Cladding carburization in irradiated liquid-metal fast breeder reactor carbide pins is analyzed with particular emphasis on sodium-bonding conditions. Original data from the French Project for advanced fuels and the Swelling Project performed by the European Institute for Transuranium Elements are discussed and compared with published results. The mechanisms of carbon transfer from the fuel to the steel cladding are examined and evaluated concluding that cladding carburization cannot be avoided with the present sodium-bonded pin design if hyperstoichiometric fuel is adopted. An assessment of the pin failure risks involved is made for different steels. Austenitic steels customarily used for cladding do not exhibit a fully satisfactory carburization resistance. Recently developed ferritic alloys are suggested for carbide fuel cladding in future applications.