MCS/FRAPCON Multi-physics Coupled Simulation of Westinghouse 3-loop PWR Wholecore Analysis

Abstract

Coupled neutronics, thermal-hydraulic and fuel performance (N/TH/FP) simulation results of a Westinghouse 3-loop (WH3L) pressurized water reactor (PWR) are analyzed in this paper. The analysis is conducted with the Monte Carlo code MCS and the fuel performance code FRAPCON coupled code system. The work in this study is divided into two parts. In the first part, coupled neutronics and thermal-hydraulic (N/TH) analysis of the WH3L is performed by MCS using the built-in (internal) one-dimensional (1D) single-phase closed-channel TH solver (TH1D). In TH1D, two-phase and lateral cross flow are not considered. The pressure through the coolant flow is assumed to be constant. Only radial heat conduction in the fuel pellet is modeled. A temperature-dependent fuel thermal conductivity and a constant pellet-clad gap thermal conductance is used. The axial heat convection in the coolant is represented by the mass and energy conservation equations. TH1D obtains the power distribution from MCS and returns the fuel/coolant temperature and coolant densities, to update the temperature dependent cross sections. In the second part, the TH1D solver in MCS is replaced with FRAPCON. FRAPCON is a fuel performance code, with singlechannel TH and a burnup solver. FRAPCON obtains the power distribution and burnup interval from MCS. The burnup interval is used to solve the transmutation equations to update the material properties of the fuel. Then FRAPCON returns the fuel/coolant temperature and densities to MCS and also evaluates fuel performance properties including cladding hoop strain, stress, and zirconium oxide layer thickness. In FRAPCON, the fuel thermal conductivity is temperature and burnup-dependent, and effects such as thermal expansion, irradiation swelling, and densification are considered. The thermal conductance of the pellet-clad gap depends on the thermo-mechanical interactions. The MCS/FRAPCON coupled system results in a higher fidelity solution since FRAPCON models the fuel burnup and uses more reliable material properties in its TH solver. The simulation results of the neutronics and TH parameters are compared/analyzed to demonstrate the multi-physics coupling capability of MCS.