JP2008286525A - Method and device for solidifying radioactive waste - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for solidifying radioactive waste and a device therefor which can inhibit inclination of a gas in a container to become flammable due to rise of the pressure in the container or generated hydrogen. <P>SOLUTION: The method for solidifying radioactive waste comprises a mixture accommodating step wherein a mixture of radioactive waste containing radionuclide(s) and solidifying material is accommodated in a solidifying container, and a water stability improver adding step wherein a water stability improver is added to the mixture before the mixture is accommodated in the solidifying container, or wherein the water stability improver is added to the solidifying container before or after the mixture is accommodated in the solidifying container. The water stability improver maintains an electric potential at which water can be stable under alkaline conditions in a solidified body obtained by solidifying the mixture. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a solidification processing method and a solidification processing apparatus for radioactive waste generated from a nuclear power plant or the like.

Radioactive waste generated from a nuclear power plant or the like, for example, spent reactor water purification system resin waste generated at a pressurized water nuclear power plant, is subjected to elution treatment of ⁶⁰ Co or the like with sulfuric acid. The sulfuric acid subjected to the elution treatment is neutralized with sodium hydroxide and then concentrated and temporarily stored. It has been studied that this concentrated waste liquid is subjected to a solidification treatment such as cement solidification using a cement-based solidification material. The solidification method by cement solidification is cheap and easy to treat, so it is expected to be applied to solidification of many wastes. However, when waste with high radionuclide concentration is treated by cement solidification, radiation from radionuclides is expected. Therefore, water contained in the cement solidified body is decomposed and hydrogen gas is generated as a problem.

  In order to suppress the release of gas from the solidified container, it is conceivable to seal the container, but there is a concern that the internal pressure will increase during long-term storage. For this reason, it is assumed that the pressure in the container will increase after the landfill disposal, affecting the soundness of the disposal site. For this reason, a CSD-C Universal Canister with a filter attached to the top so as to be able to release the gas generated in the container containing the compressed body of the spent fuel cladding tube, which is a waste having a high radionuclide concentration, has been studied. Yes. However, when such a filter is attached, there is a concern that tritium gas is generated and radioactive gas is released to the outside of the container if water containing tritium is present inside.

  There has also been proposed a method in which a carbon dioxide fixing agent is disposed in a canister that contains radioactive waste (see, for example, Patent Document 1). However, this fixed drug absorbs carbon dioxide. In addition, if factors such as the life of the fixed drug do not function properly, the possibility of causing a pressure increase cannot be denied.

  In order to reduce the volume of the powdered foamed resin, a method of heating and dehydrating has been attempted (for example, see Patent Document 2). However, although this method is applied to a powdered foamed resin, it is difficult to apply it to a solidified material of radioactive waste by a solidifying material, in particular, a general radioactive waste cement solidified material such as a drum can.

There has also been proposed a method of vacuum drying the inside of a radioactive waste drum can containing radioactive waste (see, for example, Patent Document 3). However, this method needs to include a heating device, an evacuation device, and the like, and there is a concern that the management area increases with the increase in size of the facility. Also, in the case of a cement solidified body, since the cement fills the gaps between the wastes, the drying process is extremely difficult as compared with the case where the waste is simply contained in the drum. Furthermore, since the amount of water generated by the drying process is large, if it is discharged directly to the off-gas treatment system, there is a possibility that condensation will occur in the off-gas treatment system and the function will deteriorate.
JP 2001-228296 A JP 2004-306467 A JP 2004-340814 A

  The present invention has been made in consideration of the above-described circumstances, and is a method for solidifying radioactive waste capable of suppressing the increase in pressure in the container or the tendency of gas in the container to become flammable by generated hydrogen, and An object of the present invention is to provide a solidification processing apparatus.

  In order to achieve the above object, a method for solidifying radioactive waste according to one aspect of the present invention includes a mixture containing step of containing a mixture containing a radioactive waste containing a radionuclide and a solidifying material in a solidification container; Before containing the mixture in the solidification container, a water stability improver is added to the mixture that maintains the potential at which water is stably present under alkaline conditions in the solidified product obtained by solidification of the mixture. Or before or after the mixture is accommodated in the solidification container, comprising a water stability improver addition step of adding the water stability improver to the solidification container.

  Further, a solidification processing apparatus for a radioactive waste according to another aspect of the present invention includes a solidification container that contains a solidified body formed by including a radioactive waste containing a radionuclide and a solidification material, and the solidification And a water stability improver that is disposed in the body and maintains a potential at which water is stably present under alkaline conditions in the solidified body.

  ADVANTAGE OF THE INVENTION According to this invention, the solidification processing method and solidification processing apparatus of a radioactive waste which can suppress the raise of the pressure in a container or the tendency of combustibility of the gas in a container by generated hydrogen can be provided.

  EMBODIMENT OF THE INVENTION Below, the form for implementing this invention is demonstrated based on drawing. The present invention is not limited to these embodiments.

FIG. 1 is a cross-sectional view showing a main configuration of an example of a radioactive waste solidification processing apparatus according to an embodiment of the present invention. The radioactive waste solidification treatment apparatus 1 is composed of a storage tank 2 for a main component (for example, cement) of a solidification material, a storage tank 3 for a radioactive waste (for example, a radioactive liquid waste), and water in a stable state under alkaline conditions. Storage tank 4 for water stability improver (hereinafter also referred to as “water stability improver”), (fine) aggregate storage tank 5, kneading water storage tank 6, kneading machine 7 and solidification container 8 is provided.
In the case of using an admixture, the radioactive waste solidification processing apparatus 1 according to this embodiment can also include an admixture storage tank (not shown). The main component (for example, cement), radioactive waste, water stabilization additive, and the like of these solidifying materials are weighed, for example, by a measuring tank (not shown) installed after these storage tanks, respectively, and kneader 7 Thrown in. The radioactive waste solidification processing apparatus 1 is a water stability improver / solidification material main component mixing tank that mixes a water stability improver and a main component (for example, cement) of a solidification material as necessary. 9. A water stability improver / radioactive waste mixing tank 10 for mixing a water stability improver and radioactive waste (for example, radioactive waste liquid) may be provided. When the (fine) aggregate is not included as a constituent of the solidified material, the (fine) aggregate storage tank 5 can be omitted. Further, in the case where the radioactive waste is a radioactive waste liquid, water (kneaded water) necessary for preparing a mixture (kneaded product) obtained by kneading the solidification material and the radioactive waste (radioactive waste liquid) When the entire amount can be supplied by the water in the waste liquid, the kneading water storage tank 6 can be omitted. For example, in the case of asphalt solidification using asphalt as the solidifying material, an extruder can be used instead of the kneader 7. Since the cement solidification treatment can be performed at room temperature, a radioactive waste solidification treatment apparatus using a cement-based solidification material is preferable. In addition to the solidifying material, or instead of the solidifying material, a predetermined amount of filler may be filled into the solidifying container 8 from a storage tank (not shown) of the filler.

  Next, a method for solidifying radioactive waste according to this embodiment will be described. Any radioactive waste containing a radionuclide in this embodiment can be used as long as it contains a radionuclide. The shape of the radioactive waste containing the radionuclide may be any shape such as liquid, powder, particle, pellet, and solid. Liquid radioactive waste, that is, radioactive waste liquid includes resin treatment waste liquid (elution waste liquid) treated with reactor water purification system ion exchange resin used in nuclear reactors, for example, waste liquid eluted with sulfuric acid, laundry waste liquid, decontamination waste liquid And waste resin treatment waste liquid or concentrated waste liquid thereof. Examples of powdered or granular radioactive waste include powdered or beaded waste resin containing radioactive nuclides generated in nuclear power plants, carbides, incineration ash, bottom ash of incinerators, and inversion filters for incinerators. Examples include ash washing, granules, filter sludge, earth and sand, dust, suspended powder, waste resin treatment residue, and other treatment sludge. Moreover, what concentrated the said radioactive waste liquid, and shape | molded in powder form or the granular form, what pulverized the below-mentioned solid radioactive waste in powder form or granular form, etc. are also contained. Examples of the radioactive waste in pellet form include the above-described radioactive waste liquid and powdered or granular radioactive waste formed into a pellet. Examples of solid radioactive waste include radioactive metals generated in nuclear power plants, heat insulating materials, filters, concrete pieces, plastic products, vinyl chloride products, rubber products, glass products, and other solid items such as block-like materials Things. In addition, solid radioactive waste includes miscellaneous solids such as melts.

  Of the radioactive wastes containing these radionuclides, high-dose radioactive wastes are more likely to cause water radiolysis, and are therefore suitable as solidification objects by this method. Here, high-dose radioactive waste refers to waste having a high radioactivity concentration among so-called low-level radioactive waste.

When the radioactive waste is a liquid (a radioactive waste liquid), the radioactive waste liquid is put into the kneader 7 from the storage tank 3 of the radioactive waste liquid. Alternatively, the radioactive waste liquid storage tank 3 may not be used, and may be introduced into the kneading machine 7 from a radioactive waste liquid supply line (not shown) by adjusting the opening / closing of a valve or the like. Similarly, when the radioactive waste is powdery or granular, it can be similarly charged into the kneader 7 from the radioactive waste storage tank 3. Such radioactive waste charged into the kneader 7 is mixed and kneaded with a solidifying material and a water stability improver, which will be described later, to obtain a mixture, which is then housed in the solidification container 8 and solidified. Is done. When the radioactive waste is a solid radioactive waste (for example, activated metal), for example, a radioactive waste input device (for example, a container (for example, a mesh container) containing solid radioactive waste) is solidified. A solid radioactive waste can be thrown into (contained in) the solidification container 8 using a crane thrown into the inside (not shown) or the like. The solid radioactive waste may be fixed by a jig in the solidification container 8 as necessary. As such a jig, a spring, a bolt, a rivet, a nail, a plate, a basket, an inner lid, and the like can be used. Thus, when radioactive waste is accommodated in the solidification container 8, the below-mentioned solidification material and water stability improving material are put into the kneader 7 and mixed, and the above-mentioned radioactive waste is produced. The mixture is put (filled) into the contained solidification container 8 to form a mixture and then solidified.
In addition, when the radioactive waste is a pellet-shaped radioactive waste, depending on the size of the radioactive waste, for example, in the case of a small pellet-shaped radioactive waste, a powdered or granular radioactive waste In the case of a radioactive waste in the form of a large pellet, it can be put into the solidification container 8 as in the case of a solid radioactive waste.

  Next, the solidifying material in this embodiment will be described. The solidifying material forms a mixture with the radioactive waste and the water stability improver described later, and is solidified to form a solidified body. Cement solidification is an operation at room temperature, and since simple processing can be performed, it is preferable to use a cement-based solidifying agent. The solidifying material includes a main component (for example, cement) of the solidifying material, and (fine) aggregate, admixture, kneaded water, and the like as necessary. For example, the cement-based solidifying material includes cement, kneaded water, and (fine) aggregate as necessary. The cement-based solidifying material may further contain an admixture such as an inorganic fluidizing agent in a desired amount depending on the purpose.

Examples of the main component of the solidifying material include cement, asphalt, plastic, glass, sulfur, and ceramic. Among these, cement is preferable because it is an operation at room temperature and can be used for cement solidification that can be easily processed. In addition, it is also possible to use 1 type, or 2 or more types of these main components.
For example, as the cement, in addition to normal Portland cement and various Portland cements mainly composed of CaO, SiO ₂ , and Al ₂ O ₃ , various cements such as alumina cement, blast furnace cement, fly ash cement, and the like can be given. . Among these, those containing Portland cement and / or blast furnace cement are preferable because the quality after cement solidification is good, and those containing alumina cement are preferable because they have high early strength and good corrosion resistance.

  Examples of the filler include cement, asphalt, plastic, glass, sulfur, ceramic, sand, aggregate (coarse aggregate and / or fine aggregate), glass (for example, concrete glass and asphalt glass), and the like. These fillers can also be used alone or in combination of two or more.

  As the aggregate, aggregates (coarse aggregate and / or fine aggregate) such as sand, gravel, crushed sand, crushed stone, slag aggregate, and other similar materials can be used.

An admixture is a material other than the main component and (fine) aggregate of the above-mentioned solidifying material, and refers to a material that gives special properties to the solidifying material. For example, the fluidity of a cement-based solidifying material. Examples thereof include a fluidizing agent that improves water, a water reducing agent, and an AE agent.
The cement-based solidifying material used in this embodiment can contain kneaded water as necessary. Normal water can be used for the kneading water. The blending amount of the kneading water is appropriately determined according to desired physical properties such as the viscosity of the cement-based solidifying material. In addition, when a radioactive waste is a radioactive waste liquid as mentioned above, at least one part of the usage-amount of kneading water or the whole quantity can be abbreviate | omitted.

  The components of the solidifying material, that is, the main component of the solidifying material, and the blending ratio (weight ratio) of (fine) aggregate, kneaded water and admixture blended as necessary are the main components of the solidifying material. It can be determined appropriately according to the type of the component. Particularly, in the cement-based solidified material, the blending ratio (weight ratio) of the (fine) aggregate is 150 parts by weight or less with respect to 100 parts by weight of the cement. The mixing ratio (weight ratio) of the kneaded water can be appropriately determined according to the type of cement, the type of aggregate, and the like, but is, for example, 400 to 600 parts by weight with respect to 100 parts by weight of cement. When the admixture is used, for example, the blending ratio (weight ratio) is 5 parts by weight or less with respect to 100 parts by weight of the main component of the solidifying material. The mixing ratio (weight ratio) of solidification material (cement solidification material) and radioactive waste depends on the type of solidification material, the type of radioactive waste (for example, concentration of radioactive waste liquid), etc. It is decided appropriately. When the mixing ratio of radioactive waste is high, a large amount of radioactive waste can be treated at a time.

The solidification material (cement-based solidification material) is mixed and kneaded with the radioactive waste and the kneader 7 when the water stability improver and the radioactive waste described later are put into the kneader 7. After obtaining the mixture, it is put (contained) in the solidification container 8. When radioactive waste is stored in the solidification container 8 in advance, the solidification material is mixed and kneaded in a kneader 7 with a water stability improver described later to obtain a mixture, and then the solidification container 8 is contained (filled) into a mixture.
The mixing and kneading conditions in the kneader 7 are appropriately determined according to the type and blending ratio of the solidifying material, the presence / absence of radioactive waste, the viscosity and / or concentration, or the concentration of radioactive waste liquid. The kneading can be performed, for example, at room temperature for 10 minutes to 1 hour.

The water stability improver used in this embodiment will be described. The water stability improver means an agent capable of maintaining a potential at which water is stably present under alkaline conditions in the solidified body. It is possible to maintain the potential at which water is stably present under alkaline conditions in the solidified body, and that the electrochemical water stable region (water is present in a stable state) under alkaline conditions in the solidified body. It can be made close to an area where the water can be obtained, preferably an electrochemical water stable area. By adding a water stability improver, the potential at which water is stably present under alkaline conditions in the solidified body can be maintained, and at least close to the stable region of water (region where water can exist in a stable state). Therefore, release of hydrogen from the solidified body can be suppressed. In this embodiment, the suppression of the generation of hydrogen means that the generation of hydrogen in the solidified body hardly affects the increase in pressure in the sealed container, that is, suppresses the generation of hydrogen to a level (level) that does not cause a problem. To do. In this embodiment, the water stability improver particularly suppresses the generation of hydrogen due to radiolysis of water (for example, pore water or crystal water) present in the solidified body or accelerates the water generation reaction of the generated hydrogen. To do. In this embodiment, the alkaline condition in the solidified body refers to the alkalinity in the solidified body, that is, the pH is 8 or more, particularly the pH is 10 or more, and further the pH is 10 to 13.
As such a water stability improver, specifically, at least one selected from the group consisting of iron (Fe), cobalt (Co), nickel (Ni), ruthenium (Ru) and copper (Cu) Or a compound of these metals, or these metals or a mixture containing these metals. Examples of these metal compounds include salts of these metals (for example, sulfates and nitrates), alloys that form compounds containing these metals (for example, intermetallic compounds), and minerals containing these metals. It is done. Examples of the mixture of these metals include alloys of these metals (for example, mixtures of intermetallic compounds, etc.).

  Among such water stability improvers, at least one metal selected from the group consisting of iron (Fe) and nickel (Ni) or a compound of these metals can maintain water in a more stable state. This is preferable because it is possible. Further, a salt of iron (Fe) or nickel (Ni) (for example, sulfate) is preferable because it can be easily dissolved in radioactive liquid waste and dispersed more uniformly.

  Furthermore, the shape of the water stability improver may be any of liquid, powder, granular and solid, and is dispersed in the solidified body. The water stability improver can be added, for example, in at least one of a liquid form, a mist form, a powder form, a granular form, and a solid form. For example, when the water stability improver is added in a solid form, the addition operation is easy, and when it is added as a liquid, the addition amount can be easily adjusted.

  Next, a method for adding a water stability improver will be described. FIG. 2 is a flowchart showing an outline of the procedure of the solidification processing method when the radioactive waste is a radioactive waste liquid. FIG. 3 is a flowchart showing an outline of the procedure of the solidification processing method when the radioactive waste is a solid radioactive waste. In this embodiment, the addition of the water stability improver is performed, for example, when the radioactive waste is radioactive waste liquid or the like and is charged into the kneader 7 as shown in FIG. The improver may be added and mixed in advance in the solidifying material, for example, in the main component of the solidifying material (for example, cement), (fine) aggregate, or in the admixture. As shown in (b), it may be added to the radioactive liquid waste and mixed in advance. As shown in FIG. 2B, when the water stability improver is preliminarily mixed with the radioactive liquid waste, it is preferable because the water stability improver is more uniformly dispersed. When the radioactive waste is a solid radioactive waste (for example, activated metal), as shown in FIG. 3, the water stability improver is used in the solidified material, for example, the main component of the solidified material. It can be added to (for example, cement), (fine) aggregate, or admixture and mixed in advance. Further, when radioactive waste (for example, radioactive waste liquid) is introduced into the kneading machine 7 through a radioactive waste liquid supply line (not shown), the radioactive waste (radio waste liquid) is preliminarily disposed at any location of the supply line. After mixing, it can also be put into the kneader 7. Further, when the solidifying material contains an admixture or the like, it can be mixed with the admixture or the like before being put into the kneader 7. The water stability improver can also be added to the solidification container 8 containing the radioactive waste or the mixture of the radioactive waste and the solidification material.

As described above, by adding the water stability improver, it is possible to maintain a potential at which water is stably present under alkaline conditions in the solidified body accommodated in the solidification vessel 8, and electrochemical water. It is considered that the generation of hydrogen in the solidified body can be suppressed because it can be at least close to the stable region (region where water can exist in a stable state). The mechanism of suppression of hydrogen generation, particularly suppression of hydrogen generation due to water radiolysis, is not yet fully understood, but hydrogen generation in solidified bodies is particularly hydrogen ions (H ⁺ ) due to radiolysis of water. And / or hydrogen is presumed to be generated through generation of hydrogen radicals (H.), so that the water stability improver is, for example, hydrogen ions (H ⁺ ) from water (for example, pore water, crystal water). And / or by an electrochemical mechanism that suppresses the generation of hydrogen radicals (H.), maintains the potential to maintain water in a stable state, that is, at least approaches the stable region of electrochemical water It is guessed.
An example of nickel (Ni) as a water stability improver will be described. The above solidified body (for example, cement solidified body) is considered to have a high pH (for example, pH 10 or more) due to a hydroxyl group derived from the main component (for example, cement) of the solidifying material. Here, from the potential-pH diagram (Pourbait diagram) of nickel (Ni) shown in FIG. 6, the addition of a predetermined amount of nickel and / or nickel ions is performed under alkaline conditions (for example, pH = 10.5), it is considered that the environment in the solidified body is at least close to the stable region of electrochemical water, that is, the potential at which water is stably present is maintained, and generation of hydrogen is suppressed. Guessed. In FIG. 6, since the region below the broken line (a) is a region that generates hydrogen and the region above the broken line (b) is a region that generates oxygen, the region above the broken line (a), in particular, the broken line ( It is presumed that the region between a) and the broken line (b) is a region where water is maintained in a stable state, that is, a region where water can stably maintain a potential. From such a potential-pH diagram (Pourbait diagram), the types of metals that can maintain water in a stable state in a high pH region of the solidified body are estimated.

Next, the amount of water stability improver added will be described. Nickel is in a state of pH 10 or higher (pH = 10 to 13, for example, pH 12.0) assumed in a solidified body formed of, for example, a cement-based solidifying material, and the addition amount is based on 100 parts by weight of cement. 4.8 parts by weight or more (molar concentration of nickel of 8.2 × 10 ⁻¹ mol or more per kg of cement), preferably 9.6 parts by weight or more (mol of nickel per kg of cement based on 100 parts by weight of cement) With an addition amount of 1.6 mol or more as a concentration, water in the solidified body can be maintained in a stable state (a potential at which water is stably present) can be maintained, and generation of hydrogen can be suppressed. As for iron (Fe), for example, the amount added thereof is cement 100 in a state of pH 10 or higher (pH = 10 to 13, for example, pH 12.0) assumed in a solidified body formed of a cement-type solidifying material. 1.0 parts by weight or more based on parts by weight (1.8 × 10 ⁻¹ moles or more as iron molar concentration per 1 kg of cement), preferably 5.3 parts by weight or more (100 kg of cement based on 100 parts by weight of cement) The amount of iron in the molar concentration of iron is 9.5 × 10 ⁻¹ mol or more), and the water in the solidified body can be maintained in a stable state (the potential at which water is stably present) can be maintained. Generation can be suppressed. Similarly, other water stability improvers such as cobalt (Co), ruthenium (Ru), and copper (Cu) are maintained in a stable state with the same amount of addition as nickel or iron. Therefore, it is estimated that the generation of hydrogen can be suppressed.

Next, preparation of a solidified body will be described. When the radioactive waste is, for example, radioactive waste liquid and is put into the kneader 7, the solidifying material, the water stability improver, and the radioactive waste are kneaded for a predetermined time in the kneader 7. The prepared mixture (kneaded material) is put into the solidification container 8. Then, it hardens by leaving still for a predetermined time, for example, 1 day, and produces a solidified body. When the radioactive waste is a solid radioactive waste, the mixture is prepared by kneading the solidifying material and the water stability improver for a predetermined time in the kneader 7, and the resulting mixture (kneading Is charged (filled) into the solidification container 8 containing the radioactive waste, and then allowed to stand for a predetermined time, for example, one day, and then cured to produce a solidified body.
The solidified body thus formed can suppress the radiolysis of water by the radionuclide of the radioactive waste, and can suppress the generation of hydrogen.

  Thus, according to the present embodiment, by adding the water stability improver, the water in the solidified body formed including the radioactive waste and the solidified material is maintained in a stable state (water A stable potential can be maintained), and generation of hydrogen, particularly generation of hydrogen due to radiolysis of water, can be suppressed. Therefore, it is possible to provide a radioactive waste solidification processing method and a solidification processing apparatus capable of suppressing the increase in pressure in the container or the tendency of the gas in the container to become flammable due to generated hydrogen. In particular, there is no risk of leakage of radioactive gas, and generation of hydrogen gas can be suppressed while the cement-based solidified body remains in a solidified shape.

  Hereinafter, the present invention will be described more specifically with reference to examples. However, the present invention is not limited to the examples.

Examples 1 and 2
In Example 1, the amount of nickel (Ni) added to the simulated elution waste solution mainly composed of sodium sulfate (Na ₂ SO ₄ ) was used as a parameter, and the amount of nickel added was 1.1 for each 100 parts by weight of cement. parts, 2.2 parts by weight (i.e., each molar concentration of nickel to cements ^{1.9 × 10} -4 (mol / g- ^cement), 3.7 × 10 -4 (mol / g- cement)) sulfate so as to Nickel (NiSO ₄ ) was added to the simulated elution waste. Further, in Example 2, in consideration of the case where nitric acid is mixed from groundwater or the like in the waste burial site, nitric acid equivalent to the amount of nickel added is added, and the amount of nickel added to the simulated elution waste liquid is used as a parameter. The amount of nickel added is 2.2 parts by weight and 10.0 parts by weight with respect to 100 parts by weight of cement (the molar concentration of nickel with respect to cement is 3.7 × 10 ⁻⁴ (mol / g-cement), respectively. 7 × 10 ⁻³ (mol / g-cement)) Nickel sulfate (NiSO ₄ ) was added to the simulated elution waste solution.
47.8 ml of the simulated elution waste liquid to which nickel sulfate was added, 11.9 g of alumina cement (manufactured by Toshiba Ceramics Co., Ltd.), and 44.7 g of sand as aggregate were kneaded for 20 minutes with a kneader. The kneaded material obtained by this kneading was allowed to stand for 1 day in an environment at a temperature of 25 ° C. to cure each of the cement solidified bodies.

Each cement solidified body thus obtained was finely pulverized using a pulverizer to obtain a sample for γ-ray irradiation. Each 10 g of the prepared sample for γ-ray irradiation was sealed in a glass sealed container, and irradiated from outside using a Co-60 γ-ray source under irradiation conditions of 265 C / kg / h for 16 hours.
The amount of hydrogen generated by radiolysis of water contained in the cement solidified body was measured using a gas chromatograph (manufactured by Shimadzu Corporation: GC-8A) by sampling the gas layer in the sealed container after γ-ray irradiation. The measurement results are shown in FIG. From FIG. 4, it was confirmed that the amount of hydrogen generation can be suppressed by increasing the amount of nickel (Ni) added.

In addition, when nitric acid was added, the amount of hydrogen generation increased compared to when nitric acid was not added, but it was confirmed that the amount of hydrogen generation could be reduced by increasing the amount of nickel (Ni) added. .
Therefore, from these experimental results, the addition of 4.8 parts by weight or more of nickel with respect to 100 parts by weight of cement (that is, the molar concentration of nickel with respect to cement is 8.2 × 10 ⁻⁴ (mol / g-cement) or more). It is considered that an effect of suppressing the generation of hydrogen gas, that is, an effect of maintaining water in the solidified body in a stable state can be expected.

Example 3
Ferrous sulfate (FeSO ₄ ) is used instead of nickel sulfate (NiSO ₄ ), and the amount of iron (Fe) added is 0.95 parts by weight, Ferrous sulfate (FeSO4) so that the molar concentration of iron with respect to cement is 1.7 × 10 ⁻⁴ (mol / g-cement) and 9.4 × 10 ⁻⁴ (mol / g-cement), respectively. _The experiment was conducted in the same manner as in Example 1 except that ₄ ) was added to the simulated elution waste solution. The measurement results are shown in FIG. From FIG. 5, it was confirmed that the amount of hydrogen generation can be suppressed by increasing the amount of iron (Fe) added. Further, the addition of 1.0 part by weight or more of iron based on 100 parts by weight of cement (that is, the molar concentration of iron with respect to cement is 1.8 × 10 ⁻⁴ (mol / g-cement) or more) suppresses the generation of hydrogen gas. That is, it is considered that the effect of maintaining the water in the solidified body in a stable state can be expected.

  Further, considering the results of Examples 1 to 3 based on the potential-pH diagram (Pourbaix diagram) of nickel (Ni) in FIG. 6, the addition of nickel (Ni) and iron (Fe) It is considered that the environment of the above is brought close to the stable region of electrochemical water, the potential at which water is stably present is maintained, and the generation of hydrogen is suppressed. From these facts, the same effect can be expected for nickel (Ni), cobalt (Co), ruthenium (Ru) and the like which are electrochemically similar to iron (Fe). FIG. 7 shows a potential-pH diagram of cobalt (Co). In addition, the electrochemical equilibrium may be shifted under a special environment such as in the cement solidified body. Similarly, when adding elements such as copper (Cu), the environment in the cement solidified body is electrochemically changed. There is a possibility that an effect of approaching a stable region of water can be obtained.

It is sectional drawing which shows typically the principal part structure of an example of the solidification processing apparatus of the radioactive waste which concerns on one Embodiment of this invention. (A) And (b) is a flowchart which shows the outline of the procedure of the solidification processing method of radioactive waste liquid. It is a flowchart which shows the outline of the procedure of the solidification processing method of a solid radioactive waste. It is a graph which shows the effect of the addition amount of nickel (Ni) regarding hydrogen generation amount suppression. It is a graph which shows the effect of the addition amount of iron (Fe) regarding hydrogen generation amount suppression. It is an electric potential-pH figure of nickel (Ni) -water system. It is a potential-pH diagram of cobalt (Co) -water system.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Radioactive waste solidification processing apparatus, 2 ... Storage tank of main component (cement) of solidification material, 3 ... Storage tank of radioactive waste (resin treatment waste liquid), 4 ... Storage tank of water stability improver, 5 ... (Fine) Aggregate storage tank, 6 ... Kneading water storage tank, 7 ... Kneading machine, 8 ... Solidification container, 9 ... Water stability improver / solidification material mixing tank, 10 ... Water stability improver / radioactive waste Mixing tank.

Claims (12)

A mixture containing step of containing in a solidification container a mixture containing a radioactive waste containing a radionuclide and a solidifying material;
Before containing the mixture in the solidification container, a water stability improver is added to the mixture that maintains the potential at which water is stably present under alkaline conditions in the solidified product obtained by solidification of the mixture. Or before or after the mixture is accommodated in the solidification container, and a water stability improver addition step of adding the water stability improver to the solidification container. Method.   2. The radioactive waste solidification method according to claim 1, wherein the radioactive waste containing the radionuclide is a radioactive waste having at least one of a liquid form, a powder form and a granular form. A radioactive waste containing step of containing radioactive waste containing a radionuclide in a solidification container; and
A solidification material charging step of charging the solidification material into a solidification container containing the radioactive waste;
Before the solidification material is put into the solidification container, water is stably present under alkaline conditions in the solidified material obtained by solidifying the mixture containing the solidification material and the radioactive waste. A solidification method for radioactive waste comprising a water stability improver addition step of adding a water stability improver for maintaining a potential to the solidifying material or the solidification container.   The radioactive substance according to claim 1 or 3, wherein the water stability improver is at least one metal selected from the group consisting of iron, cobalt, nickel, ruthenium and copper, or a compound of these metals. Solidification method for waste.   The method for solidifying radioactive waste according to claim 1 or 3, wherein the water stability improver is at least one metal of iron and nickel or a compound of these metals.   The method for solidifying radioactive waste according to claim 1, wherein the water stability improver is added to any of the radioactive waste, the solidifying material, and the solidification container. The radioactive waste is a radioactive liquid waste,
The method for solidifying radioactive waste according to claim 1, wherein the water stability improver is added to the radioactive liquid waste. The radioactive waste is a radioactive waste in the form of at least one of powder, granular, pellet and solid,
The water stability improver is at least one metal selected from the group consisting of iron, cobalt, nickel, ruthenium, and copper, or a compound of these metals, and is a cement-based solid mold that is the solidifying material. The radioactive waste solidification method according to claim 1, wherein the radioactive waste is solidified. The radioactive waste is a radioactive liquid waste,
The water stability improver is a nickel salt, and the amount of the water stability improver added relative to 100 parts by weight of cement in the cement-based solidifying material as the solidifying material. The method for solidifying radioactive waste according to claim 1, wherein the amount is 4.8 parts by weight or more. The radioactive waste is a radioactive liquid waste,
The water stability improver is an iron salt, and the added amount of the water stability improver is 100 parts by weight of cement in the cement-based solidifying material as the solidifying material. The solidification method for radioactive waste according to claim 1, wherein the solid waste treatment method is 1.0 part by weight or more. A solidification container for containing a solidified body formed including a radioactive waste containing a radionuclide and a solidification material;
A solidification apparatus for radioactive waste, comprising: a water stability improver which is disposed in the solidified body and maintains a potential at which water is stably present under alkaline conditions in the solidified body. The solidifying material is a cement-based solidifying material,
The radioactive waste according to claim 11, wherein the water stability improver is at least one metal selected from the group consisting of iron, cobalt, nickel, ruthenium and copper, or a compound of these metals. Solidification processing equipment.

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