Improved Radiation Dosimetry/Risk Estimates to Facilitate Environmental Management of Plutonium Contaminated Sites Page: 3 of 6
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RESEARCH OBJECTIVE
The objective of this research is to evaluate distributions of possible alpha radiation doses to the
lung, bone, and liver, and associated health-risk distributions for plutonium (Pu) inhalation-
exposure scenarios relevant to environmental management of PuO2-contaminated sites.
Currently available dosimetry/risk models do not apply to exposure scenarios where relatively
small numbers of highly radioactive PuO2 particles are presented for inhalation (stochastic
exposure [SE] paradigm). For the SE paradigm, distributions of possible risks are more relevant
than point estimates of risk. The main goal of the project is to deliver a computer program that
will allow evaluation of the indicated risk distributions for the SE paradigm. However, some of
our work also relates to the deterministic exposure [DE] paradigm where large numbers of
airborne particles (resuspended dust containing PuO2) are presented for inhalation to members
of the public residing or working at a remediated Department of Energy (DOE) site.
RESEARCH PROGRESS AND IMPLICATIONS
This report summarizes work after 2 years of a 3-year project. To date, research has mainly
focused on two areas.
Research Area 1 relates to evaluating, by the Monte Carlo method, the variability in the
respiratory tract intake of plutonium dioxide (PuO2) by DOE workers during
decommissioning/decontamination operations. Our present focus is on the variability in
radioactivity intake associated with inhaling relatively small numbers of polydisperse (i.e.,
varying sizes) PuO2 particles. For polydisperse PuO2, a single, large, high-specific-activity
particle can exceed the annual limit on intake (ALI). Only a few such particles can greatly
exceed the ALI. Further, when relatively small numbers of very highly radioactive particles are
inhaled, there can be considerable variability in the amount of radioactivity deposited in the
respiratory tract. Our research provides tools for characterizing that variability. Workers at the
Rocky Flats Environmental Technology Site near Denver are the present at-risk population being
considered.
Research Area 2 relates to evaluating possible respiratory tract intake of radioactivity by the
public from airborne dust contaminated with PuO2 arising from the Rocky Flats Site after
remediation. The specific activity of the contaminated dust is orders of magnitude lower than for
PuO2 so that large numbers of such particles must be inhaled to lead to significant radiation
exposure. Starting from single dust particle intake, we have calculated, via the numerical
convolution method, the variability in radioactivity intake by adult males associated with inhaling
up to 5,000,000 dust particles (density 2 g/cm3) containing PuO2. Members of the public who at
some future time after site remediation might reside at what is presently the Rocky Flats
Environmental Technology Site near Denver are the present at-risk population being considered.
Specific achievements/findings are summarized below.
" A Monte Carlo-based computer program, which wepreviously developed to calculate the
distribution of radioactivity intake via inhalation of 2 PuO2 by male adults engaged in light
exercise, has been improved. Respiratory tract deposition probability is based on the ICRP
66 publication.
" Single-particle and multiple-particle intake distributions were generated for 244PuO2, 242PuO2,
239 240 238 236
PuO2, PuO2, PuO2, and PuO2 (ordered here by increasing specific activity), based
on a density of 10 g/cm3, a polydisperse size distribution (truncated lognormal: AMAD= 5
pm; ag =2.5; maximum aerodynamic diameter = 26 pm). The intake distributions were
conditional on particle deposition in the respiratory tract, and results indicated that
considerable variability in intake would be expected for exposure during
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Scott, Bobby R. Improved Radiation Dosimetry/Risk Estimates to Facilitate Environmental Management of Plutonium Contaminated Sites, report, June 1, 1999; United States. (https://digital.library.unt.edu/ark:/67531/metadc779648/m1/3/: accessed April 23, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.