Impact of circumferential variation in power, neutron flux and spacer grids on structural behavior of SiC-SiC cladding

Silicon carbide (SiC) cladding is being studied for its potential application in light water reactors for improved accident tolerance. SiC-SiC composite material undergoes irradiation-induced, temperature-dependent swelling. The circumferentially non-uniform neutron flux and power generation in the fuel rod, will produce circumferentially non-uniform swelling and thermal expansion, ultimately leading to bending of the cladding. This bending will cause interaction between the cladding and the spacer grids and can be detrimental to the structural integrity of both the cladding and spacer grids. In this study we have analyzed the bending behavior of the cladding, the stress development in the cladding and the effects of spacer grids. The sensitivity of the cladding stress to the spacer grid material, extent of circumferential variation in power have been also evaluated. The results indicate that the spacer grids do not significantly affect the cladding stresses. The stress generated in the spacer grids due to its interaction with the cladding is found to be well below the strength of the spacer grid material. The sensitivity studies showed that changing the spacer grid material have negligible impact on the stresses in both cladding and spacer grid, while the extent of circumferential variation in power can lead to significant increase in the stresses in spacer grid.