Mechanical property evaluation of high burn-up nuclear fuel cladding using the ring tensile test

摘要

In order to evaluate the degradation of the mechanical properties of Zr-based nuclear fuel cladding tubes under severe accident conditions such as a RIA (reactivity initiated accident) and LOCA (loss of coolant accident), mechanical tests that can properly simulate the degradation of these properties are needed. In the present paper, modified ring tensile tests were performed in order to evaluate the mechanical properties of high burn-up fuel cladding under a hoop loading condition in a hot cell. The tests were performed with Zircaloy-4 nuclear fuel cladding, which has a burn-up of approximately 65,000 MWd/tU in a temperature range of room temperature to 800 °C. As the first step, the hoop loading grip for the ring tensile test was designed such that a constant curvature of the specimen could be maintained during the deformation, and graphite lubricant was used to minimize the friction between the outer surface of the die insert and the inner surface of the ring specimen. The specimen for the ring tensile test was designed to limit the deformation within the gauge section and to maximize the uniformity of the strain distribution. It was confirmed that the mechanical properties under a hoop loading condition can be correctly evaluated by using this test technique. In this study, experimental results on the ductility and toughness degradation of Zircaloy-4 fuel cladding tubes under a hoop directional mechanical load simulating the RIA condition are presented.