JP2013002855A - Used fuel reprocessing method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To more efficiently precipitate and collect uranium in an oxalic acid precipitation step in a used fuel reprocessing method.SOLUTION: A used fuel reprocessing method 1 includes a dissolution step 2 of dissolving a used oxide fuel to a nitric acid solution, electrolytic reduction valence adjustment step 4 for uranium extraction of reducing plutonium to be trivalent, a centrifugal extraction step 5 of collecting hexavalent uranium, an electrolytic reduction valence adjustment step 6 for oxalic acid precipitation of adjusting valence of uranium residual in the nitric acid solution from hexavalent to quadrivalent, an oxalic acid precipitation step 7 of precipitating valence adjusted uranium, minor actinide and fission product as oxalic acid precipitate, an oxide transformation step 8 of transforming the oxalic acid precipitate to a precipitate oxide, and an electrolytic reduction step 9 of immersing the precipitate oxide in mixed fused salt, bringing the precipitate oxide in contact with a cathode and collecting uranium, plutonium and minor actinide in the precipitate oxide.

Description

  The present invention relates to a spent fuel reprocessing method in which unnecessary fission products are separated from spent fuel and reused as fuel.

  Spent fuel generated from nuclear power plants contains fission products such as alkali metals, alkaline earth metals and rare earths in addition to uranium and transuranium elements. Can be reused.

  In the conventional wet reprocessing method including the Purex method, after the spent fuel is dissolved in an aqueous nitric acid solution, the fission product is separated in the co-decontamination step, and then U and Pu are separated in the U and Pu distribution step. Separation, U and Pu are purified in U purification process and Pu purification process, respectively, Pu solution is mixed with U solution and denitrated, and U and Pu are once separated in distribution process It is hard to say that there is absolute nuclear non-proliferation.

  Therefore, most of the uranium is separated from the spent fuel solution by the wet reprocessing method to recover high purity uranium oxide for light water reactors, and minor actinides such as Pu, Np, Am, and Cm (MA) by the dry reprocessing method. A so-called hybrid reprocessing method combining a wet reprocessing method and a dry reprocessing method has been developed (see, for example, Patent Document 1). According to this method, it is possible to realize a reprocessing process with high nuclear non-proliferation, that is, Pu that cannot be recovered alone.

  In addition, in the conventional wet reprocessing method, a technology has been developed to adjust the amount of U and Pu precipitated in the oxalic acid precipitation process by providing an electrolytic reduction process before the oxalic acid precipitation process and adjusting the valence of uranium. (For example, see Patent Document 2).

JP 2009-288178 A Japanese Patent No. 3100022

  However, although the technique described in Patent Document 1 described above employs an oxalic acid precipitation method to precipitate and recover Pu and U from an aqueous nitric acid solution containing Pu and U obtained from the wet reprocessing process. In the nitric acid aqueous solution, some U exists as hexavalent uranyl ions, so in the oxalic acid precipitation step, U exists as hexavalent uranyl ions to produce oxalic acid and salts, and precipitate and recover uranium. There was a problem that it was difficult.

  In addition, the technique described in Patent Document 2 described above is performed for the purpose of adjusting the precipitation amount of U and Pu, and further, uranium oxide for light water reactors in spent fuel is reduced to the total amount of uranium that has not been separated and recovered. On the other hand, since the electrolytic reduction valence adjustment is performed, there is a problem that the cost of equipment capacity and processing time increases.

  Accordingly, an object of the present invention is to provide a spent fuel reprocessing method capable of precipitating and recovering uranium more efficiently in the oxalic acid precipitation step.

  In order to achieve the above object, the spent fuel reprocessing method of the present invention comprises a melting step of disassembling a spent oxide fuel and dissolving a sheared fuel in an aqueous nitric acid solution, and a plutonium dissolved in the aqueous nitric acid solution. The uranium oxide is obtained by contacting the fuel that has undergone the uranium extraction electroreduction valence adjustment step for reducing to trivalent and the uranium extraction electroreduction valence adjustment step with an organic solvent, and extracting hexavalent uranium into the extractant. Extraction step for recovering uranium, electroreduction valence adjustment step for oxalic acid precipitation for adjusting uranium remaining in aqueous nitric acid solution from hexavalent to tetravalent in the centrifugal extraction step, and electrolytic reduction valence adjustment for oxalic acid precipitation An oxalic acid precipitation step in which uranium, minor actinides and fission products whose valences have been adjusted in the process are precipitated as an oxalic acid precipitate by an oxalic acid precipitation method, and dehydrating the oxalic acid precipitate, An oxide conversion step in which it is converted into a precipitate oxide in a crystallization atmosphere, and in a mixed molten salt obtained by dissolving an alkali metal oxide in an alkali metal chloride molten salt or in an alkaline earth metal chloride molten salt Electrolysis in which precipitate oxide is immersed in a mixed molten salt in which alkaline earth metal oxide is dissolved, and this precipitate oxide is brought into contact with the cathode to recover uranium, plutonium and minor actinides in the precipitate oxide. A reduction step.

  According to the present invention, uranium can be collected and recovered more efficiently in the oxalic acid precipitation step of the spent fuel reprocessing method.

1 is a schematic flowchart showing a spent fuel reprocessing method according to a first embodiment of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic cross-sectional view showing a batch electrolyzer used in a U extraction electroreduction valence adjustment step of a spent fuel reprocessing method according to a first embodiment of the present invention. The schematic sectional drawing which shows the flow electrolysis apparatus used at the electrolytic reduction valence adjustment process for oxalic acid precipitation of the spent fuel reprocessing method concerning the 1st Embodiment of this invention. The schematic sectional drawing which shows the electrolytic reduction apparatus used at the electrolytic reduction process of the spent fuel reprocessing method which concerns on the 1st Embodiment of this invention. The schematic flowchart which shows the spent fuel reprocessing method which concerns on the 2nd Embodiment of this invention. The schematic flowchart which shows the spent fuel reprocessing method which concerns on the 3rd Embodiment of this invention.

  Embodiments of the present invention will be described below.

(First embodiment)
(Constitution)
Hereinafter, a spent fuel reprocessing method according to a first embodiment of the present invention will be described with reference to FIGS. 1 to 4. FIG. 1 is a schematic flowchart showing a spent fuel reprocessing method according to the first embodiment of the present invention.

  The spent fuel reprocessing method 1 includes a dissolution step 2, a centrifugal clarification step 3, a U extraction electrolytic reduction valence adjustment step 4, a centrifugal extraction step 5, and an oxalic acid precipitation electrolytic reduction valence adjustment step 6. , Oxalic acid precipitation step 7, oxide conversion step 8, electrolytic reduction step 9, electrolytic purification step 10, distillation step 11, injection molding step 12, FP treatment / waste salt treatment step 13, Zr, The Ru / Tc removal process 14, the back extraction / U concentration process 15, the U purification / denitration process 16, and the platinum group FP recovery process 17 are configured.

  The wet process 21 includes a dissolution step 2, a centrifugal clarification step 3, a U extraction electrolytic reduction valence adjustment step 4, a centrifugal extraction step 5, a Zr, Ru, Tc removal step 14, and a back extraction / U concentration step. 15 and a U refining / denitration step 16. The wet process 21 uses a light water reactor SFL (Spent Fuel) 31 which is a spent oxide fuel, a dissolution step 2, a centrifugal clarification step 3, a U extraction electrolytic reduction valence adjustment step 4, a centrifugal extraction step 5, Zr, Ru , Tc removal step 14, back extraction / U concentration step 15, and U refining / denitration step 16 are sequentially performed to obtain a light water reactor FL (Fuel) which is an oxide fuel.

  The improved aqua pyro process 22 includes an electrolytic reduction valence adjustment step 6 for oxalic acid precipitation, an oxalic acid precipitation step 7, an oxide conversion step 8, an electrolytic reduction step 9, and a platinum group FP recovery step 17. The The improved aqua pyro process 22 comprises an electrolytic reduction valence adjustment process 6 for oxalic acid precipitation, an oxalic acid precipitation process 7, an oxide conversion process 8 and an electrolytic reduction process 9 using an aqueous nitric acid solution in the centrifugal extraction process 5 of the wet process 21. Do in order. Further, the platinum group FP recovery step 17 is performed using the filtrate 36 in the oxalic acid precipitation step 7.

  The dry process 23 includes an electrolytic refining step 10, a distillation step 11, an injection molding step 12, and an FP treatment / waste salt treatment step 13. The dry process 23 uses the U, Pu and fast reactor SFL32 reduced and recovered in the electrolytic reduction process 9 of the improved aqua pyro process 22 to perform the electrolytic purification process 10, the distillation process 11 and the injection molding process 12 in this order, thereby changing the fast reactor FL34. obtain. Further, the FP treatment / waste salt treatment step 13 is performed using impurities and residues in the electrolytic purification step 10 and the distillation step 11.

(Function)
The operation of the first embodiment of the present invention will be described below. First, a method for obtaining the fast reactor FL34 from the light water reactor SFL31 by the wet process 21, the improved aqua pyro process 22, and the dry process 23 will be described.

  In the melting step 2, the entire amount of the light water reactor SFL31 disassembled and sheared is dissolved with nitric acid. At this time, U exists in a hexavalent state and Pu exists in a tetravalent state. Further, in the centrifugal clarification step 3, insoluble components contained in the lysate are removed by centrifugation.

  Next, in the electrolytic reduction valence adjustment step 4 for U extraction, Pu is electrolytically reduced to trivalent. FIG. 2 is a schematic cross-sectional view showing a batch electrolysis apparatus used in the U extraction electroreduction valence adjustment step of the spent fuel reprocessing method according to the first embodiment of the present invention. In the batch electrolysis apparatus 50, a cathode chamber 51 and an anode chamber 52 are separated by a diaphragm 53. A catholyte 54 is stored in the cathode chamber 51, and a cathode 55 and a reference electrode 56 are inserted into the catholyte 54. An anolyte 57 is stored in the anodic chamber 52, and an anode 58 is inserted into the anolyte 57. The cathode 55 and the anode 58 are connected to a power source 59. A cathode 55 and a reference electrode 56 are connected to a potentiometer 60. As the reference electrode 60, for example, a silver / silver chloride electrode is used. The cathode chamber 51 is provided with a stirrer 61 for stirring the catholyte 54.

  At this time, by reducing the cathode potential to −100 mV or less, Pu is reduced to trivalent while Np is maintained at pentavalent. The partially tetravalent reduced U is also used to reduce Pu from tetravalent to trivalent, while U itself is mostly oxidized to hexavalent.

  Next, in the centrifugal extraction process 5, when the nitric acid aqueous solution whose valence was adjusted in the electrolytic extraction valence adjustment process 4 for U extraction was extracted with TBP (tributyl phosphate) -30% dodecane, most (about 90%) Hexavalent U is extracted into a TBP-30% dodecane solution. The trivalent ion of Pu and the pentavalent ion of Np remain in the aqueous nitric acid solution together with some U tetravalent ions. In the centrifugal extraction step 5, the aqueous nitric acid solution and TBP are separated using a centrifuge. In the rotating cylinder of the centrifuge, the aqueous phase having a large specific gravity is collected by the centrifugal force on the outer periphery of the rotating cylinder and flows to the aqueous phase receiving part through the hole formed in the rotating cylinder. The solvent phase having a small specific gravity gathers near the rotation axis, flows upward through the hole in the upper end partition plate, and flows out to the solvent receiver.

  The nitric acid aqueous solution in the centrifugal extraction step 5 is used for the step of purifying the fast reactor FL 34 in the modified aqua pyro process 22. In addition, most (90%) of TBP containing hexavalent U is used in the purification process of the light water reactor FL33 described later.

  First, the purification process of the fast reactor FL34 using a nitric acid aqueous solution will be described. Since U normally exists stably as hexavalent uranyl ions in an aqueous nitric acid solution, U present as tetravalent ions remaining in the aqueous nitric acid solution in the centrifugal extraction step 5 is oxidized again to hexavalent uranyl ions. Therefore, in the electrolytic reduction valence adjustment step 6 for oxalic acid precipitation of the improved aqua pyro process 22, the electrolytic reduction valence adjustment is performed on the nitric acid aqueous solution remaining in the centrifugal extraction step 5, and U is changed from hexavalent to tetravalent ions. Adjust the valence.

  An apparatus using flow electrolysis is applied to the electrolytic reduction valence adjustment of U in the electrolytic reduction valence adjustment step 6 for oxalic acid precipitation. FIG. 3 is a schematic cross-sectional view showing a flow electrolysis apparatus used in the electrolytic reduction valence adjusting step for oxalic acid precipitation in the spent fuel reprocessing method according to the first embodiment of the present invention.

  The flow electrolysis apparatus 70 includes a diaphragm cylinder 71, carbon fibers 72, a metal wire 73, a housing 74, a power source 75, a cathode tank 76, an anode tank 77, and a reference electrode 78. As the diaphragm cylinder 71, porous cylindrical alumina or ceramics can be applied. The casing 74 has a structure in which the diaphragm cylinder 71 is housed, an aqueous nitric acid solution in which spent fuel is dissolved is introduced from one end, and the aqueous nitric acid solution is discharged from the other end through the diaphragm cylinder 71. Further, a cathode tank 76 is formed inside the diaphragm cylinder 71, and an anode tank 77 for holding a nitric acid aqueous solution is formed around the diaphragm cylinder 71.

  A carbon fiber 72 is provided in the cathode chamber 76 inside the diaphragm cylinder 71. A metal wire 73 is wound around the diaphragm cylinder 71. A power source 75 is connected with the carbon fiber 72 as the cathode and the metal wire 73 as the anode. Further, the diaphragm cylinder 71 is used as a reference electrode 78. Electrolytic reduction is performed while flowing a nitric acid aqueous solution in which spent fuel is dissolved from one end of the casing 74 to the cathode tank 76 inside the diaphragm cylinder 71. At this time, the diaphragm cylinder 71 acts as a diaphragm, and ions that have permeated through the diaphragm cylinder 71 are oxidized by the anode of the metal wire 73 and dissolved in the nitric acid aqueous solution inside the anode tank 77.

  Since the flow electrolyzer 70 has a large electrode area, the valence of hexavalent uranyl ions can be adjusted to tetravalent ions as shown in the following formula (1). Furthermore, the valence may be adjusted from a hexavalent uranyl ion to a trivalent ion. At this time, since most of U is removed in the centrifugal extraction step 5 of the previous step, the U for performing valence adjustment can be minimized, and the power consumption and equipment capacity can be reduced. Furthermore, in order to adjust the valence of hexavalent uranyl ions to the total amount of tetravalent or trivalent ions, the amount of valence-adjusted ions is measured as needed, and the ratio of hexavalent and tetravalent or trivalent ions is adjusted. There is no need to do.

UO ₂ ²⁺ + 4H ⁺ + 2e ⁻ → U ⁴⁺ + 2H ₂ O (1)
Next, in the oxalic acid precipitation step 7, oxalic acid is added to the aqueous solution whose valence has been adjusted in the oxalic acid precipitation electrolytic reduction valence adjustment step 6, thereby producing an oxalic acid precipitate 35. The oxalic acid precipitate 35 contains Pu, minor actinides such as Np, Am, and Cm, rare earth elements (RE), and a part of alkaline earth metal elements. Further, since U is valence adjusted to tetravalent or trivalent in the electrolytic reduction valence adjusting step 6 for oxalic acid precipitation, U is also efficiently precipitated in the oxalic acid precipitation 35.

  In the oxalic acid precipitation step 7, U, Pu, minor actinides, rare earth elements and the like are recovered as the oxalic acid precipitation 35. In the oxalic acid precipitation step 7, alkali metal elements and platinum group elements of the fission products are dissolved in the filtrate 36 without being precipitated. The platinum group element is an element containing a platinum group FP including palladium, ruthenium, and rhodium. The platinum group FP is recovered in a platinum group FP recovery step 17 described later.

  Next, in the oxide conversion step 8, when moisture is removed while heating ozone or oxidizing gas into the oxalic acid precipitation 35 recovered in the oxalic acid precipitation step 7, U, Pu, minor actinides and rare earth elements are removed. The oxide 37 is formed. Further, the moisture of the oxide 37 is completely removed while pulling oxygen to a vacuum.

Next, in the electrolytic reduction process 9, U, Pu, and the minor actinide metal 18 are reduced and recovered. FIG. 4 is a schematic cross-sectional view showing the electrolytic reduction apparatus used in the electrolytic reduction process of the spent fuel reprocessing method according to the first embodiment of the present invention. The electrolytic reduction apparatus 81 is charged in a molten salt electrolysis tank 83 in which an oxide 37 is placed in a cathode basket 82 made of stainless steel and a mixed molten salt is held therein. Here, the mixed molten salt is preferably prepared by dissolving an alkali metal or alkaline earth metal oxide in a molten salt of an alkali metal or alkaline earth metal chloride. More specifically, for example, a mixed molten salt obtained by dissolving Li ₂ O in a molten salt of LiCl, a mixed molten salt obtained by dissolving MgO in a molten salt of MgCl ₂ , and CaO dissolved in a molten salt of CaCl ₂ . Any of the mixed molten salts is preferred.

  A cathode basket 82 containing U, Pu, minor actinides, and rare earth element oxide 37 is connected to a cathode 85 of a power source 84, and an insoluble anode 85 made of platinum or glassy carbon is installed. Connect to the anode. A voltage is applied to the cathode basket 82 and the anode 85 in the molten salt 87, and oxygen ions in the U, Pu, and minor actinide oxides in the cathode basket 82 are extracted and reduced to metal, and U, Pu, and minor actinides are reduced. to recover. Since fission products such as Cs, alkali metal elements such as Cs, alkaline earth metal elements such as Sr, and rare earth elements such as Ce and Nd are dissolved in the molten salt, they can be separated from U, Pu and minor actinides. it can.

  Finally, in the dry process 23, the fast reactor FL34 is obtained from U, Pu and minor actinides obtained in the electrolytic reduction step 9. First, in the electrolytic purification step 10, electrolytic purification is performed using U, Pu, minor actinides obtained in the electrolytic reduction step 9, and the fast reactor SFL32. Further, in the distillation step 11, impurities are further removed by distillation, and in the injection molding step 12, a fast reactor FL34 is formed.

  Further, in the platinum group FP recovery step 17 of the improved aqua pyro process 22, a platinum group fission product (platinum group FP) is recovered from the filtrate 36 obtained in the oxalic acid precipitation step 7. Among the fission products, alkali metal elements and platinum group elements are not precipitated with oxalic acid but dissolved in the filtrate 36. Here, the apparatus used in the platinum group FP recovery step 17 may be the batch electrolyzer 50 shown in FIG. 2 used in the U-extraction electrolytic reduction valence adjustment step 4.

In the platinum group FP recovery step 17, the filtrate 36 in which the fission product is dissolved is placed in the cathode chamber 51, and the insoluble cathode 55 is immersed therein to perform electrolysis. When a voltage is applied to the anode 58 and the cathode 55 by the power source 59, among the fission products contained in the filtrate 36 of the cathode chamber 51, platinum group FPs Pd, Ru, Rh, Mo, and Tc are applied to the cathode 55. Precipitation is recovered. On the other hand, an acid anolyte 57 is placed in the anode chamber 52. At this time, the alkali metal element such as Cs and the alkaline earth element such as Sr in the filtrate which is the catholyte 54 remain in the filtrate 36 and can be separated from the platinum group FP.

  The applied voltage is controlled by controlling the potential difference between the reference electrode 56 immersed in the cathode chamber 51 and the cathode 55 with a potentiometer 60 and depositing the platinum group FP on the cathode 55 without generating hydrogen. Since the platinum group FP does not migrate into the high-level waste, it is possible to reduce the burden in manufacturing the vitrified body. Furthermore, the amount of high-level waste generated can be reduced.

Finally, a method for obtaining the light water reactor FL33 in the wet process 21 will be described. About 90% of U in the light water reactor SFL31 is dissolved in the TBP in the centrifugal extraction step 5. First, in the Zr, Ru, Tc removal step 14, Zr, Ru, Tc contained in TBP in which U is dissolved is electrolytically reduced and recovered. In the back extraction / U concentration step 15, U is back-extracted from TBP into an aqueous nitric acid solution to evaporate the aqueous phase and concentrate U. Further, in the U refining / denitration step 16, U is washed with nitric acid, then converted to an oxide and recovered as high-purity UO ₂ to obtain a light water reactor FL33.

(effect)
According to the first embodiment of the present invention, the oxalic acid precipitation electrolytic reduction valence adjusting step 6 is provided before the oxalic acid precipitation step 7, and U contained in the nitric acid aqueous solution remaining in the centrifugal extraction step 5 is hexavalent. By adjusting the valence to 4 valent ions, U can be efficiently recovered by precipitation in the oxalic acid precipitation step 7.

  The oxide conversion step 8 and the electrolytic reduction step 9 in the improved aqua pyro process 22 can be replaced with a chlorination step, a dehydration step, and a molten salt electrolysis step. In this case, in the chlorination step, hydrochloric acid is added to the oxalic acid precipitate 35 and dissolved at 100 ° C. or lower, and then hydrogen peroxide is added to decompose the oxalic acid into water and carbon dioxide. U, Pu and minor actinides in oxalic acid precipitate 35 are converted to chloride in this chlorination step.

  Next, in the dehydration step, the water in the hydrochloric acid solution is removed by evaporation, and then the water is completely removed at about 200 ° C. in a stream of a reducing inert gas (for example, argon or nitrogen). This produces anhydrous U, Pu and minor actinide chlorides (anhydrous chlorides). Furthermore, by electrolyzing anhydrous chloride in the molten salt electrolysis process, U, Pu and minor actinide metals that can be used as fast reactor fuel can be recovered.

(Second Embodiment)
(Constitution)
The spent fuel reprocessing method according to the second embodiment of the present invention will be described below with reference to FIG. The same parts as those in the spent fuel reprocessing method according to the first embodiment are denoted by the same reference numerals, and description of the same configuration is omitted.

  FIG. 5 is a schematic flowchart showing a spent fuel reprocessing method according to the second embodiment of the present invention. The second embodiment is different from the first embodiment in that the oxalic acid precipitation electrolytic reduction valence adjustment step 6 is provided in the subsequent stage of the oxalic acid precipitation step 7 instead of the previous stage of the oxalic acid precipitation step 7. It is. The electrolytic reduction valence adjustment step 6 for oxalic acid precipitation adjusts the valence of the filtrate 36 in the oxalic acid precipitation step 7.

(Function)
The operation of the second embodiment of the present invention will be described below. In the oxalic acid precipitation step 7 in the present embodiment, since the uranium valence is not adjusted in advance, uranium existing as hexavalent uranyl ions remains in the filtrate 36 without being precipitated.

  In the electrolytic reduction valence adjusting step 6 for oxalic acid precipitation, the filtrate 36 in the oxalic acid precipitation step 7 is electrolytically reduced. At this time, the hexavalent uranium that has not precipitated in the oxalic acid precipitation step 7 is adjusted to a valence of 4, and is precipitated from the filtrate 36 to become an oxalic acid precipitate 35.

  In the subsequent oxide conversion step 8, the above-described oxide conversion is performed using the oxalic acid precipitation 35 precipitated in the oxalic acid precipitation step 7 and the oxalic acid precipitation 35 precipitated in the oxalic acid precipitation electrolytic reduction valence adjusting step 6. .

(effect)
According to the second embodiment of the present invention, the electrolytic reduction valence adjusting step 6 for oxalic acid precipitation is provided after the oxalic acid precipitation step 7 to precipitate uranium in the oxalic acid precipitation step 7, and the oxalic acid precipitation step. Uranium that has not been precipitated in 7 can be precipitated in the electrolytic reduction valence adjusting step 6 for oxalic acid precipitation.

  In addition, not only the order of the electrolytic reduction valence adjustment step 6 for oxalic acid precipitation and the oxalic acid precipitation step 7 is replaced, but also the electrolytic reduction valence adjustment step 6 for oxalic acid precipitation and the oxalic acid precipitation step 7 are alternately repeated, It is also possible to perform the oxalic acid precipitation step 7 by adding oxalic acid while performing the electrolytic reduction valence adjusting step 6 for oxalic acid precipitation in the flow electrolyzer 70.

(Third embodiment)
(Constitution)
Hereinafter, a spent fuel reprocessing method according to a third embodiment of the present invention will be described with reference to FIG. The same parts as those in the spent fuel reprocessing method according to the first embodiment are denoted by the same reference numerals, and description of the same configuration is omitted.

  FIG. 6 is a schematic flowchart showing a spent fuel reprocessing method according to the third embodiment of the present invention. The third embodiment is different from the first embodiment in that the platinum group FP recovery step 17 is replaced by a post stage of the centrifugal clarification step 3 of the wet process 21 instead of the post stage of the oxalic acid precipitation step of the improved aqua pyro process 22. It is a point provided. The platinum group FP recovery step 17 recovers the platinum group FP from the nitric acid aqueous solution that has undergone the centrifugal clarification step 3.

(Function)
The operation of the third embodiment of the present invention will be described below. In the platinum group FP recovery step 17, the aqueous nitric acid solution after the centrifugal clarification step 3 is placed in the cathode chamber 51 of the batch electrolysis apparatus 50 shown in FIG. 2, and the insoluble cathode 55 is immersed in the cathode chamber 51 for electrolysis. To do.

(effect)
According to the third embodiment of the present invention, the platinum group FP recovery step 17 is provided after the centrifugal extraction step 5 of the wet process 21, thereby recovering the platinum group FP from the aqueous nitric acid solution after the centrifugal clarification step 3. It can be carried out.

DESCRIPTION OF SYMBOLS 1 ... Used fuel reprocessing method 2 ... Dissolution process 3 ... Centrifugal clarification process 4 ... Electrolytic reduction valence adjustment process 5 for U extraction Centrifugal extraction process 6 ... Oxalic acid precipitation Electrolytic reduction valence adjustment process 7 ... Oxalic acid precipitation process 8 ... Oxide conversion process 9 ... Electrolytic reduction process 10 ... Electrolytic purification process 11 ... Distillation process 12 ... Injection molding process 13 ... FP treatment / waste salt treatment step 14 ... Zr, Ru, Tc removal step 15 ... Back extraction / U concentration step 16 ... U purification / denitration step 17 ... Platinum group FP recovery step 21 ... Wet process 22 ... Improved aqua pyro process 23 ... Dry process 31 ... Light water reactor SFL
32 ... Fast Reactor SFL
33 ... Light water reactor FL
34 ... Light water reactor FL
35 ... Oxalic acid precipitation 36 ... Filtrate 37 ... Waste 50 ... Batch electrolysis device 51 ... Cathode chamber 52 ... Anode chamber 53 ... Diaphragm 54 ... Catholyte 55 ... cathode 56 ... reference electrode 57 ... anolyte 58 ... anode 59 ... power source 60 ... potentiometer 61 ... stirrer 70 ... flow electrolysis device 71 ... diaphragm Cylinder 72 ... Carbon fiber 73 ... Metal wire 74 ... Housing 75 ... Power source 76 ... Cathode tank 77 ... Anode tank 78 ... Reference electrode 81 ... Electrolytic reduction device 82 ... Cathode basket 83 ... Molten salt electrolytic cell 84 ... Power source 85 ... Cathode 86 ... Anode

Claims (5)

A dissolution process in which spent oxide fuel is disassembled and the sheared fuel is dissolved in an aqueous nitric acid solution;
An electroreduction valence adjusting step for extracting uranium for reducing plutonium dissolved in the nitric acid aqueous solution to trivalent;
A centrifugal extraction step of bringing the fuel that has undergone the electrolytic reduction valence adjustment step for uranium extraction into contact with an organic solvent, extracting hexavalent uranium into an extractant, and recovering uranium oxide;
An electrolytic reduction valence adjustment step for oxalic acid precipitation for adjusting the uranium remaining in the aqueous nitric acid solution in the centrifugal extraction step from hexavalent to tetravalent or trivalent;
An oxalic acid precipitation step of precipitating the uranium, minor actinide and fission product adjusted in the electrolytic reduction valence adjustment step for oxalic acid precipitation as an oxalic acid precipitate by an oxalic acid precipitation method;
An oxide conversion step of dehydrating the oxalic acid precipitate and converting it to a precipitate oxide in an oxidizing atmosphere;
In the mixed molten salt obtained by dissolving an alkali metal oxide in an alkali metal chloride molten salt, or in the mixed molten salt obtained by dissolving an alkaline earth metal oxide in an alkaline earth metal chloride molten salt. An electrolytic reduction step of immersing a material oxide and bringing the precipitate oxide into contact with a cathode to recover the uranium, the plutonium and the minor actinide in the precipitate oxide. Fuel reprocessing method. Instead of the oxide conversion step and the electrolytic reduction step,
A chlorination step of adding hydrochloric acid to the oxalic acid precipitate to convert it to chloride;
A dehydration step of synthesizing the anhydrous chloride by dehydrating the chloride in a reducing inert gas stream;
The spent fuel reprocessing method according to claim 1, further comprising a molten salt electrolysis step of dissolving the anhydrous chloride in the molten salt and recovering uranium, plutonium and minor actinides at the cathode by electrolysis. The electrolytic reduction valence adjustment step for oxalic acid precipitation is provided in the subsequent stage of the oxalic acid precipitation process instead of the previous stage of the oxalic acid precipitation process,
In the electrolytic reduction valence adjustment step for oxalic acid precipitation, the uranium remaining in the filtrate remaining without precipitation in the oxalic acid precipitation step is adjusted from hexavalent to tetravalent or trivalent instead of the aqueous nitric acid solution. The spent fuel reprocessing method according to claim 1, wherein the spent fuel is reprocessed.   The filtrate remaining without being precipitated in the oxalic acid precipitation step is put into a cathode chamber, a cathode made of an insoluble material is inserted into the cathode chamber, and the cathode chamber is acidic in an anode chamber separated by a partition wall. 4. The platinum group FP recovery step further comprising a platinum group FP recovery step of depositing and recovering a platinum group FP remaining in the filtrate on the cathode by adding a solution and performing electrolysis. A spent fuel reprocessing method described in 1.   The platinum group FP recovery step is provided after the dissolution step instead of the oxalic acid precipitation step, and collects the platinum group FP from the nitric acid aqueous solution instead of the filtrate. 4. The spent fuel reprocessing method according to 4.

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