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.