Optimization Study of Dry Storage Canister Layout Scheme for Spent Fuel Assembly of PWR

According to the requirements for critical safety and thermal safety of spent fuel assembly and the principle of optimization of radiation protection, the lumped parameter point burn-up model is typically used to calculate the source term of the spent fuel assemblies and determine the loading arrangement of spent fuel assemblies in dry storage canister. Considering the decay heat differences of spent fuel assemblies loaded in the same canister, the source term dispersion factor for the loading arrangement is derived. Based on the dispersion degree of the source term, it is determined whether a uniform or zoned loading arrangement should be adopted for the dry storage canister. The lumped-parameter point burn-up model homogenizes spent fuel assemblies and neglects the spatial burn-up distribution within an assembly. This leads to significant differences in the surface dose rate of the dry storage canister when the same spent fuel assembly is placed in radially symmetric but azimuthally different corner cells of the dry storage canister. Based on the burn-up fractions of different fuel rods within the same spent fuel assembly, a burn-up tilt factor was introduced in this paper. Additionally, considering the distance function relationship between the canister surface dose rate and the source term of spent fuel assemblies, as well as self-shielding effect from adjacent assemblies, a weight factor for corner cells of the dry storage canister was established. An optimization method for spent fuel assembly loading arrangements was proposed based on the burn-up tilt factor and the corner cell weight factor. Spent fuel assemblies with relatively high decay heat were selected and arranged in the edge cells, while those with relatively low decay heat were selected and arranged in the corner cells. Assemblies with a smaller burn-up quadrant tilt factor were arranged in the edge cells of Zone Ⅲ, and four assemblies with a larger burn-up quadrant tilt factor were placed in the four corner cells of Zone Ⅱ. The corner and edge cells at the symmetric positions of the canister were grouped, and the corner and edge of spent fuel assemblies with a smaller fuel rod burn-up quadrant factor were oriented toward the inner wall of the canister, ensuring that the surface with a lower radiation source term faces the inner surface of the dry storage canister. Applying this optimization method in engineering practice to arrange spent fuel assemblies in canister can reduce the surface dose rate of the dry storage canister. This achieves an approximately 20% reduction in contact dose rates during operations such as canister lid re-installation, surface decontamination and sealing process. The method realizes the engineering application of radiation protection optimization and contributes significantly to the health of worker and environmental protection.