USOO7323153B2

(12) United States Patent (10) Patent No.: US 7,323,153 B2 Amamoto et al. (45) Date of Patent: Jan. 29, 2008

(54) REPROCESSING METHOD BY FLUORIDE 3,708,568 A * 1/1973 Golliher et al...... 423.6 PROCESS USING 3.963.564 A * 6/1976 Lecocq ...... 376/310 FRACTIONAL DISTILLATION 4,710,222 A * 12/1987 FitzPatrick et al...... 75,393 5,076,839 A * 12/1991 Boyd et al...... 75/631 (75) Inventors: Ippei Amamoto, Higashi-Ibaraki-gun 5,118,343 A * 6/1992 Coops ...... 75/396 (JP); Koji Sato, Higashi-Ibaraki-gun 6,442,226 B1* 8/2002 Venneri et al...... 376/17O (JP) (73) Assignee: Japan Nuclear Cycle Development FOREIGN PATENT DOCUMENTS Institute, Ibaraki-Ken (JP) JP 2001-153991 6, 2001 (*) Notice: Subject to any disclaimer, the term of this RU 2108295 C1 * 4, 1998 patent is extended or adjusted under 35 U.S.C. 154(b) by 0 days. * cited by examiner (21)21) Appl. No.:No 11/097,2449 Primary Examiner Ngoc-Yen Nguyen (22) Filed: Apr. 4, 2005 (4) torney Agent, or Firm Wenderoth, Lind & Ponack,

(65) Prior Publication Data (57) ABSTRACT US 2006/0057042 A1 Mar. 16, 2006 (30) Foreign Application Priority Data or a fluorine compound is Subjected to a reaction with a spent oxide fuel to produce fluorides of and Jul. 30, 2004 (JP) ...... 2004-224444 , and recovering the fluorides using a difference in (51) Int. Cl volatility behavior. The method includes steps of subjecting opic io/44 (2006.01) a mixture of UO and PuO with hydrogen fluoride mixed CIG 43/6 (200 6. 01) with hydrogen to HF-fluorinate uranium and plutonium into UF and PuF; subjecting UF, and PuF with a fluorine gas COIG 56/00 (2006.01) tO F fluorinate uranium and plutonium into UF and PuF: (52) U.S. Cl...... 423 is: it. and 2fractionating UF, and PuF using a difference6 in phase6s 58) Field of Classification S s h s s 423 (3 change of obtained UF and PuF, removing a part of UF (58) Field of Classification Search ...... s and volatilizing the remaining UF, and PuF at the same 423/19, 489, 249, 251, 253, 258, 259 time. By Such a reprocessing method, PuF hard to undergo See application file for complete search history. a reaction is prevented from being formed as an intermediate (56) References Cited fluoride, the material of a reactor is hard to be corroded, and a consumption of expensive fluorine gas is reduced. U.S. PATENT DOCUMENTS 3,644,104 A * 2, 1972 Manevy et al...... 423.3 4 Claims, 3 Drawing Sheets

Spent oxide fuel

O2 - PuO2 Operating temp. 350-430°C HF supply: 1.1–1.3 times, HF fluorination step conc. 60-90 vol% HF-2 (fluidized bed furnace) H2 Supply: 1.1-1.3 times, conc. 10-30 wo%

UF4 - PuF3

Operating temp. 500-750C Hz fluorination step F2 supply: 1. 1-1.3 times, (fluidized bed furnace) conc. 20-40 vol%

Separation and volatilization step (cold traps) U.S. Patent Jan. 29, 2008 Sheet 1 of 3 US 7,323,153 B2

F.G. 1

Spent oxide fuel

UO2 - Pu O2

Operating temp. 350-430°C HF supply: 1.1–1.3 times, HF fluorination step Conc. 60-90 vol% HF -- H2 (fluidized bed furnace) H2 Supply: 1.1-1.3 times, ConC. 1 O-3O vol%

UF 4 - PuF3

Operating temp. 500-750C F H2 fluorination step F2 Supply: 1.1-1.3 times, 2 (fluidized bed furnace) Conc. 20-40 vol%

UF6 - PuF6

Separation and volatilization step (cold traps)

UF6 UF6 - PuF6 U.S. Patent Jan. 29, 2008 Sheet 2 of 3 US 7,323,153 B2

FIG.2

Spent oxide fuel (Main constituent elements: U.Pu,O,Zr, Nb, Mo, Tc, Ru,Sb,Te,Cs,Np,Am,Cm) UO2--PuO2 Operating temp. 400C HF fluorination HFHisty supply: 1.51.15 times,times, conc.conc. 3070 vol% vol% (fluidized bed furnace) ---> H2O UF4- PuF3 Operating temp. 500-750C F2 fluorination F2 supply: 1.15 times, (fluidized bed furnace) --> Alef, conc. 20-40 vol% UF6 - PuF6 Operating temp. -70 to OC Pressure 50 kPa Condensation of UFs PuFs --St. 2,TeF6,

Operating temp. 53.1-56.5°C Pressure 83.633-83.686-KPa Separation of UF6/PuF6 Operating temp. 53-56.5°C Volatilization of UF6 PuF6 Pressure 50 kPa Cold traps

Operating temp. 300C SSification SASof UF - - - - b. PuF6,CsF

Operating temp. 120C (MgF2Purification traps) of UF6 b- NbF6,RuFs,SbF5,NpF6 MoF6, TcF6, UF6--PuFa Operating temp. 300-400C NES of UF6 ------> ZrF4, Rufs,NbF6 UFs "-taura of Pu enrichment Operating temp. -70 to OC

Pressure 50 kPa Condensation of UF6Condensation of UFs-PuFs Operating temp. 70 to 80C Volatilization of UF6 Volatilization of UF6PuFs Pressure 50 kPa (cold traps) (cold traps) Filling in cylinder for UF6 | To MOX reconversion process To UO2 recorversion process U.S. Patent Jan. 29 2008 Sheet 3 of 3 US 7,323,153 B2

)©

91

9|

01 21 2Ond+2On US 7,323,153 B2 1. 2 REPROCESSING METHOD BY FLUORIDE there are disadvantages that temperature adjustment for VOLATILITY PROCESS USING conversion conditions of a target Substance is impossible, a FRACTIONAL DISTILLATION large amount of expensive fluorine gas is used, and so on. BACKGROUND OF THE INVENTION SUMMARY OF THE INVENTION 1. Field of the Invention Problems to be solved by the present invention are to The present invention relates to a method of separating establish a method for producing PuF in which PuF hard and purifying nuclear fuel Substances using a difference in to fluorinate further is prevented from being formed as an fluorination volatility behavior of uranium, plutonium and 10 intermediate fluoride, to establish a method for producing other elements in a spent oxide fuel to reprocess the spent PuF. in which the material of a reactor is harder to corrode, oxide fuel. to reduce a consumption of expensive fluorine gas, and so 2. Description of the Related Art O. A fluoride volatility process is one of methods for dry According to the present invention, there is provided a reprocessing of a spent fuel, in which nuclear fuel Sub 15 reprocessing method by a fluoride volatility process using stances such as uranium and plutonium and various kinds of fractional distillation in which fluorine or a fluorine com products are separated and recovered using a pound is Subjected to a reaction with a spent oxide fuel in difference in volatility behavior when they are fluorinated. two stages to produce fluorides of uranium and plutonium, Techniques for applying the fluoride volatility process to a and recover uranium and plutonium as the fluorides using a reprocessing process have been developed in the U.S. and difference in volatility behavior, the reprocessing method other various countries since 1950s. However, each of those comprising the steps of: techniques has problem in higher fluorination and purifica HF fluorination of the spent oxide fuel containing UO. tion of plutonium. None of these techniques has reached a and PuO in the reaction thereof with hydrogen fluoride practical phase, and there has been no progress since 1970s. mixed with hydrogen to produce UF and PuF as a first In Japan, Japan Atomic Energy Research Institute has 25 Stage, carried out the fluoride volatility process, and many advan F. fluorination of UF and PuF in the reaction thereof tages have been found, but development of the technique has with fluorine gas to produce UF and PuF as a second stage; been ended without establishing a plutonium purification and step. In the fluoride volatility process carried out in that separation and Volatilization of the resulting UF, and institute, uranium and plutonium are separated by two-stage 30 PuF, by fractionally distillating them (separating a gas and a fluorination using a fluidized bed furnace as a reactor with liquid) due to a difference in phase change therebetween to the temperature and fluorine concentration being changed. remove a part of UF as gas, and then volatilizing the For example, in the first stage, uranium is fluorinated with an remaining UF, and PuF at the same time. F concentration of 20% at the operating temperature of In the reprocessing method, the first stage HF fluorination 330° C., and in the second stage, plutonium is fluorinated 35 step is carried out preferably by Supplying a hydrogen with an F. concentration of 100% at the operating tempera fluoride gas containing 10 to 30 vol% of hydrogen using a ture of 330 to 550° C. fluidized bed furnace operated in the temperature range of However, there is a disadvantage that it takes much time 350 to 430°C., and the second stage F. fluorination step is to convert uranium into uranium (UF) because carried out preferably by Supplying a fluorine gas diluted to the reaction temperature in “fluorination of uranium’ of the 40 20 to 40 vol% using a fluidized bed furnace operated in the first stage is low, and that plutonium easily forms the most temperature range of 500 to 750° C. stable plutonium tetrafluoride (PuF). Further, in “fluorina The separation and volatilization step is carried out by tion of plutonium’ of the second stage, there is a disadvan using at least one cold trap, and the removal of the part of tage that plutonium is hard to be converted into plutonium UF is carried out by fractional distillation (gas-liquid sepa hexafluoride (PuF) (the conversion ratio or conversion rate 45 ration) at the operating temperature and pressure controlled decreases) from the point of view of thermodynamics and so that UF is in a gas region and PuF is in a liquid region reaction temperature because plutonium forms into PuF of in the phase diagrams of UF and PuF. an intermediate fluoride in the first stage, and the fluorine In the reprocessing method by the fluoride volatility concentration is so high that incomplete fluidization easily process using fractional distillation according to the present OCCU.S. 50 invention, the spent oxide fuel is subjected to a reaction with Thus, a reprocessing process according to a fluoride hydrogen fluoride mixed with hydrogen in the first stage, Volatility process using a flame furnace as a reactor has been and the resultant fluorides are subjected to a reaction with a proposed (see, for example, Japanese Patent Laid-Open fluorine gas in the second stage, and thus PuF hard to Specification No. 2001-153991). Unlike the fluidized bed undergo a reaction into a higher fluoride is never produced furnace, the flame furnace is a reactor operating under 55 as an intermediate fluoride, thus making it possible to conditions of high temperature and high fluorine gas atmo improve the ratio and rate of conversion into PuF and to sphere. reduce a consumption of expensive fluorine gas. In addition, If plutonium is converted under the conditions, a direct since the fluidized bed furnaces are used to carry out fluorination reaction of PuO +3F (or 6F)->PuF+O. reactions under lenient conditions in both first and second occurs, and therefore PuF is never produced as an interme 60 stages, the furnaces are hard to be corroded or deteriorated. diate fluoride. In addition, because the fluorination tempera ture and fluorine concentration are high, decomposition BRIEF DESCRIPTION OF THE DRAWINGS reaction of PuF is hard to proceed. However, since a corrosive gas at high temperatures and in high concentra FIG. 1 is an explanatory diagram showing a basic process tions is required for the reaction, and conversion conditions 65 of a reprocessing method by a fluoride volatility process are severe, the reactor is easily corroded and deteriorated, using fractional distillation according to the present inven thus causing a problem in terms of materials. In addition, tion; US 7,323,153 B2 3 4 FIG. 2 is a process flow showing one example of the Consequently, UF is vaporized and PuF is liquefied, thus reprocessing method by the fluoride volatility process using making it possible to separate them. The conditions are set fractional distillation according to the present invention; and in consideration of an operation on the negative pressure FIG. 3 is a block diagram of an apparatus for carrying out side, and therefore have a quite limited range, but if a the reprocessing method by the fluoride volatility process separation operation is possible on the positive pressure side using fractional distillation according to the present inven as well, an allowable range of pressure and temperature is tion. wider. Then, the pressure is reduced to about 50 kPa, whereby the remaining UF, and PuF are vaporized at the DETAILED DESCRIPTION OF THE same time. PREFERRED EMBODIMENTS 10 In this way, the fluoride volatility process can be applied to recover uranium and plutonium as UF and UFe+PuF. FIG. 1 is an explanatory view showing a basic process of This reprocessing process can be used for a light water a reprocessing method by a fluoride Volatility process using reactor nuclear fuel cycle, FBR nuclear fuel cycle or the like. fractional distillation according to the present invention. If the processing object is a spent metal fuel, the method of This is a reprocessing method in which fluorine or a fluorine 15 the present invention can be applied by oxidizing the metal compound is Subjected to a reaction with a spent oxide fuel fuel as preprocessing. in two stages to produce fluorides of uranium and plutonium, and uranium and plutonium are recovered as UF and EXAMPLES UF-PuF using a difference in volatility behavior. The first stage is an HF-fluorination step, where HF FIG. 2 is a process flow showing one example of the fluorination of a spent oxide fuel containing UO and PuO reprocessing method by the fluoride volatility process using is conducted in the reaction thereof with hydrogen fluoride fractional distillation according to the present invention. mixed with hydrogen to produce UF and PuF. The HF This is an example of a process of reprocessing a spent oxide fluorination step is carried out by Supplying a hydrogen fuel. The spent oxide fuel as a raw material has been fluoride gas (Supply: 1.1 to 1.3 times the Stoichiometric ratio, 25 Subjected to decladding processing, and its main constituent concentration: 60 to 90 vol%) containing 10 to 30 vol% of elements include U, Pu, O, Zr, Nb, Mo, Tc, Ru, Sb, Te, Cs, hydrogen using a fluidized bed furnace operated in the Np, Am and Cm, and uranium exists in a form of UO and temperature range of 350 to 430° C. For the H gas, plutonium exits in a form of PuO. These raw materials are dependency on the concentration is not significant as long as fluorinated in two stages. a sufficient amount is Supplied, and its concentration may be 30 5 vol% or greater, but is preferably 10 to 30 vol% when the In the first-stage HF fluorination, a raw material (spent HF concentration is 70 vol%. For the supply of hydrogen oxide fuel) is subjected to a reaction with an HF gas (Supply: fluoride gas, an optimum amount was found to be 1.15 times 1.15 times the stoichiometric ratio, concentration: 70 vol%) the stoichiometric ratio from thermodynamic calculation using a fluidized bed furnace (operating temperature: 400° and empirically, and the Supply of hydrogen fluoride gas 35 C.). At this time, an H gas is also supplied, and the Supply which is 1.1 to 1.3 times the stoichiometric ratio brought thereof is greater than 0.5 times the stoichiometric ratio to about a preferred result. Both UF, and PuF produced in this PuO and the concentration may be any of 5 to 100 vol%. way tend to form into easily from a thermo but should be 30 vol% if the H gas is supplied along with dynamic viewpoint. The used amount of expensive fluorine 70 vol% HF. Consequently, UF and PuF are produced. gas can be reduced by about 60% compared to conventional 40 methods because an HF gas is used in the HF fluorination. Most impurities in the raw material remain oxides without The second stage is an F. fluorination step, where F. undergoing a reaction, or form into fluorides or oxyfluorides. fluorination of UF and PuF is conducted in the reaction Resulting reactions are as shown below. thereof with a fluorine gas to produce UF and PuF. The F. fluorination step is carried out by Supplying a fluorine gas 45 (supply: 1.1 to 1.3 times the stoichiometric ratio) diluted to 20 to 40 vol% using a fluidized bed furnace operated in the temperature range of 500 to 750° C. Conversion of UF by In the second-stage F. fluorination, the intermediate fluo the fluorine gas is not particularly cumbersome because it rides produced in the first-stage HF fluorination are con has been already performed on a commercial scale, and 50 conversion of PuF into PuF can be carried out at a low verted into the hexafluorides. The operating temperature of temperature (500 to 750° C.) easily, speedily and stably the fluidized bed furnace is set to 500 to 750° C., and the intermediate fluoride is subjected to a reaction with a compared to the conversion of PuF into PuF. In the above fluorine gas to produce the hexafluorides of uranium and two-stage fluorination process according to the present plutonium. The supplied fluorine gas is diluted with an N invention has an advantage that PuF can be produced 55 without the intermediation of PuF. gas to adjust the concentration of the fluorine gas to 20 to 40 The resulting UF, and PuF are fractionally distillated vol % and the excess fluorine gas ratio to 1.15 times the using a difference in phase change thereof to remove a part Stoichiometric ratio. By F. fluorination, uranium (UF) and of UF as gas, and then the remaining UF, and PuF are plutonium (PuF) are volatilized along with many impuri Volatilized at the same time (separation and volatilization 60 ties, but ZrE, CsP, PuF, AmF, CmF and the like remain step). Cold traps are used in this step, and a part of UF is along with a bed material because of the low vapor pressure. removed by fractional distillation at the operating tempera Some oxides that are not completely fluorinated (UO, etc.), ture and pressure controlled so that UF is in a gas region oxyfluorides (UO. F., etc.) and double salts (Cs UFs, etc.) and PuF is in a liquid region in the well-known phase also remain. diagrams of UF and PuF. Conditions for the separation are 65 set so that the pressure is about 83.6 kPa in the temperature Volatilized UF and PuF are condensed in cold traps. The range of 53 to 56.5°C. (about 85.01 kPa at 53.4 to 57°C.). operating temperature is -70 to 0° C., and the working US 7,323,153 B2 5 6 pressure is about 50 kPa. Many volatile substances are condensed under the conditions, but most of F (boiling A mixed gas of volatilized UF and PuF and UF purified point: -188.24° C.), HF (: -84.79° C., boiling by the chemical traps are mixed together in a desired ratio point: 19.67° C.) and TeF (boiling point: -39.55° C.) each using a gas mixer, and the plutonium enrichment is adjusted. having a low melting or boiling point remains gaseous, and 5 For operating conditions of the gas mixer, a slightly negative therefore solids and gases are separated from condensates. pressure and a temperature of about 70 to 80°C. are adopted. If the cold traps are decompressed to about 83.6 kPa at UF not used for adjustment of the plutonium enrichment, 53.1 to 56.5° C. (about 85.01 kPa at 53.4 to 57° C.), for of UF purified by the chemical traps, or a mixed gas of UF example, UF is vaporized and PuF is liquefied (for this 10 after adjustment of the plutonium enrichment and PuF is purpose, the temperature and pressure are set so that UF is condensed. The operating temperature is -70 to 0°C., and in a gas region and PuF is in a liquid region in the phase the pressure is about 50 kPa. diagrams of UF and PuF). UF and PuF can be fraction ally distillated under the conditions. Volatilized amount of UF can be optionally set by appropriately controlling the 15 The temperature is increased to 70 to 80° C. with the temperature and pressure in actual operations. In light of the pressure (50 kPa) unchanged, whereby the condensed UF melting or boiling point of each Substance, a part of PuF. or mixture of UF and PuF is vaporized and provided for a and impurities having relatively low boiling points, such as reconversion process. NbF5, MoF TcF, RuPs, SbF5, TeF and NpF, likely If vaporized simple UF is filled in a cylinder for UF, it behave in conjunction with UF. can be used as a raw material for uranium enrichment, and this process can be used in a light water reactor fuel cycle. As an option, by setting conditions for liquefying UF, in A certain amount of UF is volatilized, and then the which the temperature of the cold traps trapping UF is 64° pressure is reduced to about 50 kPa with the temperature of C. or higher and the pressure is 152 kPa or greater, UF can the cold traps unchanged, whereby UF and PuF can be 25 be liquefied and filled in the cylinder. vaporized at the same time. The temperature and pressure FIG. 3 is a block diagram of an apparatus for carrying out can be set in accordance with characteristics of the cold traps the above reprocessing method by a fluoride volatility referring to the phase diagrams of UF and PuF. process using fractional distillation. A raw material (spent oxide fuel) in a raw material supply tank 10 is fed to an HF 30 fluorination furnace (fluidized bed furnace) 12, reacts with UF produced by F. fluorination contains a very small an HF-H gas into an intermediate material, and is stored in amount of PuF and volatile impurities. These impurities are an intermediate fluoride supply tank 14. The intermediate made to pass through chemical traps filled with a Substance fluoride in the intermediate fluoride supply tank 14 is fed to having an action of chemically adsorbing the impurities, an F. fluorination furnace (fluidized bed furnace) 16, and whereby the impurities can be removed to purify UF. 35 reacts with an F gas into a hexafluoride. Chemical traps are installed in multiple stages as required. The obtained hexafluoride is introduced into first cold (1) LiF UO, F Traps traps 18, where UFPuF is condensed, UF/PuF is sepa In this process, chemical traps using (LiF) rated, and UF6.PuF6 is volatilized. UF is purified through and uranyl fluoride (UOF) either alone or in combination LiF/UO, F traps 20, MgF, traps 22 and NaF traps 24. UF as a filler are used in the first stage for the purpose of 40 and UF PuF are introduced into second cold traps 26, removal of PuF. Instead thereof, any filler having an action where UF is condensed and volatilized, and UF PuF is of reducing PuF may be used, and use of UF and UFs can condensed and volatilized, and they are provided for the be considered as well. The reaction between LiF and PuF reconversion process. is a reversible reaction, PuF is adsorbed to LiF at the 45 operating temperature of 300° C., and detached from LiF by What is claimed is: heating it to 450° C. Thus, LiF is used at the operating 1. A reprocessing method by a fluoride volatility process temperature of 300° C. CsF is adsorbed at the temperature, using fractional distillation in which fluorine or a fluorine too. PuF adsorbed to UOF can be used in an MOX (mixed compound is Subjected to a reaction with a spent oxide fuel oxide) reconverting process as a raw material without being 50 in two stages to produce fluorides of uranium and plutonium, detached. and recover uranium and plutonium as the fluorides using a difference in volatility behavior, the reprocessing method (2) MgF Traps comprising the steps of: Chemical traps using MgF2 as a filler are provided in the second stage. MgF2 has an action of adsorbing NbF. MoF HF fluorination of the spent oxide fuel containing UO. 55 and PuO in the reaction thereof with hydrogen fluoride TcP, RuFs, SbFs and NpF and is used at the operating mixed with hydrogen to produce UF and PuF as a first temperature of 120° C. here. stage, the HF fluorination step being carried out by (3) NaF Traps Supplying a hydrogen fluoride gas in a Supply amount Chemical traps using NaF as a filler are installed in the of 1.1 to 1.3 times the stoichiometric ratio and con third stage. NaF is known to adsorb UF through the reaction 60 taining 10 to 30 vol% of hydrogen to a fluidized bed of UF+2NaF->Na, UF at 25 to 250° C. Na-UFs decom furnace operated in the temperature range of 350 to poses into NaF and UF again at 300 to 400° C., but NaF 430° C.; forms double salts with RuFs and NbF. It has an action of F. fluorination of UF and PuF in the reaction thereof adsorbing ZrF, but most of ZrF remains in the fluidized with fluorine gas to produce UF and PuF as a second bed furnace as a nonvolatile substance along with the bed 65 stage; and material, and only a very Small amount thereof is removed separation and Volatilization of the resulting UF, and by the NaF traps. PuF by fractionally distillating them due to a difference US 7,323,153 B2 7 8 in phase change therebetween to remove a part of UF temperature and pressure controlled so that UF is in a gas as gas, and then volatilizing the remaining UF, and region and PuF is in a liquid region in the phase diagrams PuF. at the same time. of UF and PuF. 2. The reprocessing method by a fluoride volatility pro 4. The reprocessing method by a fluoride volatility pro cess using fractional distillation according to claim 1, wherein the second stage F. fluorination step is carried out cess using fractional distillation according to claim 2, by supplying a fluorine gas diluted to 20 to 40 vol% to a wherein the separation and volatilization step is carried out fluidized bed furnace operated in the temperature range of by using at least one cold trap, and the removal of the part 500 to 750° C. of UF is carried out by fractional distillation at an operating 3. The reprocessing method by a fluoride volatility pro- 10 temperature and pressure controlled so that UF is in a gas cess using fractional distillation according to claim 1, region and PuF is in a liquid region in the phase diagrams wherein the separation and volatilization step is carried out of UF and PuF. by using at least one cold trap, and the removal of the part of UF is carried out by fractional distillation at an operating