Uncertainty analysis of exposure to radon released from the former Feed Materials Production Center

Radon and its decay products escaped from two storage silos on the site of the former Feed Materials Processing Center (FMPC) near Cincinnati, Ohio, exposing workers and nearby residents. The releases began in the early 1950s as the silos were filled with 226Ra-bearing ore from which uranium had been extracted, and they continued at relatively high rates until mid-1979, when vent pipes and other penetrations in the silo domes were closed. Subsequent releases were at lower rates, and monitored concentrations in air at the site boundary have been near background. A dose reconstruction study sponsored by the Centers for Disease Control and Prevention (CDC) estimated the historic releases of radionuclides and developed methods for calculating dose to individuals living in the vicinity of the facility. Uncertainties in release and transport parameters that propagated into dose estimates were analyzed and presented as distributions of dose to individuals with specified exposure histories. This paper discusses the use of data from the site and models of radon release and atmospheric transport to estimate distributions of working-level months (WLM) at locations remote from the point of release. Uncertainty in atmospheric transport contributes most significantly to uncertainty in predicted WLM, with nominal composite uncertainty factors of 4–5 (95th percentile/median) indicated for distances between 3 and 10 km from the source.