JP2024066666A - Radioactive waste liquid treatment system, radioactive waste liquid treatment method, charge determination device, and charge determination method - Google Patents

Abstract

[Problem] To remove ionic α-nuclides contained in radioactive waste liquid and fine particles to which ionic α-nuclides are attached under conditions where the adsorption performance of an α-nuclide removal material is fully exhibited, thereby reducing the amount of radioactive waste containing long-half-life α-nuclides generated. [Solution] A radioactive waste liquid treatment system equipped with a waste liquid treatment unit that treats radioactive waste liquid containing α-nuclides, the waste liquid treatment unit having an α-nuclide concentration measuring device that measures the concentration of α-nuclides contained in the radioactive waste liquid, a charge determining device that determines the zero charge point of fine particles dispersed in the radioactive waste liquid, a pH adjuster injection device that adjusts the pH based on the zero charge point of the fine particles, and an adsorbent injection device that injects an α-nuclide removal material into the radioactive waste liquid that has been pH-adjusted. [Selected Figure] Figure 2

Description

This disclosure relates to a radioactive waste liquid treatment system, a radioactive waste liquid treatment method, an electric charge determination device, and an electric charge determination method.

Filter sludge and other radioactive organic waste containing cellulose-based filter aids and ion exchange resins, etc., generated from the reactor coolant purification system and fuel pool coolant purification system of nuclear power plants are stored for long periods in storage tanks. These radioactive organic wastes are generated on a regular basis during the operation of nuclear power plants.

In order to secure storage space for radioactive organic waste, volume reduction processing technology is needed to efficiently reduce the volume of radioactive organic waste currently in storage.

Patent Document 1 discloses a method for treating radioactively contaminated water in which zeolite powder is added to the radioactively contaminated water to adsorb the radioactive substances, and the zeolite to which the radioactive substances have been adsorbed is separated from the treated water by solid-liquid separation, thereby continuously treating the radioactively contaminated water.

Patent Document 2 discloses a method in which iron ions in or added to radioactive liquid waste are formed as a precipitate together with radioactive nuclides by adjusting the pH of the radioactive liquid waste to within the range of 9 to 12, a magnetic powder consisting of gamma-iron trioxide (γ-Fe ₂ O ₃ ) powder or triiron tetroxide (Fe ₃ O ₄ ) powder is added as a flocculant to the radioactive liquid waste from which the precipitate has been formed, thereby imparting sedimentation properties to the precipitate, and the radioactive liquid waste to which the flocculant has been added is subjected to solid-liquid separation into a precipitate and a supernatant.

Patent Document 3 discloses a radioactive waste liquid treatment system that treats radioactive waste liquid containing alpha nuclides, comprising a water quality adjustment device that adjusts the water quality of the radioactive waste liquid containing alpha nuclides, and a filter that is disposed downstream of the water quality adjustment device and to which the radioactive waste liquid with adjusted water quality is supplied. Patent Document 3 also discloses that colloids of alpha nuclides are generated in radioactive waste liquid whose pH has been adjusted to a range of 4 or more and less than 8 with a pH adjuster, that this colloid is removed with a filter, that at least one of an acid, an oxidizing agent, and a reducing agent for adjusting the water quality may be injected together with an alkali for adjusting the water quality, that ascorbic acid or sulfite, which is a reducing agent, is used as an oxidation-reduction potential adjuster, and that the residual rate of alpha nuclides in the radioactive waste liquid discharged from the filter decreases as the oxidation-reduction potential decreases.

JP 2013-50418 A JP 2010-190749 A JP 2021-120662 A

If the cladding tube of a fuel rod contained in a fuel assembly loaded in the reactor core is damaged, the nuclear fuel material in the fuel rod, namely actinides, which are alpha nuclides such as uranium (U), plutonium (Pu), neptunium (Np), americium (Am) and curium (Cm), will leak into the cooling water. The cooling water containing these alpha nuclides is led to the purification device of the reactor coolant purification system, where each alpha nuclides is removed by the ion exchange resin in the purification device. The alpha nuclides have a long half-life.

Ion exchange resin that has adsorbed alpha nuclides is treated as waste resin. Alpha nuclides, etc. are eluted from this ion exchange resin using an aqueous solution of an organic acid and an aqueous solution of an organic salt. Even if the aqueous solution of an organic acid containing the eluted alpha nuclides, etc. is concentrated through a prescribed process, a large amount of radioactive waste containing long-half-life alpha nuclides will still be generated. It is desirable to reduce the amount of radioactive waste containing long-half-life alpha nuclides generated.

The technologies described in Patent Documents 1 to 3 make it possible to reduce the residual rate of alpha nuclides in radioactive liquid waste.

However, even with these technologies, if the radioactive waste liquid contains fine particles with ionic alpha nuclides attached, a large amount of removal material may be required to remove the fine particles.

The objective of this disclosure is to remove alpha nuclides contained in radioactive liquid waste and microparticles to which ionic alpha nuclides are attached under conditions in which the adsorption performance of the alpha nuclide removal material is fully exhibited, thereby reducing the amount of radioactive waste containing alpha nuclides with long half-lives.

The radioactive waste liquid treatment system of the present disclosure includes a waste liquid treatment unit that treats radioactive waste liquid containing alpha nuclides, and the waste liquid treatment unit includes an alpha nuclide concentration measurement device that measures the alpha nuclide concentration contained in the radioactive waste liquid, a charge determination device that determines the zero charge point of the particles dispersed in the radioactive waste liquid, a pH adjuster injection device that adjusts the pH based on the zero charge point of the particles, and an adsorbent injection device that injects an alpha nuclide removal material into the radioactive waste liquid that has been pH adjusted.

According to the present disclosure, it is possible to remove ionic alpha nuclides contained in radioactive liquid waste and fine particles to which ionic alpha nuclides are attached under conditions in which the adsorption performance of the alpha nuclide removal material is fully exhibited, thereby reducing the amount of radioactive waste containing alpha nuclides with long half-lives.

1 is a flowchart showing a method for treating radioactive liquid waste according to a first embodiment. 1 is a configuration diagram showing an example of a radioactive waste liquid treatment system according to a first embodiment. FIG. 3 is a configuration diagram showing the main parts of the radioactive waste liquid treatment system of FIG. 2. 1 is a graph showing the difference in pH change depending on whether or not fine particles are dispersed in an aqueous solution. 1 is a graph showing the effect of pH on the amount of ionic α-nuclides adsorbed by an α-nuclides removal material. 1 is a graph showing the effect of pH on the amount of fine particles having ionic α-nuclides attached thereto, removed by an α-nuclides removal material. FIG. 4 is a block diagram showing the charge determining device of FIG. 3 . 1 is a flowchart illustrating an example of a charge determination method according to the present disclosure.

This disclosure relates to a radioactive waste liquid treatment system, and in particular to a radioactive waste liquid treatment system that is applied to the treatment of radioactive waste liquid generated during the cleaning of waste resin generated from nuclear power plants and radioactive waste liquid generated during nuclear fuel reprocessing.

Below, examples of the present disclosure are described in detail with reference to the drawings. However, the structures, materials, and various other specific configurations shown in the examples are not limited to those discussed here, and can be appropriately combined or improved without changing the gist of the disclosure. In addition, elements that are not directly related to the present disclosure are not shown.

Example 1 relates to a radioactive waste liquid treatment system that is applied to the treatment of radioactive organic waste generated in a boiling water nuclear power plant.

If the cladding tube of a fuel rod constituting a fuel assembly loaded in the core inside the reactor pressure vessel of a nuclear power plant, for example a boiling water nuclear power plant currently in operation, or a spent fuel assembly stored in a fuel storage pool, is damaged, the nuclear fuel material in the fuel rod (including alpha nuclides uranium, plutonium, neptunium, americium, curium, etc.) 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 the ion exchange resin in the purification device of the reactor coolant purification system. The alpha nuclides that leak into the cooling water in the fuel storage pool are also removed by the ion exchange resin in the purification device of the fuel pool coolant purification system.

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

Figure 1 is a flow chart showing the method for treating radioactive liquid waste according to the first embodiment.

In this diagram, first, a first cleaning process S1 (crud dissolution process) is carried out on the radioactive organic waste (organic waste) containing cation exchange resin that has been removed from the high-dose resin storage tank.

In this first cleaning step S1, the radioactive organic waste is immersed in an aqueous solution of a reducing organic acid (e.g., an aqueous solution of oxalic acid), and the organic acid contained in the aqueous solution dissolves the crud, such as iron oxide, contained in the radioactive organic waste. Radioactive nuclides, such as cobalt-60, contained in the crud move into the aqueous organic acid solution as the crud dissolves.

The reason for using an organic acid in the first cleaning step S1 is that since the organic acid contains carbon and at least one of the elements hydrogen, oxygen, and nitrogen, when the organic acid aqueous solution, which is the cleaning waste liquid generated in the first cleaning step S1, is oxidized using, for example, ozone (waste liquid decomposition step S4 described below), no non-volatile residue is generated in the waste liquid. As the organic acid, for example, formic acid, oxalic acid, acetic acid, or citric acid is preferably used.

The organic acid aqueous solution (clad dissolving solution), which is the cleaning waste liquid generated in the first cleaning process S1 and contains dissolved components of the clad, is subjected to the waste liquid decomposition process S4.

In this waste liquid decomposition step S4, an oxidizing agent such as hydrogen peroxide or ozone is aerated into the aqueous organic acid solution, and the organic acid and organic acid salts are decomposed by the oxidizing action of the oxidizing agent.

After the first cleaning process S1 has been performed and the crud has been removed from the radioactive organic waste, the second cleaning process S2 (radioactive nuclide elution process) is carried out.

In this second cleaning step S2, the radioactive organic waste from which the crud has been removed is immersed in an aqueous solution of an organic acid salt, and the organic acid salt contained in the aqueous solution elutes radioactive nuclides such as alpha nuclides adsorbed to the radioactive organic waste.

The organic acid salt used in the second cleaning step S2 is preferably an organic acid salt that dissociates in an aqueous solution to produce cations that are more easily adsorbed by a cation exchange resin than hydrogen ions. In other words, the organic acid salt contains at least one of hydrogen, oxygen, and nitrogen, and is preferably one that does not produce non-volatile residues in the waste liquid when the organic acid salt aqueous solution, which is the cleaning waste liquid after the second cleaning step S2, is oxidized using, for example, ozone (waste liquid decomposition step S4). As the organic acid salt, it is preferable to use, for example, ammonium salts, barium salts, or cesium salts of formic acid, oxalic acid, acetic acid, or citric acid. Hydrazine formate may also be used as the organic acid salt.

Ammonium salts are decomposed into nitrogen gas and water by oxidation treatment, and therefore can reduce the amount of radioactive waste generated compared to barium salts and cesium salts. Ammonium salts of formic acid, oxalic acid, acetic acid, or citric acid, barium salts, or cesium salts dissociate in aqueous solution to become NH4 ⁺ , Ba2 ⁺ , or Cs ⁺ . ^NH4+ , Ba2 ⁺ , or Cs ⁺ are cations that are more easily adsorbed by cation exchange resins than hydrogen ions.

The wastewater decomposition process S4 is carried out on the aqueous organic acid salt solution, which is the washing wastewater containing eluted radionuclides such as alpha nuclides, generated in the second washing process S2. In the wastewater decomposition process S4, the aqueous organic acid salt solution is aerated with an oxidizing agent such as ozone or hydrogen peroxide, and in the process, the organic acid salt is decomposed by the oxidizing agent.

After the waste liquid decomposition process S4, the alpha nuclide concentration of the residual aqueous solution (radioactive waste liquid) containing the remaining radioactive nuclides is measured (alpha nuclide concentration measurement process S5).

Here, the alpha nuclide concentration can be measured by sampling the radioactive waste liquid and measuring it with an analytical device, or by measuring it with a survey meter.

If the alpha nuclide concentration is equal to or lower than a predetermined concentration in the alpha nuclide concentration measurement process S5, the volume reduction process S10 is performed without performing any process such as alpha nuclide removal. On the other hand, if the alpha nuclide concentration is higher than the predetermined concentration, the charge determination process S6 is performed.

Here, the charge determination step S6 may involve sampling the radioactive waste liquid and measuring it with a charge determination device (described later), or it may be measured online.

After the charge determination process S6, the pH adjustment process S7 is carried out. Then, the radioactive nuclide adsorption and removal process S8 is carried out, followed by the filtering process S9.

The pH adjuster used in the pH adjustment step S7 can be an inorganic acid (hydrochloric acid, sulfuric acid, nitric acid, etc.), an inorganic alkali (sodium hydroxide, calcium hydroxide, magnesium hydroxide, etc.), an organic acid (carboxylic acid, ascorbic acid, etc.), or an organic alkali (ammonium-based, etc.).

Examples of alpha nuclide adsorbents (alpha nuclide removal materials) used in the radioactive nuclide adsorption and removal process S8 include cation exchange resins, Fe oxides, titanic acid compounds, titanate compounds, ferrocyanide compounds, chelating resins, activated carbon, oxine-impregnated activated carbon, and zeolites.

Note that pH is the hydrogen ion exponent.

In the filtering process S9, a cross-flow filter is used to separate the alpha nuclide removal material and solids such as slurry generated by pH adjustment from the waste liquid from which radioactive nuclides have been removed. The above solid-liquid separation may also be performed using a press filter or the like.

The solids and waste liquid separated by the filtering process S9 are each subjected to a concentration process or a dry powder process in the volume reduction process S10, and then a container filling or solidification process S11 is carried out.

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 powdering process is filled into a container and stored, or solidified in the container with a solid agent such as cement.

Next, we will explain an example of the configuration of a radioactive liquid waste treatment system that performs each of the above steps S1 to S11.

Figure 2 is a configuration diagram showing an example of a radioactive waste liquid treatment system according to the first embodiment.

The radioactive waste liquid treatment system 1 shown in this figure includes a chemical cleaning section 10 that treats radioactive organic waste, and a waste liquid treatment section 19 that treats the cleaning waste liquid (radioactive waste liquid) discharged from the chemical cleaning section 10.

Of the various steps shown in FIG. 1, the chemical cleaning section 10 performs a first cleaning step S1 for dissolving the crud and a second cleaning step S2 for eluting radioactive nuclides from the radioactive organic waste.

The chemical cleaning section 10 has a first receiving tank 3, a chemical reaction tank 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. A second receiving tank 11 and an incineration facility 12 are provided downstream of the chemical cleaning section 10. Here, the incineration facility 12 may be a cement solidification facility or may include a cement solidification facility.

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.

The chemical reaction tank 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 tank 4.

The cleaning liquid supply tank 6 is connected to the chemical reaction tank 4 by a cleaning liquid supply pipe 33 equipped with a transfer pump 32.

A return pipe 36 equipped with a transfer pump 34 and a valve 35 is connected to the bottom of the chemical reaction tank 4, allowing the liquid in the chemical reaction tank 4 to be returned to the cleaning liquid supply tank 6.

In addition, an organic acid tank 7, an organic acid salt tank 8, and a transfer water tank 9 are connected to the cleaning liquid supply tank 6.

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

The organic acid salt tank 8 is connected to the cleaning liquid supply tank 6 by a pipe 30 having 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 a pipe 29 downstream of the valve 26.

The transfer water tank 9 is connected to the cleaning liquid supply tank 6 by a pipe 31 having a valve 28. The transfer water tank 9 is filled with water to be used as the transfer water. The pipe 31 is connected to the pipe 30 downstream of the valve 27.

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

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

On the other hand, the waste liquid treatment unit 19 has a waste liquid decomposition device 13, an alpha nuclide concentration measurement device 14, an electric charge determination device 15, an alpha nuclide removal device 16, a pH adjuster injection device 112, an adsorbent injection device 121, a filter treatment device 131, and a treated water recovery tank 18.

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

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

In the waste liquid decomposition device 13, an organic acid aqueous solution (clad dissolving solution) and an organic acid salt aqueous solution (nuclide eluting solution) are stored, and the organic acid and organic acid salt are decomposed by injected oxidizing agents such as hydrogen peroxide or ozone.

An alpha nuclide concentration measuring device 14, a charge determining device 15, and a pH adjuster injection device 112 are connected to the piping 45.

The alpha nuclide removal device 16 is connected to the treated water recovery tank 18 via piping 46. The piping 46 is provided with a filter treatment device 131. In addition, the alpha nuclide removal device 16 is connected to an adsorbent injection device 121.

In the filter processing device 131, for example, the radioactive waste liquid is filtered using a cross-flow filter method using a membrane with a pore size on the order of micrometers or less (1 μm or less), and the alpha nuclide adsorbent that has adsorbed the alpha nuclide from the radioactive waste liquid and the slurry generated by pH adjustment are separated.

A pipe 55 is also connected to the filter treatment device 131. The pipe 55 is connected to the return pipe 36 of the chemical cleaning section 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 generated in the filter treatment device 131 is sent to the return pipe 36 through the pipe 55. In the filter treatment 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 preferable 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 tank 4 and the filtered water from the pipe 55 can be switched.

The timing of transferring the radioactive waste liquid from the chemical cleaning section 10 to the waste liquid treatment section 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 alpha nuclide concentration reaches a predetermined concentration.

Furthermore, a drying powdering device 20 and a solidification facility 21 are provided downstream of the waste liquid treatment unit 19. The treated water recovery tank 18 and the drying powdering device 20 are connected via a pipe 48. A transfer pump 47 is provided on the pipe 48. The drying powdering device 20 and the solidification facility 21 are connected via a pipe 49. Note that a radioactive waste liquid concentrator may be used instead of the drying powdering device 20.

Figure 3 is a schematic diagram showing the main parts of the radioactive waste liquid treatment system shown in Figure 2.

Figure 3 shows the detailed configuration of the waste liquid treatment unit 19, from the alpha nuclide concentration measurement device 14 to the filter treatment device 131.

An alpha nuclide concentration measuring device 14 and an electric charge determining device 15 are connected to the piping 45 upstream of the alpha nuclide removal device 16. The electric charge determining device 15 may not be connected to the waste liquid treatment unit 19, but may instead determine the electric charge of the sampled radioactive waste liquid and have the result of this determination reflected in the amount of pH adjuster injected by the pH adjuster injection device 112.

The alpha nuclide removal device 16 is composed of a waste liquid treatment tank that contains radioactive waste liquid sent from the waste liquid decomposition device 13 through piping 45.

The alpha nuclide concentration of the radioactive waste liquid is measured by the alpha nuclide concentration measuring device 14, and if the alpha nuclide concentration is equal to or lower than a predetermined concentration, the liquid is returned to the return pipe 36 (Figure 2) via pipe 54 and may be circulated as circulating water.

When the alpha nuclide concentration is equal to or higher than a predetermined concentration, the charge of the radioactive waste liquid is measured by the charge determination device 15. After that, a pH adjuster is injected by the pH adjuster injection device 112 to adjust the pH, and the radioactive waste liquid is supplied to the alpha nuclide removal device 16. Note that the pH adjuster injection device 112 may be connected to the alpha nuclide removal device 16 instead of the piping 45. Even with this configuration, the pH can be adjusted in the same way.

The alpha nuclide removal device 16 is configured to inject an alpha nuclide removal material (adsorbent) from an adsorbent injection device 121. This removes the alpha nuclides contained in the radioactive liquid waste. The radioactive liquid waste is then supplied to the filter treatment device 131 through piping 46. The filtered water, from which the adsorbent has been filtered in the filter treatment device 131, is supplied to the treated water recovery tank 18 (Figure 2) through piping 46. The filtered water may be returned to the return piping 36 (Figure 2) through piping 55 and circulated as circulating water.

Next, we will explain charge determination.

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

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

As shown in this figure, in the case of an aqueous solution containing only ions without dispersed microparticles (□), the pH is about 4 when 0 mL of NaOH is added initially, and when the amount added exceeds 0.1 mL, the pH rises from 4 to about 10 as the amount added increases. On the other hand, when microparticles (FeOOH) are dispersed (○), the pH is about 6 in the initial state, and due to the pH buffering effect of the microparticles, the pH rises very slowly even when the amount added increases, remaining below pH 7.

From the above, it can be seen that the conditions for adjusting the pH differ depending on whether or not microparticles are present. The charge of the microparticles is determined from the intersection of two curves obtained from the data shown in this figure, and this intersection is called the "point of zero charge." In this figure, the pH of the zero charge point is approximately 6, and a range lower than the pH of the zero charge point is determined to be a positive charge, and a range higher than the pH of the zero charge point is determined to be a negative charge.

The pH buffering effect of the microparticles is believed to be due to hydroxide ions (OH ^- ) adsorbed to the surface of the microparticles. Therefore, even after OH ^- is bound to and neutralized by the ions of the α-nuclear species dissolved in the liquid and the ions of the α-nuclear species adsorbed to the surface of the microparticles, further added OH ^- is adsorbed, and the increase in the pH of the liquid is suppressed.

Next, we will explain the pH conditions under which the adsorption performance of the alpha nuclide removal material is fully demonstrated when removing ionic alpha nuclides and fine particles with ionic alpha nuclides attached thereto.

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 shows the pH of the aqueous solution, and the vertical axis shows the amount of ionic α-nuclides adsorbed by the α-nuclide removal material, _Qeq . The unit of _Qeq is the amount of adsorption (mg) per 1 g of the α-nuclide removal material.

This figure shows the case where magnetite (Fe ₃ O ₄ ) is used as an α nuclide remover in an aqueous solution containing only ions without dispersed fine particles such as goethite (FeOOH). Americium (Am) is used as the α nuclide.

As shown in the figure, _Qeq increases with increasing pH. Therefore, in the case of an aqueous solution containing only ions, a pH of 10 is desirable from the viewpoint of removing alpha nuclides.

Figure 6 is a graph showing the effect of pH on the amount of microparticles with ionic alpha nuclides attached by an alpha nuclide removal material.

In this figure, magnetite ( _Fe3O4 ) is used as the α nuclide removal material, and goethite ( _FeOOH ) is used as the fine particles to which ionic α nuclide is attached, as an example. The charge of the α nuclide removal material is determined by a method using a graph such as that shown in Figure 4, with the pH of the zero charge point being approximately 8, and the charge being positive in the range below the pH of the zero charge point, and negative in the range above the pH of the zero charge point.

As shown in Figure 6, under conditions of pH 4 or 10 where the charges of the alpha nuclide removal material and the microparticles are of the same sign, the amount of microparticles with ionic alpha nuclides attached to them removed by the alpha nuclide removal material is small. In contrast, under conditions of pH 6 where the charges of the alpha nuclide removal material and the microparticles are of opposite signs, the amount of microparticles with ionic alpha nuclides attached to them removed by the alpha nuclide removal material is relatively large.

From the above results (Figures 5 and 6), and from Figure 4, by adjusting the pH to the alkaline side (in this embodiment, the pH is adjusted to about pH 8 for an aqueous solution containing only ions without dispersed microparticles) within the range of conditions where the charges of the alpha nuclide removal material and the microparticles are of opposite signs, and then removing the alpha nuclides with the alpha nuclide removal material, both ionic alpha nuclides and microparticles with ionic alpha nuclides attached can be removed under pH conditions where the adsorption performance is fully demonstrated.

In FIG. 2, the filtered water supplied to the treated water recovery tank 18 through the pipe 46 is supplied in a predetermined amount to the dry powder processing device 20 through the pipe 48 by driving the transfer pump 47. The filtered water containing radioactive nuclides other than alpha nuclides is powdered in the dry powder processing device 20 (volume reduction step S10 in FIG. 1). The obtained powder has had most of the long half-life alpha nuclides removed in the processing up to step S9.

The powder produced by the dry powder generator 20 is then transferred to the solidification equipment 21 (or filling equipment). In the solidification equipment 21, the powder is filled into a solidification container, and a solidification material (e.g., cement) is injected into the solidification container. The powder in the solidification container is solidified by the solidification material (container filling or solidification step S11).

The solidification container is sealed and kept in a storage area. If filling equipment is used, the container is filled with powder, sealed, and then kept in a storage area.

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

According to this embodiment, both ionic alpha nuclides and fine particles with ionic alpha nuclides attached can be removed under pH conditions that fully demonstrate the adsorption performance of the alpha nuclide removal material, and radioactive waste containing alpha nuclides can be reduced.

In this embodiment, the charge determination (charge determination of the fine particles) is performed by the charge determination device 15, but literature values for the point of zero charge (pzc) specific to the fine particle material may be stored in a database, and the above-mentioned processes such as pH adjustment may be performed by referring to these values.

Further, goethite (FeOOH) has been used as an example of fine particles in the above description, but other applicable fine particles include magnetite (Fe ₃ O ₄ ), ferrite (Fe ₂ O ₃ ), silica fine particles, alumina fine particles, and the like.

As another preferred embodiment of the present disclosure, a radioactive waste liquid treatment system according to Example 2 will be described.

Example 2 is also a radioactive waste liquid treatment system applied to the treatment of radioactive organic waste generated in a boiling water nuclear power plant.

In the radioactive waste liquid treatment system of Example 2, the amount of pH adjuster is determined from the charge measurement results of FIG. 4 obtained by the charge determination device 15 in charge determination S6, and the pH is adjusted by injecting a pH adjuster using the pH adjuster injector 112, and then alpha nuclides are removed using the alpha nuclide removal device 16. Note that the configuration diagram is the same as that of FIG. 3 shown in Example 1.

In Example 1, in order to remove both the ionic α-nuclides and the fine particles with ionic α-nuclides attached shown in Figures 5 and 6 under pH conditions that fully demonstrate the adsorption performance, the pH was adjusted to be on the alkaline side (about pH 8 in this example) within the range of conditions in which the charges of the α-nuclides removal material and the fine particles have opposite signs as shown in Figure 4, and then the α-nuclides were removed by the α-nuclides removal material.

In contrast, in Example 2, the pH is not controlled by the range of pH using the results in Figure 4, but by adjusting the amount of pH adjuster added. From the results in Figure 4, the range of 0.1 M NaOH added under conditions where the charges of the alpha nuclide removal material and the fine particles have opposite signs is 0.2 mL to 2 mL (Figure 4 shows up to 1 mL). Therefore, regardless of the presence or absence of fine particles in the liquid, by adding NaOH in the above range, both ionic alpha nuclides and fine particles with ionic alpha nuclides attached can be removed under pH conditions where the adsorption performance is fully demonstrated.

For example, when 0.3 mL of 0.1 M NaOH is added, the pH of the liquid in which the fine particles are not dispersed is about 10, and the pH is adjusted to a high pH (alkaline) condition as shown in FIG. 5, and the amount of ionic alpha nuclides adsorbed by the alpha nuclide removal material increases. On the other hand, when fine particles are dispersed in the liquid, the pH becomes about 6 due to the pH buffering effect of the fine particles. Therefore, as shown in FIG. 6, the pH is adjusted to a condition in which the charges of the alpha nuclide removal material and the fine particles are opposite signs, and the amount of fine particles adsorbed by the alpha nuclide removal material with ionic alpha nuclides attached increases. This is because when the charges of the alpha nuclide removal material and the fine particles are opposite signs, the alpha nuclide removal material and the fine particles are easily coagulated due to electrical affinity between them. This makes it easier to perform processes such as precipitation separation and filtration separation.

According to this embodiment, regardless of the presence or absence of fine particles in the liquid, both ionic alpha nuclides and fine particles with ionic alpha nuclides attached can be removed under pH conditions that fully demonstrate the adsorption performance of the alpha nuclide removal material, thereby reducing radioactive waste containing alpha nuclides.

Next, we will explain the zero charge point determination device and method shown in Figure 4.

Figure 7 is a diagram showing the configuration of the charge determination device in Figure 3.

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

The alkaline treatment tanks 211 and 212 are capable of collecting radioactive waste liquid containing alpha nuclides through a pipe branched off from the pipe 45. A pH adjuster (alkaline agent) such as 0.1 M NaOH can be added to the alkaline treatment tanks 211 and 212.

A filter section 201 is provided between the pipe 45 and the alkaline treatment tank 211. The radioactive waste liquid introduced into the alkaline treatment tank 211 is filtered out of fine particles such as goethite (FeOOH) in the filter section 201.

The calculation unit 220 acquires the measurement data (such as the data shown in FIG. 4) obtained in the alkaline treatment tanks 211 and 212, and calculates the zero charge point of the above-mentioned fine particles. In addition, it is preferable that the calculation unit 220 has a function of controlling the amount of pH adjuster added.

Figure 8 is a flowchart showing an example of a charge determination method (a method for determining the zero charge point) according to the present disclosure.

As shown in this figure, when determining the charge of radioactive waste liquid containing alpha nuclides, two waste liquid samples (radioactive waste liquid) are collected (step S50). One of the waste liquid samples is filtered to remove solids (fine particles such as goethite (FeOOH)) (step S51). Both waste liquid samples are treated with alkali and the pH is measured (step S52). The alkali treatment is performed by adding a pH adjuster (alkaline agent) such as 0.1 M NaOH. The zero charge point of the fine particles is then calculated from the intersection of the curve of pH versus the amount of alkali added (step S53).

Below, we summarize preferred embodiments of this disclosure.

The radioactive liquid waste treatment system is equipped with a filter treatment device that removes alpha nuclides by filtration from radioactive liquid waste into which an alpha nuclide removal material has been injected.

The zero charge point of a microparticle is determined when the alpha nuclide concentration is equal to or greater than a predetermined concentration.

The pH adjuster injection device adjusts the pH of the radioactive waste liquid so that it is in a range equal to or greater than the pH value corresponding to the zero charge point of the microparticles and equal to or less than the pH value corresponding to the zero charge point of the alpha nuclide removal material.

The pH adjuster injection device injects a pH adjuster so that the pH of the radioactive waste liquid is greater than 7.

The charge determination device performs a neutralization titration and determines the zero charge point of the microparticles based on the results.

The charge determination device includes a filter unit that removes fine particles from the radioactive waste liquid, a first pH adjustment treatment tank configured to inject a pH adjuster into the liquid sent from the filter unit from which the fine particles have been removed, a second pH adjustment treatment tank configured to inject a pH adjuster into the radioactive waste liquid containing the fine particles, and a calculation unit, and 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.

The zero charge point is calculated from the intersection of two curves that show the pH versus the amount of pH adjuster added in the first pH adjustment treatment tank and the second pH adjustment treatment tank, which are created based on the measurement data.

The pH adjuster injection device adjusts the pH of the radioactive waste liquid so that the charge of the microparticles and the charge of the alpha nuclide removal material have opposite signs.

The pH adjuster injection device injects a pH adjuster so that the pH of the radioactive waste liquid is greater than 7, in other words, so that the radioactive waste liquid becomes alkaline.

The pH adjuster includes at least one of the following substances: 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.

The alpha nuclide removal material includes at least one of the following: cation exchange resin, Fe oxide, titanic acid compound, titanate compound, ferrocyanide compound, chelating resin, activated carbon, oxine-impregnated activated carbon, and zeolite.

The fine particles include at least one of iron oxide fine particles, including goethite, magnetite, or ferrite, silica fine particles, and alumina fine particles.

The filter processing device is configured as a cross-flow filter using a membrane with a pore size of 1 μm or less.

The contents of this disclosure are not limited to the above-mentioned embodiments and examples, but include various modified examples. For example, the above-mentioned examples are described in detail to easily explain the contents of this disclosure, and are not necessarily limited to those having all of the configurations described.

1: Radioactive liquid waste treatment system, 4: Chemical reaction tank, 7: Organic acid tank, 8: Organic acid salt tank, 9: Water transfer tank, 10: Chemical cleaning section, 12: Incineration equipment, 13: Liquid waste decomposition equipment, 14: Alpha nuclide concentration measurement device, 15: Charge determination device, 16: Alpha nuclide removal device, 19: Liquid waste treatment unit, 20: Drying powder device, 21: Solidification equipment, 112: pH adjuster injection device, 121: Adsorbent injection device, 131: Filter treatment device, 201: Filter section, 211, 212: Alkaline treatment tank, 220: Calculation unit, S1: First cleaning process, S2: Second cleaning process, S4: Liquid waste decomposition process, S5: Alpha nuclide concentration measurement, S6: Charge determination, S7: pH adjustment process, S8: Adsorption and removal of radioactive nuclides, S9: Filter treatment process.

Claims (15)

A waste liquid treatment unit is provided for treating radioactive waste liquid containing alpha nuclides,
The waste liquid treatment unit includes:
an α nuclide concentration measuring device for measuring the α nuclide concentration contained in the radioactive liquid waste;
a charge determination device for determining a zero charge point of the particles dispersed in the radioactive waste liquid;
a pH adjuster injection device for adjusting the pH based on the point of zero charge of the microparticle;
an adsorbent injection device that injects an alpha nuclide removal material into the radioactive waste liquid after the pH adjustment has been performed. The radioactive waste liquid treatment system according to claim 1, wherein the waste liquid treatment unit further comprises a filter treatment device that removes the alpha nuclides by filtration from the radioactive waste liquid into which the alpha nuclide removal material has been injected. The radioactive waste liquid treatment system according to claim 1, wherein the zero charge point of the microparticle is determined when the alpha nuclide concentration is equal to or greater than a predetermined concentration. The radioactive waste liquid treatment system according to claim 3, wherein the pH adjuster injection device adjusts the pH of the radioactive waste liquid to a value equal to or higher than the pH value corresponding to the zero charge point of the microparticles and equal to or lower than the pH value corresponding to the zero charge point of the alpha nuclide removal material. The radioactive waste liquid treatment system according to claim 4, wherein the pH adjuster injection device injects a pH adjuster so that the pH of the radioactive waste liquid is greater than 7. The radioactive waste liquid treatment system according to claim 1, wherein the charge determination device performs neutralization titration and determines the zero charge point of the microparticles based on the results. The charge determining device is
A filter unit for removing the fine particles from the radioactive liquid waste;
a first pH adjustment treatment tank configured to inject a pH adjuster into the liquid sent from the filter unit from which the fine particles have been removed from the radioactive liquid waste;
A second pH adjustment treatment tank configured to inject the pH adjuster into the radioactive waste liquid containing the fine particles;
A calculation unit,
2. The radioactive waste liquid treatment system according to claim 1, wherein the calculation unit calculates the zero charge point of the particles from measurement data obtained in the first pH adjustment treatment tank and the second pH adjustment treatment tank. The radioactive waste liquid treatment system according to claim 7, wherein the zero charge point is calculated from the intersection of two curves that show the pH versus the amount of the pH adjuster added in the first pH adjustment treatment tank and the second pH adjustment treatment tank, which are created based on the measurement data. The radioactive waste liquid treatment system according to claim 3, wherein the pH adjuster 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 have opposite signs. The radioactive waste liquid treatment system according to claim 9, wherein the pH adjuster injection device injects a pH adjuster so that the pH of the radioactive waste liquid is greater than 7. A method for treating radioactive liquid waste containing alpha nuclides, comprising the steps of:
Measuring the concentration of alpha nuclides contained in the radioactive liquid waste;
determining a zero charge point of particulates dispersed in the radioactive liquid waste;
adjusting the pH based on the point of zero charge of the microparticle;
and injecting an alpha nuclide removal material into the radioactive waste liquid after the pH adjustment. An apparatus for determining a zero charge point of a particle in a radioactive waste liquid containing an alpha nuclide and in which the particle is dispersed, comprising:
A filter unit for removing the fine particles from the radioactive liquid waste;
a first pH adjustment treatment tank configured to inject a pH adjuster into the liquid sent from the filter unit from which the fine particles have been removed from the radioactive liquid waste;
A second pH adjustment treatment tank configured to inject the pH adjuster into the radioactive waste liquid containing the fine particles;
A calculation unit,
The calculation unit calculates the zero charge point of the particles from measurement data obtained in the first pH adjustment treatment tank and the second pH adjustment treatment tank. The charge determination device according to claim 12, wherein the zero charge point is calculated from the intersection of two curves that show the pH versus the amount of the pH adjuster added in the first pH adjustment treatment tank and the second pH adjustment treatment tank, which are created based on the measurement data. 1. A method for determining a point of zero charge of a particle in a radioactive waste liquid containing an alpha nuclide, the particle being dispersed therein, comprising:
removing the particulates from the radioactive liquid waste;
a first pH adjustment step of injecting a pH adjuster into the liquid from which the fine particles have been removed from the radioactive liquid waste;
A second pH adjustment step of injecting the pH adjuster into the radioactive waste liquid containing the fine particles;
A charge determination method, comprising: calculating a zero charge point of the microparticle from measurement data obtained in the first pH adjustment step and the second pH adjustment step. The charge determination method according to claim 14, wherein the zero charge point is calculated from the intersection of two curves that show the pH versus the amount of the pH adjuster added in the first pH adjustment process and the second pH adjustment process, the curves being created based on the measurement data.

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