JP2966349B2 - Elemental separation method from mixed melt of high-level radioactive waste and glass raw material - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a technique for separating various elements such as useful elements from high-level radioactive waste generated in a reprocessing process of spent nuclear fuel, and more particularly, to a technique for separating high-level radioactive waste in a melting furnace. BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for separating various elements contained in waste from a mixed melt in a melting furnace when mixing and melting a level radioactive waste with a glass raw material and performing vitrification treatment.

[0002]

2. Description of the Related Art Fission products, actinide elements, corrosion products, etc. (hereinafter, referred to as high-level waste) contained in wastes such as high-level radioactive liquid waste discharged from a reprocessing process of spent nuclear fuel (hereinafter, referred to as high-level waste) The waste component) is melted at a high temperature together with the glass raw material in order to fix it in a stable form from the viewpoint of treatment, storage and disposal, and is turned into a vitrified high-level waste. That is, a high-level waste and a glass raw material are charged into a melting furnace having a pair of electrodes therein, and an alternating current is applied to the electrodes, so that the high-level waste and the glass raw material between the electrodes are directly energized and heated. (Self-heating by Joule heat) to mix and fuse. Next, the mixed melt is taken out of the melting furnace and cooled to be a vitrified body.

[0003] However, various elements are contained in high-level waste, and separating reusable elements from high-level waste before vitrification treatment is an effective use of resources. As a method of separating useful elements from waste components in high-level waste, a solvent that selectively extracts a desired waste component in a solvent by contacting an extraction solvent with high-level waste and separating the solvent is used. Proposal of extraction method, molten salt electrolysis method, etc., which separates the target element using the difference in solubility of waste component elements in molten salts such as fluorides and chlorides of alkali metals and alkaline earth metals Has been studied.

[0004]

The waste after separating various elements from the high-level waste by the above-mentioned separation method is mixed and melted with a glass raw material to form a vitrified body as in the conventional case. . Therefore, the element separation method described above is added to the standard vitrification process, which complicates the entire vitrification process and increases design and manufacturing costs related to the vitrification process.
Furthermore, in the element separation method using an extraction solvent or a molten salt, the extraction solvent or the molten salt itself is generated as radioactive waste (secondary waste), and the amount of secondary waste generated is smaller than in a standard vitrification process. A problem arises in that the management burden of the radioactive waste treatment and disposal due to is large.

Accordingly, an object of the present invention is to provide a method for separating various elements from high-level waste without using an extraction solvent or a molten salt, thereby reducing the amount of secondary waste generated. It is to provide.

[0006]

That is, the first aspect of the present invention.
In the embodiment, the high-level waste and the glass raw material are charged into a melting furnace having a pair of electrodes therein, and an alternating current is applied to the electrodes, whereby the high-level waste and the glass raw material between the electrodes are supplied. Is heated and directly mixed to melt, and then the mixed melt is taken out of the melting furnace and cooled to form a vitrified material. A DC current is passed through the electrode to perform electrolysis, and the elements in the mixed melt that are oxidized or reduced by the electrolysis are deposited on the electrode surface or the mixed melt. This is a method for separating elements from a mixed melt of high-level radioactive waste and glass raw materials.

In a second embodiment of the present invention, a high-level radioactive waste and a glass raw material are charged into a melting furnace having a pair of AC electrodes therein, and an AC current is applied to the AC electrodes. The high-level radioactive waste between the AC electrode and the glass material is directly heated by heating and mixed and melted, and then the mixed molten material is taken out of a melting furnace and cooled to form a vitrified high-level radioactive waste. During the solidification process, a pair of DC electrodes is inserted into the mixed melt in the melting furnace, and a DC current is passed through the DC electrodes to perform electrolysis. A method for separating an element from a mixed melt of a high-level radioactive waste and a glass raw material, wherein an element in the melt is deposited on the surface of the direct current electrode or the mixed melt.

According to the method of the present invention described above, since element separation and mixed melting are performed in the same glass melting furnace, a separate element separation step is not required, the process is simple, and standard glass melting is performed. Since only a few facilities need to be added to the furnace, facility costs can be reduced. Further, since it is not necessary to use an extraction solvent or a molten salt, which is required for the conventional element separation method, and the element can be directly separated from the mixed melt in the glass melting furnace, the amount of secondary waste generated is reduced.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A first embodiment of the present invention will be described with reference to the schematic diagram of the apparatus shown in FIG. A predetermined amount of the high-level waste and the glass raw material are put into a melting furnace 1 provided with a pair of electrodes 2, and an alternating current is applied to the electrodes 2 from an AC power supply 3, and the mixture is directly melted by heating. The temperature of the mixed melt is measured by the thermocouple 4 and the temperature indicator 5 during direct current heating, and when a predetermined melting temperature is reached, the current flowing through the electrode 2 is changed by the power switch 6 from the DC power supply 7 Switch to current.

[0010] In the mixed melt that is melted at a high temperature, some elements of the waste components are ionized, and the potential of the direct current passed through the electrode 2 changes the potential of the ionized element. If the potential is the same, the ionized element is reduced or oxidized and precipitates and separates on the surface of the electrode 2 or in the mixed melt.

The mixed melt after some of the elements of the waste components have been separated is removed by flowing down from the nozzle 8 at the bottom of the melting furnace 1 in the same manner as in a standard vitrification process.
It is poured into a storage container (not shown) such as a canister to be a vitrified body.

FIG. 2 is a schematic view of an apparatus for carrying out a second embodiment of the present invention. The same members as those in FIG. 1 are denoted by the same reference numerals, and description thereof will be omitted. In the second embodiment, the element separation method of the present invention is performed using an existing melting furnace 1 provided with an AC electrode 11 for exclusively supplying an AC current. Direct heating is performed by an AC current from the AC power supply 7 via the AC electrode 11, and the AC power supply 7 is turned off when the mixed melt reaches a predetermined melting temperature. Next, by inserting a pair of DC electrodes 12 into the mixed melt in the melting furnace and applying a DC current from the DC power supply 7,
According to the same principle as described above, the ionized element is reduced or oxidized and precipitates and separates on the surface of the DC electrode 12 or in the mixed melt.

[0013]

EXAMPLE A waste glass simulating a high-level waste and a glass material mixed and melted in a melting furnace by direct current heating was prepared. Table 1 shows the composition of this simulated waste glass.

[0014]

The simulated waste glass was placed in a ceramic crucible, placed in an electric furnace, and heated indirectly with a heater to melt the simulated waste glass in the crucible to 1200 ° C. Next, a pair of electrodes made of Inconel was inserted into the melt in the crucible from an opening provided in the upper part of the electric furnace, and a DC current of 3.25 A was supplied for 23 minutes to perform constant current electrolysis. After the completion of the energization, the electrode was taken out of the crucible, and the deposit on the cathode surface was analyzed with an X-ray microanalyzer (EPMA).
The results of analyzing different parts of the cathode surface are shown in FIGS. As can be seen from these figures, the main elements deposited on the cathode surface are the platinum group elements Pd, R
In addition to u and Rh, Mo was observed.

The weight of the simulated waste glass tested was 8
With respect to 1 g, the weight of the precipitate on the cathode surface after the constant current electrolysis was about 1 g, of which the platinum group element was about 0.3 g. That is, the recovery rate of elements separated and recovered as precipitates among the waste components was 1.2%, of which the recovery rate of platinum group elements was 37%.

[0017]

As can be seen from the above description, according to the present invention, in the vitrification process of mixing and melting high-level waste and glass raw materials in a melting furnace, a direct current is applied to the mixed melt in the melting furnace. , It is possible to separate useful elements such as platinum group elements from waste components.

That is, by employing the method of the present invention, a pretreatment for separating elements from high-level waste is not required, so that the amount of secondary waste generated is small, and the waste component can be simply and effectively used. Can provide a vitrification process that can separate elements from the glass.

[Brief description of the drawings]

FIG. 1 is a conceptual diagram of an apparatus that can be preferably used in the first embodiment of the present invention.

FIG. 2 is a conceptual diagram of an apparatus that can be preferably used in a second embodiment of the present invention.

FIG. 3 shows EPMA of a deposit at a cathode portion in Examples.
Analysis result graph.

FIG. 4 shows EPMA of a deposit at a cathode portion in Examples.
Analysis result graph.

FIG. 5 shows EPMA of a deposit at a cathode portion in Examples.
Analysis result graph.

FIG. 6 shows EPMA of a deposit at a cathode portion in Examples.
Analysis result graph.

FIG. 7 shows EPMA of a deposit at a cathode portion in an example.
Analysis result graph.

FIG. 8 shows EPMA of a deposit at a cathode portion in Examples.
Analysis result graph.

────────────────────────────────────────────────── ─── front page of the continuation (72) inventor Kawamura Kazuhiro Ibaraki Prefecture Naka-gun, Tokai-mura, Oaza Muramatsu address 4 33 power reactor and nuclear fuel development Corporation Tokai plant (58) investigated the field (Int.Cl. ^6, DB G21F 9/16 G21F 9/06 G21F 9/30

Claims (2)

(57) [Claims] 1. A high-level radioactive waste and a glass raw material are charged into a melting furnace having a pair of electrodes therein, and an alternating current is applied to the electrodes to reduce the high-level radioactive waste between the electrodes. After directly heating and mixing and melting the glass raw material, the mixed melt is taken out of the melting furnace and cooled to form a vitrified body. A direct current is applied to the melt through the electrode to perform electrolysis, and the elements in the mixed melt that are oxidized or reduced by the electrolysis are deposited on the electrode surface or the mixed melt. A method for separating elements from a mixed melt of a high-level radioactive waste and a glass raw material. 2. A high-level radioactive waste and a glass raw material are charged into a melting furnace having a pair of alternating current electrodes therein, and an alternating current is applied to the alternating current electrodes. In the solidification treatment of high-level radioactive waste, the waste and the glass raw material are directly heated by heating and mixed and melted, and then the mixed melt is taken out of the melting furnace and cooled to form a vitrified material. A pair of DC electrodes is inserted into the mixed melt in the inside, and a DC current is passed through the DC electrode to perform electrolysis, and the elements in the mixed melt that are oxidized or reduced by the electrolysis are removed by the DC electrode. A method for separating an element from a mixed melt of a high-level radioactive waste and a glass raw material, wherein the element is deposited on a surface or in the mixed melt.