Reduction in the onset time of breakaway oxidation on zircaloy cladding ruptured under simulated LOCA conditions

Yamato, Masaaki; Nagase, Fumihisa ; Amaya, Masaki  

Breakaway oxidation, which is characterized by sudden increases in oxidation rate and significant hydrogen absorption after longer exposure in high-temperature steam, was examined for the ballooned and ruptured cladding. As a result, the onset time of breakaway oxidation for ruptured claddings was significantly reduced compared with that for non-ruptured claddings. The onset time of breakaway oxidation was reduced only in the case where thick and porous oxide was formed on the inner surface of the cladding after rupture. Results of the parametric experiments suggest that the tensile stress in the circumferential direction generated by the thick oxide film formed on the inner surface is a main cause of the reduction of the onset time of breakaway oxidation.