SHIELDING ANALYSIS OF DUAL PURPOSE CASK FOR SPENT NUCLEAR FUEL UNDER NORMAL STORAGE CONDITION

摘要

A large increase in the number of casks for transport and storage of spent nuclear fuel is predicted in Korea, in view of the spent fuel storage requirements and the expected shortage of storage capacities at reactor sites. Therefore the metal and/or concrete casks for storage system are anticipated for either at reactor site of away from reactor for interim storage. With the purpose of interim storage, a dual purpose metal cask containing 21 spent fuel assemblies is under development by Korea Radioactive Waste Agency (KORAD) in Korea. Under normal storage conditions, the design of the cask is based on the safety requirements of 10 CFR Part 72. Radiation shielding analysis of metal storage cask optimized for 21 design basis fuels was performed for two cases, one for a single cask and another for 2×10 casks array. In the case for a single metal cask, dose rates were evaluated at the external surface of the metal cask, 1m and 2m away from the cask surface. In the case for a 2×10 casks array center point of the array and the center of height of metal casks. The results of the shielding analysis for the single metal cask show dose rates were considerably higher at the lower side (from the bottom of cask to bottom of neutron shielding) of the cask, over 2mSv/hr at the external surface of the cask. However, this area will be provided with supplementary shielding in the storage facility. The shielding analysis results of a 2×10 casks array showed exponential decrease with distance off the sources with controlled area boundary, 25mrem/yr at approximately 280m. Dose rates within controlled area boundary will be actually smaller than 25mrem/yr, due to decay of radioactivity of spent fuel in storage.