CORROSION OF URANIUM IN AIR AND WATER-VAPOR - CONSEQUENCES FOR ENVIRONMENTAL DISPERSAL

An evaluation of published data for reaction of uranium in dry air, wa ter vapor, and humid air provides a comprehensive and consistent pictu re of corrosion kinetics. Effects of temperature, oxygen pressure, and water pressure are quantified. Arrhenius data presented for eight kin etic regimes show that the corrosion rate in air varies by more than 1 0(8) over the 25-1500 degrees C range. Below 500 degrees C, kinetics a re bounded by the slow rate for the reaction of dry air and by the rap id rate for the reaction of water at saturation pressures. in the auto thermic regime above 500 degrees C, humidity effects are absent and in volvement of nitrogen in the corrosion process is evident. Convergence of Arrhenius curves for dry and moist conditions at 500 degrees C clo ses a temperature-humidity envelope that confines the kinetic behavior of uranium in humid air at low temperatures. Kinetic relationships wi thin the envelope suggest a competition between rate enhancement by mo isture and rate suppression by oxygen. Suppression of the rate by O-2 in moist air is complete below 35-40 degrees C, but moisture enhanceme nt is observed at higher temperatures where chemical behavior is consi stent with a water-catalyzed cycle that promotes the corrosion of uran ium by oxygen. Reaction rates of U and Pu are similar in dry air and w ater vapor, but diverge in humid air and at elevated temperatures. Par ticle size data for corrosion products are reviewed and their combined application with the kinetic results in defining source terms for dis persal of uranium metal is examined. (C) 1998 Elsevier Science S.A. Al l rights reserved.