A CONSISTENT COUPLING OF NODAL EXPANSION METHOD, ANALYTIC NODAL METHOD, AND FINITE DIFFERENCE METHOD FOR 3-DIMENSIONAL REACTOR CORE ANALYSIS

摘要

A high order and low order hybrid method has been proposed for the efficient and accurate 3-rndimensional LWR core analysis. This method uses nodal expansion method (NEM) or analytic nodalrnmethod (ANM) for coarse-mesh z-directional coupling and fine-mesh finite difference method (FDM)rnin x-, y-direction. NEM, ANM, and FDM are consistently coupled using the node interface currentsrnand the transverse leakage. The advantage of the new hybrid method is that nornhomogenization/dehomogenization is required and fine-mesh FDM comparable results can bernachievable within reasonable time. When control rods are inserted into a core consisting ofrnheterogeneous assemblies, the flux and transverse leakage change dramatically around the tip of therncontrol rod. Consequently, the conventional NEM and transverse leakage approximations do not workrnwell. These problems were overcome successfully by applying partially ANM for the flux calculationrnand obtaining the transverse leakage shape from a small local problem which is defined in thernneighborhood of the tip of control rod. The benchmark calculations demonstrate that the new method isrnnumerically stable and accurate enough to be applied to 3-dimensional reactor core analyses, and alsornmuch faster than the conventional fine-mesh FDM.