Following an accident, the passive nuclear power plant CAP1400 mainly uses cooling water evaporation on the outer containment surface to remove the decay heat inside containment to outside environment to ensure the plant to a stable status. But the outside surface of the containment vessel is attached by a large number of different forms of the disorder structure including circumferential welds and longitudinal welds on the containment surface, and small local bulge, which may affect water film flow and coverage outside containment surface. Once a large amount of water splashes and can’t return to the containment surface, the heat removal capacity of the system during and after an accident will be significantly reduced, and the safety of power plants will be threatened.
This paper simulates the water flow characteristics on the containment surface. Firstly, a simplified analysis model of water film flow structure is established considering different forms of structures including the circumferential weld, small local bulge and etc. The circumferential weld is simplified with the horizontal protrusion. Local small uplift is simulated with point-like protrusion. Computational fluid dynamics (CFD) software STAR CCM+ is applied in this simulation with the volume of fluid method and surface tension model, and sets contact angle and other parameters according to the characteristics of the containment surface coating, so as to establish the CFD analysis method. The analysis results and water flow test results agree well. And then, the CFD analysis method is used to analyze the flow patterns of water film on the surface of the wall under different conditions.
The results show that the circumferential weld has a certain influence on the initial water film covering only. But the film coverage rate of the water film is stable after the water film is stable, and there is no loss of the water film. For the circumferential weld on the vertical wall, the effect on the water film coverage is little. Water film loss of low-flow is negligible, and water film loss of high-flow is no more than 1%. For the form of local small protrusions, little change of the flow characteristics of water film can be observed.
The structure form of the containment outside wall is various. According to the rules of the water film, including the water film covering width and the water film loss, it can be used as the design input of the accident analysis program WGOTHIC to guide the system design.