Abstract: To predict the accident scenario caused by the total instantaneous inlet blockage of single fuel subassembly at full power(TIB) in fast reactors, a model was developed according to the SCARABEE experiments. The calculation results for the SCARABEE BE+1 experiment agree well with the experimental observation. The model was then applied to an actual reactor to predict the consequences of TIB. In actual reactors, the cooling condition outside the hexcan-wall of blocked fuel subassembly is analogous to its counterparts in the SCARABEE BE+ experiments. The upward and downward heat transfer could be neglected, while the radial heat transfer plays a key role in slowdown the accident scenario. As time goes on, the dominant radial heat transfer mechanism is liquidus sodium convection at first, and then gradually transforms into sodium condensation near the inner surface of the hexcan-wall, and finally becomes volume heated boiling pool convection.