COMBINE-6 development at INEL

The development of COMBINE-6, a FORTRAN77 computer code for generation of spectrum-averaged multigroup neutron cross section data suitable for use in diffusion and transport theory reactor design analysis, is described. The cross-section data base used by COMBINE-6 is derived from the Evaluated Nuclear Data Files (ENDF/B), Version 6. The NJOY code was used for the Bondarenko multigroup cross section preparation, but a resolved resonance library was separately prepared for the Nordheim treatment of resolved resonances. The validity of the code was established for thermal and fast reactor systems by comparing with benchmark experiments. The calculational results carried out with COMBINE-6 and ANISN/TWODANT for selected benchmark cases are presented. Comparisons are made between Bondarenko and Nordheim treatments, and between Reich-Moore and its SLBW or MLBW approximation.