The annular fuel assembly of lead-bismuth cooled fast reactor has many safety advantages, but during its operation, due to the corrosive effect of lead-bismuth coolant, it is prone to blockage accidents, resulting in deterioration of heat transfer and jeopardizing the integrity of the first barrier. Therefore, it is urgent to research and analyze the blockage accident for the annular fuel assembly of the lead-bismuth-cooled fast reactor.

A 5×5 single annular fuel assembly model was established, and numerical simulations for blockage of the inner and outer channel were carried out with different blockage areas, blockage thicknesses, and axial position of the blockage based on the computational fluid dynamics (CFD) software Fluent. The temperature distribution of the claddings, the flow field distribution near the blockage, the mass flow change of the channel, the radial temperature distribution, and the heat distribution of the fuel element at the blockage are compared with the result in no-blockage case.

Simulation results indicate that the increase in the blockage area leads to a significant increase in the cladding temperature of the blockage area, an expansion of the scope of the recirculation area expands, the position of the highest temperature point of the fuel pellet shifts to the blockage side, and the heat flux density on the blockage side decreases. When the blockage fraction is large, the changes of parameters are similar to the above conclusions as the blockage thickness increases; when the blockage is located at the entrance, the local temperature rise of the cladding is smaller than that when the blockage is located at the center; with the increase of the blockage area and thickness and as the blockage position gets closer to the entrance of the active zone, the flow loss of the inner channel increases significantly, while the flow of the outer channel is almost unaffected.

Therefore, the damage is more serious when the blockage accident occurs in the inner channel.