Effect of pre-hydriding on thermal shock resistance of Zircaloy-4 cladding under simulated loss-of-coolant accident conditions

Nagase, Fumihisa ; Fuketa, Toyoshi

Experiments simulating loss-of-coolant accident (LOCA) conditions were performed to evaluate effect of pre-hydriding on thermal-shock resistance of oxidized Zircaloy-4 cladding. Artificially hydrided (400 to 600 ppm) and non-hydrided claddings were subjected to the tests. Since cladding fracture on quenching primarily depends on the oxidation amount, fracture threshold was evaluated in terms of "Equivalent Cladding Reacted (ECR)". Under axially non-restrained condition, the fracture threshold is 56% ECR and the influence of pre-hydriding is not seen. The fracture threshold is decreased by restraining the test rods on quenching, and it is more remarkable in pre-hydrided claddings than in non-hydrided claddings. Consequently, the fracture threshold was 20% ECR and 10% ECR for non-hydrided and pre-hydrided claddings, respectively, under the fully restrained condition. These results indicate possible decrease of fracture threshold of high burnup fuel claddings under LOCA conditions.