Patent Number: 
Section: claims

1. A process of recycling sodium salt in a wet reprocessing process of a spent nuclear fuel, comprising:a neutralization step in which a nitric acid liquid waste or an off-gas having nitric acid dissolved therein which is produced through a wet reprocessing process comprising a dissolution step for dissolving a spent nuclear fuel in nitric acid is neutralized by adding or contacting one or more sodium salts selected from the group consisting of sodium hydroxide, sodium hydrogencarbonate and sodium carbonate to or with the nitric acid liquid waste or the off-gas, thereby yielding a sodium nitrate liquid waste;a sodium nitrate-decomposition step in which the sodium nitrate liquid waste obtained in the neutralization step is reductively decomposed with a reducing agent, thereby decomposing sodium nitrate into a nitrogen gas and the sodium salt(s); anda recycle step for recycling the sodium salt(s) produced in the sodium nitrate-decomposition step into the neutralization step or the wet reprocessing process,wherein the reductive decomposition in the sodium nitrate-decomposition step is carried out by reductive decomposition using a reducing agent and a catalyst or by reductive decomposition using a reducing agent under supercritical conditions where water serves as a supercritical fluid. 2. The process according to claim 1, further comprising an evaporative concentration step in which the sodium nitrate liquid waste obtained in the neutralization step is concentrated by evaporation, and the concentrated sodium nitrate liquid waste obtained in the evaporative concentration step is reductively decomposed in the sodium nitrate-decomposition step. 3. The process according to claim 1, wherein a part of the sodium salt(s) to be recycled in the recycle step is brought and mixed in a solidified substance of a radioactive waste for solidification. 4. The process according to claim 1, wherein a part of the sodium salt(s) to be recycled in the recycle step is brought and mixed in a vitrified waste of a high-level radioactive waste for use as a part of a glass raw material. 5. A process of recycling sodium salt in a wet reprocessing process of a spent nuclear fuel, comprising:an organic solvent washing step in which an organic solvent used in a wet reprocessing process of a spent nuclear fuel is washed with one or more sodium salts selected from the group consisting of sodium hydroxide, sodium hydrogencarbonate and sodium carbonate;a neutralization step in which a liquid waste of the sodium salt(s) produced in the organic solvent washing step is neutralized with nitric acid, thereby yielding a sodium nitrate liquid waste;a sodium nitrate-decomposition step in which the sodium nitrate liquid waste produced in the neutralization step is reductively decomposed with a reducing agent, thereby decomposing sodium nitrate into a nitrogen gas and the sodium salt(s); anda recycle step for recycling the sodium salt(s) produced in the sodium nitrate-decomposition step into the organic solvent washing step or the wet reprocessing process,wherein the reductive decomposition in the sodium nitrate-decomposition step is carried out by reductive decomposition using a reducing agent and a catalyst or by reductive decomposition using a reducing agent under supercritical conditions where water serves as a supercritical fluid. 6. The process according to claim 5, further comprising an evaporative concentration step in which the sodium nitrate liquid waste obtained in the neutralization step is concentrated by evaporation, and the concentrated sodium nitrate liquid waste obtained in the evaporative concentration step is reductively decomposed in the sodium nitrate-decomposition step. 7. The process according to claim 5, wherein a part of the sodium salt(s) to be recycled in the recycle step is brought and mixed in a solidified substance of a radioactive waste for solidification. 8. The process according to claim 5, wherein a part of the sodium salt(s) to be recycled in the recycle step is brought and mixed in a vitrified waste of a high-level radioactive waste for use as a part of a glass raw material. 9. The process according to any one of claims 1 to 6, wherein a part of the sodium salt(s) to be recycled in the recycle step is brought and mixed in a solidified substance of a radioactive waste for solidification. 10. The process according to any one of claims 1 to 6, wherein a part of the sodium salt(s) to be recycled in the recycle step is brought and mixed in a vitrified waste of a high-level radioactive waste for use as a part of a glass raw material.