MECHANICAL PERFORMANCE OF COATED ATF CLADDING UNDER LOCA CONDITIONS

During the operation of nuclear reactor, the massive and rapid loss of coolant in the primary loop system leads to the Loss of Coolant Accident (LOCA), which is one of the design basis accidents for nuclear fuel cladding. Furthermore, LOCA is also a critical condition which has effect on structural integrity and safety margin of cladding. In order to analyze the mechanical behavior of coated Accident Tolerant Fuel (ATF) cladding under extreme conditions after the accident, the temperature variations in the initial and middle stages of LOCA were first determined in this study. On this basis, considering the coupling effect of force, heat and irradiation, the mechanical responses of ATF cladding at different operation times over two complete fuel cycles (0-48 months) were simulated. The plastic strain distribution characteristics of two types of coated ATF cladding (Cr-coated and FeCrAl-coated) and the accumulation behavior of plastic strain at different LOCA stages were clarified. The results show that the plastic strain within cladding increases gradually with operation time during the fuel cycle, with noticeable differences between coating materials. Meanwhile, the extreme value ranges of total strain at different stages were obtained. Some critical regions within cladding, such as inner surface, outer surface, interface between coating and Zircaloy substrate were identified. By comparing the mechanical responses of Cr coating and FeCrAl coating in the initial and middle stages of LOCA at different operation months, and combining the inhomogeneity characterized by the coefficient of variation of hoop strain, the evolution of strain energy and plastic dissipation within ATF cladding was systematically analyzed. It is further revealed that the coating type and operation time of nuclear reactor have significant influence on the structural safety of cladding. Relevant results and conclusions in this study can provide a reference for the design optimization and engineering application of fuel cladding.