Oxidation kinetics of plutonium in air from 500 to 3500°C: Application to source terms for dispersal

Abstract

The oxidation kinetics of plutonium in air are described for the autothermic regime using literature data and are applied in defining source-term relationships for dispersal. The oxidation rate of static plutonium is temperature independent ( E a=0) above the 500°C ignition point, but that of ignited droplets is temperature dependent ( E a=9.6 kcal mol −1) during free fall in air. Kinetic dependences on humidity and alloying with gallium are absent. The appearance of a constant rate (0.2 g PuO 2 cm −2 min −1) for oxidation of static metal above 500°C is attributed to formation of an oxygen-depleted boundary layer of nitrogen at the gas–solid interface during oxidation. The rate is temperature dependent under dynamic conditions that disturb or destroy the boundary layer. The ignition point of Pu is accurately predicted using a first-principles kinetic model and rate data for dynamic conditions. Arrhenius behavior, which is defined by combining the kinetic results with data for low temperature oxidation, is reflected in aerosol release rates reported for self-sustained oxidation of plutonium. The time-dependent source term for continuous release of PuO 2 particles during reaction is defined, and the dependences of the airborne release fraction on oxidation temperatures and air velocity are described.