Radioactive waste liquid treatment system, radioactive waste liquid treatment method, charge determination device, and charge determination method

Abstract

To provide a radioactive waste liquid treatment system capable of reducing the generation amount of radioactive waste including alpha nuclide of long half-life by removing alpha nuclide under conditions where the adsorption performance of the alpha nuclide removal material of the ionic alpha nuclide included in the radioactive waste liquid and the fine particles to which the ionic alpha nuclide is attached are removed is fully executed.SOLUTION: The radioactive waste liquid treatment system includes a waste liquid treatment unit that processes radioactive waste liquid including alpha nuclide. The waste liquid treatment unit includes: an alpha nuclide concentration measuring unit that measures the concentration of alpha nuclide included in radioactive waste fluid; a charge determination unit that determines the zero charge point of particles dispersed in radioactive waste liquid; and a pH adjuster injection unit that adjusts pH based on the zero charge point of fine particles; and an adsorbent injection unit that injects alpha nuclide removal material into radioactive waste liquid after the pH adjustment.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] This disclosure relates to a radioactive waste liquid treatment system, a radioactive waste liquid treatment method, a charge determination device, and a charge determination method. [Background technology]

[0002] Cellulose-based filter aids, ion exchange resins, and other radioactive organic waste generated from nuclear power plant reactor coolant purification systems, fuel pool coolant purification systems, etc., are stored in storage tanks for long periods. This radioactive organic waste is generated regularly as a result of the operation of nuclear power plants.

[0003] In order to secure storage space for radioactive organic waste, volume reduction technologies are needed to efficiently reduce the volume of radioactive organic waste currently in storage.

[0004] Patent Document 1 discloses a method for treating radioactive contaminated water, which involves adding zeolite powder to the radioactive contaminated water to adsorb radioactive materials, and then separating the zeolite with the adsorbed radioactive materials from the treated water using solid-liquid separation, and which allows for continuous treatment of the radioactive contaminated water.

[0005] Patent Document 2 discloses a method for generating precipitates containing radioactive nuclides by adjusting the pH of the radioactive waste liquid to within the range of 9 to 12, and then adding magnetic powder consisting of γ-ferrous oxide (γ-Fe2O3) powder or triiron tetroxide (Fe3O4) powder as a coagulant to the radioactive waste liquid into which the precipitates have been generated, thereby imparting settling properties to the precipitates, and finally separating the radioactive waste liquid with the added coagulant into a solid-liquid mixture of precipitates and supernatant.

[0006] Patent Document 3 discloses a radioactive waste treatment system for treating radioactive waste containing α-nuclides, comprising a water quality adjustment device for adjusting the water quality of the radioactive waste containing α-nuclides, and a filter located downstream of the water quality adjustment device to which the adjusted radioactive waste is supplied. Patent Document 3 also discloses that α-nuclide colloids are generated in the radioactive waste adjusted to a pH range of 4 or more and less than 8 using a pH adjusting agent, that these colloids are removed by a filter, that at least one of an acid, an oxidizing agent and a reducing agent for water quality adjustment may be injected along with an alkali, that ascorbic acid or sulfite is used as a reducing agent and an oxidation-reduction potential adjusting agent, and that the residual rate of α-nuclides in the radioactive waste discharged from the filter decreases as the oxidation-reduction potential decreases. [Prior art documents] [Patent Documents]

[0007] [Patent Document 1] Japanese Patent Publication No. 2013-50418 [Patent Document 2] Japanese Patent Publication No. 2010-190749 [Patent Document 3] Japanese Patent Publication No. 2021-120662 [Overview of the Initiative] [Problems that the invention aims to solve]

[0008] If the cladding of a fuel rod in a fuel assembly loaded into the reactor core is damaged, the nuclear fuel material within the fuel rod, namely actinides (alpha nuclides such as uranium (U), plutonium (Pu), neptunium (Np), americium (Am), and curium (Cm)), will leak into the cooling water. This cooling water containing these alpha nuclides is then guided to a purification system within the reactor coolant purification mechanism, where each alpha nuclide is removed by ion exchange resins within the purification system. Alpha nuclides have long half-lives.

[0009] Ion exchange resins that have adsorbed alpha-nuclides are treated as waste resins. Alpha-nuclides and other radioactive materials are eluted from these ion exchange resins using aqueous solutions of organic acids and organic acid salts. Even after the organic acid solutions containing the eluted alpha-nuclides are concentrated through prescribed treatment, a large amount of radioactive waste containing long-lived alpha-nuclides is generated. It is desirable to reduce the amount of radioactive waste containing long-lived alpha-nuclides.

[0010] According to the technologies described in Patent Documents 1 to 3, it is possible to reduce the residual rate of alpha nuclides in radioactive waste liquid.

[0011] However, even with these technologies, if radioactive waste liquid contains fine particles to which ionic alpha-nuclides are attached, the amount of removal material required to remove these particles may increase.

[0012] The purpose of this disclosure is to remove ionic α-nuclides and fine particles to which ionic α-nuclides are attached from radioactive liquid waste under conditions in which the adsorption performance of the α-nuclide removal material is fully utilized, thereby reducing the amount of radioactive waste containing long-half-life α-nuclides. [Means for solving the problem]

[0013] The radioactive waste liquid treatment system of this disclosure includes a waste liquid treatment unit for treating radioactive waste liquid containing α-nuclides, the waste liquid treatment unit having an α-nuclide concentration measuring device for measuring the α-nuclide concentration contained in the radioactive waste liquid, a charge determination device for determining the zero charge point of fine particles dispersed in the radioactive waste liquid, a pH adjusting agent injection device for adjusting the pH based on the zero charge point of the fine particles, and an adsorbent injection device for injecting an α-nuclide removal material into the radioactive waste liquid whose pH has been adjusted. [Effects of the Invention]

[0014] According to this disclosure, ionic α-nuclides contained in radioactive liquid waste and fine particles to which ionic α-nuclides are attached can be removed under conditions in which the adsorption performance of the α-nuclide removal material is fully utilized, thereby reducing the amount of radioactive waste containing long-half-life α-nuclides.

Brief Description of the Drawings

[0015] [Figure 1] It is a flowchart showing a method for treating radioactive waste liquid according to Example 1. [Figure 2] It is a configuration diagram showing an example of the radioactive waste liquid treatment system of Example 1. [Figure 3] It is a configuration diagram showing the main part of the radioactive waste liquid treatment system of FIG. 2. [Figure 4] It is a graph showing the difference in pH change depending on whether or not fine particles are dispersed in an aqueous solution. [Figure 5] It is a graph showing the influence of pH on the ionic α nuclide adsorption amount of the α nuclide removal material. [Figure 6] It is a graph showing the influence of pH on the removal amount by the α nuclide removal material of fine particles to which ionic α nuclides are attached. [Figure 7] It is a configuration diagram showing the charge determination device of FIG. 3. [Figure 8] It is a flowchart showing an example of the charge determination method according to the present disclosure.

Modes for Carrying Out the Invention

[0016] The present disclosure relates to a radioactive waste liquid treatment system and the like, and particularly relates to a radioactive waste liquid treatment system and the like applicable to the treatment of radioactive waste liquid generated by washing waste resins generated from nuclear power plants and radioactive waste liquid generated by nuclear fuel reprocessing.

[0017] Hereinafter, examples according to the present disclosure will be described in detail with reference to the drawings. However, the structures, materials, and other various specific configurations shown in the examples are not limited to those taken up here, and appropriate combinations and improvements are possible without changing the gist. In addition, elements not directly related to the present disclosure are omitted from the illustration.

Examples

[0018] Example 1 relates to a radioactive waste liquid treatment system applicable to the treatment of radioactive organic waste generated at a boiling water reactor nuclear power plant.

[0019] If the cladding of a fuel rod constituting a fuel assembly loaded into the reactor core of a nuclear power plant, such as an operating boiling water reactor, or a spent fuel assembly stored in a fuel storage pool, is damaged, the nuclear fuel material (including alpha nuclides such as uranium, plutonium, neptunium, americium, and curium) within the fuel rod will leak into the cooling water in the reactor pressure vessel or the cooling water in the fuel storage pool. The alpha nuclides that leak into the cooling water in the reactor pressure vessel are removed by ion exchange resins in the purification device of the reactor coolant purification system. Similarly, the alpha nuclides that leak into the cooling water in the fuel storage pool are removed by ion exchange resins in the purification device of the fuel pool coolant purification system.

[0020] Filter sludge (radioactive organic waste) containing cellulose-based filter aids and ion exchange resins generated from the reactor coolant purification system, fuel pool coolant purification system, etc., of boiling water reactor nuclear power plants is stored for a long period of time in high-dose resin storage tanks. After a predetermined storage period has elapsed, the radioactive organic waste stored in these high-dose resin storage tanks is removed from the tanks.

[0021] Figure 1 is a flowchart showing the treatment method for radioactive waste liquid according to Example 1.

[0022] In this diagram, first, the radioactive organic waste (organic waste) containing cation exchange resin, which has been removed from the high-dose resin storage tank, undergoes the first washing process S1 (cladding process).

[0023] In this first washing step S1, radioactive organic waste is immersed in an aqueous solution of a reducing organic acid (for example, an aqueous solution of oxalic acid), and the organic acid contained in the aqueous solution dissolves the cladding, such as iron oxides, contained in the radioactive organic waste. Radioactive nuclides such as cobalt-60 contained in the cladding move into the organic acid aqueous solution as the cladding dissolves.

[0024] The reason for using an organic acid in the first washing step S1 is that, since organic acids contain carbon and at least one of the elements hydrogen, oxygen, and nitrogen, when the organic acid aqueous solution, which is the washing wastewater generated in the first washing step S1, is oxidized using, for example, ozone (wastewater decomposition step S4 described later), no non-volatile residue is produced in the wastewater. As the organic acid, it is desirable to use, for example, formic acid, oxalic acid, acetic acid, or citric acid.

[0025] For the organic acid aqueous solution (cladding dissolving solution), which is the cleaning wastewater containing cladding dissolving components generated in the first cleaning step S1, a wastewater decomposition step S4 is performed.

[0026] In this wastewater decomposition process S4, an oxidizing agent such as hydrogen peroxide or ozone is aerated into an aqueous solution of organic acid, and the organic acid and organic salt are decomposed by the oxidizing action of the oxidizing agent.

[0027] For radioactive organic waste that has undergone the first washing process S1 and had its cladding removed, the second washing process S2 (radionuclide elution process) is carried out.

[0028] In this second washing step S2, the radioactive organic waste from which the cladding has been removed is immersed in an aqueous solution of organic acid salts, and the organic acid salts contained in the aqueous solution elute radioactive nuclides such as alpha nuclides that have been adsorbed onto the radioactive organic waste.

[0029] The organic acid salt used in the second washing step S2 is preferably an organic acid salt that dissociates in aqueous solution and produces cations that are more readily adsorbed by the cation exchange resin than hydrogen ions. That is, the organic acid salt also contains at least one of the elements hydrogen, oxygen, and nitrogen, and it is desirable that when the aqueous solution of the organic acid salt, which is the washing wastewater after the completion of the second washing step S2, is oxidized using, for example, ozone (wastewater decomposition step S4), no non-volatile residue is produced in the wastewater. As the organic acid salt, it is desirable to use, for example, ammonium salts, barium salts, or cesium salts of formic acid, oxalic acid, acetic acid, or citrate. Formic acid hydrazine may also be used as the organic acid salt.

[0030] Ammonium salts decompose into nitrogen gas and water through oxidation, thus reducing the amount of radioactive waste generated compared to barium and cesium salts. Ammonium, barium, or cesium salts of formic acid, oxalic acid, acetic acid, or citric acid dissociate in aqueous solution, forming NH3. 4+ Ba 2+ or Cs + It will become NH 4+ Ba 2+ or Cs + This is a cation that is more readily adsorbed by cation exchange resins than hydrogen ions.

[0031] In the second washing step S2, a wastewater treatment process S4 is carried out on the organic acid salt aqueous solution, which is washing wastewater containing radioactive nuclides such as eluted alpha nuclides. In the wastewater treatment process S4, the organic acid salt aqueous solution is aerated with an oxidizing agent such as ozone or hydrogen peroxide, and the organic acid salt is decomposed by the oxidizing agent in the process.

[0032] After the waste liquid decomposition process S4, the α-nuclide concentration of the residual aqueous solution (radioactive waste liquid) containing the remaining radionuclides is measured (α-nuclide concentration measurement process S5).

[0033] Here, the alpha nuclide concentration may be measured by sampling the radioactive waste liquid and measuring it with an analytical instrument, or by measuring it with a survey meter.

[0034] If the α-nuclide concentration is below a predetermined concentration in the α-nuclide concentration measurement step S5, the volume reduction step S10 is performed without any processing such as α-nuclide removal. On the other hand, if the α-nuclide concentration is higher than the predetermined concentration, the charge determination step S6 is performed.

[0035] In this step S6, the charge determination step may involve sampling the radioactive waste liquid and measuring it using a charge determination device (described later), or it may be measured online.

[0036] After the charge determination step S6, the pH adjustment step S7 is performed. Then, after the adsorption and removal of radionuclides step S8 is performed, the filtering step S9 is carried out.

[0037] As pH adjusting agents used in pH adjustment step S7, inorganic acids (hydrochloric acid, sulfuric acid, nitric acid, etc.), inorganic alkalis (sodium hydroxide, calcium hydroxide, magnesium hydroxide, etc.), organic acids (carboxylic acids, ascorbic acid, etc.), and organic alkalis (ammonium-based, etc.) can be used.

[0038] As the α-nuclide adsorbent (α-nuclide remover) used in the radioactive nuclide adsorption and removal process S8, cation exchange resins, Fe oxides, titanate compounds, titanate compounds, ferrocyanide compounds, chelate resins, activated carbon, oxin-impregnated activated carbon, zeolites, etc., can be used.

[0039] pH is the hydrogen ion concentration.

[0040] In the filtering process S9, a cross-flow filter is used to separate the solid material, such as the slurry generated by the α-nuclide removal material and pH adjustment, from the waste liquid from which the radionuclides have been removed. Alternatively, the above solid-liquid separation may be performed using a press filter or the like.

[0041] The solid and waste liquid separated in the filtering process S9 are subjected to concentration or drying powdering in the volume reduction process S10, respectively, and then filled into containers or solidified in the solidification process S11.

[0042] In the container filling or solidification process S11, the concentrated waste liquid generated by the concentration process, or the radioactive waste powder generated by the drying and pulverization process, is filled into a container for storage, or solidified in the container with a solidifying agent such as cement.

[0043] Next, we will describe an example of the configuration of a radioactive wastewater treatment system that performs each of the above steps S1 to S11.

[0044] Figure 2 is a diagram showing an example of the radioactive waste liquid treatment system of Example 1.

[0045] The radioactive waste liquid treatment system 1 shown in this figure includes a chemical cleaning unit 10 for treating radioactive organic waste, and a waste liquid treatment unit 19 for treating the cleaning waste liquid (radioactive waste liquid) discharged from the chemical cleaning unit 10.

[0046] In the chemical cleaning section 10, among the processes shown in Figure 1, the first cleaning step S1, which dissolves the cladding, and the second cleaning step S2, which elutes radionuclides from the radioactive organic waste, are performed.

[0047] The chemical cleaning section 10 includes a first receiving tank 3, a chemical reaction vessel 4 (cleaning tank), a cleaning liquid supply tank 6, an organic acid tank 7, an organic acid salt tank 8, and a transfer water tank 9. A high-dose resin storage tank 2 is provided upstream of the chemical cleaning section 10. Downstream of the chemical cleaning section 10 are a second receiving tank 11 and an incineration facility 12. Here, the incineration facility 12 may be a cement solidification facility, or it may include a cement solidification facility.

[0048] The high-dose resin storage tank 2 and the first receiving tank 3 are connected by an organic waste supply pipe 23 equipped with a transfer pump 22.

[0049] The chemical reaction vessel 4 is connected to the first receiving tank 3 by an organic waste transfer pipe 25 equipped with a transfer pump 24. A heating device 5 is arranged around the chemical reaction vessel 4.

[0050] The cleaning solution supply tank 6 is connected to the chemical reaction vessel 4 by a cleaning solution supply pipe 33 equipped with a transfer pump 32.

[0051] A return pipe 36, equipped with a transfer pump 34 and a valve 35, is connected to the bottom of the chemical reaction vessel 4, allowing the liquid from the chemical reaction vessel 4 to be returned to the washing liquid supply tank 6.

[0052] Furthermore, the cleaning solution supply tank 6 is connected to an organic acid tank 7, an organic acid salt tank 8, and a transfer water tank 9.

[0053] The organic acid tank 7 is connected to the cleaning fluid supply tank 6 by a pipe 29 equipped with a valve 26. The organic acid tank 7 is filled with an aqueous solution of organic acid, for example, an aqueous solution of oxalic acid. The aqueous solution of oxalic acid filled in the organic acid tank 7 is a saturated aqueous solution, and its oxalic acid concentration is, for example, 0.8 mol / L.

[0054] The organic acid salt tank 8 is connected to the cleaning fluid supply tank 6 by a pipe 30 equipped with a valve 27. The organic acid salt tank 8 is filled with an aqueous solution of an organic acid salt, for example, an aqueous solution of hydrazine formate. The pipe 30 is connected to pipe 29 downstream of the valve 26.

[0055] The transfer tank 9 is connected to the cleaning fluid supply tank 6 by a pipe 31 equipped with a valve 28. The transfer tank 9 is filled with water to be transferred. The pipe 31 is connected to pipe 30 downstream of the valve 27.

[0056] A pipe 38 with a valve 37 is connected to the bottom of the chemical reaction vessel 4. The pipe 38 is connected to the second receiving tank 11.

[0057] The second receiving tank 11 is connected to the incineration facility 12 via piping.

[0058] On the other hand, the wastewater treatment unit 19 includes a wastewater decomposition device 13, an α-nuclide concentration measuring device 14, a charge determination device 15, an α-nuclide removal device 16, a pH adjusting agent injection device 112, an adsorbent injection device 121, a filter treatment device 131, and a treated water recovery tank 18.

[0059] The waste liquid decomposition device 13 is supplied with liquid from the chemical reaction vessel 4 through a waste liquid supply pipe 40 connected to a return pipe 36. The waste liquid supply pipe 40 is connected between the transfer pump 34 and the valve 35. A valve 39 is also provided in the waste liquid supply pipe 40.

[0060] The waste liquid decomposition unit 13 is connected to the alpha nuclide removal unit 16 via piping 45. A transfer pump 43 and a valve 44 are provided in piping 45. Piping 45 and 46 constitute a radioactive waste liquid supply pipe that guides radioactive waste liquid containing alpha nuclides.

[0061] In the waste liquid decomposition device 13, an aqueous solution of organic acid (clad dissolving solution) and an aqueous solution of organic acid salt (nuclide eluent) are stored, and the organic acid and organic acid salt are decomposed by an oxidizing agent such as hydrogen peroxide or ozone that is injected.

[0062] The piping 45 is connected to an alpha-nuclide concentration measuring device 14, a charge determination device 15, and a pH adjusting agent injection device 112.

[0063] The alpha-nuclide removal device 16 is connected to the treated water recovery tank 18 via piping 46. A filter treatment device 131 is installed in piping 46. An adsorbent injection device 121 is also connected to the alpha-nuclide removal device 16.

[0064] In the filter processing apparatus 131, for example, a cross-flow filter system using a membrane with a pore size of micrometer order or less (1 μm or less) filters the radioactive waste liquid to separate the α-nuclide adsorbent that has adsorbed α-nuclides from the radioactive waste liquid, as well as the slurry generated by pH adjustment.

[0065] Furthermore, a pipe 55 is connected to the filter processing device 131. The pipe 55 is connected to the return pipe 36 of the chemical cleaning unit 10. In this figure, the pipe 55 is connected between the transfer pump 34 and the valve 35 of the return pipe 36. The filtered water produced in the filter processing device 131 is sent to the return pipe 36 through the pipe 55. In the filter processing device 131, the adsorbent and the slurry generated by carbon dioxide removal are separated by filtration. In this way, the filtered water can be circulated as circulating water. It is desirable to provide a three-way valve (not shown) at the connection between the return pipe 36 and the pipe 55 so that the liquid from the chemical reaction vessel 4 and the filtered water from the pipe 55 can be switched.

[0066] Furthermore, the timing of transferring the radioactive waste liquid from the chemical cleaning unit 10 to the waste liquid processing unit 19 may be determined by attaching a sampling valve to the return pipe 36 and periodically analyzing the radioactive waste liquid collected by the sampling valve, so that the transfer occurs when the measured α-nuclide concentration reaches a predetermined concentration.

[0067] Furthermore, a drying and pulverizing device 20 and a solidification device 21 are provided downstream of the wastewater treatment unit 19. The treated water recovery tank 18 and the drying and pulverizing device 20 are connected via piping 48. A transfer pump 47 is provided in piping 48. The drying and pulverizing device 20 and the solidification device 21 are connected via piping 49. Note that a radioactive wastewater concentration device may be used instead of the drying and pulverizing device 20.

[0068] Figure 3 is a diagram showing the main components of the radioactive waste liquid treatment system shown in Figure 2.

[0069] Figure 3 shows the detailed configuration of the wastewater treatment unit 19, from the α-nuclide concentration measuring device 14 to the filter treatment unit 131.

[0070] An alpha-nuclide concentration measuring device 14 and a charge determination device 15 are connected to the piping 45 upstream of the alpha-nuclide removal device 16. Alternatively, the charge determination device 15 may not be connected to the waste liquid processing unit 19, but rather perform charge determination on the sampled radioactive waste liquid, and the determination result may be reflected in the pH adjuster injection amount of the pH adjuster in the pH adjuster injection device 112.

[0071] The alpha-nuclide removal device 16 consists of a waste liquid treatment tank that contains radioactive waste liquid sent from the waste liquid decomposition device 13 through piping 45.

[0072] The α-nuclide concentration of the radioactive waste liquid is measured using the α-nuclide concentration measuring device 14. If the α-nuclide concentration is below a predetermined concentration, it may be returned to the return pipe 36 (Figure 2) via the pipe 54 and circulated as circulating water.

[0073] If the α-nuclide concentration is above a predetermined concentration, the charge of the radioactive waste liquid is measured by the charge determination device 15. Then, the pH is adjusted by injecting a pH adjusting agent using the pH adjusting agent injection device 112, and the radioactive waste liquid is supplied to the α-nuclide removal device 16. Note that the pH adjusting agent injection device 112 may be connected to the α-nuclide removal device 16 instead of the piping 45. pH adjustment can be performed similarly with this configuration as well.

[0074] The alpha-nuclide removal device 16 is configured to receive alpha-nuclide removal material (adsorbent) from the adsorbent injection device 121. This removes alpha-nuclides contained in the radioactive waste liquid. The radioactive waste liquid is then supplied to the filter treatment device 131 through piping 46. The filtered water, after filtering the adsorbent in the filter treatment device 131, is supplied to the treated water recovery tank 18 (Figure 2) through piping 46. Alternatively, the filtered water may be returned to the return pipe 36 (Figure 2) through piping 55 and circulated as circulating water.

[0075] Next, I will explain how to determine the charge.

[0076] Figure 4 is a graph showing the difference in pH change depending on whether or not fine particles are dispersed in an aqueous solution. The horizontal axis represents the amount of 0.1M sodium hydroxide aqueous solution (NaOH), which is an alkaline agent, added, and the vertical axis represents the pH of the aqueous solution. In other words, this figure shows a neutralization titration curve.

[0077] In the example shown in this figure, 100 mL of 50-fold diluted seawater is used as the aqueous solution (test solution), 1 g of goethite (FeOOH) is used as the fine particles, and sodium hydroxide is used as the pH adjuster.

[0078] As shown in this figure, in the case of an aqueous solution containing only ions without fine particles dispersed (□ mark), the pH is approximately 4 when the amount of NaOH added in the initial state is 0 mL, and when the added amount exceeds 0.1 mL, the pH rises from 4 to about 10 as the added amount increases. On the other hand, in the case where fine particles (FeOOH) are dispersed (○ mark), the pH is approximately 6 in the initial state, and due to the pH buffering effect of the fine particles, even when the added amount increases, the rise in pH is very gradual and the pH is less than 7.

[0079] From the above, it can be seen that the conditions for adjusting the pH differ depending on the presence or absence of fine particles. And the charge of the fine particles is determined from the intersection of the two curves obtained from the data shown in this figure, and the intersection is called the "point of zero charge". In this figure, the pH of the point of zero charge is approximately 6, and it is determined that the fine particles have a positive charge in the range lower than the pH of the point of zero charge and a negative charge in the range higher than the pH of the point of zero charge.

[0080] Note that the pH buffering effect of the fine particles is considered to be due to the adsorption of hydroxide ions (OH - ) on the surface of the fine particles. Therefore, even after the OH - ions dissolved in the liquid and the OH - ions adsorbed on the surface of the fine particles are combined and neutralized, the further added OH

[0081] is adsorbed, and it is considered that the rise in the pH of the liquid is suppressed.Next, we will explain the pH conditions under which the adsorption performance is fully exhibited when using an α-nuclide removal material to remove ionic α-nuclides and fine particles to which ionic α-nuclides are attached.

[0082] Figure 5 is a graph showing the effect of pH on the amount of ionic α-nuclides adsorbed by the α-nuclide removal material. The horizontal axis represents the pH of the aqueous solution, and the vertical axis represents the amount of ionic α-nuclides adsorbed by the α-nuclide removal material Q. eq They are taking it. Q eq The unit is the amount of adsorption (mg) per gram of alpha-nuclide removal material.

[0083] This figure shows the case where magnetite (Fe3O4) is used as an α-nuclide removal agent in an aqueous solution containing only ions, without dispersed fine particles such as goethite (FeOOH). Americium (Am) is used as the α-nuclide.

[0084] As shown in this figure, Q eq This value increases with increasing pH. Therefore, in the case of an aqueous solution containing only ions, it is desirable to set the pH to 10 from the viewpoint of alpha-nuclide removal.

[0085] Figure 6 is a graph showing the effect of pH on the amount of ionized α-nuclides removed from fine particles by an α-nuclide removal agent.

[0086] In this figure, magnetite (Fe3O4) is used as the α-nuclide removal material, and goetite (FeOOH) is used as the fine particles to which ionic α-nuclides are attached, as an example. The charge of the α-nuclide removal material is determined using a graph-based method as shown in Figure 4. The pH at the zero-charge point is approximately 8, and a range below the pH at the zero-charge point is determined to be positively charged, while a range above the pH at the zero-charge point is determined to be negatively charged.

[0087] As shown in Figure 6, under pH 4 or 10 conditions where the charge of the α-nuclide removal material and the fine particles are of the same sign, the amount of fine particles to which ionic α-nuclides are attached by the α-nuclide removal material is small. In contrast, under pH 6 conditions where the charge of the α-nuclide removal material and the fine particles are of opposite signs, the amount of fine particles to which ionic α-nuclides are attached by the α-nuclide removal material is relatively large.

[0088] From the results above (Figures 5 and 6), as shown in Figure 4, by adjusting the pH to be on the alkaline side (in this embodiment, approximately pH 8 when adjusting the pH for an aqueous solution containing only ions without dispersed fine particles) within the range where the charges of the α-nuclide removal material and the fine particles are of opposite signs, and then removing the α-nuclide with the α-nuclide removal material, both ionic α-nuclides and fine particles to which ionic α-nuclides are attached can be removed at pH conditions in which the adsorption performance is fully exhibited.

[0089] In Figure 2, filtered water supplied to the treated water recovery tank 18 through piping 46 is supplied in a predetermined amount to the drying and pulverizing device 20 through piping 48 by driving the transfer pump 47. Filtered water containing radioactive nuclides other than α-nuclides is pulverized in the drying and pulverizing device 20 (volume reduction step S10 in Figure 1). In the resulting powder, most of the long-half-life α-nuclides have been removed during the processing up to step S9.

[0090] Subsequently, the powder generated in the drying and pulverizing device 20 is transferred to the solidification equipment 21 (or filling equipment). In the solidification equipment 21, the powder is filled into a solidification container, and a solidifying agent (e.g., cement) is injected into the container. The powder in the solidification container is solidified by the solidifying agent (container filling or solidification process S11).

[0091] The solidification containers are sealed and stored in a designated storage area. If filling equipment is used, the containers are filled with powder, the containers are sealed, and then the containers are stored in a designated storage area.

[0092] The adsorbent and slurry separated in the filter processing apparatus 131 may be supplied (stored) in a separately prepared receiving tank, or, as in the above process, may be supplied separately to the drying and powdering apparatus 20 to perform the volume reduction process S10, and then transferred to the solidification equipment 21 (or filling equipment) to perform container filling or solidification process S11 (not shown).

[0093] According to this embodiment, both ionic α-nuclides and fine particles to which ionic α-nuclides are attached can be removed under pH conditions that allow the adsorption performance of the α-nuclide removal material to be fully utilized, thereby reducing radioactive waste containing α-nuclides.

[0094] In this embodiment, charge determination (charge determination of fine particles) is performed using the charge determination device 15. However, literature values ​​regarding the material-specific zero charge point (pzc) of the fine particles may be stored in a database, and the above-mentioned processes such as pH adjustment may be performed by referring to this database.

[0095] Furthermore, while goethite (FeOOH) was used as an example of fine particles in the explanation, other applicable fine particles include magnetite (Fe3O4), ferrite (Fe2O3), silica fine particles, and alumina fine particles. [Examples]

[0096] As another preferred embodiment of the present disclosure, the radioactive wastewater treatment system of Example 2 will be described.

[0097] Example 2 is also a radioactive waste liquid treatment system applied to the treatment of radioactive organic waste generated at a boiling water reactor nuclear power plant.

[0098] In the radioactive wastewater treatment system of Example 2, the amount of pH adjusting agent is determined from the charge measurement results shown in Figure 4 obtained by the charge determination device 15 of the charge determination S6. After adjusting the pH by injecting the pH adjusting agent using the pH adjusting agent injection device 112, the α-nuclide is removed using the α-nuclide removal device 16. The configuration diagram is the same as that shown in Figure 3 of Example 1.

[0099] In Example 1, in order to remove both the ionic α-nuclides and the fine particles to which the ionic α-nuclides are attached, as shown in Figures 5 and 6, under pH conditions that allow the adsorption performance to be fully exhibited, the pH was adjusted to be on the alkaline side (approximately pH 8 in this example) within the range where the charges of the α-nuclide removal material and the fine particles are of opposite signs, as shown in Figure 4. Then, the α-nuclides were removed using the α-nuclide removal material.

[0100] In contrast, in Example 2, instead of controlling the pH range using the results in Figure 4, the pH is adjusted by the amount of pH adjusting agent added. From the results in Figure 4, the range of 0.1M NaOH addition amounts for conditions where the charges of the α-nuclide removal material and the fine particles are of opposite signs is 0.2 mL to 2 mL (only up to 1 mL is shown in Figure 4). Therefore, regardless of the presence or absence of fine particles in the liquid, adding NaOH within the above range allows both ionic α-nuclides and fine particles to which ionic α-nuclides are attached to be removed at pH conditions where the adsorption performance is fully exhibited.

[0101] For example, when 0.3 mL of 0.1 M NaOH is added, the pH of the liquid without dispersed fine particles becomes approximately 10, and as shown in Figure 5, the pH is adjusted to a high pH (alkaline) condition, increasing the amount of ionic α-nuclides adsorbed by the α-nuclide removal material. On the other hand, when fine particles are dispersed in the liquid, the pH becomes approximately 6 due to the pH buffering effect of the fine particles. Therefore, as shown in Figure 6, the pH is adjusted to a condition where the charges of the α-nuclide removal material and the fine particles are of opposite signs, increasing the amount of ionic α-nuclides adsorbed by the fine particles to which the α-nuclide removal material has attached. This is because when the charges of the α-nuclide removal material and the fine particles are of opposite signs, they become electrically compatible and more likely to aggregate. This makes processing such as precipitation separation and filtration separation easier.

[0102] According to this embodiment, both ionic α-nuclides and ionic α-nuclides attached to fine particles can be removed under pH conditions that allow the adsorption performance of the α-nuclide removal material to be fully demonstrated, regardless of the presence or absence of fine particles in the liquid, thereby reducing radioactive waste containing α-nuclides.

[0103] Next, we will describe the zero-charge point determination device and determination method shown in Figure 4.

[0104] Figure 7 is a diagram showing the configuration of the charge determination device shown in Figure 3.

[0105] In Figure 7, the charge determination device 15 (zero charge point determination device) comprises a filter unit 201, alkaline treatment tanks 211 and 212 (pH adjustment treatment tanks), and a calculation unit 220. Here, alkaline treatment tank 211 is also called the "first pH adjustment treatment tank," and alkaline treatment tank 212 is also called the "second pH adjustment treatment tank."

[0106] Alkaline treatment tanks 211 and 212 are designed to collect radioactive waste liquid containing alpha nuclides via piping branched from pipe 45. pH adjusting agents (alkaline agents) such as 0.1M NaOH can be added to alkaline treatment tanks 211 and 212.

[0107] A filter section 201 is provided between the piping 45 and the alkaline treatment tank 211. The radioactive waste liquid introduced into the alkaline treatment tank 211 is filtered by the filter section 201 to remove fine particles such as goethite (FeOOH).

[0108] The calculation unit 220 acquires measurement data (such as the data shown in Figure 4) obtained in the alkaline treatment tanks 211 and 212 and calculates the zero charge point of the fine particles. It is also desirable that the calculation unit 220 has a function to control the amount of pH adjusting agent added.

[0109] Figure 8 is a flowchart showing an example of a charge determination method (zero charge point determination method) according to this disclosure.

[0110] As shown in this figure, when determining the charge of radioactive waste liquid containing alpha nuclides, the waste liquid sample (radioactive waste liquid) is divided into two portions and collected (step S50). One of the waste liquid samples is filtered to remove solid components (fine particles such as goetite (FeOOH)) (step S51). Both waste liquid samples are subjected to alkali treatment and the pH is measured (step S52). Alkali treatment is performed by adding a pH adjusting agent (alkaline agent) such as 0.1 M NaOH. The zero charge point of the fine particles is then calculated from the intersection of the pH curve with respect to the amount of alkali added (step S53).

[0111] The following describes preferred embodiments related to this disclosure.

[0112] The radioactive waste liquid treatment system includes a filter treatment device that removes alpha nuclides from the radioactive waste liquid into which an alpha nuclide removal material has been injected by filtration.

[0113] The zero-charge point of a particle is determined when the α-nuclide concentration is above a predetermined concentration.

[0114] The pH adjusting agent injection device adjusts the pH of the radioactive waste liquid so that it is within the range of the pH value corresponding to the zero charge point of the fine particles and within the pH value corresponding to the zero charge point of the alpha-nuclide removal material.

[0115] The pH adjusting agent injection device injects a pH adjusting agent so that the pH of the radioactive waste liquid becomes greater than 7.

[0116] The charge determination device performs a neutralization titration and determines the zero charge point of the particles based on the results.

[0117] The charge determination device comprises a filter unit for removing fine particles from radioactive waste liquid, a first pH adjustment treatment tank configured to inject a pH adjusting agent into the liquid sent from the filter unit from which the fine particles have been removed from the radioactive waste liquid, a second pH adjustment treatment tank configured to inject a pH adjusting agent into the radioactive waste liquid containing fine particles, and a calculation unit. The calculation unit calculates the zero charge point of the fine particles from the measurement data obtained in the first and second pH adjustment treatment tanks.

[0118] The zero charge point is calculated from the intersection of two curves that show the pH for the amount of pH adjusting agent added in the first and second pH adjustment treatment tanks, which are created based on measurement data.

[0119] The pH adjusting agent injection device adjusts the pH of the radioactive waste liquid so that the charge of the fine particles and the charge of the alpha-nuclide removal material are of opposite signs.

[0120] The pH adjusting agent injection device injects a pH adjusting agent so that the pH of the radioactive waste liquid becomes greater than 7, in other words, so that the radioactive waste liquid becomes alkaline.

[0121] The pH adjuster contains at least one substance from among inorganic acids including hydrochloric acid, sulfuric acid, or nitric acid; inorganic alkalis including sodium hydroxide, calcium hydroxide, or magnesium hydroxide; organic acids including carboxylic acid or ascorbic acid; and ammonium-based organic alkalis.

[0122] The α-nuclide removal material includes at least one of the following: cation exchange resin, Fe oxide, titanate compound, titanate compound, ferrocyanine compound, chelate resin, activated carbon, oxin-impregnated activated carbon, and zeolite.

[0123] The fine particles include at least one of the following: iron oxide fine particles containing goethite, magnetite, or ferrite, silica fine particles, and alumina fine particles.

[0124] The filter processing device has a cross-flow filter configuration using a membrane with a pore size of 1 μm or less.

[0125] It should be noted that the contents of this disclosure are not limited to the embodiments and examples described above, but include various modifications. For example, each of the embodiments described above is described in detail in order to explain the contents of this disclosure in an easy-to-understand manner, and is not necessarily limited to having all of the configurations described. [Explanation of symbols]

[0126] 1: Radioactive wastewater treatment system, 4: Chemical reaction tank, 7: Organic acid tank, 8: Organic acid salt tank, 9: Transfer water tank, 10: Chemical washing section, 12: Incineration equipment, 13: Wastewater decomposition device, 14: α-nuclide concentration measuring device, 15: Charge determination device, 16: α-nuclide removal device, 19: Wastewater treatment section, 20: Drying and powdering device, 21: Solidification equipment, 112: pH adjuster injection device, 121: Adsorbent injection device, 131: Filter treatment device, 201: Filter section, 211, 212: Alkali treatment tank, 220: Calculation unit, S1: First washing process, S2: Second washing process, S4: Wastewater decomposition process, S5: α-nuclide concentration measurement, S6: Charge determination, S7: pH adjustment process, S8: Adsorption and removal of radioactive nuclides, S9: Filter treatment process.

Claims

1. It is equipped with a wastewater treatment section for treating radioactive wastewater containing alpha-nuclides, The aforementioned waste liquid treatment unit is An α-nuclide concentration measuring device for measuring the α-nuclide concentration contained in the aforementioned radioactive waste liquid, A charge determination device for determining the zero charge point of fine particles dispersed in the aforementioned radioactive waste liquid, A pH adjusting agent injection device that adjusts the pH based on the zero charge point of the fine particles, The system includes an adsorbent injection device for injecting an α-nuclide removal material into the radioactive waste liquid whose pH has been adjusted, The zero charge point of the fine particles is determined when the α-nuclide concentration is above a predetermined concentration. A radioactive wastewater treatment system comprising a pH adjusting agent injection device that adjusts the pH of the radioactive wastewater so that the pH of the radioactive wastewater is within a range that is greater than or equal to the pH value corresponding to the zero charge point of the fine particles and less than or equal to the pH value corresponding to the zero charge point of the α-nuclide removal material.

2. The radioactive wastewater treatment system according to claim 1, wherein the wastewater treatment unit further comprises a filter treatment unit that removes the α-nuclide from the radioactive wastewater into which the α-nuclide removal material has been injected by filtration.

3. The radioactive waste treatment system according to claim 1, wherein the pH adjusting agent injection device injects a pH adjusting agent so that the pH of the radioactive waste liquid becomes greater than 7.

4. The radioactive waste liquid treatment system according to claim 1, wherein the charge determination device performs a neutralization titration and determines the zero charge point of the fine particles based on the result.

5. The charge determination device is A filter unit for removing the fine particles from the radioactive waste liquid, A first pH adjustment treatment tank having a configuration for injecting a pH adjusting agent into the liquid sent from the filter section, from which the fine particles have been removed from the radioactive waste liquid, A second pH adjustment treatment tank having a configuration for injecting the pH adjusting agent into the radioactive waste liquid containing the fine particles, It has a calculation unit, The radioactive wastewater treatment system according to claim 1, wherein the calculation unit calculates the zero charge point of the fine particles from the measurement data obtained in the first pH adjustment treatment tank and the second pH adjustment treatment tank.

6. The radioactive wastewater treatment system according to claim 5, wherein the zero charge point is calculated from the intersection of two curves showing the pH with respect to the amount of pH adjusting agent added in the first pH adjustment treatment tank and the second pH adjustment treatment tank, which are created based on the measurement data.

7. A wastewater treatment unit for treating radioactive wastewater containing α-nuclides, The aforementioned waste liquid treatment unit is An α-nuclide concentration measuring device for measuring the α-nuclide concentration contained in the aforementioned radioactive waste liquid, A charge determination device for determining the zero charge point of fine particles dispersed in the aforementioned radioactive waste liquid, A pH adjusting agent injection device that adjusts the pH based on the zero charge point of the fine particles, The system includes an adsorbent injection device for injecting an α-nuclide removal material into the radioactive waste liquid whose pH has been adjusted, The zero charge point of the fine particles is determined when the α-nuclide concentration is above a predetermined concentration. The pH adjusting agent injection device is a radioactive wastewater treatment system that adjusts the pH of the radioactive wastewater so that the charge of the fine particles and the charge of the α-nuclide removal material are of opposite signs.

8. The radioactive wastewater treatment system according to claim 7, wherein the pH adjusting agent injection device injects a pH adjusting agent so that the pH of the radioactive wastewater becomes greater than 7.

9. A method for treating radioactive waste liquid containing alpha-nuclides, A step of measuring the concentration of α-nuclides contained in the aforementioned radioactive waste liquid, A step of determining the zero charge point of the fine particles dispersed in the radioactive waste liquid, A step of adjusting the pH based on the zero charge point of the fine particles, The process includes injecting an α-nuclide removal agent into the radioactive waste liquid whose pH has been adjusted, The zero charge point of the fine particles is determined when the α-nuclide concentration is above a predetermined concentration. A method for treating radioactive waste liquid, wherein the pH adjustment is performed so that the pH of the radioactive waste liquid is within a range that is greater than or equal to the pH value corresponding to the zero charge point of the fine particles and less than or equal to the pH value corresponding to the zero charge point of the α-nuclide removal material.

10. A device for determining the zero charge point of fine particles in radioactive waste liquid containing an α-nuclide, in which fine particles are dispersed, A filter unit for removing the fine particles from the radioactive waste liquid, A first pH adjustment treatment tank having a configuration for injecting a pH adjusting agent into the liquid sent from the filter section, from which the fine particles have been removed from the radioactive waste liquid, A second pH adjustment treatment tank having a configuration for injecting the pH adjusting agent into the radioactive waste liquid containing the fine particles, It comprises a calculation unit, The calculation unit is a charge determination device that calculates the zero charge point of the fine particles from the measurement data obtained in the first pH adjustment treatment tank and the second pH adjustment treatment tank.

11. The charge determination device according to claim 10, wherein the zero charge point is calculated from the intersection of two curves that show the pH with respect to the amount of pH adjusting agent added in the first pH adjustment treatment tank and the second pH adjustment treatment tank, which are created based on the measurement data.

12. A method for determining the zero charge point of fine particles in radioactive waste liquid containing an α-nuclide in which fine particles are dispersed, A step of removing the fine particles from the radioactive waste liquid, A first pH adjustment step involves injecting a pH adjusting agent into the liquid from which the fine particles have been removed from the radioactive waste liquid, A second pH adjustment step involves injecting the pH adjusting agent into the radioactive waste liquid containing the fine particles, A charge determination method for calculating the zero charge point of the fine particles from measurement data obtained in the first pH adjustment step and the second pH adjustment step.

13. The charge determination method according to claim 12, wherein the zero charge point is calculated from the intersection of two curves that show pH with respect to the amount of pH adjusting agent added in the first pH adjustment step and the second pH adjustment step, which are created based on the measurement data.

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