Spent fuel reprocessing method

Abstract

A spent fuel reprocessing method has a dissolution step of dissolving the spent fuel in nitric acid solution, an electrolysis/valence adjustment step of reducing Pu to trivalent, maintaining the pentavalent of Np, a uranium extraction step of collecting UO 2 by bringing the fuel into contact with organic solvent and extracting hexavalent U by means of an extraction agent, an oxalic acid precipitation step of causing MA and the fissure products remaining in the nitric acid solution to precipitate together as oxalic acid precipitate, a chlorination step of converting the oxalic acid precipitate into chlorides by adding hydrochloric acid to the oxalic acid precipitate, a dehydration step of synthetically producing anhydrous chlorides by dehydrating the chlorides in a flow of Ar gas, and a molten salt electrolysis step of dissolving the anhydrous chlorides into molten salt and collecting U, Pu and MA at the cathode by electrolysis.

1 . A spent fuel reprocessing method comprising:
 a disassembly/shear step of disassembling and shearing spent oxide nuclear fuel;   a dissolution step of dissolving the fuel subjected to the disassembly/shear step in nitric acid solution;   an electrolysis/valence adjustment step of reducing plutonium to trivalent, maintaining the pentavalent of neptunium for the fuel subjected to the dissolution step;   a uranium extraction step of collecting uranium oxide by bringing the fuel subjected to the electrolysis/valence adjustment step into contact with organic solvent and extracting hexavalent uranium by means of an extraction agent;   an oxalic acid precipitation step of causing the minor actinides and the fissure products remaining in the nitric acid solution after the uranium extraction step to precipitate together as oxalic acid precipitate by means of an oxalic acid precipitation method;   a chlorination step of converting the oxalic acid precipitate into chlorides by adding hydrochloric acid to the oxalic acid precipitate;   a dehydration step of synthetically producing anhydrous chlorides by dehydrating the chlorides in a flow of reductive inert gas; and   a molten salt electrolysis step of dissolving the anhydrous chlorides into molten salt and collecting uranium, plutonium and minor actinides at the cathode by electrolysis.   
     
     
         2 . A spent fuel reprocessing method comprising:
 a disassembly/shear step of disassembling and shearing spent oxide nuclear fuel;   a dissolution step of dissolving the fuel subjected to the disassembly/shear step in nitric acid solution;   an electrolysis/valence adjustment step of reducing plutonium and neptunium respectively to trivalent and pentavalent for the fuel subjected to the dissolution step;   a uranium extraction step of collecting uranium oxide by bringing the fuel subjected to the electrolysis/valence adjustment step into contact with organic solvent and extracting hexavalent uranium by means of an extraction agent;   an oxalic acid precipitation step of causing the minor actinides and the fissure products remaining in the nitric acid solution after the uranium extraction step to precipitate together as oxalic acid precipitate by means of an oxalic acid precipitation method;   an oxidation/dehydration step of dehydrating the oxalic acid precipitate and subsequently converting it into precipitate oxides in an oxidation atmosphere; and   an electrolysis/reduction step of immersing the precipitate oxides in a mixture of molten salts obtained by dissolving alkali metal oxides in molten salts of chlorides of alkali metals or a mixture of molten salts obtained by dissolving alkaline-earth metal oxides in molten salts of chlorides of alkaline-earth metals, bringing the precipitate oxides into contact with a cathode to drawn out oxygen ions in the precipitate oxides, removing the oxygen ions as oxygen gas or carbon dioxide gas at the side of an anode in the molten salts and collecting uranium, plutonium and minor actinides in the precipitate oxides at the cathode.   
     
     
         3 . The method according to  claim 2 , wherein
 the electrolysis/reduction step is conducted by containing the precipitate oxides in a stainless-steel-made cathode basket, immersing the cathode basket in the molten salts and connecting the cathode to the cathode basket.   
     
     
         4 . The method according to  claim 2 , wherein
 the mixture of molten salts is a mixture of molten salts obtained by dissolving Li 2 O in molten salt of LiCl, a mixture of molten salts obtained by dissolving MgO in molten salt of MgCl 2  or a mixture of molten salts obtained dissolving CaO in molten salt of CaCl 2 .   
     
     
         5 . The method according to  claim 3 , wherein
 the mixture of molten salts is a mixture of molten salts obtained by dissolving Li 2 O in molten salt of LiCl, a mixture of molten salts obtained by dissolving MgO in molten salt of MgCl 2  or a mixture of molten salts obtained dissolving CaO in molten salt of CaCl 2 .   
     
     
         6 . The method according to  claim 1 , further comprising:
 a fission product collection step of putting the filtrate left without precipitating in the oxalic acid precipitation step into a cathode chamber, putting a cathode made of an insoluble material into the cathode chamber, putting acidic solution into an anode chamber separated from the cathode chamber by a diaphragm for electrolysis and depositing and collecting fission products of the platinum group remaining in the filtrate at the cathode.   
     
     
         7 . The method according to  claim 2 , further comprising:
 a fission product collection step of putting the filtrate left without precipitating in the oxalic acid precipitation step into a cathode chamber, putting a cathode made of an insoluble material into the cathode chamber, putting acidic solution into an anode chamber separated from the cathode chamber by a diaphragm for electrolysis and depositing and collecting fission products of the platinum group remaining in the filtrate at the cathode.   
     
     
         8 . The method according to  claim 1 , wherein
 the electrolysis/valence adjustment step is conducted at or lower than −100 mV relative to a silver/silver chloride electrode operating as reference electrode.   
     
     
         9 . The method according to  claim 2 , wherein
 the electrolysis/valence adjustment step is conducted at or lower than −100 mV relative to a silver/silver chloride electrode operating as reference electrode.   
     
     
         10 . The method according to  claim 1 , wherein
 the electrolysis/valence adjustment step is conducted with a cathode current density between 20 mA/cm 2  and 40 mA/cm 2  relative to a silver/silver chloride electrode operating as reference electrode.   
     
     
         11 . The method according to  claim 2 , wherein
 the electrolysis/valence adjustment step is conducted with a cathode current density between 20 mA/cm 2  and 40 mA/cm 2  relative to a silver/silver chloride electrode operating as reference electrode.