Calculation of the fuel composition and the deterministic reloading pattern in the second cycle of the BUSHEHR VVER-1000 reactor using the weighting factor method

To calculate the optimum reloading pattern in the second cycle of BUSHEHR VVER-1000 reactor, it was necessary to first calculate the burnup and fuel composition of each fuel assembly at the end of the first operational cycle so that the types of applicable fuel assemblies in the second cycle could be determined. Time-dependent calculations were performed using the WIMSD-5B and CITATION-LDI2 codes coupled with thermo-hydraulic computations during the first cycle. A weighting factor was defined for all 16 types of fuel assemblies in the second cycle based on their types and fuel compositions. In the process of calculating the deterministic reloading pattern, the number of probable arrangements was reduced from 7.55 × 1022 cases to just 1 856 cases by using a weighting-factor method and the structural constraints of the reactor core. The thermo-neutronic parameters of each of the 1 856 arrangements were then calculated by coupling the WIMSD-5B and CITATION-LDI2 codes with the thermo-hydraulic program. Afterwards, the processes of screening the probable arrangements and searching for the optimal reloading pattern were carried out based on the values of these parameters.