Development of 3D transient neutronics and thermal-hydraulics coupling procedure and its application to a fuel pin analysis

Abstract

This paper develops a three-dimensional fine-mesh coupled neutronics and thermal-hydraulics platform based on the open-source software OpenFOAM. For the neutronics, a three-dimensional multi-group multi-region neutron diffusion solver is developed for steady and transient problems with macroscopic cross-sections generated by the Monte Carlo code OpenMC. By modeling and calculating three typic neutronic benchmark problems, the results are compared with that of other programs to verify the correctness of this solver to solve neutron diffusion equations. The thermal-hydraulics is solved by the built-in solid-fluid conjugated heat transfer solver for steady or transient fluid flow and solid heat conduction between different regions. The unified solution of a coupled neutronic and thermal-hydraulic problem is implemented in the solver with the same time step size and the same set of meshes. The feasibility and rationality of this coupling procedure is verified through the simulation the 5×5 PWR assembly. Furthermore, the operator-splitting semi-implicit (OSSI) method and the fixed-point implicit (FPI) method have been applied to the coupling procedure. The performance of the above two neutronic and thermal-hydraulic coupling algorithms is evaluated by simulating the coolant inlet temperature decrease accident in a single fuel pin model of the pressurized water reactor. The numerical results indicate that the FPI coupling method outperforms the OSSI coupling method due to its accuracy and stability.