The evaluation of the influence of hydride rim and biaxial stress condition on the cladding failure under a reactivity-initiated-accident by using EDC test method

EDC (Expansion-Due-to-Compression) test is one of the test methods on the mechanical property of fuel cladding tube, and it focuses on the stress condition generated by PCMI (Pellet-Cladding Mechanical Interaction) under a RIA (Reactivity-Initiated Accident). In this study, we conducted EDC tests which simulated the mechanical conditions in the high burnup fuel cladding during a RIA. Specimens were unirradiated cladding tubes with the hydride segregated densely at the periphery of tube in order to simulate 'hydride rim' that is a typical morphology of hydride observed in the high burnup fuel cladding. Circumferential residual strain observed in post-test specimens tended to decrease with increasing hydrogen concentration and the thickness of hydride rim. We also prepared the cladding tube with a pre-crack on its outer surface (Roll-After-Grooving tube, RAG tube) in order to simulate a crack generated during a RIA in the hydride rim, and performed EDC tests. In these EDC tests, circumferential total strains at failure tended to decrease with increasing the depth of the pre-crack of RAG tube specimen. Furthermore, we conducted EDC tests for RAG tube specimens under biaxial stress conditions. It was observed that circumferential total strain at failure under biaxial stress conditions tended to decrease compared to the results of the EDC tests under uniaxial tensile condition. (author)