JP3614401B2 - Tritium decontamination decontamination method - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
TECHNICAL FIELD The present invention relates to a tritium decontamination method and a decontamination method, and more particularly to a tritium decontamination decontamination method that suppresses tritium accumulation or removes tritium in nuclear fusion-related and tritium handling facilities.
[0002]
[Prior art]
A large amount of tritium accumulates in the form of water or hydrocarbons on the plasma facing material of a deuterium-tritium fusion reactor, especially diverters, but it is required to reduce the tritium inventory from the viewpoint of ensuring safety. In addition, since a considerable amount of tritium-containing material is discharged as the reactor is repaired or replaced, not only in the reactor but also in the glove that treats the removed member in order to improve the operation rate of the fusion reactor. There is a need for a method for efficiently performing tritium decontamination in a box.
[0003]
The repair work of the plasma facing device of the fusion reactor is carried out by transferring it from the vacuum vessel to a building called a hot cell. Therefore, it is important to minimize the amount of tritium in the equipment before repair and replacement work. In order to increase the operating rate of the fusion reactor, it is required to improve the efficiency of the tritium decontamination process in the vacuum vessel.
[0004]
Conventional methods used for tritium decontamination include isotope dilution, chemical decontamination, baking, and ultraviolet irradiation.
The isotope dilution method is a method of diluting and processing radioactive tritium by flowing a large amount of hydrogen or water, and the chemical decontamination method is a method of washing the surface layer with a decontamination solution such as an acid, In any case, there is a problem that the generation amount of secondary waste of gas or liquid after treatment becomes large.
The baking method is a method in which contaminated structures are heated to vaporize and desorb tritium compounds and purge them, and there is a limit to the materials that can be applied due to the need for high temperatures, and a large amount of energy is required for heating. There is.
[0005]
Furthermore, the ultraviolet irradiation method is a method in which a tritium compound is irradiated with ultraviolet rays to give energy larger than the chemical bond energy, thereby breaking the C—H bond and vaporizing it as hydrogen gas or hydrocarbon gas.
The Journal of Plasma and Fusion Research, Vol. 76, No. 10 (October 2000), pp. 1021-1028 describes a sample that simulates a co-deposition layer by sputtering in an acetylene gas atmosphere to form a carbon film. Irradiation with 0.2 mJ of 172 nm ultraviolet rays for 20 minutes can release a large amount of hydrogen and a small amount of hydrocarbons from the carbon film in addition to water, carbon monoxide, and carbon dioxide adhering to the sample surface. It is described that it was observed.
[0006]
However, the conventional ultraviolet irradiation method has a problem that a high level of energy is required and the time required for the reaction is long.
In addition, since ultraviolet rays are considered to have a decontamination effect only from a few atomic layers from the surface, it is difficult to sufficiently decontaminate after a large amount of deposition even in the ultraviolet irradiation method.
[0007]
[Problems to be solved by the invention]
Therefore, the problem to be solved by the present invention is to suppress the accumulation of tritium more efficiently in the tritium decontamination method using the ultraviolet irradiation method, particularly in the fusion-related and tritium decontamination methods in the tritium handling facility, It is to provide a method for removing tritium.
[0008]
[Means for Solving the Problems]
In order to solve the above-mentioned problems, the tritium decontamination / decontamination method of the present invention is a method in which a metal oxide photocatalyst is applied to a surface that comes into contact with tritium, and the contact surface is irradiated with ultraviolet rays, thereby containing tritium on the contact surface. It is characterized by preventing the deposition of organic compounds or promoting the decomposition of tritium compounds deposited on the contact surface.
The photocatalyst applied to the contact surface is particularly preferably a photocatalyst containing anatase type titanium oxide.
[0009]
The photocatalyst promotes the decomposition of the organic substance by a radical substance generated when the surface is irradiated with ultraviolet rays. Many oxides can be used as photocatalysts, but titanium oxide is preferable because of its excellent functionality and safety. Titanium oxide includes three types of crystals, anatase type, rutile type, and brookite type, and an amorphous type, and it is known that anatase type titanium oxide has the strongest photocatalytic activity.
The specification of Japanese Patent No. 2918112 owned by the present applicant describes the effect of the anatase-type titanium oxide photocatalyst.
[0010]
Tritium contamination in plasma facing devices of fusion reactors and other tritium handling devices is caused by the deposition and deposition of organic substances containing tritium as hydrogen.
In the present invention, a photocatalyst is coated on the surface layer of a structural material possibly contaminated with tritium, and the tritium-containing organic compound attached to the surface is catalyzed by irradiating with ultraviolet rays such as sunlight or an ultraviolet lamp or laser light. Decomposes efficiently using the action and prevents deposition on the surface.
Also, the tritium compound deposited on the surface is efficiently decomposed by the action of the photocatalyst and becomes a gas such as CO ₂ , H ₂ O, hydrocarbon gas, etc. and is released to the surface of the structure. Tritium decontamination can be performed by flowing and collecting the gas.
[0011]
The recovered sweep gas needs to be appropriately treated to prevent leakage of radioactivity, but the amount of the collected sweep gas is extremely small compared to the isotope dilution method and the like, so the load on the processing apparatus is small.
Further, compared with the conventional ultraviolet irradiation method, the decontamination time is significantly shortened, and the input energy can be reduced.
The method of the present invention has a great effect when applied to an inner wall of a tritium passage of a deuterium-tritium fusion reactor or an inner wall of a glove box for treating a tritium contaminant such as a structure of a fusion reactor.
[0012]
For example, when applied to a nuclear fusion reactor, etc., by irradiating ultraviolet rays while the equipment is in operation, the tritium compound that comes in contact with the surface is efficiently decomposed before adhering to it, making it difficult to contaminate. It prevents deposition and keeps the tritium inventory low.
Further, by intermittently irradiating with ultraviolet rays for a predetermined time, the attached organic system and lithium can be decomposed and decontaminated.
Furthermore, even when the equipment is stopped for repair or replacement of parts, it can be easily decontaminated by irradiating the surface coated with the photocatalyst with ultraviolet rays.
[0013]
Also, in a tritium contaminant treatment apparatus, a photocatalyst is applied to the surface of a glove box or other member that may come into contact with tritium, and is irradiated with sunlight or ultraviolet rays from an ultraviolet lamp at all times or when necessary. For example, it is possible to prevent the tritium compound from being deposited or to remove the attached tritium compound.
In addition, since the method of the present invention only applies a photocatalyst to the surface and irradiates ultraviolet rays and does not require harsh conditions such as high-temperature treatment, it is not limited to steel materials but can be applied to various materials such as glass and resin. Can do. Moreover, since the procedure is the same even if the target material is changed, the operation is easy and the processing cost can be reduced.
The method of the present invention is a method that can be widely applied to facilities and equipment that require anti-tritium decontamination and decontamination, such as spent nuclear fuel reprocessing facilities and equipment, heavy water reactor equipment, etc., other than fusion-related facilities. is there.
[0014]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the tritium decontamination method of the present invention will be described in detail with reference to the drawings based on examples.
FIG. 1 is a perspective view for explaining an embodiment of the present invention, FIG. 2 is a drawing for explaining the photocatalytic action, and FIG. 3 is a graph for explaining the effect of the photocatalyst.
[0015]
The method of the present invention can be applied to a structural material or the like that may be subjected to tritium contamination, and can be applied to a glove box 1 that treats a tritium-contaminated object.
As shown in FIG. 1, a glove box 1 is formed with a transparent acrylic resin plate 2. The glove box 1 is provided with an opening 3 into which a hand can be inserted and a highly sensitive glove made of a resin such as rubber at the end of the glove box 1 so that the atmosphere remains outside the box even if the object inside is handled by hand. It is designed not to leak.
[0016]
A slurry titanium oxide photocatalyst is applied to the inner surface of the acrylic resin plate 2 and treated at a temperature of about 100 ° C. to form a photocatalyst layer 5. It is preferable to use anatase type titanium oxide as the titanium oxide photocatalyst because it has a large photocatalytic effect and can be easily slurried.
Since the transparency of the photocatalyst layer is high, it can be handled by hand while visually observing the object in the glove box. Note that the photocatalytic effect is sufficiently sustained even in a photocatalytic layer formed by spraying on the surface and naturally drying.
[0017]
An ultraviolet lamp 6 is provided outside the glove box, and the ultraviolet rays pass through the acrylic resin plate 2 and the photocatalyst layer 5 to irradiate the processing object in the glove box and the inner wall of the box. In place of the ultraviolet lamp 6, sunlight 7 may be introduced. This is because sunlight contains a large amount of ultraviolet light and other light components that contribute to the decomposition reaction of organic matter.
Although not shown, the glove box 1 is provided with a nozzle for introducing a sweep gas and a pipe for sending to a tritium processing apparatus for processing tritium contained in the gas mixed with tritium.
[0018]
As shown in FIG. 2, when ultraviolet rays are incident on the photocatalyst layer 12 formed on the surface of the structural material 11 in the state where the organic substance H ^3- (C _a H _b O _c ) containing tritium H ³ is in contact, an oxidation reaction There organism by ^activated, and ^{_{H 3 -C d H e, H}} 3 -H, H 3 -OH, since decomposed like CO _2, not deposited on the surface of the photocatalyst layer 12 (where, a, b , C, d, and e are appropriate integers). Therefore, when the facility is operated in the state of being irradiated with ultraviolet rays, the tritium inventory inside the facility is significantly reduced.
[0019]
In addition, if it does not irradiate with an ultraviolet-ray, a tritium will adhere and deposit on the structural material 11 as an organic compound.
However, if the photocatalytic layer 12 is formed on the structural material 11, the tritium compound is irradiated with ultraviolet rays before a large amount of tritium compound is deposited, and the decomposition of the tritium compound deposited so far is promoted and removed. Inventory can be reduced. Ultraviolet rays are considered to have a decontamination effect on only a few atomic layers on the surface. However, tritium decontamination can be effectively carried out by intermittently irradiating with ultraviolet rays to prevent deposition on the surface layer or more.
[0020]
Also, a structure in which a tritium compound is deposited on a structure 11 having a photocatalyst layer 12 formed on the surface thereof can be stored in a glove box and irradiated with ultraviolet rays UV. Upon irradiation with ultraviolet rays, and _^H 3 _-C d ^H _e is decomposed from the surface layer of the ^sediment, H 3 ^-H, like H 3 -OH to float on the separation surface. These gaseous components are collected in a tritium processing apparatus with a sweep gas. Deposits gradually decompose from the surface, and tritium decontamination is completed when treated for an appropriate time.
In addition, since the photocatalyst layer is also formed on the inner wall of the glove box, the tritium component generated by the processing of the deposit is prevented from being deposited on the inner wall surface, so that tritium staining is effectively performed.
[0021]
In order to confirm the effect of the photocatalyst on the organic matter decomposition reaction by ultraviolet rays, a comparative test using acetaldehyde was conducted.
FIG. 3 shows the experimental results when acetaldehyde was decomposed with ultraviolet rays using a photocatalyst. The horizontal axis represents the passage of time, and the vertical axis represents the acetaldehyde concentration and the carbon dioxide concentration in the gas in the container.
Two glass containers with a capacity of 2 liters were prepared, and one container used anatase-type titanium oxide as a photocatalyst and slurried titanium oxide powder (Forium (trade name) manufactured by Kawasaki Heavy Industries, Ltd.) on the inner surface of the container. After application, it was dried to obtain a photocatalyst layer.
[0022]
In each of the two glass containers, only 550 ppm of acetaldehyde is sealed, and UV light from a low-pressure mercury lamp is irradiated at an intensity of 0.3 mW / cm ² to change the concentration of acetaldehyde in the container and the concentration of carbon dioxide gas as a decomposition product. It was measured.
From the figure, it can be seen that in the glass container without the photocatalyst layer, the decomposition reaction proceeds slowly because acetaldehyde AA gradually decreases and carbon dioxide CO ₂ continues to increase little by little even when UV irradiation is started. .
On the other hand, in the glass container coated with the photocatalyst, it can be seen that the concentration of acetaldehyde decreases drastically as soon as the ultraviolet rays are irradiated, it becomes almost zero after 10 minutes, and the carbon dioxide gas increases rapidly.
In addition, it is considered that the acetaldehyde concentration is already different before the ultraviolet irradiation because acetaldehyde is adsorbed by the photocatalyst.
From the test results shown in FIG. 3, it was confirmed that the photocatalytic effect was remarkable in the decomposition reaction of acetaldehyde.
[0023]
By applying the photocatalyst that promotes the photochemical reaction by ultraviolet rays to the surface of the structure and the inner wall of the container, the decomposition of the tritium compound is significantly accelerated and the reaction efficiency is improved. The energy required for this is also greatly reduced.
In addition, although anatase type titanium oxide crystal particles have a particularly high degree of catalytic action, it is known that other rutile type, brookite type crystal bodies, and amorphous bodies also have a photocatalytic action. Some oxides of metals other than titanium have a photocatalytic action.
In addition, since it is not necessary to heat the photocatalyst coating to a high temperature, a wide variety of materials can be used for the glove box and the structure, and the optimum one can be selected according to the purpose of the apparatus.
[0024]
【The invention's effect】
As described above, the tritium decontamination and decontamination method using the ultraviolet irradiation method of the present invention more effectively suppresses tritium contamination in devices that are likely to be contaminated with tritium, particularly in fusion-related and tritium handling facilities. Therefore, accumulation of tritium can be suppressed and tritium can be removed.
In addition, it can be applied to spent nuclear fuel reprocessing facilities / equipment, heavy water reactor equipment, etc. in the same way to prevent and decontaminate tritium.
[Brief description of the drawings]
FIG. 1 is a perspective view showing a glove box to which a tritium decontamination method according to an embodiment of the present invention is applied.
FIG. 2 is a drawing for explaining the action of the photocatalyst in the present invention.
FIG. 3 is a graph illustrating the effect of a photocatalyst.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Globe box 2 Transparent acrylic resin board 3 Opening 4 Gloves 5 Photocatalyst layer 6 of inner wall Ultraviolet lamp 7 Sunlight 11 Structure material 12 Photocatalyst layer

Claims (4)

A metal oxide photocatalyst is applied to the surface in contact with tritium, and the contact surface is irradiated with ultraviolet rays to prevent the deposition of the tritium-containing organic compound on the contact surface, or the tritium-containing organic compound deposited on the contact surface Tritium decontamination decontamination method characterized by promoting decomposition of The tritium anti-decontamination method according to claim 1, wherein the metal oxide photocatalyst is anatase type titanium oxide. 3. The tritium anti-decontamination decontamination method according to claim 1, wherein the surface in contact with the tritium is an inner wall of a tritium passage of a deuterium-tritium fusion reactor or an inner wall of a glove box for treating tritium contaminants. Method. The tritium decontamination method according to any one of claims 1 to 3, wherein the ultraviolet rays are contained in sunlight.

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