The Steady States and DLOFC Accident Analysis of HTR-PM in the OTTO Operation Scheme

Abstract High Temperature gas-cooled Reactor – pebble bed module (HTR-PM) located in Shidao Bey, Shangdong province, China, which is the first commercial HTR in the world, adopts spherical fuel element with TRISO particle and graphite material as moderator. As the national demonstration project of China, the outlet coolant temperature of HTR-PM can reach 750 degrees and more than 550 degrees of steam, this reactor can be used not only in electrical power generation, but also in industrial heat source supply, hydrogen production and petrochemical industries. Besides, the module design can decrease the financial cost during the construction period, and shorten the time in manufacturing. For the online reloading operation, the MEDUL scheme was adopted in HTR-PM operation with 15 fuel batches. To shorten the running-in phase and simplify the reloading system, the OTTO scheme can be adopted to replace MEDUL in HTR-PM operation, in this paper, the steady states calculation based on VSOP-THERMIX has demonstrated the neutronic and thermal hydraulics parameters of HTR-PM in the OTTO scheme from initial critical situation to equilibrium states. With different assumed OTTO operation schemes, the spatial displacement of max power density and max fuel temperature in the core is shown in every loading step. Meanwhile, due to the moderation ability of graphite, the isotope content of uranium and plutonium compared with different loading methods. Last, based on the coupled calculation of equilibrium states, the maximum fuel temperature analysis of DLOFC in every loading stage by THERMIX demonstrates HTR-PM with OTTO scheme still keeping inherent safety features. The results show the fraction of fuel elements in different loading stages has an effective influence on maximum fuel temperature.