DEVELOPMENT OF A 3-DIMENSIONAL CORE DYNAMICS ANALYSIS PROGRAM FOR COMMERCIAL BOILING WATER-REACTORS

Development and qualification results are described for a three-dimens ional, time-domain core dynamics analysis program for commercial boili ng water reactors (BWRs). The program allows analysis of the reactor c ore with a detailed mesh division, which eliminates calculational ambi guity in the nuclear-thermal-hydraulic stability analysis caused by re actor core regional division. During development, emphasis was placed on high calculational speed and large memory size as attained by the l atest supercomputer technology. The program consists of six major modu les, namely a core neutronics module, a fuel heat conduction/transfer module, a fuel channel thermal-hydraulic module, an upper plenum/separ ator module, a feedwater/recirculation flow module, and a control syst em module. Its core neutronics module is based on the modified one-gro up neutron kinetics equation with the prompt jump approximation and wi th six delayed neutron precursor groups. The module is used to analyze one fuel bundle of the reactor core with one mesh (region). The fuel heat conduction/transfer module solves the one-dimensional heat conduc tion equation in the radial direction with ten nodes in the fuel pin. The fuel channel thermal-hydraulic module is based on separated three- equation, two-phase flow equations with the drift flux correlation, an d it analyzes one fuel bundle of the reactor core with one channel to evaluate flow redistribution between channels precisely. Thermal margi n is evaluated by using the GEXL correlation, for example, in the modu le. In the upper plenum/separator module, the upper plenum is modeled as a single volume in the thermal-equilibrium state and wafer spiralin g in the separator is modeled by an effective length in the momentum e quation. In the feedwater/recirculation flow module, the single-phase flow model is solved with the assumption of incompressive flow. Finall y, the control system module includes the recirculation flow control m inimodule, the pressure control minimodule, and the feedwater control minimodule, as well as the interlock functions, which work during a tr ansient to allow analysis of general transient phenomena. The program was verified to provide satisfactory results within reasonable computa tional time based on application analysis of stability and scram pheno mena in a BWR-5 type plant.