition addendum, Erwin, Tennessee. Retrieved from SRDB Ref. ID 28218