JP3858369B2 - Zirconium alloy waste decontamination method and apparatus - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a zirconium alloy waste decontamination method and apparatus, and more particularly to a technique for separating zirconium from actinide elements such as uranium.
[0002]
[Prior art]
When radioactive waste generated at nuclear power plants, fuel manufacturing facilities, reprocessing facilities, etc. is contaminated metal materials, the amount of generated waste is large, and the demand for reduction in storage and disposal volume increases. Yes.
[0003]
Technical Example 1: In Japanese Patent Publication No. 05-062319, a metal waste contaminated with radioactive materials is made into a completely molten state, and is separated into a slag phase and a molten metal phase using a specific gravity difference. The crucible provided below is cast and solidified, and then the decontamination rate is further increased by the zone purification method.
Technical Example 2: In Japanese Patent Publication No. 08-033494, Zircaloy (Zr alloy) is dissolved in a copper bath, and using a difference in affinity with oxygen, zirconium and activated iron and chromium containing isotopes are contained. Try to separate.
[0004]
[Problems to be solved by the invention]
However, in Technical Example 1, there is a difficulty in mass processing due to material diffusion and device restrictions. In Technical Example 2, since the affinity of oxygen between zirconium and actinide elements such as uranium is almost equal, The problem remains that it is difficult to separate.
[0005]
The present invention is intended to effectively solve such problems and achieve the following objects.
(1) To separate and react zirconium at a relatively low temperature.
(2) To improve the separation between zirconium and other metal components.
(3) Production separation of high-concentration uranium-based elements from zirconium.
(4) To enable efficient fractionation by using zirconium and actinide elements or uranium or plutonium as a halogen compound.
[0006]
[Means for Solving the Problems]
Zirconium alloy waste contaminated with radioactive material is put into a melting furnace in an inert gas atmosphere, mixed and melted so as to be Cu- (47 to 53 wt%) Zr, and chlorine is added to the molten molten metal. Blowing gas, preferentially producing and recovering zirconium chloride by sublimation, and before mixing with the upper limit of nuclide element chloride, replace chlorine gas with oxygen gas or make a mild acidification atmosphere Is added to make slag, and both zirconium and nuclide elements float as oxides from the molten metal, and this mixed oxide is collected and separated.
The mixed oxide is separated as a chloride into a decontaminated product and a high-concentration radioactive material by molten salt electrolysis or fractional distillation.
When using chlorine gas, the temperature of a molten metal is set to 900-930 degreeC.
This also applies when the radioactive substance is an actinide element or a compound thereof.
Also adopted is a technology in which fluorine gas is sprayed instead of chlorine gas to molten metal obtained by mixing and melting zirconium alloy waste contaminated with radioactive materials to form Cu- (47 to 53 wt%) Zr. In this case, it is separated from Cu-Zr by preferentially producing and evaporating U and Pu fluoride, and when the required decontamination rate is obtained, oxygen gas is brought into contact with the molten metal to obtain zirconium. Is levitated as an oxide, separated from copper, and recovered.
When fluorine gas is used, the temperature of the molten metal is set to 895 to 905 ° C.
In the melting furnace, in order to bring halogen gas and oxygen gas into contact with the copper alloy bath, a halogen gas blowing process and an oxygen gas blowing process are performed. An induction melting furnace using a refractory crucible can also be adopted as a melting furnace (cold crucible furnace) as a melting furnace when blowing oxygen gas.
[0007]
DETAILED DESCRIPTION OF THE INVENTION
A first embodiment of a zirconium alloy waste decontamination method and apparatus according to the present invention will be described below with reference to FIG.
[0008]
[Zirconium alloy waste input]
As shown in FIG. 1, a zirconium alloy waste (zirconium alloy) X contaminated with radioactive material is introduced into a carbon crucible (melting tank) 1 in an inert gas atmosphere, and a solvent Y made of pure copper is added. Supply at the same time.
In this case, the composition of the zirconium component and the copper component in the zirconium alloy waste X is set so as to be Cu- (47 to 53 wt%) Zr.
[0009]
[Dissolution of zirconium alloy waste]
A high frequency heating coil (heating means) 2 is arranged around the carbon crucible 1, and a high frequency current of, for example, about 500 to 3000 Hz is supplied to the high frequency heating coil 2 while being maintained in an inert gas atmosphere. And the zirconium alloy waste X is induction-heated to a suitable processing temperature.
As shown in FIG. 2, when the zirconium component with respect to the alloy component is 47 to 53 wt% (weight%), the melting point is the lowest in the Cu—Zr system, and a molten metal is formed.
[0010]
(Halide generation)
Chlorine gas diluted with chlorine gas or nitrogen gas or the like is sprayed on a molten metal held at a temperature of 900 to 930 ° C. to preferentially produce zirconium chloride.
When the halogen gas is chlorine gas, for example, the boiling points of chlorides of Zr, U, and Pu are 336 ° C., 795 ° C., and 1780 ° C., respectively, and the molten metal is magnetically stirred based on induction heating In combination with the reaction with chlorine gas, zirconium chloride is preferentially sublimated and recovered from the carbon crucible 1 as a gas component.
Since zirconium is sequentially consumed by the generation of chloride, the zirconium alloy waste X is appropriately added to maintain the Cu-Zr ratio so that the molten metal component does not become 47% Zr or less.
FIG. 3 shows a standard free energy generation diagram of chloride. When Zr and Cu chlorides are compared, there is a large difference in standard free energy of formation, Cu chloride is hardly generated, Cu consumption and evaporates Very little contamination.
[0011]
[Recovery of chloride]
Zirconium chloride taken out of the carbon crucible 1 in a gasified state is sent to the halide recovery means 3 and cooled to be solidified and recovered.
The gasified zirconium chloride and other gas components taken out of the carbon crucible 1 are disposed of as off-gas after necessary processing such as removal of harmful gases.
[0012]
[Concentration of nuclide elements]
By evaporating chloride and adding additional zirconium alloy waste X, the nuclide element in the molten metal is gradually concentrated.
In other words, the amount of actinide elements such as uranium, which is a source of contamination, is increased, and the amount of nuclide elements mixed in is required in consideration of the inclusion of nuclide chlorides in zirconium chloride. Before reaching the allowable amount calculated from the dyeing rate (decontamination coefficient: DF> 100, for example), the chlorine gas spraying is stopped.
[0013]
(Oxide generation)
When the carbon crucible 1 is used as a melting tank, the oxides of zirconium and nuclide elements (U, Pu, etc.) can be obtained by spraying the molten gas instead of oxygen on the molten metal and bringing the molten gas into contact with the oxygen gas. Generated. As shown in FIG. 1, the oxide floats from the molten metal.
FIG. 4 shows an oxide standard generation free energy diagram. From this diagram, it is clear that Zr, U, and Pu easily become oxides even in the presence of carbon (C).
[0014]
[Oxide recovery]
The oxide floating from the molten metal is collected and separated by a method of scraping and removing, a method of flowing it out, etc., taken out of the carbon crucible 1, sent to the oxide recovery means 4, and solidified by being cooled. Recovered in a state.
[0015]
[Post-treatment of mixed oxide]
As described above, the oxide recovered by the oxide recovery means 4 is zirconium, nuclide elements (U, Pu, etc.), and other mixed oxides. The method uses the difference in sublimation temperature between Zr halides and actinide-based halides to separate them into decontamination products that do not contain nuclide elements and high-concentration radioactive materials that are enriched in nuclide elements. And store it.
[0016]
[Reuse of solvent]
In the molten metal from which the oxide has been removed, pure copper, which is the solvent Y, remains as a melt. Therefore, as shown by the arrows in FIG. 1, the addition of new zirconium alloy waste X and the solvent Y commensurate with the amount of zirconium. And the following steps are repeated.
[0017]
Next, a second embodiment of the zirconium alloy waste decontamination method and apparatus according to the present invention will be described.
Even in the second embodiment, the zirconium alloy waste X is charged into the melting tank in an inert gas atmosphere and melted at the aforementioned Cu-Zr blending ratio, but fluorine instead of chlorine gas is used. Fluoride is produced using gas.
However, with the use of fluorine gas, it is necessary to improve the corrosion resistance and safety of the reaction vessel, piping system, etc., and it becomes an extremely expensive facility, so the amount of processing is small and the equipment does not need to be enlarged. This is the preferred technique.
[0018]
When fluorine gas is blown onto the molten Cu—Zr, U, Pu and Zr fluorides have different boiling points (UF ₆ : 51 ° C., PuF ₆ : 62 ° C., ZrF ₄ : 908 ° C.). Therefore, the U and Pu fluorides are evaporated and separated from Cu-Zr. In this case, the concentrated actinide element can be recovered in the form of fluoride.
When the required decontamination rate of the remaining molten metal is obtained, oxygen gas is blown into the molten metal to float zirconium as an oxide, which is separated from copper and collected.
[0019]
[Other Embodiments]
In the present invention, the following techniques can be employed.
a) A floating induction melting furnace (cold crucible furnace) should be used as a melting furnace when halogen gas is blown.
b) An induction melting furnace using a refractory crucible is applied as a melting furnace when blowing oxygen gas.
c) The melting tank is composed of a water-cooled copper crucible, and the entire molten metal ball is used as the reaction part.
d) When applying a water-cooled copper crucible, solidify the melt once prior to performing the [Oxide Generation] step, and then re-solidify the solidified alloy body in an atmosphere induction melting furnace using a refractory (carbon-containing) crucible. Dissolve and oxidize, and collect mixed oxides.
[0020]
【The invention's effect】
The zirconium alloy waste decontamination method and apparatus according to the present invention have the following effects.
(1) Setting the compounding ratio of Cu-Zr, making zirconium a liquid phase at a relatively low temperature, and performing a reaction with chlorine gas in a liquid phase-gas phase state, thereby making zirconium a chloride state, Separation can be performed with high efficiency.
(2) The efficiency of the chlorination reaction of zirconium can be further improved by inductively heating and stirring the molten metal.
(3) By bringing oxygen into contact with the remaining molten metal from which the chloride of zirconium has been recovered, the actinide-based element in the molten metal can be oxidized and the separability can be improved.
(4) By further converting the slag oxide into a halide, the actinide-based element and its compound can be concentrated and separated and disposed of.
(5) By generating fluorides of U and Pu using fluorine gas, the fluorides of U and Pu can be preferentially evaporated to concentrate these actinide elements and improve the separability.
(6) Due to the above, the amount of secondary waste generated can be reduced.
[Brief description of the drawings]
BRIEF DESCRIPTION OF DRAWINGS FIG. 1 is a schematic diagram showing an implementation status in a first embodiment of a zirconium alloy waste decontamination method and apparatus according to the present invention.
FIG. 2 is a relationship diagram of the melting point depending on the amount of zirconium component with respect to the copper component in the molten metal in the melting tank shown in FIG.
FIG. 3 is a standard free energy diagram of chloride formation.
FIG. 4 is a standard free energy diagram of oxide generation.
[Explanation of symbols]
1 Carbon crucible (melting tank)
2 High-frequency heating coil (heating means)
3 Halide recovery means 4 Oxide recovery means X Zirconium alloy waste (zirconium alloy)
Y solvent

Claims (7)

  Mixing and melting the zirconium alloy waste contaminated with radioactive material so as to be Cu- (47 to 53 wt%) Zr, and contacting the molten metal with chlorine gas to produce zirconium chloride and recover it A method for decontaminating zirconium alloy waste, comprising: a step of bringing the molten metal into contact with an oxygen gas to float the nuclide element as an oxide and separating the oxide. The method for decontaminating zirconium alloy waste according to claim 1, wherein the temperature of the molten metal is set to 900 to 930 ° C. Instead of contacting the oxygen gas to the molten metal, the decontamination method according to claim 1 or 2 zirconium alloy wastes, wherein the to oxidizing atmosphere. The method for decontamination of zirconium alloy waste according to any one of claims 1 to 3, wherein the separated oxide is separated into a decontamination product and a high-concentration radioactive material by molten salt electrolysis or fractionation. .   A step of mixing and melting zirconium alloy waste contaminated with radioactive material so as to be Cu- (47 to 53 wt%) Zr, and bringing fluoride gas into contact with the molten metal to produce fluoride of an actinide element. A method for decontaminating zirconium alloy waste, comprising: a step of recovering this, and a step of bringing oxygen gas into contact with the molten metal to float zirconium as an oxide for separation.   The method for decontaminating zirconium alloy waste according to claim 5, wherein the temperature of the molten metal is set to 895 to 905 ° C.   A melting furnace (1) into which zirconium alloy waste contaminated with radioactive material is charged, and a heating means (2) for heating the zirconium alloy waste (X) charged into the melting furnace to an appropriate treatment temperature in a halogen gas atmosphere A halide recovery means (3) for recovering halides generated inside the melting furnace, and an oxide recovery means (4) for collecting and separating oxides generated by bringing oxygen gas into contact with the molten metal A zirconium alloy waste decontamination apparatus comprising:

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