Behavior of pre-hydrided Zircaloy-4 cladding under simulated LOCA conditions

Nagase, Fumihisa ; Fuketa, Toyoshi

Regarding high burn-up fuel behavior under LOCA conditions, LOCA-simulated experiments were performed with unirradiated Zircaloy-4 claddings. Claddings containig 100 to 1450 ppm were isothermally oxidized at at 1220 to 1500 K in steam flow, and quenched by flooding water. Axial shrinkage of the rods during the quench was restrained controlling the maximum restraint load at four different levels. Primarily depending on fraction of the cladding thickness oxidized, the claddings fractured into two pieces during the quench, with circumferential cracking. The fracture/non-fracture threshold as for the oxidized fraction decreases as both initial hydrogen concentration and axial restraint load increase. Consequently, it was shown that the threshold is higher than 20% cladding oxidation, e.g. sufficiently higher than the limit in the Japanese ECCS acceptance criteria, irrespective of hydrogen concentration, when the restraint load is below 535 N.