Trans. of KNS Spring meeting, CD-ROM, 2010.
The subgroup method is one of the most employed methods for resonance treatment in the lattice transport or the direct whole core transport codes such as HELIOS and DeCART. It requires the subgroup parameters which consist of subgroup levels and subgroup weights. Subgroup weights are produced from the given subgroup levels by solving an error minimization problem for the resonance shielded effective cross sections. The subgroup parameters have a significant impact on the accuracy of the effective cross section which is estimated by the subgroup method. The available subgroup levels for each resonance group of the existing libraries were not been thoroughly optimized. The purpose of this work is to devise a way to determine proper subgroup levels which can further reduce the error in the effective cross section errors. Needless to say, more correct resonance effective cross sections would improve the accuracy of the lattice transport or the direct whole transport calculation.
