JP2002339091A - Method for removing cesium in metallic sodium and apparatus therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for selectively extracting cesium in metallic sodium and purifying sodium, by which separation into residue containing impurities of high concentration in a small amount and purified metallic sodium in a high yield to the amount of sodium to be treated is made in a short time with low electric power consumption. SOLUTION: D.C. voltage is applied, and the electric current is flowed to the space between a liquid sodium anode solution and a liquid sodium cathode solution using a solid electrolyte having conductivity for cesium ion as a membrane. The cesium ion in the liquid sodium anode solution is moved from the anode side to the cathode side through the membrane, so that cesium in the sodium on the anode side is concentrated into the sodium on the cathode side and is removed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method and an apparatus for purifying metallic sodium containing impurities, and more particularly to a method and an apparatus for purifying metallic sodium containing cesium as an impurity.

[0002]

2. Description of the Related Art Metallic sodium, which is used as a coolant for a nuclear reactor, changes into impurities that are unsuitable as a coolant during use, and impurities contained therein change into radionuclides. Becomes Moreover, the purified residue must be disposed of as waste, but from the viewpoint of radioactive waste, the volume must be reduced as much as possible to reduce the processing cost. Furthermore, in terms of the cost of refining large amounts of sodium, the lowest cost method must be found. To that end, it is important to devise and adopt an appropriate method depending on the type of impurity.

The so-called cold trap method using zirconia, which is effective in removing oxygen and hydrogen impurities, is effective in removing oxygen and hydrogen. However, metals other than sodium oxide and sodium hydroxide or metals other than sodium oxide and sodium hydroxide are effective. It is not suitable for removing metal oxides.

In this regard, a high-purity sodium purifying apparatus using an alkali metal thermoelectric power generation technique has been proposed (Japanese Patent Laid-Open No. 6-172883). However, such a device requires a high temperature condition of 623 ° C., the sodium ion conductive solid electrolyte to be used is severely degraded, and a device such as a device for producing conditions such as maintaining a vapor pressure difference and maintaining a temperature difference. There were problems such as increased operating costs.

[0005] In order to solve the above problems, the present inventors have proposed in Japanese Patent Application No. 2000-192514 a sodium purifying apparatus and a purifying system which have a simple configuration and do not deteriorate the solid electrolyte. This unpublished prior application technology purifies sodium by selectively moving the sodium of the impure sodium on the anode side to the cathode side through a sodium ion conductive solid electrolyte.

However, in recent years, sodium cesium in the coolant of fast breeder reactors and decommissioning reactors in a certain country contains a lot of activated cesium, and this treatment is a problem, and this treatment requires effective separation of cesium. ing.

[0007] In the above-mentioned undisclosed prior art, since sodium is moved and impurities are left in the residue, it is necessary to ion-move the entire amount of sodium, which is inefficient and consumes time and power. But large and costly.

[0008]

SUMMARY OF THE INVENTION Accordingly, the present invention has been made in view of the above problems, and is a method and an apparatus for selectively extracting and purifying cesium in metallic sodium. An object of the present invention is to provide a method and an apparatus which can separate high-concentration, small-quantity impurity-containing residues and high-yield purified metal sodium in comparison with the amount of sodium to be treated with a small amount of time and power.

[0009]

According to the present invention, there is provided a method for removing cesium from metallic sodium, comprising applying a dc voltage between a liquid sodium anolyte and a liquid sodium catholyte with a cesium ion conductive solid electrolyte as a diaphragm. Through the membrane to move cesium ions in the liquid sodium anolyte solution from the anode side to the cathode side, thereby concentrating the cesium in the anode side sodium into the cathode side sodium to remove the cesium in the anode side. It is characterized by being removed.

The anode cell is filled with the raw material sodium to be purified, and the cathode cell is filled with a sufficient amount of sodium to be able to apply the initial load required for this ion transfer. Melting point (98 ° C)
If a current is applied from the anode to the cathode by applying a DC voltage between the two electrodes while maintaining the temperature above cesium, the cesium in the anode tank emits electrons and cesium cations in the cesium ion conductive solid electrolyte membrane. Then, it passes through the cornea and moves to the cathode cell side, where electrons are obtained on the cathode side to become cesium and stay in the cathode cell. Thus, the cesium is selectively concentrated in the cathode cell.

The minimum temperature for the purification is to maintain the liquid phase of the bipolar tank solution, but a temperature at which a load with an appropriate current density is applied is preferable. However, if the temperature is too high, a problem of the heating device and a problem of the material of the device arise. Therefore, it is preferable to appropriately advance the temperature, for example, in the range of 200 to 500 ° C.

The current density related to the load needs to be changed depending on the properties of the raw material sodium to be treated and the amount of the catholyte, but can be, for example, about 200 mmA / cm ² .

Furthermore, the method for removing cesium from metallic sodium according to the present invention is characterized in that the cesium ion conductive solid electrolyte is a solid electrolyte produced by ion-exchanging sodium in sodium ion conductive beta alumina with cesium. There is a feature.

The term "beta-alumina" as used herein is a double oxide of sodium and aluminum, and is Na ₂ O · x
A compound represented by a composition formula of Al ₂ O _{3 and having} a composition in which x is approximately 11 to 5 is known. In general, in a double oxide having good sodium ion conductivity, x is around 5. A double oxide called β ″ alumina containing a large amount of the crystalline phase of the composition is considered to be preferable.

The β ″ alumina is also preferable for the raw material used for producing the cesium ion conductive solid electrolyte of the present invention.

For example, the production of a cesium ion conductive solid electrolyte is carried out by preparing a powder β ″ in a molten salt bath of cesium nitrate.
It can be obtained by charging alumina and performing high-temperature treatment. Although cesium nitrate has a melting point of 414 ° C., it tends to decompose at higher temperatures, so it is desirable to perform ion exchange at 450 ° C. or lower. Since the compound has no boiling point and decomposes at a high temperature, the temperature range must be appropriately selected.
In addition, cesium nitrate remaining unreacted and excessively remaining in the mixed oxide powder after the exchange may be removed by washing with water or the like, and may be dried promptly. Thereafter, it can be appropriately molded and fired to obtain a desired diaphragm structure. A cesium ion-conductive electrolyte tube can be produced by molding into a cylindrical shape with the best strength and a bottom and sintering.

Further, the method for removing cesium from metallic sodium according to the present invention uses liquid sodium from which cesium has been removed by the above method as an anolyte, and uses sodium ion-conducting beta-alumina as a diaphragm to form the anolyte and the liquid sodium cathode. By applying a DC voltage between the liquids to cause a current to flow, sodium ions are moved from the anode side to the cathode side through the diaphragm, so that the cesium on the anode side remains on the anode side, thereby further improving the sodium purity on the cathode side. It is characterized by increasing.

[0018] Sodium containing cesium as an impurity is very likely to contain impurities other than cesium, and most of the cesium as impurities is efficiently concentrated to reduce the volume as waste. After the conversion, the method can be used to further reduce the cesium concentration. The present method can be carried out by using the apparatus and system described in the above-mentioned unpublished prior application technology for separating sodium from cesium at one end. Alternatively, it can be performed continuously with equipment.

Further, in the apparatus for removing cesium from metallic sodium according to the present invention, an anode cell having an anode and a cathode cell having a cathode are adjacent to each other with a cesium ion-conductive solid electrolyte diaphragm interposed therebetween, and a DC voltage is applied between the positive and negative electrodes. Power supply that can apply
The current is passed by the power supply and through the diaphragm,
By moving the cesium ions in the liquid sodium anolyte from the anode side to the cathode side, the cesium in the anode side sodium can be concentrated in the cathode side sodium and the anode side cesium can be removed. And

It is preferable that the anode tank and the cathode tank are provided with heating means for maintaining a temperature at which sodium and cesium are kept in a liquid state. Further, a means for shielding from the atmosphere is required so as not to cause a double reaction such as oxidation or moisture absorption hydrolysis. Further, the electrode must be made of a material that is not affected by sodium or cesium. For example, it can be selected from molybdenum, tungsten, stainless steel, and the like.

The form of the diaphragm is not particularly limited, and there is no need to be circular, square or flat, but the catholyte is in contact on one side and the anolyte is on the other side at the same time.
The larger the area in contact with the catholyte and the anolyte, the larger the amount of ion movement per unit time.

Further, in the apparatus for removing cesium in metallic sodium according to the present invention, the bottomed cylinder itself is formed by using one of the anode and cathode tanks as a bottomed cylinder composed of a cesium ion conductive solid electrolyte. A diaphragm and one tank,
The other tank as an outer cylinder container in which the bottomed cylinder is provided,
One of the tanks is provided with one electrode of an anode or a cathode, and the other tank is provided with the other electrode.

That is, the present invention is characterized in that the bottomed cylinder itself has the function of a diaphragm and the function of a tank, and the area of the diaphragm is increased. And, by installing the inner cylinder in the outer cylinder container, only one other tank that requires a vessel wall material that is resistant to sodium or cesium and can withstand the processing temperature is required.

Further, in the apparatus for removing cesium in metallic sodium according to the present invention, the cesium ion conductive solid electrolyte is a solid electrolyte produced by ion exchange of sodium in sodium ion conductive beta alumina with cesium. It is characterized by the following.

That is, most types of diaphragms can be manufactured by molding and firing the cesium ion conductive solid electrolyte powder obtained by the ion exchange.

[0026]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, an embodiment of the present invention will be exemplarily described with reference to the drawings. However, the dimensions, shapes, materials, relative arrangements, and the like of the components described in the present embodiment are not intended to limit the scope of the present invention only to them, unless otherwise specified. Not just.

Embodiment 1 FIG. 1 is a conceptual diagram showing an example of an apparatus for removing cesium in metallic sodium having a cesium ion conductive solid electrolyte membrane according to the present invention.

In FIG. 1, reference numeral 101 denotes a diaphragm composed of a cesium ion conductive solid electrolyte. This diaphragm 10
No. 1 was prepared as follows.

The powder β ″ alumina was put into a molten salt bath of cesium nitrate heated and maintained at (450 ° C.), and subjected to a high temperature treatment with stirring (10 hours). Thereafter, the molten salt mixture was cooled and solidified. Pulverized into fine particles, the powder was washed with water to remove residual unreacted cesium nitrate, dried,
A cesium ion conductive solid electrolyte powder substituted with Cs was obtained. A small amount of a binder was mixed into the powder, compression-molded into a rectangular plate shape, and fired in a firing furnace to form a diaphragm 101.

The center of a rectangular parallelepiped container is partitioned by the diaphragm 101 to form a partition wall, one of which is a cathode tank 102, and a cathode 104.
, And the other was used as the anode tank 103, and the anode 105 was provided to constitute a device for removing cesium in metallic sodium.

The cathode tank 102 is filled with liquid sodium containing cesium as an impurity to the extent that the cathode 104 is immersed, and the anode tank 103 is almost completely filled with liquid sodium containing cesium as the same impurity. While maintaining the temperature at (300 ° C.) while heating with a heating device, a DC power supply 106 is connected and the current density is set to (200 mmA /
cm ² ), cesium is moved from the anode cell 103 to the cathode cell 102 through the diaphragm 101 and the anode cell 10
Cesium was extracted from sodium 3 to increase its purity.

A schematic diagram of the mechanism by which cesium moves through the diaphragm 101 is shown in the circular enlarged view of FIG.
That is, cesium on the anode 105 side emits electrons on the diaphragm 101 to become cesium ions, and the cesium ions move in the diaphragm 101 to reach the cathode 104 side, and similarly acquire electrons on the diaphragm 101 to become cesium. , Cathode 104
Stay on the side.

Embodiment 2 FIG. 2 shows the anode 204 according to the present invention.
Alternatively, it is a conceptual diagram showing an example of an apparatus for removing cesium from metallic sodium in which one tank of a cathode 205 is a bottomed cylinder 201 made of a cesium ion conductive solid electrolyte.

A cesium ion conductive solid electrolyte powder was prepared in the same manner as in Example 1. A small amount of a binder was mixed into the powder, compression-molded into a bottomed cylinder, and fired in a firing furnace to produce a bottomed cylinder 201 which itself functions as a cesium ion conductive solid electrolyte diaphragm. This bottomed cylinder 201 is disposed in an outer cylinder, a cathode 205 is provided in the bottomed cylinder, and an anode 204 is disposed in a space between the outer cylinder and the bottomed cylinder 201 to remove cesium in metallic sodium. The device was configured.

The inside of the bottomed cylinder 201 is a cathode tank 202, the space between the outer cylinder container and the bottomed cylinder 201 is an anode tank 203, and a liquid containing cesium as an impurity to the extent that the cathode 205 is immersed in the cathode tank 202. Sodium is filled, and the anode tank 203 in which the anode 204 is immersed is almost completely filled with liquid sodium containing cesium as the same impurity, and is heated (300 ° C.) while being heated by a heating device (not shown). 206 and a current density of (20
0 mmA / cm ² ) and a diaphragm (bottomed cylinder 20)
Move cesium from anode tank to cathode tank through 1),
Cesium was extracted from the sodium in the anode tank to increase the purity.

(Embodiment 3) FIG. 3 is a process flow chart of an example in which the method of the present invention is continuously performed. In FIG. 3, the electromagnetic pump 3
The cesium-contaminated sodium Na quantitatively taken out by the action of the delivery side pressure of 03 is purified through the average residence time in the apparatus for removing cesium in metallic sodium 301 of the present invention through an average residence time to increase the purity and again to the electromagnetic pump 303 suction side. It was sucked and supplied as a coolant for the reactor 302. Although the flow path of sodium is not shown,
The fluid was maintained at a temperature equal to or higher than the melting point of sodium by providing a heat retaining means.

Example 4 FIG. 4 shows a process flow of an example of a method for extracting cesium in the first step of the present invention, then extracting the purified sodium, and further extracting the sodium in the second step to increase the purity. FIG.

In FIG. 4, the process according to the present embodiment comprises a raw material supply means 401, a cesium removal apparatus 405, a waste sodium decomposition means 413, and a sodium purification apparatus 427.
And

The raw material supply means 401 includes a raw material tank 402 and a supply pipe connected from the outlet of the tank to a bottomed cylindrical anode tank 406 of a cesium removing device 405 via a valve 404.

The cesium removing device 405 includes a cathode vessel 407 having an outer cylindrical container having a bottomed cylindrical anode vessel 406 therein, an anode 409 disposed in the bottomed cylindrical anode vessel 406, and the above-mentioned bottomed cylindrical anode vessel 406. A cathode 408 arranged in a space between the outer vessel cathode chamber 407, a raw material supply port connected to the supply pipe to introduce a raw material into the bottomed cylindrical anode vessel 406, and an anolyte solution from which cesium has been removed A discharge port connected to a transfer pipe, a discharge port provided at the bottom of the cathode vessel 407 of the outer cylinder, a discharge valve 419 connected thereto, and a DC power supply 41.
Contains 0.

The sodium purifier 427 comprises an outer vessel container anode vessel 429 having a bottomed cylindrical cathode vessel 428 therein, a cathode 430 disposed in the bottomed cylindrical cathode vessel 428, and a bottomed cylindrical cathode vessel 428. An anode 431 disposed in a space between the cylindrical vessel anode tank 429, a transfer pump 435, and a transfer pipe connected to the transfer pump 435 delivery side by a transfer pipe to remove the anolyte solution from which the cesium of the cesium removal device has been removed. A supply port for introducing into the space between the bottomed cylindrical anode vessel 428 and the outer vessel container cathode vessel 429, a removal port for connecting purified sodium to a suction side of a removal pump 436 by a removal pipe, and a delivery of the removal pump 436. Sodium tank 437 connected to the side, a discharge port provided at the bottom of the outer vessel container cathode tank 429, and a discharge valve 44 connected thereto. And, including the DC power supply 432.

The waste sodium decomposing means 413 is a waste sodium decomposing tank 41 which can be cooled by a water cooling jacket 418.
7, valve 421 and piping, sodium decomposition tank 4
An alcohol supply tank 416 capable of supplying alcohol 424 to the tank 17; a buffer tank 415 having an inlet connected to a discharge valve 419 of the cesium removing device via a pipe and an outlet connected to a waste sodium decomposition tank 417 via a valve 420 by a pipe; Buffer tank 41 having an inlet connected to a discharge valve of the sodium purifier by piping and an outlet connected to waste sodium decomposition tank 417 via valve 422 by piping.
4 is included.

In the above process flow, the raw material tank 402 of the raw material supply means 401 is filled with cesium-containing sodium 403, and valves 404 and 438 are operated to charge a predetermined amount of the raw material into the bottomed cylindrical anode tank 406. The anolyte 412 is used. The catholyte 411 also contains cesium-containing sodium 403 in bulbs 404 and 43.
Operate 9 to charge the electrode to the extent that it is immersed. Thereafter, while maintaining the temperature at (300 ° C.) with a heating device (not shown), the voltage of the DC power supply 410 is increased to approximately (0.5 V).
An electric current was applied between the anode 409 and the cathode 408. At this time, the initial current was (200 mmA / cm ² ), but as the process progressed, the current changed. Therefore, the applied voltage was adjusted to keep the current constant. When the transition to is approaching the end, the load is no longer applied, so the operation is terminated.

After the cesium removal is completed, the catholyte 411 is discharged into the buffer tank 415 by operating the discharge valve 419 at the lower part of the cathode vessel 407 of the outer cylinder.
25 waste sodium 1

The anolyte 412 of the cesium removal device 401 from which the cesium removal has been completed activates the transfer pump 435 of the sodium purification device 427 to cause the sodium purification device 42 to operate.
7 is transferred to the outer cylinder container anode tank 429. Bottomed cylinder 428
Is charged with high-purity sodium in advance.

Thereafter, while maintaining the temperature at (300 ° C.) by a heating device (not shown), a voltage of the DC power supply 432 was applied (approximately (0.5 V)) between the anode 431 and the cathode 430 to flow a current. At this time, the initial current is (200 mmA
/ Cm ² ), but the current changes as the process proceeds. Therefore, the applied voltage is adjusted to keep the current constant.

Thus, when most of the anolyte 434 has been transferred to the catholyte 433, the sodium purification is terminated.
The removal pump 436 is activated to transfer the catholyte 433 to the purified sodium tank 437 for storage.

The anolyte 434 is withdrawn from the discharge valve 440 of the outer vessel container anode tank 429 and transferred to the buffer tank 414 to make 423 waste sodium 2.

The waste sodium 1 or 2 is supplied from the buffer tank 414 or 415 to the valve 422 or 420
Is transferred to a waste sodium decomposition tank, the alcohol 424 in the alcohol tank 416 is added by operating the valve 421, and is decomposed while cooling to obtain a waste sodium alcoholate 426.

[0050]

As described above, according to the present invention, there is provided a method and apparatus for selectively extracting and purifying cesium in metallic sodium, comprising a high-concentration, small-quantity impurity-containing residue in a short time with low power. And a method and an apparatus which can be separated into high-yield purified metal sodium in comparison with the amount of treated sodium.

[Brief description of the drawings]

FIG. 1 is a conceptual diagram showing an example of an apparatus for removing cesium in metallic sodium having a cesium ion conductive solid electrolyte diaphragm according to the present invention.

FIG. 2 is a conceptual diagram showing an example of the apparatus for removing cesium in metallic sodium according to the present invention, in which one of the anode and cathode tanks is a bottomed cylinder made of a cesium ion conductive solid electrolyte.

FIG. 3 is a process flow diagram of an example in which the method of the present invention is continuously performed.

FIG. 4 is a process flow diagram of an example of a method for extracting cesium in the first step of the present invention, and then extracting the purified sodium in a second step to further extract sodium to increase the purity.

[Explanation of symbols]

101 Diaphragm composed of cesium ion conductive solid electrolyte 102 Cathode vessel 103 Anode vessel 104 Cathode 105 Anode 106 DC power supply 201 Bottomed cylinder composed of cesium ion conductive solid electrolyte 202 Cathode vessel 203 Anode vessel 204 Cathode 205 Anode 206 DC power supply 301 Apparatus for removing cesium in metallic sodium 302 Nuclear reactor 303 Electromagnetic pump 401 Raw material supply means 402 Raw material tank 403 Cesium-containing sodium 404 Valve 405 Cesium remover 406 Bottom cylindrical anode tank 407 Outer cylinder cathode tank 408 Cathode 409 Anode 410 DC power supply 411 Catholyte 412 Anolyte 413 Waste sodium decomposition means 414 Buffer tank 415 Buffer tank 416 Alcohol supply tank 417 Waste sodium decomposition tank 418 Water cooling jacket 19 Discharge valve 420 Outlet valve 421 Valve 422 Valve 423 Waste sodium 2 424 Alcohol 425 Waste sodium 1 426 Waste sodium alcoholate 427 Sodium purifier 428 Bottom cylindrical cathode vessel 429 Outer vessel vessel anode vessel 430 Cathode 431 Anode 432 DC power supply 433 Catholyte 434 Anolyte 435 Transfer pump 436 Removal pump 437 Purified sodium tank 438 Valve 439 Valve 440 Valve

Claims (6)

[Claims] A cesium ion in a liquid sodium anolyte is passed through said diaphragm by applying a DC voltage between a liquid sodium anolyte and a liquid sodium catholyte with a cesium ion conductive solid electrolyte as a diaphragm. By moving from the anode side to the cathode side, cesium in sodium on the anode side is concentrated in sodium on the cathode side,
A method for removing cesium in metallic sodium, comprising removing cesium on the anode side. 2. A cesium ion conductive solid electrolyte,
The method for removing cesium from metallic sodium according to claim 1, wherein the solid electrolyte is produced by ion-exchanging sodium in beta-alumina having sodium ion conductivity with cesium. 3. A liquid sodium from which cesium has been removed by the method of claim 1 is used as an anolyte, and a direct current voltage is applied between the anolyte and the liquid sodium catholyte using sodium ion-conductive beta alumina as a diaphragm. By passing an electric current and moving sodium ions from the anode side to the cathode side through the diaphragm, cesium on the anode side is left on the anode side to further increase the purity of sodium on the cathode side. Cesium removal method. 4. An anode cell having an anode and a cathode cell having a cathode are adjacent to each other via a cesium ion conductive solid electrolyte membrane, and a power supply capable of applying a DC voltage between the positive and negative electrodes is provided.
The current is passed by the power supply and through the diaphragm,
By moving the cesium ions in the liquid sodium anolyte from the anode side to the cathode side, the cesium in the anode side sodium can be concentrated in the cathode side sodium and the anode side cesium can be removed. Cesium removal device in metallic sodium. 5. A method according to claim 1, wherein one of the tanks of the anode and the cathode is a bottomed cylinder made of a cesium ion conductive solid electrolyte, and the bottomed cylinder itself is used as a diaphragm and one of the tanks.
The other tank as an outer cylinder container in which the bottomed cylinder is provided,
The apparatus for removing cesium in metallic sodium according to claim 4, wherein one of the tanks is provided with one of an anode and a cathode, and the other tank is provided with the other electrode. 6. A cesium ion conductive solid electrolyte,
The apparatus for removing cesium in metallic sodium according to claim 4 or 5, wherein the solid electrolyte is a solid electrolyte produced by ion-exchanging sodium in beta-alumina having sodium ion conductivity with cesium.