Abstract: Sodium cooled fast reactors mostly use metal wires to space the fuel assembly, and slender and narrow flow channels are easy to accumulate corrosive sediments, which tends to cause the local sodium boiling and heat transfer deterioration of cladding. In this paper, single subassembly blockage accidents were numerically simulated by the commercial computation fluid dynamics (CFD) software STAR-CCM+, temperature of cladding inner face and coolant axial velocity distribution around blockage were analyzed and compared with the result in no-blockage case. The calculation results show that the harm of solid media blockage is more serious than that of porous media. The local highest point of cladding peak temperature is always located at the centric position of the blockage in the solid media blockage accidents. But in the porous media blockage accidents, the cladding peak temperature is found in the downstream of blockage and tends to move further downstream with the increase of blockage area. The blockage porosity is seen to exhibit significant influence on the maximum cladding temperature difference in the downstream of blockage. Further, the maximum cladding temperature difference is smaller if the porosity is larger.