Probabilistic Failure Assessment of Spent Nuclear Fuel Cladding Based on Critical Crack Depth

Due to the scarcity of post-irradiation examination (PIE) data regarding the fracture properties of spent nuclear fuel, establishing statistical distributions for fracture and crack characteristics has been challenging. This study develops a probabilistic failure model for zirconium alloy cladding—demonstrated here using Westinghouse 17×17 fuel parameters as a representative example—to provide quantitative data supporting current safety regulatory guidelines. The methodology is general and can be applied to other fuel types by substituting appropriate input parameters. Specifically, the methodology for characterizing probability density function of crack depth was extended to evaluate the failure rate of cladding under accident scenarios involving both bending stress and pinch loads, which correspond to circumferential and axial cracks, respectively. By incorporating the probability distribution of critical stress intensity factor ( ), the cladding failure rate was analyzed. The results demonstrate that the predicted failure rate remains consistent with the empirical baseline (10 -4 ) even under external loads approaching the yield strength ( 640 MPa). This implies that the cladding maintains structural integrity in most accident scenarios under the yield strength, suggesting that the loads experienced during vacuum drying are comparable to the mechanical stresses anticipated in accident conditions.