Abstract
The first nuclear power plant in Taiwan has been commercially operated for more than 34 years. The capacity of its spent fuel storage pool has been nearly exhausted. In order to solve the impending shortage problem of spent nuclear fuel storage, Taiwan Power Company is currently constructing an independent spent fuel storage installation (ISFSI) at the plant site to maintain normal plant operation. Focusing on the first storage cask TSC01, this study models the source terms and cask geometry as detailed as possible in order to predict a realistic dose rate distribution over the cask surfaces. Neutron and gamma-ray source terms of the first batch of 56 spent fuels were determined one by one according to their specifications, burnup histories, and cooling times. Energy spectra, axial distributions, and prescribed loading pattern of 56 spent fuels in the canister were included in the source description. The geometry of storage cask was modeled in detail including all the air inlets/outlets of the cask to evaluate possible radiation streaming. Monte Carlo method is the only choice for performing such complicated simulations. Effective variance reduction techniques are indispensable to making it computationally practical. MAVRIC in the SCALE 6.1 code system was used for calculating the dose rate distribution over the entire cask surface as functions of radial, axial, and azimuthal dependences. Based on the CADIS methodology and deterministic adjoint solution, MAVRIC can perform efficient radiation transport calculations for fixed-source shielding problems through consistent use of source biasing and weight window techniques. In addition to verify the conservativeness of results in the safety analysis report, the main purpose for such comprehensive and detailed modeling aims to predict a dose rate distribution as accurate as possible for making a high-quality comparison with field measurements. High-efficiency neutron proportional counter, HPIC, TLD, and integrated scanning frame were in preparation and test for measuring dose rates on the cask surfaces.