Closeout of TBD Issues on the 

Internal Exposure Coworker Model 

for United Nuclear Corporation

Uranium Refining Atomic Weapons Employers (AWE) 

Work Group 

Henry A. Anderson, MD (Chair) 

R. William Field, PhD 

David Kotelchuck, PhD, MPH

Presented to: 

The Advisory Board on Radiation and Worker Health 

Idaho Falls Meeting

August 9–10, 2016
United Nuclear – Site Description

• Located in Hematite, Missouri

• Manufactured uranium metal and uranium

compounds from natural and enriched

uranium for use as nuclear fuel for U.S. Navy

and commercial customers

• Manufactured Th-U oxide pellets in 1964

• Operations Period from 1958 to 1973

• Residual Period from 1974 to 2009
United Nuclear Corporation (UNC) 

TBD Chronology

• March 2008: NIOSH issued Appendix D to Battelle-TBD-6001

(Battelle 2008) – Site Profile for United Nuclear, Rev. 0.

• September 2009: SC&A issued its review of Battelle-TBD6001, Appendix D.

• April 2010: NIOSH issued Revision 1 of Appendix D, BattelleTBD-6001.

• June 2010: SC&A issued A Critical Review of Revision 1 of the

NIOSH Site Profile for the United Nuclear Corporation,

Missouri, Addendum to SC&A-TR-SP2009-0004.

• March 2011: NIOSH issued DCAS-TKBS-0008, Rev. 0, as its

stand-alone TBD for UNC as a replacement for Battelle-TBD6001.
UNC Work Group Meetings

• Between July 7, 2010, and September 7, 2012, the

Uranium Refining AWE Work Group conferred on

seven separate occasions for discussions and

resolutions of findings pertaining to UNC as well as

other AWE facilities.

• Status for each of the six UNC findings identified by

SC&A were presented by the Uranium Refining AWE

Work Group to the Advisory Board on September

18–20, 2012, in Denver, Colorado.

• Complete resolution/closure of findings was

recommended by the Work Group for all but

Finding 4, which pertains to NIOSH’s Internal

Coworker Model.
UNC Work Group Meetings (cont.)

• Partial resolution regarding Finding 4 included

NIOSH’s decision to make the following changes:

1) Provide guidance for use of the 95th percentile value of

the coworker model.

2) When sufficient bioassay data are available, these data will

be used to estimate intake; conversely, coworker model

data will be used only when bioassay data are either

absent or inadequate.

• While significant progress had been made toward the

complete resolution of Finding 4 at the time of the full

Board meeting held September 18–20, 2012, some

peripheral issues identified only days earlier in a Work

Group meeting held on September 7, 2012, remained.
Summary Review of Finding 4

• SC&A’s initial review of Battelle-TBD-6001 critically

compared UNC air monitoring data and urinalysis data for

consistency with the proposed internal coworker model.

• SC&A’s review of UNC monitoring records showed there

was a limited correlation between air monitoring and

urinalysis data, which provided the technical basis for

NIOSH’s coworker model for assignment of daily

inhalation values of uranium.

• Since bioassay results are given the highest priority, when

available, SC&A focused its review on bioassay data for

assessing the credibility of the NIOSH internal coworker

model.
Summary Review of Finding 4 (cont.)

• For this assessment, SC&A deliberatively selected the

monitoring records of two operators, whose bioassay data

represented high-end exposures, in order to determine if

the coworker model would be bounding for these

workers.

• Bioassay-derived inhalation intakes for the two UNC

operators yielded values that were far above the originally

recommended geometric mean (GM) and geometric

standard deviation (GSD) values cited in Battelle-TKBS- 6001, Appendix D.

• Based on this discrepancy, Finding 4 concluded that

uranium intakes recommended by NIOSH for the pre-June

1963 period would significantly underestimate the

potential internal exposures for the two UNC operators,

as well as other (unmonitored) workers.
Finding 4: Outstanding Peripheral 

Issues and Their Resolution

• During a September 7, 2012, Work Group

teleconference, NIOSH’s intention to use the 95th

percentile values for high-end unmonitored

personnel was “conditionally” recommended.

• This conditional recommendation was based on

the ability of NIOSH to (1) confirm the high

bioassay-derived intakes for the two operators

evaluated by SC&A and (2) determine whether

the bioassay data representing the two operators

had been included in the coworker model data.

• NIOSH issued a White Paper in February 2014

that addressed these outstanding issues

regarding the internal coworker model.
Summary Data and Conclusions Contained 

in NIOSH’s White Paper of February 2014

• For the two UNC operators (Operators “AAA”

and “BBB”), NIOSH identified 68 and 71

urinalyses, respectively, between December

1962 and end of 1965.

• Urine bioassay data for each operator were

entered into IMBA to derive corresponding

daily inhalation values for solubility Types M

and S uranium and for two time periods

shown in Table 1 (next slide).
Summary Data and Conclusions Contained in 

NIOSH’s White Paper of February 2014 (cont.)

Table 1. Estimated intakes from two highly exposed workers’ bioassay results and 

comparison to the coworker model

Operator AAA Operator BBB

Pre-June 1963

Type S (dpm/d) Type M (dpm/d) Type S (dpm/d) Type M (dpm/d)

NIOSH analysis 437,900 13,803 187,800 5,940

Site Profile GM 12,590 872 12,590 872

Site Profile 95th 89,277 6,183 89,277 6,183

Ratio* 4.9 2.2 2.1 0.96

Post-June 1963

NIOSH analysis 6,445 319 6,809 349

Site Profile GM 7,662 560 7,662 560

Site Profile 95th 46,681 3,412 46,681 3,412

Ratio* 0.13 0.09 0.15 0.1

* Ratio between NIOSH analysis result and the 95th percentile of the Site Profile intake.
Regarding NIOSH’s Inclusion of Operators AAA 

and BBB Bioassay Data in the Coworker Model

• NIOSH assessed bioassay data used to derive

intakes for each of the two UNC Operators and

compared these against the top 10 bioassay

results that define the coworker model for pre1963.

• Their results in Table 2 (next slide) show that 50%

or 7 bioassay data points representing the two

operators were not included in the coworker

model data set. (The reason for the omission of

most of these data points is not clear.)
Regarding NIOSH’s Inclusion of Operators AAA and 

BBB Bioassay Data into the Coworker Model (cont.)

Table 2. Comparison of 10 highest values used for “Operator Pre 06/1963” data set in 

site profile and corresponding data from operators AAA and BBB, indicating some 

missing values. Bold values are missing from coworker model.

Top 10 Bioassay results 

from pre 06/1963 data set 

(dpm/L)

Worker AAA results 

(dpm/L), pre 06/1963

Worker AAA results 

(dpm/L), pre 06/1963

320 662 44

403 1518 649

432 887 320

474 974 2380

649 1100 217

662 399 173

887 580

974 376

1518

1800
NIOSH’s Conclusions

• Bioassay-derived uranium intake values cited by NIOSH

for Operators AAA and BBB were consistent with those

previously derived by SC&A.

• The elevated bioassay-derived pre-June 1963 intakes

for the two operators are likely the result of

(1) inclusion of bioassay results deemed contaminated

or false positives; and (2) these two workers represent

exposures above the 95th percentile.

• Failure to include the 7 bioassay data points

(representing the two operators) did not significantly

affect the GM and the 95th percentile values of the

coworker model due to the discovery of new bioassay

data with lower values.
Path Forward

• The Work Group requested that SC&A review and

respond to NIOSH’s White Paper addressing the

UNC’s coworker model. SC&A issued its response in

a memorandum dated June 3, 2016.

• The memorandum concludes that, after a thorough

reevaluation of all previous documentation

pertaining to Finding 4, SC&A agrees with NIOSH’s

recommendations that the selective use of the

95th percentile value for unmonitored workers

classified as operators is appropriate and

recommends closure of Finding 4.
References

Battelle-TBD-6001, Appendix D. 2008. Site Profiles for Atomic Weapons Employers the 

Refine Uranium and Thorium – Appendix D United Nuclear Corporation, Revision 0, 

National Institute for Occupational Safety and Health. March 14, 2008.

Battelle-TBD-6001, Appendix D. 2010. Site Profiles for Atomic Weapons Employers the 

Refine Uranium and Thorium – Appendix D United Nuclear Corporation, Revision 1, 

National Institute for Occupational Safety and Health. April 30, 2010.

DCAS-TKBS-0008. 2011. Technical Basis Document for the United Nuclear Corporation 

Hematite, Missouri, Revision 0, National Institute for Occupational Safety and Health. 

March 21, 2011.

NIOSH 2014. White Paper Addressing Issues on the Coworker Model for United Nuclear 

Corporation, National Institute for Occupational Safety and Health, Cincinnati, Ohio. 

February 2014.

SC&A 2009. Draft Review of the NIOSH Site Profile for the United Nuclear Corporation, 

Missouri, Battelle-TBD-6001, Appendix D, SCA-TR-SP2009-0004, Revision 0, SC&A, Inc., 

Vienna, Virginia. September 2009.

SC&A 2010. A Critical Review of Revision 1 of the NIOSH Site Profile for the United Nuclear 

Corporation, Missouri, Addendum to SCA-TR-SP2009-0004, SC&A, Inc., Vienna, Virginia.

SC&A 2016. Memorandum: SC&A’s Review of NIOSH’s White Paper Addressing Issues on 

the Coworker Model for United Nuclear Corporation, SC&A, Inc., Vienna, Virginia. June 3, 

2016.