JP2015081898A - Decontamination method and decontamination device for radioactive waste ion exchange resin - Google Patents

Abstract

PROBLEM TO BE SOLVED: To remove an ionic radioactive matter in waste ion exchange resin, and reduce dose of the waste ion exchange resin to the extremely low level by solving and removing clad.SOLUTION: Acid which is heated to equal to or more than 60°C is brought into contact to waste ion exchange resin including clad mainly formed of ion oxide and absorbing a radioactive matter, for solving and removing the ionic radioactive matter in the waste ion exchange resin, and removing the clad. The acid waste liquid including the ionic radioactive matter used for decontamination is subjected to electro-deposition treatment, circulated and reused.

Description

  The present invention relates to a decontamination method and a decontamination method that efficiently removes radioactive materials from a waste ion exchange resin that adsorbs radioactive materials and includes a cladding mainly composed of iron oxide, which is used in nuclear power plants and the like. It relates to a dyeing device.

  In nuclear power plants, the ion exchange resin used to purify the cooling water system containing radioactive materials by directly touching the fuel rods such as the reactor water purification system (CUW) and the fuel storage pool water purification system (FPC) Because it is adsorbed in large quantities, it is stored in a resin tank inside the power plant as radioactive waste with a high dose rate. At nuclear power plants, ion-exchange resins are also used to remove radioactive substances from primary cooling system equipment and piping contaminated with radioactive substances and the surfaces of metal parts of systems containing them by chemical cleaning. The spent ion exchange resin is also stored in the resin tank as high dose rate radioactive waste. Waste containing these radioactive substances is finally kneaded with a solidification aid such as cement and stabilized, and then buried. The cost for disposal is different depending on the amount of radioactive material contained, and the higher the radioactive material concentration, the higher the cost. For this reason, it is economical to reduce the volume of waste with a high dose rate as much as possible and then use it as a solid waste. Specifically, it is desirable in terms of volume reduction if the radioactive substance can be separated from the ion exchange resin as a solid and can be contained in a shielding container. Waste ion exchange resin from which radioactive materials have been removed is a low-dose rate waste with low disposal costs, and if the radioactive materials can be removed to a level where incineration of the waste ion exchange resin can be achieved, incineration will significantly Volume reduction can be achieved.

  As a processing method of this high dose waste resin, there are methods of decomposing waste resin by wet oxidation such as Fenton method and supercritical water oxidation as proposed in Patent Document 1 and Patent Document 2. When the method is applied, in all cases, a large amount of waste liquid with a high dose rate is generated. When the waste liquid with a high dose rate is finally disposed of, it is necessary to stabilize it as a solidified body by a method such as evaporating and concentrating and kneading the concentrated liquid with cement. In this case, since a solidification aid such as cement is newly added, there is a problem that the amount of waste at a high dose rate to be finally disposed increases and the amount of waste cannot be reduced.

If the waste resin can be disposed of by incineration, the volume of radioactive waste can be significantly reduced. However, in this case, the radioactive material is concentrated in the incineration ash, resulting in a high dose of incineration ash. If the radioactive material can be completely removed from the waste resin, the incineration ash can be prevented from becoming a high dose, and the volume can be reduced by incineration. Therefore, various technologies for removing the radioactive material from the waste resin have been studied. Yes.
Conventionally, as a technique for removing radioactive substances from waste resin, Patent Document 3 discloses that sulfuric acid is passed through an eluent filled with waste resin to elute ionic radioactive substances, and the radioactive substances are obtained by diffusion dialysis from the eluent. Is disclosed, and sulfuric acid is recycled and reused. In this case as well, a waste liquid containing radioactive material is generated, but the solidification process is not covered.

  On the other hand, as a method for removing radioactive substances from waste liquids containing ionic radioactive substances, Patent Document 4 discloses that a decontamination solution in which radioactive cations are dissolved is energized while passing through an electrodeposition cell, and the radioactive cations are used. Has been disclosed in which a decontamination solution is regenerated and reused by depositing as a radioactive metal particle on a cathode. At that time, the cathode on which radioactive metal particles are deposited is described as pouring catholyte over the entire cathode to desorb the radioactive metal particles.

Japanese Patent Publication No. 61-9599 Japanese Patent No. 3657747 JP 2004-28697 A Japanese Patent No. 4438898

The high-dose waste resin used in the reactor water purification system and the fuel storage pool water purification system adsorbs radioactive material ions and is mixed with clad mainly composed of iron oxide. Since the clad also contains a radioactive substance, it is necessary to remove the clad from the waste resin at the same time in order to completely remove the radioactive substance from the waste resin.
The chemical form of the clad contained in the waste resin mainly includes magnetite (Fe ₃ O ₄ ) and hematite (α-Fe ₂ O ₃ ). As described in Patent Document 3, it is difficult to dissolve hardly-soluble hematite (α-Fe ₂ O ₃ ) in a method in which unwarmed sulfuric acid at room temperature is passed through a waste resin. Since the clad cannot be removed from the resin, there is a problem that radioactive materials remain.

  The present invention provides a decontamination method and a decontamination apparatus for reducing the dose of waste ion exchange resin to an extremely low level by removing ionic radioactive substances in waste ion exchange resin and dissolving and removing the cladding. The issue is to provide.

  As a result of intensive investigations to solve the above problems, the present inventors have used an acid heated to a predetermined temperature to elute and remove ionic radioactive substances in the waste ion exchange resin, and to remove the cladding. As a result, it was found that the acid waste solution obtained by this decontamination treatment can be recycled by electrodeposition, and the present invention was completed.

  That is, the gist of the present invention is as follows.

[1] A waste ion exchange resin that adsorbs a radioactive substance and contains a clad composed mainly of iron oxide is brought into contact with an acid heated to 60 ° C. or more, so that the ionic radioactivity in the waste ion exchange resin is contacted. A method for decontaminating radioactive waste ion exchange resin, comprising a step of decontaminating a substance and dissolving and removing the clad.

[2] The method for decontaminating a radioactive waste ion exchange resin according to [1], wherein the acid is sulfuric acid and / or oxalic acid.

[3] The radioactive waste ion exchange according to [1] or [2], wherein the acid is a 5 to 40% by weight sulfuric acid solution and / or a 0.1 to 40% by weight oxalic acid solution. Resin decontamination method.

[4] The radioactive waste ion-exchange resin decontamination method according to any one of [1] to [3], wherein the radioactive substance contains cobalt-60.

[5] By introducing an acid waste solution containing an ionic radioactive substance discharged from the decontamination step into an electrodeposition tank having an anode and a cathode, and energizing between the anode and the cathode, ions in the acid waste solution Electrodepositing the radioactive radioactive material on the cathode to remove the ionic radioactive material from the acid waste solution, and the treatment liquid obtained by removing the ionic radioactive material in the electrodeposition step, The decontamination method for a radioactive waste ion exchange resin according to any one of [1] to [4], further comprising a circulation step of recycling and reusing the decontamination step.

[6] In the electrodeposition tank, an anode chamber in which an anode is installed and a cathode chamber in which a cathode is installed are separated by a cation exchange membrane, and the acid waste liquid is introduced into the anode chamber, and the anode chamber The ionic radioactive material in the acid waste liquid permeates through the cation exchange membrane, moves to the cathode chamber, and is electrodeposited on the cathode [5] Decontamination method of radioactive waste ion exchange resin as described in 1.

[7] The radioactive waste ion-exchange resin decontamination method according to [5] or [6], wherein cobalt-60 and iron which is a melt of the clad are electrodeposited on the cathode. .

[8] A waste ion exchange resin that adsorbs a radioactive substance and contains a clad composed mainly of iron oxide is brought into contact with an acid heated to 60 ° C. or more, so that the ionic radioactivity in the waste ion exchange resin is contacted. A radioactive waste ion exchange resin decontamination apparatus comprising a decontamination means for dissolving and removing a substance and dissolving and removing the clad, the decontamination means comprising a packed tower filled with the waste ion exchange resin, An introduction pipe for introducing the heated acid into the packed tower, a heating means provided in the introduction pipe, and a discharge pipe for discharging the acid waste liquid containing ionic radioactive substances from the packed tower. Characterized decontamination equipment for radioactive waste ion exchange resin.

[9] An electrodeposition tank having an anode and a cathode, a means for energizing the anode and the cathode, a means for introducing the acid waste liquid into the electrodeposition tank, and a treatment liquid in the electrodeposition tank Means to circulate upstream, and by conducting electricity between the anode and cathode, the ionic radioactive material in the acid waste solution is electrodeposited on the cathode, and the ionic radioactive material is removed from the acid waste solution. The decontamination apparatus for radioactive waste ion exchange resin according to [8], wherein the treatment liquid obtained by removing the ionic radioactive substance is reused by the decontamination means.

[10] The electrodeposition tank includes an anode chamber in which an anode is installed, a cathode chamber in which a cathode is installed, and a cation exchange membrane that separates the anode chamber and the cathode chamber. When introduced into the anode chamber and energized between the anode and the cathode, the ionic radioactive material in the acid waste liquid passes through the cation exchange membrane and moves to the cathode chamber, and is electrodeposited on the cathode. The decontamination apparatus for radioactive waste ion exchange resin according to [9], wherein

[11] The radioactive waste ion exchange resin decontamination apparatus according to [9] or [10], wherein cobalt-60 and iron which is a melt of the clad are electrodeposited on the cathode. .

According to the present invention, since the acid heated to 60 ° C. or higher is brought into contact with the waste ion exchange resin, the radioactive metal ions adsorbed on the cation exchange resin of the waste ion exchange resin are ion-exchanged with H ⁺ ions and eluted. In addition to being able to be removed, the clad containing hematite mixed in the waste ion exchange resin can also be efficiently dissolved and removed.

  In addition, an acid waste solution containing radioactive metal ions discharged from this decontamination process and iron ions that are dissolved in the clad is introduced into an electrodeposition tank provided with an anode and a cathode, and electricity is passed between the anode and the cathode. Thus, radioactive metal ions and iron ions can be simultaneously electrodeposited on the cathode and removed, and the electrodeposition treatment liquid can be reused for the decontamination treatment of the waste ion exchange resin. In addition, by replacing the electrode used for electrodeposition or removing the electrodeposition layer on the electrode and performing electrodeposition, decontamination of the waste ion exchange resin and removal of radioactive substances from the acid waste liquid are continued. It is possible to process a large amount of waste ion exchange resin.

  According to the present invention, it is possible to obtain a waste ion exchange resin having a radiation dose reduced to an extremely low level, and the treated waste ion exchange resin can be incinerated. And it can reduce to the capacity | capacitance of 1/100-1/200 by incinerating waste ion exchange resin to make incineration ash.

It is a systematic diagram of the decontamination apparatus of the radioactive ion exchange resin which shows an example of embodiment of this invention. 3 is a graph showing the results of Example 1. It is a systematic diagram which shows the electrodeposition apparatus used in Experimental example 2. It is a systematic diagram which shows the electrodeposition apparatus used in Experimental Examples 3-9 and Comparative Experimental Examples 1-8. 6 is a graph showing the electrodeposition test results of Comparative Experimental Example 2. It is a graph which shows the electrodeposition test result of Experimental Examples 3-9 and Comparative Experimental Example 6.

  Hereinafter, embodiments of the present invention will be described in detail.

  In the present invention, a waste ion-exchange resin that adsorbs a radioactive substance and contains a clad composed mainly of iron oxide is heated to 60 ° C. or higher (hereinafter sometimes referred to as “eluent”). Is contacted to elute and remove the ionic radioactive material in the waste ion exchange resin, and dissolve and remove the clad.

  In the present invention, the radioactive waste ion-exchange resin to be decontaminated adsorbs radioactive substances that become cations in the eluent, such as cobalt-60 and nickel-63, and iron oxide. (Including iron oxide as a main component means that 50 wt% or more of iron oxide is contained in the cladding). In addition, there is no restriction | limiting in particular in the adsorption amount of the radioactive substance of a waste ion exchange resin, and content of a clad.

  As an eluent, an aqueous solution of an inorganic acid such as sulfuric acid, hydrochloric acid or nitric acid, or an organic acid such as formic acid, acetic acid or oxalic acid can be used. These acids may be used singly or in combination of two or more. However, when heated to 60 ° C. or higher, the acid does not easily volatilize and / or sulfuric acid does not fall under the category of hazardous substances and / or It is preferable to use oxalic acid.

The acid concentration in the eluent has a suitable concentration depending on the acid used. For example, the sulfuric acid concentration is preferably 5 to 40% by weight, more preferably 10 to 30% by weight. The oxalic acid concentration is preferably 0.1 to 40% by weight, more preferably 1 to 20% by weight. When the acid concentration is lower than the above range, the dissolution efficiency of hematite (α-Fe ₂ O ₃ ), which is the main component of the cladding, is lowered. That is, the clad is present in a form mixed with or entering the waste ion exchange resin, the main component of which is hardly soluble hematite, and it is difficult to dissolve with a low concentration of acid. If the acid concentration in the eluent is high, the amount of hydrogen generated in the subsequent electrodeposition process becomes excessive, and the electrodeposition efficiency decreases.

  In the present invention, the eluent is heated to 60 ° C. or higher, preferably 70 to 120 ° C., more preferably 80 to 100 ° C. If this temperature is too low, the dissolution efficiency of the clad is poor, and if it is too high, water evaporation and acid volatilization become excessive, which is not preferable in terms of work.

  The method for contacting the heated eluent and the waste ion exchange resin is not particularly limited, and may be a batch type in which the waste ion exchange resin is put into the eluent and stirred, as shown in FIG. In addition, a flow-through type in which the eluent is passed through a packed column filled with waste ion exchange resin may be used.

In the case of batch processing, the contact time between the eluent and the waste ion exchange resin is preferably about 0.5 to 24 hours, and more preferably about 2 to 12 hours. Further, in the case of the liquid passing type, the liquid passing SV is preferably about 0.2 to 10 hr ^{−1 with} respect to the packed column volume.

  In contact with the waste ion exchange resin, the ionic radioactive material adsorbed on the waste ion exchange resin is eluted and the clad mixed in the waste ion exchange resin is dissolved to contain an eluent (hereinafter referred to as “acid waste liquid”). Is introduced into an electrodeposition tank having an anode and a cathode, and an electric current is passed between the anode and the cathode of the electrodeposition tank, so that the iron derived from the cationic radioactive material in the acid waste liquid and the clad It is preferable that ions are electrodeposited on the cathode to be removed from the acid waste solution, and the resulting treatment solution is reused as an eluent.

  Hereinafter, an apparatus suitable as an apparatus for decontaminating waste ion exchange resin and reusing the acid waste liquid obtained by decontamination treatment by electrodeposition will be described with reference to FIG.

  The apparatus of FIG. 1 includes an eluent storage tank 1 that stores an eluent, an elution tank 2 that is a packed tower filled with a waste ion exchange resin 10, and an acid waste liquid storage tank that stores an acid waste liquid discharged from the elution tank 2. 3, an electrodeposition tank 4 into which the acid waste liquid from the acid waste liquid storage tank 3 is introduced, and an electrodeposition liquid storage tank 5 for storing the electrodeposition liquid supplied to the electrodeposition tank 4. The electrodeposition tank 4 has a structure in which an anode chamber 6 having an anode 6A and a cathode chamber 7 having a cathode 7A are separated by a cation exchange membrane 8, and the acid waste liquid is passed through the anode chamber 6 for electrodeposition. The liquid is passed through the cathode chamber 7. Although 9A and 9B are heat exchangers, any means may be used as long as the heat exchanger 9A can be heated and the heat exchanger 9B can be cooled, and an electric heater can be used as the heat exchanger 9A.

Eluent of the eluent storage tank 1, after being heat exchanger 9A heated to 60 ° C. or more in the process of being fed to the elution tank 2 through the pipe 11 by the pump P _1, upflow the elution vessel 2 The effluent (acid waste liquid) passes through the pipe 12, and the heat exchanger 9B reduces the deterioration of the cation exchange membrane 8 in the electrodeposition tank 4 to a temperature lower than 60 ° C., for example, 10 ° C. or higher and lower than 60 ° C. After being cooled, it is fed to the acid waste liquid storage tank 3. Acid waste liquid in the acid waste liquid tank 3 by the pump P ₂ is introduced into the anode chamber 6 of the through pipe 13 electrodeposition tank 4, electrodeposition processing liquid is circulated eluent storage tank 1 from the pipe 14, re as eluent Used.
On the other hand, the electrodeposition liquid in the electrodeposition liquid storage tank 5 is introduced into the cathode chamber 7 of the electrodeposition tank 4 through the pipe 15 by the pump P ₃ and returned to the electrodeposition liquid storage tank 5 through the pipe 16.
The eluent storage tank 1 is appropriately replenished with acid from the pipe 21, and the electrodeposition liquid reservoir 5 is appropriately replenished with the electrodeposition liquid from the pipe 22.

In this apparatus, by passing the heated eluent through the elution tank 2 filled with the waste ion exchange resin 10, the ionic radioactive substance adsorbed on the waste ion exchange resin 10 is eluted and removed. Then, the clad mixed in the waste ion exchange resin 10 or entering the resin particles is dissolved and removed. In contact with the waste ion exchange resin 10, an eluent (acid waste liquid) containing ionic radioactive material and clad dissolved material is introduced into the anode chamber 7 of the electrodeposition tank (electrodeposition cell) 4 through the acid waste liquid storage tank 3. Is done. By energizing the anode 6A and the cathode 7A of the electrodeposition tank 4, the radioactive metal ions in the acid waste liquid and the iron ions derived from the clad permeate through the cation exchange membrane 8 and move to the cathode chamber 7, and on the cathode 7A. Is electrodeposited. The acid waste liquid treatment liquid from which radioactive metal ions and iron ions have been removed in the electrodeposition tank 4 is returned to the eluent storage tank 1 and recycled.
The electrodeposition liquid in the cathode chamber 7 is circulated and reused while being circulated between the electrodeposition liquid storage tank 5 by the pump P ₃ and the reduced amount of the electrodeposition liquid is added to the electrodeposition liquid storage tank 5.

In addition, as an electrodeposition liquid, it has dicarboxylic acid and its salt (henceforth a "dicarboxylic acid (salt)") which has two carboxyl groups in a molecule | numerator, and has three carboxyl groups in a molecule | numerator. One or more additives selected from tricarboxylic acid and salts thereof (hereinafter sometimes referred to as “tricarboxylic acid (salt)”) (hereinafter sometimes referred to as “additive of the present invention”) are included. It is preferable to use an aqueous solution.
Dicarboxylic acids (salts) and tricarboxylic acids (salts) suppress the generation of suspended substances during electrodeposition due to their chelating effects, and have an excellent effect in improving the electrodeposition effect.
On the other hand, in a monocarboxylic acid having one carboxyl group in the molecule, a radioactive metal ion such as Co-60 (the radioactive material is not limited to Co-60 at all. In addition, the bonding force with Fe ions from the clad is weak, and a suspended substance composed of Co or Fe hydroxide is generated in the liquid, or the electrode is not uniformly electrodeposited on the cathode. . In addition, when a carboxylic acid having four or more carboxyl groups in the molecule is used, the binding force with Co ions and Fe ions is too strong, and Co and Fe are retained in the liquid, and the rate of electrodeposition is significantly reduced. Problem arises.

  As the dicarboxylic acid (salt) and tricarboxylic acid (salt), those represented by the following formula (1) are particularly preferable in that suspended substances are hardly generated and electrodeposition proceeds rapidly. The dicarboxylic acid (salt) or tricarboxylic acid (salt) represented by the following formula (1) has 1 to 3 carbon atoms between the carboxyl groups in the molecule, and is derived from its shape. Thus, it is estimated that an appropriate binding force can be obtained between Co ions and Fe ions.

_{^{M 1 OOC- (CHX 1) a}} - (NH) b - (CX 2 X 4) c -CX 3 X 5 -COOM 2
... (1)
(In the formula (1), X ¹ , X ² and X ³ each independently represent H or OH, X ⁴ and X ⁵ each independently represent H, OH or COOM ³ , M ¹ , M ² , M ³ each independently represent H, monovalent alkali metal or ammonium ion, and a, b, and c each independently represent an integer of 0 or 1. However, in Formula (1), X ⁴ and X ⁵ are simultaneously COOM ³ will never be reached.)

Suitable dicarboxylic acids in the present invention, for example, oxalic acid (ethanedioic acid, HOOC-COOH), malonic acid (propanedioic acid, _HOOC-CH 2 -COOH), succinic acid (butanedioic acid, HOOC-CH ₂ -CH ₂ -COOH), glutaric acid (pentanedioic _{acid, HOOC-CH 2 -CH 2 -CH} 2 -COOH), malic acid (2-hydroxybutanedioic _{acid, HOOC-CH 2 -CH (OH} ) -COOH) , Tartaric acid (2,3-dihydroxybutanedioic acid, HOOC—CH (OH) —CH (OH) —COOH), iminodiacetic acid (HOOC—CH ₂ —NH—CH ₂ —COOH), etc. Acid, succinic acid, malic acid, tartaric acid and iminodiacetic acid are particularly preferred. Examples of the tricarboxylic acid include citric acid (HOOC—CH ₂ —COH (COOH) —CH ₂ —COOH), 1,2,3-propanetricarboxylic acid, and citric acid is particularly preferable. In addition, examples of salts of these dicarboxylic acids and tricarboxylic acids include alkali metal salts such as sodium salts and potassium salts, and ammonium salts.

  In the electrodeposition solution, an ammonium salt is preferably present together with a dicarboxylic acid (salt) and / or a tricarboxylic acid (salt). When no ammonium salt is added, the electrodeposition rate of Co is usually higher than that of Fe, and an Fe electrodeposition layer is formed on the Co electrodeposition layer. However, an ammonium salt should be added. As a result, the electrodeposition rates of Co and Fe are substantially equal, and Co and Fe are electrodeposited in an alloy form. If the electrodeposition rates of Co and Fe are different and electrodeposition is performed separately for the Co layer and the Fe layer, the electrodeposit tends to float or peel off, and there is a possibility that continuous electrodeposition processing cannot be performed.

  Any ammonium salt may be used as long as it produces ammonium ions in the liquid. For example, ammonium chloride, ammonium sulfate, ammonium oxalate, and ammonium citrate are preferable. These ammonium salts may be used alone or in combination of two or more. In particular, if ammonium dicarboxylate such as ammonium oxalate or ammonium tricarboxylate such as ammonium citrate is used, the ammonium salt and the additive of the present invention can be used, and the suspended substance due to the chelating effect of dicarboxylic acid or tricarboxylic acid It is possible to obtain the effect of suppressing the generation of copper and the effect of equalizing the electrodeposition rates of Co and Fe with one agent.

  The pH of the electrodeposition liquid is preferably 1 to 9, and more preferably 2 to 8.5. If the pH of the electrodeposition solution is too low, Co or Fe electrodeposited on the cathode may be redissolved, and the electrodeposition rate may be reduced. On the other hand, if the pH is too high, Co or Fe hydroxide is likely to be generated as a suspended substance in the liquid. For this reason, when the pH is out of the above range, it is preferable to appropriately adjust the pH with an alkali or an acid. The acid used for pH adjustment is preferably the same dicarboxylic acid and / or tricarboxylic acid as the additive of the present invention in the electrodeposition solution.

As the electrodeposition liquid, for example, an aqueous solution containing 0.01 to 20% by weight, preferably 0.1 to 5% by weight of the additive of the present invention and having a pH of 1 to 9, preferably a pH of 2 to 8.5 is used.
If the amount of the additive of the present invention in the electrodeposition solution is too small, the effect of inhibiting suspended substances due to the use of the additive of the present invention cannot be sufficiently obtained, and if too much, the chelating effect increases. The electrodeposition rate is too low.
When an ammonium salt is used, the ammonium salt is preferably contained in an amount of 0.01 to 20% by weight, preferably 0.1 to 5% by weight. If the concentration of the ammonium salt is too low, the above-mentioned effect due to the use of the ammonium salt cannot be sufficiently obtained, and if it is too high, the effect is not improved and the amount of chemical used is wasted.

The electrodeposition conditions (current value, current density, temperature, etc.) are not particularly limited, but the current density is preferably 5 to 600 A / cm ² with respect to the cathode area in terms of electrodeposition efficiency.

FIG. 1 shows an example of a decontamination apparatus suitable for carrying out the present invention, and the decontamination apparatus of the present invention is not limited to the illustrated one.
In FIG. 1, the eluent is passed through the elution tank 2 in an upward flow, but may be a downward flow. However, when the waste ion exchange resin is in the form of a powder, it is preferable to make the flow upward because the differential pressure is likely to increase during liquid flow. In the electrodeposition tank 4, the acid waste solution and the electrodeposition solution may be passed through the cation exchange membrane 8 in the opposite directions. Furthermore, it is possible to exchange heat between the eluent introduced into the elution tank 2 and the discharged acid waste liquid.
Moreover, although the electrodeposition tank 4 is a closed system, since hydrogen gas is generated from the cathode, it is preferable to use an open system with the upper part opened. In addition, when replacing the cathode electrodeposited with metal, the replacement is easier if the upper part of the electrodeposition tank is open.

  The present invention relates to a waste ion exchange resin used for purification of a water system directly touching a fuel rod such as a reactor water purification system and a fuel storage pool water purification system in a nuclear power plant, and a primary cooling system device contaminated with a radioactive material. Adsorbs ionic radioactive substances such as waste ion exchange resin used for the treatment of decontamination waste liquid discharged when radioactive substances are chemically removed from the surface of metal members of pipes, pipes, and systems containing them It is effectively applied to waste ion exchange resin containing a clad mainly composed of iron oxide.

  Hereinafter, the present invention will be described in more detail with reference to experimental examples and examples.

[Experimental Example 1]
500 mL of an eluent (aqueous solution) having an acid concentration and pH shown in Table 1 was prepared, and 1 g of a simulated clad (manufactured by High Purity Chemical Laboratory, α-Fe ₂ O ₃ , manufacturer's nominal diameter 1 μm) was placed in the eluent. The dissolution test was conducted at the liquid temperature and dissolution time shown in Table 1.
The Fe (cladding) dissolution rate was examined from the Fe concentration in the eluent, and the results are shown in Table 1.

  As apparent from Table 1, No. 1 was subjected to a dissolution test at a low temperature. 7-12, although the dissolution rate is low, No. 1 using sulfuric acid and / or oxalic acid aqueous solution heated to 90 ° C. In 1 to 6, the clad can be efficiently dissolved.

[Example 1]
The mixed resin adsorbing Co was dissolved in an aqueous solution in which 96 mg of cobalt (II) chloride hexahydrate was dissolved, and the powdered H-type cation exchange resin (manufactured by Mitsubishi Chemical Corporation, exchange capacity: 5.1 meq / g, particle size) 10-200 [mu] m: 95%) and powdered OH type anion exchange resin (Mitsubishi Chemical Corporation, exchange capacity 4.1 meq / g, particle size 0-100 [mu] m: 74%, 10-250 [mu] m: 93%). It was prepared by mixing 0 g at a time and stirring for 12 hr. As a result of measuring the Co concentration in the supernatant water with an atomic absorption photometer after 12 hours, it was below the lower limit of detection, so it was confirmed that almost all of the Co ions were adsorbed on the ion exchange resin. A simulated waste resin was prepared by adding 4.0 g of iron oxide (manufactured by High Purity Chemical Laboratory, α-Fe ₂ O ₃ , manufacturer's nominal diameter 1 μm) as a simulated cladding to the mixed resin and mixing them. Then, this simulated waste resin was put into 1.6 L of 10 wt% sulfuric acid eluent (aqueous solution) heated to 90 ° C., and maintained at 90 ° C. while stirring with a hot stirrer, and the dissolution behavior was confirmed.
After adding the simulated waste resin to the 10 wt% sulfuric acid eluent, several mL of sulfuric acid eluent was collected every predetermined time, and Fe in the filtered sample was analyzed with an atomic absorption photometer, and Co was analyzed by ICP-MS. Analyzed in
As a result, as shown in FIG. 2, about 100% of the amount of Fe in the added simulated cladding was dissolved in the sulfuric acid eluent, and re-adsorption to the cation exchange resin occurred after dissolution of the simulated cladding. I found that there was no. The reason why the dissolution rate exceeds 100% after 2 hours is due to evaporation of water in the eluent by heating. As for Co, almost 100% of the amount of Co in the added cobalt chloride was eluted in the sulfuric acid eluent, and it was confirmed that Co ions could be eluted well from the resin.

[Experiment 2]
CoCI _2, FeCl ₃ and sulfuric acid are dissolved in water to prepare a simulated acid waste solution having the properties shown in Table 2, and citric acid is dissolved in water to simulate the simulated electrodeposition solution (catholyte) having the properties shown in Table 2. Was prepared, and an electrodeposition test for Co and Fe was performed using the apparatus shown in FIG. In FIG. 3, members having the same functions as those of the apparatus shown in FIG. In FIG. 3, reference numeral 31 denotes a pipe for returning the electrodeposition treatment liquid to the acid waste liquid storage tank 3. The electrodeposition conditions are as shown in Table 2. The anode used was a Pt-plated Ti plate, and the cathode used a Cu plate.

Co and Fe in the simulated acid waste solution after 6 hours of energization were measured with an atomic absorption photometer. As a result of energization for 6 hours, 19% of Co and 10% of Fe in the simulated acid waste solution could be removed and A kimono was obtained.
In this electrodeposition apparatus, the metal ions were moved to the cathode chamber through the cation exchange membrane without bringing the strongly acidic waste liquid into direct contact with the cathode, so that the electrodeposition could be efficiently performed.

[Experimental Examples 3-9, Comparative Experimental Examples 1-8]
Using various additives and CoCl ₂ and FeCl ₃ , 400 mL of an electrodeposition solution having the composition shown in Table 3 was prepared, and the electrodeposition test was performed using the apparatus shown in FIG. Went. Energization was performed at 8 hr, 1 A (current density 62.5 mA / cm ² ). A Pt-plated Ti plate was used for the anode and a Cu plate was used for the cathode. In FIG. 4, members having the same functions as those of the apparatus shown in FIGS. Reference numeral 20 denotes a power source.
Table 3 shows the presence or absence of suspended solids and the pH of the liquid before and after energization. 5 and 6 show the results of analyzing the changes over time in the concentrations of Co and Fe in each of the electrodeposition liquids of Experimental Examples 3 to 9 and Comparative Experimental Examples 2 and 6 where there is no suspended matter both before and after energization. . From the energization result for 8 hours, it can be seen that in Experimental Examples 3 to 9, Co and Fe could be electrodeposited over time.

DESCRIPTION OF SYMBOLS 1 Eluent storage tank 2 Elution tank 3 Acid waste liquid storage tank 4 Electrodeposition tank 5 Electrodeposition liquid storage tank 6 Anode chamber 6A Anode 7 Cathode chamber 7A Cathode 8 Cation exchange membrane 9A, 9B Heat exchanger 10 Waste ion exchange resin

Claims (11)

  While adsorbing radioactive material, waste ion exchange resin containing a clad composed mainly of iron oxide is brought into contact with an acid heated to 60 ° C. or more to elute the ionic radioactive material in the waste ion exchange resin. A decontamination method for a radioactive waste ion exchange resin, comprising a decontamination step of dissolving and removing the clad while removing the clad.   The method for decontaminating radioactive waste ion exchange resin according to claim 1, wherein the acid is sulfuric acid and / or oxalic acid.   The method for decontaminating radioactive waste ion exchange resin according to claim 1 or 2, wherein the acid is a 5 to 40 wt% sulfuric acid solution and / or a 0.1 to 40 wt% oxalic acid solution. .   The method for decontaminating radioactive waste ion exchange resin according to any one of claims 1 to 3, wherein the radioactive substance contains cobalt-60.   By introducing an acid waste liquid containing an ionic radioactive substance discharged from the decontamination step into an electrodeposition tank having an anode and a cathode, and energizing between the anode and the cathode, the ionic radioactive substance in the acid waste liquid Electrodeposition on the cathode to remove the ionic radioactive material from the acid waste liquid, and the treatment liquid obtained by removing the ionic radioactive material in the electrodeposition step to the decontamination step The method for decontaminating radioactive waste ion exchange resin according to any one of claims 1 to 4, further comprising a circulation step of recycling and recycling the waste.   In the electrodeposition tank, an anode chamber in which an anode is installed and a cathode chamber in which a cathode is installed are separated by a cation exchange membrane, and the acid waste liquid is introduced into the anode chamber, and The ionic radioactive substance in the acid waste liquid permeates through the cation exchange membrane, moves to the cathode chamber, and is electrodeposited on the cathode. Decontamination method for radioactive waste ion exchange resin.   The method for decontaminating radioactive waste ion exchange resin according to claim 5 or 6, wherein cobalt-60 and iron which is a melt of the clad are electrodeposited on the cathode.   While adsorbing radioactive material, waste ion exchange resin containing a clad composed mainly of iron oxide is brought into contact with an acid heated to 60 ° C. or more to elute the ionic radioactive material in the waste ion exchange resin. A decontamination apparatus for a radioactive waste ion exchange resin that includes a decontamination means for removing the clad and dissolving the clad, wherein the decontamination means comprises a packed tower filled with the waste ion exchange resin, and the packed tower A heating pipe provided in the introduction pipe, and a discharge pipe for discharging the acid waste liquid containing the ionic radioactive substance from the packed tower. Decontamination equipment for radioactive waste ion exchange resin.   An electrodeposition tank having an anode and a cathode; means for energizing the anode and cathode; means for introducing the acid waste liquid into the electrodeposition tank; and a treatment liquid in the electrodeposition tank upstream of the heating means. A means for circulating, and by energizing between the anode and the cathode, the ionic radioactive material in the acid waste liquid is electrodeposited on the cathode to remove the ionic radioactive material from the acid waste liquid, The radioactive waste ion-exchange resin decontamination apparatus according to claim 8, wherein a treatment liquid obtained by removing ionic radioactive substances is reused by the decontamination means.   The electrodeposition tank has an anode chamber in which an anode is installed, a cathode chamber in which a cathode is installed, and a cation exchange membrane that separates the anode chamber and the cathode chamber, and the acid waste liquid is placed in the anode chamber. Introduced and energized between the anode and the cathode, the ionic radioactive material in the acid waste liquid passes through the cation exchange membrane and moves to the cathode chamber, and is electrodeposited on the cathode. The decontamination apparatus for radioactive waste ion exchange resin according to claim 9.   11. The radioactive waste ion exchange resin decontamination apparatus according to claim 9, wherein cobalt-60 and iron which is a melt of the clad are electrodeposited on the cathode.

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