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National Institute for Occupational Safety and Health
Summary of Dose Reconstruction Feasibility for Subcontractor Construction Trades Workers (CTWs) at the Savannah River Site (SRS) – SEC00103
Timothy D. Taulbee, PhD, CHPAssociate Director for ScienceJohn J. Cardarelli II, PhD, CHP, CIH, PEResearch Health Physicist
Advisory Board on Radiation and Worker Health MeetingApril 14, 2021
Key Dose Reconstruction Documents for Unmonitored Subcontractor Construction Trades Workers (sCTWs) DCAS-IG-006: Criteria for the Evaluation and Use of Co-Exposure
Datasets (March 2020)
– Section 2.0 Data Adequacy and Completeness• Completeness: “determine if there are sufficient measurements to
ensure that the data are either bounding or representative of the exposure potential for each job/exposure category at the facility”
• Guidance also indicates that there should be consideration for temporal gaps in the data and provides an example with respect to completeness from the Nevada Test Site (NTS)
ORAUT-OTIB-0081: Internal Dosimetry Co-Exposure Data for the Savannah River Site (September 2020)– 9 Radionuclide models for both CTWs and non CTWs
4/14/2021 2
Job Specific vs. Routine Bioassay Samples “The purpose of the job-specific bioassay sampling program is to collect bioassay
samples from workers whose routine bioassay program does not include some or all of the radionuclides present at the work site or who are not on a routine program.” (SRDB# 167757)
Most workers, including subcontractor Construction Trades Workers (sCTW), were on a routine bioassay schedule.
1997 DOE Notice of Violation (NOV) indicated only 21% (68/324) compliance of submitting job-specific bioassays. The workers who did not submit job-specific bioassays (79% or 256/324 workers) were followed-up and none indicated an internal exposure. (SRDB# 167497)
At SRS in 1997 there are over 6,000 routine non-tritium bioassays. This indicates that job-specific bioassays comprises a relatively small fraction (≈5%) of the overall internal monitoring program and likely has an insignificant impact on co-exposure models.
4/14/2021 3
Documentation Evaluating Subcontractor CTW Monitoring for Completeness and Representativeness RWP Analysis - ORAUT-RPRT-0092: Evaluation of Bioassay Data for
Subcontracted Construction Trade Workers at the Savannah River Site NOCTS Data Evaluation – ORAUT-RPRT-0094: Bioassay for Subcontractor
Construction Trade Workers at the Savannah River Site from 1972 to 1997 Plutonium Bioassay Logbook Analysis: 11,316 bioassay samples from
7,028 subcontractors CTWs between 1972-1990 Response to SCA Finding #3
Savannah River Site Plutonium Construction Trade Worker Stratification Refinement 2019 White Paper
Analysis of Uncertainty in Co-Exposure Models 2021 Bootstrap White Paper
Practical Implications of the Bootstrap Uncertainty Analysis on Co-Exposure Models 2021 Practical Implications White Paper
4/14/2021 4
Conclusion - Weight of the Evidence Weight of evidence from evaluations, stratification, & uncertainty analysis
– Robust subcontractor CTWs monitoring in the 1990s– Acceptable subcontractor CTW monitoring (>50%) in the 1980s– Limited monitoring data in the 1970s (DuPont CTWs are bounding)
We do not see any evidence where subcontractor construction trades workers were not monitored to a degree that would bias the current co-exposure models
Based on the weight of the evidence, NIOSH believes that the co-exposure models are bounding and representative of the exposures that would be received by an unmonitored subcontractor construction trades worker
NIOSH concludes that dose reconstruction is feasible
4/14/2021 5
Questions?
NIOSH December 2020 Presentation on Dose Reconstruction Feasibility
6
For more information, contact CDC1-800-CDC-INFO (232-4636)TTY: 1-888-232-6348 www.cdc.gov
The findings and conclusions in this report are those of the authors and do not necessarily represent the official position of the Centers for Disease Control and Prevention.
Extra SlidesThese slides are for clarification purposes to assist in answering potential questions
Subcontractor Monitoring Limited assessment of 3200
bioassay requirements –33% compliance on Job-specific bioassay
Full assessment –“about21% compliance” on Job-specific bioassay ≈ 324 Job-specific ≈ 6481 total bioassay
1997 Total # of samples NOT
s
3200 Samples95%
5%
3.35%
1.65%
95%
107 Samples
67%, 79%
33%, 21%
s96.65%
3092 Sample
received was 256
100% follow-up of 256workers indicated no intake
SRDB# 16775712/9/2020 8
Subcontractor CTW monitoring in NOCTS Only NOCTS data (Claimant Data)
– 6097 Total SRS Claimants– 886 (15%) Subcontractor CTWs– Most, if not all, subCTW job titles are
Electrician26%
Pipefitter22%
Laborer9%
Other8%
Painterrepresented
NIOSH Evaluation– External Monitoring– Internal Monitoring
• Tritium bioassay• non-tritium bioassay (actinides)• Whole Body Counting (fission products)
3/23/2021 9
Why the simplistic internal monitoring approach?
Radionuclide specific internal monitoring depends on where the worker conducted their work (SRS is a Very Large Site)– Subcontractors in reactor areas likely didn’t need plutonium
monitoring, but may have needed tritium or fission products– Subcontractors in plutonium areas likely didn’t need tritium
monitoring– Subcontractors in tritium areas likely didn’t need plutonium or
fission product monitoring
Fundamental question: Are subcontractors sufficiently represented or bounded in the co-exposure models?
3/29/2021 10
Comparison RWP Analysis and NOCTS Claimant DataNOCTS Data from Table 5-4
12/9/2020 11
Effect of limited monitoring on Co-exposure models
Based on NOCTS data analysis (RPRT-0094) there are six years (1974-1979) where the percentage of internal monitoring via non-tritium and WBC is less than 50%
To bias the co-exposure models, exposures to unmonitoredsubcontractor CTWs would have to be significantly higher than the monitored subcontractor CTWs– Considering the zero-intake policy and defense in depth approach to
radiological protection, coupled with the Health Physics coverage of the construction jobs, we don’t believe this is plausible especially considering that for most years the monitored subcontractors outnumber the unmonitored subcontractors
12/9/2020 12
Subcontractor CTWs identified from SRS Pu bioassay logbooks
Decrease in Pu monitoring
Significant increasein Pu monitoring
260 198 159 136 129 71 56217
583 652 637538 507 517
1042
740
1860
1289
283
0
500
1000
1500
2000
1972 1973 1974 1975 1976 1977 1978 1979 1980 1981 1982 1983 1984 1985 1986 1987 1988 1989 1990
7,028 unique subCTWs11,316 records b/w 1972-1990
12/9/2020 13
Approximate # Pu bioassay samples forsubCTWs by Area (1972-1990)
N=11,316
C area likely contains CS samples due its
location adjacent to Central Shops
1
250
438
932
62
1835
170
2822
528
1877
338
620
83224
13
668
32 983
322
0
500
1000
1500
2000
2500
3000
21 TC-1 A C CMX CS D F G H K L M P R S Tech TNX Z Missing
Central Shops (CS) area
signifies CTWs
Main Pu potential exposure area
12/9/2020 14
Plutonium Sub-stratification analysis
Over 95% of the plutonium bioassay data is below the reportable level of 0.1 dpm/day
Bioassay data from DuPont or prime CTWs (Roll 2) appear to be slightly greater than subcontractor CTWs (Roll 4, 5, and 6)
When co-exposure models are developed, the Pu intakes for the two populations are quite similar
12/9/2020 15
Sub-stratification Type-S Plutonium Intake Results
Yearprime-CTW
50th %(dpm/d)
subCTW50th %
(dpm/d)
prime-CTW95th %
(dpm/d)
subCTW95th %
(dpm/d)
1973-1978 15.71 6.97 268.7 169.4
1979-1987 26.38 22.65 279.2 326.1
Bold denote higher 50th% IntakesUnderline denote higher 95th% Intakes
12/9/2020 16
Analysis of Uncertainty (Bootstrap analysis of 1986 tritium co-exposure model confidence bands and density plots)
50
5
0.5
0.1-3 -2 -1 0 1 2 3
Standard Normal Quantiles
Dose
(mre
m)
sub-CTWs, and DuPont CTWs Confidence Bands for all CTWs,
2 4 6 8 10 12 1450th percentile (mrem)
500
400
300
200
100
0
Dens
ity
Density Plots of the 50th percentile
3/23/2021 17
Uncertainty Analysis of Tritium Co-exposure Models
Subcontractor CTWs exposures were generally lower than DuPont CTWs between 1972 and 1990.
There is no practical difference between the two groups and the currentcombined CTW model.
Geometric Mean with confidence intervals
1975 1980 1985 1990Year
70
60
50
40
30
20
10
0
Triti
um D
ose
(mre
m)
183/23/2021
Analysis of Uncertainty: Downward trend in tritium dose
Downward trend in
tritium doses between
1972 and 1990.
Typical of improved
radiological controls and
decreased exposure
potential over time.
95th percentile with confidence intervals
1975 1980 1985 1990Year
350
300
250
200
150
100
50
0
Triti
um D
ose
(mre
m)
3/23/2021 19
1972 1975 1980 1985 1990Year
80
60
40
20
0
Num
ber o
f wor
kers
(Ann
ual D
oses
)
Analysis of Uncertainty: Representativeness
Smaller number of subCTWs than DuPont CTWs in the 1970s
Larger number of subCTWs than DuPont CTWs in the 1980s
3/23/2021 20
NOCTS Percent subCTWs with dosimetry data and monitored for tritium exposures (adapted from Table 5-3)
0%
20%
40%
60%
80%
100%
72 74 76 78 80 82 84 86 88 90 92 94 96Year (1972 - 1997)
3/23/2021 21