KR101693775B1 - Methods and devices using liquid metal including Bi or Pb or Bi-Pb alloy for separating actinides and rare earth elements in high-level radioactive molten salts from pyroprocessing - Google Patents

Abstract

The present invention relates to a method and a device to purify a whole high level radioactive waste into a middle level radioactive waste or a low level radioactive waste by separating an actinide element group and a rare earth element group from a molten salt generated from a used nuclear fuel pyrochemical process by using a liquid metal including bismuth (Bi) or bismuth-lead (Bi-Pb) alloy at high temperatures to lower the radiation level and thermal density of a final radioactive waste generated from a pyrochemical process. According to the present invention, the actinide element group and the rare earth element group included in the molten salt are reduced and melted to the inside of the liquid metal including Bi or Bi-Pb by electrolytic refining to form a heterogeneous metal compound of a liquid type or a solid type in the liquid metal including Bi or Bi-Pb alloy, and an equilibrium potential among elements in the same element group comes close, thereby making it difficult to separate each element. However, since the density of the heterogeneous metal compound is higher or lower than that of the liquid metal including Bi or Bi-Pb alloy, the heterogeneous metal compound of the two element groups is able to be separated by using a difference in the density. For this separation, configured is a device having a purifier, an agitator, a centrifuge, a magnetic field generator, a pipe, and a valve therein. Moreover, the liquid metal itself including Bi or Bi-Pb alloy remaining after collecting the heterogeneous metal compound is purified after separation, and the purified liquid metal is able to be reused in an electrolytic deposition.

Description

TECHNICAL FIELD The present invention relates to a method for separating a group of actinide element group (s) and a rare earth element group contained in a high-level radioactive molten salt generated in pyro processing using bismuth or bismuth-lead alloy liquid metal (Methods and devices using liquid metal including Bi or Pb or Bi-Pb alloy for separating actinides and rare earth elements in high-level radioactive molten salts from pyroprocessing}

The present invention is based on the finding that a low concentration of actinide element group and rare earth element group remaining in the molten salt generated by pyroprocessing, which is a key part of the dry separation process, is converted to high purity plutonium And a method for recovering the group of actinide elements while preventing the refining of the sensitive nuclear material such as the actinide group of the radioactive waste containing the rare earth element group and minimizing the content of the rare earth element group in the recovered actinide element group. To a method for minimizing the content of element groups. Bismuth or bismuth-lead alloys Liquid metals collectively refer to pure liquid bismuth or pure liquid lead, or mixtures thereof.

As a fundamental solution to the problem of carbon dioxide generation, nuclear power generation systems are being actively applied at home and abroad. Nuclear power plants produce high-activity spent fuel as a by-product in the process of power or energy production. However, nuclear power generation is severely degrading the environmental protection effect due to the generation of high-level waste. Effective use of spent nuclear fuel is necessary to ensure sustainability of nuclear power generation.

Pyro-processing method, which is a key part of dry separation process for spent fuel processing developed in Korea, uses high temperature molten salt instead of water as a solvent and charges oxide fuel to make chloride after electrolytic reduction. The potential difference between the actinide element group and the rare earth element group is used for separation. This method has excellent process safety against nuclear critical accidents and high radioactivity, and is a technique that has a strength in comparison with the wet re-treatment technology currently commercialized in terms of secondary waste generation amount, nuclear diffusion resistance, and future nuclear conversion technology.

Spent fuel contains a large amount of long-lived high-level wastes such as actinite group elements with a half-life exceeding tens of thousands of years, and a large number of long-lived nuclear radionuclides such as a rare rare earth element group. Although the volume of waste generated in the pyro processing - based dry separation process currently under development at home and abroad has been reduced, it has not been proven that the disposal of high - level waste has been proven in the safety and safety aspects of any country in the world. Considering population density countries using nuclear power generation, the highest level of the group of actinide elements in the high-level waste discharged from the dry separation process is minimized, minimizing the radioactive level and heat density of the disposed wastes, Or low-level wastes.

The pyrolytic process currently under development at home and abroad includes electrolytic refining for recovering uranium using a solid cathode, electrolytic refining for recovering uranium element using a liquid cathode such as cadmium, electrolytic refining, and waste molten salt generated in electrolytic refining And a molten salt purification process for partially recovering the uranium element. Nonetheless, the content of long-lived nuclear and high-radionuclides included in the final radioactive waste is high and should be treated as high-level waste.

On the other hand, the advanced pyrolytic process using the bismuth or bismuth-lead alloy liquid metal of the present invention is currently being developed in the domestic and foreign countries through the electrolytic refining and electrolytic smelting processes to produce actinide element group ions such as uranium and ultra uranium element and rare earth element group ions And to purify the high-level radioactive molten salt. The molten salt purification technique of the present invention comprises electrolytic electrodeposition using a bismuth or bismuth-lead alloy liquid metal cathode and oxidation extraction through oxidant injection and is based on patented technology. Additionally, the well known bismuth or bismuth-lead alloy utilizes the formation of dissimilar metal compounds between the liquid metal and the group of actinide elements and also the phenomenon of the dissimilar metal compound formation between the bismuth or bismuth-lead alloy liquid metal and the rare earth element group. The feature of the present invention is that the density of the actinide group element is higher than that of the bismuth or bismuth-lead alloy liquid metal due to the difference in density between the two element groups after formation of the dissimilar metal compound, while the rare earth element group is composed of bismuth or bismuth- The fact that the density is smaller than the liquid metal is used to improve the purification efficiency. The densities of gallium and cadmium, which are liquids at high temperatures, are lower than those of the actinide and rare earth elements, while the densities of bismuth or bismuth-lead alloy liquid metals are lower than those of the actinide elements and higher than the rare earth elements. .

Cadmium is a liquid metal used in the pyrolysis process currently under development at home and abroad, but is advantageous in terms of dissolution of the electrodeposit compared to the liquid metal. However, cadmium is disadvantageous in terms of separation performance between the actinide element group and the rare earth element group. Thereby causing pollution of facilities.

In the present invention, when considering the domestic situation where disposal of high-level waste based on spent fuel and domestic radioactive waste classification standard law is difficult, bismuth or cadmium improved the disadvantages of group separation for the actinide group of cadmium molten salt purification technology Bismuth-lead alloy liquid-metal-molten salt.

On the other hand, Patent Document 1 discloses a method of separating an actinide group element and a rare earth element group through electrolytic electrodeposition and oxidation extraction using liquid bismuth and bismuth chloride, There are differentiating points regarding the separation method.

KR 10-2011-0087907

In the present invention, the actinide group element group is separated from the molten salt purification technique using the liquid cadmium metal, and the group of the actinide element group and the rare earth element group present in the remaining molten salt are further separated and separated by using a bismuth or bismuth- The purpose of this paper is to provide a method for

In order to accomplish the above object, the present invention provides an electrolytic refining technique using a bismuth or bismuth-lead alloy liquid metal as a cathode to deposit an actinide group element group ion and a rare earth element group ion present in the molten salt into a bismuth or bismuth- And electrodeposited on the substrate.

The present invention relates to a process for electrodeposition of a mixture of a heterometallic compound of the group of liquid metal-actinide elements and a liquid metal-actinide group of the liquid metal-actinide element group while electrodepositing the actinide group element and the rare earth element group to exceed the solubility in liquid metal of bismuth or bismuth- Thereby producing a heterometal compound of the rare earth element group.

The present invention relates to a method for preparing a bismuth or bismuth-lead alloy liquid metal by dissolving a different metal compound of the liquid metal-actinide group element group and a different metal compound of the liquid metal-rare earth element group in the bismuth or bismuth- , Magnetic separation using magnetism, or a combination of these techniques.

The present invention relates to a method for producing a bismuth-based alloy, comprising: contacting a bismuth or bismuth-lead alloy liquid metal with a molten salt comprising an actinide element group ion and a rare earth element group ion; Attaching a highly stable metal rod to the molten salt and connecting a current supply mechanism to the metal rod and the bismuth or bismuth-lead alloy liquid metal; Applying an electric current to the bismuth or bismuth-lead alloy liquid metal metal and electroplating the actinide group element ions and the rare earth element group ions in the molten salt to a bismuth or bismuth-lead alloy liquid metal metal; And separating the liquid metal-rare earth element group dissimilar metal compound and the liquid metal-actinide element group dissimilar metal compound produced in the electrodepositing step by density difference.

Further, as an embodiment of the present invention

The separation method of the group of actinide element and rare earth element in the molten salt using the bismuth or bismuth-lead alloy liquid metal of the present invention is a method of separating the rare earth element group finally generated in the pyro processing of spent nuclear fuel into radioactive waste It is possible to reduce the radioactivity level of the waste by reducing the proportion of the actinide element group component present, thereby improving the environment of the radioactive waste repository finally.

1 is a sectional view showing an electrolytic smelting cell for electrodepositing an actinide element group and a rare earth element group to a bismuth or bismuth-lead alloy liquid metal in the present invention;
FIG. 2 is a cross-sectional view showing the electrodeposition process of an actinide element group and a rare earth element group on a bismuth or bismuth-lead alloy liquid metal in an electrolytic smelting process.
3 is a cross-sectional view showing an apparatus for separating the liquid metal-actinide group element dissimilar metal compound from the liquid bismuth or bismuth-lead alloy liquid metal and the liquid metal-rare earth element group dissimilar metal compound into a gravity-acting principle.
4 is a cross-sectional view showing an apparatus for separating a dissimilar metal compound of the liquid metal-actinide group element group produced in a bismuth or bismuth-lead alloy liquid metal and a dissimilar metal compound of the liquid metal-rare earth element group by centrifugal separation principle.
5 is a flow diagram illustrating the entire process of separating the liquid metal-actinide element group dissimilar metal compound and the liquid metal-rare earth element group dissimilar metal compound from a liquid bismuth or bismuth-lead alloy liquid metal.

A method of further separating an actinide element group and a rare earth element group present in the molten salt of the present invention using a bismuth or bismuth-lead alloy liquid metal will be described with reference to the accompanying drawings.

As shown in Fig. 1, a bismuth or bismuth-lead alloy liquid metal is brought into contact with a hot molten salt in which an actinide element group ion and a rare earth element group ion exist. When the molten salt is loaded with an actinide element group such as tungsten, a rare earth element group, and a cathode metal rod having a higher standard electrode potential than the molten salt, and a bismuth or bismuth-lead alloy liquid metal is formed as a cathode and connected to a current supply mechanism, .

A metal rod with a high standard electrode potential acts as an inert anode and chlorine gas is generated by the oxidation reaction of chloride ions at the anode when current is applied. The bismuth or bismuth-lead alloy liquid metal acts as a negative electrode. When the current is applied, the metal is electrodeposited by the reduction reaction of the actinide element group and rare earth element group in the molten salt present in the negative electrode. One of the improvement techniques is to use a sacrificial anode using the same bismuth or bismuth-lead alloy liquid metal as the anode as the cathode material to promote the production of the dissimilar metal compound in the electrolytic electrodeposition without contaminating the molten salt.

In the LiCl-KCl molten salt at 500 ° C., the actinide group element group has a standard electrode potential as high as about 0.5 to 1 V as compared with the rare earth element group. Therefore, it is reduced prior to the rare earth element group as shown in FIG. 2 and is converted to a bismuth or bismuth- And is electrodeposited on the cathode. After reduction of the sufficient group of actinide elements, the rare earth element group is reduced and electrodeposited to the bismuth or bismuth-lead alloy liquid metal cathode.

According to the equilibrium phase equilibrium between the liquid metal and the actinide group and the equilibrium phase equilibrium between the liquid metal and the rare earth element group, the actinide group element and the rare earth element group show very low solubility to the liquid metal And forms a dissimilar metal compound with the liquid metal when the element exceeds the solubility and is electrodeposited on the liquid metal.

Bismuth or bismuth-lead alloys Dissimilar metal compounds that the liquid metal forms with the actinide and rare earth element families have a melting point of at least 830 degrees and a bismuth or bismuth- Lt; / RTI >

Considering that the density of actinide metals is 12 to 20 g / cm ³ , the density of rare earth metals is 4.5 to 7.9 g / cm ³ and the density of bismuth or bismuth-lead alloy liquid metals at 500 degrees is about 9.7 to 11.3 g / cm ³ The bismuth or bismuth-lead alloy liquid metal obtained through electrolytic smelting and the dissimilar metal compound of the liquid metal-actinide group and the liquid metal-rare earth element group are mixed with each other by the difference in density of each component, Of the bismuth or bismuth-lead alloy liquid metal. The principle of sedimentation by gravity, centrifugation principle, magnetic separation using magnetism, or a combination of these techniques is applied to separate heterometallic compounds distributed at different positions on a bismuth or bismuth-lead alloy liquid metal by density difference do. Each application method is as follows.

Bismuth or bismuth-lead alloy In the device shown in Fig. 3 which utilizes the principle of gravity to separate the liquid metal-actinide element group dissimilar metal compound present in the liquid metal and the liquid metal-rare earth element group dissimilar metal compound, Since the bismuth-lead alloy liquid metal has a lower density, the floating liquid metal-rare earth element group dissimilar metal compound is removed on a bismuth or bismuth-lead alloy liquid metal metal using a filter device capable of filtering solid particles Then, the valve of the piping connected to the lower part of the apparatus is opened and the bismuth or bismuth-lead alloy liquid metal is flowed downward by gravity, and the liquid metal-actinide element group dissimilar metal compound is recovered from the filter installed inside the piping.

As an alternative to the liquid metal-actinide element group dissimilar metal compound present in the bismuth or bismuth-lead alloy liquid metal and the liquid metal-rare earth element group dissimilar metal compound, an apparatus utilizing the principle of centrifugation as shown in FIG. 4 can be utilized have. A bismuth or bismuth-lead alloy liquid metal comprising a solid heterometallic compound at high temperature is rotated to radially disperse the heterometallic compound, the pure bismuth or bismuth-lead alloy liquid metal, the liquid metal- Actinide group element in a rotating bismuth or bismuth-lead alloy liquid metal edge by arranging the heterogeneous metal compound in the liquid metal-actinide element group, Metal compounds are collected to achieve group separation between the actinide element group and the rare earth element group.

5, the bismuth or bismuth-lead alloy liquid metal from which the dissimilar metal compound has been removed is reused as the negative electrode in the electrolytic smelting cell of FIG. The dissimilar metal compounds of the liquid metal-rare earth element group collected are stabilized using a vitrification process of radioactive waste, and then disposed of as radioactive waste having a low radioactive level. The dissimilar metal compound of the liquid metal-actinide group collected in the above process is dissolved in the molten salt to generate an actinide group ion and recycled to the dry separation electrolytic smelting process of pyroprocessing.

Claims (12)

A method for separating a group of actinide elements and a group of rare earth elements contained in a high-level radioactive molten salt generated in pyro-processing using a bismuth or bismuth-lead alloy liquid metal, comprising the steps of: Forming a compound and separating the two element groups using the difference in density of the formed dissimilar metal compound is included in the high level radioactive molten salt generated in the pyro processing using the bismuth or bismuth-lead alloy liquid metal And separating the actinide element group and the rare earth element group. A method for separating a group of actinide elements and a group of rare earth elements contained in a high-level radioactive molten salt generated in pyro-processing using a bismuth or bismuth-lead alloy liquid metal,
Contacting a bismuth or bismuth-lead alloy liquid metal with a molten salt comprising an actinide element group ion and a rare earth element group ion with a bismuth or bismuth-lead alloy liquid metal;
Attaching a highly stable metal rod to the molten salt and connecting a current supply mechanism to the metal rod and the bismuth or bismuth-lead alloy liquid metal;
Applying an electric current to the bismuth or bismuth-lead alloy liquid metal metal and electroplating the actinide group element ions and the rare earth element group ions in the molten salt to a bismuth or bismuth-lead alloy liquid metal metal; And
The step of separating the liquid metal-rare earth element group dissimilar metal compound and the liquid metal-actinium group element dissimilar metal compound produced in the electrodepositing step by density difference;
And a rare earth element group contained in a high-level radioactive molten salt generated in pyro processing by using a bismuth or bismuth-lead alloy liquid metal. delete The method of claim 1, wherein the dissimilar metal compound is formed using electrolytic electrodeposition wherein a current is applied to the bismuth or bismuth-lead alloy liquid metal between the two groups of elements to form a bismuth or bismuth-lead alloy liquid metal A method for separating a group of actinide elements and a group of rare earth elements contained in a high-level radioactive molten salt generated in pyro processing. The bismuth or bismuth-lead alloy liquid metal according to claim 1 or 2, wherein the vapor pressure of the bismuth or bismuth-lead alloy liquid metal is used to lower the liquid metal contamination and improve the productivity of the separation process plant. And separating the group of actinide elements and the group of rare earth elements contained in the high-level radioactive molten salt generated in the processing. 3. A process according to claim 1 or 2, characterized in that the group separation between the two groups of elements is combined in a multistage continuous process to improve the group separation capacity between the two groups of elements. A bismuth or bismuth- A method for separating a group of actinide elements and a group of rare earth elements contained in a high-level radioactive molten salt generated in pyro processing. 3. The method of claim 2, wherein the electrodepositing step comprises dissolving the actinide group element ions and the rare earth element group ions in the liquid metal-rare earth element group dissimilar metal compound and the bismuth- A group consisting of an actinide element group and a rare earth element group contained in a high-level radioactive molten salt generated in pyro processing using a bismuth or bismuth-lead alloy liquid metal, which is characterized by producing a liquid metal-actinide element group dissimilar metal compound / RTI > 3. The method of claim 2,
Separating the liquid metal-rare earth element group dissimilar metal compound from the bismuth or bismuth-lead alloy liquid metal metal by a filtration device on top of the bismuth or bismuth-lead alloy liquid metal; And
Separating the liquid metal-actinide element group dissimilar metal compound from the bismuth or bismuth-lead alloy liquid metal metal by gravity, centrifugal force, magnetic force or a combination thereof under bismuth or bismuth-lead alloy liquid metal;
And a rare earth element group contained in a high-level radioactive molten salt generated in pyro processing by using a bismuth or bismuth-lead alloy liquid metal. 3. The method according to claim 1 or 2, further comprising separating the actinide group element and the rare earth element group using a high-temperature centrifugation principle of the dissimilar metal compound of the two element groups having the density difference, wherein the bismuth or bismuth- A method for separating a group of actinide elements and a group of rare earth elements contained in a high-level radioactive molten salt generated in pyro-processing using a lead alloy liquid metal. The process according to claim 2, wherein the metal rod is selected from the group consisting of actinide elements contained in the high-level radioactive molten salt generated in the pyro processing using the bismuth or bismuth-lead alloy liquid metal and the standard electrode potential higher than the molten salt. A method for separating a rare earth element group. A bismuth or bismuth-lead alloy liquid metal according to claim 1 or 2, characterized by a sacrificial anode using the same bismuth or bismuth-lead alloy liquid metal as the cathode as the cathode material for driving electrodeposition And separating the actinide element group and the rare earth element group contained in the high-level radioactive molten salt generated in pyro processing. An apparatus for separating a group of actinide elements and a group of rare earth elements contained in a high-level radioactive molten salt generated in pyro processing using a bismuth or bismuth-lead alloy liquid metal,
An electrolytic smelting cell in which a molten salt containing an actinide element group ion and a rare earth element group ion is brought into contact with a bismuth or bismuth-lead alloy liquid metal;
A metal rod used as an inert anode in the molten salt;
A power supply for supplying current to the metal rod and the bismuth or bismuth-lead alloy liquid metal;
The method of claim 1, wherein a current is applied to the bismuth or bismuth-lead alloy liquid metal metal, and the actinide group element ions and the rare earth element group ions in the molten salt undergo a reduction reaction to form the liquid metal- A filter for separating the rare-earth element group dissimilar metal compound and the liquid metal-actinide element group dissimilar metal compound by density difference;
Comprising a bismuth or bismuth-lead alloy liquid metal, which comprises a high-level radioactive molten salt generated in pyro-processing, and separates the group of actinide elements and the group of rare earth elements contained in the high-level radioactive molten salt.

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