Few-group condensation via two-material coexisting ring model for fast reactor core analysis

To improve the currently used simplified fast reactor analysis method for few-group condensation, a two-material coexisting ring model is proposed in this study. In the two-material coexisting ring model, the θ-direction homogenized model from the R-θ-Z geometry is solved, but the neutron flux for each material in the homogenized region is obtained separately. In the numerical results on simple 2-D fast reactor test problems, the newly proposed two-material coexisting ring model shows excellent neutron spectrum agreement with the reference, as compared to the conventional simplified model. In addition, the few-group calculation result shows better keff estimation when a two-material coexisting ring model is used for group condensation. Because relative errors on the neutron spectrum are much flattened when the newly proposed model is used, accurate few-group cross sections can be generated even if a small few-group structure is selected for condensation.