Trans. of KNS Spring meeting , CD-ROM, 2008.
The multigroup cross section data used in the lattice transport or the direct whole core transport codes such as HELIOS and DeCART have a significant impact on the accuracy of the criticality prediction. If a large discrepancy is noted in the analysis of critical experiments, it is customary to adjust the resonance integral (RI) data of U-238 given in the cross section library in order to match the measurement. In case of HELIOS, the unadjusted library gives about 300∼550 pcm lower reactivity than the adjusted one. The sole adjustment of the U238 RI, however, is to blame only U238 for all the discrepancies that can originate from various sources. One of the sources of the error would be the inaccuracy of subgroup parameters used in the a group codes which employ the subgroup method for resonance treatment. The inconsistency problem noted in the subgroup parameter generation and usage steps which was reported in our previous work can be smeared out by the RI adjustment. Thus such blind adjustment of the resonance integral is to be avoided. In this work, we examine a new procedure for generating multigroup cross section data from the ENDF/B files, which would not require any forced adjustment. One of the distinct steps in the procedure is to employ a consistent method of generating subgroup parameters formulated by imposing a shielded cross section conservation principle rather than the resonance integral conservation. In order to check the validity of the procedure, multigroup data are generated only for a group of primary nuclides which appear in a fresh fuel UO2 pin cell, namely, U-235, U-238, H-1, O-16, and Zr. The accuracy of the new library is assessed by comparing the reactivity with those obtained from corresponding continuous energy Monte Carlo calculations. Since recently the ENDF/B-VII file was released which reflects improvements in the U238 resonance data, the difference between the multigroup cross section libraries generated from the new ENDF file and its previous version (ENDF/B-VI Release 8) is also assessed
