JP2015075474A - Radioactive cesium extraction device, radioactive cesium treatment system mounted with the same, radioactive cesium extraction method and radioactive cesium treatment method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a pretreatment device and method to extract radioactive cesium from a solid, and to provide a radioactive cesium treatment device and method using the pretreatment device and method.SOLUTION: A radioactive cesium extraction device 20 comprises: a halogen removal section 21; an extraction section 22 which extracts radioactive cesium by immersing a solid in nitric acid or deuterated nitric acid; a condensing section 23 which produces radioactive cesium nitrate from extraction liquid; and an adjustment section 24 which produces solution or deuterium oxide solution of the radioactive cesium nitrate. A radioactive cesium treatment system 1 comprises: a radioactive cesium adding section 30 which adds the radioactive cesium to a surface of a structure using the solution or the deuterium oxide solution of the radioactive cesium nitrate; and a nuclei transformation section 10 which performs nuclide transformation of the radioactive cesium added to the structure into another stable element.

Description

  The present invention relates to an apparatus and method for extracting radioactive cesium adsorbed on a solid material. The present invention also relates to an apparatus and method for treating radioactive cesium separated from a solid material by the apparatus and method by nuclide conversion.

  A large amount of radioactive material is released into the environment following an accident at a nuclear power plant. Specifically, in the case of the accident at the Fukushima Daiichi nuclear power plant, radioactive materials are released into the atmosphere due to a hydrogen explosion in a building and adhere to soil, trees, rubble, and the like. In addition, due to damage to the reactor, cooling water and the like are contaminated with radioactive materials.

Particularly in the accident at the Fukushima Daiichi Nuclear Power Station, the treatment of contaminated water containing high concentrations of radioactive cesium has become a problem. There are ¹³⁷ Cs (half-life: about 30.1 years) and ¹³⁴ Cs (half-life: 2.0562 years) as radioactive cesium generated by fission of uranium fuel in the nuclear reactor. At present, the contaminated water containing radioactive cesium is treated by passing it through a cesium adsorption device having an adsorbent (zeolite, silica sand, Prussian blue, etc.) cartridge disposed therein. When a certain amount of cesium is adsorbed, the cartridge is replaced.

  However, soil, rubble and adsorbent cartridges are only stored in isolation without further treatment with radioactive cesium. Since it takes many years to reduce the effects of radiation, the number of used adsorbent cartridges is increasing. For this reason, an enormous amount of land and facilities are required for storage, and there is a problem of management methods over a long period of time.

On the other hand, Patent Documents 1 to 3 disclose a technique for converting nuclide from ¹³³ Cs, which is a stable nuclide of cesium, to praseodymium ( ¹⁴¹ Pr).

Japanese Patent No. 4346838 Japanese Patent No. 4347261 Japanese Patent No. 4347262

  As described above, there is a concern about the influence of radiation in the storage of radioactive cesium. Therefore, it can be expected that radiocesium is converted to stable nuclides using nuclide conversion technology to reduce the effects of radiation.

  An object of the present invention is to provide an apparatus and a method used for pretreatment for extracting radioactive cesium from a solid material such as an adsorbent cartridge in performing radionuclide conversion treatment of radioactive cesium. Furthermore, an object of this invention is to provide the processing apparatus and processing method of radioactive cesium including the said pre-processing apparatus and the pre-processing method.

  The radioactive cesium extraction apparatus according to an aspect of the present invention includes a halogen removing unit that removes halogen from the solid material by washing the solid material on which the radioactive cesium is adsorbed with water, and the halogen is contained in nitric acid or deuterated nitric acid. The removed solid material is immersed to extract the radioactive cesium from the solid material, and an extract is generated, and the extract is heated to evaporate the nitric acid or deuterated nitric acid from the extract. A concentration unit for producing the radioactive cesium nitrate, and an adjustment unit for dissolving the radioactive cesium nitrate in water or heavy water to produce an aqueous solution or heavy aqueous solution of the radioactive cesium nitrate having a predetermined concentration.

  In the method for extracting radioactive cesium according to one embodiment of the present invention, the solid matter on which the radioactive cesium is adsorbed is washed with water to remove halogen from the solid matter, and the solid from which the halogen has been removed An extraction step in which a substance is immersed in nitric acid or deuterated nitric acid, and the radioactive cesium is extracted from the solid substance into the nitric acid or deuterated nitric acid; and the extract from which the radioactive cesium is extracted is heated, A concentration step of evaporating the nitric acid or the deuterated nitric acid to produce the radioactive cesium nitrate; And an adjustment step to be prepared.

In the present invention, radioactive cesium adsorbed on a solid substance is extracted and separated using nitric acid (HNO ₃ ) or deuterated nitric acid (DNO ₃ ) as pretreatment for performing the nuclide conversion reaction.
In the nuclide conversion reaction described later, when deuterium permeates through the structure, the nuclide conversion from cesium to another stable element occurs in the structure. However, as a result of the study by the present inventors, it has been found that the permeation of deuterium is inhibited when halogens (iodine) are present. Therefore, in the present invention, before extracting and separating radioactive cesium from the solid material, a step of installing a halogen removing unit to remove halogens adhering to the solid material is performed.
When the adsorbent cartridge of the cesium adsorption device is targeted, the cartridge that adsorbs a large amount of radioactive cesium has a high temperature due to the heat generated by the decay of the radioactive cesium. By washing the adsorbent cartridge (solid material) with the halogen removing unit, the cartridge can be cooled.
By evaporating the radioactive cesium extract to dryness, a nitrate from which excess nitric acid or heavy nitric acid has been removed is prepared. After that, by adjusting to an aqueous solution or heavy aqueous solution of radioactive cesium nitrate (cesium nitrate) with an appropriate concentration for performing nuclide conversion, it is possible to obtain radioactive cesium nitrate with sufficient purity to perform the nuclide conversion reaction. It becomes possible.

  In the above radioactive cesium extraction apparatus, it is preferable that the extraction unit immerses the solid matter in the nitric acid or deuterated nitric acid having a concentration of nitric acid or deuterated nitric acid of 6 mol / L or higher and 90 ° C. or higher under normal pressure. .

  In the radioactive cesium extraction method, the solid substance is immersed in the nitric acid or the heavy nitric acid having a concentration of 6 mol / L or higher and 90 ° C. or higher under normal pressure, and the radioactive substance is immersed in the nitric acid or the heavy nitric acid. It is preferable to be extracted.

By performing extraction under the above conditions, radioactive cesium adsorbed on a solid material can be extracted with a high recovery rate.
As a result of the extraction of radioactive cesium, the amount of radioactive cesium remaining in the solid material after the extraction treatment can be greatly reduced, and the amount of radiation emitted from the solid material after the treatment can be greatly reduced. Therefore, it becomes easy to handle the solid matter after the treatment.

  In the above radioactive cesium extraction apparatus, the extraction unit has a pressure of 16 atm or more, a concentration of nitric acid or deuterated nitric acid of 0.5 mol / L to 5.0 mol / L and 200 ° C. or more of the nitric acid or the heavy It is preferable to immerse the solid in nitric acid.

  In the radioactive cesium extraction method, the solid matter is immersed in the nitric acid or the heavy nitric acid having a concentration of 0.5 mol / L or more and 5.0 mol / L or less and 200 ° C. or more under a pressure of 16 atmospheres or more. The radioactive substance is preferably extracted into the nitric acid or the heavy nitric acid.

By performing extraction under the above conditions, the extraction rate of radioactive cesium can be improved, and the radiation dose of the solid material after treatment can be reduced.
For example, when an adsorbent cartridge is targeted, extraction under the above conditions can prevent damage to adsorbents such as zeolite. If extraction is performed under the above conditions, the solid matter after extraction can be reused.

  The radioactive cesium extraction apparatus preferably further includes a cooling unit that collects and cools the evaporated nitric acid or the heavy nitric acid, and supplies the liquid nitric acid or the heavy nitric acid to the extraction unit.

  The radioactive cesium extraction method preferably further comprises a circulation step of collecting and cooling the evaporated nitric acid or deuterated nitric acid and supplying the nitric acid or deuterated nitric acid in a liquid state to the extraction unit.

  By setting it as the said structure, it becomes possible to reduce the usage-amount of nitric acid or heavy nitric acid.

  A radioactive cesium treatment system according to one embodiment of the present invention includes palladium, a palladium alloy, or hydrogen other than palladium, using the radioactive cesium extraction device according to the above embodiment and an aqueous solution of the radioactive cesium nitrate generated by the adjustment unit. Radioactive cesium addition part for adding the radioactive cesium to one surface of a structure including a hydrogen storage alloy other than the storage metal or palladium alloy, and the radiocesium added to the structure is nuclide-converted into another stable element A radionuclide conversion part, wherein the radioactive cesium addition part contains a container containing an aqueous solution of nitrate of the radioactive cesium, an anode disposed opposite to the one surface of the structure, and the structure as a cathode A voltage generating unit that applies a voltage between the anode and the structure, and the nuclide conversion unit includes the radioactive member The deuterium high-pressure part, the deuterium high-pressure part and the deuterium high-pressure part that are arranged so as to sandwich the structure from both sides and form a closed space that can be sealed by the structure, and the deuterium high-pressure part And a high pressure means for increasing the pressure of deuterium relative to the low pressure portion of deuterium, and a state where the pressure of deuterium is relatively low relative to the high pressure portion of deuterium. Pressure reducing means, wherein the deuterium permeates the structure from the deuterium high concentration portion toward the deuterium low concentration portion, so that the radioactive cesium added to the structure surface is Nuclide conversion.

  The radioactive cesium processing method which concerns on 1 aspect of this invention is a radioactive cesium processing method which processes the said radioactive cesium extracted by the radioactive cesium extraction method of the said aspect, Comprising: A radioactive cesium addition process and a nuclide conversion process are included. The radioactive cesium addition step includes immersing a structure containing palladium or palladium alloy, or a hydrogen storage metal other than palladium or a hydrogen storage alloy other than palladium alloy in an aqueous solution of the radioactive cesium nitrate, and In the aqueous solution, an anode is disposed to face the structure, and a voltage is applied between the structure and the anode using the structure as a cathode, whereby a surface of the structure facing the anode is provided. An electrodeposition step in which the radioactive cesium is added by electrodeposition, and the nuclide conversion step is performed before the structure. Deuterium is supplied to the deuterium high-pressure part on the surface side to which radioactive cesium has been added, and the deuterium low-pressure part on the opposite side of the surface to which the radioactive cesium has been added is relative to the deuterium high-pressure part. The pressure of the deuterium is reduced to a low level, and a pressure difference of the deuterium is generated between the deuterium high-pressure part and the deuterium low-pressure part across the structure. A permeation step in which deuterium permeates through the structure, and a conversion step in which the radioactive cesium is converted into another stable element when the deuterium permeates through the structure.

In the above aspect, a structure containing palladium or a palladium alloy, or a hydrogen storage metal other than palladium or a hydrogen storage alloy other than a palladium alloy by electrodeposition using a radioactive cesium nitrate aqueous solution prepared by the extraction apparatus and the extraction method described above. Add radioactive cesium to one surface of the body. Because cesium is present at a high concentration on the structure surface, nuclide conversion occurs with high efficiency.
In the said aspect, the halogen concentration in the radioactive cesium added by pre-processing is reduced significantly. Therefore, deuterium can permeate the structure during nuclide conversion, and a decrease in the nuclide conversion rate is suppressed.

  A radioactive cesium treatment system according to another aspect of the present invention includes palladium, a palladium alloy, or other than palladium, using the radioactive cesium extraction apparatus of the above aspect and a heavy aqueous solution of the radioactive cesium nitrate generated by the adjustment unit. Using a radioactive cesium addition part for adding the radioactive cesium to one surface of a structure containing a hydrogen storage alloy other than a hydrogen storage metal or a palladium alloy, and a heavy aqueous solution of the radioactive cesium nitrate produced in the adjustment part, A radionuclide conversion unit that converts the radioactive cesium into another stable element, wherein the radioactive cesium addition unit is opposed to the container containing the heavy aqueous solution of the radioactive cesium nitrate and the one surface of the structure. An anode to be arranged, and a voltage generation for applying a voltage between the anode and the structure using the structure as a cathode And the nuclide conversion unit is disposed so as to sandwich the structure from both sides, and the deuterium high-concentration unit and the heavy ion isolated by the structure. A low hydrogen concentration portion, a high concentration means for increasing the concentration of deuterium near the surface of the structure on the deuterium high concentration portion side, and the deuterium low concentration portion, the deuterium high concentration portion And a concentration reducing means for reducing the concentration of the deuterium, wherein the concentration increasing means is spaced from the voltage generating portion and the surface of the structure on the deuterium high concentration portion side. And an electrolytic solution supply unit that supplies a heavy aqueous solution of the radioactive cesium nitrate to the deuterium high-concentration unit, and the structure is used as a cathode by the voltage generation unit. A voltage difference between the body and the anode Electrolysis of the solution generates the deuterium, and the deuterium permeates the structure from the deuterium high concentration portion toward the deuterium low concentration portion, whereby the radioactive cesium in the structure. Is converted to other stable elements.

  The radioactive cesium processing method which concerns on another aspect of this invention is a radioactive cesium processing method which processes the said radioactive cesium extracted by the radioactive cesium extraction method of the said aspect, Comprising: A radioactive cesium addition process and a nuclide conversion process are carried out. And the step of adding the radioactive cesium includes immersing a structure containing palladium or a palladium alloy, or a hydrogen storage metal other than palladium or a hydrogen storage alloy other than a palladium alloy in a heavy aqueous solution of the radioactive cesium nitrate. In the aqueous solution, an anode is disposed to face the structure, and a voltage is applied between the structure and the anode using the structure as a cathode, thereby facing the anode of the structure. An electrodeposition step in which the radioactive cesium is added to the surface by electrodeposition, and the nuclide conversion step includes the structure A heavy aqueous solution supplying step in which a heavy aqueous solution of the radioactive cesium nitrate obtained in the adjustment step is supplied to the deuterium high concentration portion on the surface side to which the radioactive cesium is added, and the deuterium high concentration portion An anode is disposed in the heavy aqueous solution so as to face the structure, and a voltage is applied between the structure and the anode using the structure as a cathode, whereby the heavy water is electrolyzed and deuterium is generated. And the deuterium low concentration portion on the other surface side of the structure is placed in a state in which the deuterium concentration is relatively low with respect to the deuterium high concentration portion, thereby sandwiching the structure. A deuterium concentration difference occurs between the deuterium high-concentration portion and the deuterium low-concentration portion, and a permeation step in which the deuterium permeates the structure due to the concentration difference; When passing through the structure, the heavy water of the structure Having having a nuclide process including the radioactive cesium on the surface of the high density portion side and a conversion step of nuclide into another stable elements.

In the above aspect, palladium or palladium alloy, or a hydrogen storage metal other than palladium or a hydrogen storage alloy other than palladium alloy is immersed in the heavy aqueous solution of radioactive cesium nitrate prepared by the extraction apparatus and extraction method described above, Radioactive cesium nuclide conversion is caused on the surface of the structure by deuterium generated by electrolysis permeating the structure. Because cesium is present at a high concentration on the structure surface, nuclide conversion occurs with high efficiency.
Also in the above aspect, since the halogen concentration in the radioactive cesium added by the pretreatment is greatly reduced, the decrease in the nuclide conversion rate due to the halogen inhibiting the deuterium permeation is suppressed.

  In the present invention, radioactive cesium is nuclide converted into another stable element having no radioactivity. The “stable element” in the present invention means an element that does not emit radiation such as α rays, β rays, γ rays, and neutrons at a level harmful to the human body. Therefore, according to the present invention, the radioactivity level can be reduced.

According to the present invention, radioactive cesium can be extracted from a solid material with high yield, and the treatment rate of radioactive cesium can be increased. Moreover, since the radiation dose of the solid matter after extraction can be greatly reduced, the subsequent handling of the solid matter becomes easy. Moreover, since the extracted radioactive cesium is converted into other stable stable elements, the radioactivity level can be reduced.
Therefore, this invention can process radioactive cesium to a safe state in a short time compared with the natural decay | disintegration of radioactive cesium. As a result, the processing of the solid material to which radioactive cesium is attached is promoted, the storage space can be reduced, and waste management becomes easy.

It is the schematic of the radioactive cesium processing system which concerns on 1st Embodiment. It is the schematic of a radioactive cesium addition part. It is a longitudinal cross-sectional view of an example of a structure. It is the schematic of the nuclide conversion part of 1st Embodiment. It is the schematic of the radioactive cesium processing system which concerns on 2nd Embodiment. It is the schematic of the nuclide conversion part of 2nd Embodiment. It is the schematic of the test apparatus used in the nuclide conversion experiment by the gas permeation method. It is a SIMS spectrum of the structure surface before and after the nuclide conversion experiment by the gas permeation method. It is the schematic of the test apparatus used in the nuclide conversion experiment by the electrolysis method. It is a SIMS spectrum of the structure surface after performing the nuclide conversion experiment by the electrolysis method. It is an XPS spectrum in the center part and edge part of a structure. It is a section schematic diagram of a glass tube. It is the schematic of the apparatus used for addition of ¹³⁷ Cs. It is the cross-sectional schematic of the container which stores the structure which added ¹³⁷ Cs. It is a radioactivity measurement result of ¹³⁷ Cs before and after the nuclide conversion experiment.

<First Embodiment>
In the first embodiment, radioactive cesium ( ¹³⁴ Cs, ¹³⁷ Cs) adsorbed on a solid object is a processing target. In particular, ¹³⁷ Cs has a long half-life and occupies most of the radioactive cesium contained in rubble and contaminated water.

Examples of the solid material include soil, felled trees, rubble such as buildings, and cesium adsorbent. Examples of the cesium adsorbent include zeolite, silica sand, Prussian blue (hexacyanoiron (II) potassium iron (II) oxide, KFe [Fe (CN) ₆ ] ₃ ) and the like. This cesium adsorbent is used in a cesium adsorption device that purifies contaminated water in which radioactive cesium is dissolved. The cesium adsorption device is specifically a treatment device made by Kurion, a treatment device made by Toshiba (SARRY), or the like.

FIG. 1 is a schematic view of a radioactive cesium treatment system according to the first embodiment.
The radioactive cesium processing system 1 includes a nuclide conversion unit 10 that processes radioactive cesium by nuclide conversion, and a radioactive cesium extraction device 20 that performs pretreatment to perform nuclide conversion. The radioactive cesium extraction apparatus 20 includes a halogen removal unit 21, an extraction unit 22, a concentration unit 23, and an adjustment unit 24. The radioactive cesium extraction device 20 further includes a cooling unit 25. The cooling unit 25 is connected to the extraction unit 22 and the concentration unit 23.

  In the radioactive cesium treatment system 1 of the first embodiment, a radioactive cesium addition unit 30 is installed between the adjustment unit 24 and the nuclide conversion unit 10.

Below, the radioactive cesium processing system 1 of 1st Embodiment and the radioactive cesium processing method are demonstrated concretely.
[Extraction of radioactive cesium]
First, the radioactive cesium extraction apparatus 20 extracts radioactive cesium adsorbed on a solid material.

<Halogen removal part, halogen removal process>
In the halogen removing step, the halogen removing unit 21 accommodates a solid material on which radioactive cesium has been adsorbed, and wash the solid material with water. Thereby, halogen (iodine, chlorine, etc.) adhering to the solid material is removed.
The halogen removing unit 21 includes a washing unit for washing a solid material with water. Specifically, the cleaning unit may be a spray that sprays water toward a solid object in the container, or may be one that supplies water into the container to immerse the solid object.

  When the solid material is an adsorbent cartridge of a cesium adsorption device that removes radioactive cesium from contaminated water, the temperature is high due to heat generated by decay of the radioactive cesium. For example, the center temperature of a cartridge of a cesium adsorption device manufactured by Kurion is about 360 ° C., and the center temperature of a cartridge of a cesium adsorption device manufactured by Toshiba is about 450 ° C. The cartridge is cooled with water by washing with water in this step.

<Extraction unit, extraction process>
In the extraction process, the extraction unit 22 accommodates the solid matter discharged from the halogen removal unit 21. Nitric acid or heavy nitric acid is supplied into the extraction unit 22, and the solid is immersed in nitric acid or heavy nitric acid. The radioactive cesium adsorbed on the solid substance is extracted with nitric acid or heavy nitric acid by being dissolved as nitrate or heavy nitrate.
In this extraction process, in order to sufficiently extract radioactive cesium, one of the following two conditions is adopted at the time of immersion.

(Condition 1)
Pressure: Normal pressure (about 1 atmosphere),
Nitric acid or heavy nitric acid concentration: 6 mol / L or more,
Nitric acid or heavy nitric acid temperature: 90 ° C or higher,
Solid-liquid ratio (weight ratio of liquid to solid): 1 or more.

(Condition 2)
Pressure: 16 atmospheres or more
Nitric acid or heavy nitric acid concentration: 0.5 mol / L or more and 5.0 mol / L or less,
Nitric acid or heavy nitric acid temperature: 200 ° C or higher,
Solid-liquid ratio: 200 or more.

By carrying out the extraction step under the above conditions, the amount of radioactive cesium extracted from the solid material can be increased.
The upper limit of the temperature in the extraction step is a temperature at which nitric acid or heavy nitric acid can exist as a liquid at the pressure of each condition. In the case of condition 2, nitric acid or heavy nitric acid is accommodated in the pressure vessel. In this case, the temperature and pressure at which nitric acid or heavy nitric acid does not boil in the container are selected.
Under condition 2 (extraction under high pressure), if the concentration of nitric acid or heavy nitric acid is high, the zeolite is destroyed. Therefore, the upper limit of the nitric acid or heavy nitric acid concentration in Condition 2 is preferably 5.0 mol / L.

Condition 1 has the advantage that the pressure and temperature are lower than that of condition 2, and the amount of nitric acid or deuterated nitric acid required to treat the same amount of solid matter can be reduced. Under condition 1, 6 mol / L or more of concentrated nitric acid or concentrated heavy nitric acid is required to sufficiently extract radioactive cesium. When the zeolite (absorbent cartridge) is extracted at this concentration, the structure of the zeolite is destroyed.
On the other hand, in the condition 2, the extraction is performed with a low concentration of nitric acid or heavy nitric acid. At this concentration, no destruction of the zeolite occurs.

  Prussian blue has a decomposition temperature of 230 ° C. When the solid material is Prussian blue, the structure of Prussian blue is not destroyed if extraction is performed at a temperature lower than the decomposition temperature of Prussian blue when performing extraction under Condition 2.

  After the extraction step, the extract and the solid are taken out from the extraction unit 22 separately.

  The solid matter discharged from the extraction unit 22 is conveyed to the processing unit 40. The processing unit 40 contains a solid material and neutralizes nitric acid or heavy nitric acid adhering to the solid material. For the neutralization treatment, for example, NaOH can be used. After the neutralization treatment, the solid material is washed with water.

The solid matter that has been washed with water and discharged from the processing unit 40 can be treated as general waste if it has a radioactive level that is less than or equal to the regulated value.
Since the zeolite is not destroyed when treated under condition 2 in the extraction step, the zeolite adsorbent cartridge can be reused after the neutralization treatment and the water washing treatment.
Moreover, in the said extraction process, when Prussian blue is processed without decomposing | disassembling, Prussian blue becomes reusable after the neutralization process and the water washing process.

There is a possibility that a radioactive substance (radiocesium) is contained in the cleaning liquid after the water washing process in the halogen removing unit 21 and the treated water after the neutralization process and the water washing process in the processing unit 40. Therefore, these treated waters are supplied to the cesium adsorption device 50 for treating the contaminated water, and after the radioactive substance is adsorbed, the treated water is discharged as clean treated water. The discharged treated water having properties may be reused as cooling water or washing water in the halogen removing unit 21 after passing through a treatment device such as a reverse osmosis membrane.
In addition, the adsorbent cartridge of the cesium adsorption apparatus 50 in FIG. 1 is processed by the radioactive substance extraction method of this embodiment as a solid material.

<Concentration part, concentration process>
The concentration unit 23 receives the extracted liquid discharged from the extraction unit 22. In the concentration unit 23, the extract is evaporated to dryness. The heating temperature at this time is 120.5 ° C. or higher.
Alternatively, the concentration unit 23 may vacuum dry the extract. The vacuum drying is performed under a condition of 2000 Pa or less, and the vacuum drying time is appropriately set according to the amount of the extract.
As a result of this concentration step, crystals of radioactive cesium nitrate (CsNO ₃ ) are recovered.

<Cooling section, circulation process>
The gas (nitric acid or deuterated nitric acid) evaporated in the concentration unit 23 is conveyed to the cooling unit 25. In the cooling unit 25, nitric acid or heavy nitric acid is cooled to a temperature below the boiling point and condensed. Specifically, nitric acid or heavy nitric acid is cooled to 120.5 ° C. or lower.
The condensed nitric acid or heavy nitric acid is circulated and supplied to the extraction unit 22.

The air after the nitric acid or heavy nitric acid is condensed is released into the environment. The radioactive substance remaining in the air may be removed by passing through the air filter 60 before discharge.
The filter part of the air filter 60 on which the radioactive substance is adsorbed may be reused after the processing by the radioactive cesium extraction method of the present embodiment is performed as a solid material.

<Adjustment unit, adjustment process>
The radioactive cesium nitrate recovered by the concentration unit 23 is conveyed to the adjustment unit 24. In the adjustment step, the adjustment unit 24 adjusts the radioactive cesium nitrate to a solution suitable for nuclide conversion, which is a subsequent step.

Specifically, the radioactive cesium nitrate conveyed to the adjusting unit 24 is added to water (light water) to be adjusted to an aqueous solution having a predetermined concentration. A pH adjusting agent may be added to the aqueous solution to adjust to a predetermined pH. As the pH adjuster used in the present embodiment, an alkali such as CsOH (Cs may not be a radioisotope) or an acid such as HNO ₃ can be used. However, an acid containing halogen such as HCl is not used in this embodiment.
In this embodiment, considering the treatment in the subsequent radioactive cesium addition step, the concentration of the aqueous cesium nitrate solution is preferably adjusted to 0.001 to 1 mol / L and the pH to about 7 to 13.

[Treatment of radioactive cesium]
<Radiocesium addition part, Radiocesium addition process>
The aqueous nitrate solution adjusted by the adjusting unit 24 is conveyed to the radioactive cesium adding unit 30.
FIG. 2 is a schematic view of the radioactive cesium addition unit 30. The radioactive cesium addition unit 30 includes a container 31, a power source 32, and an anode 33 connected to the power source 32. The anode 33 is platinum or the like. A structure 70 is attached to the cathode side and connected to the power source 32. The container 31 contains the aqueous nitrate solution of radioactive cesium adjusted by the adjusting unit 24, and the anode 33 and the structure 70 are immersed therein.

  FIG. 3 shows an example of the structure 70. The structure 70 shown in FIG. 3 has a configuration in which 10 layers of CaO layers 72 (thickness: 2 nm) and Pd layers 73 (thickness: 20 nm) are alternately stacked on a bulk Pd (palladium) substrate 71. Is done. The CaO layer 72 and the Pd layer 73 are alternately formed on the Pd substrate 71 after the etching process by an argon ion beam sputtering method. The outermost surface is a Pd layer 73.

Pd is a metal having a hydrogen storage property, and CaO is a substance having a relatively low work function with respect to Pd. Instead of Pd, the structure 70 may be made of a Pd alloy, a hydrogen storage metal other than Pd, or a hydrogen storage alloy other than a Pd alloy. Further, instead of CaO, a substance having a relatively low work function with respect to Pd alloy, a hydrogen storage metal other than Pd, or a hydrogen storage alloy other than Pd alloy may be used. A substance having a relatively low work function is a substance having a work function of less than 3 eV, such as Y ₂ O ₃ or TiC.

  In FIG. 2, the structure 70 is disposed with the Pd layer 73 facing the anode 33. A predetermined voltage is applied between the anode 33 and the structure 70, and radioactive cesium is electrodeposited on the surface of the Pd layer 73 of the structure 70 with an aqueous nitrate solution. By forming the radioactive cesium layer, radioactive cesium is added to the structure 70.

  The voltage to be applied and the application time are appropriately set according to the amount of radioactive cesium added to the structure and the concentration of the aqueous solution. For example, when a 1 mM radioactive cesium nitrate aqueous solution is used, electrodeposition is performed at a voltage of 1 V for 10 seconds.

<Nuclide conversion part, nuclide conversion process>
FIG. 4 is a schematic diagram of the nuclide conversion unit of the first embodiment. In this embodiment, the nuclide conversion reaction is performed by a gas permeation method.
The nuclide conversion unit 10 of FIG. 4 can hold the structure 70 with the deuterium high-pressure unit 11 on the Pd layer 73 side of the structure 70 and the deuterium low-pressure unit 12 on the Pd substrate 71 side to keep the inside airtight. Is formed. In the structure 70, a radioactive cesium layer is formed on the surface of the Pd layer 73 by the radioactive cesium addition step. The deuterium high pressure unit 11 includes a deuterium cylinder 13 as a high pressure means. A vacuum pump 14 is provided as means for reducing the pressure.

Using the nuclide conversion unit 10 in FIG. 4, nuclide conversion is performed by the following steps.
The deuterium cylinder 13 introduces deuterium (D ₂ ) gas into the deuterium high-pressure part 11 at a pressure of 1.01325 × 10 ⁵ Pa, for example. In the deuterium low pressure section 12, the vacuum pump 14 evacuates the deuterium low pressure section 12. Thereby, the pressure of deuterium in the deuterium low-pressure part 12 becomes lower than that in the deuterium high-pressure part 11, and a deuterium pressure difference is generated between the deuterium low-pressure part 12 and the deuterium high-pressure part 11. To do. Due to this pressure difference, deuterium permeates through the structure 70 from the deuterium high-pressure part 11 toward the deuterium low-pressure part 12.

  In the present embodiment, the halogen removal unit 21 is provided in the radioactive cesium extraction device 20 to prevent the halogen from being mixed into the extracted radioactive cesium. In addition, no chemicals containing halogen are used in the radioactive cesium extraction process. For this reason, the halogen concentration in the radioactive cesium layer added to the structure 70 is extremely small. As a result, deuterium permeation inhibition by halogen does not occur in this step.

When deuterium permeates through the structure 70, the following reaction occurs in the structure 70, and radioactive cesium is converted into another stable element. The term “stable element” as used herein means an element that does not emit radiation such as α rays, β rays, γ rays, neutrons, etc. at a level harmful to the human body. For example, it is expected that ¹³⁷ Cs is converted to ¹⁵³ Eu and ¹³⁴ Cs is converted to ¹³⁸ La and the like.
The permeation of deuterium gas is set for a predetermined time, for example, several tens to several hundreds hours. The amount of nuclide conversion tends to increase as the permeation time of deuterium increases.

Second Embodiment
FIG. 5 is a schematic diagram of a radioactive cesium treatment system according to the second embodiment. In FIG. 5, the same components as those in the first embodiment are denoted by the same reference numerals.
In the radioactive cesium treatment system 101 of the second embodiment, the configuration of the radioactive cesium extraction device 120 is the same as that of the first embodiment. The radioactive cesium processing system 101 is provided with a nuclide conversion unit 110 different from the first embodiment.

Below, the radioactive cesium processing system 101 and the radioactive cesium processing method of 2nd Embodiment are demonstrated concretely.
[Extraction of radioactive cesium]
The halogen removal step to the concentration step are performed in the same manner as in the first embodiment.
<Adjustment unit, adjustment process>
In the adjustment process of the second embodiment, the radioactive cesium nitrate transported to the adjustment unit 124 is added to heavy water and adjusted to a heavy aqueous solution having a predetermined concentration. A pH adjuster may be added to the heavy aqueous solution to adjust to a predetermined pH. As the pH adjuster used in the present embodiment, an alkali such as CsOH (Cs may not be a radioisotope) or an acid such as HNO ₃ can be used. However, an acid containing halogen such as HCl is not used in this embodiment.
In the present embodiment, in consideration of the nuclide conversion step, it is preferable that the concentration of the radioactive cesium nitrate heavy aqueous solution is adjusted to 0.001 to 1 mol / l and the pH to 7 to 13.

[Treatment of radioactive cesium]
<Radiocesium addition part, Radiocesium addition process>
The aqueous nitrate heavy solution adjusted by the adjusting unit 124 is conveyed to the radioactive cesium adding unit 30. In the radioactive cesium addition part 30, a radioactive cesium layer is formed on the structure surface by the same process as the first embodiment.

<Nuclide conversion part, nuclide conversion process>
FIG. 6 is a schematic diagram of the nuclide conversion unit of the second embodiment. In this embodiment, the nuclide conversion reaction is performed by an electrolytic method.
6 includes a structure 70, a deuterium high concentration unit 111, a deuterium low concentration unit 112, a high concentration unit 113, and a low concentration unit.

The structure 70 has the same configuration as the structure of the first embodiment. A deuterium high-concentration portion 111 is formed on the Pd layer side and a deuterium low-concentration portion 112 is formed on the Pd substrate side so that the inside of the structure 70 can be kept airtight.
The deuterium high concentration part 111 is provided with a high concentration means 113, and the deuterium concentration is maintained higher than that of the deuterium low concentration part 112.

  The high concentration means 113 includes a voltage generator 115, an anode 116, and an electrolytic solution supply unit 117. The anode 116 is platinum or the like. The anode 116 is disposed in the deuterium high-concentration portion 111 so as to face the Pd layer side surface of the structure 70 with a gap. The voltage generator 115 is located outside the deuterium high concentration part 111 and can give a voltage difference between the anode 116 and the cathode (structure 70).

The electrolytic solution supply unit 117 is connected to the adjustment unit 124 of the radioactive cesium extraction apparatus 20 and supplies the radioactive cesium nitrate heavy aqueous solution adjusted by the adjustment unit 124 to the deuterium high concentration unit 111 as an electrolytic solution. At this time, the electrolytic solution supply unit 117 supplies the electrolytic solution to the deuterium high concentration unit 111 together with an inert gas such as nitrogen (N ₂ ) or argon (Ar).
Cesium nitrate (cesium nitrate) is an electrolyte and exists as nitrate ions in heavy aqueous solution.

  The gas discharge path 114 is connected to the deuterium high concentration section 111 via a check valve (<1 atm) so that the gas in the deuterium high concentration section 111 can be discharged to the outside.

  The deuterium low concentration unit 112 includes a concentration reducing means. Although the concentration reducing means is not shown in FIG. 6, it is an exhaust device such as a turbo molecular pump and a dry pump, and the deuterium low concentration portion 112 is deuterated more than the deuterium high concentration portion 111 by evacuation. Maintain low pressure.

Using the nuclide conversion unit 110 in FIG. 6, nuclide conversion is performed by the following steps.
The heavy nitrate aqueous solution of radioactive cesium adjusted to a predetermined concentration by the adjustment unit 124 is supplied to the high deuterium concentration unit 111 via the electrolytic solution supply unit 117. The structure 70 and the anode 116 are immersed in the heavy nitrate aqueous solution by the heavy nitrate aqueous solution.

  Next, the deuterium low concentration portion 112 is brought into a low deuterium pressure state by the concentration reducing means. In detail, the inside of the deuterium low concentration part 112 is made into a vacuum state using a vacuum pump, and this is maintained. The pressure in the deuterium low concentration portion 112 is preferably <0.1 Pa.

Next, a voltage is applied to the anode 116 by the voltage generator 115 to generate a voltage difference between the anode 116 and the cathode (structure 70). At this time, a voltage difference equal to or higher than the water electrolysis threshold (1.23 V) is applied. Thereby, heavy water (D ₂ O) is electrolyzed on the surface (Pd layer) of the structure 70, and deuterium (D ₂ ) is generated. Considering the electrolysis reaction rate and the like, the voltage difference is at least 1.5 V or more, and the electrolysis is performed in the range of several V to several tens V.
Due to the electrolysis of heavy water, the amount of nitrate heavy aqueous solution in the deuterium high concentration portion 111 is reduced. Therefore, a nitrate heavy aqueous solution is continuously supplied from the electrolytic solution supply unit 117 so that the anode 116 and the structure 70 can be immersed.

Due to the low concentration step and the high concentration step, a deuterium concentration gradient is generated between the deuterium high concentration portion 111 side and the deuterium low concentration portion 112 side of the structure 70. Thereby, deuterium on the deuterium high concentration part 111 side permeates the structure 70 and moves to the deuterium low concentration part 112 side. At this time, radioactive cesium in the radioactive cesium layer on the surface of the structure 70 is converted into another stable element.
The permeation of deuterium gas is set for a predetermined time, for example, several tens to several hundreds hours. The amount of nuclide conversion tends to increase as the permeation time of deuterium increases.

  Further, cesium nitrate is an electrolyte, and radioactive cesium exists as ions in water or heavy water. Due to the voltage difference between the anode 116 and the structure 70, the cesium ions move toward the structure 70. When the cesium ions come into contact with the surface of the structure 70 facing the anode 116, the cesium ions are nuclide-converted to other proposed elements during deuterium permeation.

  In the present embodiment, the nuclide conversion unit 110 may be integrated with the radioactive cesium addition unit. That is, the deuterium high concentration part 111, the voltage generator 115, and the anode 116 of the nuclide conversion part 110 perform the same function as the radioactive cesium addition part demonstrated in FIG. By doing so, the apparatus configuration of the radioactive cesium treatment system 101 can be simplified.

  In this case, before the nuclide conversion is performed in the nuclide conversion unit 110 (before deuterium is allowed to permeate the structure 70 by the operation of the concentration reducing means), the voltage generator 115 is connected to the anode 116 and the structure 70. Is applied to the surface of the structure 70 to form a radioactive cesium layer, whereby the radioactive cesium is added. Thereafter, the nuclide conversion step is performed by the above-described steps.

Below, the radioactive cesium processing method of 1st Embodiment and 2nd Embodiment is demonstrated by an experiment example.
First, the feasibility of the nuclide conversion process employed in the above embodiment will be described.

[Nuclide conversion experiment by gas permeation method]
An experiment was conducted to confirm the nuclide conversion of Cs by the gas permeation method. In this experiment, ¹³³ Cs was used in consideration of safety in conducting the experiment.
(1) Production of structure The structure was degreased by ultrasonically cleaning a Pd substrate (25 mm × 25 mm × thickness 0.1 mm, purity 99.5% or more) in acetone for a predetermined time. Thereafter, annealing was performed in a vacuum (for example, 1.33 × 10 ⁻⁵ Pa or less) at a temperature of, for example, 900 ° C. for a predetermined time (for example, 10 hours).
Next, for example, the Pd substrate annealed at room temperature was etched with heavy aqua regia for a predetermined time (for example, 100 seconds) to remove impurities on the surface.

  Next, a CaO layer and a Pd layer were alternately formed on the Pd substrate after the etching process by sputtering using an argon ion beam sputtering. For example, a CaO layer having a thickness of 10 nm and a Pd layer having a thickness of 10 nm are alternately stacked, and a Pd layer is formed at the uppermost portion with a thickness of 40 nm to form a structure.

(2) Addition of Cs In this experiment, ¹³³ Cs was added to the surface of the Pd layer of the structure using an ion implantation method. Ion implantation was performed at an acceleration energy of 20 keV and a dose of 10 ¹⁶ ions / cm ² .

(3) Nuclide conversion experiment The structure 210 produced by the above process was placed on the sample stage in the test apparatus 200 shown in FIG. In the structure 210, the ¹³³ Cs-added surface was arranged toward the storage chamber (deuterium high-pressure part) 201 side.
After the structure was placed, the storage chamber 201 and the discharge chamber (deuterium low pressure part) 202 were exhausted to 1 × 10 ⁻⁵ Pa or less using the turbo molecular pump 204 and the rotary pump 205 with the valve V1 opened. The structure 210 was heated to about 70 ° C.

After the degree of vacuum was sufficiently stable and the temperature of the structure 210 was stabilized, the valve V1 was closed. Next, the valves V2 and V3 were opened, and deuterium was continuously supplied from the deuterium tank 203 to the storage chamber 201. The pressure in the storage chamber 201 was 1.013 × 10 ⁵ Pa (1 atm).
After 150 hours from the introduction of the deuterium gas, the valves V2 and V3 were closed, the valve V1 was opened, and the deuterium in the storage chamber 201 was exhausted. Thereafter, the turbo molecular pump 204 and the rotary pump 205 were stopped, and the storage chamber 201 and the discharge chamber 202 were opened to the atmosphere. After releasing the atmosphere, the structure 210 was taken out.

なお、図８によると、質量数１３７（^１３７Ｌａ、半減期：６万年）も計測されたが、計測数は少なかった。 (4) Elemental analysis on the surface of the structure Elemental analysis of the surface on the Pd layer side was performed on the structures before and after the nuclide conversion experiment using SIMS (secondary ion mass spectrometer). FIG. 8 is a SIMS spectrum. In the figure, the horizontal axis represents the mass number, and the vertical axis represents the SIMS count number.
In the structure before the experiment, only the mass number 133 ( ¹³³ Cs) was measured. In the structure after the experiment, the number of measurements of the mass number 133 decreased and the mass number 141 was measured compared to before the experiment. This means that ¹³³ Cs was converted to ¹⁴¹ Pr by nuclide conversion.
In this nuclide conversion, the following reactions are considered to occur.

In addition, according to FIG. 8, mass number 137 ( ¹³⁷ La, half-life: 60,000 years) was also measured, but the number of measurements was small.

From the above results, it was confirmed that when deuterium permeates through the structure, cesium is nuclide-converted and converted to another stable element ( ¹⁴¹ Pr in this experiment).

[Nuclide conversion experiment by electrolysis]
An experiment was conducted to confirm the nuclide conversion of Cs by electrolysis. In this experiment, ¹³³ Cs was used in consideration of safety in conducting the experiment.

(1) Creation of structure A structure was produced in the same process as the gas permeation method described above.

(2) Cs addition ¹³³ Cs was added to the surface of the Pd layer of the structure in the same process and conditions as the gas permeation method described above.

(3) Nuclide Conversion Experiment FIG. 9 is a schematic diagram of the test apparatus used in this experiment. The test apparatus 300 has a cylindrical container 301, and a structure 310 similar to that shown in FIG. At this time, the Pd substrate of the structure 310 was placed toward the bottom of the container 301. The structure 310 was connected as a cathode to a power source (not shown).
A 0.1MCsNO ₃ —D ₂ O solution was placed in the space on the Pd layer side in the container 301, and the anode (platinum electrode) 302 was immersed in the solution so as to face the structure 310.
The space opposite to the inside of the container 301 across the structure 310 was depressurized (1 × 10 ⁻⁵ Pa or less) by a pump (not shown). A voltage of 4.5 V was applied between the structure 310 and the anode 302 for 250 hours to electrolyze heavy water. After electrolysis, structure 310 was removed.

(4) Elemental analysis of the structure surface Elemental analysis of the surface on the Pd layer side was performed using SIMS. Here, two places of the center part and the end part of the structure were measured. In the test apparatus 300 of FIG. 9, the wall surface protrudes inward in the radial direction of the container at the bottom of the container. For this reason, deuterium can pass through the center of the structure 310, but deuterium cannot pass through the end of the structure 310.
FIG. 10 shows SIMS spectra at the center and end of the structure. In the figure, the horizontal axis represents the mass number and the vertical axis represents the count number. In the central part of the structure, the count number of mass number 133 ( ¹³³ Cs) is reduced as compared with the end of the structure. Although mass numbers other than 133 were not detected at the end of the structure, mass numbers 139 and 140 were mainly detected at the center of the structure.

There are several possible composites (combinations of two elements) that can have a mass number of 139 and 140. However, when the natural abundance ratio is taken into consideration, there are no combinations of elements existing in nature that have mass numbers of 139 and 140. Therefore, the mass number 139 and the mass number 140 are estimated to be ¹³⁹ La and ¹⁴⁰ Ce, which are stable elements, respectively.

From the above results, it was confirmed that when deuterium permeates through the structure, cesium is nuclide-converted and converted to other stable elements ( ¹³⁹ La and ¹⁴⁰ Ce in this experiment).

In the following experiment, the presence or absence of a nuclide conversion reaction was verified using a structure in which a Y ₂ O ₃ layer was formed as a substance having a low work function.
A structure was produced in the same process as the gas permeation method described above, except that the CaO layer was replaced with a Y ₂ O ₃ layer. Further, ¹³³ Cs was added to the surface of the Pd layer of the structure in the same process and conditions as in the gas permeation method described above.

The nuclide conversion reaction was performed using the test apparatus of FIG. Incidentally, with 0.5MCsNO ₃ -D ₂ O solution in this experiment.
FIG. 11 shows XPS spectra at the center and end of the structure. In the figure, the horizontal axis is energy, and the vertical axis is the count number. As described above, deuterium permeates at the center of the structure, and deuterium does not permeate at the end side. As shown in FIG. 11, a Pr peak was detected at the center of the structure, but not at the end.
From the above results, it was confirmed that nuclide conversion occurred even when Y ₂ O ₃ was applied as a substance having a low work function.

[Verification of halogen removal effect]
The necessity of halogen removal in the radioactive cesium extraction method of this embodiment will be described by the following experiment.
Iodine was added to the surface of the structure of FIG. 3 (size: 25 mm × 25 mm × 0.1 mm) by (a) electrodeposition and (b) ion implantation.
(A) Conditions for electrodeposition method Electrolytic solution: 1 mM NaI-D ₂ O solution Voltage: 1 V
Electrolysis time: 10 seconds Iodine addition amount: 80 ng / cm ²
(B) Ion implantation method Acceleration energy: 18 keV
Injection amount: 1.0 × 10 ¹⁴ ions / cm ²

¹³³ Cs was added as a nuclide conversion substance by electrodeposition to the surface of the Pd layer of the structure to which iodine was added in each of the electrodeposition method and the ion implantation method.

本実験の条件で核種変換を発生させるには、重水素透過量は１ｓｃｃｍ必要である。上記結果から、ヨウ素により重水素の透過が阻害されることが確認できた。 The structure to which iodine was added was placed between the deuterium high pressure part and the deuterium low pressure part. Deuterium gas was supplied to the deuterium high-pressure section so that the pressure was 1.01325 × 10 ⁵ Pa. The deuterium low pressure part was evacuated with a vacuum pump so that the pressure became 1 × 10 ⁻⁴ Pa.
Table 1 shows the amount of deuterium permeated through each structure. The amount of deuterium permeation was measured with a vacuum gauge configured with a mass flow controller.

In order to generate nuclide conversion under the conditions of this experiment, 1 sccm of deuterium permeation is required. From the above results, it was confirmed that the deuterium permeation was inhibited by iodine.

[Radiocesium extraction and nuclide conversion experiments]
A demonstration experiment of the radioactive cesium treatment method described in the first embodiment will be described below.

[1] Extraction of ¹³⁷ Cs In this experiment, the possibility of extraction of ¹³⁷ Cs adsorbed on a solid material with nitric acid was examined.
(1) Adsorption to ion exchange resin 1 cc of ion exchange resin (Mitsubishi Resin Co., Ltd.) was filled in a glass tube shown in FIG. Glass wool is packed at the tip of the glass tube in order to prevent the ion exchange resin from being discharged from the glass tube.
1 cc of 1N hydrochloric acid was injected into a glass tube filled with the ion exchange resin to wash the ion exchange resin. This operation was repeated twice.
Next, 1 cc of 1N nitric acid was injected into the glass tube to wash the ion exchange resin. This operation was repeated 8 times.
Next, 1 cc of pure water was injected into the glass tube to wash the ion exchange resin. This operation was repeated 10 times.
0.5 cc of a ¹³⁷ Cs reagent solution (0.1N hydrochloric acid solution, 1.85 MBq) was injected into the glass tube. Thereafter, an operation of injecting 0.1 cc of pure water into the glass tube three times in total was performed.
^In the injection of the ¹³⁷ Cs reagent solution and the subsequent pure injection, a beaker was installed at the bottom of the glass tube to collect the liquid that passed through the ion exchange resin. The ¹³⁷ Cs radioactivity of the liquid recovered by the Ge measuring device was measured but not detected.

(2) Extraction of ¹³⁷ Cs A PFA container was placed under the glass tube. 1 cc of 1N nitric acid was injected into a glass tube filled with ¹³⁷ Cs adsorption ion exchange resin. This operation was repeated 5 times. The liquid that passed through the glass tube was collected in a PFA container.
When the ¹³⁷ Cs radioactivity of the liquid collected by the portable radiation measuring instrument was measured, it was below the detection limit.

[2] Concentration of radioactive cesium An aluminum plate was placed on a hot plate (maximum temperature 50 ° C.), and a PFA container was fixed thereon.
A glass bell jar was placed on the aluminum plate, and the inside of the bell jar was evacuated using a rotary pump. The valve was opened halfway up to 2 kPa (15 Torr) after evacuation to prevent scattering of liquid in the PFA container. After becoming less than 2 kPa, the valve was fully opened and vacuum drying was performed for 2 hours.

[3] Preparation of heavy nitrate aqueous solution 0.5 cc of heavy water was placed in a PFA container. The container was covered, and CsNO ₃ ( ¹³⁷ Cs nitrate) adhering to the inner wall surface of the container was dissolved. The CsNO ₃ concentration at this time was 1 mM.

[4] Addition of ¹³⁷ Cs to structure (1) Production of structure A structure having the same structure as that shown in FIG. 3 was produced in the same manner as described in [Nuclide conversion experiment by gas permeation method].

(2) Addition of ¹³⁷ Cs FIG. 13 shows a schematic view of an apparatus used for adding ¹³⁷ Cs. In the cesium addition device 400, the structure 410 is installed on the SUS holder 401. At this time, the Pd substrate is placed in contact with the SUS holder 401. A SUS holder 401 is connected to a power source (not shown) as a cathode.
A Teflon holder 402 is placed on the structure 410, and the structure 410 is fixed by the SUS holder 401 and the Teflon holder 402. The Teflon holder 402 has an opening 403 smaller than the structure 410 at the center. By the contact between the Teflon holder 402 and the structure 410, the opening 403 is liquid-tight.

The cesium nitrate heavy aqueous solution adjusted as described above was placed in the opening 403. Thereafter, the anode (platinum electrode) 404 was fixed in contact with the liquid surface of the heavy nitrate aqueous solution. The anode 404 is connected to a power source (not shown).
Electrodeposition was performed by applying a potential difference of 1.0 V between the anode 404 and the structure 410 with a power source for 20 seconds to form a radioactive cesium ( ¹³⁷ Cs) layer on the Pd layer. At this time, the current value was monitored with an ammeter.
After electrodeposition, the solution was sucked and collected with a pipette.

The structure 410 was removed from the holder and dried in the atmosphere for about 5 to 10 minutes. Thereafter, the structure 410 was immersed in 50 cc of ultrapure water for 10 seconds. As a result, CsNO ₃ remaining on the surface was removed. Thereafter, the structure 410 was dried in the atmosphere for about 5 to 10 minutes.
As shown in FIG. 14, the structure 410 manufactured by the above process was accommodated in an acrylic container 420 with the Cs layer facing upward. In this state, the radioactivity of ¹³⁷ Cs was measured with a Ge measuring instrument.

[5] Radionuclide Conversion Experiment by Gas Permeation Method Using the structure produced by the above process, a ¹³⁷ Cs nuclide conversion experiment was conducted by the gas permeation method using the test apparatus of FIG. The experiment was performed under the conditions described in (3) of [Nuclide conversion experiment by gas permeation method].
The structure taken out from the radioactive cesium addition apparatus 400 was accommodated in the container 420 of FIG. In this state, the radioactivity of ¹³⁷ Cs was measured with a Ge measuring instrument.

FIG. 15 shows the results of radioactivity measurement of ¹³⁷ Cs before and after the nuclide conversion experiment. In the figure, the horizontal axis represents the sample number and the vertical axis represents the amount of radioactivity. The experiment was performed on a total of 12 samples. The solid line of the initial value in FIG. 15 indicates the average value of the radioactivity before the experiment, and the dotted line of the initial value indicates the variation from the average value. The average radioactivity before the experiment was 567 Bq. The average value of the radioactivity after the experiment was 521 Bq, which was 8.1% lower than before the experiment.

As a result of examining the inside of the storage chamber 201, the inside of the discharge chamber 202, and the periphery of the sample stage after the experiment by the smear method, ¹³⁷ Cs was not detected. That is, it was confirmed that there was no scattering of ¹³⁷ Cs into the apparatus.
In the test apparatus 200, a molecular sieve 220 is installed between the turbo molecular pump 204 and the rotary pump 205. Γ-ray measurement of ¹³⁷ Cs was performed on the molecular sieves 220 and the oil of the rotary pump 205 after the experiment using a Ge detector. As a result, all were below the detection limit. That is, it was confirmed that there was no ¹³⁷ Cs scattering to the exhaust system.

From the above results, it was confirmed that the radioactivity decreased after the experiment because ¹³⁷ Cs was nuclide-converted. Since the radiation dose was reduced, ¹³⁷ Cs was converted to a stable nuclide.

The inventors of the present application have confirmed that ¹³⁷ Cs has been converted to a stable nuclide by the nuclide conversion apparatus and the nuclide conversion method described in the second embodiment.

DESCRIPTION OF SYMBOLS 1,101 Radiocesium processing system 10,110 Nuclide conversion part 11 Deuterium high pressure part 12 Deuterium low pressure part 13 Deuterium cylinder 14 Vacuum pump 20,120 Radiocesium extraction apparatus 21 Halogen removal part 22 Extraction part 23 Concentration part 24 Adjustment part 25 Cooling unit 30 Radioactive cesium addition unit 31 Container 32 Power source 33, 116 Anode 40 Processing unit 50 Cesium adsorption device 60 Air filter 70 Structure 71 Pd substrate 72 CaO layer 73 Pd layer 111 Deuterium high concentration unit 112 Deuterium low concentration unit 113 Concentration means 114 Gas discharge path 115 Voltage generator 117 Electrolytic solution supply unit

Claims (12)

A halogen removing unit that removes halogen from the solid by washing the solid adsorbed with radioactive cesium with water;
An extraction section for immersing the solid material from which the halogen has been removed in nitric acid or deuterated nitric acid to extract the radioactive cesium from the solid material, and generating an extract;
A concentration unit for heating the extract to evaporate the nitric acid or the deuterated nitric acid from the extract to produce the radioactive cesium nitrate;
An adjustment unit for dissolving the radioactive cesium nitrate in water or heavy water to produce an aqueous solution or heavy aqueous solution of the radioactive cesium nitrate in a predetermined concentration;
A radioactive cesium extraction apparatus comprising:   2. The radioactive cesium extraction apparatus according to claim 1, wherein the extraction unit immerses the solid matter in the nitric acid or the heavy nitric acid having a nitric acid or heavy nitric acid concentration of 6 mol / L or more and 90 ° C. or more under normal pressure. .   The extraction unit immerses the solid matter in the nitric acid or the deuterated nitric acid at a pressure of 16 atm or more and a nitric acid or deuterated nitric acid concentration of 0.5 mol / L or more and 5.0 mol / L or less and 200 ° C. or more. The radioactive cesium extraction apparatus of Claim 1.   The radioactive cesium extraction apparatus according to claim 1, further comprising a cooling unit that collects and cools the evaporated nitric acid or the heavy nitric acid and supplies the extracted nitric acid or the heavy nitric acid to the extraction unit. The radioactive cesium extraction apparatus according to any one of claims 1 to 4,
Using an aqueous solution of the radioactive cesium nitrate produced in the adjustment unit, the radioactive cesium is deposited on one surface of a structure containing palladium or a palladium alloy, or a hydrogen storage metal other than palladium or a hydrogen storage alloy other than palladium alloy. A radioactive cesium addition part to be added;
A radionuclide conversion part that converts the radiocesium added to the structure into another stable element, and
The radioactive cesium addition part,
A container containing an aqueous solution of the radioactive cesium nitrate;
An anode disposed opposite to the one surface of the structure;
Using the structure as a cathode, a voltage generator for applying a voltage between the anode and the structure;
With
The nuclide conversion unit is
The structure to which the radioactive cesium is added; and
A deuterium high-pressure part and a deuterium low-pressure part, which are arranged so as to sandwich the structure from both sides and form a closed space that can be sealed by the structure;
High pressure means for setting the deuterium high pressure part to a state in which the pressure of deuterium is higher than the deuterium low pressure part;
A depressurizing means for setting the deuterium low-pressure portion to a state where the pressure of deuterium is relatively low with respect to the deuterium high-pressure portion;
With
A radioactive cesium treatment system in which the radioactive cesium added to the surface of the structure is nuclide-converted when the deuterium permeates the structure from the deuterium high concentration part toward the deuterium low concentration part. The radioactive cesium extraction apparatus according to any one of claims 1 to 4,
Using a heavy aqueous solution of the radioactive cesium nitrate produced in the adjustment unit, palladium or palladium alloy, or a hydrogen occluding metal other than palladium or a hydrogen occluding alloy other than palladium alloy on one surface of the radioactive cesium A radioactive cesium addition part for adding,
Using a heavy aqueous solution of the radioactive cesium nitrate produced by the adjustment unit, and a nuclide conversion unit that converts the radioactive cesium into another stable element,
The radioactive cesium addition part,
A container containing a heavy aqueous solution of the radioactive cesium nitrate;
An anode disposed opposite to the one surface of the structure;
Using the structure as a cathode, a voltage generator for applying a voltage between the anode and the structure;
With
The nuclide conversion unit is
The structure to which the radioactive cesium is added; and
A deuterium high-concentration portion and a deuterium low-concentration portion that are arranged so as to sandwich the structure from both sides and are separated by the structure;
High concentration means for increasing the concentration of deuterium near the surface of the structure on the deuterium high concentration side;
A concentration reducing means for setting the deuterium low concentration portion to a state in which the concentration of the deuterium is lower than that of the deuterium high concentration portion,
The concentration increasing means
A voltage generator;
An anode disposed opposite to the deuterium high-concentration portion side surface of the structure at an interval;
An electrolytic solution supply part for supplying a heavy aqueous solution of the radioactive cesium nitrate to the deuterium high concentration part,
Using the structure as a cathode, the voltage generator generates a voltage difference between the structure and the anode to electrolyze the heavy aqueous solution to generate the deuterium,
A radioactive cesium treatment system in which the radioactive cesium is nuclide-converted into another stable element in the structure by allowing the deuterium to pass through the structure from the deuterium high concentration part toward the deuterium low concentration part. . A halogen removal step in which a solid substance adsorbed with radioactive cesium is washed with water and halogen is removed from the solid substance;
An extraction step in which the solid matter from which the halogen has been removed is immersed in nitric acid or deuterated nitric acid, and the radioactive cesium is extracted from the solid matter into the nitric acid or deuterated nitric acid;
Heating the extract from which the radioactive cesium has been extracted, evaporating the nitric acid or the deuterated nitric acid from the extract, and a concentration step for producing the radioactive cesium nitrate;
An adjustment step in which the radioactive cesium nitrate is dissolved in water or heavy water to prepare an aqueous solution or heavy aqueous solution of the radioactive cesium nitrate at a predetermined concentration;
A radioactive cesium extraction method comprising:   8. The solid substance is immersed in the nitric acid or the deuterated nitric acid having a concentration of 6 mol / L or more and 90 ° C. or more under normal pressure, and the radioactive substance is extracted into the nitric acid or the deuterated nitric acid. The radioactive cesium extraction method of description.   Under a pressure of 16 atmospheres or more, the solid substance is immersed in the nitric acid or the heavy nitric acid having a concentration of 0.5 mol / L or more and 5.0 mol / L or less and 200 ° C. or more, and the radioactive substance is converted into the nitric acid. Or the radioactive cesium extraction method of Claim 7 extracted to the said heavy nitric acid.   The radioactive cesium extraction method according to claim 7, further comprising a circulation step of collecting and cooling the evaporated nitric acid or heavy nitric acid and supplying the nitric acid or heavy nitric acid that has become liquid to the extraction unit. A radioactive cesium treatment method for treating the radioactive cesium extracted by the radioactive cesium extraction method according to any one of claims 7 to 10,
Including a radioactive cesium addition step and a nuclide conversion step,
The radioactive cesium addition step includes
A step of immersing a structure containing a palladium or palladium alloy, or a hydrogen storage metal other than palladium or a hydrogen storage alloy other than palladium alloy in an aqueous solution of the radioactive cesium nitrate;
In the aqueous solution, an anode is disposed to face the structure, and a voltage is applied between the structure and the anode using the structure as a cathode, whereby a surface of the structure facing the anode An electrodeposition step in which the radioactive cesium is added by electrodeposition,
The nuclide conversion step includes
Deuterium is supplied to the deuterium high-pressure portion on the side of the structure to which the radioactive cesium is added, and the deuterium low-pressure portion on the opposite side of the surface to which the radioactive cesium is added of the structure is the deuterium. The deuterium pressure is relatively lower than that of the high pressure part, and a pressure difference of the deuterium occurs between the deuterium high pressure part and the deuterium low pressure part across the structure, A permeation step in which the deuterium permeates the structure by the pressure difference;
A radioactive cesium treatment method including a conversion step in which the radioactive cesium is nuclide-converted into another stable element when the deuterium permeates the structure. A radioactive cesium treatment method for treating the radioactive cesium extracted by the radioactive cesium extraction method according to any one of claims 7 to 10,
Including a radioactive cesium addition step and a nuclide conversion step,
The radioactive cesium addition step includes
A step in which a structure containing a palladium or palladium alloy, or a hydrogen storage metal other than palladium or a hydrogen storage alloy other than palladium alloy is immersed in a heavy aqueous solution of the radioactive cesium nitrate;
In the aqueous solution, an anode is disposed to face the structure, and a voltage is applied between the structure and the anode using the structure as a cathode, whereby a surface of the structure facing the anode An electrodeposition step in which the radioactive cesium is added by electrodeposition,
The nuclide conversion step includes
A heavy aqueous solution supply step in which a heavy aqueous solution of the radioactive cesium nitrate obtained in the adjustment step is supplied to the deuterium high concentration portion on the surface side to which the radioactive cesium of the structure is added;
An anode is disposed in the heavy aqueous solution of the deuterium high-concentration portion so as to face the structure, and a voltage is applied between the structure and the anode using the structure as a cathode. Is electrolyzed to generate deuterium, and the deuterium low-concentration portion on the other surface side of the structure is brought into a state where the deuterium concentration is relatively lower than the high-deuterium concentration portion. As a result, a deuterium concentration difference occurs between the deuterium high concentration portion and the deuterium low concentration portion across the structure, and the deuterium permeates the structure due to the concentration difference. A permeation process;
A radionuclide conversion step including a conversion step in which the radioactive cesium is converted into another stable element on the surface of the structure on the high deuterium concentration side when the deuterium permeates the structure. Cesium processing method.

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