Applicability of the enhanced neutron current method for non-convex fuel shapes

The enhanced neutron current method is applied for the evaluation of the background cross-section for fuels with non-convex shape. The evaluated background cross-sections are compared with those obtained by the conventional method (the equivalence theory) commonly used in the resonance calculation. However, the Dancoff factor for a fuel with non-convex shape is not directly obtained by the traditional method currently used in the resonance calculation. Therefore, a new method for the evaluation of the Dancoff factor is also proposed, which utilizes the variation of moderator density and is applicable to the non-convex shapes. The test calculations for fuels with non-convex shape indicate that the background cross-section obtained by the enhanced neutron current method and the conventional method agree well with each other. Since the enhanced neutron current method can be applicable not only for the convex shapes but also for non-convex shapes, it will be useful for the resonance calculations in complicated geometry.