Reference computations of public dose and cancer risk from airborne releases of plutonium. Nuclear safety technical report

Abstract

SUMMARYThis report presents results of computations of doses and the associated health risks of postulated accidental atmospheric releases from the Rocky Flats Plant (RFP) of one gram of weapons-grade plutonium in a form that is respirable. These computations are intended to be reference computations that can be used to evaluate a vaxiety of accident scenarios by scaling the dose and health risk results presented here according to the amount of plutonium postulated to be released, instead of repeating the computations for each scenario. The MACCS2 code has been used as the basis of these computations.The basis and capabilities of MACCS2 are summarized, the parameters used in the evaluations are discussed, and results are presented for the doses and health risks to the public, both the Maximum Offsite Individual (a maximally exposed individual at or beyond the plant boundaries) and the population within 50 miles of RFP. A number of Merent weather scenarios are evaluated, including constant weather conditions and observed weather for 1990, 1991, and 1992. In particular, the doses and health risks for unfavorable and typical weather conditions are evaluated. The evaluations used a variety of dry deposition velocities for both "no fire" and "with 6 MW fire" conditions. For "no fire" the MOI dose is about 2 rem for unfavorable weather conditions and 0.1 rem for typical conditions, for this one gram release; for "with fire" the MOI dose is about 0.1 rem for unfavorable weather conditions and 0.03 rem for typical. The total number of latent cancer fatalities within 50 miles of RFP is found to be about 0.1 for unfavorable weather conditions and 0.01 for typical conditions for this one-gram release; the presence or absence of fire makes little difference for the population cancer rate. These doses and health risks are quoted to only one significant figure because of the uncertainties in the model and its parameters and because of year-to-year variations of about a factor of two in doses and health risks, due to differences in meteorological conditions.The isotopic mix of weapons-grade plutonium will change as it ages, the 2a1Pu decaying into "lAm. The "' Am reaches a peak concentration after about 72 years. The doses to the bone surface, liver, and whole body will increase slightly but the dose to the lungs will decrease slightly. The overall cancer risk will show almost no change over this period. This change in cancer risk is much smaller than the year-to-year variations in cancer risk due to weather.Finally, xlQ values are also presented for other applications, such as for hazardous chemical releases. These include the xlQ values for the MOI, for a collocated worker at 100 meters downwind of an accident site, and the xlQ value integrated over the population out to 50 miles.

Evolving Defect Chemistry of (Pu,Am)O2±x

“…However, under storage conditions, aged PuO 2 contains significant ingrowth of Am produced by 241 Pu decaying into 241 Am. Am builds up relatively quickly due to the short half-life of 241 Pu (14.4 years), with Am concentrations peaking after approximately 70 years, at which point, it too begins to decay faster than it is produced . Incorporation of Am is predicted to alter the defect chemistry of PuO 2 ; in a density functional theory (DFT) investigation on Pu–Am mixed oxide surfaces, Chen et al report that the presence of Am promotes the formation of O vacancies that increase the favorability of molecular adsorption of water on PuO 2 surfaces while reducing the favorability of dissociative water adsorption.…”