Estimation of self-shielded cross section by employing interference correction factors in subgroup method

The purpose of this study is to conserve the effective cross section by subgroup method in the presence of resonance interference effect. The technique of handling the resonance interference among resonance isotopes is improved through the introduction of interference correction factors in subgroup method. A mathematical relationship based on subgroup formulism is derived to compute the interference correction factors. This new approach has been implemented in method of characteristics (MOC) based 3-D neutron transport calculations code nTRACER. Sample calculations have been performed for various pin and assembly problems with satisfactory performance. The calculation results for effective resonance cross sections show maximum error of less than 4% and an improvement in reactivity estimation by 24 pcm-101 pcm for fuel pin problems. Whereas the computed results show improvement in reactivity estimation by 59-134 pcm for fuel assembly problems and 300 pcm for MOX fuel respectively.