Investigating the neutronic, thermal-hydraulic, and solid mechanics analysis for AP-1000 nuclear reactor

Abstract

ABSTRACT This study investigates the neutronic, thermal-hydraulic, and solid mechanics analyses for one of the central fuel assemblies with 2.35% U235 enrichment in the AP-1000 Reactor. MCNPX 2.7 computer code, which depends on a Monte Carlo algorithm, was applied to perform the neutronic calculations. Both COMSOL-Multiphysics, based on the numerical solution for the centered rod sub-channel model, and MATLAB, based on the analytical solution for the same model, were applied to perform the thermal-hydraulic analysis. COMSOL-Multiphysics was used to perform the solid mechanics analysis. The neutronic, thermal hydraulics, and solid mechanics analyses play an essential role in the control, design, and safety of nuclear reactors. The calculations of criticality, reactivity, fuel burn-up, neutron flux, and power mapping were performed.‎ From the power mapping, the hot channel was determined and its maximum PPF. Upon getting the maximum PPF, which occurred in channel number 30 and equals 1.357, the thermal-hydraulic calculations using both COMSOL-Multiphysics and MATLAB were applied to determine the temperature distribution of the fuel, clad, and coolant. The departure from nucleate boiling ratio (DNBR) distribution was calculated to determine the minimum departure from ‎nucleate boiling ratio (MDNBR). The MDNBR results were 2.154 based on the analytical approach and 2.20 based on ‎the numerical approach. These values are higher than the limiting value of 1.75, which assure that no nucleate boiling ‎problems will occur. The solid mechanics calculations were investigated by coupling three kinds of physics using COMSOL-Multiphysics (the heat transfer in solid physics to perform the thermal load, turbulence flow RANS K-OMEGA to perform the pressure load, and solid mechanics physics). This coupling was used to determine the von-Mises stress, volumetric strain, and the total displacement for both the fuel and the clad material. The total fuel outer surface displacement was calculated to assure that no surface contact would happen between the ‎fuel and clad material to avoid chemical interactions between them. The displacement was calculated to be 0.007 mm, which is less than the He-gap ‎thickness, 0.008 mm. The coupling between different physics is one of the most well-developed techniques used for simulating the exact situation inside nuclear reactors. This coupling was done using the computational fluid dynamics (CFD) approach. All the calculations for the benchmark problem (a single fuel Assembly (G-9), near Beginning of Life, hot Full Power, equilibrium Xenon, and unrodded Core) were conducted. The obtained results were within the safety limits outlined in the design control document (DCD). Eventually, the results were in line with earlier efforts that utilized different codes for simulating neutronic analysis.