Implementation of the Direct S(A,B) method in the KENO Monte Carlo code

Abstract

The Monte Carlo code KENO contains thermal scattering data for a wide variety of thermal moderators. This data is processed from ENDF formatted data les by AMPX and stored as double differential probability distribution functions. The method examined in this paper uses S(A,B ) probability distribution functions that have been derived from the ENDF data files directly instead of being converted to double differential cross sections. This allows the size of thecross section data on disk to be reduced by a substantial amount. KENO has also been updated to allow interpolation in temperature on this data so that problems can be run at any temperature. Results are shown for several simplifed problems for a variety of moderators. In addition, benchmark models based on the KRITZ reactor in Sweden are run and the results compared with the previous versions of KENO without the Direct S(A, B ) method. Results from the Direct S(A, B) method compare favorably with the original results obtained using the double differential cross sections. Sampling the data increases the run-time of the Monte Carlo calculation, but memory usage is decreased substantially.