Sensitivity analysis of rod rearrangement in criticality safety for PWR fuel assemblies under transportation accidents

摘要: To ensure the safe transportation of radioactive materials, numerous countries have established specific stan dards. For the transfer of fissile materials, it is imperative that the material within the packaging remains in a subcritical state during routine, normal, and accidental transport conditions. In the event of an accident, the rods within the storage tank may become rearranged, introducing uncertainty that must be accounted for to ensure that criticality analysis results are conservative. Historically, this uncertainty was addressed overly conserva tively due to limited research on non-uniform arrangement scenarios, which proved unsuitable for criticality safety analysis of spent fuel packages. This paper introduced three distinct methods to non-uniformly rearrange fuel rods—Uniform Arrangement by Blocks, Layer-by-Layer Determination, and Birdcage Deformation—and meticulously evaluates the influences of rod rearrangement on the effective multiplication factor of neutrons, keff, utilizing the Monte Carlo method. Ultimately, this study presents a holistic method capable of encompassing the entire spectrum of potential effects stemming from the rearrangmenet of fuel rods during rods mispositioning accident. By augmenting the safety margin, this approach proves to be adeptly suited for the criticality safety analysis of nuclear fuel transport containers.