The Natural Circulation Characteristic Analysis of AP1000 IRWST

The natural convection passive residual heat removal system is an essential system of AP1000 nuclear power plants, which works in the non-LOCA accident. It can discharge the waste heat in the reactor core timely, and prevent the reactor accident. The In-Containment Refueling Water Storage Tank (IRWST) is one of the most important equipments of passive residual heat removal system, which supplies the hot trap to the system. The purpose of the paper is to research the natural circulation characteristic of fluid in IRWST. In this paper, FLUENT hydrodynamics analysis software was used to simulate the flow and heat-transfer characteristics of natural convection. Temperature field and flow field in different time or locations were compared to analyze the course of natural circulation. The error was evaluated by comparing the average temperature on the outlet of heat exchanger and the design temperature. The result showed that FLUENT could simulate the flow and heat-transfer characteristics of natural convection, and the error of the simulation was acceptable. In conclusion, natural convection heat exchanger of the study can discharge the waste heat in the reactor core timely. Due to the complex structure of the heat exchanger and the IRWST, the “heat-transfer dead zones” and “flow dead zones” are generated in local parts. The presence of dead zones affects the formation of natural convection. With the development of natural circulation, the temperature field and flow field in the IRWST keep stable and the temperate rise rate become slowly.