SC&A’s Evaluation of the NIOSH SEC ER 

Proposed Use of FAP Bioassay Indicator 

Radionuclides (in Conjunction with 

OTIB-54 and TBD-5) for Assessment of 

FAP and Actinide Intakes at INL

Ron Buchanan, PhD, CHP

S. Cohen and Associates

Contractor to:

Advisory Board on Radiation and Worker Health/ABRWH

Center For Disease Control and Prevention

November 10, 2015
2 

Four Important Assumptions for 

Assigning FAP and Actinide Intakes

A) Sr-90 and Cs-137 – Sufficient fission-activation 

product (FAP) bioassay records are available to 

assign Sr-90 and/or Cs-137 intakes. 

B) FAPs – Using a bioassayed indictor 

radionuclide (Sr-90 and/or Cs-137) all other 

significant FAP intakes can be assigned by 

using the ratio method.
3 

Four Assumptions (continued)

C) Actinides – Using a bioassayed indictor 

radionuclide (Sr-90 and/or Cs-137), all 

significant actinide (alpha-emitter) intakes can 

be assigned by the ratio method.

D) Special Bioassay – If actinide intakes 

occurred that were not directly associated 

with an FAP indicator (Sr-90 and/or Cs-137) 

in a known ratio, “special” bioassays were 

performed and are available in the worker’s 

records. 
4 

This Presentation

Addresses:

• Item B – FAPs

• Item C – Actinides

• Item D – Special Bioassays

 Item A (sufficiency of FAP bioassays) is 

addressed in a separate report.
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FAP and Actinide Intakes

• NIOSH’s ER recommends using Sr-90 

and/or Cs-137 bioassay results in 

conjunction with ratios in OTIB-0054 to 

assign FAP intakes.

• NIOSH’s ER recommends using Sr-90 

and/or Cs-137 bioassay results in 

conjunction with ratios in TKBS-0007-5 

to assign actinide intakes.
6 

Evaluation of Ratios

• The ratio values were derived mostly by 

computer simulation (ORIGEN)

• SC&A searched for documentation that 

would provide measured radionuclide 

ratios

• SC&A searched the following:

NOCTS 

SRDB 

INL electronic bioassay database
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Evaluation of Ratios (continued)

 SC&A located measured quantitative 

radionuclide analyses of:

Nasal swabs

Urinalyses 

Fuel element scale

Fuel storage contamination swipes

Air filters 

 A total of 42 samples were located and 

analyzed for radionuclide ratios.
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Example of Resulting Plots

Measured BGRR Fuel Scale Radionuclide Ratios vs. 

NIOSH Ratios, Based on Sr-90

0.1

1.0

10.0

100.0

Sr-90 Cs-137 Ce-144 Ru-106 U-234

Radionuclide Present in Fuel Scale

Comparison of 

Measured ratio 

to NIOSH ratio

NIOSH ratio > Meas. Meas. ratio > NIOSH

Measured BGRR Fuel Scale Radionuclide Ratios vs. 

NIOSH Ratios, Based on Cs-137

0.1

1.0

10.0

100.0

Sr-90 Cs-137 Ce-144 Ru-106 U-234

Radionuclide Present in Fuel Scale

Comparison of 

Measured ratio 

to NIOSH ratio

NIOSH ratio > Meas. Meas. ratio > NIOSH
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Summary of Results

1. FAP intakes assigned using NIOSH’s 

recommendations in OTIB-0054 based 

on Sr-90 intake values are generally (but 

not always) equal to, or greater than, 

those derived from actual measured 

values.
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Summary of Results (continued)

2. The Cs-137/Sr-90 ratios are not always 

1:1 as assumed in OTIB-0054 and TKBS0007-5; frequently, large variations in the 

ratio exist. This brings into question the 

validity of using an indicator radionuclide 

when deriving FAP and actinide intakes. 

This may be the most important result of 

this study, because a Cs-137/Sr-90 value 

of 1:1 is one of the cornerstones for use 

of the ratio method at the INL. 
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Summary of Results (continued)

3. Actinide intakes assigned using 

NIOSH’s recommendations in TKBS0007-5, Table 5-22, based on Sr-90 

intake values, or Table 5-23, based on 

Cs-137 intake values, are sometimes 

significantly less than those derived from 

actual measured values.
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Summary of Results (continued)

4. Special bioassays. It is difficult to 

evaluate when “special” (situations 

where actinides were not tied to a fission 

product in a given ratio) bioassays were 

needed, if they were performed, and if 

they are indicated as such in the 

bioassay records.
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Recommendation #1

 It needs to be determined if records of 

analyses of dissolver contents 

(containing the fuel elements) are 

available; preferably, for a variety of INL 

reactor fuel elements, and also fuel 

elements from off-site reactors.
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Recommendation #2

 Further INL document research is 

needed to evaluate NIOSH’s 

recommended ratio values, especially for 

actinides and Cs-137/Sr-90. Records 

with quantitative radionuclides analyses 

are especially important.
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“Special” Bioassays

 In the past, there was no apparent need 

to recognize, or emphasize, radionuclide 

ratios for assigning intakes and doses; 

hence, there was no obvious reason to 

treat bioassays taken for situations 

where actinides were not tied to an 

indicator FAP radionuclide any different 

than other bioassays. 
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Recommendation #3

 It needs to be determined if special or nonroutine bioassays were associated with 

special exposure events, such as are 

referred to in the ER, or if instead the term 

“special,” or “non-routine,” bioassay was 

applied to the priority of processing over 

“routine” bioassays. 

 How will special bioassays be identified to 

insure adequacy for dose reconstruction?
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Comments and Questions