Numerical Simulation And Optimized Design Of Passive Residual Heat Removal Heat Exchanger In AP1000

Responsible for discharging decay heat safe and reliable, Passive Residual Heat Removal Heat Exchanger (PRHR HX) and In Containment Refueling Water Storage Tank (IRWST) are key equipments for passive cooling that ensure the safety of the reactor in AP1000. The decay heat is removed by PRHR HX, which is cooled in IRWST. The temperature distribution, flow distribution, thermal stratification and other factors in IRWST have had a significant impact on heat transfer capability of PRHR HX. However, because of complex structure of IRWST and asymmetric arrangement of heat exchanger, the temperature distribution and flow distribution in IRWST is not clear. Furthermore, in order to expand the development of AP1000nuclear power plant technology, higher power of advanced pressurized water reactors have been designed, causing that PRHR HX does not meet the requirement of higher power core. To obtain a greater heat removal capacity, the optimized design on structural of PRHR HX is required to propose. To sum up, The study on IRWST and PRHR HX research is very meaningful.After summarizing previous studies, a model had been established which was obtained by a similarity theory, called Hierarchical Two-Tiered Scaling (H2TS). FLUENT code analyzed the scaled model for2000seconds of transient to investigate the temperature distributions and flow distributions in different locations at different time. The variation of the temperature field and flow field had been summed up. Then, the results of numerical simulation were compared with experimental data. The comparison showed that the numerical simulation can be well simulated single-phase natural convection in tank. Thus, the calculation model and assumption of the numerical simulation were verified to be reasonability.The centralized layout of PRHR HX tubes, which looks like a circle in a section, makes the temperature of fluid outside tubes higher at the locations that closer to the upper of the circle in the horizontal tube section and closer to the center of the circle in the vertical tube section. The temperature difference between the tube side and fluid side is smaller, causing the heat exchanger efficiency is worse at these locations. Then total heat and natural circulation pressure head are decreased. In order to improve the heat transfer effect of PRHR HX, two improved models on structure had been proposed. These models were established and simulated by FLUENT with the calculation model and assumption that had been verified. In comparison results, the effects on heat transfer coefficient under different structure were obtained. It contributes to provide ideas on optimized design of structure for improving the heat transfer effect of PRHR HX.