Probabilistic view of SiC/SiC composite cladding failure based on full core thermo-mechanical response

As part of Accident Tolerant Fuel (ATF) campaign, Silicon carbide (SiC) is being considered as a promising alternative cladding material. A new numerical model for mechanical calculation of multi-layer claddings was established and implemented in FRAPCON 4.0. The upgraded FRAPCON 4.0 was used to simulate fuel performance of a Pressurized Water Reactor (PWR) using a two layer Composite/Ceramic SiC cladding design. A probabilistic assessment was carried out based on the full core simulation to determine the possibility for SiC material cracking, referred to as “failure” probability. The results indicated that the large stresses induced during the refueling period in SiC cladding can be mitigated if high conductivity fuel.e.g. UO₂ with center void and BeO additive, is utilized. However, it was found that full core average leakage probability from failure of the monolithic SiC layer and clad fracture rate from failure of both layers were higher than the failure probability of current Zircaloy cladding. According to the failure risk map, Pellet Cladding Mechanical Interaction (PCMI) is the primary leading cause of failure. The result of the PCMI sensitivity study on the influence of relocation recovery on SiC cladding failure risk motivates the need to develop a more mechanistic fuel cracking model relevant to SiC based ceramic fuel/cladding system.