Optimization of the on-power refueling strategy for the slightly enriched uranium core of Atucha-II NPP

Abstract

The development of an on-power refueling strategy requires meticulous consideration due to its impact on relevant reactor parameters during operation. The rapid increase in computational power promotes the use of heuristic (or metaheuristic) methods for optimizing systems with numerous core calculations, such as designing a refueling strategy. Building on the previous success of optimizing the on-power refueling strategy for the Atucha-I core using the Simulated Annealing algorithm, the approach was extended to design an enhanced refueling strategy for the future use of slightly enriched uranium fuel in Atucha-II. Previous efforts manually achieved an acceptable refueling strategy, consistent with 3 irradiation paths, each having 3 burnup zones. The primary goal of the optimization was to reduce the usage of the refueling machine, a critical component for plant availability and performance. To achieve this, the number of burnup zones for the optimization was set at 2 per irradiation path. An acceptable optimized refueling strategy was obtained and, subsequently, manual refinements were introduced to improve the time-average channel power distribution. To assess the feasibility of the obtained 2-burnup-zones per path refueling strategy, a simulation of the reactor operation including on-power refueling consistent with this refueling strategy was conducted for 4 years at full power. The simulation predicts a 25.6 % reduction in the refueling machine’s use at full power and savings of 2.9 fuel assemblies per year compared to operation with the 3-burnup-zones per path refueling strategy. The compelling advantages in the performance of the 2-burnup-zones per path refueling strategy have led to its formal adoption as the new official refueling strategy for the design phase of the use of slightly enriched uranium fuel in the Atucha-II core.