Abstract: Background: The passive residual heat removal system (PRHR) is an important safety facility for passive nuclear power plants. In the station blackout accident, most of the core decay heat is transferred to the in-containment refueling water storage tank through PRHR heat exchanger to ensure the safety of nuclear reactors. The transfer process of PRHR heat exchanger is not steady, and the transfer mechanism is very complex. Purpose: This study aims at the flow and heat transfer characteristics of the PRHR system by computational analysis. Methods: The computational fluid dynamics (CFD) software was employed to establish the geometric model for PRHR in the passive reactor cooling system test facility, and the physical model (turbulence, thermal phase change) and boundary conditions were defined for numerical calculation. Results: The temperature field, velocity field and heat transfer coefficient of the heat transfer tubes in in-containment refueling water storage tank (IRWST) were obtained, and their regularities were analyzed. Conclusions: Obvious temperature stratification phenomenon was found along the vertical height, and the temperature distribution in the horizontal direction tends to be uniform. The flow in IRWST is mainly along the vertical section of the C-type heat transfer tubes, and the velocity increases gradually. In the two-phase stage, the flow of the upper tank is obviously enhanced. The heat transfer coefficient of the upper horizontal segment and the upper vertical segment of the C-type heat transfer tube is obviously higher than that of the other area, and the heat transfer coefficient of the joint of upper horizontal segment and the vertical segment is the largest. The heat transfer coefficient of the upper region in tank increases obviously in the two-phase stage.

Key words: PRHR, IRWST, Heat exchanger, Numerical simulation