Nuclear Science and Engineering / Volume 149 / Number 1 / January 2005 / Pages 51-64
Multigroup cross sections are one of the major factors that cause uncertainties in the results of deterministic transport calculations. Thus, it is important to prepare effective cross-section libraries that include an appropriate group structure and are based on an appropriate spectrum. There are several multigroup cross-section libraries available for particular applications. For example, the 47-neutron, 20-gamma group BUGLE library that is derived from the 199-neutron, 42-gamma group VITAMIN-B6 library is widely used for light water reactor (LWR) shielding and pressure vessel dosimetry applications. However, there is no publicly available methodology that can construct problem-dependent libraries. Thus, the authors have developed the Contributon and Point-wise Cross Section Driven (CPXSD) methodology for constructing effective fine- and broad-group structures. In this paper, new fine-group structures were constructed using the CPXSD, and new fine-group cross-section libraries were generated. The 450-group LIB450 and 589-group LIB589 libraries were developed for neutrons sensitive to the fast and thermal energy ranges, respectively, for LWR shielding problems. As compared to a VITAMIN-B6-like library, the new fine-group library developed for fast neutron dosimetry calculations resulted in closer agreement to the continuous-energy predictions. For example, for the fast neutron cavity dosimetry, ~4% improvement was observed for the 237Np(n,f) reaction rate. For the thermal neutron 1H(n, ) reaction, a maximum improvement of ~14% was observed in the reaction rate at the middowncomer position.