Tensile properties of irradiated Zircaloy 4 cladding submitted to fast transient loading

Knowledge of transient mechanical properties of irradiated Zircaloy 4 cladding is needed for the modelling of reactivity initiated accidents of PWRs and for the interpretation of power burst tests performed in CABRI and NSRR. Clad samples from 59 GWD/t U irradiated rods, as well as unirradiated ones, have been tensile tested in the rolling direction after either rapid or slow heating up to the test temperature (400 to 1100 deg C); three strain rate values have been applied. On unirradiated samples, the yield stress (YS) and the ultimate tensile strength (UTS) are observed to increase with increasing strain rate without any marked influence of the heating conditions. The YS and the UTS of the irradiated cladding are close to those of the fresh material. The likelihood of early loading of a cold cladding during RIAs and the potential of a severe embrittlement due to hydride accumulations have been demonstrated by the first RIA test in CABRI. (R.P.)