Development of a code system for the BN and BFS reactor analysis (II). Development of a three-dimensional Hex-Z geometry transport code system for reactor core analysis

The following codes were developed to enhance the applicability of the three-dimensional Hex-Z geometry codes that can model the BN and BFS reactor core accurately. The neutron flux reconstruction method in the three-dimensional transport-based perturbation code SNPERT-HEXZ was modified to improve the calculation accuracy. New functions to calculate design parameters, such as peaking coefficients, maximum linear power etc., based on the reconstructed neutron flux were added to the three dimensional Hex-Z geometry transport burn-up code NSHEX-BURN. The three-dimensional Hex-Z finite difference transport code MINIHEX was modified to improve the computational performance. First, cash-tuning and a flux extrapolation method were applied to MINIHEX. This modification reduced the computational time by a factor of 3.8 at most. Second, the modified MINIHEX was parallelized with MPI by an angular space decomposition method. A series of performance check calculations was performed on GP7000 and DEC/alpha EWS cluster. Speed-up obtained on GP7000 was at most 5.3 for 9 PE and that on DEC/alpha cluster was at most 1.5 for 4 PE. The parallelization of MINIHEX also enhanced the applicability of the code to larger scale computational problems and more detailed reactor core modeling. An interface to MINIHEX was added to the three-dimensional Hex-Z geometry reaction rate calculation code LAGOON-HEXZ. The added interface enables the code to calculate reaction rates using neutron flux obtained by MINIHEX. A three-dimensional transport-based perturbation code for MINIHEX was developed based on the three-dimensional transport-based perturbation code NSHEX-HEXZ. This code makes it possible to evaluate reactivity change from the neutron flux and eigenvalue obtained by MINIHEX. (author)