Radioactive waste liquid processing apparatus

Abstract

To reduce an amount of an adsorbent containing an α nuclide, generated when removing the α nuclide from radioactive waste liquid containing the α nuclide, a β nuclide, and a γ nuclide, and to facilitate processing of the radioactive waste liquid from which the α nuclide has been removed.SOLUTION: A radioactive waste liquid processing apparatus for removing an α nuclide from radioactive waste liquid containing the α nuclide includes a configuration for bringing the radioactive waste liquid into contact with an adsorbent, wherein the adsorbent is an oxine-impregnated active carbon.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present disclosure relates to a radioactive liquid waste treatment apparatus. [Background technology]

[0002] One technique for removing radionuclides from radioactive liquid waste is to use adsorbents.

[0003] Patent Document 1 discloses a method for removing alpha nuclides from radioactive liquid waste by injecting a pH adjuster into the radioactive liquid waste containing alpha nuclides and supplying an alpha nuclide adsorbent to the radioactive liquid waste containing the alpha nuclides and the pH adjuster.

[0004] Patent Document 2 discloses a method for treating radioactive liquid waste, which comprises supplying radioactive liquid waste containing colloidal matter, particulate matter having a particle size larger than that of colloidal matter, and radioactive material to a filtration device to remove the particulate matter, removing the colloidal matter contained in the radioactive liquid discharged from the filtration device with an electrostatic filter, and removing the radioactive material contained in the radioactive liquid from which the colloidal matter has been removed with an adsorption device.

[0005] Patent Document 3 discloses a radioactively contaminated water decontamination system which controls the piping section to connect a first adsorption tower and a second adsorption tower in series, one of which is upstream and the other is downstream, and passes radioactively contaminated water through the first adsorption tower and the second adsorption tower. When the measurement value measured by a measuring section installed between the first adsorption tower and the second adsorption tower exceeds a set value, an output is issued to indicate that the upstream adsorption tower needs to be replaced.

[0006] Moreover, Patent Documents 1 to 3 disclose oxine-impregnated activated carbon as an example of an adsorbent. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] JP 2020-187030 A [Patent Document 2] JP 2015-040826 A [Patent Document 3] JP 2014-016211 A Summary of the Invention [Problem to be solved by the invention]

[0008] As part of the decommissioning process for the Fukushima Daiichi Nuclear Power Plant (hereafter referred to as "1F"), fuel debris removal work is planned. During the fuel debris removal work, a large amount of reactor water will be injected into the reactor containment vessel (PCV), and when this water comes into contact with the fuel debris, the fuel debris components, namely actinides, which are alpha nuclides such as Pu (plutonium), Am (americium), Cm (curium), U (uranium), and Np (neptunium), will dissolve into the water.

[0009] In addition, fission products produced during the operation of the reactor consist mainly of the alkali metal Cs (gamma nuclide) and the alkaline earth metal Sr (beta nuclide), and it has been reported that they are present in large amounts in the contaminated water at 1F.

[0010] Therefore, the contaminated water accumulated in the PCV of 1F and the alpha nuclide-containing waste liquid generated during the fuel debris removal work contain not only alpha nuclides, but also beta and gamma nuclides.

[0011] When treating such radioactive liquid waste, if alpha nuclides are removed using highly selective oxine-impregnated activated carbon, the amount of radiation emitted from the treated adsorbent can be reduced, potentially simplifying the shielding used in the equipment used to post-treat the treated adsorbent.

[0012] Oxine has the property of easily forming complexes with transition metals but not easily forming complexes with alkali metals or alkaline earth metals, and is therefore considered to be a candidate for selective adsorption and removal of alpha nuclides when treating radioactive liquid waste containing multiple nuclides.

[0013] Oxine-impregnated activated carbon is activated carbon with a very large surface area impregnated with oxine. Oxine-impregnated activated carbon particles are dispersed in radioactive liquid waste to adsorb alpha nuclides, and then the solid-liquid separation is performed by precipitation or filtration, allowing the removal of alpha nuclides from the radioactive liquid waste.

[0014] Patent Documents 1 to 3 exemplify oxine-impregnated activated carbon. However, it is not clear how to use oxine-impregnated activated carbon to reduce the size of the device, to reduce radioactive waste, or to solve other problems, and there is thought to be room for improvement.

[0015] An object of the present disclosure is to reduce the amount of adsorbent containing alpha nuclides that is generated when removing alpha nuclides from radioactive liquid waste containing alpha, beta and gamma nuclides, and to facilitate the treatment of radioactive liquid waste from which the alpha nuclides have been removed. [Means for solving the problem]

[0016] The radioactive waste liquid treatment device of the present disclosure is a device for removing alpha nuclides from radioactive waste liquid containing alpha nuclides, and has a configuration in which the radioactive waste liquid is contacted with an adsorbent, and the adsorbent is oxine-impregnated activated carbon. Effect of the Invention

[0017] According to the present disclosure, it is possible to reduce the amount of adsorbent containing alpha nuclides that is generated when removing alpha nuclides from radioactive liquid waste containing alpha, beta and gamma nuclides, and to facilitate the treatment of radioactive liquid waste from which the alpha nuclides have been removed. [Brief description of the drawings]

[0018] [Figure 1] FIG. 1 is a schematic diagram showing an apparatus for treating radioactive liquid waste containing α-nuclides according to a first embodiment. [Diagram 2] FIG. 1 is a schematic diagram showing an apparatus for treating radioactive liquid waste containing α-nuclides according to a second embodiment. [Diagram 3]1 is a graph showing the results of an adsorption test using oxine-impregnated activated carbon with particle sizes of 300 to 840 μm. [Figure 4] 1 is a graph showing the results of an adsorption test using oxine-impregnated activated carbon with particle sizes of 45 to 50 μm. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0019] The present disclosure relates to a radioactive waste liquid treatment apparatus (radioactive waste liquid treatment apparatus containing α-nuclides) that selectively removes α-nuclides from radioactive liquid waste containing α-nuclides, β-nuclides and γ-nuclides.

[0020] An embodiment of the present disclosure will be described below. In this specification, the term "equipment" refers to a component that may be replaced with "unit." EXAMPLES

[0021] Example 1 relates to an apparatus for treating radioactive liquid waste containing α-nuclides, which has a batch-type adsorption tank.

[0022] FIG. 1 is a schematic diagram showing the configuration of an apparatus for treating radioactive liquid waste containing α-nuclides according to this embodiment.

[0023] In this figure, an α-nuclide-containing radioactive waste liquid treatment device 1 has an adsorption tank facility 2, an adsorbent supply facility 3, and a solid-liquid separation facility 4. The adsorption tank facility 2 is a facility for storing α-nuclide-containing radioactive waste liquid, and has an adsorption tank. The adsorption tank facility 2 is configured so that α-nuclide-containing radioactive waste liquid is supplied through a connection pipe 5.

[0024] An agitator for agitating the stored liquid is provided inside the adsorption tank. The adsorption tank equipment 2 and the solid-liquid separation equipment 4 are connected by a connection pipe 7. The connection pipe 7 has a transfer pump for transferring the liquid or slurry resulting from the treatment in the adsorption tank equipment 2 to the solid-liquid separation equipment 4. The adsorbent supply equipment 3 is equipment for supplying the adsorbent to the adsorption tank equipment 2, and includes a storage tank for a slurry containing the adsorbent, and a transfer pump for transferring the slurry to the adsorption tank equipment 2. The adsorption tank equipment 2 and the adsorbent supply equipment 3 are connected by a connection pipe 6. The transfer pump of the adsorbent supply equipment 3 may be disposed in the connection pipe 6.

[0025] In solid-liquid separation equipment 4, the used adsorbent is removed from the adsorption-treated liquid produced in adsorption tank equipment 2. In this case, the adsorbent (used adsorbent) that has settled at the bottom of the adsorption tank in adsorption tank equipment 2 may also be transferred to solid-liquid separation equipment 4 together with the adsorption-treated liquid, and subjected to solid-liquid separation treatment. The filtrate separated in solid-liquid separation equipment 4 is discharged from connection piping 8 as adsorption-treated water.

[0026] Powdered oxine-impregnated activated carbon is used as the α nuclide adsorbent, which is the adsorbent supplied from the adsorption tank supply equipment 3 to the adsorption tank equipment 2. The oxine-impregnated activated carbon is activated carbon impregnated with oxine. In this embodiment, coconut shell activated carbon is used as the activated carbon. Note that the activated carbon is not limited to coconut shell activated carbon, and may be one manufactured using coal, pitch, wood, or the like as a raw material.

[0027] Here, oxine is a substance represented by the following structural formula (1) and is also called 8-hydroxyquinoline.

[0028] [ka]

[0029] The solid-liquid separation equipment 4 preferably includes a cross-flow filter equipment and a cartridge filter equipment. The cross-flow filter equipment is configured to remove moisture from the adsorption-treated liquid until the solid content concentration reaches a few percent, and to concentrate the concentration of the solid components (adsorbent) contained therein. The cartridge filter equipment is configured to further remove moisture from the cross-flow concentrated water resulting from the solid content concentration treatment in the cross-flow filter equipment, and to convert it into sludge until the solid content concentration reaches several tens of percent.

[0030] A description will be given of a treatment method of this embodiment using the α-nuclide-containing radioactive liquid waste treatment device 1. In the treatment method of α-nuclide-containing radioactive liquid waste of this embodiment, radioactive liquid waste containing α-nuclides generated from a nuclear power plant where a core meltdown or the like has occurred is treated.

[0031] Radioactive liquid waste containing alpha nuclides is supplied to the adsorption tank equipment 2. By driving a transfer pump installed in the connecting pipe 6, the adsorbent slurry is supplied from the adsorption tank supply equipment 3 to the adsorption tank equipment 2 through the connecting pipe 6. By driving the agitator in the adsorption tank, the radioactive liquid waste containing alpha nuclides and the adsorbent in the adsorption tank are stirred, and the alpha nuclides are adsorbed by the adsorbent. After the adsorption process, by driving a transfer pump installed in the connecting pipe 7, the radioactive liquid waste containing the adsorbent with the alpha nuclides adsorbed is transferred from the adsorption tank equipment 2 to the solid-liquid separation equipment 4.

[0032] In the solid-liquid separation equipment 4, the adsorbent is turned into sludge by solid concentration treatment using a cross-flow filter equipment and dehydration treatment using a cartridge filter equipment. Thereafter, the sludge containing alpha-nuclides is taken out from the alpha-nuclides-containing radioactive liquid waste treatment equipment 1.

[0033] As described above, the treatment method using the α-nuclide-containing radioactive liquid waste treatment apparatus 1 makes it possible to remove the α-nuclide from the radioactive liquid waste containing the α-nuclide as sludge.

[0034] The oxine-impregnated activated carbon used as the α-nuclide adsorbent in this embodiment is preferably a powder with a small particle size and a large specific surface area, because the area of ​​contact between the α-nuclide-containing radioactive liquid waste and the oxine becomes large, which is advantageous in that the adsorption speed becomes faster and the adsorption capacity becomes larger.

[0035] Therefore, according to this embodiment, the amount of adsorbent used when removing α-nuclides from radioactive liquid waste containing α-nuclides can be reduced. Also, compared to Example 2 described later, the amount of α-nuclides adsorption represented by the U adsorption rate per unit weight of the adsorbent is larger. EXAMPLES

[0036] Example 2 relates to an apparatus for treating radioactive liquid waste containing α-nuclides, which has a column-type adsorption tower.

[0037] FIG. 2 is a schematic diagram showing the configuration of the apparatus for treating radioactive liquid waste containing α-nuclides according to this embodiment.

[0038] In this figure, the α-nuclide-containing radioactive waste liquid treatment device 1A has a waste liquid storage tank 2A ​​and an adsorption tower equipment 3A. The waste liquid storage tank 2A ​​stores radioactive waste liquid containing α-nuclide and supplies it to the adsorption tower equipment 3A. The waste liquid storage tank 2A ​​is configured so that radioactive waste liquid containing α-nuclide is supplied to it through a connecting pipe 5A. The adsorption tower equipment 3A has one or more adsorption towers 4A containing an α-nuclide adsorbent. The waste liquid storage tank 2A ​​and the adsorption tower equipment 3A are connected by a connecting pipe 6A. In the adsorption tower equipment 3A, the α-nuclide-containing radioactive waste liquid is passed through the adsorption tower 4A, and the α-nuclide is adsorbed by the α-nuclide adsorbent, thereby removing the α-nuclide from the radioactive waste liquid containing α-nuclide.

[0039] The adsorbent packed in the adsorption tower 4A is oxine-impregnated activated carbon.

[0040] A treatment method of this embodiment using the α-nuclide-containing radioactive liquid waste treatment device 1A will be described. In the treatment method of α-nuclide-containing radioactive liquid waste of this embodiment, radioactive liquid waste containing α-nuclides generated from a nuclear power plant where a core meltdown or the like has occurred is treated.

[0041] The radioactive waste liquid containing alpha nuclides stored in the waste liquid storage tank 2A ​​is supplied from the waste liquid storage tank 2A ​​to the adsorption tower 4A of the adsorption tower equipment 3A through the connecting pipe 6A by driving the transfer pump installed in the connecting pipe 6A. In the adsorption tower 4A, the alpha nuclides are removed by contacting the loaded adsorbent with the radioactive waste liquid. Therefore, the liquid discharged from the adsorption tower 4A does not contain alpha nuclides. This liquid is discharged from the connecting pipe 7A as treated water.

[0042] The oxine-impregnated activated carbon used as the α-nuclide adsorbent in this embodiment is granular. The reason is that by filling the adsorption tower 4A with granular activated carbon having a relatively large particle size, the flow resistance in the adsorption tower 4A can be reduced, and the pressure difference when the radioactive waste liquid is passed through can be reduced, making the water passing treatment easier.

[0043] According to this embodiment, the amount of adsorbent used when removing alpha nuclides from radioactive liquid waste containing alpha nuclides can be reduced. In addition, compared to Example 1, there is an advantage that solid-liquid separation treatment of the adsorbent is not required.

[0044] Oxine-impregnated activated carbon has a high adsorption rate for actinides, which are the alpha nuclides to be removed, and a low adsorption rate for alkali metals and alkaline earth metals, such as Cs and Sr, which are beta or gamma nuclides. Therefore, in both the treatment methods of Example 1 and Example 2, it is possible to selectively remove alpha nuclides from radioactive liquid waste containing alpha, beta and gamma nuclides. This makes it possible to reduce the amount of radioactive material contained in the waste adsorbent sludge generated after treatment. In this case, the beta and gamma nuclides remaining in the radioactive liquid waste are treated separately.

[0045] Below, we will explain the results of an adsorption test using uranium (U), a representative example of an alpha nuclide, with oxine-impregnated activated carbon.

[0046] FIG. 3 is a graph showing the results of an adsorption test using oxine-impregnated activated carbon with particle sizes of 300 to 840 μm. The horizontal axis shows the oxine impregnation rate, and the vertical axis shows the U adsorption rate (uranium adsorption rate) per unit weight of the adsorbent. Here, the unit of the oxine impregnation rate is weight %, i.e., wt.%. In other words, it is a percentage with the sum of the weight of the impregnated oxine and the weight of the activated carbon as the denominator. The denominator of the U adsorption rate is the weight of the activated carbon before oxine was impregnated.

[0047] As shown in this figure, when oxine-impregnated activated carbon with particle sizes of 300 to 840 μm is used, the U adsorption rate is an increasing function in the range of oxine impregnation rates from 9 wt.% to 20 wt.%. However, when the oxine impregnation rate is 15 wt.% or more, the increase in the U adsorption rate becomes smaller. Therefore, when the oxine impregnation rate is 15 wt.% or more, the effect of improving the U adsorption rate by oxine impregnation cannot be expected to be sufficient.

[0048] Fig. 4 is a graph showing the results of an adsorption test using oxine-impregnated activated carbon with particle sizes of 45 to 50 µm. The horizontal axis shows the oxine impregnation rate, and the vertical axis shows the U adsorption rate per unit weight of the adsorbent. In other words, the horizontal and vertical axes are the same as those in Fig. 3. For comparison, this figure also shows the results of an adsorption test using oxine-impregnated activated carbon with particle sizes of 300 to 840 µm (Fig. 3).

[0049] As shown in FIG. 4, when oxine-impregnated activated carbon with a particle size of 45 to 50 μm is used, the U adsorption rate is more than three times higher when the oxine impregnation rate is 20 wt.% than when it is 9 wt.%.

[0050] 3 and 4 show that smaller particle size allows for a higher U adsorption rate when the oxine impregnation rate is increased.

[0051] The reason for this will be explained next.

[0052] It is believed that as the oxine impregnation rate increases, the oxine particles begin to stack. In other words, it is believed that there is a transition from monolayer adsorption to multilayer adsorption. When the particle size is 300-840 μm, up to an oxine impregnation rate of 15 wt.%, oxine forms a monolayer on the surface of the activated carbon particles, and since most of the impregnated oxine molecules come into contact with the liquid to be treated, it is believed that almost the entire amount of the impregnated oxine contributes to the adsorption site for alpha nuclides.

[0053] However, when the entire surface of the activated carbon is covered with oxine, the adsorption proceeds to a multilayer structure in which other oxines are layered on the oxine adsorbed on the surface, and it is considered that many oxine molecules do not come into contact with the liquid to be treated. Therefore, it is considered that the oxine adsorption rate reaches the threshold value because it becomes difficult to increase when it shifts from monolayer adsorption to multilayer adsorption.

[0054] In the case of oxine-impregnated activated carbon with a particle size of 45 to 50 μm, the U adsorption rate is high even when the oxine impregnation rate is 20 wt.%. This is thought to be because when the particle size is relatively small, the apparent specific surface area of ​​the activated carbon becomes large, making it easier to secure an area for monolayer adsorption of oxine.

[0055] From the above, by using oxine-impregnated activated carbon with the particle size of the base activated carbon particles and the impregnation rate of oxine in an appropriate range as an adsorbent, alpha nuclides can be selectively removed in the treatment of radioactive liquid waste containing alpha nuclides, and the amount of adsorbent used can be reduced, thereby reducing the amount of waste material derived from the adsorbent generated in the treatment of radioactive liquid waste containing alpha nuclides.

[0056] It is possible to increase the oxine impregnation rate above 20 wt.%. However, in this case, the impregnated oxine is more likely to be in a state of multilayer adsorption, and it is considered that the proportion of oxine contributing to the adsorption of alpha nuclides will decrease. Excess oxine may peel off from the activated carbon base material in the aqueous solution. Even if oxine and alpha nuclides form a chelate complex, if oxine peels off, the alpha nuclides that should be removed will flow downstream together with the radioactive waste liquid. Such excess oxine also results in a loss in terms of cost.

[0057] From the results shown in FIGS. 3 and 4, the desirable structure of the oxine-impregnated activated carbon is considered to be as follows.

[0058] The oxine impregnation rate in the oxine-impregnated activated carbon is preferably in the range of 15 wt.% to 20 wt.%.

[0059] When the particle size of the oxine-impregnated activated carbon is in the range of 45 μm or more and less than 150 μm, it is desirable to use a batch-type adsorption tank.

[0060] When the particle size of the oxine-impregnated activated carbon is in the range of 150 μm or more and 840 μm or less, it is preferable to use a column-type adsorption tower. [Explanation of symbols]

[0061] 1, 1A: Radioactive waste liquid treatment equipment containing α-nuclide, 2: Adsorption tank equipment, 2A: Waste liquid storage tank, 3: Adsorbent supply equipment, 3A: Adsorption tower equipment, 4: Solid-liquid separation equipment, 4A: Adsorption tower, 5, 5A, 6, 6A, 7, 7A, 8: Connection piping.

Claims

1. An apparatus for removing alpha nuclides from a radioactive liquid waste containing the alpha nuclides, comprising: The radioactive waste liquid is contacted with an adsorbent, The radioactive liquid waste treatment device, wherein the adsorbent is oxine-impregnated activated carbon.

2. an adsorption tank facility for contacting the radioactive waste liquid with the adsorbent; an adsorbent supply facility for supplying the adsorbent to the adsorption tank facility; a solid-liquid separation facility for separating used adsorbent from the radioactive waste liquid, the used adsorbent resulting from contacting the radioactive waste liquid with the adsorbent in the adsorbent supply facility; 2. The radioactive liquid waste treatment device according to claim 1, wherein the oxine-impregnated activated carbon has a particle size of 45 μm or more and less than 150 μm, and an oxine impregnation rate of 15 wt. % or more and 20 wt. % or less.

3. A waste liquid storage tank for storing the radioactive waste liquid; an adsorption tower facility incorporating the adsorbent; 2. The radioactive liquid waste treatment device according to claim 1, wherein the oxine-impregnated activated carbon has a particle size of 150 μm or more and 840 μm or less, and an oxine impregnation rate of 15 wt. % or more and 20 wt. % or less.

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