Development of Hybrid Core Calculation System using two-dimensional full-core heterogeneous transport calculation and three-dimensional advanced nodal calculation

This paper presents a description of the Hybrid Core Calculation System which is based on a very rigorous but practical method utilizing best estimate core design calculations and taking advantage of the recent remarkable progress of computers. The basic idea of this system is to generate the correction factors for assembly-homogenized cross sections, discontinuity factors, etc. by comparing the CASMO-4 and SIMULATE-3 2-D full-core calculation results under the consistent calculation condition and applying them to the SIMULATE-3 3-D calculation. The CASMO-4 2-D heterogeneous core calculation is performed for each depletion step using the core conditions previously determined by ordinary SIMULATE-3 core calculations. This avoids time-consuming iterative calculations of the critical boron concentration search and the thermal hydraulic feedback. These calculations are instead performed in the final SIMULATE-3 3-D calculation using the previously determined correction factors. The Hybrid Core Calculation System was verified using data from a commercial PWR for several cycles, and it was demonstrated that the accuracy of core calculation is improved.