He jishu (Nov 2021)
The impact of large-grained UO2 pellet and coated zirconium cladding on design criteria for PWR fuel rod
Abstract
BackgroundLarge-grained UO2 pellet and coated zirconium cladding are the most practical fuel pellet and cladding material scheme for accident tolerant fuel (ATF) solutions, which are expected to be commercially available in the next few years. However, the existing fuel rod design criteria for commercial pressurized water reactor (PWRs) are based on the material characteristics and application experience of traditional UO2 pellets and zirconium alloy cladding. If the properties of the constituent material of fuel rod change, it is necessary to re-examine the usability of the design criteria based on the corresponding research results.PurposeThe study aims to clarify the potential problems of large-grained UO2 pellet and coated zirconium cladding through the fuel rod design standards, and to provide a reference for the follow-up materials testing.MethodsBased on these two material schemes for ATF on the design criteria, latest research on the material properties of large-grained UO2 pellet and coated zirconium cladding were investigated, and the influence of new ATF fuel rod based on these two schemes on fuel rod design criteria was analyzed.ResultsThe results show that most of the design standards can still be used, and the new ATF fuel rods have certain performance improvements in oxidation and hydrogenation, hence the corresponding design margin is increased. However, the newly added cladding coating may introduce new fuel rod failure mechanisms, including cold spraying and some other coating processes that may damage the zirconium substrate and cause a significant decrease in the fatigue performance, local oxidation after coating damage, etc. Due to the influence of the cladding coating, the equivalent cladding reacted coefficient (ECR) originally used to evaluate the embrittlement level of zirconium alloy cladding is no longer applicable.ConclusionTherefore, in view of these new phenomena, it is necessary to carry out further research work and improve the corresponding design criteria accordingly.
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