OXIDATION-KINETICS OF PLUTONIUM IN AIR FROM 500 TO 3500-DEGREES-C - APPLICATION TO SOURCE TERMS FOR DISPERSAL

The oxidation kinetics of plutonium in air are described for the autot hermic regime using literature data and are applied in defining source -term relationships for dispersal. The oxidation rate of static pluton ium is temperature independent (E-a=0) above the 500 degrees C ignitio n point, but that of ignited droplets is temperature dependent (E-a=9. 6 kcal mol(-1)) during free fall in air. Kinetic dependences on humidi ty and alloying with gallium are absent. The appearance of a constant rate (0.2 g PuO2 cm(-2) min(-1)) for oxidation of static metal above 5 00 degrees C is attributed to formation of an oxygen-depleted boundary layer of nitrogen at the gas-solid interface during oxidation. The ra te is temperature dependent under dynamic conditions that disturb or d estroy the boundary layer. The ignition point of Pu is accurately pred icted using a first-principles kinetic model and rate data for dynamic conditions. Arrhenius behavior, which is defined by combining the kin etic results with data for low temperature oxidation, is reflected in aerosol release rates reported for self-sustained oxidation of plutoni um. The time-dependent source term for continuous release of PuO2 part icles during reaction is defined, and the dependences of the airborne release fraction on oxidation temperatures and air velocity are descri bed. (C) 1998 Elsevier Science S.A.