Abstract: A method of vitrifying a high-level radioactive liquid waste comprising removing a precipitate composed mainly of Mo and Zr from the high-level liquid waste, mixing the resulting high-level liquid waste with a raw glass material having a chemical composition wherein the B.sub.2 O.sub.3 /SiO.sub.2, ZnO/Li.sub.2 O and Al.sub.2 O.sub.3 /Li.sub.2 O ratios are at least 0.41, at least 1.00 and at least 2.58, respectively, and melt-solidifying the mixture to thereby form a vitrified waste. By using such a raw glass material, there can be obtained a vitrifled waste having the waste content of about 45% by oxide weight in which the same leaching rate as that of a conventional vitrified waste having the waste content of 25% by oxide weight is ensured without suffering from yellow phase separation.

Abstract: A method of recovering volatile ruthenium, which is separated and formed by constant potential electrolysis from high-level radioactive liquid waste discharged from the reprocessing step of spent nuclear fuel by purex process, in the form of stable solid. The method comprises electrolyzing at a constant potential a high-level radioactive liquid waste from which palladium has substantially been removed in advance, thereby vaporizing ruthenium, bringing the vaporized ruthenium into contact with an aqueous solution of formic acid to precipitate ruthenium oxide, and separating the precipitate from the aqueous solution of formic acid.

Abstract: A method of treatment of a high-level radioactive waste containing platinum group elements is provided in which boron and a boron compound is added to a calcined material of the high-level radioactive waste in an amount of 0.5 to 10% by weight in terms of boron as a simple substance, and the resultant mixture is heated at a temperature of about 1000.degree. C. or above under a reduction condition to melt the mixture and to alloy the platinum group elements present in the calcined material with boron. A layer of the resultant platinum group element alloys is then separated and recovered from a layer of residual oxides through sedimentation. The layer of the residual oxides is solidified to form a highly volume-reduced high-level radioactive solidified waste.