The thermal-fluid-solid coupling effect in nuclear reactor vessel with direct vessel injection

Different from conventional cold leg safety injection, a newly designed reactor type CAP1400 directly connects the injection pipeline of the emergency cooling system with the pressure vessel. However, these structures have been found to potentially have adverse effects on the pressure vessel. This paper employs both physical experiment and numerical analysis to investigate the dynamic oscillating load and the structural response. A 1:9 scale model is adopted for the experimental section. The uncertainty of the measurement quantities is within 3%. The CFD code and the FEM code are used to simulate the transient fluid flow and solid structure deformation , respectively. The sequential coupling method is used for the thermal-fluid-solid coupling calculation. The overall error of the calculation is within ±10%. The result shows that the fluctuation of the physical quantity near the wall is caused by turbulence eddy and thermal mixing, and the flow, heat transfer and structural deformation near the wall of the pressure vessel are closely coupled. The effect of the turbulence eddy can be seen within the entire range of frequency measured, while that of the thermal mixing can be seen only within the low frequency range. The influence law of the loop flow ratio, the flow rate of the downcomer and the loop temperature difference in the structural response are obtained. Through the research of this paper, the law of interaction between the thermal-fluid load and the structural response under direct safety injection is more deeply understood. Thus, it provides a design reference for the safety of reactors. • The mechanism of thermal-fluid-solid coupling phenomena during the direct safety injection process is studied. • Experiment and numerical study for fluid dynamic load and structural response are performed. • The LES method is used to capture the small and broadband pulsation of pressure and temperature in the flow field.