Automatic coarse energy group structure optimization by minimizing reaction rate differences for the SCALE and CASL code systems

A new algorithm has been developed to automatically optimize the coarse energy group structure for the SCALE multigroup procedures based on either a pointwise slowing down calculation or intermediate resonance approximation for resonance self-shielding. A coarse group structure will be determined to minimize reactivity differences between the fine and coarse group calculations for several variations of states. A new 56-group structure has been developed for the pressurized water reactor and boiling water reactor fuels by using the algorithm with the SCALE 252-group structure, which could be used in the regular SCALE and intermediate resonance approaches. The computational results for benchmark problems show that the new 56-group structure developed by using coarse group optimization is reasonable. (authors)