Development of FEMAXI-ATF for fuel performance modeling of SiC cladded fuel involving PCMI

The SiC cladded fuel is being developed as a candidate for the accident tolerant fuel of light water reactors, in which the cladding wall consists of the inner SiC/SiC layer and the outer monolithic (mSiC) layer. The FEMAXI-ATF fuel performance modeling code is being developed based on the experience of FEMAXI-7 with the focus on evaluation of the pellet-cladding mechanical interaction (PCMI). In the preceding study, the capability of FEMAXI-ATF to show the PCMI failure limit of the SiC cladded fuel was successfully demonstrated by modeling the SiC/SiC layer with a continuum finite calculation element and reducing Young's modulus of the failed element to practically zero, so that the stress on the cladding wall is redistributed among the remaining cladding wall elements. In this study, FEMAXI-ATF has been further developed to consider pseudo-ductility of SiC/SiC and improvement to the temperature dependent SiC swelling model. The new FEMAXI-ATF was applied in the BWR normal operation conditions to show a possible scenario. That is, the SiC cladded fuel may experience partial failure of the SiC/SiC layer during the reactor shutdown depending on the swelling characteristics of SiC. Consequently, PCMI may induce large mechanical load on the mSiC layer in the subsequent operation.