JP2003014890A - Disposal method for radioactivated graphite and its system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To remove radioactive nucleides adhering to activated graphite and reduce discharge of radioactive nucleides from the activated graphite to be buried. SOLUTION: The activated graphite is washed with ultrasonic or a chemical decontamination agent and C-14 in washing liquid is mineralized and C1-36 is recovered by adsorption. By heating the activated graphite after washing, included C1-36 is removed by evaporation. The heated activated graphite is solidified. For the condition of washing activated graphite, it is proper to irradiate with ultrasonic in solution of oxidation processing below pH 4 and temperature of nearly 80 deg.C. The heating processing of the activated graphite is proper to heat from below to 900 deg.C under the existence of inert gas. C1-36 is recovered in a trap which a cooling device is installed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and apparatus for disposing activated graphite.

[0002]

2. Description of the Related Art A large amount of activated graphite is generated with the decommissioning of a high temperature gas reactor. In order to safely dispose of these activated graphite, it is necessary to prevent the radionuclide from leaching out from the activated graphite after the disposal. C-14 and Cl-36 are considered to be important nuclides for exposure assessment after waste disposal. It is known that the radionuclides present in the bulk of graphite, especially C-14, are not released to the outside of the system because graphite used in HTGR has high crystallinity and is thermodynamically stable. There is.

For example, Japanese Patent Application Laid-Open No. 3-179299 discloses a method of gasifying activated graphite by hydrogenation or combustion and separating C-14 by isotope separation of the gas. Further, for example, Japanese Patent Laid-Open No. 2000-121795 discloses a method in which C-14 contained in radioactive graphite waste is preferentially oxidized and then immobilized.

Generally, the methods of disposing activated graphite are roughly classified into incineration disposal and buried disposal. For incineration, activated graphite generated as waste is incinerated in the gas phase in the presence of a catalyst. For the landfill disposal, a method has been proposed in which CO ₂ generated from incineration of activated graphite is collected, only C-14 is separated and collected, and then fixed again, and then landfilled.

[0005]

With the conventional method of burial disposal, 100% of the generated CO ₂ containing C-14 cannot be recovered and may be released to the natural world. In addition, in graphite currently used in high temperature gas furnaces, metals as impurities are in the range of several tens of ppm.
Since it is contained, a large amount of incineration occurs due to incineration, and it is necessary to add a new disposal method for incinerated ash.

In addition to C-14, activated graphite has a long half-life.
It contains 100-300 Bq g ^-1 (3 × 10 ⁵ years) of Cl-36, which is counted as an important radionuclide for disposal evaluation, and some disposal methods for C-14 have been proposed. , Due to incineration
Techniques to trap Cl-36 emissions have not been investigated at this time.

On the other hand, it has been known that, in the case of burial disposal, activated graphite is instantly released when groundwater or the like comes into contact with it after burial, and about 10% of the total inventory is released in about one month. C-14 is released only when it comes in contact with the wetted surface, and the release rate can be maintained at 10 ^-4 / year, but the chemical form of C-14 released is almost the organic compound form. Therefore, it is difficult to make it adsorb to the solidifying material.

In activated graphite, Cl in the form of chloride is used.
-36 is taken in and released to the outside by contact with liquid. After or before washing, the activated graphite is heated without incineration to evaporate chloride contained in the activated graphite and remove Cl-36.

C-14 contained in cleaning solution, which is important for evaluation of exposure
By solidifying and Cl-36, almost all radionuclides from graphite waste can be contained and buried. At this time, C-14 has a form of an organic compound and an inorganic compound, and the form of the inorganic compound can be solidified, but the form of the organic compound is C-14. Is difficult to convert.

The present invention has been made in order to solve the above-mentioned problems. First, the activated graphite is first washed to remove the radionuclide that is instantaneously released, and then it is disposed of by burial, so that activation after burial is performed. It is an object of the present invention to provide a method for disposing activated graphite and an apparatus therefor capable of significantly reducing the nuclide leaching rate from graphite.

The present invention also provides a method and apparatus for disposing radioactive graphite, which can be solidified by chemically changing C-14 in the form of an organic compound which is instantly released from activated graphite into an inorganic compound. To provide.

[0012]

The invention according to claim 1 is
It is characterized in that the radioactive graphite containing the radioactive nuclide is washed in advance to release the radioactive nuclide before the buried disposal of the graphite containing the radioactive nuclide.

According to the second aspect of the present invention, before burying the graphite containing the radionuclide, the activated graphite containing the radionuclide is washed in advance to release the radionuclide, and then heated in an inert gas. It is characterized in that it is treated to reduce the radionuclide.

According to the present invention, radioactive nuclides adhering before the disposal is removed by cleaning the activated graphite generated during the dismantling of the high temperature gas reactor, for example, and the radioactive nuclides released after the disposal is discharged. To reduce. As a result, the leaching rate of radioactive nuclides, which is important for exposure assessment from activated graphite, can be suppressed to a low level, and it can be made a region where there is no problem in safety assessment.

That is, by washing the activated graphite with an oxidizing agent to oxidize the organic component of C-14 to the inorganic component of CO ₂ , C-14 which is an organic component released in advance.
Can be solidified into a solidified material by making all of them inorganic. Further, by heating the activated graphite in an inert gas, the Cl-36 contained in the activated graphite is burned without burning the graphite.
Can be removed by evaporation.

The invention according to claim 3 is characterized in that the cleaning treatment is cleaning of the activated graphite with a chemical decontaminating agent containing an acid. According to the present invention, the radionuclide adhering to the activated graphite can be dissolved and peeled by the chemical detergent. In particular, since the radionuclide of the metal is in the form of oxide, it can be dissolved and removed by the reducing organic acid contained in the chemical detergent.

The invention according to claim 4 is characterized in that the chemical detergent is an oxidizing agent or a reducing agent, or both, which changes the radionuclide contained in the cleaning solution of the activated graphite into a chemical form.

According to the present invention, the radionuclide contained in the cleaning liquid is chemically reacted with the reducing agent and the oxidizing agent contained in the chemical decontaminating agent to change the chemical form. In particular, C-14, which is a chemical form of organic compounds, is one of the most important nuclides for exposure assessment because it has low adsorption to solidifying agents such as cement.

Therefore, C-14 having a chemical form of an organic compound is chemically reacted with a redox agent contained in a chemical decontamination reagent to form a chemical form of an inorganic compound, thereby improving the adsorbability for solidification. Can be planned. Further, by using an oxidizing agent as a chemical decontaminating agent, C-14 having a chemical form of an organic compound is changed to a chemical form of carbon dioxide (CO ₂ ) to improve the adsorbability to a solidifying agent. be able to.

The invention according to claim 5 is characterized in that the oxidizing agent is used together with ultraviolet (UV) irradiation. According to the present invention, the adsorbability to the solidifying agent can be improved by using the oxidizing agent and ultraviolet rays (UV) together. C-14
The organic compound containing is a low molecular weight compound having 1 to 2 carbon atoms, and can be decomposed into CO ₂ by irradiating with ultraviolet rays in the presence of an oxidizing agent. C-1 thus obtained
CO ₂ containing 4 can be adsorbed on the solidifying agent.

The invention according to claim 6 is characterized in that the oxidizing agent is ozone or hydrogen peroxide, or a combination of ozone and hydrogen peroxide. According to the present invention, by using ozone gas or hydrogen peroxide as an oxidant, C- having a form of an organic compound which is a low molecular weight compound can be obtained.
14 can be decomposed to CO ₂ .

The invention according to claim 7 is characterized in that ultrasonic irradiation is applied to the cleaning process. According to the present invention, the radionuclide attached to the activated graphite can be physically separated by ultrasonic waves.

The invention of claim 8 is characterized in that the heat treatment heats the activated graphite at a temperature of 900 ° C. to 1300 ° C. in an inert gas. According to this invention, the radionuclide and chloride contained in graphite can be removed by evaporation by heating the generated activated graphite waste to a high temperature without incineration.

Further, the activated graphite is heated in an inert gas in a high temperature induction heating furnace from 900 ° C. to 1300 ° C. instantaneously, and the chloride contained in the activated graphite is not burned. The substance is removed by evaporation. As a result, the volatile Cl-36 contained in the activated graphite can be removed.

If the temperature is lower than 900 ° C., chloride is difficult to vaporize, and if the temperature is higher than 1300 ° C., the boiling point becomes higher than the boiling point, which is not preferable because the heating device becomes complicated due to operational problems such as temperature adjustment and increase in heat capacity.

The invention according to claim 9 is a cleaning tank, an inner tank provided in the cleaning tank for accommodating activated graphite, and an ultrasonic transducer provided between the inner tank and the cleaning tank. And a circulation pipe in which the cleaning liquid flows out from the lower side and flows in from the upper side in the cleaning tank, and an ion exchange resin tower provided in the circulation pipe.

According to the present invention, it is possible to wash the graphite block by stirring the washing water in the washing tank by ultrasonic irradiation from the ultrasonic vibrator. Further, the ion-exchange resin tower can remove the radionuclide contained in the wash water.

According to a tenth aspect of the present invention, there is provided a cleaning tank, an inner tank provided in the cleaning tank for accommodating activated graphite, and an ultrasonic transducer provided between the inner tank and the cleaning tank. And an ozone generator connected to the cleaning tank by piping.

According to the present invention, ozone is blown from the ozone generator while irradiating the cleaning liquid with ultrasonic waves by the ultrasonic vibrator. C-14 existing in the surface layer of the graphite block in the cleaning solution is eluted by irradiating with ultrasonic waves,
By blowing ozone, it can be made inorganic up to CO ₂ , which makes it easy to fix it to the solidifying agent.

The invention according to claim 11 provides a cleaning tank, an outlet pipe provided in the cleaning tank, a circulation pump connected to the outlet pipe, a discharge side pipe of the circulation pump, and the cleaning tank. Circulation pipe connected to the inlet pipe provided, a heating heater, a hydrogen peroxide supply device, and an ultraviolet decomposing device sequentially provided in the circulation pipe along the downstream side, an outlet side circulation pipe of the heating heater, and the ultraviolet light. And a water quality measuring device branched from an outlet side circulation pipe of the decomposition device and connected by bypass.

According to the present invention, the decontaminating agent and the cleaning solution of the aqueous solution can be circulated and reused. After the cleaning tank is filled with the cleaning solution after cleaning the activated graphite, the redox agent is added to the cleaning tank and the cleaning solution is circulated by the circulation pump.
At this time, the temperature of the cleaning liquid is raised by a heater to 80 ° C. or higher to dissolve the oxide impurities contained in the activated graphite.

When ultraviolet rays are irradiated from the ultraviolet decomposition device in a state in which the oxidant is dissolved in the solution, ozone or water molecules are broken in chemical bonds to generate active radicals having unpaired electrons, which are dissolved in the solution. Can decompose organic compounds to CO ₂ . This decomposition can be confirmed by a water quality measuring device.

According to a twelfth aspect of the present invention, there is provided an ion exchange resin column which is branched from the outlet pipe of the cleaning tank and the outlet side circulation pipe of the heater and is bypass-connected.

According to this invention, in the invention of claim 11, the metal ion such as Co-60 eluted from the activated graphite contained in the heated cleaning liquid circulating in the circulation system for cleaning is ion-exchange resin column. Can be collected at.

According to a thirteenth aspect of the present invention, a vertical heating furnace, a movable high-frequency heater provided in the heating furnace, an outlet provided in the lower portion of the heating furnace, and a pipe connection to the outlet An inert gas generator, a circulation pipe provided between the outlet and the upper part of the heating furnace, and a circulation pump and a radionuclide chloride trap provided in the circulation pipe. Characterize.

According to the present invention, the inert gas is circulated through the heating furnace by aeration, and the activated high-frequency heater instantly heats the activated graphite from below. By heating in an inert gas, the contained Cl-3 can be used without burning activated graphite.
6 can be removed by evaporation. Further, Cl-36 can be collected by, for example, a radionuclide chloride trap that collects CsCl.

[0037]

BEST MODE FOR CARRYING OUT THE INVENTION A first embodiment of a method of disposing activated graphite according to the present invention will be described with reference to FIG.
FIG. 1 is a flow chart of activated graphite disposal according to the present embodiment. First, after shutting down the decommissioned HTGR 1,
Attenuate short half-life radionuclides such as -60. The activated graphite 3 generated at the time of the dismantling process 2 is cut and shredded 4 into a size that can be filled in a drum can, for disposal as a waste at the disposal site.

Activated graphite block 5 cut and shredded 4
The chips and graphite powder 6 generated by the cutting are subjected to ultrasonic treatment and acid-based chemical decontamination by a cleaning process 7. In the cleaning process 7, the decontaminating agent aqueous solution 9, the graphite block 5 and the graphite powder 6 are stored in the cleaning tank 8 and then the decontaminating agent aqueous solution 9 is washed while being stirred by the stirrer 10.

The activated radioactive graphite block 5 and the chips and the graphite powder 6 which have been washed are further heat-treated in an inert gas as necessary to reduce radionuclides, and then solidified as graphite waste 13. After processing 14, buried processing
It will be buried by 15.

At this time, the cleaning waste liquid 12 and the graphite waste 13 containing the radionuclide generated in the cleaning treatment 7 are sequentially solidified into a solidifying material 14 and then embedded in the same manner as activated graphite 15 in the embedding treatment 15. It is filled and solidified as a waste together with the embedding material 17 and buried in the embedding pit 16. If necessary, the cleaning waste liquid 12 after cleaning is concentrated and solidified 14 with a solidifying material.

When the concentration of Cl-36 in the activated graphite is below the detection limit value, washing is omitted and the activated graphite block 5, chips and graphite powder 6 are placed in an inert gas. It can be heated to reduce radionuclides.

According to the present embodiment, it is possible to remove the radionuclide that is instantaneously released from the surface portion with which the activated graphite comes in contact with the liquid after the burial disposal. In other words, C-14 and Cl-36 are considered to be important nuclides in the exposure assessment after burial of graphite waste. C-14 contained in activated graphite is produced by nuclear reaction of nitrogen contained as an impurity with neutrons. ¹⁴ N (n, p) ¹⁴ C (1)

Since the produced C-14 exists in the bulk of the activated graphite, it does not leach into the solution system due to the liquid contact after embedding, and only C-14 localized on the surface of the activated graphite is in the solution system. Seep into. On the other hand, Cl-36 is produced by the nuclear reaction of Cl-35, which is an impurity in graphite, with neutrons. ³⁵ Cl (n, γ) ³⁶ Cl (2)

It is known that chloride ions from graphite are extremely fast and have a leaching rate of about 10 ^-1 / year.
Irrespective of the factors such as temperature that accelerate the leaching, they are released immediately when they come into contact with the liquid. Since the form of Cl-36 contained in graphite is chloride ion, it is released into the solution upon contact with the liquid.

Therefore, in order to reduce the amount of radionuclides released immediately after burying the activated graphite, cleaning before burying is necessary.
By performing treatment such as heating, it is possible to set the disposal method according to the radioactivity level by reducing the radionuclide before burial.

Next, referring to FIG. 2, a first embodiment of the radioactive graphite disposal apparatus according to the present invention will be described. The present embodiment is the first example of the activated graphite cleaning apparatus used in the cleaning process 7 described in FIG. 1 as a part of the activated graphite disposal apparatus. In FIG. 2, reference numeral 18 is a vertical cleaning tank, an inner tank 19 for housing the graphite block 5 is installed in the cleaning tank 18, and an ultrasonic transducer 20 is installed between the inner tank 19 and the cleaning tank 18. Has been done. Circulation pipes 22 to 24 connected to the ion exchange resin tower 21 are provided at both upper and lower ends of the cleaning tank 18. Reference numeral 25 is a drain pipe connected to the lower portion of the cleaning tank 18.

Inner tank of the cleaning tank 18 equipped with the ultrasonic transducer 20
The activated graphite block 5 and the graphite powder 6 cut in the dismantling process 2 are housed in 19. The cleaning liquid is poured into the cleaning tank 18, and the inner tank 19
Add wash solution until the is completely submerged. As a means for stirring the cleaning liquid, ultrasonic waves are radiated from the ultrasonic vibrator 20, the cleaning liquid is heated to 80 ^° C. or higher, the cleaning water is rotated, and the cleaning water is stirred to fill the inner tank 19 with graphite. Wash block 5.

At this time, the ion exchange resin column 21 is installed in the cleaning tank 18.
Alternatively, the circulation pipes 22 to 24 equipped with an electrolyzer are attached to remove the radionuclide contained in the cleaning liquid. After washing, the inner tank 19 containing the graphite block 5 and the graphite powder 6 is taken out, and the washed graphite block 5 and the graphite powder 6 are filled in a drum can. After filling the drum, a solidifying material such as ordinary Portland cement or 1/9 cement (ordinary Portland cement: blast furnace slag = 1: 9) is filled to form a waste.

According to this embodiment, the activated graphite block 5 and the graphite powder 6 can be quickly washed,
The ion-exchange resin tower 21 can remove the radionuclide dissolved in the wash water.

Next, a second embodiment of the activated graphite disposal apparatus according to the present invention will be described with reference to FIG. FIG. 3 showing the present embodiment corresponds to the second example of the activated graphite cleaning device described in FIG. 2. In FIG. 3, the same parts as those in FIG. Is omitted.

This embodiment is different from FIG. 2 in that a cleaning tank is used.
An ozone generator 26 is provided in 18 via a ventilation pipe 27, and ozone gas 29 from the ozone generator 26 is passed through the ventilation pipe 27 into an inner tank 19
It is configured to be ejected inside. A hollow perforated plate 28 connected to the ventilation pipe 27 is installed at the bottom of the inner tank 19, and ozone gas 29 becomes bubbles from the hollow perforated plate 28 to rise in the inner tank 19.

That is, the graphite block 5 or graphite powder 6 of activated graphite is housed in the inner tank 19, and the inner tank 19 is inserted into the cleaning tank 18. A cleaning liquid containing water or a carboxylic acid such as oxalic acid is poured into the cleaning tank 18 until the graphite block 5 or the graphite powder 6 is submerged.

The ozone 29 is blown from the ozone generator 26 while the ultrasonic wave is applied by the ultrasonic vibrator 20. By irradiating with ultrasonic waves, it is relatively easy to elute in the cleaning liquid existing in the surface layer portion of the graphite block 5 or the graphite powder 6.
C-14 is eluted and converted to CO ₂ by blown ozone, making it easy to fix to the solidified material.

Radioactive graphite also contains a large amount of radioactive metal elements, and most of them take the chemical form of oxides. Put an organic acid composed mainly of carboxylic acids such as oxalic acid cleaning tank 18 containing the radiation graphite block 5 as chemical decontamination agent, in the form of oxide by heating to 80 ⁰ C near Dissolve and remove the impurities that are present. The chemical form of radionuclides that are metals is often metal oxides, which dissolve well in aqueous oxalic acid solutions at temperatures above 80 ^° C.

The metal oxide present in the portion in contact with the chemical decontaminating agent is acid-dissolved or reduced-dissolved, and the radioactive element of the metal in contact with the chemical decontaminating agent is dissolved in the cleaning solution of the decontaminating agent aqueous solution mainly containing an organic acid. To start.

Further, particularly by using a decontaminating agent and an oxidizing agent such as permanganate or ozone, it is possible to convert all C-14 leaching into the cleaning liquid into a chemical form of CO ₂ . Half of C-14 that leaches into the cleaning liquid due to cleaning takes the chemical form of an organic compound, and it is difficult to immobilize it on the solidifying material.

This is because the inorganic CO ₂ is Ca ²⁺ in the solidified material.
Inorganic C-14 is easy because it forms an ionic compound with the organic C-14 because the organic form of C-14 does not form an ionic compound with Ca ²⁺ in the solidifying material. Immobilization is difficult. Therefore, C-14 leaching as a compound is CO
Oxidation to ₂ facilitates immobilization of C-14.

The use of ozone as an oxidant is considered to be effective from the viewpoint of reducing secondary wastes because it is finally decomposed to O ₂ . Ozone is a gas having an oxidizing power, and ozone dissolved in water is decomposed by the reactions represented by the following formulas (3) to (7) to generate various active oxygen species.

[0059] ^{_{O 3 + OH - → HO 2}} + O 2 - ... (3) O 3 + HO 2 → 2O 2 + OH ... (4) O 3 + OH → O 2 + HO 2 ... (5) 2HO 2 → O 3 + H 2 O ... (6) HO ₂ + OH → O ₂ + H ₂ O (7) Ozone and these active oxygen species have strong oxidizing power.

Next, a third embodiment of the activated graphite disposal apparatus according to the present invention will be described with reference to FIG. In the present embodiment, a cleaning loop that circulates and reuses the cleaning solution 9 of the decontaminating agent aqueous solution in the cleaning process 7 shown in FIG. 1 is configured to irradiate the organic matter in the cleaning solution 9 of the decontaminating agent aqueous solution with ultraviolet rays. It is an activated graphite cleaning device that becomes inorganic.

That is, in FIG. 4, a circulation pump 32, a flow meter 33, a heater 34, a header loop pipe 35, and an ultraviolet ray are provided between an outlet pipe 30 connected to the bottom of the cleaning tank 18 and an inlet pipe 31 connected to the upper part. A disassembling device 36 is provided. Also, heater
A water quality measuring device 37 and a flow meter 38 are connected by a bypass pipe 39 from the downstream side to the upstream side between the outlet side of 34 and the outlet side of the ultraviolet decomposing device 36.

Further, a hydrogen peroxide supply device 40 and a pump 41 are connected to the downstream side of the header loop pipe 35, and an ion exchange resin column 42, a flow meter 43 and a flow meter 43 are provided between the discharge side of the pump 41 and the outlet pipe 30. Circulating pump 44 to bypass pipe 45, 46
To connect.

In the above-mentioned structure, after the cleaning tank 18 is filled with the waste liquid (cleaning liquid) in which the activated graphite has been cleaned, the redox agent is added to the cleaning tank, and the cleaning liquid 9 in the cleaning tank 18 is circulated by the circulation pump 32. . At this time, the temperature of the cleaning liquid is raised by the heater 34, and the cleaning liquid 9 circulating in the circulation system is heated to 80 ^° C. or higher to dissolve impurities of oxides contained in graphite. Metal ions such as Co-60 eluted from the activated graphite by washing are collected by the ion exchange resin column 42.

When an oxidizer such as ozone is dissolved in the solution, the UV decomposer 36 irradiates the UV with ultraviolet rays to break the chemical bonds of ozone or water molecules to generate active radicals having unpaired electrons. Organic compounds dissolved in 9 can be decomposed to CO ₂ . The reaction formulas of main organic compounds and ozone are shown below.

CH ₃ OH + 3O ₃ → CO ₂ + 3O ₂ + 2H ₂ O (8) HCHO + 2O ₃ → CO ₂ + 2O ₂ + H ₂ O ... (9) HCOOH + O ₃ → CO ₂ + O ₂ + H ₂ O ... (10) C ₂ H ₅ OH + 4O ₃ → 2CO ₂ + 3O ₂ + 3H ₂ O ... (11) CH ₃ CHO + 3O ₃ → 2CO ₂ + 2O ₂ + 2H ₂ O ... (12) CH3COOH + 2O ₃ → 2CO ₂ + O ₂ + 2H ₂ O… (13)

Organic compounds eluted from radioactive waste are methanol (CH ₃ OH), formaldehyde (HCHO), formic acid.
(HCOOH), ethanol (C ₂ H ₅ OH), acetaldehyde (CH ₃ C
HO) and acetic acid (CH ₃ COOH) are known to be small molecules with 1 to 2 carbon atoms. At this time, including carboxylic acids such as oxalic acid used as a decontaminating agent, C-14 dissolved in the form of an organic compound is oxidized to an inorganic form of CO ₂ ,
C-14 can be solidified by forming a carbonate with calcium present in the solidifying material.

Next, the method of cleaning the graphite waste cleaning liquid will be described with reference to FIG. The graphite waste is stored in the cleaning tank 18,
The cleaning liquid 9 is poured until the graphite block is submerged. The cleaning liquid 9 is circulated in the system by using the circulation pump 32, and heated to 80 ^° C. or higher by the heater 34. After the decontamination is completed, the cleaning liquid 9 is passed through the ion exchange resin column 42 to remove the metal ions dissolved in the cleaning liquid 9.

The oxalic acid decontaminating agent dissolved in the cleaning liquid 9 and the eluted organic compound are oxidatively decomposed by ozone. At this time, an equivalent amount or more of hydrogen peroxide water is introduced from the hydrogen peroxide supply device 40, and the oxalic acid cleaning liquid is passed through the ultraviolet decomposing device 36, whereby the oxalic acid in the cleaning liquid can be easily decomposed. Confirmation of the decomposition of oxalic acid in the cleaning solution is performed during water quality confirmation. It is judged that the decomposition is completed when the pH and the conductivity are sufficiently lowered.

Next, a fourth embodiment of the activated graphite disposal apparatus according to the present invention will be described with reference to FIG. This embodiment is an activated graphite heating type Cl-36 evaporation removal apparatus for heating the graphite block 5 and the graphite powder 6 in an inert gas in FIG. 1 to reduce the radionuclide.

In FIG. 5, reference numeral 47 is a heating furnace, 48 is a movable high-frequency heater, 49 is an outlet, 50 is a gas generator, 55 is a CsCl trap as a radionuclide chloride, and 56 is a cooling device.
Reference numerals 57 respectively indicate inlet pipes.

That is, the graphite block 5 and the activated graphite of the graphite powder are heated in an inert gas to evaporate and remove the radionuclide contained in the activated graphite. In FIG.
The activated graphite 3 generated after the dismantling 2 of the high temperature gas furnace 1 is cut 4 into a size that can be filled in a drum, and is filled in the heating furnace 47.

Inert gas (rare gas or nitrogen) is supplied to the inert gas supply pipe by the gas generator 50 and the circulation pump 53.
It is supplied into the heating furnace 47 via 51, and is further circulated through the heating furnace 47 through the outlet pipe 52, the circulation pipe 54 and the inlet pipe 57 in order. The movable high-frequency heater 48 instantly heats the heating furnace 47 filled with the activated graphite to the vicinity of 1000 ^° C. from below.

The movable high-frequency heater 48 is gradually moved to above the heating furnace 47 to heat the whole filled activated graphite block 5 to 1000 ^° C. By heating in an inert gas, the activated graphite block 5 is not incinerated, but the contained Cl
-36 can be removed by evaporation.

[0074] Activated graphite contains a large amount of Cl-36, which is one of the nuclides important for exposure evaluation, and is contained in the chemical form of cesium chloride (CsCl). CsCl boiling point is 1306
^{It is o} C and vaporizes at 900 ^o C and above. According to the present embodiment, Cl-36 in the activated graphite can be removed by evaporation by heating the activated graphite to 1000 ^° C in an inert gas.

A CsCl trap 55 is attached to the outlet of the heating furnace 47 upstream of the inert gas circulation system and kept at room temperature by the cooling device 56. The CsCl gas discharged from the heating furnace 47 is collected in the CsCl trap 55.

Next, a second embodiment of the method for disposing activated graphite according to the present invention will be described with reference to FIG. Note that FIG.
In FIG. 5, those parts which are the same as those corresponding parts in FIG.

In this embodiment, the CsCl trap 55 in which CsCl is trapped by the disposal apparatus shown in FIG. 5 is embedded in the solidifying material 58 in the solidification treatment 14 to form the CsCl waste 59, and the chlorine-removed graphite block 5a. Graphite waste body 60 in which graphite powder 6a is solidified 14 and embedded in solidified material 58 to be solidified integrally.
Is the method.

According to the present embodiment, the activated graphite 58 from which Cl-36 has been evaporated and removed can be appropriately cut and solidified into a waste 60 for disposal. Also, Cl-36 collected in the CsCl trap can be solidified and disposed of as the waste body 59 in the same manner.

[0079]

According to the present invention, radioactive nuclides adhering to activated graphite can be exfoliated and removed by chemical and physical actions to reduce the emission of radioactive nuclides from buried activated graphite. .

[Brief description of drawings]

FIG. 1 is a flow chart for explaining a first embodiment of a method of disposing activated graphite according to the present invention.

FIG. 2 is an apparatus layout diagram for explaining the first embodiment of the activated graphite disposal apparatus according to the present invention.

FIG. 3 is a device layout view for explaining a second embodiment of the activated graphite disposal device according to the present invention.

FIG. 4 is an apparatus system diagram for explaining a third embodiment of the activated graphite disposal apparatus according to the present invention.

FIG. 5 is an apparatus layout diagram for explaining a fourth embodiment of the activated graphite disposal apparatus according to the present invention.

FIG. 6 is a flowchart for explaining a second embodiment of the method of disposing activated graphite according to the present invention.

[Explanation of symbols]

1 ... High temperature gas furnace, 2 ... Demolition treatment, 3 ... Activated graphite, 4 ...
Cutting / shredding, 5 ... Graphite block, 5a ... Chlorine removed graphite block, 6 ... Graphite powder, 6a ... Chlorine removed graphite powder, 7 ... Washing process, 8 ... Washing tank, 9 ... Decontaminating agent aqueous solution, Ten
… Agitator, 11… Filtration process, 12… Washing waste liquid, 13… Graphite waste, 14… Solidification process, 15… Buried process, 16… Buried pit,
17 ... Buried material, 18 ... Cleaning tank, 19 ... Inner tank, 20 ... Ultrasonic vibrator, 21 ... Ion exchange resin tower, 22-24 ... Circulation piping, 25 ... Drain pipe, 26 ... Ozone generator, 27 ... Communication Trachea, 28 ... Hollow perforated plate, 29 ... Ozone, 30 ... Outlet tube, 31 ... Inlet tube, 32 ... Circulation pump, 33 ... Flowmeter, 34 ... Heater, 35 ... Header loop piping, 36 ... UV separation device, 37 … Water quality measuring device, 38…
Flowmeter, 39 ... Bypass pipe, 40 ... Hydrogen peroxide supply device, 41
… Pump, 42… Ion exchange resin column, 43… Flow meter, 44
... Circulation piping, 45, 46 ... Bypass pipe, 47 ... Heating furnace, 48 ... Movable high frequency heater, 49 ... Outlet port, 50 ... Gas generator, 51 ... Inert gas supply pipe, 52 ... Outlet pipe, 53 ... Circulation pump, 54 ... Circulation piping, 55 ... CsCl trap, 56 ... Cooling device,
57… Inlet pipe, 58… Curing material, 59… CsCl waste, 60… Graphite waste.

Front page continuation (51) Int.Cl. ⁷ Identification code FI theme code (reference) G21F 9/06 521 B09B 3/00 304Z 9/32 ZAB 303Z (72) Inventor Eiichi Murata Ukishima-cho, Kawasaki-ku, Kanagawa Prefecture 2-1 Incorporated company Toshiba Hamakawasaki factory (72) Inventor Naomi Toyohara No. 2 Ukishima-cho, Kawasaki-ku, Kawasaki-shi, Kanagawa 2-1 Incorporated Toshiba company Tatsuaki Sato Kawasaki, Kawasaki-shi, Kanagawa 2-1, Ukishima-cho, Ward, Ltd. Inside the Toshiba Hamakawasaki Plant, a stock company (72) Inventor Kaji Natsui 8 Shin-Sugita-cho, Isogo-ku, Yokohama-shi, Kanagawa F-term inside the Company's Toshiba Yokohama Office (reference) 3B201 AA46 AA48 AB32 BB02 BB83 BB87 BB96 BC01 CB01 4D004 AA16 AB09 CA27 CA34 CA36 CA37 CA40 CB33 CC03

Claims (13)

[Claims] 1. Before the disposal of graphite containing radionuclides by burial,
A method of disposing radioactive graphite, which comprises previously cleaning the activated graphite containing the radioactive nuclide to release the radioactive nuclide. 2. Before the disposal of graphite containing a radionuclide by burial,
The radioactive graphite containing the radioactive nuclide is washed in advance to release the soluble radioactive nuclide, and then heat treated in an inert gas to reduce the volatile radioactive nuclide, which is the disposal of the activated graphite. Method. 3. The method of disposing radioactive graphite according to claim 1, wherein the cleaning treatment is cleaning of the activated graphite with a chemical decontaminating agent containing an acid. 4. The activated graphite according to claim 2, wherein the chemical detergent is an oxidizing agent and / or a reducing agent that changes a radionuclide contained in the cleaning solution of the activated graphite into a chemical form. Disposal method. 5. The method of disposing of activated graphite according to claim 4, wherein the oxidizing agent is used together with ultraviolet irradiation. 6. The method of disposing activated graphite according to claim 4, wherein the oxidizing agent is ozone or hydrogen peroxide or a combination of ozone and hydrogen peroxide. 7. The method of disposing activated graphite according to claim 3, wherein ultrasonic wave irradiation is applied to the cleaning treatment. 8. The heat treatment is performed at 900 ° C. in an inert gas.
The method according to claim 2, wherein the activated graphite is heated at a temperature of 1 to 1300 ° C. 9. A cleaning tank, an inner tank provided in the cleaning tank for accommodating activated graphite, an ultrasonic transducer provided between the inner tank and the cleaning tank, and the cleaning tank. A circulation pipe provided with a cleaning liquid flowing out from the lower side and flowing in from the upper side,
An apparatus for disposing of activated graphite, comprising: an ion-exchange resin tower provided in the circulation pipe. 10. A cleaning tank, an inner tank provided in the cleaning tank for accommodating activated graphite, an ultrasonic transducer provided between the inner tank and the cleaning tank, and the cleaning tank. An activated graphite disposal device, comprising: an ozone generator connected to a pipe. 11. A cleaning tank, an outlet pipe provided in the cleaning tank, a circulation pump connected to the outlet pipe, a discharge side pipe of the circulation pump, and an inlet pipe provided in the cleaning tank. Circulation pipe, a heating heater, a hydrogen peroxide supply device, and an ultraviolet decomposing device that are sequentially provided in the circulation pipe along the downstream side, an outlet side circulation pipe of the heating heater, and an outlet side circulation of the ultraviolet decomposing device. A device for disposing of activated graphite, comprising a water quality measuring device branched from a pipe and connected by bypass. 12. The ion exchange resin column, which is branched from the outlet pipe of the cleaning tank and the outlet side circulation pipe of the heater and is bypass-connected.
Disposal device for activated graphite as described. 13. A vertical heating furnace, a movable high-frequency heater provided in the heating furnace, an outlet provided in the lower part of the heating furnace, and an inert gas generation pipe-connected to the outlet. An activation device comprising: an apparatus, a circulation pipe connected between the outlet and the upper part of the heating furnace, and a circulation pump and a radionuclide chloride trap provided in the circulation pipe. Graphite disposal equipment.