Analysis Of Blockage Accident For Single Assembly Of LBE-cooled Fast Reactor

The fourth-generation nuclear systems is a new generation system aiming at improving the economics, safety, proliferation resistance of the nuclear system. As one of six candidates for the generation-fourth nuclear reactor type, lead(lead-bismuth) cooled fast reactor has good prospects for development, and has gradually become an important direction for future advanced reactors.Lead-bismuth alloy have good neutron properties, thermal-hydraulic performance and inherent safety. However, reactor s cladding and structural materials would be seriously erode by lead-bismuth as the result of the extremely high temperature in the nuclear reactor. The corrosion products of lead-bismuth which accumulate in the fuel assembly will reduce the flow area of LBE coolants, namely blockage accident. This is one of the most important issues for lead-bismuth cooled reactor safety analysis works.In this paper, the10MW lead-bismuth cooled fast research reactor,which was designed by the FDS team, was studied using a commercial computational fluid dynamics (CFD) software ANSYS CFX. The single cartridge assembly blocking accident was analysised. Detailed works are described in the following:Firstly, a single cartridge assembly model and blocking flow model were constructed by the use of CFX; secondly, based on the consideration of grid independence%turbulence model and other factors, a single cartridge assembly in the normal operating conditions is simulated and analyzed; thirdly, a single cartridge assembly for blocking the corners and center of the flow channel is simulated. Results show us that, the outlet coolant temperature and the highest temperature of the fuel cladding increased accompanying the increasing blockaging area of inlet and the middle of the fuel pin bundles. the larger the blockage area the quicker the temperature arises. Corner blockage condition is more severe than the center blockage condition. Backflow occurs on the back of the clog when blockage accident happens and backflow area increases in accordance with the blockage area increase. In different blockage axial locations, the cladding temperature is the highest when x=0.5m. When corner blockage area reaches80%in the middle of the fuel pin bundles, part of the cladding temperature may beyond the melting point of materials which may result in the melt of some of the fuel claddings and then fuels has the risk to expose in the coolant.