Statement by David Kotelchuck, 

Work Group Member

Meeting of the Advisory Board on Radiation and Worker 

Health, Metals & Controls Work Group

July 13, 2023

Dr. David Kotelchuck

1
The goal

A plausible, scientifically sound, bounding model for the 

exposures of 400+ maintenance personnel claimants during 

the residual period at the Metals and Controls (M&C) facility 

(1968–1997)

2
Two basic background facts

1. No individual exposure measurements were made during 

the residual period (1968–1997) for any of the claimants.

2. Records of the individual work activities of the claimants 

during the residual period were not found.

3
These facts basically force a one-size-fits-all

exposure model

• That is, any bounding model developed must assign the 

identical exposure to each and every one of the 400+ 

claimants, except for their differing durations of 

employment.

• (It should be noted that even if several claimants have 

identical durations of employment and thus identical 

exposures, their doses and probabilities of causation may 

differ depending on their differing types of cancers.)

4
The available exposure data during the 

residual period 

1. Measured radiation exposures of personnel from the end 

of the operational period can be extrapolated into the 

residual period.

2. In 1995, two years from the end of the residual period, 

Weston workers conducted radiation measurements 

preliminary to the beginning of its D&D operations in 1998.

5
The quality limitations of these two data 

sources

1. The initial 1968 exposure data are extrapolated from the 1967 

operational period as the geometrical mean (GM) of exposures 

of all operational period maintenance workers. The bounding 

model then applies this GM annually to all maintenance worker 

claimants. But two-thirds of the claimants (70.1%) began their employment during the residual period (NIOSH SEC ER, 2017), 

so these initial data poorly characterize the exposures of most 

of these Special Exposure Cohort (SEC) claimants.

2. The exposures experienced by M&C maintenance workers in 

the subsurface environment are not adequately characterized 

in the NIOSH bounding model; thus, nor are the doses derived 

from them.

6
Attention to subsurface exposures in Bldg. 10

NOTE: The Work Group (WG) and staff generally agreed that 

the greatest exposures to the M&C maintenance workers 

came from the subsurface work in Building 10. Since the 

NIOSH bounding model is applied to all claimants, further 

discussion during this presentation focuses solely on such 

subsurface work and whether or not it is bounded.

7
M&C workers had greater exposures than expected 

(due to different job tasks than Weston employees)

• Weston, during its 10-day work period in 1995, was assigned to enter into and assess the higher radiation levels of fluids and 

sludge within subsurface pipes of Bldg. 10, meanwhile removing 

any physical obstructions, such as the fuel rod discovered within 

one of the pipes. 

• In contrast, M&C maintenance workers doing subsurface work 

routinely over the years had to snake out and repair (cut, saw, 

grind, weld) underground pipes, as well as remove observed 

obstructions.

• The Result: M&C workers were exposed to additional radioactive sources of exposure than considered in the NIOSH model.

8
Individual Weston worker exposure measurements 

NOT used in the NIOSH bounding model

Individual exposure measurements made on the Weston 

workers were available but not used in the NIOSH bounding 

model, in recognition of the differences in job tasks of the 

M&C and Weston workers.

9
M&C workers experienced greater doses than 

expected (due to lack of H&S info, training, & PPE)

• M&C maintenance workers were given no radiological health and safety 

(H&S) information or training during the residual period, and only 

occasionally received personal protective equipment (PPE). Also, after 

1983, following the NRC’s removal of radiation work restrictions for 

Building 10, they believed they were not working under hazardous radiological conditions.

• Thus, certainly after 1983, M&C maintenance workers could not be 

expected to have followed the ordinary, common-sense precautions that any intelligent person would follow when working on and near the 

piping in a potentially hazardous radiation environment.

• The Result: The M&C maintenance workers would be expected to experience greater doses of radiation than assessed in the NIOSH 

bounding model.

10
How does the NIOSH bounding model seek to 

compensate?

The current NIOSH bounding model for subsurface work in 

Bldg. 10 posits the basic equivalence of subsurface work 

activities among the Weston and M&C maintenance workers. 

It then seeks to compensate for differences in exposures and 

in doses by choosing the 95th percentile of measured Weston 

radioactivity for the bounding model, rather than the 50th as 

would ordinarily be done.

11
Bounding based on professional judgement

The determination of bounding typically rests on professional 

judgement. NIOSH notes that of 60 previous residual-period 

SEC proposals, 57 were rejected and three were approved by 

the Board. This suggests a priori that a new residual period 

SEC proposal is unlikely to be approved, but it is the Board’s 

responsibility to look at each proposal individually and seek 

out its particular, and perhaps unique, features.

12
Does the NIOSH M&C model bound?

• In terms of the varied 

exposures from the job tasks

of the M&C maintenance 

workers, does the difference 

between the 50th and 95th 

percentiles bound them? 

• This WG member does not 

know if they do and does not 

see how this could be 

determined within our limited 

data and information base.

• In terms of the differences in 

the H&S programs, their 

impact on doses appears 

inestimable to this WG 

member, so going from 50th 

to 95th percentiles may or 

may not bound these.

• I do not know, and do not 

believe we can determine this.

13
The NIOSH model does not appear to bound

Thus, in my professional judgement, I do not have confidence 

that using the 95th percentile of pipe radioactivity measured 

by Weston rather than the 50th bounds the M&C 

maintenance workers’ exposures.

14
Importance of the Mound surrogate data

model

With the limitations in quality of the two M&C data sources 

(Slide 6), developing a surrogate data model is of great 

importance. NIOSH has proposed that a trenching project at 

the Mound facility could serve as an acceptable surrogate 

model for outdoor and indoor subsurface exposures to 

maintenance workers at M&C. Again, we will consider here 

only its application to indoor subsurface work.

15
The Mound database: Collected under different 

conditions than the M&C subsurface trenching

• The Mound project trenching data were collected outdoors 

on a country lane, whereas the M&C maintenance 

subsurface exposures, of course, took place indoors in 

Building 10.

• As such, using the Mound data as surrogates for M&C 

violates one of the Criteria for the Use of Surrogate Data, 

adopted by the Board in 2014.

• At the last WG meeting (5/12/23), SC&A staff appealed to 

professional judgement that the use of Mound data for 

surrogacy was acceptable.

16
The Mound database seems a poor fit for M&C

Because of the major differences in work environments 

between Mound and M&C – an outdoor, relatively placid 

country lane vs. an indoor, dirty, often muddy industrial 

worksite, respectively – this WG member believes the Mound 

database is a poor fit for M&C surrogacy.

17
Even if accepted, Mound data alone are 

inadequate

• Even if the Mound database is accepted by the WG for 

surrogacy, based on its professional judgement, the Mound 

data alone are inadequate to fully characterize M&C 

maintenance workers’ radiological exposures.

• The Mound data seek to account for the radioactive dustloading of the soil, which, when stirred up, results in worker 

exposure to dusts and particulates. 

18
Additional sources of M&C exposures

• As noted in Slide 8, M&C maintenance workers doing 

subsurface work routinely had to snake out and repair (cut, 

saw, grind, weld) underground pipes.

• These routine components of M&C operations also created 

additional sources of radioactive dusts and particulates, 

beyond those from the (Mound-based) dust-loading.

• The current NIOSH bounding model does not appear to 

account for these and should.

19
Conclusion

Based on insufficient data to assess doses over a lengthy 

residual period, and despite serious efforts by NIOSH to 

develop a scientifically sound bounding model, I do not 

believe that the model developed for these M&C residualperiod claimants is a plausible one.

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