JP2014071004A - Water treatment method and device in nuclear power plant - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a water treatment method and device in a nuclear power plant which reduce oxidation accelerating substances in the water to be treated before demineralizing the water to be treated including the oxidation accelerating substances caused by the radiolysis of water in a nuclear power plant by an ion exchange resin and maintain the quality of the treatment water at high purity by reducing a load of a demineralizer, and extend the life of the ion exchange resin and reduce a generated amount of the spent ion exchange resin.SOLUTION: The water to be treated including the oxidation accelerating substance generated by the radiolysis of water in the nuclear power plant is brought into contact with a filter having an ion exchange functional group introduced by radiation graft polymerization on a polyolefin non-woven fabric and metallic oxidation fine particles loaded on a part of the ion exchange functional group so as to decompose the oxidation accelerating substance, and subsequently brought into contact with the iron exchange resin.

Description

  The present invention relates to a technology for treating nuclear reactor water, fuel pool water, site bunker pool water, and radioactive material-containing wastewater in a nuclear power plant. In particular, the present invention relates to a method and apparatus for treating water to be treated containing an oxidation promoting substance such as hydrogen peroxide generated by radiolysis of water in a nuclear power plant.

  In nuclear power plants, for the purpose of purifying reactor water, various pool water, condensate, wastewater, etc., condensate demineralizers, wastewater demineralizers, hollow fiber membranes, pleated filters, etc. using granular ion exchange resins are used. Purification equipment such as the filtration device used and a precoat filtration device using powder ion exchange resin is installed.

  An outline will be described taking a condensate demineralizer as an example. A boiling water nuclear power plant (BWR) plant directs steam generated in a nuclear reactor to a turbine, rotates a generator connected to the turbine to generate electricity, and condenses the steam that has finished work in the turbine with a condenser. Then, water is supplied to the reactor again. A condensate demineralizer is installed in the condensate system that supplies the condensate from the condenser to the reactor, and it is used for cooling and suspending corrosive substances mainly composed of iron oxide called clad contained in the condensate. Remove ionic impurities such as seawater components derived from the seawater used. In addition, a reactor coolant purification system is provided to remove cladding, ionic impurities, etc. contained in the reactor water, and the reactor water is filtered and removed from the reactor coolant purification system. Lead to salt equipment to remove clad and ionic impurities in reactor water. In this way, the reactor water is properly purified and kept in high purity pure water.

  When the reactor is shut down, such as during regular inspections (periodic inspections), an appropriate amount of water may always be discharged from the reactor as surplus water in order to maintain the reactor water level appropriately. In addition, when the fuel is changed, it is necessary to temporarily discharge a large amount of water as surplus water from the reactor in order to restore the reactor water level raised for the fuel change. That is, at the time of fuel exchange in the nuclear reactor, water is added to the fuel transfer path between the nuclear reactor and the fuel pool, the reactor water level is greatly increased, and the fuel level is returned to the original reactor water level after the fuel exchange is completed. For this reason, it is necessary to temporarily discharge a large amount of water from the reactor as surplus water. When draining surplus water from these reactors, after removing the cladding and ionic impurities contained in the reactor water with the reactor coolant purification system filtration demineralizer of the reactor coolant purification system, Lead excess to the liquid waste treatment system. In the liquid waste treatment system, surplus water from the reactor coolant purification system is temporarily stored in the waste liquid collection tank, and the clad and ionic impurities are further removed in the liquid waste treatment system, and the purified water is stored as condensate. Store in the pool and prepare for reuse in the plant. Here, in the condensate demineralizer, it is necessary to replace the ion exchange resin when the capacity of the ion exchange resin is reduced. The ion exchange resin is generated as radioactive waste, and the cost and location associated with the treatment of the radioactive waste are required. Therefore, it is desired to extend the life of the ion exchange resin. Therefore, during the regular inspection of the nuclear power plant, the ion exchange resin is backwashed using the water stored in the condensate storage pool to extend the life of the ion exchange resin. In addition, in fuel pools and site bunker pools installed in nuclear power plants, corrosion of stored fuel and various materials is suppressed, and radioactive substances in the pool water are removed to reduce the exposure of workers. In order to maintain soundness for a long period of time, such as by reducing, a desalinator using a granular ion exchange resin and a filtration device using a powder ion exchange resin are installed.

However, in reactor water and fuel pool water, water is decomposed by radiation from the fuel rods in the water, and oxidation promoting substances such as hydroperoxy radicals and hydroxy radicals generated from hydrogen peroxide and hydrogen peroxide (hereinafter referred to as “hydrogen peroxide”) "Oxidation promoter"). In the reactor coolant purification system and the liquid waste treatment system, these oxidation-promoting substances cannot be removed, and are stored in the fuel pool water, the site bunker pool water, and the condensate storage pool that is collected and recovered. The water still contains oxidation promoting substances. Since this oxidation promoting substance has a very strong oxidizing action, it oxidizes the cation resin of the ion exchange resin and elutes polystyrene sulfonic acid (PSS). The eluted PSS adheres to the anion resin of the ion exchange resin and decreases the reaction rate of the anion resin, resulting in a decrease in the desalting rate. In addition, due to the oxidative degradation of the cation resin due to hydrogen peroxide, sulfate ions and the like are eluted from the cation resin, increasing the conductivity at the outlet of the ion exchange resin. Furthermore, the strong oxidizing action also contributes to corrosion of steel materials such as pipes and tanks.

  During normal operation, oxidation-promoting substances are thermally decomposed and disappear, but the reactor water temperature is low in spent fuel pools such as the Fukushima Daiichi Nuclear Power Station, which are undergoing regular inspection and have been shut down since March 11, 2011. Thermal decomposition hardly occurs because it is around 50 ° C, and the hydrogen peroxide concentration in the primary light water is increased by the radiation emitted from the fuel rod, and contains hydrogen peroxide in the order of several ppm.

  The stopped reactor water is treated by a reactor coolant purification system filtration desalination apparatus of a reactor coolant purification system, a filter and a desalting tower of a liquid waste treatment system. In these reactor coolant purification system and liquid waste treatment system, the oxidation promoting substance is not treated and transferred to the condensate storage pool. Since this water is used to backwash the ion exchange resin of the condensate demineralizer, the ion exchange resin undergoes oxidative degradation. In addition, in the reactor water purification system desalination system and fuel pool purification system, these waters are directly treated with ion exchange resin, so that the oxidation promoting substance oxidizes and degrades the ion exchange resin, increasing the frequency of ion exchange resin replacement. To do.

  The main cause of deterioration of ion exchange resin is thought to be due to contact of oxidation promoting substances contained in reactor water during the regular inspection of nuclear power plants. Decomposing the oxidation promoting substance before the treatment leads to the advancement of treated water quality and the extension of the life of the ion exchange resin. Based on such knowledge, before hydrogen peroxide comes into contact with the cation exchange resin, a method of alkali decomposition using an anion exchange resin (Patent Document 1), platinum removed by a granular active material or supported on an ion exchange resin A method of decomposing using a group catalyst (Patent Document 2), a method of decomposing using a platinum-coated catalyst coating network (Patent Document 3), a method of removing using activated carbon (Patent Document 4), etc. have been proposed. However, none has been put into practical use.

JP 2000-002787 A JP-A-10-111387 JP 2003-156589 A JP 2008-232773 A

  Accordingly, an object of the present invention is to promote oxidation in treated water before desalting the treated water containing an oxidation promoting substance such as hydrogen peroxide generated by radiolysis of water in a nuclear power plant with an ion exchange resin. Reduce the amount of substances used, reduce the load on the desalination equipment, maintain the quality of the treated water, increase the life of the ion exchange resin, and generate the amount of used ion exchange resin that becomes radioactive secondary waste It is to provide a water treatment technology in a nuclear power plant that reduces the amount of water.

Means to solve the problem

  In order to solve the above-mentioned problems, the present inventors have conducted intensive research. As a result, the water to be treated containing an oxidation promoting substance such as hydrogen peroxide is passed through a specific filter before the desalting treatment with an ion exchange resin. As a result, it has been found that oxidation promoting substances in the water to be treated can be dramatically reduced, and the present invention has been completed.

  Specifically, according to the present invention, water to be treated containing an oxidation-promoting substance produced by radiolysis of water in a nuclear power plant, the ion-exchange functional group introduced into the polyolefin nonwoven fabric by radiation graft polymerization and the water A method for treating water in a nuclear power plant, comprising: contacting a filter having metal oxide fine particles attached to a part of an ion-exchange functional group to decompose the oxidation-promoting substance, and then bringing the substance into contact with an ion-exchange resin. Is provided.

  The filter introduces an ion exchange functional group into the polyolefin nonwoven fabric by radiation graft polymerization, adsorbs a metal ion selected from manganese, iron or titanium to at least a part of the ion exchange functional group, and then the metal It can be produced by oxidizing ions. The fibers constituting the polyolefin nonwoven fabric preferably have a fiber diameter of several hundred nm to several tens of μm. Unlike conventional fine particle carriers such as ion exchange resins and activated carbon used for the decomposition of hydrogen peroxide, polyolefin nonwoven fabrics have large gaps between fibers and do not provide resistance to water to be treated. Is introduced even inside the fiber constituting the polyolefin nonwoven fabric, and can be contacted uniformly with the water to be treated without impairing the amount and speed of the water to be treated. It is extremely good, and the decomposition ability of the oxidation promoting substance is remarkably improved.

The metal oxide fine particles of the filter are preferably selected from oxide fine particles of manganese, iron or titanium. The ion exchange functional group may be either a cation exchange group or an anion exchange group. In the case of a cation exchange group, a strongly acidic cation exchange group such as a sulfonic acid group is preferable. In the case of an anion exchange group, a strongly basic anion exchange group such as a quaternary ammonium group or a lower amino group, an iminodiethanol group, an iminodiacetic acid group, Weakly basic anion exchange groups such as ethylenediamine groups are preferred. When a cation exchange group is used, a metal ion such as Mn ²⁺ , Fe ³⁺ , Ti ⁴⁺ can be adsorbed and then oxidized to form a metal oxide. When an anion exchange group is used, a metal ion such as MnO ⁴⁻ , FeO ₄ ²⁻ , TiO ₃ ^2−, etc. can be adsorbed and then reduced to a metal oxide.

  The present invention is particularly effective when applied to fuel pool water, sight bunker pool water, or radioactive material-containing waste water as the treated water. Since these waters to be treated have a low temperature of about 50 ° C., oxidation promoting substances such as hydrogen peroxide are not thermally decomposed and contain a large amount of oxidation promoting substances.

  Examples of the oxidation promoting substance that can be decomposed by the method of the present invention include hydrogen peroxide, a hydroperoxy radical, and a hydroxy radical. However, since hydroperoxy radicals or hydroxy radicals are unstable and decompose immediately after generation, hydrogen peroxide is usually the substance to be decomposed.

In addition, according to the present invention, the treated water storage tank for storing the treated water containing the oxidation promoting substance generated by radiolysis of water in the nuclear power plant, and the downstream of the treated water storage tank are positioned. A filtration device filled with a filter having ion exchange functional groups introduced into a polyolefin nonwoven fabric by radiation graft polymerization and fine metal oxide particles attached to a part of the ion exchange functional groups, and ion exchange There is also provided a water treatment device in a nuclear power plant comprising a desalination device filled with a resin.

The treated water storage tank may be a fuel pool, a site bunker pool, or a radioactive material-containing wastewater tank.
The shape of the filter is not particularly limited, and is a commonly used shape such as a cartridge type in which the flat membrane is a pleated type, a wind type in which the flat membrane is wound around a water collecting pipe, and a laminated type in which the flat membrane is stacked in the direction of water flow. Good.

  According to the water treatment method and apparatus for a nuclear power plant of the present invention, an oxidation promoting substance such as hydrogen peroxide generated by radiolysis of water in the nuclear power plant can be efficiently decomposed. The quality of the treated water can be maintained at a high purity, and the life of the ion exchange resin can be extended to reduce the amount of used ion exchange resin generated as radioactive secondary waste. be able to.

  In addition, the filter used in the water treatment method and apparatus of the present invention is based on a polyolefin non-woven fabric having a large gap between fibers, so that the resistance of water to be treated is small and the amount of water to be treated is kept large. As a result, it is possible to efficiently decompose the oxidation-promoting substance in the water to be treated in a short time compared with the case where the filter treatment is not performed or when solid particles such as activated carbon and ion exchange resin are used as pretreatment. .

  Reduction of treatment time and volume of radioactive secondary waste are important issues for water treatment in nuclear power plants that are required to minimize the effects of radiation exposure, and these can be achieved. The significance of the present invention is great.

FIG. 1 is a schematic configuration diagram showing a flow of the water treatment apparatus of the present invention in the case of treating radioactive substance-containing wastewater. FIG. 2 is a schematic configuration diagram showing a flow of the water treatment apparatus of the present invention when fuel pool water is treated. FIG. 3 is a graph showing a processing result when the hydrogen peroxide concentration in Example 1 is 2 mg / L. FIG. 4 is a graph showing the treatment results when the hydrogen peroxide concentration of Example 1 is 20 mg / L. FIG. 5 is a graph showing the processing results of Example 2.

Preferred embodiment

Hereinafter, the present invention will be described with reference to the accompanying drawings, but the present invention is not limited thereto.
In FIG. 1, the schematic flow of the water treatment apparatus of this invention in the case of processing radioactive substance containing wastewater is shown. The radioactive substance containing waste water generated in a nuclear power plant is stored in the to-be-processed water storage tank 1 which is a radioactive substance containing wastewater tank. To-be-treated water is sent from the to-be-treated water storage tank 1 to the filtration device 4 by the transfer pump 2, and after the oxidation promoting substance is decomposed, it is transported to the desalting device 3 and desalted. The treated water after the desalting treatment is sent to the sample tank 5 to check the properties of the treated water. If there is no problem with the properties, the treated water is sent from the desalinator 3 to the pure water tank 7 by the transfer pump 6 and reused in the nuclear power plant or meets environmental standards. Will be released into wide area waters.

FIG. 2 shows a schematic flow of the water treatment apparatus of the present invention when treating fuel pool water. In the fuel pool 8, water is radiolyzed by radiation emitted from fuel rods stored in water. Fuel pool water (treated water) from the fuel pool 8 (treated water storage tank) is sent to the filtration device 4 by the transfer pump 11 and is sent to the desalting device 3 after the oxidation promoting substance is decomposed. Desalted. The treated water after the desalting treatment is returned to the fuel pool 8 as condensate.

  1 and 2, the filtration device 4 includes a filter having ion exchange functional groups introduced into a polyolefin nonwoven fabric by radiation graft polymerization and metal oxide fine particles attached to a part of the ion exchange functional groups. Is filled. The form of the filter is not particularly limited, and examples thereof include a pleated filter and a wind filter. The desalting apparatus 3 is filled with a granular ion exchange resin. The ion exchange resin in the desalting apparatus 3 is preferably in a mixed bed form in which a strongly acidic cation exchange resin and a strongly basic anion exchange resin are mixed in a volume ratio of 1: 3 to 6: 1.

  It is desirable that the amount of water to be treated to be passed through the filtration device 4 is in the range of about 0.1 to 2 m / h in terms of linear flow velocity.

Hereinafter, the present invention will be described in more detail with reference to examples.
[Production Example 1] Manganese oxide impregnated anion exchange filter Fabrication of 50 g / m ² polyethylene fiber with a fiber diameter of 15 µm and a nonwoven fabric with a thickness of 0.3 mm (dimensions 21 cm x 30 cm, 3.16 g) It put into the polyethylene bag, the inside of the polyethylene bag was substituted with nitrogen, and 150 gGy was irradiated with gamma rays. The nonwoven fabric was taken out and immersed in a glycidyl methacrylate solution and subjected to a graft polymerization reaction (pre-irradiation radiation graft polymerization) at 45 ° C. for 5 hours under reduced pressure conditions (0.67 kPa). The nonwoven fabric was taken out, immersed in a dimethylformamide solution and washed at 50 ° C. for 2 hours. Thereafter, it was washed with acetone and methanol and dried to obtain 7.2 g of a grafted nonwoven fabric. The graft ratio calculated from the weight change after drying was 128%. Next, this grafted non-woven fabric was immersed in a 30% iminodiethanol aqueous solution and reacted at 70 ° C. for 3 hours to introduce iminodiethanol groups. After drying, a weakly basic anion exchange nonwoven fabric having an acid adsorption capacity of 2.81 meq / g was obtained.

Next, this weakly basic anion exchange nonwoven fabric was immersed in a 0.2 mol / L potassium permanganate aqueous solution at room temperature for 10 minutes to adsorb permanganate ions to at least a part of the iminodiethanol group. This was washed 3 times with 1 liter of pure water and then dried at room temperature. As a result, it was confirmed that the color of the non-woven fabric quickly changed from dark purple to brown of manganese oxide, and that an anion exchange filter impregnated with manganese oxide was obtained. The manganese oxide deposition amount is determined by calculating the amount of Mn input from the amount of potassium permanganate used for the deposition, and the Mn ion concentration remaining after the treatment is measured using an atomic absorption photometer, and the difference between the Mn input amount and the residual amount. I asked for it. The manganese oxide deposition amount was 21.6 g / m ² as Mn.

[Production Example 2] Manufacture of manganese oxide impregnated cation exchange filter Thermal fusion with a basis weight of 55 g / m ² and a thickness of 0.2 mm composed of a 15 μm diameter fiber having a polyethylene terephthalate (PET) core / polyethylene sheath structure. One piece of nonwoven fabric (dimensions 21 cm × 30 cm, 3.34 g) was placed in a polyethylene bag with a chuck, the inside was purged with nitrogen, and 150 gGy was irradiated with gamma rays. The nonwoven fabric was taken out, immersed in glycidyl methacrylate, and subjected to a graft polymerization reaction at 45 ° C. for 4 hours under a reduced pressure condition (0.67 kPa) (pre-irradiation radiation graft polymerization). The nonwoven fabric was taken out, immersed in dimethylformamide and washed at 50 ° C. for 2 hours. Thereafter, it was washed with acetone and methanol and then dried to obtain 7.85 g of a nonwoven fabric. The graft ratio calculated from the change in weight after drying was 135%. Next, this grafted nonwoven fabric was immersed in a sulfonated liquid (an aqueous solution containing 8% sodium sulfite and 12% isopropyl alcohol) and reacted at 90 ° C. for 10 hours to introduce sulfonic acid groups. After washing with pure water, the sulfonic acid group is changed to H-type by immersing and stirring in 5% hydrochloric acid, and the neutral salt decomposition capacity is 2.62 meq / g by washing and drying again with pure water. A cation exchange nonwoven fabric was obtained.

Next, this cation exchange nonwoven fabric was immersed in 500 mL of 2% manganese (II) chloride aqueous solution for 30 minutes. Next, manganese oxide was deposited on the fiber surface of the cation exchange nonwoven fabric by immersing the nonwoven fabric in 200 mL of a 1% sodium hypochlorite aqueous solution (alkaline) to obtain a manganese oxide impregnated cation exchange filter. The manganese oxide deposition amount was measured in the same manner as in Production Example 1 and found to be 66.1 g / m ² as Mn.

[Example 1]
Using the manganese oxide-impregnated anion exchange filter produced in Production Example 1, the ability to decompose hydrogen peroxide was confirmed.

  First, the manganese oxide impregnated anion exchange filter obtained in Production Example 1 was cut into 2 cm × 2 cm to obtain a sample filter. A 200 ml beaker was charged with 100 ml of hydrogen peroxide water, a sample filter was immersed therein, and the hydrogen peroxide concentration over time was measured. The control did not soak the sample filter. Two types of hydrogen peroxide concentrations were used: 2 mg / L and 20 mg / L. The results are shown in FIGS. 3 and 4 (circles are sample filter results and closed circles are control results).

  3 and 4 show that the sample filter has a high ability to decompose hydrogen peroxide. In particular, in FIG. 4 where the hydrogen peroxide concentration is high, it can be seen that the manganese oxide-impregnated anion exchange filter has an extremely high ability to decompose hydrogen peroxide and decomposes 50% in 120 minutes after immersion.

[Example 2]
Using the manganese oxide impregnated cation exchange filter produced in Production Example 2, the hydrogen peroxide decomposition ability was confirmed.

Manganese oxide impregnated cation exchange filter 2 produced according to Production Example 2 was cut into a circle having a diameter of 16 mm and packed into a glass column having an inner diameter of 16 mm. The hydrogen peroxide removal performance of the manganese oxide impregnated cation exchange filter was examined by passing hydrogen peroxide solution adjusted to about 2 mg / L at a flow rate of 3.5 mL / min (linear velocity LV = 1 m / h). The hydrogen peroxide removal performance was similarly examined using three and five manganese oxide-impregnated cation exchange filters packed in a glass column. The test results are shown in FIG. In FIG. 5, the vertical axis represents the ratio of the hydrogen peroxide concentration (C) at the outlet to the hydrogen peroxide concentration (C ₀ ) at the inlet. When there was one manganese oxide impregnated cation exchange filter, C / C ₀ = 0.4, that is, the decomposition rate was about 60%. When three or five manganese oxide-impregnated cation exchange filters were stacked, it was found that no breakthrough occurred even in a 6-hour water passage test. Thus, it was confirmed that hydrogen peroxide in water was effectively decomposed by the cation exchange filter impregnated with manganese oxide.

In the same manner as in Examples 1 and 2, a filter having a manganese deposition amount per filter layer in the range of 10 to 100 g / m ² as Mn was manufactured, and the hydrogen peroxide removal performance was examined. Hydrogen peroxide can be decomposed. I confirmed that there was.

According to the present invention, an oxidation promoting substance such as hydrogen peroxide contained in fuel pool water, site bunker pool water, radioactive substance-containing wastewater of a nuclear power plant is decomposed, and the quality of water to be treated by a desalinator is improved. While maintaining the purity, it is possible to extend the life of the ion exchange resin used in the desalting apparatus and reduce the amount of waste generated. Reduction of treatment time and volume of radioactive secondary waste are important issues for water treatment in nuclear power plants that are required to minimize the effects of radiation exposure, and these can be achieved. The significance of the present invention is great.

Claims (7)

  Water to be treated containing an oxidation promoting substance produced by radiolysis of water in a nuclear power plant is attached to a non-woven fabric made of polyolefin by radiation graft polymerization and a part of the ion exchange functional group. A method for treating water in a nuclear power plant, comprising: contacting a filter having metal oxide fine particles, decomposing the oxidation promoting substance, and then bringing the substance into contact with an ion exchange resin.   The water treatment method according to claim 1, wherein the metal oxide fine particles of the filter are selected from oxide fine particles of manganese, iron, or titanium.   The water treatment method according to claim 1 or 2, wherein the water to be treated is fuel pool water, site bunker pool water, or radioactive material-containing waste water.   The water treatment method according to claim 1, wherein the oxidation promoting substance is hydrogen peroxide, a hydroperoxy radical, or a hydroxy radical. A treated water storage tank for storing treated water containing an oxidation promoting substance generated by radiolysis of water in a nuclear power plant;
An ion-exchange functional group, which is positioned downstream of the treated water storage tank and introduced into the polyolefin nonwoven fabric by radiation graft polymerization, and metal oxide fine particles attached to a part of the ion-exchange functional group A filtration device filled with a filter;
A demineralizer filled with an ion exchange resin;
A water treatment apparatus in a nuclear power plant.   The water treatment apparatus according to claim 5, wherein the treated water storage tank is a fuel pool, a site bunker pool, or a radioactive substance-containing wastewater tank.   The water treatment apparatus according to claim 5 or 6, wherein the metal oxide fine particles of the filter are selected from oxide fine particles of manganese, iron, or titanium.

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