Abstract: A method of melting treatment of radioactive miscellaneous solid wastes containing therein an electrically conductive substance and other waste components. This method comprises charging the radioactive miscellaneous solid wastes into a cold crucible induction melting furnace provided with a high-frequency coil; supplying a high-frequency current to the high-frequency coil of the melting furnace to thereby heat and melt the electrically conductive substance, e.g. a metal, in the miscellaneous solid wastes; indirectly heating the other components in the miscellaneous solid wasted by utilizing the electrically conductive substance as a starting source of heating and melting; and placing the whole of the radioactive miscellaneous solid wastes into a molten state.

Abstract: A method for regenerating a spent solvent generated from a nuclear fuel cycle and containing a higher hydrocarbon (n-dodecane), tributyl phosphate and degradation products thereof. The spent solvent is brought into contact with a methanol/water mixture having a water concentration of 100 to 750 g/l and the resulting mixture is subjected to phase separation to form a non-methanol/water phase and a methanol/water phase. The degradation products such as DBP in the spent solvent selectively migrate into the methanol/water phase and n-dodecane and TBP can be recovered as the non-methanol/water phase.

Abstract: The invention provides a method of recovering and storing radioactive iodine by a freeze vacuum drying process, in which off-gas generated when spent fuel is subjected to shearing and dissolving treatments is scrubbed and, when necessary, is subjected to a precipitation treatment by addition of additives, after which waste liquid containing radioactive iodine is freeze-dried by a freeze vacuum drying process to recover radioactive iodine as iodine compounds. As a result, since the radioactive iodine does not vaporize, release of the radioactive iodine into the environment can be eliminated. In addition, consumption of a collecting agent such as silver zeolite for collecting vaporized radioactive iodine can be reduced. The iodine compounds containing the recovered radioactive iodine is given the same composition as a stable, naturally occurring mineral and is solidified and mineralized as by a high-pressure press. This makes it possible to store long half-life .sup.

Abstract: A method of concentrating a plutonium nitrate solution comprising the steps of cooling the plutonium nitrate solution to a temperature of -60.degree. to -40.degree. C. to produce a frozen matter comprising water and nitric acid, and filtering the thus produced frozen matter to recover a concentrated plutonium nitrate solution as a filtrate.

Abstract: A method of separating uranium and plutonium from a mixed solution containing uranium nitrate and plutonium nitrate comprises cooling the mixed solution to a temperature ranging from -40.degree. to -20.degree. C. to thereby selectively precipitate uranyl nitrate. The precipitated uranyl nitrate is separated from the solution while leaving plutonium nitrate to remain in the solution.

Abstract: A method for thermal decomposition treatment of a radioactive waste uses an apparatus comprising a container for holding molten matter of a radioactive waste containing a sodium compound, a pair of electrodes contacting the molten matter, and a power source for applying voltage between the electrodes while changing the polarity thereof every several tens of seconds. In this apparatus, the molten matter can be heated in the container by Joule heat, which is evolved by electric current directly flowed through the molten matter, so that the sodium compound contained in the radioactive waste can be decomposed, vaporized and removed to recover a stabilized radioactive solid as a residue in the container.

Abstract: A method for the heat treatment of a radioactive substance by microwave power comprising preparing a nitrate solution of uranium, thorium, plutonium or a mixture thereof, and applying to the nitrate solution microwave energy sufficient to directly convert the nitrate solution into an oxide powder of uranium, thorium, plutonium or a mixture thereof, respectively. Such oxide powder is suitable for the manufacture of nuclear fuel pellets.

Abstract: A method for wearing and taking off a protective suit which is used when entering the inside of a working zone segregated from the outside thereof. The protective suit has a cylindrical portion made of a film-like fusible material and is designed so that one can get into or out of the suit by passing through the cylindrical portion. When wearing the protective suit, one gets into the suit by passing through the cylindrical portion, with the protective suit being kept joined to an entrance/exit section of the working zone, and then part of the cylindrical portion is fused and closed to segregate the inside of the suit from the outside thereof while sealing the entrance/exit section with a pouch-like member.