Plutonium hydride, sesquioxide and monoxide monohydride: pyrophoricity andcatalysis of plutonium corrosion

Reaction rates of air and oxygen with cubic plutonium hydride (PuHx, 1.9<x< 3), monoxide monohydride (PuOH), and Pu metal coated with these compounds a re described. along with kinetic results for the Pu+H-2 reaction, Pyrophori c tendencies are not observed for PuOH, but exposure of PuHx and PuHx- (or PuOH-) coated Pu to air or O-2 at room temperature result in spontaneous re actions that consume both O-2 and N-2. These reactions and hydriding have z ero or slightly negative activation energies and pressure-dependent rates. Pyrophoric reaction of PuHx and PuHx-catalyzed corrosion of Pu depend an th ermal maintenance of catalytic Pu2O3 at the gas-solid interface and are pre vented by formation of a protective PuO2 layer at low temperatures and law O-2 pressures. The Pu+H-2, reaction is catalyzed by Pu2O3 and PuHx is produ ced by the Pu+H2O reaction only at conditions where Pu2O3 formation is kine tically favored. Thermal ignition of Pu near 500 degreesC is attributed to autoreduction of the PuO2 surface to Pu2O3 at that temperature. At normal s torage temperatures, formation of pyrophoric corrosion products is unlikely in open oxidant-rich systems, but surfaces that catalyze rapid Pu corrosio n in air are formed during extended storage in closed systems. (C) 2001 Els evier Science B.V. All lights reserved.