Development of Thermal Analysis Capability of Dry Storage Cask for Spend Fuel Interim Storage

As most of the nuclear power plants, on-site spent fuel pools (SFP) of Taiwan’s plants were not originally designed with a storage capacity for all the spent fuel generated over the operating life by their reactors. For interim spent fuel storage, dry casks are one of the most reliable measures to on-site store over-filled assemblies from SFPs. The NUHOMS^®-52B System consisting of a canister stored horizontally in a concrete module is selected for thermal evaluation in this paper. The performance of each cask in criticality, radioactive, material and thermal needs to be carefully addressed to ensure its enduring safety. Regarding the thermal features of dry storage casks, three different kinds of heat transfer mechanisms are involved, which include natural convection heat transfer outside and/or inside the canister, radiation heat transfer inside and outside the canister, and conduction heat transfer inside the canister. To analyze the thermal performance of dry storage casks, RELAP5-3D is adopted to calculate the natural air convection and radiation heat transfer outside the canister to the ambient environment, and ANSYS is applied to calculate the internal conduction and radiation heat transfer. During coupling iteration between codes, the heat energy across the canister wall needs to be conserved, and the inner wall temperature of the canister needs to be converged. By the coupling of RELAP5-3D and ANSYS, the temperature distribution within each fuel assembly inside canisters can be calculated and the peaking cladding temperature can be identified.