JP2019163987A - Release cleaning system for radioactive contaminant - Google Patents

Abstract

An object of the present invention is to immerse a radioactive contaminant having a radioactive substance adhered to a surface thereof in a cleaning liquid, separate the adhered radioactive substance after cleaning by stripping, and reduce the radiation dose to a reference value or less to decontaminate. A separation cleaning step of separating and cleaning radioactive substances from radioactive contaminants using electrolytic hydrogen water, a separation step of separating decontaminated contaminants from radioactive cleaning water, and the separated radioactive cleaning A condensing step in which the radioactive substance is captured by the polymer condensing agent by mixing a polymer condensing agent with water to generate a radioactive substance trapping substance, and after the condensing step, the radioactive substance trapping substance and the waste water are separated. And a dewatering step. [Selection diagram] Fig. 1

Description

  The present invention relates to a radioactive contaminant peeling cleaning system, and more particularly to a radioactive contaminant peeling cleaning system in which a radioactive substance adhering to the surface of the radioactive contaminant is peeled and washed by immersing it in a cleaning liquid.

  Due to the radioactive leak caused by the nuclear accident at the Fukushima Daiichi Nuclear Power Station following the Great East Japan Earthquake in March 2011, a large amount of radioactive material was released and diffused in the environment, and various industrial fields were severely damaged. Due to decontamination work conducted after the accident, decontamination of radioactive contaminants in the radioactively contaminated area has progressed, and the area designated as a no-access area immediately after the accident has recently become more returnable. Yes. However, as the recovery progresses, new issues also arise, and there are still many problems that must be solved for the recovery of the nuclear accident.

As one of the new problems, there is a problem of processing a large amount of radioactive contaminants generated during the decontamination work.
The basic policy for the treatment of radioactive contaminants is to temporarily store radioactive contaminants generated by decontamination work in a temporary storage area, reduce the volume at an intermediate treatment facility, and finalize and store at the final treatment facility. . However, the location of the intermediate treatment plant and final treatment plant is not yet determined. Moreover, incineration, which is the most effective volume reduction means in the case of general waste, cannot be used in the case of radioactive pollutants where sealing is the principle. For this reason, the volume of radioactive contaminants accumulated and left in the temporary storage is almost untouched, and a large amount of radioactive contaminants are left in the temporary storage in each place.

One of the radioactive contaminants generated in large quantities is radioactively contaminated wood.
The radioactive material that diffused and fell into the forest after the nuclear accident was attached to the branches and leaves of the tree crown immediately after the accident, but now it is washed by rain and most of the radioactive material is converted to clay minerals on the ground in the forest. It is thought that it is adsorbed and fixed and hardly flows out. For this reason, for the time being, forests that are not accessible to humans are regarded as ecosystems that retain radioactive cesium (see, for example, Non-Patent Documents 1 to 3).

  However, decontamination work was done to cut trees within 20 meters from the satoyama and residential areas used by residents, collect dead leaves, and remove contaminated soil. As a result, a large amount of radioactive contamination was generated. Of this large amount of contaminants, most of the radioactive materials in wood are present in the bark, and it is clear that the core material has a relatively low radiation dose. Use as a raw material is under consideration. On the other hand, the bark still shows a high radiation dose.

Here, it is considered that the radioactivity attached to the surface of the bark can be peeled off by washing. In addition to the bark of wood, there are radioactive contaminants that are thought to be capable of decontamination by attaching and cleaning the radioactive material to the surface and removing it by washing.
However, in order to decontaminate by washing, a large amount of water is required, and washing by a normal method has a problem that it only diffuses radioactive contaminants into water and further expands the volume of radioactive contaminants. is there. Moreover, although the washing | cleaning by hydrogen water was proposed, the effect is inadequate (for example, refer patent document 1).
There has been a need to provide a method for efficiently stripping and cleaning radioactive contaminants attached to a solid surface.

Japanese Patent Laying-Open No. 2015-129065

Radioactive contamination of forests and forest products, Department of Forest Science, The University of Tokyo, Shinya Masmori, [Internet], http: // www. agc. a. u-tokyo. ac. jp / radioecology / pdf / 161121_radioecology. pdf # search =% 27% E6% 94% BE% E5% B0% 84% E8% 83% BD +% E6% A8% B9% E7% 9A% AE% 27 (searched on March 8, 2018) Radioactive contamination caused by the Fukushima nuclear power plant accident and its impact on forest, forestry, and timber-related industries Japan Science Council Agricultural Committee Forestry Subcommittee, September 1, 2014, [Internet], http: // www. scj. go. jp / ja / info / kohyo / pdf / kohyo-22-h140901. pdf # search =% 27% E6% A3% AE% E6% 9E% 97 +% E6% 94% BE% E5% B0% 84% 27 (searched on March 8, 2018) Transfer of decontamination method of radioactive cesium contaminated soil by water washing, Keizo Ishii, Atomic Energy Committee Regular Meeting, September 6, 2011 [Internet] http: // www. aec. go. jp / jicst / NC / iinkai / teirei / siryo20111 / siryo34 / siryo1. pdf # search = '% E6% 94% BE% E5% B0% 84% E8% 83% BD% E6% B1% 9A% E6% 9F% 93% E5% 9C% 9F% E5% A3% 8C +% E9% 99% A4% E6% 9F% 93 '(searched on March 14, 2018) Fluid physical cleaning (1), basic concept and fine particle adhesion, Toshiyuki Sanada, Masao Watanabe, The Chemical Times, 2015 (No. 2), P17-23.

  The present invention has been made in order to solve the above-described problem, and immerses radioactive contaminants having a radioactive substance on the surface in a cleaning solution, and separates the adhered radioactive substance after peeling and cleaning, thereby separating the radioactive contaminants. It is an object of the present invention to provide a radioactive contaminant peeling cleaning system that decontaminates by reducing the radiation dose to a reference value or less.

In addition, the present invention separates radioactive substances from the radioactive washing water separated from the washing liquid after washing to obtain concentrated and concentrated radioactive contaminants, and purifies the waste water so that it can be discharged into the river or the sea as it is. Is an issue.
Furthermore, the processing system for radioactive contaminants according to the present invention has an object of decontaminating the radiation dose of radioactive contaminants to an environmental standard value or less so that the radioactive contaminants can be reused.

  The stripping cleaning system for radioactive contaminants of the present invention, which has been made to solve the above problem, strips and cleans radioactive substances from radioactive contaminants to which radioactive substances have adhered using electrolytic hydrogen water as cleaning water. And a separation step of separating the decontaminated contaminants and the radioactive cleaning water from the cleaning liquid after cleaning, and mixing the polymer condensing agent with the separated radioactive cleaning water to convert the radioactive substance into the polymer condensing agent. It is characterized by comprising a condensing step for capturing radioactive substance trapped matter and a dehydrating step for separating the radioactive substance trapped matter and waste water after the condensing step.

Moreover, in the peeling cleaning step, an electrolytic hydrogen water containing the chemical formula H ₃ O ₂ ^— is used as the cleaning water, and the radioactive substance can be peeled off by the electrolytic hydrogen water containing H ₃ O ₂ ^— .
Moreover, in the said peeling washing | cleaning process, it is preferable to immerse the radioactive contaminant to which the radioactive substance adhered in the washing water, and to vibrate the radioactive contaminant in this immersion state.

In the peeling cleaning step, as the polymer condensing agent, a nonionic condensing agent containing poly (meth) acrylamide, (meth) acrylamide- (meth) acrylic acid copolymer, polycarboxylic acid, polysulfonic acid, or poly An anionic condensing agent containing γ-glutamic acid, a cationic condensing agent containing poly (meth) acrylic acid ester, and a poly (meth) acrylamide- (meth) acrylic acid- (meth) acrylic acid ester copolymer At least one of the amphoteric condensing agents can be used.
Further, the radioactive contaminant may be a bark to which a radioactive substance is attached.

The bark is preferably used in a form cut into chips.
Moreover, the waste water after the dehydration step can be discharged into a river or the sea.

  According to the stripping cleaning system for radioactive contaminants of the present invention, radioactive contaminants with radioactive substances adhered to the surface are immersed in electrolytic hydrogen water, and the contaminated radioactive substances are separated and cleaned after separation cleaning, thereby causing radioactive contamination. The radioactive material adhering to the material was peeled and washed, and the radiation dose of the contaminated material after decontamination could be reduced below the standard value.

  Further, according to the present invention, by adding a polymer condensing agent to the radioactive cleaning water containing the radioactive substance separated from the cleaning liquid, the radioactive substance is trapped in the polymer condensing agent to generate a radioactive substance trapped material, and dehydrated. By separating the radioactive material trap and the wastewater, the volume of radioactive contaminants was reduced to the radioactive material trap, and the wastewater could be discharged directly into the river and the sea.

  When the stripping cleaning system for radioactive contaminants of the present invention is applied, the radiation dose of the bark decontaminated from radioactive bark with a radiation dose of 1162-1621 Bq / kg is reduced to 89.4-121.4 Bq / kg. It can be disposed of as general industrial waste, can be used as a raw material for fertilizers and soil improvers, and the radiation dose of wastewater is below the detection limit (1 Bq / kg) and can be discharged into rivers or the sea. As a result, the radioactive substance trap was able to be reduced to 10 times or less (W / W) of the radioactive bark.

It is a block diagram which shows the process of the peeling cleaning system of the radioactive contaminant of this invention. It is a figure which shows the storage condition of the bark of the timber which was felled for decontamination and was stored in the intermediate storage facility temporary storage place.

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.
This description is for explaining the present invention, and is not intended to limit the technical scope of the present invention. The present invention can be implemented with various modifications without departing from the technical scope of the present invention.

FIG. 1 is a block diagram showing the steps of the radioactive contaminant peeling cleaning system of the present invention.
As shown in FIG. 1, the stripping cleaning system for radioactive contaminants of the present invention is decontaminated with a stripping cleaning step (S-1) for stripping and cleaning radioactive materials by immersing the radioactive contaminants in electrolytic hydrogen water. Separation step (S-2) for separating the contaminants and the radioactive cleaning liquid, and a condensation step for generating the radioactive substance trapping material by capturing the radioactive substance in the polymer condensing agent by mixing the polymer condensing agent with the radioactive cleaning liquid. (S-3) and the drainage process (S-4) which isolate | separates the condensed radioactive substance capture material and waste_water | drain can be included.

[Radioactive contamination]
The radioactive pollutant to be decontaminated by the method of the present invention is a radioactive pollutant in which radioactive material that has fallen due to a nuclear accident has adhered, or radioactive material has adhered to the surface due to secondary contamination. There is no particular limitation as long as it can be peeled and washed.

  Most of the radioactive materials that have fallen to the land after being scattered in the atmosphere due to the nuclear accident are thought to be strongly adsorbed by silicate minerals, which are micro- to nano-order fine particles of clay minerals (for example, non-patent literature) 3), in order to decontaminate radioactive contaminants adhering to the surface of the solid, the clay mineral fine particles must be washed away. However, since micro-to-nano order fine particles have a small mass, it is difficult to clean and remove them by physical cleaning means such as fluid injection, friction, and ultrasonic waves (see, for example, Non-Patent Document 4).

[Electrolytic hydrogen water]
Since the electrolyzed hydrogen water used in the present invention contains hydrogen, the water cluster becomes small and penetrates between the solid surface and the attached fine particles to peel off the fine particles attached to the solid surface. It contains a negatively-charged active ingredient represented by the chemical formula H ₃ O ₂ ^— and penetrates between the fine particles adhering to the solid surface and electrically converts the fine particles adhering to the solid surface. It has a feature that fine particles are washed away by peeling with a repulsive force.

  The water used as the raw material for the electrolytic hydrogen water is colorless and transparent, and preferably has a conductivity of 500 μS / cm or less, more preferably has a conductivity of 200 μS / cm, and most preferably has a conductivity of 100 μS / cm or less. is there.

  Electrolytic hydrogen water uses the above-mentioned clean water, high voltage of 100 to 300 V, and three-phase AC power of 50 to 300 A to treat water of 100 L / min, and 80 to 150 ° C. by generated Joule heat. Electrolytic hydrogen water produced by electrolysis at a high temperature of 5 to atmospheric pressure. The electrolytic hydrogen water is preferably colorless and transparent.

[Peeling cleaning process]
A radioactive contaminant is immersed under a water surface in a washing tank containing 4 to 20 times (weight / volume) of electrolyzed hydrogen water at 15 to 100 ° C. for 5 to 600 minutes to separate the radioactive material from the surface of the radioactive contaminant. It is preferable to carry out peeling cleaning by transferring it into the cleaning liquid.
When the amount of the electrolytic hydrogen water used here is 4 times or less, the amount of the electrolytic hydrogen water is too small to perform sufficient peeling cleaning, and even if it is used 20 times or more, the peeling cleaning effect does not increase proportionally. Is not preferable.

Moreover, the peeling cleaning effect can be further improved by vibrating or stirring while the radioactive contaminant is immersed.
Furthermore, by arranging a plurality of cleaning tanks that accommodate a plurality of cleaning tanks in parallel, by sequentially immersing radioactive contaminants from one cleaning tank to the other cleaning tank in order of facing, repeating the peeling cleaning operation a plurality of times, It is possible to improve the peeling cleaning effect and reduce the amount of electrolytic hydrogen water used.

[Separation process]
The separation step of the present invention is a step of separating the contaminant that has been decontaminated by moving the radioactive substance into the cleaning liquid and the radioactive cleaning liquid to which the radioactive substance has migrated. The separation method can be appropriately selected according to the shape of the contaminants as long as the radioactive cleaning liquid does not leak.
For example, as a practical example, a filtration method or a method in which radioactive contaminants are accommodated in a cage made of a metal net that does not allow the radioactive contaminants to pass through, immersed in an aqueous layer, and lifted after completion of cleaning can be mentioned.

[Condensation process]
In the condensation process of the present invention, a condensing agent is added to the radioactive cleaning liquid after cleaning, and the solid containing the radioactive substance dispersed in the radioactive cleaning liquid is captured by the radioactive substance condensing agent to generate a radioactive substance trapping substance, thereby capturing the radioactive substance. This is a step of separating the objects. The condensing agent used here is not particularly limited as long as it captures and separates the radioactive substance contained in the radioactive cleaning liquid and is suitable for the purpose of the present invention, but sulfate band, aluminum chloride, polyaluminum chloride, ferric chloride. Or inorganic condensing agent containing polyferric sulfate, organic condensing agent containing polyamine, melamic acid colloid or dicyandiamide, nonionic condensing agent containing poly (meth) acrylamide, (meth) acrylamide- (meth) acrylic Anionic condensing agent containing acid copolymer, polycarboxylic acid, polysulfonic acid, poly-γ-glutamic acid, cationic condensing agent containing (meth) acrylic acid ester, or poly (meth) acrylamide- (meth) acrylic acid- A polymer condensing agent containing an amphoteric condensing agent containing a (meth) acrylic acid ester, and one or more selected from Door can be.
More preferably, the condensing agent can be a polymeric condensing agent.

[Dehydration process]
A dehydration process is a process of isolate | separating the radioactive condensate produced | generated and precipitated by the condensation process, and waste_water | drain, For example, it can carry out using a centrifuge. The separated radioactive condensate is a product obtained by condensing and reducing the radioactivity of radioactive contaminants. Moreover, the radioactivity of waste water can be reduced below the environmental standard, can be discharged into the sea and rivers, and can be used for agricultural water.

[Example]
(Radioactive contamination)
As an embodiment of the present invention, the intermediate facility temporary storage place (hereinafter referred to as “flexible pack”) is peeled off from a tree felled in a forest in the satoyama area and the residential area and filled in a flexible container pack (hereinafter referred to as “flexible pack”). Taking the bark accumulated in the “temporary storage site” as an example, decontamination and volume reduction of radioactive contaminants by the radioactive contaminant exfoliation cleaning system of the present invention will be described in detail. However, the following description is for clearly explaining the present invention, and does not limit the present invention. The present invention can be variously modified and implemented without departing from the technical scope of the present invention.

FIG. 2 is a diagram illustrating a storage state of wood bark that has been cut for decontamination, filled in a “flexible pack”, and stored in a “temporary storage site”.
As shown in FIG. 2, a large amount of radioactive bark filled in a “flexible pack” is accumulated in the “temporary storage site”. The service life of “Flexon Pack” is 3 years under solar radiation conditions. Since the flexible container pack is covered with light-shielding and waterproofing, deterioration of the flexible container pack due to solar radiation and leakage of radioactivity due to rainwater are prevented for the time being. is needed.

(Electrolytic hydrogen water)
The electrolyzed hydrogen water of the present invention uses an electrolyzed hydrogen water production apparatus (GFX11-MA001, manufactured by F & O Laboratories, Inc.) at a water temperature of 3 ° C. and water having a conductivity of 148 μS / cm at a flow rate of 5.0 L / min. Then, electrolysis was performed with a three-phase alternating current (60 Hz) having a voltage of 200 V and a current of 77.6 to 83.8 A to obtain electrolytic hydrogen water having an outlet temperature of 80 to 92 ° C., which was cooled and used.

(Peeling and cleaning process)
Three radioactive bark specimens (A to C) contaminated with different radiation doses of 5.0 kg each were made into chips, uniformly contained in a metal cage using a 2 mm mesh metal mesh, and 20 ° C. electrolytic hydrogen water The radioactive material was peeled and washed by immersing it under the surface of a water tank containing 50 L and shaking for 1 hour.

(Separation process)
Then, the waste containing the decontaminated contaminants that had been separated from the radioactive material was lifted onto the water surface and shaken to drain the cleaning solution. Next, 10 L of electrolytic hydrogen water as a rinsing solution is uniformly sprayed on a bark chip in a metal cage after being sprayed uniformly, and then drained every time, and then 10 L of water is uniformly sprayed as a washing solution, followed by shaking. The decontaminated contaminants and the radioactive cleaning liquid were obtained by draining.
The electrolytic hydrogen water used as the rinse liquid can be recovered and used as the electrolytic hydrogen water of the next lot. Further, it is preferable that the water washing liquid is discharged if the radiation dose is below the reference value, and if it exceeds the reference value, it is preferably mixed with the radioactive cleaning liquid for processing.

(Comparative Example 1)
The radioactive bark used in A of the example was used in the same manner as in the example, except that tap water was used instead of the electrolytic hydrogen water, and the peeling washing step and the separation step were performed to obtain a sample of Comparative Example 1.

(Evaluation)
The radiation dose before and after decontamination of the bark of Examples A to C and Comparative Example was measured.
Measurement facility Food analysis center Tsukuba branch Measurement method Nuclide by gamma-ray spectrometry using germanium semiconductor detector
Measurement method (precision measurement)
“Not detected” in Table 1 indicates that the value is below the detection limit (1 Bq / kg).
Table 1 shows the radiation dose before cleaning and the radiation dose after decontamination of each sample (A to C) and the comparative example.

[Table 1]

  As shown in Table 1, the bark of Examples A to C can be disposed of as normal industrial waste by reducing the radiation dose of radioactive bark to 200 Bq / kg or less by decontamination by the method of the present invention. It can also be used as a raw material for compost and soil improvers.

[Example]
(Condensation process)
After adding 1.0 g of polymer condensing agent which is a polyacrylamide acrylic acid copolymer to 10 L of the radioactive cleaning liquid produced in the separation step and leaving it for 6 hours, 0.82 kg of radioactive condensate using a continuous centrifuge And 72 L of waste water containing the rinsing liquid and the washing liquid.
The radioactive condensate is a paste containing a lot of water, and has a radiation dose of 3000 Bq / kg or more according to simple measurement. It accommodated in the airtight container as it was.
The radiation dose of the wastewater is below the detection limit (1 Bq / kg) and can be discharged into the river or the sea.

As mentioned above, although preferred embodiment regarding this invention was described, this invention is not limited to the said embodiment, All the changes in the range which does not deviate from the technical scope to which this invention belongs are included.

Claims (7)

A stripping cleaning step of stripping and cleaning the radioactive material using radioactive hydrogen water as cleaning water from radioactive contaminants attached to the radioactive material;
A separation step of separating the decontaminated contaminant and the radioactive cleaning water from the cleaning liquid after cleaning;
A condensing step of capturing the radioactive substance in the polymer condensing agent by mixing the polymer condensing agent with the separated radioactive washing water to generate a radioactive substance trapping material;
After the condensation step, a dehydration step for separating the radioactive substance trapped material and the waste water,
A stripping cleaning system for radioactive contaminants, comprising: In the stripping and cleaning process, the chemical formula H ₃ O ₂ as washing water ^- claim 1, characterized by separating the radioactive material by electrolytic hydrogen water containing ^- using an electrolytic hydrogen water containing said H ₃ O ₂ The radioactive contamination treatment system described in 1.   3. The radioactive contaminant according to claim 1, wherein in the peeling cleaning step, the radioactive contaminant to which the radioactive substance is attached is immersed in the cleaning water, and the radioactive contaminant is vibrated in the immersed state. Processing system.   In the condensation step, as the polymer condensing agent, a nonionic condensing agent containing poly (meth) acrylamide, (meth) acrylamide- (meth) acrylic acid copolymer, polycarboxylic acid, polysulfonic acid, or poly-γ -An anionic condensing agent containing glutamic acid, a cationic condensing agent containing poly (meth) acrylic acid ester, and an amphoteric condensation containing poly (meth) acrylamide- (meth) acrylic acid- (meth) acrylic acid ester copolymer The system for treating radioactive contaminants according to claim 1, wherein at least one of the agents is used.   The radioactive contaminant treatment system according to any one of claims 1 to 4, wherein the radioactive contaminant is a bark to which a radioactive substance is attached.   6. The radioactive contaminant treatment system according to claim 5, wherein the bark is used in a form cut into chips. The radioactive pollutant treatment system according to claim 1, wherein the drainage after the dehydration step is discharged into a river or the sea.

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