Examination and refinement of fine energy group structure for high temperature reactor analysis

Multi-group energy structure SHEM-281 and -361 were refined using a Contributon and Point-Wise Cross Section Driven method (CPXSD). The Contributon and Point-Wise Cross Section Driven method was derived based on the product of the forward and adjoint angular fluxes, and the point-wise cross section of important isotope/material. It is an iterative method that selects effective fine- and broad-group energy structures for a problem of interest. The two selected criteria for determining fine energy group structure were 10 pcm relative deviation of Δk/k for k-effective and 1% relative deviation for reaction rates. The energy group structure refinement was subdivided into fast, epithermal and thermal regions. Firstly, the refinement was done for fast region and a new library was created and applied in the fuel cell unit until the target criteria's are met. Similar procedure was repeated for epithermal and thermal regions. The dominant parameters for each region are considered as required, fission reaction rate for fast region, absorption reaction rate for epithermal region and absorption and fission reaction rates for thermal region.