Draft

ADVISORY BOARD ON

RADIATION AND WORKER HEALTH

National Institute for Occupational Safety and Health

A DRAFT REVIEW OF ORAUT-TKBS-0017-5, REVISION 03, 

FEED MATERIALS PRODUCTION CENTER – 

OCCUPATIONAL INTERNAL DOSE

Contract No. 211-2014-58081 

SCA-TR-2017-SP004, Revision 0 

Prepared by 

Douglas Farver, CHP 

Bob Barton, CHP 

SC&A, Inc.

2200 Wilson Boulevard, Suite 300 

Arlington, Virginia, 22201 

July 2017 

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 report 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 Review of NIOSH Dose Reconstruction Program

DOCUMENT TITLE: 

A Draft Review of ORAUT-TKBS-0017-5, Revision 03, Feed 

Materials Production Center – Occupational Internal Dose

DOCUMENT NUMBER/

DESCRIPTION:

SCA-TR-2017-SP004

REVISION NO.: 0 (Draft)

SUPERSEDES: N/A

EFFECTIVE DATE: July 6, 2017

TASK MANAGER: Bob Barton, CHP [signature on file]

PROJECT MANAGER: John Stiver, MS, CHP [signature on file]

DOCUMENT 

REVIEWER(S): John Stiver, MS, CHP [signature on file] 

Record of Revisions

Revision 

Number

Effective 

Date Description of Revision

0 (Draft) 7/6/2017 Initial issue
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TABLE OF CONTENTS

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

1.0 Background and Statement of Purpose ............................................................................... 6

1.1 Relevant Background Documents ........................................................................... 7

1.1.1 ORAUT-TKBS-0017-5 ............................................................................... 7

1.1.2 ORAUT-OTIB-0078 ................................................................................... 7

2.0 Summary of Previously Identified Issues ........................................................................... 8

2.1 Exposure to Uranium-Poor Raffinate Material ....................................................... 8

2.2 Contaminant Radionuclides in Recycled Uranium ................................................. 8

2.3 Ingestion Intakes from Thorium ........................................................................... 14

2.4 K-65 Silo Radon Exposure ................................................................................... 15

2.5 Unmonitored Internal Dose to Uranium ............................................................... 15

2.6 Unmonitored Internal Dose to Thorium and Thoron ............................................ 18

2.6.1 Reconstruction of Unmonitored Thorium Doses (1979–1989)................. 18

2.6.2 Reconstruction of Unmonitored Thorium Doses (1990–1994)................. 20

2.6.3 Reconstruction of Thoron Doses ............................................................... 21

3.0 Summary of Recommendations ........................................................................................ 23

4.0 References......................................................................................................................... 26
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ABBREVIATIONS AND ACRONYMS

ABRWH or 

Board Advisory Board on Radiation and Worker Health 

Am americium

Bq becquerel 

BRS Board Review System

BZ breathing zone 

DAC derived air concentration

MDA minimum detectable activity

MgF2 magnesium fluoride

Nb niobium 

NIOSH National Institute for Occupational Safety and Health

Np neptunium 

μCi microcurie

ORAU Oak Ridge Associated Universities

ORAUT Oak Ridge Associated Universities Team

OTIB ORAUT technical information bulletin

ppb parts per billion

ppm parts per million

Pu plutonium 

Ra radium 

Rn radon 

ROS regression on order statistics

Ru ruthenium 

RU recycled uranium 

SEC Special Exposure Cohort 

TBD technical basis document

Tc technetium 

Th thorium 

TRU transuranic(s)

TWOPOS time-weighted one person–one sample 

U uranium 
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WG Work Group 

Zr zirconium
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1.0 BACKGROUND AND STATEMENT OF PURPOSE

On November 10, 2006, SC&A submitted to the Advisory Board on Radiation and Worker 

Health (ABRWH or Board) the draft report, SCA-TR-TASK1-0010, Review of the NIOSH Site 

Profile for the Fernald Environmental Management Project (Feed Materials Production Center)

(SC&A 2006). The site profile review covered the six volumes of the Fernald technical basis 

document (TBD)—ORAUT-TKBS-0017-1 though ORAUT-TKBS-0017-6—and identified 33 

findings. In October 2013, SC&A submitted report, SCA-SP-IM2013-0045, Revision 0, Fernald 

Plant Site Profile Issues Matrix – Draft Preliminary SC&A Assessment (SC&A 2013), which 

summarized those findings and other issues that SC&A believed were still open following the 

addition of two classes of workers to the Special Exposure Cohort (SEC) at the July 2013 

Advisory Board meeting. 

In April 2014, Revision 1 (SC&A 2014a) to SC&A’s site profile issues matrix was submitted,

which incorporated the National Institute for Occupational Safety and Health (NIOSH) responses 

to Revision 0 and SC&A’s responses to NIOSH’s responses. Subsequent to the release of 

Revision 1, a Fernald Work Group (WG) teleconference meeting was held on April 15, 2014, at 

which time 6 of the original 33 site profile findings were recommended to be closed. 

Revision 2 to the issues matrix (SC&A 2014b), dated September 1, 2014, incorporated additional 

SC&A responses based on our focused review of new TBD revisions provided in 2014 and 

included an attachment with responses for those findings requiring a detailed description. In 

developing Revision 2, SC&A reviewed the transcripts from 16 successive WG meetings held 

from August 2007 to July 2013, as well as many white papers and memorandum reports related 

to the SEC deliberations of the WG during that period. 

Subsequent to the release of Revision 2, the Fernald WG met on September 3, 2014, to discuss 

the status and actions required to close out the remaining site profile findings. During that 

meeting, an additional 14 findings were recommended to be closed by the WG.

Revision 3 (SC&A 2014c) to the matrix was issued in November 2014. It reflected the 

discussions and recommendations from the September 3, 2014, WG meeting and provided an 

updated status of the remaining site profile and SEC issues not recommended for closure at that 

time.

Revision 4 (SC&A 2016a) to the matrix became effective in May 2016 and reflects the 

discussions and recommendations from the December 4, 2014, WG meeting. It also provides an 

updated status of the remaining site profile and SEC issues not currently recommended for 

closure.

This report identifies unresolved findings from the most recent Fernald issues matrix that are 

related to the Fernald internal dosimetry TBD, ORAUT-TKBS-0017-5, Revision 03, Feed 

Materials Production Center – Occupational Internal Dose (NIOSH 2017a; also referred to as 

“TBD-5, Revision 03”), and provides SC&A’s recommendations for finding disposition.
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1.1 RELEVANT BACKGROUND DOCUMENTS

1.1.1 ORAUT-TKBS-0017-5 

The Fernald internal dosimetry TBD, ORAUT-TKBS-0017-5, Revision 00, became effective on 

May 28, 2004 (NIOSH 2004b). SC&A reviewed the site profile documents in 2006 and 

submitted the Fernald issues matrix in 2013, after SEC deliberations were completed. The most 

recent revision of the issues matrix has an effective date of May 2016 (SC&A 2016a). 

Revision 01 to ORAUT-TKBS-0017-5 became effective July 22, 2016 (NIOSH 2016b). The 

revision incorporated responses to comments from various white papers that were consolidated 

into ORAUT-RPRT-0052, Revision 00, Feed Materials Production Center Internal Dose Topics

(NIOSH 2011b), and changes in response to internal comments, NIOSH review comments, and 

SC&A matrix issues. Also included were the coworker data previously contained in ORAUTOTIB-0078, Revision 03, Internal Dosimetry Coworker Data for the Feed Materials Production 

Center (NIOSH 2015; hereafter referred to as “OTIB-0078”). 

Revision 02 to ORAUT-TKBS-0017-5 became effective September 30, 2016 (NIOSH 2016d). 

This revision corrected the recycled uranium (RU) contaminant intakes (becquerel per Bq 

uranium [Bq/Bq U]) in Table 5-34 and the Silo activity concentrations for radium-228 (Ra-228) 

and thorium-228 (Th-228). The primary purpose of the revision was to correct tables and typos. 

Revision 03 to ORAUT-TKBS-0017-5 became effective March 30, 2017 (NIOSH 2017a). This 

revision incorporates changes in the interpretation of HIS-20 uranium bioassay data, corrects the 

specific activity of 1% enrichment uranium for uranium coworker intakes, and revised the 

uranium coworker methodology in Attachment C. It also addresses ABRWH comments on 

OTIB-0078. 

1.1.2 ORAUT-OTIB-0078 

ORAUT-OTIB-0078, Internal Dosimetry Coworker Data for the Feed Materials Production 

Center, was originally issued on August 31, 2009 (NIOSH 2009). Since that date, the document 

has been revised on three occasions. The latest version, Revision 03, was issued on August 19, 

2015 (NIOSH 2015). SC&A reviewed OTIB-0078, Revision 03, and issued SCA-TR-2016-

SP004, Draft Review of ORAUT-OTIB-0078, Revision 03, Internal Dosimetry Coworker Data 

for the Feed Materials Production Center (SC&A 2016b), which identified two findings and six 

observations. Subsequent to the SC&A review, the guidance contained in OTIB-0078 was 

incorporated into Revision 01 to ORAUT-TKBS-0017-5, and OTIB-0078 was cancelled. 
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2.0 SUMMARY OF PREVIOUSLY IDENTIFIED ISSUES

Revision 4 to the Fernald issues matrix (SC&A 2016a) identifies 16 findings related to the 

revision of ORAUT-TKBS-0017-5. Of these, eight were closed in previous WG discussions 

(TBD 1-6 and SEC 4 and 6b), leaving eight still active as of June 2017 (TBD 7, 8, and 10 and 

SEC 3 are in progress, and TBD 9, 11, 15, and 29 are in abeyance). SC&A identified two

findings and six observations from its review of OTIB-0078, Revision 03 (SC&A 2016b). The

OTIB-0078 findings and observations have not been discussed in the WG forum. SC&A also 

identified seven findings from SC&A’s white paper, Review of Proposed NIOSH Methods for 

Reconstructing Thorium Doses at Fernald (1979–2006) (SC&A 2014d).

2.1 EXPOSURE TO URANIUM-POOR RAFFINATE MATERIAL

Section 5.3.5.2 of NIOSH 2017a provides methods for reconstructing doses to raffinate materials 

for some operations, time periods, and areas at Fernald. These sections describe raffinate 

exposures to the 1952–1956 K-65 drum transfer operation (Section 5.3.5.2.1), 

handling/processing of pitchblende ores in 1954–1958 (Section 5.3.5.2.2), and the 

processing/handling of yellowcake in 1959–1961 (Section 5.3.5.2.3). For the first situation, 

radon breath data was utilized to back-calculate a radium intake that can then be used to ratio to 

other raffinate contaminants. The second and third situations utilize uranium urinalysis data and 

assume that the inhaled material was in equilibrium with Th-230. 

However, the remaining open issue concerning raffinates was the potential for internal exposure 

to “uranium and radium poor” raffinate material for certain areas of the Plant 2/3 operations.

This is problematic, as there is very little radium present to allow for radon breath analysis and 

very little uranium present relative to Th-230 to allow for sufficiently accurate use of uranium 

urinalysis. This issue was most recently discussed at the December 2014 WG meeting (ABRWH 

2014b, pages 128–150). At that meeting, NIOSH proposed that one possible avenue was to look 

into using daily weighted exposure data in Plant 2/3 and propose a model on how to reconstruct 

Th-230 exposures to the uranium/radium-poor raffinate material. As a result of that discussion, 

this issue was designated “in progress” pending the development of a model to reconstruct those 

potential exposures (ABRWH 2014b, page 150). Currently, the Board Review System (BRS) 

lists the status of the raffinate-related TBD findings (7 and 8) as “in progress,” and SC&A 

recommends that the status remain unchanged until such time as NIOSH is ready to respond to 

this particular aspect of raffinate material exposures.

SC&A Recommendation: TBD Findings 7 and 8 should remain “in progress” pending 

development and discussion of a proposed model to reconstruct internal exposures to 

uranium/radium-poor raffinate materials. 

2.2 CONTAMINANT RADIONUCLIDES IN RECYCLED URANIUM

Section 5.3.3 of NIOSH 2017a provides methods for reconstructing doses to claimants from 

exposure to impurities in RU. This relates to original TBD Findings 9–11 and SEC Finding 3 in 

the May 2016 version of the Fernald issues matrix (SC&A 2016b). 
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RU is uranium that had been previously used as reactor fuel or as target material in plutonium 

production reactors. After irradiation, the uranium was chemically purified to remove fission 

products and plutonium and other transuranics (TRU) and was then shipped to the uranium 

enrichment, fabrication, and production plants for re-use. The RU was separated in the chemical 

processing plants at Hanford and the Savannah River Site. Because it is not possible to attain 

100% product purity in chemical separation processes, this RU was known to contain traces of 

TRU elements and fission product impurities. 

The primary contaminants in RU were plutonium-238 (Pu-238), Pu-239, americium-241 

(Am-241), neptunium-237 (Np-237), and a fission product, technetium-99 (Tc-99). The Pu-239, 

Np-237, and Tc-99 were the radionuclides of greatest concentrations and were tracked and 

documented for control purposes. 

Because this material posed a source of exposure to workers who handled it, and NIOSH really 

did not have the bioassay or the monitoring data to ascertain intakes of these constituent 

radionuclides, NIOSH proposed using the uranium bioassay data to derive intakes of these 

impurities in RU (NIOSH 2008). In this 2008 white paper, NIOSH proposed certain default 

values on a parts-per-billion uranium mass basis for plutonium, neptunium, and technetium, the 

three radionuclides of most concern from a dosimetric standpoint. These values were 100 parts 

per billion for plutonium, 3,500 for neptunium, and 9,000 for Tc-99. 

The issue of worker exposures to contaminant radionuclides in RU at Fernald has involved 

several WG meetings, spanning a period from 2008 to 2012, many white paper exchanges, and 

the expenditure of considerable Board resources. Given that 6 years have elapsed since the RU 

issue was discussed in the WG forum, a brief historical summary of the discussions and white 

paper exchanges regarding the RU issue at Fernald is provided in order to assist the reader. 

During the Fernald WG meeting on October 28, 2008, SC&A was tasked with reviewing the 

NIOSH white paper on RU (ABRWH 2008). The direction provided by the ABRWH stated that 

SC&A should focus on the appropriateness of the default values selected for RU contaminants 

(Pu-239/240 [referred to herein as Pu-239], Np-237, and Tc-99) and whether the selected values 

are bounding for all workers for all time periods. SC&A’s white paper on this issue (SC&A 

2009) identified 11 findings in the NIOSH white paper, which were the subject of extensive 

discussion in the January 29, 2010, WG meeting (ABRWH 2010a). SC&A 2009 and the 

discussion recorded in the January 29, 2010, meeting transcript (ABRWH 2010a) thoroughly 

describe SC&A’s concerns regarding RU. During the January 2010 WG meeting, NIOSH stated 

that it was not prepared at that time to address the various issues raised but agreed to prepare a 

response.

Prior to the November 9, 2010, WG meeting, NIOSH submitted the report, NIOSH Response to 

SC&A Findings Related to the White Paper on Recycled Uranium at Fernald (NIOSH 2010b), 

which provided NIOSH’s position on each of the 11 findings in SC&A 2009. The 11 findings 

and NIOSH’s responses to them were the subject of intensive discussion at the November 9, 

2010, meeting (ABRWH 2010b). Two principal unresolved issues that emerged from that 

meeting prompted the Board’s request for a second white paper from SC&A. First, SC&A 

provided a compelling argument for why the 19 subgroup process means derived in DOE 2000 

do not provide a firm basis for bounding defaults for TRU and fission products. Second, SC&A’s 
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preliminary review of the dust collector data reported in Appendix B to NIOSH 2008 indicates 

that the NIOSH default values may not be bounding for some classes of workers in some 

facilities during the proposed SEC period. 

SC&A’s second white paper on recycled uranium, SC&A Review of Issues Related to

Reconstruction of Doses for Workers Exposed to Recycled Uranium at Fernald – A Second 

White Paper (SC&A 2011a), was transmitted to the WG prior to the February 8, 2011, WG

meeting. That paper identified nine new findings that supported SC&A’s position regarding the 

questionable basis for NIOSH’s proposed RU defaults, and that some categories of workers were 

exposed to TRU and fission product levels in excess of the NIOSH defaults. The issues were 

discussed in detail at the February 8, 2011, WG meeting (ABRWH 2011a). At that meeting, 

NIOSH was tasked to respond to SC&A 2011a prior to the next WG meeting, scheduled for 

April 19, 2011. SC&A 2009 and SC&A 2011a thoroughly described SC&A’s concerns regarding 

RU. 

On April 13, 2011, SC&A transmitted Revision 1 to our second white paper on RU at Fernald 

(SC&A 2011b). That revision contained editorial corrections and a revised Table 2 that limited 

comparisons of organ doses from intakes of RU constituents to specific absorption classes. Note 

that Revision 1 did not result in changes to the findings in SC&A 2011). Thus, unless otherwise 

indicated, all references in this document to SC&A’s “second white paper” are to SC&A 2011b. 

On April 17, 2011, NIOSH provided a response to SC&A 2011a titled, NIOSH Response to 

Draft SC&A Review of Issues Related to Reconstruction of Doses for Workers Exposed to 

Recycled Uranium at Fernald – A Second White Paper – February 2011 (NIOSH 2011a). 

Because SC&A did not have time to prepare a detailed response to NIOSH 2011a prior to the 

April 19 WG meeting, we prepared preliminary observations for discussion at the meeting 

(ABRWH 2011b). It is noteworthy that at the April 19 meeting, SC&A was not tasked to 

respond to NIOSH 2011a or perform any additional work on the RU issue. 

At the Advisory Board meeting held in St. Louis, Missouri, May 24–26, 2011, SC&A presented 

the status of our six main SEC findings regarding Fernald (ABRWH 2011c). Part of that 

presentation focused on SC&A’s preliminary observations on NIOSH 2011a. At the conclusion 

of the presentation, SC&A was tasked by the Advisory Board to provide a formal response to 

NIOSH 2011a. On August 4, 2011, SC&A provided a response to NIOSH 2011a titled SC&A’s 

Evaluation of NIOSH’s Response Dated March 31, 2011, to SC&A’s Second White Paper on 

Recycled Uranium (Sec Issue #3) at Fernald (SC&A 2011c). On August 5, 2011, NIOSH 

submitted a paper, Issues Related to the Ability to Bound Internal Dose from Recycled Uranium 

Trace Level Contaminants at Fernald, Draft 01 (NIOSH 2011c), which outlined its position on 

RU default values.

On August 11, 2011, the Fernald WG met and again discussed the RU issue, including the 

concerns raised in SC&A 2011c and the position outlined in NIOSH 2011c. At that meeting, the 

WG agreed that the new proposed defaults for RU constituent radionuclides presented in NIOSH 

2011c probably provide plausible upper bounds for the most highly continuously exposed 

subgroup of workers, the Plant 5 metal production workers and associated Plant 1 millwrights 

during the period 1973–1989 (ABRWH 2011d). However, SC&A continued to express concern 

that another group of workers, those who handled the most highly contaminated feed materials 
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on the front end of processing operations (Subgroup 10A in DOE 2000), might have experienced 

exposures at levels higher than the new defaults. NIOSH indicated that it believed that those 

workers were exposed to the highest concentrations only for brief intermittent periods and 

would, therefore, be covered by the new defaults. At the conclusion of the August 11, 2011, 

meeting, the WG tasked NIOSH to provide quantitative evidence that the new proposed RU 

defaults provide a plausible upper bound for the Subgroup 10A handlers and downblenders. On 

November 1, 2011, NIOSH provided its analysis (NIOSH 2011d), and on February 6, 2012, 

SC&A provided its response to NIOSH 2011d. That report, SC&A 2012, provided our final 

position on the RU issue, excluding potential exposure to Am-241.1 

1 At the December 2014 WG meeting, NIOSH agreed to consider the Am-241 issue. TBD-5, Revision 03, provides 

NIOSH’s proposed method for dealing with Am-241; SC&A’s response to that topic is provided in this report. 

The last WG discussion of the main constituent defaults in RU took place on February 9, 2012, 

wherein the WG reached consensus on default levels of Pu, Np-237, and TC-99 for the periods 

1961–1973 and 1973–1986. NIOSH’s agreement to those values and the record of WG 

transference of SEC Issue 3 to the site profile are contained in pages 173–178 of the February 9, 

2012, WG meeting transcript (ABRWH 2012), excerpts from which are provided below: 

CHAIR CLAWSON: So, let me understand, and maybe this is for you, Mark. What 

we are looking at is a tiered step to be able to, when we do this dose -- I just want 

to make sure that I am clear that in the earlier years we are going to do, we will 

do the 100 parts per billion? 

MR. ROLFES: Yes, for the years that particular uranium was processed at 

Fernald, we are going to add in 800 [sic] parts per billion of plutonium on a 

uranium mass basis, as well as additional intake of 3500 parts per billion and 

9,000 parts per billion of neptunium-237 -- excuse me -- 9,000 was 

neptunium-237; the 3500 is -- I got that backwards. Thirty-five hundred parts per 

billion of neptunium-237 and 9,000 parts per billion of technetium-99. 

Then, beginning in, I believe it was 1976, I think was the date -- I will have to take 

a look back. 

MEMBER ZIEMER: Seventy-three. 

MR. STIVER: Seventy-three, I believe. 

MR. ROLFES: Seventy-three, we would default the 400 parts per billion of 

plutonium on a uranium mass basis. So, we would be adding in the recycled 

uranium constituents based upon the reconstructed uranium intakes. 

....

CHAIR CLAWSON: I will have to admit, I had to have John help me understand 

the stair steps. So, I have already been through this in detail. 

 
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So, if there isn’t any other questions, we will accept that and move that to the 

TBD.

....

MEMBER ZIEMER: So, we consider this issue closed then. 

CHAIR CLAWSON: It is closed and moved to the TBD. 

Those agreed-upon constituent radionuclide concentration values were subsequently 

incorporated into Tables 18a and 18b of ORAU-RPRT-0052, Revision 00, dated July 2011

(NIOSH 2011b). Those tables are reproduced below for convenience as Tables 2-1 and 2-2. Note 

that the radionuclides other than Pu, Np, and Tc-99 in Table 18a were not in contention. 

Table 2-1. Recommended RU Default Values Beginning in 1961 and to 1973 

(Table 18a, NIOSH 2011b) 

RU contaminant

Mass 

concentration 

addition

Activity concentration 

(Bq/g U)

Pu-239 100 ppb U 232.7

Np-237 3,500 ppb U 92.5

Tc-99 9,000 ppb U 5698

Th (232)

a 10,000 ppb U 0.04

Ru-103/106 50 μCi/lb 4,075

Zr/Nb-95 15 μCi/lb 1,222

Others (Sr-90) 2 μCi/lb 163

a. Th-228 should be assumed to be at 70% equilibrium with Th-232.

Table 2-2. Recommended RU Default Values Beginning in 1973 and to 1986 

(Table 18b, NIOSH 2011b) 

RU contaminant Mass concentration 

addition

Activity concentration 

(Bq/g U)

Pu-239 400 ppb U 931

Np-237 11 ppm U 291

Tc-pp 20 ppm U 20,000

TBD Findings 9 and 11 in the Fernald issues matrix (SC&A 2016a) were put into abeyance 

pending inclusion of the Table 18a and 18b values in the revised TBD-5; Finding 10 was in 

progress pending development of a method for dealing with Am-241 from NIOSH. 

Section 5.3.3 of TBD-5, Revision 03 (NIOSH 2017a), addresses the RU issue in general. The 

new default RU constituent levels are provided in Table 5-10 of NIOSH 2017a, which is 

reproduced below for the readers’ convenience.
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Table 2-3. RU Contaminant Mass Concentrations (Table 5-10, NIOSH 2017a) 

RU contaminant 1961–1972 1973–present

Pu-alphaa 10 ppb U 400 ppb U

Np-237 400 ppb U 11,000 ppb U

Tc-99 6,000 ppb U 20,000 ppb U

Th-232b 10,000 ppb U 10,000 ppb U

Ru-103/106c 50 μCi/lb 50 μCi/lb

Zr/Nb-95d 15 μCi/lb 15 μCi/lb

Sr-90 2 μCi/lb 2 μCi/lb

a. The plutonium alpha mixture is assessed as 100% Pu-239. Am-241 

and Pu-241 are assessed based on 6% weapons-grade plutonium 

mixture. 

b. An intake of Th-228 should be added and assumed to be at 70% 

equilibrium with Th-232.

c. Ru-103/106 is assumed to be 100% Ru-106 due to its longer half-life. 

d. Zr-95/Nb-95 pair is assumed to be in equilibrium with equal activities 

totaling the mass concentrations indicated in the table.

A comparison of Table 18a from NIOSH 2011b and Table 5-10 from NIOSH 2017a reveals that 

the default values from NIOSH 2011b that were agreed upon by the WG at the February 2012 

WG meeting, after years of deliberation, are not those contained in Table 5-10. In fact, the 

defaults for Pu-239, Np-237, and Tc-99 in Table 5-10 are lower than those in Table 18a of 

NIOSH 2011b by factors of 10, 8.75, and 1.5, respectively. In arriving at the Table 5-10 values 

for 1961–1972 contained in the updated TBD, the methodology has ignored the impact of the 

concentrating mechanism that occurred in the magnesium fluoride (MgF2) reduction bomb liners, 

which impacted Plant 5 workers and Plant 1 workers involved in recycling the MgF2 for reuse.

These concerns are described in detail in SC&A 2011b and were the subject of lengthy WG 

discussions in the April 2011 and August 2011 WG meetings. Those discussions provided the 

basis for accepting the Table 18a values. 

SC&A notes that Tables 5-33 and 5-34 in NIOSH 2017a, Section 5.5.1.4, which are used for 

assigning intakes of RU constituent radionuclides in dose reconstruction, contain six separate 

intervals; those intervals, however, do not directly correspond to the intervals in Table 5-9, 

which are used to account for the ingrowth of Am-241 and Pu-241. Table 5-9 is replicated below 

as Table 2-4. 

Table 2-4. Age of Plutonium Mixture in RU (Table 5-9, NIOSH 2017a) 

Period Age

1961–1965 Fresh

1966–1975 10 Year

1976–1985 20 Year

1986–2006 30 Year

Table 2-5 shows the intervals used in Tables 5-33 and 5-34 in NIOSH 2017a and the changes in 

intake values for Pu-239 over time. SC&A understands that the break point in 1965 is to account 

for the change in uranium enrichment from 1 to 2% that is assumed to have taken place that year 

and that the 1975–1976 break point is to account for the ingrowth of Am-241 and Pu-241. SC&A 
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is not clear, however, as to why the Pu-239 intakes go down post 1973 when a constant 

concentration of 400 parts per billion (ppb) U is assumed for that period. NIOSH needs to 

explain this.

Table 2-5. Intervals from Tables 5-33 and 5-34 and Changes in Intake for Pu-239 

Radionuclide 1961–1964

Bq/g U

1965

Bq/g U

1966–1972

Bq/g U

1973–1975

Bq/g U

1976–1985

Bq/g U

1986 on

Bq/g U

Pu-239 29.6 29.6 29.3 1170 1160 1150

SC&A Recommendation: TBD Findings 9 and 11 and the aspect of SEC-P 3 dealing with 

Pu-239, Np-237, and Tc-99 should be changed from “in abeyance” to “in progress,” based 

on the concerns outlined above. 

TBD Finding 10 and Finding SEC-P 3 concern the inclusion of Am-241 in the recycled uranium 

contaminants. Section 5.3.3.4 of NIOSH 2017a addresses this issue and states:

The mass balance reports established that most of the RU came from Hanford and 

was recycled from weapons-grade plutonium. Therefore, a 6% weapons-grade 

mixture that had been chemically purified in 1961 was selected for bounding 

calculations. For dose reconstruction, the plutonium alpha dose from the 

plutonium mixtures in RU is assumed to be from 100% 239Pu. Plutonium mixture 

ratios for fresh, 10-, 20-, and 30-year aged intervals after purification were used 

to estimate the 241Pu and 241Am contaminant levels. 

SC&A Recommendation: Based on the RU contaminant information cited above, TBD 

Finding 10 regarding the inclusion of Am-241 as an RU contaminant can be changed from 

“in progress” to “closed,” and the aspect of Finding SEC-P 3 dealing with Am-241 can be 

changed from “in progress” to “closed.”

2.3 INGESTION INTAKES FROM THORIUM

During SC&A’s review of ORAUT-TKBS-0017-5, Revision 00, SC&A noted that NIOSH 

proposed to use air concentration data for thorium dose reconstruction that would not consider 

ingestion dose separately. This led to TBD Finding 15 stating that ingestion doses from Th-232 

need to be explicitly considered, unless sufficient personal monitoring data are also found for 

thorium. 

The most recent TBD revision, ORAUT-TKBS-0017-5, Revision 03 (NIOSH 2017a), addresses 

thorium ingestion in Section 5.5.2.1.2 for 1995 through 2006, where thorium doses are typically 

based on breathing zone (BZ) data:

Ingestion intakes are also assigned when only BZ data are used to assign 

inhalation intakes (i.e. there are no in vitro or in vivo bioassay), as described in 

OCAS-TIB-009, Estimation of Ingestion Intakes (NIOSH 2004[a]). 

Section 5.5.2.3.2 addresses airborne thorium concentrations from 1990 to 1994: 
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Although the thorium exposure in 1990 could be limited to January to May 1990 

(due to 5 months of Project 2 duration), a full year of exposure should be assumed 

as favorable to claimants. Attachment G, Class W Thorium-232 Inhalation Intake 

Rate Based on 10% of the Derived Air Concentration, provides the assumptions 

used to derive these intake rates. Ingestion doses are assigned as described in 

OCAS-TIB-009, Estimation of Ingestion Intakes (NIOSH 2004[a]), where the 

amount of activity ingested on a daily basis can be approximated assuming it to 

be 0.2 times the activity per cubic meter of air.

SC&A Recommendation: The OCAS-TIB-009 methodology for assessing ingestion intakes 

has been previously reviewed and accepted. SC&A suggests Finding 15 be changed from 

“in abeyance” to “closed.” 

2.4 K-65 SILO RADON EXPOSURE

Revision 00 to ORAUT-TKBS-0017 described the procedure for estimating radon dose to those 

workers who opened the K-65 waste drums and load Silos 1 and 2 based on just two radon data 

points from 1953 and attempted to bound the internal intakes by using incorrect external dose 

limits. SC&A requested that NIOSH justify its assignment of radon dose to these workers, which 

resulted in Finding 29. This issue was last discussed at the September 3, 2014, WG meeting

(ABRWH 2014a, page 240). It was determined that NIOSH would incorporate the methods 

employed in ORAUT-RPRT-0052 into the Fernald internal dose TBD (ORAUT-TKBS-0017-5). 

SC&A has reviewed Section 5.3.5.2 of ORAUT-TKBS-0017-5, Revision 03, and determined 

that NIOSH has applied ORAUT-RPRT-0052 methodology, which uses radon breath analysis 

for determining a radium intake rate. 

SC&A Recommendation: The use of radon breath analysis data for determining intake 

rates of Ra-226 is a reasonable approach. Therefore, SC&A suggests Finding 29 be 

changed from “in abeyance” to “closed.” 

2.5 UNMONITORED INTERNAL DOSE TO URANIUM

NIOSH approved Revision 03 to OTIB-0078 (NIOSH 2015), which provided updated 

calculations and methods for assessing available uranium urinalysis data for the purpose of 

assigning uranium intakes to unmonitored workers. On May 12, 2016, SC&A delivered its 

review of OTIB-0078 (SC&A 2016b), which contained two findings and six observations. It is 

important to note that, subsequent to the release of NIOSH 2015 and SC&A 2016b, the method 

for calculating unmonitored uranium intakes utilizing coworker urinalysis results was merged 

into Attachment C of the Fernald internal dose TBD (NIOSH 2017a).

On July 15, 2016, NIOSH provided responses to SC&A 2016 Finding 1 and Observations 2-6 

(NIOSH 2016a). At that time, Observation 1 required the exchange of calculation files between 

NIOSH and SC&A to effectively address the observation. After the exchange of the required 

information, NIOSH provided its official response to Observation 1 via email on August 3, 2016 

(NIOSH 2016c). Finally, NIOSH provided a response to Finding 2, which was loaded to the BRS 

in May 2017 (NIOSH 2017b). The following paragraphs describe the original issues, NIOSH’s 

response, and SC&A’s recommendation to the WG. 
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Finding 1 noted that in preparing the HIS_20 database for coworker analysis, values that were 

reported as negative or zero were censored at the lowest observed positive result in the relevant 

year. NIOSH’s response indicated (1) that the original OTIB-0078 had predated the 

implementation of the statistical policies found in ORAUT-RPRT-0053, Revision 02, Analysis of 

Stratified Coworker Datasets (NIOSH 2014b) and (2) that future revisions would correctly 

handle the censoring of negative values by censoring them at “zero.” However, it is not clear to 

SC&A that the updated version of the coworker model found in Attachment C of NIOSH 2017a 

has implemented this change. Specifically, Attachment C, Section C.3, of NIOSH 2017a still 

contains the original language from OTIB-0078 (NIOSH 2015):

For years with uncensored data, values less than or equal to zero were treated as 

being censored at the lowest positive value in that year for TWOPOS 

implementation. [emphasis added] 

It is possible that this language is simply an artifact of earlier versions of the coworker model 

and the changes to negative and zero values were implemented in the most recent analysis.

SC&A requests clarification from NIOSH as to whether the appropriate adjustments were made; 

therefore, SC&A recommends Finding 1 be put “in abeyance” pending additional information. It 

should be noted that Observation 3 and Finding 1 deal with the same issue (treatment of values 

below the minimum detectable activity [MDA]); thus, SC&A recommends that Observation 3 

also be put “in abeyance.” 

A response to Finding 2 was provided by NIOSH via the BRS and was uploaded in May 2017 

(NIOSH 2017b). SC&A’s original finding had noted that there were pairs of bioassay results for 

the same worker on the same day that were exactly two orders of magnitude different. SC&A 

recommended that NIOSH investigate the suspect data pairs to determine how such pairs should

be interpreted. To this end, NIOSH obtained the medical records of 24 randomly selected 

workers who exhibited examples of the suspect bioassay pairs. NIOSH concluded that when two 

bioassay pairs were present, the higher of the two pairs was consistently the correct result based 

on comparison with the hardcopy medical records. It is believed that the mechanism causing the 

erroneous bioassay pairs was likely the presence of multiple sets of units depending on which 

original hardcopy sources were used to compile the HIS_20 database. 

As a result, NIOSH has recalculated the coworker model intake values by assuming that when 

paired bioassay results are present, the higher of the two is correct. Furthermore, unpaired results 

that provide numerical values with non-zero decimal results are assumed to be in error and are 

multiplied by 100 to obtain a urine result that is in the correct units. This second criterion was 

based on the fact that the HIS_20 database is in the units of μg/l, and no evidence exists that 

Fernald ever measured uranium urinalysis to a precision level of less than 1 μg/l. Although one 

would logically assume that an error involving incorrect units would result in a factor of 103 

difference (i.e., a result in the units of mg/l incorrectly input as μg/l), SC&A notes that the 

observed suspect bioassay pairs were consistently a factor of 102 different and not 103. 

Therefore, SC&A agrees with the suggested corrective approach proposed by NIOSH, as it is a 

claimant favorable approach and supported by actual examination of hardcopy records. NIOSH 

2017b notes that these methods have already been adopted and incorporated into the calculations 
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present in Attachment C of NIOSH 2017a. Therefore SC&A recommends that Finding 2 be 

closed. 

Observation 1 noted that SC&A was not able to recreate the urinary excretion rates reported by 

NIOSH for at least some years. SC&A and NIOSH exchanged calculation files to discover the 

source of the discrepancy. On August 3, 2016, NIOSH responded that the source of the 

discrepancy for some years was based on the specific calculation methods used by SC&A.

SC&A had used the regression on order statistics (ROS) method outlined in ORAUT-PROC0095, Revision 00, Generating Summary Statistics for Coworker Bioassay Data (NIOSH 2006). 

NIOSH clarified that coworker datasets that contain multiple left-censoring levels are better 

approximated using the ROS methodology described in ORAUT-RPRT-0053 (NIOSH 2014b). 

SC&A has reviewed the response and associated documentation and accepts NIOSH’s

clarification on how certain annual excretion data points were calculated. Therefore, SC&A 

recommends Observation 1 be closed. 

Observation 2 simply pointed out that the use of the time-weighted one person–one sample 

(TWOPOS) method (instead of the traditional pooled approach) did not appreciably change the 

calculated median urinary excretion rates. However, the TWOPOS method did markedly reduce 

the variability in those calculated results. The reduction in variability was expected to be a 

characteristic of the new calculation methods. However, this observation was noted because the 

revision of OTIB-0078 using the TWOPOS approach was one of the first coworker models to 

implement the new methodology. In its response, NIOSH agreed with the observation as well as 

the mechanism behind it. Therefore, SC&A recommends Observation 2 be closed.

Observations 4 and 5 describe information that was contained in the “comments column” of the 

HIS_20 database. In the case of Observation 4, often a censored urinalysis value in the “results 

column” was coupled with a much lower value (likely the actual measurement value) in the 

comments column. Also, approximately 300 database entries contained comments such as “preemployment,” “re-employment,” or “invalid” (Observation 5). These types of samples should not 

have been included in coworker assessment. 

In its response, NIOSH noted that the comments section had not been used in the formulation of 

the OTIB-0078 coworker intakes; however, in future revisions of the coworker methodology 

relevant comments would be taken into account. It is not clear from the text of Attachment C of 

NIOSH 2017a whether these comments were incorporated into the newly derived coworker 

intakes. In fact, Attachment C reports the same number of total samples used in the coworker 

model as previously seen in OTIB-0078. Therefore, it seems unlikely that the inappropriate 

samples identified in Observation 5 were removed. Therefore, SC&A recommends placing these 

observations in abeyance pending confirmation from NIOSH that these adjustments were 

actually made in the recalculated intakes presented in NIOSH 2017a. 

The final observation (Observation 6) discusses additional intake information that is often 

provided with each HIS_20 urinalysis result. This information includes designations of the intake 

pathway (inhalation or ingestion) and solubility type of the contaminant. NIOSH responded that 

there is little information available about how the designations of intake pathway and solubility 

type were reached in the original database. NIOSH notes that in the absence of reliable 

information on intake pathway, inhalation is the default assumption when evaluating bioassay 
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data. Furthermore, because information is also lacking about the solubility type of the inhaled 

contaminants, NIOSH calculates intakes for all applicable solubility types and assigns the most 

favorable type to the claimant. SC&A agrees with this approach, given the absence of 

information, and thus recommends that Observation 6 be closed. 

SC&A Recommendation: Given the previous discussion, SC&A recommends that OTIB0078 Finding 1 and Observations 3–5 be put “in abeyance” pending further clarification 

and/or confirmation from NIOSH that those items have been addressed and implemented.

SC&A recommends that Finding 2 as well as Observations 1, 2, and 6 be closed based on 

NIOSH’s response and/or adjustments made to the derived coworker model values.

2.6 UNMONITORED INTERNAL DOSE TO THORIUM AND THORON

On June 24, 2014, NIOSH transmitted a white paper, Fernald Dose Reconstruction Methodology 

for the Post Special Exposure Cohort (SEC) Period, 1979–2006, Revision 2 (NIOSH 2014a), 

which contains the proposed dose reconstruction methods for assigning internal thorium doses to 

unmonitored workers.2

2 Coworker dose assessment is only proposed for 1979–1994 in NIOSH 2014a; after this time, only monitored 

worker doses are reconstructed.

 Subsequent to this, SC&A was tasked with reviewing the white paper to 

assess whether the proposed methods represent a plausible, sufficiently accurate, and claimantfavorable approach to assigning coworker intakes. The contents of NIOSH 2014a were also 

presented and discussed during the Fernald WG meeting on September 3, 2014 (ABRWH 

2014a), which facilitated preliminary points of clarification regarding the coworker model. 

SC&A presented its review of NIOSH 2014a during the December 4, 2014, WG meeting 

(ABRWH 2014b). 

Application of unmonitored thorium doses can be effectively split into two periods: 1979–1989 

and 1990–1994. The former period utilizes in vivo monitoring data, which measured the thorium 

daughter products actinium-228 and lead-212 in order to develop unmonitored coworker intakes. 

The latter period utilizes a fraction of the derived air concentration (DAC) for assignment of 

thorium doses. Specifically, the method assigns 10% of the Class W DAC value to unmonitored 

workers (5×10-13 microcurie per milliliter [μCi/ml]). Each separate period and SC&A’s review 

findings are discussed in the sections below.

2.6.1 Reconstruction of Unmonitored Thorium Doses (1979–1989) 

SC&A’s 2014d review identified three findings that were specific to the proposed dose 

reconstruction methods for thorium in the 1979–1989 period. Findings 1–3 all relate to the 

practical implementation of the proposed thorium coworker intakes. Specifically, Finding 1 

noted that the majority of thorium-related activities were associated with re-drumming and 

repackaging activities; however, there was evidence to suggest that small-scale handling and 

production occurred after 1979. The workers who may have been involved in either thorium 

activity are not currently known; thus, it appears appropriate to assign unmonitored thorium dose 

to all workers. 

Finding 2 discusses the fact that the in vivo monitoring program was not focused on thorium 

operations but rather the significantly more prevalent uranium operations at the Feed Materials 

 
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Production Center. Because the monitoring program was not necessarily focused on actual 

thorium operations (and therefore exposure potential), SC&A recommended that the 95th

percentile be assigned to assure that the assigned doses to unmonitored workers who might have 

been exposed to thorium are sufficiently bounded. 

Finding 3 noted the wide variety of job types and locations identified among claimants who had 

not been identified as a “thorium worker” in NIOSH 2014a but who indicated exposure to 

thorium in their computer-aided telephone interview. Because there is no plausible method 

currently available to sufficiently identify which workers may have been exposed to thorium, it 

would be appropriate to assign unmonitored intakes to the entire population of potential workers. 

Or conversely, specific irrefutable evidence should be identified and discussed if unmonitored 

thorium intakes are deemed inappropriate to assign to a given claimant. The pertinent section of 

the TBD regarding the assignment of thorium intakes during the period from 1979 through 1989 

states the following: 

Thorium coworker doses are assigned to all unmonitored workers, unless there is 

a reason why they should be excluded (e.g., a secretary or administrative 

individual who worked only in nonradiological areas). The 95th-percentile intake 

rate, with a constant distribution, is assigned to those with the highest potential 

for exposure. Workers with a baseline thorium fecal sample are included in this 

group, as well as subcontractors from IT Corporation working during 1988 and 

1989. All others are assigned the 50th-percentile intake rate with a lognormal 

distribution. [NIOSH 2017a, Section 5.5.2.3.1]

The TBD language instructing dose reconstructors to assign unmonitored coworker intakes to the 

entire worker population satisfies SC&A’s concerns as described in Findings 1 and 3. Therefore, 

SC&A recommends closure of these findings. However, the language appears to suggest that the 

95th percentile be assigned to “those with the highest potential” and then notes that workers with 

baseline fecal sampling for thorium and subcontractors from IT Corporation during the years 

1988 and 1989 would qualify. It is not clear to SC&A whether the list of candidates to receive 

the 95th percentile is exhaustive or merely illustrative. 

As noted in Finding 2, the monitoring program for thorium was not focused on thorium work 

occurring at the site but rather uranium work. Given this characteristic of the monitoring 

program, as well as the inability to identify which workers were potentially exposed to thorium 

and not monitored, SC&A maintains its recommendation that the 95th percentile be assigned to 

all claimants who would be considered “full-time radiological workers.” This would appear to be 

consistent with guidance provided in Neton 2015 (Section 3.2): 

For workers that are considered to have worked in environments with a potential 

for elevated exposure, the 95th percentile of the distribution should be used as an 

upper bound of their exposure during the modeled time period. Although it could 

be argued that the job categories that fall under this criterion should be listed, 

any attempt to do so might be artificially restrictive. For workers who were less 

likely to be highly exposed and/or were intermittently exposed in the workplace, 

the full distribution (i.e., the geometric mean and its associated standard 
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distribution if a lognormal fit is used) should be used as representative of their 

potential for exposure during the modeled period. 

In the case of Fernald, it is not possible to know which radiological workers actually performed

thorium-related work and thus would have the potential for higher exposures. Given this site 

characteristic, it would seem prudent to put emphasis on the Neton 2015 instructions concerning 

assignment of the full distribution. Namely that it should be assigned to workers who were 

“intermittently exposed in the workplace.” This is also consistent with coworker modeling 

approaches taken at other sites, such as Simonds Saw and Steel.

3 SC&A acknowledges that such

policy decisions about the level of dose assignment are ultimately subjective and site specific.

3 Section 3.3 of the Simonds Saw and Steel TBD states (NIOSH 2014c): “The 95th-percentile intake rates in 

Table 3-13 should be applied to all Simonds mill workers, any other worker whose job could have involved work in 

or around the rolling mills or forge shop areas, and workers whose job is unknown. Workers whose job would not 

have required work in those areas (i.e., office workers) should be assigned the median intake rate to allow for being 

occasionally exposed in the general area of uranium processing areas.” 

SC&A Recommendation: SC&A recommends that Finding 2 of SC&A 2014d remain “in 

progress” pending WG discussion as to the appropriateness of assigning the 95th percentile 

versus the full distribution of coworker intakes to claimants considered “radiological 

workers.” As discussed in the previous section, SC&A recommends that Findings 1 and 3 

be closed.

2.6.2 Reconstruction of Unmonitored Thorium Doses (1990–1994) 

For the latter period in which unmonitored thorium coworker dose was evaluated, the SC&A 

2014d review produced two additional findings (Findings 4 and 5). Finding 4 noted that NIOSH 

had selected the DAC value for solubility Class W for assignment as unmonitored intake. SC&A 

noted that the Class Y DAC for thorium was a factor of 2 higher (1×10-12 μCi/ml). NIOSH 

provides the following justification in the revised TBD (NIOSH 2017a, page 55): 

Airborne areas would have been controlled to the lower Class W DAC. It is 

standard industry practice for the lowest DAC value to be used because, for a 

given air concentration, this results in a higher exposure in DAC-hours. 

[emphasis added]

SC&A does not find any technical issues with NIOSH’s position; however, it is often desirable 

to obtain site-specific evidence and information to verify that the industry standards were in 

practice. Therefore, it would be beneficial to obtain documentation from Fernald that the lower 

DAC value was always utilized during relevant thorium activities. Absent specific information to 

scientifically justify one assumed value over another, it is generally accepted to use the more 

claimant favorable approach under the auspices of the Energy Employees Occupational Illness 

Compensation Program. However, when such evidence does exist, the value that provides the 

greater scientific merit is clearly appropriate.

Finally, Finding 5 found that for the period 1990–1994 NIOSH 2014a had stipulated that thorium 

exposures should only be applied if the claimant had submitted a pre-job baseline fecal sample 

for thorium. Similar to Finding 1 and 3 in the previous section, SC&A recommended that the 

 
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assignment of unmonitored thorium intakes be expanded to all radiological workers unless clear 

and convincing evidence exists that thorium exposure could not have occurred. The original 

language indicating baseline fecal sampling as a prerequisite to the assignment of thorium 

intakes has not been included in the revised TBD instructions (see Section 5.5.2.3.2 of NIOSH

2017a). Therefore, SC&A assumes that unmonitored thorium intakes will be assigned in a 

manner consistent with the previous period (1979–1989), in which intakes are assigned unless 

specific information exists that the claimant could not have been exposed (i.e., not a radiological 

worker). 

SC&A Recommendation: SC&A recommends that clarification, by way of additional sitespecific documentation or justification, be provided to assure that use of the lower Class W 

DAC value is more scientifically appropriate than the higher Class Y DAC value 

(Finding 4). Regarding Finding 5, SC&A requests confirmation that unmonitored thorium 

exposures in the 1990–1994 timeframe will be applied to all potentially exposed workers 

and only withheld if clear evidence exists that the claimant was not exposed.

2.6.3 Reconstruction of Thoron Doses

As presented in SC&A’s report 2014d and described in NIOSH 2014a, exposures to radon-220 

(Rn-220) and associated daughters (also known as thoron) are derived based on characterizing 

the source term (by weight) of thorium in specific buildings, establishing the release fractions for 

Rn-220 in stored material as well as materials in process, and finally converting it to exposure 

using an assumed volume of respirable air in each facility. 

Table F-5 of NIOSH 2014a gives the summary of thoron exposure estimates for various time 

periods. SC&A reviewed the thoron exposure estimates and the underlying assumptions used in 

their calculation. Section 9.0 of SCA 2014d discusses each of the assumptions and identifies two

findings: 

Finding 6: The underlying assumptions employed in NIOSH 2014a to reconstruct 

doses to thoron are not well established or referenced. The assumptions 

concerning thorium source term inventory, release fraction, equilibrium factor, 

occupancy time, and specific activity of thoron must be thoroughly defined based 

on credible documentation and site specific records. 

Finding 7: It is necessary that NIOSH evaluate the thoron/thoron daughters’ 

exposures due to Ra-228. Independent of the time assumed after separation, it is 

necessary to evaluate if workers could have worked in areas where Ra-228 was 

handled or stored and consider the associated thoron exposures. As stated on 

page 105 of NIOSH 2014a, Ra-228 has a half–life long enough to permit its 

presence in the workplace for years independent of the original parent isotope 

(Th-232). 

In Attachment B of NIOSH 2017a, NIOSH provides an analysis of potential thoron exposures 

and discusses SC&A’s concerns from SCA 2014d. SC&A believes it would be better to have an 

interactive discussion with the entire WG, rather than attempt a lengthy response in this report. 
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SC&A Recommendation: SC&A suggests a WG discussion pertaining to assumptions 

employed to reconstruct coworker thoron (Finding 6) and thoron/thoron daughters’ 

exposures due to Ra-228 (Finding 7). 
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3.0 SUMMARY OF RECOMMENDATIONS

Table 3-1 contains a list of the actionable issues and SC&A’s recommendations based on our 

review ORAUT-TKBS-00170-5, Revision 03. 

Table 3-1. SC&A Recommendations Summary

Doc No Finding Text SC&A 

Recommendation

TBD 7 

The TBD does not specify a method for estimating doses in the raffinate streams, 

which are uranium poor, from ore processing in Plant 2/3. These doses may be very 

difficult to calculate, especially for high-grade ores, notably pitchblende ore from 

Congo.

In progress

TBD 8 

Workers who may have worked with raffinates may be missed by the protocol 

specified in Volume 5 of the TBD. The guidelines for determining which workers 

were exposed to raffinate dusts are too restrictive and place far too great a reliance 

on completeness of records for job assignments, or in the alternative, place the 

burden of proof on the claimant. They have not been adequately justified by 

measurements and are not claimant favorable.

In progress

TBD 9 

The data on trace contaminants in RU in the Fernald TBD are incomplete and appear 

to be incorrect. Different official documents have very different values for various 

aspects of RU data, including production and contamination. The contradictions 

have not been sorted out in the TBD.

In progress

TBD 10

The radionuclide list for RU in the TBD is incomplete. Furthermore, the 

concentrations of trace radionuclides in the raffinates, which are much higher than 

those in the feed material, are not adequately discussed.

Close

TBD 11

The suggested approach for RU dose estimation in the TBD is claimant favorable for 

many RU workers, but not claimant favorable for others and for some periods; it is 

not based on an evaluation of the available data.

In progress

TBD 15 Ingestion doses are not considered in the TBD. Close

TBD 29 Occupational internal exposure to radon is estimated based on just two radon data 

points from 1953. This is an inadequate basis to reconstruct occupational radon dose. Close

SEC P 3 

Default concentrations (on U mass basis) of Pu-239, Np-237, and other isotopes 

associated with RU at Fernald may not be bounding for some classes of worker 

activities, buildings, and time periods.

In progress

OTIB-78 1 

Although claimant favorable, the censoring of negative and zero bioassay results at 

the minimum observed positive value in a given year is inconsistent with the 

guidance provided in ORAUT-RPRT-0053, Revision 02, Analysis of Stratified 

Coworker Datasets (NIOSH 2014b), which specifies that all negative bioassay 

values be censored at zero. Note that the treatment of negative, zero, and results less 

than the MDA is an ongoing topic of discussion with the SEC Issues Work Group.

In abeyance

OTIB-78 2 

NIOSH should closely examine questionable bioassay pairs that demonstrate 

differences of exactly two orders of magnitude on the same day for the same worker 

to assure that all of the numerical results used in OTIB-0078 accurately reflect the 

daily excretion rates for monitored workers at Fernald and are being interpreted 

correctly.

Close

OTIB-78 Obs 1

SC&A was able to recreate the annual daily excretion rates reported in Table 2-3 of 

OTIB-0078 with a reasonable degree of accuracy for most years. However, SC&A 

was not able to recreate the values reported for the years 1986–1997.

Close
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Doc No Finding Text SC&A 

Recommendation

OTIB-78 Obs 2

A comparison of the median urinary excretion rates derived in Revision 03 to OTIB0078 (using the TWOPOS method) with the excretion rates calculated in Revision 

01 to OTIB-0078 (using the pooled sample approach) showed very little difference. 

However, as expected, the use of TWOPOS methods results in a significant 

reduction in the variability of the derived distributions, and thus excretion rates at 

the 84th percentile were markedly lower using the TWOPOS method.

Close

OTIB-78 Obs 3

Sample results that were below the detection limit were not reported in a consistent 

fashion in the HIS_20 ORAU database. NIOSH has elected to treat negative and 

zero results by censoring the value at the lowest observed positive result by year. 

This approach is claimant favorable compared to using the negative and zero values 

as is although not consistent with the methodology in ORAUT-RPRT-0053 (see 

Finding 1).

In abeyance

OTIB-78 Obs 4

NIOSH appears to have used reported values at the MDA/control limit in situations 

where a lower numerical result was provided in the comments section of the 

bioassay entry. This is a claimant favorable interpretation of these records.

In abeyance

OTIB-78 Obs 5

SC&A observed 313 sample entries that should likely have been removed from the 

coworker model due to comments indicating the sample was an invalid result or the 

sample was for pre-employment/re-employment purposes. Given the relatively small 

incidence of such samples, the cumulative effect of excluding those results is likely 

to be insignificant.

In abeyance

OTIB-78 Obs 6

OTIB-0078 would benefit from a discussion of the additional intake information 

(intake pathway and solubility type) available in the HIS_20 ORAU database. 

Neither the pedigree and accuracy of such indicators nor whether appropriate 

adjustments to the intake model may be warranted are known at this time.

Close

SCA 

2014d 1 

While it appears that the majority of the thorium exposure potential at Fernald in the 

post-SEC period was related to redrumming and repackaging activities, some 

evidence exists that small-scale handling and possibly production may have occurred 

after 1979. Given that it is currently infeasible to identify which workers were 

involved in these operations and potentially exposed, and by extension whether 

those workers were properly monitored, NIOSH should assign unmonitored thorium 

intakes for all workers who may have entered radiological areas and been exposed to 

thorium materials.

Close

SCA 

2014d 2 

Given that the monitoring program does not appear to be directly focused on areas 

where thorium exposure potential existed, coupled with the inability to effectively 

identify which workers may have handled thorium materials, NIOSH should instruct 

the dose reconstructors to assign the 95th percentile coworker intake value to all 

unmonitored claimants who may have been directly involved in thorium operations.

In progress

SCA 

2014d 3 

Given the broad work locations and duties contained among worker job types not 

currently defined as a thorium worker in NIOSH 2014a, NIOSH should provide 

explicit instructions to the dose reconstructor that thorium coworker intakes should 

be assigned unless sufficient evidence exists that the claimant did not enter 

radiological areas where thorium exposure potential may have existed.

Close

SCA 

2014d 4 

Unless sufficient evidence exists that thorium exposure potential at Fernald was 

restricted to solubility Class W, NIOSH should consider using the more conservative 

and claimant favorable DAC value for solubility Class Y.

Discussion 

SCA 

2014d 5 

NIOSH should not restrict the assignment of thorium intakes to workers who 

submitted pre-employment fecal samples, but rather assign intakes based on the 

potential for radiological exposure.

Discussion

SCA 

2014d 6 

The underlying assumptions employed in NIOSH 2014a to reconstruct doses to 

thoron appear to be arbitrary and are not well established or referenced. The 

assumptions concerning thorium source term inventory, release fraction, equilibrium 

factor, occupancy time, and specific activity of thoron should be more carefully 

defined based on credible documentation and site-specific records

Discussion
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Doc No Finding Text SC&A 

Recommendation

SCA 

2014d 7 

It is necessary that NIOSH evaluate the thoron/thoron daughters’ exposures due to 

Ra-228. Independent of the time assumed after separation, it is necessary to evaluate 

whether workers could have worked in areas where Ra-228 was handled or stored 

and consider the associated thoron exposures. As stated on page 105 of NIOSH 

2014a, Ra-228 has a half–life long enough to permit its presence in the workplace 

for years independent of the original parent isotope (Th-232).

Discussion
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