KR101576612B1 - Recovery method of the residual actinide element from the chloride molten salt - Google Patents

Abstract

The present invention relates to a method for recovering residual actinide elements in a chloride molten salt. More specifically, the present invention relates to a method for recovering a residual actinide element in a chloride molten salt, characterized in that a rare earth metal is added to the chloride molten salt to recover the actinide group metal. In the chloride molten salt, A method for recovering a liquid.
In particular, in order to recover the amount of the rare earth element which can be recovered together with the actinide element and which can damage the nuclear fuel cladding, in order to use the recovering actinide element as a nuclear fuel, the rare earth metal as the reducing agent is Gd or Y Is selected and used.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for recovering a residual actinide element from a chloride molten salt,

The present invention relates to a method for recovering residual actinide elements in a chloride molten salt. More particularly, the present invention relates to a method for recovering residual Actinide (An) elements in a chloride molten salt, comprising the step of adding a rare earth (RE) metal to the chloride molten salt to recover an actinide group metal And recovering the residual actinide element in the molten chloride salt.

Uranium (U) and transuranics (TRU) contained in nuclear fuel in a pyroprocess, which processes dry nuclear fuel using molten chloride at high temperature for volume reduction and recycling of metallic fuel after use, The actinide element, such as elemental elements, is an electrowinning process in which uranium and uranium that remain in the molten salt are recovered by using electrorefining to separate pure uranium from solid anodes and liquid anodes. .

For example, in the LiCl-KCl eutectic salt, the spent metal fuel is charged into the anode, the uranium and the uranium element are dissolved by applying electricity, and the uranium and the uranium elements are added to the iron or liquid cadmium cathode (LCC) Electrodeposited and recovered.

When a large amount of nuclear fuel is treated by electrolytic refining and electrolytic smelting processes, the fission product is accumulated in the molten salt, so the process of removing the fission product by using the waste molten salt treatment process follows. The amount of high-level waste generated in the pyrogen process and the amount of actinide elements sent to the repository should be minimized as much as possible to alleviate the burden on the environment, and the economical efficiency of the process can be increased by the patent 10-1047838. However, since some of the actinide elements such as uranium and ultra-uranium remain in the molten salt, these actinide elements must be sufficiently removed before the waste molten salt treatment step.

As a method for recovering a conventional residual actinide element, a reduction extraction method [K. Kinoshita, et al., "Separation of Uranium and Transuranic Elements from Rare Earth Elements by Means of Multistage Extraction in LiCl-KCl / Bi System ", J. Nucl. Sci. Tech., 36 (2), 189 (1999)), electrolytic recovery method [M. Iizuka, et al., "Actinides Recovery from Molten Salt / Liquid Metal System by Electrochemical Methods ", J. Nucl. Mat., 247, 183 (1997); ANL ' s Chemical Technology Division Annual Technical Report 1994, ANL-95/24, p. 91 (1995)) and oxide formation.

In Japan, a multi-stage countercurrent reduction extraction method is proposed to recover residual actinide elements from pulverized molten salts by the Central Research Institute of Electric Power (CRIEPI). Kinoshita, et al., "Separation of Uranium and Transuranic Elements from Rare Earth Elements by Means of Multistage Extraction in LiCl-KCl / Bi System ", J. Nucl. Sci. Tech., 36 (2), 189 (1999)).

However, it is not easy to construct a multi-stage reduction extracting apparatus in which a molten salt having a large difference in specific gravity is brought into contact with the liquid metal in a countercurrent manner so as to flow in three to five steps while facing each other and contacted in two phases. Complex. In addition, when it is practically used, it is difficult to increase the capacity and continuous operation of the multistage reduction extraction apparatus when a large amount of waste molten salt generated in a large-scale pyrogen process needs to be treated.

In the United States, the Argonne National Laboratory (ANL) reviewed an electrolytic recovery method using an Li-Cd anode material and a steel solid cathode [ANL's Chemical Technology Division Annual Technical Report 1994, ANL-95/24, p. However, in this solid-state cathodic electrolytic recovery method, a disproportionation reaction occurs in which an electrodeposited metal reacts with a +3 -valent ion to generate a +2 valency, which is an inevitable reaction, so that the recovery efficiency can be greatly reduced.

In order to reduce the volume of spent nuclear fuel from nuclear power plants, it is necessary to minimize the amount of actinide elements in the high-level wastes to be disposed of in order to increase the reliability of economics and radiation safety when using Pyroprocess technology.

 The Korea Atomic Energy Research Institute has developed the "Residual Actinides Recovery (RAR)" technology to recover the maximum amount of actinide elements such as uranium and TRU from the molten salt waste from the electrolytic smelting process of the Pyro process. We have registered patents in Korea and the United States.

The RAR technique was applied in a two-step procedure of recovering the actinide element in the molten salt by the LCC electrolysis step and the oxidation extraction step in which the CdCl ₂ oxidizing agent was added. The residual concentration of the actinide element was 0.01 wt% (100 ppm) (Cl ₂ ) gas is generated when LCC is electrolyzed. Therefore, it is necessary to separate equipment for collecting and treating the chlorine (Cl ₂ ) gas, and a high purity and high cost CdCl ₂ oxidizing agent is required. A driving time of about 15 hours is required.

In order to put the RAR technology into practical use in the future, it is necessary to develop an innovative concept process and apparatus having a simpler and simpler RAR process, which is efficient and economical, in the restricted space of the hot cell of the high-level radiation zone.

In addition, it is necessary to minimize the amount of the rare earth elements as rare earth elements recovered together with the actinide elements may damage the nuclear fuel cladding to utilize the recovered actinide elements in nuclear fuel fabrication.

In order to solve the above-mentioned problems, the present invention provides a process for recovering residual rare earth elements, which is generated after electrolytic refining or electrolytic refining of spent nuclear fuel and which is recovered together with an actinide group element in a chloride molten salt containing an actinide group element and a rare earth element, And to provide a method for recovering actinide elements.

In order to accomplish the above object, the present invention provides a method for recovering residual actinide elements in a chloride molten salt, which comprises recovering an actinide group metal by adding a rare earth metal as a reducing agent to the chloride molten salt, Thereby providing a recovery method of the residual actinide group element in the salt.

According to the method for recovering the residual actinide group element in the chloride molten salt of the present invention, the rare earth metal is charged into the LiCl-KCl eutectic salt and used as a reducing agent to reduce the actinide group metal ion to produce various kinds of actinide The amount of the rare earth element to be recovered together with the actinide element can be minimized, the recovery time can be greatly shortened, and the process and apparatus can be simplified, thereby remarkably improving the efficiency of the recovery process.

FIG. 1 is a schematic diagram of an RAR innovation technique in which a rare earth (RE) metal is introduced into a molten salt to convert an actinide element into a metal state from an ionic state and recover it.
FIG. 2A is a reaction equilibrium distribution diagram of an actinide group metal chloride in a molten salt and a rare earth metal using an HSC code according to a two-component equilibrium reaction.
FIG. 2B is a diagram showing a reaction equilibrium distribution curve of an actinide group metal chloride in a molten salt and a rare earth metal using an HSC code according to a multicomponent equilibrium reaction.
FIG. 3A is a graph showing the amount of change of metal chloride in the LiCl-KCl eutectic salt, the concentration of which is measured by the ICP quantitative analysis method, and shows the concentration change of U and Nd.
FIG. 3B is a graph showing the amount of change of metal chloride in the LiCl-KCl eutectic salt measured by ICP quantitative analysis, showing the change in the concentration of Ce and La.
FIG. 4 is a schematic diagram of an RAR innovation technique in which a eutectic salt is contained in a large vessel and a small vessel containing a rare-earth metal and a stirrer is charged into a eutectic salt and an actinide element reduced from an ion to a metal is collected into a small vessel and recovered.
FIG. 5 is a schematic view of a RAR innovation technique for converting an actinide (An) element into a fine particle state and then converting cadmium (Cd) into a cadmium alloy form in the eutectic salt to separate actinide elements from eutectic salts to be.

The present invention provides a method for recovering residual actinide elements in a chloride molten salt.

The present invention relates to a method for recovering a residual actinide group element in a chloride molten salt,

And recovering the actinide group metal by adding a rare earth metal as a reducing agent to the chloride molten salt, and recovering the actinide group metal in the chloride molten salt.

The chloride molten salt may be a LiCl-KCl eutectic salt.

The rare earth metal may be characterized in that the Gibbs free energy (-ΔG) is greater than that of the actinide group metal.

The rare earth metal may be at least one selected from Gd, Y, Nd, Pr, Ce and La.

After collecting the actinide elements, a small vessel containing a rare earth metal, a reducing agent and a stirrer, was charged into a large vessel containing eutectic salts to separate the actinide elements from metal ions into fine metal particles. And collected in a small container and recovered.

In order to separate only the actinide element contained in the eutectic salt in the small vessel from the rare earth metal fine particles which have been partially reduced, cadmium (Cd) is added to the eutectic salt after the actinide element (An) ) Is added and converted into a Cd-An alloy form to separate the eutectic salt and the Cd-An alloy.

In order to recover the actinide element so as to minimize the content of the rare earth element which may be recovered together with the actinide element to damage the nuclear fuel cladding, the selection of the rare earth metal is preferably performed in such a way that the metal chloride forming Gibbs free energy (-ΔG) And Gd or Y close to the Gibbs free energy (-? G) value of the metal is used.

A rare earth metal such as Gd or Y, which is a reducing agent, is added to the eutectic salt, and a rare earth metal such as Gd or Y, which is a reducing agent, is taken out from the eutectic salt 2 hours after completion of the reduction reaction of the actinide group element, Thereby minimizing the amount of reduction.

Hereinafter, the method for recovering the residual actinide element in the chloride salt of the present invention will be described in detail.

Rare earth ( RE ) The metal acts as a reducing agent Actinide  By using the reaction that the ions are reduced to metal, Actinide  How to recover metal

Innovative RAR (Innovative RAR) technology has been developed to improve existing RAR process equipment technology.

Inner-RAR (RAR) technology thermodynamically forms the metal chlorides Gibbs free energy (-ΔG) to recover all the various actinide elements contained in the LiCl-KCl eutectic salt more than the actinide metals It features a simple method of recovering in one step using a large rare-earth (RE) metal, using oxidation-reduction reactions based on chemical potentials.

Inner-RAR technology features Rare earth (RE) metals in molten salt to induce the reduction of chemical actinide metal ions and simplify the process of recovery of actinide metals to improve process efficiency.

FIG. 1 is a schematic diagram showing a method of recovering an actinide group metal in a molten salt by using a rare earth (RE) metal as a reducing agent and reducing an actinide ion to a metal.

All of the actinide ions in the chloride state in the LiCl-KCl eutectic salt are converted into the fine particles of various kinds of actinide metals as the reduction reaction induced by the rare earth (RE) metal charged into the eutectic salt proceeds Very dense actinide metals are deposited on the bottom of the container. At this time, however, some reduced rare earth metals float to the upper surface of the eutectic salt.

The tendency of such reduction reactions to proceed follows the order of magnitude of the formation Gibbs free energy value of the metal chloride shown in Table 1. In Table 1, (a) is the document value and (b) is the calculated value of HSC 6.0.

[Table 1]

Formation of metal chlorides Gibbs free energy (-ΔG)

Hereinafter, the present invention will be described in more detail with reference to Examples and Experimental Examples. However, the following examples and experimental examples are intended to further illustrate the present invention, but the scope of the present invention is not limited thereto.

[ Example ]

(RE) elements such as Gd, Y, Nd, Ce, and La in the LiCl-KCl eutectic salt for binary or multicomponent systems using the HSC version 6.0, The equilibrium of the oxidation-reduction reaction of the actinide ions was calculated and an equilibrium distribution curve of the reaction products was prepared (FIGS. 2A and 2B).

The reaction equilibrium distribution curves of binary or multicomponent systems calculated using HSC codes were examined and analyzed. As a result, the rare-earth (RE) metal acts as a reducing agent based on the order of Gibbs free energy values (Table 1) It was confirmed that all of the actinide group metal chlorides were converted to the metal state.

 [ Experimental Example ] Nd  Uranium recovery by metal

U recovery was performed using Nd metal. UCl ₃ , CeCl ₃ Nd metal rod (length 25 mm) was placed in the LiCl-KCl eutectic salt with LaCl ₃ concentration of 0.17, 0.4 and 0.18 wt%, respectively. The molten salt was stirred at 70 rpm for U reduction reaction.

Residual concentrations of U, Nd, Ce and La were quantitatively analyzed by ICP analysis using a cyclic voltammetry (CV) technique. The equilibrium distribution curves (Figs. 2A and 2B) using the HSC codes in the U-La binary system molten salt of the Nd reduction reaction were prepared and the recovery behavior of U was confirmed.

When the Nd metal is added to the eutectic salt mixture (LiCl + KCl + UCl ₃ + CeCl ₃ + LaCl ₃ ), the reaction of substituting UCl ₃ with Nd is proceeded while Nd acts as a reducing agent.

As a result, NdCl ₃ is gradually formed in the molten salt, and at the same time, the U ion is reduced and U metal is produced.

As a result of the U recovery test, the U concentration in the UCl ₃ state was measured to be about 10 ppm after 2 hours from the start of the reduction reaction, and the determination of the end time of the recovery reaction was performed by real- Respectively.

After the start of the recovery reaction, the first 4 samples were collected at intervals of 20 minutes, and the remaining 4 samples were collected at intervals of 60 minutes to measure the decrease in U concentration. About 120 minutes after the start of the reduction reaction It was confirmed that the reduction reaction was completed (FIG. 3A).

It can be seen that the concentration of Ce and La in which the metal chloride formation Gibbs free energy (-ΔG) is larger than Nd is slightly reduced as the metal ions are reduced and formed as metal particles (FIG. 3b).

Compared with the conventional RAR process that combines the LCC electrolytic recovery of an actinide metal and the oxidation of rare earth (RE) metal to the LCC, the recovery reaction is terminated about 2 hours after the start of the reaction, (U) recovery reaction by the reducing action of (RE) metal.

According to the method for recovering the residual actinide source in the chloride molten salt according to the present invention, the rare earth metal is charged into the LiCl-KCl eutectic salt and used as a reducing agent to reduce the actinide group metal ion to produce various kinds of actinides Group elements at the same time, greatly shortening the collection processing time and simplifying the process and the apparatus, thereby dramatically improving the efficiency of the collection process.

 The residual concentration of actinide in the eutectic salt after recovery of the actinide group element using the rare earth metal as a reducing agent can be less than 100 ppm within about 2 hours. In particular, when Gd or Y is used as the rare earth metal as the reducing agent, The content of the rare earth metal recovered together with the actinide group element can be greatly lowered compared to the conventional RAR process.

From the equilibrium distribution curve for the actinide element reduction of rare earth metals prepared using the HSC 6.0 computer code, the theoretical recovery of the actinide metals can be as high as 99.9% or more

Claims (8)

A method for recovering a residual actinide element in a chloride molten salt,
In order to separate the actinide group element from the eutectic salt by adding rare earth metal as a reducing agent to the chloride molten salt, a small vessel containing a rare earth metal as a reducing agent and a stirrer is placed in a vessel containing a eutectic salt And collecting the actinide group element reduced from the metal ion into the metal fine particle state into a small container and recovering the recovered actinide group element in the chloride molten salt. The method of claim 1, wherein the chloride molten salt is a LiCl-KCl eutectic salt. The method of claim 1 wherein said rare earth metal is characterized in that the metal chloride forming Gibbs free energy (-? G) is greater than that of the actinide group metal. The method of claim 1, wherein the rare earth metal is at least one selected from the group consisting of Gd, Y, Pr, Nd, Ce and La. delete The method according to claim 1, wherein, in order to separate the actinide (An) element into a small vessel and to separate only the actinide element contained in the eutectic salt in the small vessel from the partially reduced rare earth metal microparticles, Wherein the cadmium (Cd) is added to the eutectic salt and the cadmium salt is converted into a Cd-An alloy form to separate the eutectic salt and the Cd-An alloy. The method of claim 1, wherein the rare earth metal is selected from the group consisting of metal chloride forming Gibbs free energy (-? G) to recover the actinide element so as to minimize the content of rare earth element that is recovered together with the actinide element and which can damage the nuclear fuel cladding. Wherein Gd or Y close to the Gibbs free energy (-? G) value of the actinide group metal is used. 8. The method according to claim 7, wherein a rare earth metal such as Gd or Y, which is a reducing agent, is added to the eutectic salt in order to recover the actinide element so as to minimize the content of the rare earth element which is recovered together with the actinide element and which can damage the nuclear fuel cladding Wherein a rare earth metal such as Gd or Y, which is a reducing agent, is withdrawn from the eutectic salt and the amount of rare earth metal ions other than Gd or Y is reduced after 2 hours after the completion of the reduction reaction of the actinide group element in the chloride molten salt, Method of recovery of group elements.

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