Thermohydraulic transient studies of the Chinese 200 MWe HTR-PM for loss of forced cooling accidents

Abstract

Pressurized and Depressurized Loss Of Forced Cooling (PLOFC and DLOFC) are two important design basis accidents for high temperature gas-cooled reactors. Analysis of the reactor characteristic behaviors during LOFC can provide useful reference to the physics, thermohydraulic and structure designs of the reactor core, and can also verify the design of the Residual Heat Removal System (RHRS). The 200 MWe High Temperature gas-cooled Reactor Pebble-bed Module project (HTR-PM), designed by the Institute of Nuclear and New Energy Technology (INET) of Tsinghua University in China, is characterized by its inherent safety features, such as shutdown ability via negative temperature coefficients of reactivity, passive mechanism of decay heat removal and so on. In this paper, two cases of loss of forced cooling accidents have been analyzed by using THERMIX code based on the preliminary design of the HTR-PM. With respect to the DLOFC, the effects of related key parameters on the maximum temperatures of fuel element and the reactor pressure vessel (RPV), as well as the decay heat removal by the RHRS are studied in detail. From the calculation results, it is shown that, in the LOFC accidents, the maximum temperatures of the fuel element and the RPV are below the safety limits and the RHRS can effectively remove the decay heat from the core, so as to keep the reactor in a safe state. As compared with the PLOFC accident, the DLOFC accident will lead to a much higher fuel element temperature but lower RPV temperatures and RHRS heat load. The analyses also illustrate that the decay heat level, the emissivity of RPV and water-cooling panel, and the average temperature of the water-cooling panel, play important roles in the DLOFC accident.