Reprocessing method for spent nuclear fuel

Spent nuclear fuels are dissolved to form a dissolution solution containing uranium, plutonium, minor actinoids and fissionable nuclides. Ammonium peroxodisulfate is added to the dissolution solution in a denitrating/valency controlling vessel to control the uranium, americium, neptunium, plutonium to VI valency. Further, TBP is added to them in an extraction vessel to discharge fissionable nuclides containing rare earth elements as high level liquid wastes, and uranium, plutonium, neptunium and americium are extracted by a solvent. An aqueous solution of nitric acid containing a reducing agent is supplied to the organic phases in a distributer to maintain uranium to VI valency, plutonium to III valency, neptunium to V valency, and americium to III valency, and the mixture of plutonium, americium and neptunium is back-extracted. This can avoid sole extraction of plutonium, thereby enabling to simplify the processing step sufficiently. (T.M.)