Patent ID: 6793799
Filing Date: 2004-09-21
Classification: C01B,C25C,G21C,G21F,G21G,H01M,Y02E,Y02P,Y02W

Abstract:
A method of separating and recovering rare FP in spent nuclear fuels comprising:a step A of supplying a nitric acid solution to be processed at a nitric acid concentration of 0.1 to 4.5 M containing one or more of rare FP (fission products) selected from the group consisting of platinum group elements, Ag (silver), Tc (technetium), Se (selenium) and Te (tellurium) generated from a reprocessing step of spent nuclear fuels used in nuclear power generation facilities including light water reactors or fast reactors, to a cathode chamber together with Pd2+ (palladium) or Fe2+ (iron) as a catalyst, and conducting electrolytic reduction at a current density of 1 to 3000 mA/cm2 while supplying a pure nitric acid solution at a nitric acid concentration of 0.1 to 4.5 M to an anode chamber, thereby collectively depositing Ru (ruthenium), Rh (rhodium) and Pd as platinum group elements, and Ag, Tc, Se and Te in the nitric acid solution to be processed on the cathode; a step B of switching the cathode to the anode and conducting electrolytic oxidation at a set potential of 1.5 to 3 V while supplying a pure nitric acid solution at a nitric acid concentration of 3 to 5 M, thereby collectively dissolving the deposits on the electrode into the pure nitric acid solution; a step C of switching the anode to the cathode and conducting electrolytic reduction at a current density of 1 to 25 mA/cm2 while supplying the deposit-dissolved nitric acid solution at a nitric acid concentration of 0.1 to 4.5 M to the cathode chamber and supplying a pure nitric acid solution at a nitric acid concentration of 0.1 to 4.5 M to the anode chamber, thereby selectively depositing Pd and Ag in the deposit-dissolved nitric acid solution on the cathode; a step D of switching the cathode to the anode and conducting electrolytic oxidation at a set potential of 1.5 to 3 V while supplying a pure nitric acid solution at a nitric acid concentration of 3 to 5 M, thereby dissolving the deposits Pd and Ag on the electrode into the pure nitric acid solution and recovering them; a step E of switching the anode to the cathode and conducting electrolytic reduction at a current density of 25 to 100 mA/cm2 while supplying the deposit-dissolved and Pd.Ag-removed nitric acid solution at a nitric acid concentration of 0.1 to 4.5 M to the cathode chamber and supplying a pure nitric acid solution at a nitric acid concentration of 0.1 to 4.5 M to the anode chamber, thereby selectively depositing Se and Te in the deposit-dissolved and Pd.Ag-removed nitric acid solution on the cathode; a step F a switching the cathode to the anode and conducting electrolytic oxidation at a set potential of 1.5 to 3 V while supplying a pure nitric acid solution at a nitric acid concentration of 3 to 5 M, thereby dissolving the deposits Se and Te on the electrode into the pure nitric acid solution and recovering them; a step G of switching the anode to the cathode and conducting electrolytic reduction at a current density of 100 to 700 mA/cm2 while supplying the deposit-dissolved and Pd.Ag.Se.Te-removed nitric acid solution at a nitric acid concentration of 0.1 to 4.5 M to the cathode chamber and supplying a pure nitric acid solution at a nitric acid concentration of 0.1 to 4.5 M to the anode chamber, thereby selectively depositing Ru, Rh and Tc in the deposit-dissolved and Pd.Ag.Se.Te-removed nitric acid solution on the cathode; and a step H of switching the cathode to the anode and conducting electrolytic oxidation at a set potential of 1.5 to 3 V while supplying a pure nitric acid solution at a nitric acid concentration of 3 to 5 M, thereby dissolving deposits Ru, Rh and Tc on the electrode into the pure nitric acid solution and recovering them.