Effects of oxide and hydrogen on the behavior of Zircaloy-4 cladding during the loss of the coolant accident (LOCA)

Effects of surface oxide and absorbed hydrogen on the behavior of the loss of the coolant accident (LOCA) were investigated in this study. High temperature ballooning and thermal quench tests were performed for Zircaloy-4 cladding which had been prepared with up to 50 μm of oxide and 1000 ppm of hydrogen, respectively. In the high temperature ballooning test, the initially pressurized cladding was heated until a rupture. Threshold oxidation (ECR) of each condition was evaluated in the thermal quench test in which oxidized cladding at the LOCA temperature was quenched by water. Ring compression test was performed to assess the ductility of the quenched cladding The results showed that both the oxide and hydrogen affected the high temperature ballooning property due to the constraint of the α phase by the surface oxide as well as the expansion of the β phase by the absorbed hydrogen. In the quench test, the pre-oxide and absorbed hydrogen did not affect the high temperature oxidation whereas the threshold ECR decreased in the hydrogen charged cladding because the absorbed hydrogen increased the maximum oxygen solubility inside the residual β layer to reduce the cladding ductility.