JP5717348B2 - Tritium contaminant decontamination method and system - Google Patents

Description

The present invention relates to a method for removing tritium from radioactive contaminants contaminated with tritium (tritium: ³ H) generated from nuclear power plants, radioactive material handling facilities, fusion research facilities, etc., and decontaminating the contaminants, and Regarding the system.

  In nuclear power plants, radioactive material handling facilities, fusion research facilities, etc., especially facilities that use heavy water, tritium adheres to the piping material, etc. along with heavy water during operation, adheres to the material, or diffuses into the material. It is in solid solution. Materials contaminated with tritium are decontaminated during periodic inspections, repairs, and dismantling. In general, in the case of light contamination due to adhesion or adhesion of tritium, a method of decontamination with a facility or equipment installed is employed. This decontamination method includes various methods such as drying by heated air or the like, washing by water or a steam blow method. However, materials that are severely contaminated with tritium and those that are severely fatigued for other reasons such as stress corrosion along with tritium contamination need to be disassembled and replaced. In the future, with the aging of nuclear facilities, a large amount of tritium-contaminated waste will be generated when it is demolished. The material disassembled in this way is sealed and stored as contaminated waste.

When the degree of tritium contamination is slight, the tritium concentration can be reused by burying it in a state where the concentration of tritium is lowered or diluting the tritium concentration below the legal concentration that allows environmental release. In that case, removal of tritium on the surface of the material and reduction of the tritium concentration can be performed by a relatively simple method such as a surface wiping method in addition to the method described above. In addition, for a tritium-contaminated material, a method of mechanically, physically, or chemically removing a surface-contaminated portion of the material as a tritium decontamination method can be employed. Specific methods include cutting the surface contaminated portion, irradiating the contaminated surface in a molten state with high-energy laser light irradiation and removing the contaminated portion by dissolving the contaminated portion using an acid solution, etc. A removal method is employed. Further, in Patent Document 1, in order to improve the problems of these methods, for example, problems such as a decrease in decontamination efficiency, deterioration of workability, or a large amount of secondary waste, an oxidation reaction and A gas phase gasification decontamination method using a fluorination reaction is disclosed. The method for removing a radioactive element using a chemical reaction by a gas phase gas is not related to a method for removing tritium, but is also disclosed in Patent Document 2. Patent Document 2 includes a mixed gas of supercritical CO ₂ gas, halogen gas, and water vapor or alcohol gas for pretreatment of carbonylation reaction and fluorination reaction or in combination with these reactions. The use of reactive gases is described.

  However, materials that have been dismantled due to severe contamination of tritium and dismantled materials after aging exist not only because tritium adheres to and adheres to the surface, but also diffuses and penetrates into the material. It is difficult to reduce the concentration of tritium distributed inside the tritium-contaminated material by the surface decontamination method described above. Even if the tritium on the material surface can be removed or the tritium concentration can be reduced, the tritium present inside the material diffuses outside the material during disposal, storage or storage, Will contaminate. In addition, when the discarded material is damaged and the internal structure of the material is exposed to the outside atmosphere, the influence of environmental contamination by tritium cannot be ignored. In that case, the problem of tritium contamination reignites, causing not only a major problem in terms of safety and security, but also a problem in terms of maintaining material strength. Therefore, in Patent Document 3 and Patent Document 4, focusing on the material contaminated with tritium to the inside, a decontamination method for tritium existing inside is studied. Patent Document 3 discloses a method for decontaminating tritium from heavy water adsorbed on the surface of a material by supplying a gas of 200 ° C. or less containing light water vapor. It is described that since the dissolved tritium is confined in the material, the radiation level based on the solid dissolved tritium is low and does not cause a problem in exposure. Further, in Patent Document 4, as a method for removing solid solution tritium existing in the material, after heating with hot air of 200 ° C. or less, the solution is heated and held with hot air heated from 200 ° C. to 600 ° C. to form solid solution tritium. A method for decontaminating tritium contaminated metals is disclosed.

JP 2002-162498 A Japanese Patent Laid-Open No. 9-257993 Japanese Patent Laid-Open No. 11-281792 JP 2004-271200 A

  However, Patent Document 3 does not mention the diffusion of tritium present inside the material to the outside due to long-term use or neglect. In addition, it cannot be said that there is no influence due to fluctuations in the environment (temperature, humidity, etc.) during standing, storage or storage, and a major problem remains in terms of safety and security in the future. Although Patent Document 4 discloses a method for removing solid solution tritium present in the material, it is necessary to raise the hot air temperature to a high temperature of 600 ° C. in order to increase the decontamination efficiency. When high-temperature hot air is used, although the processing equipment is maintained at a negative pressure, there is a high risk of the gas containing tritium leaking from the piping and equipment, and secondary contamination of the surrounding environment by the gas containing tritium May occur. In the case of radioactive contamination materials, leakage of radioactive substances to the outside must never occur, and strict management and control of the decontamination method and decontamination equipment are indispensable to completely prevent this problem. In addition, when the method described in Patent Document 4 is applied to the decontamination treatment of a tritium-contaminated material having a large and complicated shape, the temperature of the hot air is uniformly adjusted at all locations of the contaminated material. Since high skill and skill are required, it is difficult to increase the reproducibility of tritium removal. In particular, in long-term application, it is conceivable that the decontamination capability and efficiency due to deterioration of the apparatus and the like are reduced. As described above, the conventional tritium decontamination method using a heated gas cannot recover tritium safely and easily from the tritium-contaminated material.

  Therefore, the object of the present invention is not only to remove the tritium adhering to and adsorbing to the surface of the tritium-contaminated material, but also to remove the tritium existing inside the material at a lower temperature and more efficiently than the conventional method using hot air. A decontamination method for tritium contaminants and a decontamination system thereof that can be reliably removed at a low cost and below an allowable concentration limit. In addition, tritium is collected safely and easily without causing secondary contamination of the surrounding environment by gas containing tritium, which has been a problem with conventional methods, and the amount of tritium-contaminated waste discharged after decontamination treatment It is an object to provide a method for decontaminating tritium contaminants and a decontamination system thereof.

In order to remove tritium distributed not only on the surface of a tritium-contaminated material but also inside the tritium-contaminated material efficiently, simply, safely and reliably at a low temperature below the allowable concentration limit, the present invention has the following configuration. The present invention relates to a contaminant decontamination method and a decontamination system thereof.
(1) After sealing tritium-contaminated material in which tritium is distributed on the surface and inside of the material and light water (hereinafter, normal water H ₂ O not containing tritium) in a sealed container, the temperature is 50 to 400 Heat treatment at ℃ promotes the migration of tritium present on the surface of the tritium material into water vapor, and at the same time, diffusion of tritium present inside the tritium material to the material surface and water vapor on the surface by heating. The present invention relates to a method for decontaminating tritium contaminants, which is characterized by facilitating the migration of tritium.
(2) In the method for decontaminating tritium contaminants according to (1) above, after the heat treatment of a sealed container enclosing the tritium-contaminated material and light water at a temperature of 50 to 400 ° C., the sealed container is heated to the heat treatment temperature. A method of condensing tritium-containing water in the sealed container by cooling to a temperature lower than the temperature and / or condensing the tritium-containing water in the sealed container and / or using a decompression means to take out the water vapor from the sealed container and cooling trap to cool the tritium-containing water. The present invention relates to a method for decontaminating tritium contaminants, characterized in that tritium-containing water is separated and recovered from the tritium-contaminated material by a method of coagulating water.
(3) In the above (1) or (2), the operation of heat-treating the sealed container enclosing the tritium-contaminated material and light water at a temperature of 50 to 400 ° C. is performed in two or more stages. The present invention relates to a method for decontaminating tritium contaminants.
(4) In the method for decontaminating tritium contaminants according to any one of (1) to (3) above, by recycling the tritium-containing water collected after use in the decontamination treatment, secondary waste and The present invention relates to a method for decontaminating tritium contaminants characterized by a method for reducing the generation of contaminated waste of tritium-containing water and its solidified product.
(5) Supercritical water, subcritical water, supercritical carbon dioxide containing water, or subcritical dioxide containing water in a closed container containing tritium contaminated material in which tritium is distributed on the surface and inside of the material. While circulating any of the carbon and heat-treating the sealed container containing the tritium-contaminated material at a temperature of 50 to 400 ° C., the transition of tritium existing on the surface of the tritium-contaminated material into water vapor is promoted at the same time. Further, the present invention relates to a method for decontaminating tritium contaminants, characterized by promoting the diffusion of tritium present in the tritium-contaminated material to the material surface and the transition to water vapor on the surface by heating.
(6) In the decontamination method for tritium contaminants described in (1) to (5) above, the tritium-containing water used for the decontamination treatment is diluted with light water and discarded, or the tritium-containing water or its The present invention relates to a method for decontaminating tritium contaminants, wherein the decontamination waste is stored in isolation or stored as contaminated waste of a solidified product.
(7) (A) A sealed container having a heating function, equipment for supplying light water (H ₂ O) free of tritium for decontamination and / or washing into the sealed container, and after decontamination treatment Tritium-containing water and / or tritium decontamination equipment having equipment for recovering washing water after washing as a drain water, (B) In order to supply tritium contamination to the sealed container, the sealed container (C) Tritium decontamination chamber provided adjacent to the tritium decontamination chamber; (C) Tritium decontamination equipment and / or equipment for discharging the tritium decontamination gas from the tritium decontamination chamber; And (E) temperature and / or pressure in the sealed container, and (E) equipment for supplying and / or exhausting the purified gas not containing water to the tritium decontamination equipment and / or the tritium decontamination chamber The amount of the light water and / or drain water present in the sealed container, the internal pressure of the tritium decontamination chamber, the tritium concentration of the drain water, and the tritium concentration in the tritium decontamination chamber and / or piping; Temperature of the sealed container containing tritium-contaminated material and light water in which tritium is distributed on the surface of the material as well as in the device, using equipment configured to measure or monitor at least one of A decontamination system for tritium contaminants, which is heat-treated at 50 to 400 ° C.
(8) The tritium-containing water after the decontamination treatment is supplied to the sealed container containing the tritium contaminants once or twice or more and reused to recycle the tritium. The tritium contaminant decontamination system according to (7) above.
(9) Supercritical water obtained by high-pressure pump and heating, subcritical water, supercritical carbon dioxide containing water in a sealed container containing tritium-contaminated material in which tritium is distributed on the surface and inside of the material, or While circulating any of the subcritical carbon dioxide containing water, the closed container containing the tritium-contaminated material is heated at a temperature of 50 to 400 ° C., followed by a decontamination process of tritium contaminants, and then the supercritical Tritium characterized by separating and recovering only water containing tritium through a process of expanding either water, subcritical water, supercritical carbon dioxide containing water, or subcritical carbon dioxide containing water The present invention relates to a contaminant decontamination system.
(10) Equipment for diluting and discarding tritium-containing water after being used for tritium decontamination treatment with light water, or for storage and storage in isolation as contaminated waste of tritium-containing water or its solidified product It has an installation, It is related with the decontamination system of the tritium contaminant in any one of said (7)-(9) characterized by the above-mentioned.
(11) The method for decontaminating tritium contaminants according to (3), wherein the treatment by multistage operation is performed using two or more decontamination containers. About.
(12) In the method for decontaminating tritium contaminants by multistage treatment as described in (3) or (11) above, when applying the recovered tritium-containing water, the tritium-containing water used in the subsequent decontamination treatment is The present invention also relates to a method for decontaminating tritium contaminants, characterized in that the tritium concentration is lower than the tritium-containing water used in the preceding treatment.
(13) In the method for decontaminating tritium contaminants according to (5), the tritium-contaminated material is made of critical water, subcritical water, supercritical carbon dioxide containing water, or subcritical carbon dioxide containing water. Any of the above-mentioned supercritical water containing tritium, subcritical water, water contained in supercritical carbon dioxide, or water contained in subcritical carbon dioxide after being treated by any of the above and expanded to lower the pressure. The present invention relates to a method for decontaminating tritium contaminants, which is directly recovered and separated from the tritium contaminant material.
(14) In the method for decontaminating tritium contaminants according to (6), after the tritium-containing water is subjected to concentration treatment by electrolysis, the tritium-containing water is separated from water not containing tritium and solidified from tritium or solidified therefrom. The present invention relates to a method for decontaminating tritium contaminants, wherein the decontamination waste is stored in isolation or stored as contaminated waste.
(15) The tritium decontamination system according to (7), wherein the tritium decontamination chamber is maintained at a negative pressure.
(16) The tritium contaminants according to any one of (7) to (8) and (15) above, wherein two or more of the sealed containers are provided side by side to perform tritium decontamination treatment. It relates to a decontamination system.
(17) In the decontamination system for tritium contaminants in which two or more of the sealed containers described in (16) are provided and decontamination treatment of tritium is performed in series, water used for decontamination of tritium is The present invention relates to a decontamination system for tritium contaminants, characterized in that the tritium concentration in the subsequent treatment is lower than that in the previous treatment.
(18) The tritium-contaminated contaminant decontamination system according to (10), wherein the tritium-containing water is separated from tritium-free water by using an electrolysis concentrator, or tritium-enriched water or a solidified product thereof. The present invention relates to a system for decontaminating tritium contaminants, wherein the decontamination system is isolated and stored as contaminated waste.

  The present invention relates to a tritium-contaminated material by decontaminating a tritium-contaminated material in which tritium is distributed on the surface and inside of the material using heated water as a decontamination medium in a sealed container under a high temperature condition. The tritium present not only on the surface but also in the interior can be efficiently and reliably removed at a low temperature up to an allowable concentration limit or less. By using supercritical water, subcritical water, supercritical carbon dioxide containing water, or subcritical carbon dioxide containing water as the high-temperature heated water used for the decontamination medium, a thick and complex shape The tritium decontamination from the tritium-contaminated material having the above can be performed efficiently and uniformly. By performing the decontamination operation of tritium from the lithium-contaminated material in multiple stages, reliable decontamination of tritium distributed inside the tritium-contaminated material can be performed efficiently and continuously. By reusing the tritium-containing water used for the tritium decontamination treatment according to the tritium concentration, it is possible to reduce the generation of contaminated waste. Since the tritium concentration of the tritium-contaminated water substantially matches the decrease amount of the tritium concentration distribution inside the tritium-contaminated material, it can be easily determined whether or not it is suitable for reuse according to the tritium concentration. Therefore, in the decontamination treatment by reusing the tritium-containing water, tritium distributed inside the tritium-contaminated material can be reliably removed by selecting and using tritium-containing water having a low tritium concentration. In addition, the tritium-containing water after the decontamination treatment is stored and stored separately as the contaminated waste of the tritium-enriched water obtained by the concentration treatment or its solidified product, so that the volume of the contaminated waste can be reduced. Can be achieved.

  When tritium decontamination from tritium-contaminated materials with water vapor under high-temperature and high-pressure conditions, the conditions and atmosphere of the decontamination process are measured or monitored, and the decontamination conditions are within a predetermined range based on the measured values and monitoring values. By constructing a decontamination system for adjusting and controlling the temperature, it is possible to establish a stable decontamination method for tritium contaminants with excellent reproducibility. Also, by adopting a decontamination system that uses supercritical water, subcritical water, supercritical carbon dioxide containing water, or subcritical carbon dioxide containing water as a decontamination medium, the surface of tritium contaminants and The concentration of tritium distributed inside can be efficiently reduced.

The figure which shows the mechanism of tritium discharge | release. The figure which shows the tritium decontamination method performed using the airtight container of this invention. The figure which shows the tritium internal distribution after decontamination for 24 hours at each temperature of this invention. The figure which shows the tritium decontamination process by the heating water of this invention. The figure which shows the tritium multistage decontamination process by the heating water of this invention. The figure which shows the heating water system tritium decontamination equipment and its decontamination system of this invention. The figure which shows the tritium decontamination system performed using the critical water or subcritical water of this invention. The figure which shows the tritium decontamination system performed using the critical or subcritical carbon dioxide containing the water of this invention. The figure which shows the time dependence of the tritium decontamination process by the heating water of this invention. The figure which shows the tritium decontamination efficiency simulation result of the stainless steel in this invention.

The mechanism of tritium release in the heating water decontamination method of the present invention is shown in FIG. 1 in comparison with the conventional heating decontamination method. T in FIG. 1 represents tritium, and so on. In the conventional heat decontamination method, in order to remove tritium in the vicinity of the surface of the tritium-contaminated material and tritium in the tritium-containing hydroxyl group in the form of HT or HTO, high temperature treatment and long-time heating are required. Removal is difficult. In contrast, the heated water decontamination method of the present invention promotes the exchange reaction between tritium-containing hydroxyl groups distributed near the surface and hydrogen in light water because liquid phase water and vapor phase water vapor exist. As can be removed. This exchange reaction is represented by the following reaction formula (1).
H ₂ O + —OT → HTO + —OH (1)
Further, by heating the sealed container to a high temperature, the tritium present in the tritium-contaminated material promotes the exchange reaction by H⇔T with the hydrogen of the hydroxyl group (—OH) on the surface. By this exchange reaction, tritium T diffuses to the surface and is finally removed from the tritium-contaminated material as HTO. Since the above reaction formula (1) proceeds relatively easily, the tritium distributed on the surface and inside of the tritium-contaminated material can be removed at a lower temperature and more quickly than the conventional heat decontamination method. .

In the present invention, tritium decontamination can be performed from the tritium-contaminated material 4 by using a sealed container 1 having an outer jacket 2 made of stainless steel and an inner container 3 made of Teflon (registered trademark) as shown in FIG. . A predetermined amount of light water 5 as a tritium decontamination medium is placed in a sealed container shown in FIG. 2 together with a tritium-contaminated material, and sealed with a sealing lid, and then heated at a temperature of 50 to 400 ° C. for a predetermined time. Accordingly, the present invention is a method for decontaminating tritium using light water sealed in the sealed container as heated water. The temperature of the sealed container can be adjusted by putting it in a thermostatic chamber heated to a predetermined temperature.
In the present invention, the water vapor pressure in the sealed container can be adjusted by the amount of light water contained in the sealed container. For example, when light water is sealed in an airtight container in an amount equal to or greater than the saturated water vapor amount, the saturated water vapor pressure corresponding to each temperature is obtained by heating. In the present invention, when a sealed container enclosing tritium-contaminated material and light water having a saturated water vapor amount or more is heated at 50 to 400 ° C., the water vapor pressure in the sealed container is in the range of 0.12 to 311 atmospheres (atm). Become. The saturated water vapor pressure at each temperature can be determined by the Tetens equation expressed by the following equation (2). At 50 ° C. and 400 ° C., the saturated water vapor pressure is about 0.12 atm and about 311 atm, respectively. is there.
E (T) = 6.11 × 10 ^{7.5T / (T + 273.3)} (2)
Here, T is a temperature (° C.), and E (T) is a saturated vapor pressure at a temperature T ° C. In addition, since the amount of water vapor at each temperature can be calculated from the gas equation of state, in order to obtain a pressure of 0.12 to 311 atmospheres at 50 to 400 ° C., the amount of water equal to or greater than the amount of water vapor at each temperature is sealed container. What is necessary is just to set according to the volume of this and to enclose in the said sealed container.

The present invention has little influence on the efficiency of decontamination even if the inside of the sealed container is not set to the saturated water vapor pressure. Therefore, there is no problem as long as sufficient water is present in the sealed container so that tritium can be removed from the tritium-contaminated material, and the present invention can perform the tritium decontamination treatment with the pressure in the sealed container being less than the saturated water vapor pressure. That is, an amount of water less than the saturated water vapor pressure at the heat treatment temperature may be enclosed in the sealed container. In the present invention, a pressure-resistant type is normally used as the sealed container, but in this way, it is not necessary to use a high-voltage type or an ultra-high-voltage type. Not only that, but safety equipment in high-pressure operation can also be made inexpensive, so a low-cost decontamination equipment can be constructed. In addition, since the volume of the tritium-containing water after the decontamination process that becomes the secondary waste can be reduced, it has the effect that the environmental load can be reduced.

  In the present invention, when the heating temperature of the sealed container is less than 50 ° C., the effect of decontaminating tritium present inside the tritium-contaminated material cannot be obtained. In the present invention, the decontamination rate of tritium existing in the tritium-contaminated material can be estimated by the diffusion rate of tritium. Therefore, when the tritium-contaminated metal material is thicker than 5 mm, the temperature is less than 50 ° C. If it exists, even if decontamination time passes 1000h, the change of an internal tritium density | concentration is not seen. As a material used in a nuclear facility to which the present invention is applied, a metal material having a thickness of 5 mm or more is often used. Therefore, a tritium decontamination method that can be applied to a metal material having a thickness of 5 mm or more is particularly required. ing. In order to apply the present invention to a thick and complicated tritium-contaminated material, the heating temperature of the sealed container is more preferably 100 ° C. or higher. On the other hand, since tritium decontamination is accelerated as the heating temperature increases, it is possible to set the upper limit to 600 ° C as the heating temperature. However, if it exceeds 400 ° C, it is difficult to ensure temperature uniformity, The problem arises that the degree varies depending on the location of the material. In addition, a device or facility that can withstand high temperature heating of 400 ° C. or higher needs to use a highly durable member, and its life is shortened because deterioration is easily promoted. In addition, there is a problem that the cost for manufacturing and maintaining the apparatus and equipment increases rapidly. Further, since the present invention can be processed at a lower temperature than in the case of the conventional heated gas method, the upper limit value of the heating temperature can be set lower in consideration of workability, safety, cost, etc. Has characteristics. Therefore, in the present invention, it is preferable to set the heating temperature to 400 ° C. or less.

  In the present invention, the processing time when heat-treating the sealed container at 50 to 400 ° C., more preferably 100 to 400 ° C., includes the heating temperature, the material, thickness and shape of the tritium contaminated material, and the residual tritium concentration after decontamination. However, the predetermined time can be set in the range of 1 to 1000 hours, preferably 10 to 500 hours.

  In the present invention, after the decontamination treatment of tritium is completed by leaving it for a predetermined time using high-temperature steam, the sealed container containing the tritium-contaminated material is treated at a temperature lower than the heat treatment temperature, preferably 50 ° C. or less. From this point of view, the water vapor in the sealed container is further converted to water by cooling to 30 ° C. or lower and reducing the pressure, and then separated and recovered from the tritium-contaminated material as drain water. The water collected in this manner contains extracted tritium.

  In the present invention, as another method for recovering tritium-containing water from a sealed container after decontamination treatment, a sealed container enclosing tritium-contaminated material and light water is heated at a temperature of 50 to 400 ° C., and then a decompression means is used. Thus, it is possible to adopt a method in which water vapor in the sealed container is separated from the tritium-contaminated material, taken out of the sealed container, and condensed and recovered by cooling trapping. The decompression process is performed by a vacuum pump or the like. The temperature at which the decompression process is performed is not limited to the same temperature as that during heating, and a temperature lower than that temperature can be employed. Moreover, it is also possible to perform at a temperature slightly higher than at the time of heating, and in that case, water vapor can be recovered in a short time. In this method, when water larger than the saturated water vapor amount corresponding to the treatment temperature is sealed in the sealed container, the supersaturated water remains even after removing only the water vapor containing tritium by the decompression treatment. The water can be heated again and used as water vapor. Therefore, only water having a high tritium concentration can be removed as water vapor, and subsequently, decontamination treatment can be performed using water having a low tritium concentration, so that continuous decontamination treatment is possible and the utility is high. This recovery method can be combined with the method of cooling and depressurizing the closed container according to the recovery conditions.

  The tritium-containing water collected in this manner is diluted with light water to a level below the market acceptable limit of tritium and then discarded, or is isolated and stored as tritium-containing water or a solidified product thereof. The present invention can employ a method of concentrating tritium-containing water by electrolysis in order to reduce the volume of tritium-containing water that is a secondary waste. As a concentration method by electrolysis of tritium-containing water, for example, a known technique as disclosed in Japanese Patent Application Laid-Open No. 2001-286737 or Japanese Patent Application Laid-Open No. 2005-21757 can be applied. In the method for decontaminating tritium-contaminated materials of the present invention, since the waste containing tritium is liquid, unlike the case of a tritium-containing gas, the risk of volatilization outside the system is very small, so that tritium can be safely removed. It can be recovered.

  In the present invention, tritium distributed inside from the surface of the tritium-contaminated material can be removed to a desired concentration by using high-temperature heated water. An example in the decontamination process of the present invention is shown in FIG. FIG. 3 shows the tritium concentration in the region of 250 μm from the surface of the tritium-contaminated stainless steel material after heating at 120 to 200 ° C. for 24 hours. The internal distribution of tritium in the tritium contaminated material shown in FIG. 3 was determined by the aqua regia etching method. As can be seen from FIG. 3, the tritium concentration shows a substantially constant value within 100 μm or more from the surface of the tritium-contaminated material before the decontamination treatment. Further, by adopting a higher temperature as the heat treatment temperature, tritium present in the contaminated material can be greatly reduced. However, tritium diffused on the surface of the contaminated material after treatment may remain at a high concentration. In particular, when the amount of water sealed in the hermetic container is small, tritium is highly deposited in the water or water vapor after the decontamination treatment, so that the surface adhesion of tritium increases. Therefore, the present invention can be combined with a conventional surface decontamination method such as a hot water cleaning method, a gas purge method, a water vapor purge method or a baking method in order to decontaminate tritium adhering to the surface. After the heat treatment of the sealed container containing the tritium-contaminated material is performed at 50 to 400 ° C., the tritium-containing water and / or water vapor is removed, and then the surface of the tritium-contaminated material after the decontamination treatment is washed with warm water. In this method, water vapor purge, gas purge, or high temperature baking is performed. Here, the temperature at the time of high temperature baking should just be the grade which can remove the tritium adhering to the surface, and is 200 degrees C or less normally. Moreover, since these surface decontamination methods can be performed without moving the tritium-contaminated material after performing the decontamination treatment in a closed system, the tritium decontamination treatment can be performed continuously.

  The decontamination method of the present invention is a batch type treatment method, but the accuracy and efficiency of the treatment can be improved by performing the operation by heat treatment of the sealed container in two or more stages.

  As a treatment method to be performed in two or more stages, first, after the first decontamination process is completed using a single sealed container, tritium-containing water or water vapor is discharged from the sealed container, and then new light water is used. And a second decontamination process is performed. In this method, since the water used in the first decontamination treatment is replaced with water not containing tritium, the removal of tritium from the tritium contaminated material is accelerated and the water is present inside the tritium contaminated material. The tritium concentration can be reduced quickly. At that time, the heating temperature and the heating time of the sealed container are changed for each processing stage according to the material and physical properties of the material. For example, the first treatment stage is performed at a high temperature for a short time, and then the water is replaced in the second treatment stage. In the second treatment stage, the material is heated at a slightly low temperature for a long time without causing damage. By this method, the tritium concentration can be reduced to a desired value without damaging the material. The number of times of processing in this method is not limited to 2 times, and 3 or more times may be employed depending on circumstances.

As shown in FIG. 4, the present invention can be carried out by reusing recovered tritium-containing water after decontamination treatment. The tritium contained in the tritium-contaminated material is partially recovered from the light water H ₂ O after the decontamination treatment, but is recovered as liquid water when there is little exchange reaction of H ₂ O to HTO. As a result, the tritium content does not increase. Therefore, depending on the temperature, time, or frequency of the decontamination treatment, the tritium-containing water collected after being used for the decontamination treatment can be used again for the decontamination treatment. In particular, at the time of decontamination treatment carried out in two or more stages, the reuse of recovered tritium-containing water can achieve a great effect because it can reduce the volume of tritium-containing water that is a secondary waste. Specifically, the first treatment stage of the treatment method is performed using the collected tritium-containing water, and then the second decontamination treatment is performed using water having a lower tritium concentration. Here, as the tritium concentration used in the second decontamination treatment, either recovered tritium-containing water or virgin light water not containing tritium may be used. Here, the tritium concentration of water in the sealed container can be obtained by a solid scintillation method or a liquid scintillation method. Even in the case of three or more decontamination treatments, the same treatment can be performed by reusing the collected tritium-containing water.

  Examples of the multistage treatment method of the present invention include a method using two or more decontamination treatment sealed containers. The plurality of sealed containers can be arranged in parallel and / or in series. When arranged in parallel, the decontamination processing amount of the tritium-contaminated material can be increased. In particular, when the volume of the sealed container cannot be increased, or when tritium contaminated materials with extremely different shapes and thicknesses are simultaneously decontaminated, they are arranged in parallel and simultaneously decontaminated, so efficient decontamination Can do. Moreover, when arrange | positioning in series, as shown in FIG. 5, since a decontamination process is repeatedly performed according to a tritium decontamination efficiency, a tritium decontamination can be performed reliably. When performing decontamination equipment using a plurality of sealed containers, the tritium-containing water collected after the decontamination treatment can be reused as described above. The tritium-containing water used in each decontamination process is used properly according to the treatment status of each stage based on the measured value after measuring the concentration of tritium contained. As described above, the collected tritium-containing water is disposed of after diluting with light water to the tritium concentration below the market acceptable limit concentration, or disposed of as tritium-containing water or its solidified product. Or kept in isolation. The plurality of closed containers may be arranged in combination of parallel and series in consideration of the processing amount and the processing efficiency.

  The present invention employs a decontamination system using the tritium decontamination equipment shown in FIG. 6 when performing tritium decontamination. The tritium decontamination equipment shown in FIG. 6 includes (A) a sealed container 10 having a heating function 13, equipment for supplying light water into the sealed container for decontamination and / or washing (19 and 21 in the figure). ), And tritium decontamination equipment 9 having equipment (15 to 17 in the figure) for recovering tritium-containing water after decontamination treatment and / or washing water after sealing container washing as drain water, (B) tritium In order to supply contaminants to the sealed container, the tritium decontamination chamber 6 provided adjacent to the sealed container, (C) water vapor and / or contaminated gas containing tritium is supplied to the tritium decontamination equipment and / or Or, equipment for discharging from the tritium decontamination chamber (22, 25, 26 in the figure), (D) supplying a purified gas not containing tritium to the tritium decontamination equipment and / or the tritium decontamination chamber And / or equipment for discharging (22, 24-26 in the figure), and (E) temperature and / or pressure in the sealed container, water containing the soft water present in the sealed container and / or For measuring or monitoring at least one of the amount of drain water, the internal pressure of the tritium decontamination chamber, the tritium concentration of the drain water, and the tritium concentration in the tritium decontamination chamber and / or piping The apparatus (16, 28, 30 in the figure) is comprised.

  In the present invention, the tritium decontamination chamber is placed under a negative pressure in order to prevent the gas containing tritium from being discharged to the outside when the tritium contaminants carried to the tritium decontamination chamber are taken out and inserted into the sealed container. It is preferable to maintain. In the present invention, it is not always necessary to set the tritium decontamination equipment including the sealed container to a negative pressure. However, in order to completely prevent the diffusion of radiation pollutants to the outside, the tritium having the sealed container is used. More preferably, a chamber for storing the contamination equipment is provided and the chamber is maintained at a negative pressure. These rooms are set to a negative pressure by using a tritium removal facility 22 having an intake / exhaust pump for the negative pressure maintaining function 23. When exhausting tritium-containing gas to the outside, a tritium recovery device (see FIG. It is necessary to keep the tritium concentration below the allowable concentration limit. In order to grasp the tritium concentration contained in the exhaust gas, it is preferable to install a monitoring device 28 for measuring the tritium concentration in the tritium removal facility or a pipe portion from the tritium removal facility to the exhaust.

  In the present invention, in addition to supplying light water for decontamination, light water is supplied and discharged to clean the inside of the pressure-resistant container after decontamination as necessary. Further, the tritium-containing water discharged after the decontamination process is sent out to the electrolysis concentration apparatus through the pipe 31. When concentration by electrolysis is not performed, the pipe 32 is sent to a storage tank and stored or stored as secondary waste.

  In the present invention, when a plurality of sealed containers are installed, in the tritium decontamination equipment, equipment for supplying light water into the sealed container for decontamination and washing in (A) above, and The equipment for recovering the tritium-containing water after the decontamination treatment and / or the washing water after washing the sealed container as drain water and the apparatus for controlling the equipment (C) to (E) are one control system. Can be summarized as: In addition, tanks for storing virgin light water and recovered tritium-containing water, tritium removal equipment for performing intake and exhaust of polluted gas and purified gas, or power supply for decontamination equipment, etc., depending on the processing amount and processing efficiency The tritium decontamination system of the present invention can be made compact and inexpensive by using it as a common facility when using a plurality of sealed containers.

  In the present invention, any one of supercritical water, subcritical water, supercritical carbon dioxide containing water, or subcritical carbon dioxide containing water can be used as heated water under a high temperature and high pressure environment. The critical temperature and critical pressure of supercritical seawater and supercritical carbon dioxide are 374.2 ° C. and 22.1 MPa and 31.1 ° C. and 7.4 MPa, respectively. The subcritical water is liquid water at 200 to 350 ° C., and the saturated vapor pressure is 1.55 MPa and 16.5 MPa at 200 ° C. and 350 ° C., respectively. Thus, since supercritical water or subcritical water can be used as a heating water fluid, it can be used as it is in the decontamination method of the present invention. In addition, since supercritical or submarine carbon dioxide containing water can be used as a fluid for carrying heated water, the amount of water used for tritium decontamination is reduced. This has the effect of reducing the volume of tritium-containing water, which is finally a secondary waste.

  FIG. 7 shows a process and a decontamination system for performing a tritium decontamination method using supercritical water or subcritical water. The light water 39 is brought into a supercritical or subcritical state by the high-pressure pump 34 and the heating body 13 and then introduced into the decontamination tank 33 containing the tritium-contaminated material, and the decontamination tank is circulated for a predetermined time. Thereafter, after switching the supercritical water or subcritical water flow path to the expansion valve 36 by closing the switching valve 38 installed in the circulation flow path, the expansion valve 36 is opened and the pressure is reduced by expansion. Then, the tritium-containing water 40 is recovered by condensation with a cooling trap 35 or the like. Here, the collected tritium-containing water 40 can be reused as a decontamination medium when the concentration of tritium contained is small. Moreover, the present invention can increase the decontamination efficiency by installing a plurality of decontamination tanks containing tritium-contaminated materials in parallel and / or in series. In FIG. 7, the flow path for circulating the decontamination tank containing the tritium-contaminated material and the flow path of the supercritical water or subcritical water is a closed system, and has the same function and action as the closed container during the circulation.

  FIG. 8 shows a process and a decontamination system for performing a tritium decontamination method with supercritical or subcritical carbon dioxide having light water. FIG. 8A shows that carbon dioxide is made supercritical or subcritical by the high-pressure pump 34 and the heating body 13, mixed with light water 39, and then passed through a decontamination tank 33 containing tritium contaminated material. Then, the pressure is reduced by the expansion valve 36, and the tritium-containing water 40 contained in the supercritical or subcritical state is recovered in the separation tank 37. At this time, the tritium-containing water 40 can be reliably recovered by cooling the flow path to the separation tank by the cooler 35. The tritium-containing water 40 thus recovered is reused and used as a decontamination medium. When the collected tritium-containing water is not reused as decontamination water, virgin light water is introduced by a switching valve or the like to perform decontamination treatment. In order to achieve the effect of the present invention, it is necessary to use water heated to 50 to 400 ° C. Since the critical temperature of carbon dioxide is 31.1 ° C., in the tritium decontamination system shown in FIG. 8, the temperature of supercritical or subcritical carbon dioxide is usually set to a predetermined temperature of 50 to 400 ° C. . When the temperature of supercritical or subcritical carbon dioxide is circulated below 50 ° C., the decontamination treatment is performed by setting the temperature of the decontamination tank 33 containing the tritium-contaminated material and its surroundings to a temperature of 50 ° C. or higher. be able to. In the tritium decontamination system shown in FIG. 8, carbon dioxide can be liquid as well as gas. Moreover, when it is desired to increase the decontamination efficiency, a plurality of decontamination tanks can be installed in parallel and / or in series.

  The tritium-containing water recovered in the tritium-contaminated system of FIGS. 7 and 8 is disposed after being diluted with light water to a level below the market acceptable limit of tritium based on the tritium concentration, or discarded, or tritium-containing water or a solidified product thereof. As quarantined or quarantined. In order to reduce the volume of tritium-containing water that is a secondary waste, a method of concentrating tritium-containing water by electrolysis in the same manner as described above can be employed.

The present invention is illustrated by the following examples, but the present invention is not limited to these examples.

<Example 1>
SS316 stainless steel exposed to tritium gas and contaminated by tritium is placed in a sealed pressure-resistant vessel (autoclave: sample decomposition vessel HUS-50 manufactured by Sanai Science Co., Ltd.) having the configuration shown in FIG. After being put together with 4 ml of ion-exchanged water and hermetically sealed, the hermetic pressure vessel was kept in a constant temperature dryer heated to a predetermined temperature of 120 to 200 ° C. for 24 hours. After the heating and holding, the above-described sealed pressure vessel was cooled, the sample SS316 stainless steel was returned to room temperature, and the decontamination process was completed. Thereafter, the tritium content of water in the sealed pressure vessel was measured, and the internal distribution of tritium was determined by an etching method for SS316 stainless steel after the decontamination treatment. The concentration of water tritium was measured using the liquid scintillation method.

The measurement results are shown in FIG. The horizontal axis in FIG. 3 indicates the depth from the surface, and the vertical axis indicates the tritium concentration. The tritium internal distribution in SS316 immediately after the exposure has a high tritium concentration region in the surface layer of about 8 μm from the surface, and the internal tritium concentration distribution is almost uniform. After tritium-contaminated SS316 was kept in a sealed container at 120-200 ° C. for 24 hours, a decrease in internal tritium concentration was observed. The degree of decrease in the tritium concentration was increased as the heating temperature was increased, and the internal tritium concentration was very small at the heating temperature of 200 ° C. Thus, the tritium decontamination method of the present invention has an effect of greatly reducing the concentration of tritium distributed inside the tritium-contaminated material. The tritium distributed on the surface of SS3316 after the decontamination treatment in FIG. 3 is a short time treatment (surface decontamination treatment) of several hours or less by hot air of 200 ° C. or less, warm water washing with hot water of less than 100 ° C. or steam purge. Thus, it was possible to easily decontaminate to a level of less than 0.1 MBq / cm ³ .

<Example 2>
Except for changing the heating time of the hermetic container, decontamination treatment of tritium-contaminated SS316 stainless steel was performed in the same manner as in Example 1. At heating temperatures of 150 ° C. and 200 ° C., holding times were 1 day, 3 days, and 9 days. FIG. 9 shows the internal distribution of tritium for SS316 stainless steel after the decontamination treatment. As can be seen from FIG. 9, even at the same heating temperature, the tritium concentration inside SS316 stainless steel decreased as the holding time (decontamination time) increased. When the heating temperature was 150 ° C., it was 9 days, and when it was 200 ° C., it was 2 days. It was possible to decontaminate 99% or more of tritium present in SS316 immediately after the exposure. The concentration of tritium adhering to the surface of SS316 stainless steel was reduced to less than 0.1 MBq / cm ³ by the same surface decontamination treatment as in Example 1.

<Example 3>
Using the same method as in Example 1 and Example 2 with the heating temperature and the heating holding time as parameters, the decontamination mechanism in the decontamination process of the present invention was examined, and the decontamination rate was estimated. Since it was found that the decontamination rate of tritium determined in the examination of Example 1 and Example 2 was determined by the diffusion rate of tritium inside the sample, the residual tritium inside SS3 16 stainless steel 5 mm thick based on the diffusion coefficient The amount was calculated by simulation. In the fusion experimental device, the use of stainless steel up to a thickness of about 5 mm is considered, and a tritium decontamination method that can handle this thickness has a very high future need. It is.

  The result of the simulation is shown in FIG. The horizontal axis represents the treatment time, and the vertical axis represents the ratio of the residual concentration to the concentration immediately after exposure for tritium remaining inside the sample. The internal tritium is not decontaminated at room temperature, and a decrease in the internal tritium concentration begins to be observed at 50 ° C. It can be seen that the present invention requires the heating temperature to be set to 50 ° C. or higher. At 200 ° C. employed in Examples 1 and 2, about 40% of tritium remains even after 500 hours. In the case of 5 mm thick stainless steel, it is effective to raise the processing temperature to 400 ° C. in order to shorten the processing time. On the other hand, when the processing temperature exceeds 400 ° C., it has been difficult to maintain temperature uniformity in the sealed container. Not only the durability of various types of equipment including airtight containers is drastically reduced, but also a large load is generated in order to construct safety equipment against high temperature and high pressure. Temperature could not be adopted.

<Example 4>
Based on the decontamination process shown in FIG. 4, the tritium-contaminated material was decontaminated by reusing the tritium-containing water collected after the tritium decontamination. The recovered tritium-containing water was subjected to decontamination treatment by holding SS316 stainless steel contaminated with tritium in Example 1 in a sealed pressure vessel together with virgin light water, and then holding at 120 ° C. for 24 hours. Cooled to room temperature. Here, since the amount of tritium-containing water was slightly smaller than the initial 4 ml, the decontamination treatment by holding at 120 ° C. for 24 hours was performed three times independently to secure 4 ml or more as the amount of tritium-containing water. As the tritium-contaminated SS316 stainless steel, the one immediately after exposure to tritium used in Example 1 was used. In the same manner as in Example 1, instead of the initial light water, 4 ml of the collected tritium-containing water was enclosed in a sealed pressure-resistant container, and then decontamination treatment was performed by maintaining at 200 ° C. for 24 hours. When the internal distribution of the tritium concentration of the SS316 stainless steel after the decontamination treatment was measured by an etching method, the same result as in the case of holding the heat treatment at 200 ° C. for 24 hours shown in FIG. 3 was obtained.

  As another experiment, instead of the new tritium-contaminated SS316 stainless steel, the SS316 stainless steel after being decontaminated by holding at 120 ° C. for 24 hours was sealed with 4 ml of the recovered tritium-containing water. It was sealed in a heat-resistant container and kept at 200 ° C. for 18 hours for decontamination treatment. The SS316 stainless steel after decontamination treatment at 120 ° C. used as a sample for 24 hours has the same internal distribution of tritium concentration as in the case of treatment at 120 ° C. for 24 hours in FIG. By adding a decontamination treatment with heating at 200 ° C. for 18 hours, this SS316 stainless steel can reduce the internal distribution of tritium concentration to the same level as when decontamination treatment was performed at 200 ° C. for 24 hours as shown in FIG. It was.

  As described above, the present invention can obtain the desired decontamination effect even if the tritium-containing water collected after the tritium decontamination is reused.

<Example 5>
Based on the multistage decontamination process shown in FIG. 5, the effect of the tritium decontamination method of the present invention by multistage treatment and reuse of tritium-containing water was verified. In the first-stage decontamination process shown in FIG. 5, SS316 stainless steel immediately after exposure to tritium was sealed in a sealed pressure-resistant container together with reused tritium-containing water in the same manner as in Example 1, and then at 150 ° C. for one day (24 Time) and decontamination treatment was performed. Here, the reused tritium-containing water was previously decontaminated in the same manner as in Example 1 by holding SS316 stainless steel immediately after exposure to tritium at 150 ° C. for 24 hours with virgin light water. Then, it was recovered after cooling to room temperature. Three SS316 stainless steels obtained by this decontamination treatment were sealed in another sealed pressure vessel having an internal volume of 100 ml together with 10 ml of reused tritium-containing water, and then heated and held at 150 ° C. for 8 days. Then, the decontamination process was performed again (second stage decontamination process). The reused tritium-containing water used here was recovered by cooling to room temperature after carrying out decontamination treatment at 120 ° C. for 24 hours in Example 4. SS316 stainless steel that has been decontaminated while maintaining 150 ° C heating for a total of 9 days (1 day for 1st stage decontamination + 8 days for 2nd stage decontamination) shows the internal distribution of tritium concentration. It was possible to reduce to the same level as in the case of the decontamination treatment by heating at 150 ° C. for 9 days shown in FIG.

  In the second-stage decontamination process, an experiment was conducted in which virgin light water was used instead of the tritium-containing water collected by cooling to room temperature after maintaining the temperature at 120 ° C. for 24 hours. In this case, in the case of decontamination treatment by heating at 150 ° C. for 9 days, the internal distribution of tritium concentration of SS316 stainless steel subjected to decontamination treatment by heating at 150 ° C. for 7 days is shown in FIG. It was found that it can be reduced to the same level. In the second stage decontamination process, the internal distribution of tritium concentration could be reduced in a short time by performing decontamination treatment using water not containing tritium.

  The multistage decontamination process shown in FIG. 5 can be applied not only to the two-stage decontamination process described above, but also to a three-stage or more decontamination process. The tritium-containing water to be reused in the decontamination process at each stage may be selected from those applicable to the decontamination process at each stage by measuring the tritium concentration in advance before use. In this way, efficient decontamination processing can be performed. Furthermore, when the tritium-containing water collected in the decontamination process at each stage becomes high, when it is high, dilute with tritium-free water and discard it, or as it is, tritium-containing water or its solidified product. Quarantined or quarantined. The tritium-containing water stored or preserved in this manner is particularly preferably reduced in volume by electrolysis in this example in order to reduce the load on the external environment. In the multi-stage treatment process using multiple sealed decontamination containers, the work man-hours are slightly increased in terms of material replacement, etc., but by standardizing the decontamination treatment conditions, a large number of samples can be continuously added. The decontamination process can be performed, and the decontamination process of tritium distributed inside the sample can be reliably performed. Therefore, it is possible to construct a decontamination process suitable for mass processing of tritium contaminated materials.

<Example 6>
About 20 sheets of SS316 stainless steel (70 cm long x 50 cm wide x 5 mm thick) contaminated with tritium, decontamination was performed using the heated water type tritium decontamination equipment shown in FIG. A container containing 20 sheets of tritium-contaminated SS 316 arranged on the arrangement table 8 with an interval between each one is stored in the tritium decontamination chamber 6 maintained at a negative pressure, and then the container is placed in the arrangement state. After being automatically inserted into the pressure vessel 10 (internal volume: about 1 m ³ ) as a tritium contaminant insertion portion by a sliding method, the door 11 of the pressure vessel was closed and sealed with a fastener 12. After supplying 50 liters of light water from the water supply device (19, 21 in the figure) into this sealed pressure vessel, it is heated at 300 ° C. and held for 300 hours, and then the cooling vessel provided in the pressure vessel Cooled to room temperature with circulating water. Thereafter, the water used for decontamination from the heat-resistant container is extracted as drain water using a tritium-containing water recovery facility (15 to 17 in the figure), and the discharge port of the tritium-containing water recovery facility is closed. Then, purified gas was supplied into the sealed container by a purified gas circulation device (22, 24 in the figure). At this time, if the monitoring device 16 capable of measuring the amount of drain water is applied, the remaining state of the drain water can be grasped in the pressure vessel, so the timing of introducing the purified gas into the pressure vessel is adjusted. In some cases. In addition, the purified gas was heated by the heating body 13, and the sealed container was again heated to 200 ° C. The purified gas circulated in the sealed container was discharged to the tritium removal facility 22 by the pollutant gas discharge facility and regenerated as the purified gas, and then supplied to the sealed container by the purified gas circulation device. Circulation with this purified gas was continued for 1 hour. Here, the tritium removal facility is composed of a tritium recovery device (not shown) in which tritium absorption tanks are arranged in series, and has a negative pressure maintaining function 23 for preventing leakage of tritium to the outside. Have. The gas from which tritium has been removed is discharged to the outside through the pipe 29 when not used as a purified gas. At this time, the discharge of gas to the outside is controlled by providing the tritium monitor 28 so that the tritium concentration is less than the allowable concentration (for example, 0.5 Bq / cc or less).

About 20 sheets of SS316 stainless steel decontaminated in this way, 5 sheets with different arrangement positions were randomly extracted and the internal distribution of tritium concentration was measured. As a result, it was confirmed that the internal distribution of tritium concentration was less than 0.1 MBq / cm ^{3 for all} five sheets. Also, the tritium concentration at the surface of SS316 stainless steel is less than 0.1 MBq / cm ³ due to the surface decontamination treatment by circulating the heated refined gas, and the tritium concentration is reduced on the surface and inside of SS316 stainless steel. I was able to.

<Example 7>
In the same manner as in Example 6, after holding a sealed pressure vessel containing 20 sheets of SS316 stainless steel contaminated with tritium at 300 ° C. for 300 hours, the water vapor present in the sealed vessel was removed from the pollutant gas discharge facility. Was discharged to the tritium removal facility in the form of contaminated water vapor gas by the decompression means attached to. Here, when water vapor present in the sealed container is discharged to the tritium removal facility, the contaminated water vapor gas can be recovered as tritium-containing water by providing the trap device 27 by cooling in the middle. After completing the contaminated water vapor gas at 300 ° C., the purified gas was supplied into the sealed container by a purified gas circulation device, and the purified gas was circulated for 1 hour in the same manner as in Example 6. At this time, the temperature of the sealed container was lowered from 300 ° C. to 200 ° C., and purified gas was circulated in a state set to 200 ° C. After circulating the purified gas, the sealed container was cooled, 20 sheets of SS316 stainless steel after the decontamination treatment were taken out, 5 of them were taken out, and the internal distribution of the tritium concentration was measured. The SS316 stainless steel after the decontamination treatment had a tritium concentration of less than 0.1 MBq / cm ³ both on the surface and inside, and the tritium concentration on the surface and inside of the SS316 stainless steel could be reduced. As described above, the method for discharging and collecting the tritium-containing water after the decontamination treatment in the form of the contaminated water vapor gas by the decompression means can simplify the decontamination system.

  The tritium-containing water recovered in the decontamination process of Example 6 or Example 7 is introduced into the HTO drain treatment facility 15 provided in the tritium decontamination facility power source 14 shown in FIG. After the tritium concentration is checked by the above, if the tritium concentration is low, it is stored in the tritium-containing water storage tank 18 and reused for the next decontamination process. In addition, the decontamination system of Example 6 or Example 7 is configured by applying the heated water type tritium decontamination equipment shown in FIG. 6 to a multi-stage process or a process using a plurality of pressure vessels. Can be constructed as

<Example 8>
The effect of this invention was verified about the decontamination method performed using supercritical water or subcritical water by the decontamination system shown in FIG. After putting SS316 stainless steel (thickness 5 mm) contaminated with tritium into the decontamination tank, light water was introduced into the decontamination tank as supercritical water or subcritical water using the high-pressure pump 34 and the heating element 13. . Thereafter, the supercritical water or the subcritical water was circulated with the switching valve 38 and the expansion valve 36 on the water supply side closed. After passing through the decontamination tank 33, the supercritical water or subcritical water is cooled by the cooling pipe 35 and converted into liquid water. Then, it is introduced into the decontamination tank 33. Since the circulation form of supercritical water or subcritical water by this repetition forms a closed system, the decontamination method in the closed container has the same function and action. Supercritical water or subcritical water is set at a temperature of 200 to 400 ° C., but the temperature was set to 300 to 400 ° C. in order to process SS316 stainless steel having a thickness of 5 mm in a short time. The pressure of supercritical water or subcritical water was adjusted to a level that can maintain the state of supercritical water or subcritical water at a temperature of 300 to 400 ° C.

  Supercritical water or subcritical water is circulated at a temperature of 300 to 400 ° C. for a predetermined time (300 to 50 hours), then the expansion valve 36 is opened to lower the pressure, and the cooling valve 35 is used to cool the supercritical water or subcritical water. And separated into a separation tank as tritium-containing water. Thereafter, the operation of introducing water vapor at 200 ° C. or lower into the decontamination tank was continuously performed for 30 minutes, thereby decontaminating tritium adhering to the SS316 stainless steel surface by the water vapor purge. The introduction of the water vapor purge can be performed in either a closed system or an open system. In this embodiment, surface decontamination may be performed with a gas not containing tritium at 200 ° C. or lower instead of water vapor at 200 ° C. or lower. The tritium-containing water collected in the separation tank can be reused as a decontamination medium. In this embodiment, light water or recovered tritium-containing water can be appropriately replaced during the decontamination process. In this way, water with a low tritium concentration is used during the decontamination process, so that the decontamination efficiency can be improved.

SS316 stainless steel obtained after decontamination treatment by circulating supercritical water or subcritical water at 300 ° C. for 300 hours, 350 ° C. for 200 hours or 400 ° C. for 50 hours has a tritium concentration of 0 on both the surface and inside. It was less than 1 MBq / cm ^3, and the tritium concentration could be reduced on the surface and inside of SS316 stainless steel.

<Example 9>
The effect of the present invention was verified for a decontamination method performed using supercritical water-containing carbon dioxide or subcritical carbon dioxide containing water by the decontamination system shown in FIG.

  The SS316 stainless steel contaminated with tritium and the decontamination treatment conditions were the same as in Example 8 except that supercritical water-containing subcritical carbon dioxide or water-containing subcritical carbon dioxide was used instead of supercritical water or subcritical fluid water. The same thing. Since supercritical carbon dioxide has a critical temperature of 31.1 ° C., the decontamination effect with water cannot be sufficiently obtained at this temperature. Therefore, supercritical or subcritical carbon dioxide is usually heated to 50 ° C. or higher for decontamination treatment. However, in this example, in order to perform complete decontamination of the surface and the interior of a stainless material having a thickness of 5 mm, supercritical carbon dioxide needs to be heated at 300 ° C. or higher. It is not realistic to set the carbon to 300 ° C. or higher because the difference from the critical temperature is large. Therefore, by heating only the decontamination tank 33 and its peripheral portion shown in FIG. 8 to a temperature of 300 ° C. to 400 ° C., the supercritical or subcritical carbon dioxide used in this example has a temperature of 50 ° C. or less. It becomes possible to set. The supercritical or subcritical carbon dioxide after passing through the decontamination tank is reduced in pressure by opening the expansion valve 36, cooled, and separated into the separation tank 37 through the switching valve 38 as tritium-containing water 40. Carbon dioxide circulates as a gas and is used again as supercritical or subcritical carbon dioxide by a high-pressure pump and a heating element. As shown in FIG. 8, the tritium-containing water separated in the separation tank is reused and mixed with supercritical or subcritical carbon dioxide and used for decontamination treatment. At this time, when the tritium concentration of the tritium-containing water is increased, the tritium-containing water is replaced with water having a low tritium concentration or virgin light water and mixed with supercritical or subcritical carbon dioxide.

Based on such a process, it is obtained after decontamination treatment by heating water contained in supercritical or subcritical carbon dioxide at 300 ° C. for 300 hours, 350 ° C. for 200 hours, or 400 ° C. for 50 hours. The SS316 stainless steel had a tritium concentration of less than 0.1 MBq / cm ³ both on the surface and inside, and the tritium concentration on the surface and inside of the SS316 stainless steel could be reduced.

  As described above, the present invention uses any one of critical water, subcritical water, supercritical carbon dioxide containing water, or subcritical carbon dioxide containing water as heated water for tritium decontamination treatment. The present invention can be applied to an effective tritium decontamination method and a decontamination system thereof.

  The tritium decontamination method and the decontamination system of the present invention can efficiently and inexpensively remove tritium distributed on the surface of tritium contaminants and the inside thereof, and are safe and secure. Because of its superiority, it can be expected to be used in the field of contaminated waste disposal and reuse from nuclear facilities and radioactive handling facilities. The tritium decontamination method and the decontamination system of the present invention are not limited to metal materials, and can be applied to materials such as plastics, ceramics, and inorganic glass by adjusting the temperature and processing time during the decontamination process. Since it is possible, it is highly useful.

  DESCRIPTION OF SYMBOLS 1 ... Airtight container, 2 ... External jacket, 3 ... Internal container, 4 ... Tritium contamination, 5 ... Light water, 6 ... Tritium decontamination chamber, 7 ... Container for carrying in / out of tritium contamination material, 8 ... Arrangement table, 9 ... Tritium decontamination equipment, 10 ... pressure vessel, 11 ... pressure vessel door, 12 ... fastener, 13 ... heating element, 14 ... tritium decontamination equipment power source, 15 ... drain treatment equipment, 16 ... water amount monitor for tritium contaminated water, 17 ... Tritium contaminated water discharge pipe, 18 ... Tritium-containing water storage tank, 19 ... Light water storage tank, 20 ... Tritium-containing water supply pipe, 21 ... Light water supply pipe, 22 ... Tritium removal equipment, 23 ... Negative pressure maintenance function, 24 ... purified gas supply pipe, 25 ... pollutant gas discharge pipe, 26 ... gas flow rate adjusting device, 27 ... cooling device, 28 ... tritium monitor, 29 ... exhaust, 30 ... temperature / pressure monitor, 31 ... electrical component Piping connected to the concentrator, 32 ... piping connected to the storage tank, 33 ... decontamination tank, 34 ... high pressure pump, 35 ... cooler, 36 ... expansion valve, 37 ... separation tank, 38 ... switching valve, 39 ... for decontamination Light water or tritium-containing water, 40 ... tritium-containing water, 41 ... high-pressure pump.

Claims (4)

  Any of supercritical water, subcritical water, supercritical carbon dioxide containing water, or subcritical carbon dioxide containing water in a closed vessel containing tritium contaminated material in which tritium is distributed on and inside the material. And circulating the closed container containing the tritium-contaminated material at a temperature of 50 to 400 ° C. to promote the transition of tritium present on the surface of the tritium-contaminated material into water vapor and at the same time by heating. A method for decontaminating tritium contaminants, which promotes diffusion of tritium present in the tritium-contaminated material to the material surface and transfer to water vapor on the surface.   3. The method for decontaminating tritium contaminants according to claim 1, wherein the tritium-containing water used for the decontamination treatment is diluted with light water and discarded, or as a contaminated waste of tritium-containing water or its solidified product. A method for decontaminating tritium contaminants, wherein the decontamination method is characterized by being isolated and stored.   Supercritical water, subcritical water, supercritical carbon dioxide containing water, or water obtained by high-pressure pump and heating is contained in a sealed container containing tritium contamination material in which tritium is distributed on the surface of the material as well as inside. While circulating any of the subcritical carbon dioxide, the closed container containing the tritium-contaminated material is heat-treated at a temperature of 50 to 400 ° C. and passed through the decontamination process of the tritium contaminants. Tritium contaminants characterized by separating and recovering only water containing tritium through a process of expanding either critical water, supercritical carbon dioxide containing water, or subcritical carbon dioxide containing water. Decontamination system.   The system for decontamination of tritium contaminants according to claim 3, wherein the tritium-containing water used for the tritium decontamination treatment is diluted with light water and discarded, or tritium-containing water or a solidified product thereof. A system for decontaminating tritium contaminants, comprising equipment for isolated storage or preservation as contaminated waste.

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