Fuel lattice design with Path Relinking in BWR’s

In this paper a new system, called ohtli-PR, is presented. This system was developed for fuel lattice design optimization in Boiling Water Reactors (BWR) using the Path Relinking and Scatter Search techniques. As input data, the system uses an initial uranium enrichment and gadolinia percentage. At the beginning of the optimization process, the system generates a random seed fuel lattice, which is used to generate a set with 100 fuel lattices. From this set, a subset is chosen and then an iterative process is carried out until an optimized fuel lattice design is attained. During the iterative process, the system performs at each iteration, two stages. In the first one, the Scatter Search technique is applied. In this stage, a new fuel lattice is constructed using combination pairs of elements. In the second stage, two elements are used to create a path between the best and the worst solutions of the initial subset; this stage is known as Path Relinking. In both stages, if the new element does not improve any solution of the subset, the process continues with the same subset in the next iteration, but using another pair of elements to build either a new combination or a new path. The system uses an objective function with both the Power Peaking Factor (PPF) and the Infinite Neutron Multiplication Factor (kinf) at the beginning of life of the fuel lattice. The main idea is to keep the Infinite Neutron Multiplication Factor inside a proposed interval and to minimize the Power Peaking Factor. These parameters are calculated with the CASMO-4 code. When the PPF and kinf parameters are satisfied, the fuel lattice is evaluated taking into account a fuel reload and its respective control rod pattern to verify both the energy obtained and the thermal limits. In this work, the designed fuel lattices correspond to the bottom of the fuel assembly and two different uranium enrichments were used.