Development and Assessment of Multiphase Sub-channel Code of COSINE

COSINE software package provides various functions in thermal-hydraulic analysis of pressurized water reactor (PWR) after years of development. In order to meet the engineering design and safety analysis requirements of the advanced passive reactor CAP1400, the multiphase field sub-channel code with higher calculation accuracy was developed based on the homogeneous sub-channel program (cosSUBC) in COSINE software package. The multiphase sub-channel code contained 11 basic equations including the mass conservation equations of the vapor, continuous liquid, and droplet, the axial momentum conservation equations of the gas, continuous liquid phase, droplet phase, the transverse momentum conservation equation of the gas, continuous liquid, and droplet, and the energy conservation equations of the gas and total liquid phases. The continuous liquid and the droplet were in energy equilibrium states in one cell was assumed, therefore the continuous liquid and droplet were merged into total liquid phases in energy conservation equation. The constitutive relation models between different phases were introduced in the code to realize the closure of the basic equations, the staggered discrete format in space and a semi-implicit time discrete format were adopted in multiphase field sub-channel code. The typical test cases and representative experiments were modeled and calculated in this paper to verify the calculation capability of the code. First, the test of droplet behavior was modeled to verify the correctness of droplet model adopted in the code. Then the turbulent mixing experiment was modeled to verify the correctness of turbulent mixing model used in the code. In the end, the wall heat transfer experiment and the reflooding process experiment were modeled to verify the simulation ability in the heat transfer regime especially in the post critical heat flux (post-CHF) condition. The results show that the droplet behaviors including the generation and the flow distribution of droplet phase are in good agreement with the reference code. And the code can well simulate the flow distribution phenomenon according the comparison between the calculation results and experimental data in flow distribution experiment and the turbulent mixing experiment. Besides, the code can well simulate the distribution of the wall temperature and the reflooding process in the post-CHF and heat transfer condition. Therefore, the calculation of the thermal-hydraulic phenomena in the core of reactor by the multiphase field sub-channel code is reasonable and right, and the code has the ability to calculate and simulate the thermal-hydraulic conditions in the core of PWR.