Preliminary Investigation of THFR Passive Residual Heat Removal System

Abstract The RELAP5 code was employed to study the natural circulation characteristics and core thermal-hydraulic parameters of THFR (Tsinghua High Flux Reactor) under the condition that only the passive residual heat removal system was used when the emergency cooling pump powered by the battery bank shut down due to power exhaustion. To achieve a higher neutron flux, high flux reactor possesses several distinctive properties, including high power density, narrow coolant channels, and low coolant pressure., so the loss of heat sinks under accident conditions can be catastrophic, Therefore, it is necessary to establish a passive residual heat removal system. This study compared the two-loop and three-loop schemes, The results showed that both schemes can reliably establish natural circulation and efficiently remove core residual heat. Throughout the process, the maximum temperatures of the coolant, cladding surface, and fuel meat were below the design limits. Because the maximum temperature of the cladding surface was lower than the saturation temperature, the DNB phenomenon did not appear in the core. The three-loop scheme, with lower total resistance and higher coolant flow rate, is more favorable for improving the thermal safety of the reactor. It also has a lower overall heat transfer area, which helps reduce the cost of heat exchangers.