A Study on Criticality Safety for Loss of Single Rod from 14ⅹ14 Nuclear Fuel Assembly of Kori Unit 1

June 18, 2017, Kori Unit 1 was permanently shut down, and KHNP will submit the application for decommissioning approval to the NSSC (Nuclear Safety and Security Commission) within 5 years. To perform decommissioning, all SNF (spent nuclear fuel) stored temporarily in spent nuclear pool must be transported and stored elsewhere. According to the NUREG/CR-6835, the NRC expects that the potential for nuclear fuel failures will increase because of the increase of the burnup for fuel discharged from lightwater reactors and the degradation of fuel and clad material properties. Therefore, the NRC conducted nuclear criticality analysis from an academic point of view, rather than recommending nuclear criticality performance procedures based on fuel failure scenarios. Although the fuel failure scenarios considered go beyond credible conditions, no one has conducted nuclear criticality assessments for the fuel failure scenarios in the domestic. In this study, it is conducted the theoretical limit on the effects of severe accident conditions. Therefore, this study evaluated the scenario 1(Individual fuel rod collapse resulting in rods being absent from the assembly lattice) among the fuel failure scenarios assumed in NUREG/CR-6835. At present, there is no commercial cask that can transport or storage SNF into a dry storage facility in Korea. So, KN-12, which is transporting between NPP, was selected and evaluated. First, a basket-cell model of KN- 12 loaded WH 14ⅹ14 OFA and STD fuel was created, and the effective multiplication factor was calculated for single fuel rod loss case and compared with the reference model. Secondly, 3D-full model of the same fuel-loaded KN-12 transport cask is created and the effective multiplication factor is calculated for a single fuel rod loss depending on the fuel rod and basket position. The nuclear criticality analysis for the KN-12 transport cask 3-D full model has affected the reactivity depending on the fuel type and fuel rod location. It was evaluated to meet critical criteria