A Criticality safety study for the disposal of damaged fuel debris

Liu, X.*; Ahn, J.*; Hirano, Fumio 

The present work focuses on neutronics analysis for the disposal of damaged fuels from Fukushima Nuclear Power Plants. MCNP calculations were performed for a canister containing fuel debris surrounded by buffer in deep geologic repository in a water-saturated reducing environment at different times after canister emplacement. The damaged fuel debris is modeled as spherical particles in a hexagonal lattice. Four different cases were compared based on various assumptions about moderation and fuel relocation. Based on the numerical results, the key findings include, (a) the calculated neutron multiplication factor () is sensitively dependent on assumptions related with moderation, (b) the carbon steel canister plays an important role in reducing the likelihood of criticality, (c) the maximum of the canister-buffer system could be achieved after a certain fraction of fissile nuclides has been released from the canister, and (d) under several assumptions, the maximum of the canister-buffer system could be only determined by the dimension and composition of the canister rather than the initial fuel loading.