Patent Number: 049816160
Section: summary

BACKGROUND OF THE INVENTION This invention relates to a method of treating spent fuel utilizable in a spent nuclear fuel retreatment process, scrap nuclear fuel wet reclamation process, etc. Ordinarily, in spent nuclear fuel re-treatment and scrap nuclear fuel wet reclamation processes, organic solvent used in an extraction process is degraded by the effects of acidity and radiation. Consequently, the degraded products are removed from the organic solvent by a solution of sodium hydroxide or sodium carbonate, after which the solvent is reused. Certain shortcomings, however, exist in such conventional methods. These are as follows: (1) Reclamation of organic solvent in which there is advanced deterioration is impossible, and the solvent becomes a liquid radioactive waste that is difficult to treat. (2) A solution containing sodium is mixed with radioactive liquid waste of the nitrate family, after which the resulting solution is reduced in volume and solidified in glass or asphalt. However, owing to the large amount of sodium contained, the reduction in volume has its limitations. This also accounts for complicated solidification treatments. In view of the foregoing, there is a need to develop a process which minimizes the use of sodium as well as a solvent reclamation process. Further, though evaporation cans are used to concentrate radioactive material in treatment of liquid radioactive wastes, these are disadvantageous because decontamination is inefficient and the cans are subject to considerable corrosion. It is desired, therefore, that a treatment process with a higher decontaminating efficiency and less corrosion be developed. SUMMARY OF THE INVENTION This invention has been devised to solve the foregoing problems and its object is to provide a method of treating spent fuel in which a salt-free process is capable of being employed. Another object of the invention is to provide a method of treating spent fuel in which, by using a freeze-vacuum drying process, material corrosion is eliminated by operation at low temperatures, safety is enhanced by eliminating the danger of fire, explosion and the like, and use of organic substances containing sodium is minimized to enable reduction and simplification of equipment for asphalt and glass solidification. Still another object of the invention is to provide a method of treating spent fuel in which recovered solution can be reutilized and liquid radioactive waste reduced in volume. A further object of the invention is to provide a method of treating spent fuel in which solvent can be reutilized and liquid radioactive waste reduced in volume by employing a vacuum distillation process, which has a high decomtamination efficiency, in the recovery of the solvent. The invention provides a method of treating spent fuel in a spent nuclear fuel retreatment process and scrap nuclear fuel wet reclamation process, characterized by separating a spent solvent of a solvent cleansing process into tri-n-butyl phosphate (hereinafter referred to as TBP), n-dodecan and dibutyl phosphate (hereinafter referred to as DBP) by using a freeze-vacuum drying process and vacuum distillation process. Further, the invention provides a method of treating spent fuel in a spent nuclear fuel retreatment process and scrap nuclear fuel wet reclamation process, characterized by separating a liquid radioactive waste into liquid and residue by using a freeze-vacuum drying process in treatment of the liquid radioactive waste. Further, the invention provides a method of treating spent fuel in a spent nuclear fuel retreatment process and scrap nuclear fuel wet reclamation process, characterized by obtaining a nitrate by powdering a plutonium solution and a uranium solution using a freeze-vacuum drying process, denitrifying the nitrate and subjecting the same to roasting reduction to obtain an oxide powder. Other features and advantages of the present invention will be apparent from the following description taken in conjunction with the accompanying drawing.