National Institute for Occupational Safety and Health

Assessment of Los Alamos National Laboratory Plutonium Bioassay 

Programs 1996 to 2001 (ORAUT- RPRT-0102)

LaVon Rutherford, CHP

Health Science Administrator

LANL Work Group Meeting

March 23, 2022
Presentation Overview

■ Background

■ Report Overview

■ Study Design

■ Data Analysis

■ Summary and Conclusions
Background

 The 1999 audit of the Los Alamos National Laboratory (LANL) 

bioassay program listed several deficiencies in the bioassay program 

that were of regulatory significance 

 Of particular concern to this report was finding 1

– Radiation workers are not consistently placed on the appropriate routine 

bioassay program 

– The issues discussed in this finding included ineffective HP checklists, workers 

failing to submit bioassay samples per RWP requirements, and Johnson 

Controls Northern New Mexico (JCNNM) personnel not fully participating in 

required bioassay programs 
Background cont.

 The finding prompted the work group to ask NIOSH

– Do the 1999 LANL findings regarding bioassay program deficiencies imply data

inadequacy and incompleteness significant enough to impair dose

reconstruction?

 At the Nov. 25th, 2018, work group meeting, NIOSH committed to

reviewing RWPs and developing a sampling plan for determining

whether workers were complying with bioassay requirements and

what affect that may have on dose reconstruction

 After capturing RWPs, we decided a sampling plan would not be

necessary, we would include all the RWPs that met the study design

criteria for the analysis
Report Overview
Report Overview cont.

 Since co-exposure models are used to perform dose 

reconstructions for individuals without monitoring data, the 

question by the work group changes to

– Do the indicated bioassay program deficiencies imply data inadequacy and 

incompleteness significant enough to impair development of a co-exposure 

model? 

 Report 102 was developed to answer the question for plutonium

– Bioassay programs for plutonium are specifically addressed because 

plutonium posed the greatest radiological hazard to workers at LANL during 

the study period (1996 to 2001)

– If LANL was correctly monitoring for plutonium what evidence makes us think 

the monitoring was different for other radionuclides of concern
Co-exposure Models

 The goal of a co-exposure study is to estimate the probability 

distribution of external doses or internal intakes to a “target 

population”

 All members of the target population who were monitored are 

referred to as the “study population” 

 The distribution of intakes in the study population is referred to as a 

“co-exposure model,” and it can be used to estimate the 

distribution of intakes in the target population 

 The co-exposure model is then used to estimate intakes to exposed 

workers who were unmonitored 
Co-exposure Models cont.

 In the event the entire study population is not available, the coexposure model is constructed from the “study sample” 

 Three conclusions can be made

– All the workers in the target population do not have to be monitored to 

construct a co-exposure model 

– If the co-exposure model is generated from the study population, a bounding 

model can be generated if a significant portion of the most highly exposed 

workers in the target population are monitored

– If the co-exposure model is generated from a study sample, a bounding model 

can be generated if the previous condition holds, and the study sample is not 

missing a significant portion of the most highly exposed workers from the 

study population
Co-exposure Models - Diagram
Regulatory Compliance vs Co-exposure Modeling

Regulatory Compliance

 The 1999 audit was intended to assess whether LANL was in 

compliance with the regulations promulgated in 10 C.F.R. Part 835

 These regulations established criteria for limiting dose to workers 

and for acceptable design and implementation of internal 

dosimetry programs that were used to demonstrate compliance 

with these dose limits 

 Because compliance with regulations helps to minimize and limit 

dose received by individuals, even one instance of noncompliance is 

of interest to the regulator and the site 
Regulatory Compliance vs Co-exposure Modeling cont.

Dose Reconstruction

 Dose reconstruction is concerned with making a reasonable 

estimate of the radiation doses received by an individual 

 To obtain a reasonable estimate of radiation exposure based on a 

co-exposure model, it need only be based on a representative (or 

bounding) sample of the workers performing radiological work 

 Compliance with the regulations in place at the time the 

radiological work was performed is not required in order to perform 

a dose reconstruction or develop a co-exposure model
Study Design
Study Design cont.

 The approach used in this study was to assemble and analyze all the 

relevant available data about the plutonium monitoring program at 

LANL during the 1996 to 2001 study period

– Health Physics Checklists (HPC)

– Bioassay Enrollment Scheduling and Tracking (BEST)

– Plutonium in vitro bioassay

– Plutonium in vivo bioassay

– External dose

– RWPs that require plutonium bioassay 
Health Physics Checklist

 The HPC is a paper form that a worker, the manager, and a 

representative from Environmental Safety and Health (ESH) filled in 

to make changes in the worker’s in vitro, in vivo, and external dose 

monitoring programs 

 ORAUT captured HPCs covering years 1985 to 2002

 An HPC database was developed for the study period 1996 to 2001

 The study looked at the HPC adds which means an individual was 

added to the plutonium bioassay program
Health Physics Checklist Adds
Bioassay Enrollment, Scheduling, and Tracking 

 BEST is a system that was used to manage bioassay program 

enrollments, which included adding and removing workers from 

routine, baseline, termination, and special monitoring programs

 BEST data set

– enrollments that placed workers on bioassay programs are referred to as adds 

which always had an associated sample request that is referred to as an Enroll 

Request 

– Sample requests not associated with adds were for routine (e.g., annual) 

samples, which are referred to as Non-enroll Requests 

– Sum of the Enroll Requests and Non-enroll Requests is the total of number of 

plutonium bioassay requests in a year 
BEST Sample Requests 1996 - 2001
In vitro Bioassay Dataset

 The in vitro bioassay dataset was already created in support of 

ORAUT-OTIB-0063, LANL Bioassay Repository Database

 The dataset includes 12,666 plutonium urine and fecal bioassay 

samples from 3,219 workers during the study period

– The 12,619 urine bioassay results are the data that would be used for a coexposure model for plutonium LANL
In vitro Bioassay Dataset 1996 - 2001
In vivo Bioassay Dataset

 The in vivo bioassay dataset was already created in support of 

ORAUT-OTIB-0063, LANL Bioassay Repository Database

 The dataset includes 6,817 plutonium/americium chest counts from 

3,282 workers during the study period

 The number of workers monitored by chest counting and in vitro 

bioassay is essentially constant over the study period

 Approximately 80% of the workers monitored for plutonium by in 

vitro bioassay also were monitored by chest counting
In vivo Bioassay Dataset 1996-2001
External Dose Dataset

 The external dose records of LANL workers provide a 

comprehensive list of individuals who performed radiological work 

 The external dosimetry records were used to help identify 

individuals who were missing employee numbers in other datasets 

and as an aid in the entry of those datasets 

 The external dose data consists of the 3.4 million records in the 

Access dataset 

 There were approximately 11,000 workers at LANL who were 

monitored for external dose each year during the study period 
Radiological Work Permit - Overview

 RWPs were used to control work with a high potential for exposures 

to radiation

– All other radiological work was performed according to Safe 

Operating Procedures

 RWPs with plutonium access list (PAL) checked required that a 

person be on a plutonium monitoring program before performing 

work under the RWP
Radiological Work Permit and Acknowledgment 

Sheets

 RWPs and acknowledgment sheets were transcribed by the ORAU 

Team from the documents that were captured during the nine 

targeted visits

 Notable RWPs were targeted for capture, where a “notable” RWP is 

defined as an RWP that 

– Occurred within the study period (Jan. 1,1996 to Dec. 31, 2001)

– Required urinalysis as noted on the RWP by having “Special Urinalysis” or “Pu 

Access List” checked or contained other equivalent terminology or notation 

indicating urinalysis was required 

– Contained an associated roster (acknowledgment sheet) with names of 

personnel acknowledging the RWP
Plutonium Access List and Acknowledgement Sheets

 PALs were generated monthly and mailed as a memorandum to 

designated field contacts

 Workers signed an acknowledgment sheet during the pre-work 

briefing, which was required before working under the RWP

 The signature on the acknowledgment sheet indicated that the 

worker understood the monitoring requirements of the RWP

– Note that a worker could have signed an acknowledgment sheet and never 

performed work under that RWP; it is not a sign-in sheet
Radiological Work Permit Dataset

 During the study period there are 19,568 records in the RWP 

dataset, where each record is the signature of one worker on the 

acknowledgment sheet of a particular RWP that had a PAL 

requirement

– There are signatures from 1,942 workers

 A reasonable number of RWPs were obtained for the primary 

plutonium facilities at LANL
Data Analysis
Dataset - Diagram

 The LANL datasets are 

interrelated 

 Analysis of the HPC -> BEST -

> IN-VITRO branch should 

indicate if a worker placed on 

a plutonium bioassay 

program submitted samples 

for analysis 
Issues with Health Physics Checklist

 There is a known problem of HPCs not being submitted consistently

– Analysis of the HPC -> BEST -> IN-VITRO branch cannot indicate anything if the 

HPC was never submitted

 To address this issue, we analyzed the RWP -> ACKNOWLEDGMENT 

SHEET -> IN-VITRO/IN-VIVO branch 

– This will show if a worker who did work with potential for exposure to 

plutonium was monitored for plutonium

– Note that this analysis is independent of whether a worker submitted an HPC. 

– if an individual performed radiological work that required monitoring for 

plutonium and was properly monitored, the HPC paperwork is irrelevant 
Analysis of Dataset 

 From this data set we should be able to answer three critical 

questions

– Were workers who signed an RWP acknowledgment sheet with a PAL 

requirement monitored in a timely fashion? 

– What fraction of workers who signed the acknowledgment sheet for a given 

RWP was monitored?

– What were the relative exposures of different groups to plutonium? 
Comparison BEST vs In vitro Dataset

 Overall, out of 13,895 requests made through BEST for samples to 

be analyzed for plutonium, 11,914 (85.7%) were fulfilled

 All requests from BEST were tracked and most were accounted for 

with reasons being given for why sample requests were not fulfilled 

– Of the 1,981 samples not received, 1,613 have legitimate reasons for not 

being received such as termination or extended leave of the individual
Plutonium Samples Requested through BEST and 

Received for all Workers
Samples requested from JCNNM workers through 

BEST that were received and analyzed for plutonium
Comparison HPC vs BEST

 There are 1,856 adds via HPCs during the study period for 

plutonium

 A detailed comparison of the HPC with BEST showed that: 

– 1,802 out of 1,856 = 97.09% of the plutonium adds in HPCs matched BEST 

(when only considering BEST), and 

– 1,848 out of 1,856 = 99.57% matched when also considering samples in the in 

vitro dataset that did not have a request in BEST 

 Therefore, workers who submitted HPC add forms almost certainly 

were entered in the BEST system
Compliance with Radiation Work Permits

 A key part of this report is to quantify the extent to which the LANL 

workforce complied with the bioassay requirements for work 

involving plutonium 

 Workers were required to sign the RWP acknowledgment sheet for 

an RWP to indicate they understood the monitoring and personal 

protection equipment requirements of that RWP

– As indicated earlier their signatures did not denote that they performed any 

work, only that they understood the requirements to work under that RWP
Compliance with Radiation Work Permits cont.

 In the report, Table 10-1 Summary of Statistics for monitoring of 

RWP Work introduces a couple of terms that need to be explained

– The table is recreated on the following slide

 Work and Worker columns refer to the percentage of work and 

workers, respectively, who were properly monitored as determined 

using the active RWP period and post-RWP window 

 Work(O) and Worker(O) columns refer to the percentage of work 

and workers, respectively, who were properly monitored as 

determined using the active RWP period, post-RWP window, and 

open window
Compliance with Radiation Work Permits Results

Group Number of 

workers

Number of 

RWPs

Work

(%)

Worker

(%)

Work (O)

(%)

Worker (O)

(%)

JC 703 1396 81.0 65.1 92.6 83.5

ESH 227 2128 96.5 84.1 98.1 87.8

NMT 660 1393 97.1 95.3 99.0 98.2

Other 556 579 70.6 63.3 81.4 74.5
Plutonium Results for JCNNM, Environmental Safety and 

Health, Nuclear Metals Technology, and other groups

 NIOSH feels we have established that there is a considerable 

amount of data available on which to base a co-exposure model for 

plutonium at LANL

 However, when you break the data into groups (i.e., JCNNM, ESH, 

etc.), some groups have more plutonium monitoring data than 

others 

 Therefore, it is of interest to compare some measure of relative 

exposures of the groups to see if the groups with less data are more 

highly exposed 

 An approximate measure of the exposures to each of the four 

groups is the plutonium in urine analytical results for the groups 
Comparison of Pu239 in Urine of JCNNM, ESH, and 

NMT Workers
Plutonium Results for Johnson Controls, Environmental Safety 

and Health, Nuclear Metals Technology, and other cont.

 The data for the four groups are similar, with NMT and ESH being 

slightly higher

 The few relatively high results of 239PU for JCNNM workers appears 

to have been a single event
Summary and Conclusions
Summary

• Comparison of BEST vs. In vitro Dataset

• 85.7% of sample requests were fulfilled

• Comparison of HPC vs. BEST

• 97% of additions matched BEST

• Compliance with RWP required sampling

• Approximately 97% of the 2,252 RWP had 50% or more of the workers 

monitored. 

• Comparison of Pu In vitro results across various Groups

• Results were similar across Groups with ESH and NMT slightly higher
Conclusions

 The evidence supports the conclusion that the plutonium bioassay 

data reported by LANL in the 1996 to 2001 study period include a 

significant portion of the most highly exposed workers

 The data is adequate to construct a co-exposure model for 

plutonium
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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.