Development of a Two-step Pin-by-Pin Core Calculation System for Commercial Nuclear Design Applications

Abstract

A pin-wise three-dimensional nuclear design code newly has been developed as an effort to establish more accurate, yet practically applicable to commercial nuclear designs. As neutronics solvers, the numerical methods based on the traditional diffusion theory are implemented with the pin-wise finite difference method (FDM) and coarse mesh finite difference (CMFD) method coupled with the semi-analytic nodal method and evaluated which numerical method is practically desired. The planar parallelization method and the two-level CMFD acceleration method are incorporated to achieve high calculating performance. Since the lattice calculation based on MOC is still used to generate pin-wise group constants for each slice of an assembly, the pin-wise equivalence factors such as the flux discontinuity factors or the super homogenization factors are examined to preserve the higher order solutions of the lattice calculation. The accuracy and performance of the proposed methods are tested with the C5G7MOX, VERA, BanDi-50 and APR1400 benchmark problems. The results indicate the superiority of the pin-wise calculations compared to the traditional node-wise calculations and the computing time and resources are reasonable for the commercial reactor core designs. To assess transient calculation capability, SPERT III E-Core transient problems are solved. With the proper kinetic nuclear parameters, the pin-wise transient calculation shows good agreement on the higher order solutions.