A conversion techology of long-lived radioactive nuclides is to separate the elements involved in spent fuel and convert them into physical and chemical type suited to fuel for transmutation. This study has been i9nvestigated the experiments for fluorination-dissolution of Zr, UO₂, and CeO₂. These compounds are components involved in spent fuel and especially, Zr is the cladding material of fuel. The fraction of fluorination-dissolution was increased linearly with time. Zr and UO₂ were converted respectively 24.2,5.2% after 3hours. CeO₂ was converted into fluoride only 0.19%. This is considered to be due to the solubility of H₂ in the LiF-BeF₂ molten salt. Because hydrogen is used to reduce CeO₂ to CeF₃ but the solubility of H₂ is very low in the molten salt.