Development of a system-CFD coupling method based on pressure correction iteration for simulation in reactor thermal-hydraulic analysis

[Background] The coupled simulation of system analysis codes and computational fluid dynamics (CFD) code is a key technical approach in numerical reactor research. This coupling method combines the advantages of both codes to achieve high-precision, rapid multi-scale simulations. It addresses the requirements for global effect analysis while accurately capturing detailed phenomena in critical regions, thus providing precise support for reactor design optimization and safety evaluation. [Purpose] This study develops a domain-decomposition-based semi-implicit one-dimensional-three-dimensional pressure correction iterative coupling method, integrating the commercial CFD code FLUENT with the system analysis code NUSOL-SYS. [Methods] The method initialized consistent pressure values at the coupling boundary, established a sensitivity matrix between pressure and mass flow rate differences by iteratively adjusting the boundary pressure, and then calculated the coupling pressure correction by incorporating the mass flow rate differences across the boundary at the current iteration step. During the iteration process, the coupling boundary pressure was continuously corrected to ensure mass flow rate consistency on both sides, thereby achieving convergence and advancing the time step. [Results] The coupling calculation results based on the single-pipe flow problem show a high consistency with the results of NUSOL-SYS standalone calculations, and convergence is achieved within two iterations. The coupling method has been further validated by simulating a parallel flow problem with varying time steps and flow channels. The results show that the coupling program reduces the mass flow residual by 1 to 3 orders of magnitude in each iteration under different conditions. Subsequently, the tool has been applied to analyze the core inlet flow distribution during a main coolant pump trip scenario in the ACP100, a modular small pressurized water reactor. The results indicate that no uneven flow distribution occurs at the core inlet following the accident. Moreover, the system parameters predicted by the coupled code are consistent with those obtained from standalone NUSOL-SYS simulations, while the code also successfully captures localized three-dimensional flow phenomena. [Conclusions] The semi-implicit iterative coupling method demonstrates good stability and convergence, providing a scientific approach for optimizing reactor component design and enhancing system accident resistance, while laying an important foundation for the further development of numerical reactors.