Process for the processing of irradiated reactor fuel 12-40 times higher substances

摘要

An aqueous solution of irradiated nuclear fuel is subjected to a single cycle extraction with an organic solvent and then the organic phase is contacted with an aqueous extraction agent to produce an aqueous extract stream containing uranium and at least one of the fission products ruthenium, zirconium and niobium, the aqueous stream is dehydrated, the solid residue fluorinated, and uranium fluoride separated from fission product fluoride. In a process described with reference to a flow diagram, uranium dioxide fuel elements are dissolved in nitric acid and the solution is introduced at about the middle of an extraction column where it flows downwards in countercurrent with diethoxybutane or dimethoxypentane; a stripping nitric acid solution is fed into the top of the column. The organic solvent extracts uranium, plutonium, and some of the fission products specified above, leaving the rest of the fission products in the aqueous phase which is evaporated and calcined, nitric acid being recovered. The organic phase is contacted in a second column with a nitric acid solution containing ferrous iron, which reduces and extracts the plutonium. The organic phase from the second column contains uranium and the specified fission products, all of which are returned to aqueous solution by contact in a third column with very dilute nitric acid. The solvent from this column is purified by distillation and used again for extraction; the aqueous solution is evaporated, the residue calcined and treated with HF at 250-350 DEG C. and with F2 at 300-600 DEG C. to form volatile fluorides. The vapours are passed through a partial condenser and a separator, where fission product fluorides are removed, leaving a stream of pure UF6. Alternatively fluorination may take place with F2 alone, and separation of the fluorides may be effected by fractional distillation. In a modified process, the organic solvent is a solution of tributyl phosphate in kerosene, which is purified by extraction with aqueous sodium carbonate solution. Other organic solvents referred to are methyl isobutyl ketone, dibutyl carbitol, and amines.