Dose reconstruction for plutonium-239 intakes at the Rocky Flats Plant

Abstract

Purpose

The Rocky Flats (RF) Plant was a weapons manufacturing facility that operated from the early 1950s to 1989. Its primary missions were the production of plutonium (Pu) pits for thermonuclear weapons and the processing of retired weapons for Pu recovery. The purpose of this study was to estimate radiation doses to a cohort of 4499 RF workers from an intake of ²³⁹Pu, the primary plutonium isotope handled at the site.

Materials and methods

The latest biokinetic models of the International Commission on Radiological Protection, or site-specific variations of those models, were used to estimate ²³⁹Pu intakes for each worker based on model fits to bioassay data often coupled with lung measurements.

Results

Urinary excretion and lung retention data for most ²³⁹Pu intakes could be fit reasonably well by a mixture of Pu dioxide and moderately soluble material. For some workers, better fits were obtained by application of other absorption types including Type S, ²³⁹Pu nitrate, or pure ²³⁹Pu dioxide, or by assuming intake via a wound. The lungs typically received the highest tissue doses, with fifty-year committed equivalent doses in the range of 0.5–1 Sv for 275 workers, 1–5 Sv for 115 workers, and greater than 5 Sv for 12 workers.

Conclusions

RF was a unique site regarding a large number of lung measurements available for determining the appropriate absorption types for inhaled material. This provided higher confidence in reconstructed ²³⁹Pu doses than is generally gained from urinary data alone.

Keywords:

• Million person study
• rocky flats plant
• plutonium
• dose reconstruction
• dioxide
• nitrate

Acknowledgments

We are grateful to Oak Ridge Institute for Science and Education (ORISE), managed by Oak Ridge Associated Universities (ORAU) on behalf of the US Department of Energy, and the U.S. Transuranium and Uranium Registries (USTUR) for providing the primary data sets used in this study. Special thanks go to Maia Avtandilashvili (USTUR) for assembling the detailed USTUR autopsy data for the Rocky Flats workers and to Ashley Golden and Dave Girardi (ORAU) for assembling the voluminous bioassay data and lung measurements used in this study.

Data availability statement

This manuscript has been authored by UT-Battelle, LLC under Contract No. DE-AC05-00OR22725 with the US Department of Energy. The United States Government retains and the publisher, by accepting the article for publication, acknowledges that the United States Government retains a non-exclusive, paid-up, irrevocable, worldwide license to publish or reproduce the published form of this manuscript or allow others to do so, for United States Government purposes. The Department of Energy will provide public access to these results of federally sponsored research in accordance with the DOE Public Access Plan (http://energy.gov/downloads/doe-public-access-plan).

Disclosure statement

No potential conflict of interest was reported by the author(s).

Additional information

Funding

The work described in this manuscript was sponsored by the Office of Environment, Health, Safety, and Security, U.S. Department of Energy; National Council on Radiation Protection and Measurements, under Interagency Agreement DOE No. 14B759101, under contract No. DE-AC05-00OR22725 with UT-Battelle; and National Center for Environmental Health, The Centers for Disease Control and Prevention (CDC), under Interagency Agreement DOE No. 42WZ05105 and 42WZ46502, under contract No. DE-AC05-00OR22725 with UT-Battelle. The dose reconstruction for RF workers was a component of the Million Person Study, which was financially supported in part by grants from the U.S. Department of Energy [DE-SC0008944] awarded to the National Council on Radiation Protection and Measurements, which included interagency support from the U.S. Nuclear Regulatory Commission, the U.S. Environmental Protection Agency, and the National Aeronautics and Space Administration; and more recent grants [DE-AU0000042, DE-AU0000046]; a grant from the U.S. Nuclear Regulatory Commission [NRC-HQ-60-14-G-0011]; grants from the Centers for Disease Control and Prevention [5UE1EH000989, 5NUE1EH001315]; and grants from the National Aeronautics and Space Administration [NNX15AU88G, 80NSSC17M0016, 80NSSC19M0161]. Contract support was received from the Naval Sea Systems Command [N00024-17-C-4322]. Further, contract support was received by Oak Ridge National Laboratory from the National Center for Environmental Health, The Centers for Disease Control and Prevention, under Interagency Agreement DOE No. 42WZ05105 and 42WZ46502, under contract No. DE-AC05-00OR22725 with UT-Battelle; and contract support was received by Oak Ridge Associated Universities from the U.S. Department of Energy under contract No. DE-SC0014664. The work described in this manuscript was sponsored by the Office of Environment, Health, Safety, and Security, U.S. Department of Energy; National Council on Radiation Protection and Measurements, under Interagency Agreement DOE No. 14B759101, under contract No. DE-AC05-00OR22725 with UT-Battelle; and National Center for Environmental Health, The Centers for Disease Control and Prevention (CDC), under Interagency Agreement DOE No. 42WZ05105 and 42WZ46502, under contract No. DE-AC05-00OR22725 with UT-Battelle.

Notes on contributors

Caleigh Samuels

Caleigh Samuels is an associate staff member in the Center for Radiation Protection Knowledge at Oak Ridge National Laboratory. Her research focuses on developing and enhancing biokinetic models used in radiation protection and dose reconstruction and application of advanced Monte Carlo techniques in dosimetric modeling. She has been a collaborator on the Million Person Study for three years and is currently focusing on organ dose reconstructions following intakes of several radionuclides at the Hanford Site.

Rich Leggett

Rich Leggett is a research scientist in the Environmental Sciences Division at Oak Ridge National Laboratory (ORNL). His main research interest is in physiological systems modeling, with primary applications to the biokinetics and dosimetry of radionuclides and radiation risk analysis. He was a member of Committee 2 of the International Commission on Radiological Protection (ICRP) from 2009 to 2021 and is currently a member of the ICRP Task Group on Internal Dosimetry (INDOS). His physiological systems models of the human circulation, skeleton, and gastrointestinal transfer and his systemic biokinetic models for many elements are used by the ICRP as dosimetry and bioassay models. He is the author of ICRP Publication 70, Basic Anatomical and Physiological Data for Use in Radiological Protection: The Skeleton, and coauthor of several other ICRP reports.