OCAS-PER-031, Subtasks 1–3

EVALUATION OF THE NATIONAL 

SECURITY COMPLEX (Y-12) TBD 

REVISIONS

SC&A Report Dated July 15, 2013

Presented to the

Advisory Board’s Procedures Review Subcommittee

November 7, 2013

1
OCAS-PER-031 Summary

• The Y-12 TBD (six volumes numbered 

ORAUT-TKBS-0014-1 through ORAUTTKBS-0014-6) was revised numerous 

times between 2003 and 2012.

• OCAS-PER-031 (2007) was issued due to 

the TBD change in the Th-228/Th-230 

ratio from 1:1 to 0.8:1. 

2
NIOSH’s Issue

• NIOSH stated that this change would result in 

an increase in assigned dose.

3
NIOSH’s Number of Claims

• NIOSH identified 693 Y-12 claims that were 

completed prior to the date of issuance of 

PER-031 (December 18, 2007) and had a 

probability of causation (POC) below 50%. 

4
NIOSH’s Corrective Action

• NIOSH will review the DR for each of these 

693 claims to determine if the evaluation of 

dose involved exposure to, and intake from, 

purified thorium. 

5
SC&A’s Subtasks 1 & 2

• SC&A performed a paragraph-by-paragraph 

comparison of the first three revisions (up to 

and including Rev. 1 PC-2 dated January 12, 

2006, that was used in OCAS-PER-031) of 

ORAUT-TKBS-0014-5 (referred to as TBD-5) 

to identify changes that could potentially 

impact the assigned dose.

6
SC&A’s Subtasks 1 & 2 (continued)

• SC&A’s comparison of the different Y-12 

TBD-5 versions did not identify any changes 

that would impact the assigned doses, 

except for the method of determining 

purified thorium (Th-232 and Th-228) body 

burdens. 

7
SC&A Finding #1

• Finding #1: Change in Assigned Dose – The 

change in the Th-228/Th-232 ratio would 

actually reduce the assigned dose, not 

increase it, if thorium intakes and resulting 

doses are based on recorded mg values of 

thorium from chest counts, as was observed in 

the case files SC&A has reviewed to date.

8
SC&A Finding #2

 Finding #2: Chest Counts Conversion to 

Th-232 Body Burden – The method NIOSH 

uses (in both the old and new TBD-5) to 

assign Th-232 body burden assumes that 

the gamma counts obtained during the 

chest counts are directly related to Th-232 

(in mg) in the lungs, using an empirically 

derived calibration factor that applies to all 

Y-12 workers at all times.

9
Finding #2 (continued)

 This assumption is incorrect because the 

gammas from Ac-228 and Pb-212 are being 

counted, and (1) Ac-228 is not in equilibrium 

with Th-232, (2) Pb-212 is not in equilibrium 

with Th-228, and (3) Th-228 is not in 

equilibrium with Th-232. Additionally, a given 

equilibrium cannot be assumed because it is 

constantly changing for many years after the 

purification of thorium. 

10
Finding #3

• Finding #3: Different Solubility of Thorium 

and Decay Products in the Lung – The lung 

may retain thorium, being relatively 

insoluble, longer than the more soluble 

decay products in some cases. Therefore, a 

lung count based on the decay product (i.e., 

Ac-228 and/or Pb-212) would not 

necessarily have a consistent relationship to 

the thorium (Th-232 and/or Th-228) body 

burden. 

11
Finding #3 (continued)

• Additionally, the solubility of the decay 

products themselves (inhaled or formed in the 

lungs) may have different solubility and not 

have consistent ratios.

12
Finding #4

• Finding #4: MDA or LOD Value – NIOSH 

assumed an Ra-228 to Th-232 ratio of 0.6 

(page 31 of ORAUT-TKBS-0014-5, 2006) for 

determining the minimum detectable activity 

(MDA) of 0.6 nCi; this would require 

approximately 8 years from purification to 

counting. This is not a valid assumption for 

almost all workers and is not constant 

between each chest count.

13
Finding #4 (continued)

• The limit of detectability (LOD) value was not 

directly based on counting statistics, but it was 

empirically derived and meant to be used only 

as a screening tool, not to accurately assign 

dose (West 1965, Scott 1961).

14
SC&A’s Subtask 3 (Number of claims)

• At the time that OCAS-PER-031 was issued 

(12/18/2007), NIOSH identified 693 Y-12 

claims that were completed prior to that date 

and had a POC below 50%. This establishes an 

upper-bound estimate of the number of 

claims that may be impacted. NIOSH intends 

to screen these claims.

15
SC&A’s Subtask 3 (# of claims) 

(continued)

• The application of these screening criteria will 

undoubtedly exclude many of the 693 

potential claims from impacts associated with 

OCAS-PER-031 and the need for the 

reconstruction of the organ dose. However, 

until NIOSH reviews all of these claims, the 

actual number of cases that will be affected by 

OCAS-PER-031 and require a new dose 

assessment remains unknown.

16
SC&A’s Subtask 3 (# of claims) 

(continued)

• In addition, based on the outcome of the 

findings identified as a result of our technical 

review of ORAUT-TKBS-0014-5, there may be a 

need to cancel OCAS-PER-031 and reissue a 

PER after appropriate changes have been 

made to the Occupational Internal Dose TBD.

17
SC&A’s Subtask 4

Selection of DRs to audit 

• SC&A identified four findings that question 

the technical merit of the Y-12 Occupational 

Internal Dose TBD and corrective actions 

taken by NIOSH in OCAS-PER-031.

• SC&A recommends that the selection of 

Subtask 4 cases be delayed until the 

Subcommittee on Procedures Review can 

further investigate SC&A’s findings and 

concerns.

18
Questions?

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