Criticality Safety Evaluation for High-Density Spent-Fuel Storage Racks

Using as a starting base the high-density spent-fuel storage racks to be put into the Chinshan and Kuo-shang nuclear power plants, a series of criticality analyses with various combinations of fuel assemblies and storage rack designs were performed using an AMPX-KENO/XSDRNPM computer code package. The calculated k_∞ value for the storage pools in the two subject plants using Boral (0.013 g/cm^{2 10}B) poisoned rack lattices and 3.2 wt% enriched fuel assemblies is 0.900 under conservative assumptions. Considering all the calculation biases and statistical and manufacturing uncertainties, the maximum k_∞ value is estimated to be 0.929 under normal storage conditions. Variation in water temperature and density or abnormal positioning of fuel assemblies will result only in a negative effect on value. The deviation of the calculated k_∞ values between the one-dimensional S_n XSDRNPM code and the KENO-IV code is within the normal Monte Carlo variations. Based on XSDRNPM calculations,K_∞ values and the associated uncertainties due to fuel and rack manufacturing tolerances are tabulated. These interpolations can be used for the estimation of the value for any particular fuel and rack combination based on the tabulated data.