JP6668215B2 - Radioactive waste treatment method and treatment device - Google Patents

Description

  Embodiments of the present invention relate to a method and an apparatus for treating radioactive waste containing radioactive nuclides that are easily soluble.

  When a large-scale accident occurs at a nuclear power plant, a large amount of cooling water is injected for cooling the reactor, so that a large amount of high-level contaminated water is generated. Also, when radionuclides are released to the environment, a situation occurs in which the soil around the nuclear power plant is contaminated with the radionuclides.

Such half-life in the high-level contaminated water or contaminated soil 28.8 years of radioactive strontium ^{(90 Sr)} and 30.2 years of radioactive cesium ^{(137 Cs)} half-life, such as is included long radionuclides Therefore, these radionuclides need to be eliminated because they may have long-term adverse effects on the environment.

  In general, as a measure against high-level contaminated water, means for removing radionuclides by using an adsorbent such as zeolite for reducing the radioactivity concentration and reducing the volume is known. As for contaminated soil, a method has been proposed in which radionuclides are eluted using an extractant such as an acidic solution and the extracted acidic solution is brought into contact with an adsorbent such as zeolite to remove the radionuclides.

JP 2013-96982 A JP 2014-16311 A

By the way, among radionuclides, radioactive strontium ( ⁹⁰ Sr) and radioactive cesium ( ¹³⁷ Cs) have a property of being easily soluble in water (easy solubility). Therefore, the adsorbent to which the readily soluble radionuclide is adsorbed needs to be stored in a stable form for a long time so that the radionuclide does not elute into the environment.

  Embodiments of the present invention have been made in order to solve the above-described problems, and stably solidify an adsorbent on which a readily soluble radionuclide is adsorbed, and produce a solidified body capable of suppressing elution of the radionuclide. An object of the present invention is to provide a method and an apparatus for treating waste.

In order to solve the above problems, a method for treating a radioactive waste according to an embodiment of the present invention includes a radioactive waste containing a readily soluble radionuclide and an adsorbent containing titanium oxide adsorbing the readily soluble radionuclide. and shall to Yusuke a compression step of compressing the mixture obtained in the mixing step and the mixing step of mixing the door, and a firing step of firing the compressed product obtained in the compression step.

Further, a radioactive waste treatment apparatus according to an embodiment of the present invention is a radioactive waste treatment apparatus for performing the radioactive waste treatment method according to any one of claims 1 to 5 , A mixing device for mixing a radioactive waste containing a readily soluble radionuclide and an adsorbent containing a titanium oxide adsorbing the readily soluble radionuclide , a compression device, and a firing device are provided.

  ADVANTAGE OF THE INVENTION According to embodiment of this invention, elution of a radionuclide from the adsorbent which the radioactive nuclide with the easy solubility was adsorbed can be suppressed.

The processing flow figure of the radioactive waste concerning a 1st embodiment. The block diagram of the processing apparatus of the radioactive waste concerning 1st and 2nd embodiment. The figure which shows the component of the solidification body which concerns on 1st and 2nd embodiment. The processing flow figure of the radioactive waste concerning a 2nd embodiment.

Hereinafter, embodiments of a method and an apparatus for treating radioactive waste according to the present invention will be described with reference to the drawings.
In the following description, radioactive strontium will be described as an example of a radionuclide to be treated, but the present invention can also be applied to other easily soluble radionuclides such as radioactive cesium.

[First Embodiment]
A method and apparatus for treating radioactive waste according to the first embodiment will be described with reference to FIGS.

(Constitution)
In the present embodiment, radioactive strontium contained in high-level contaminated water is adsorbed on an adsorbent composed of, for example, a titanate-based adsorbent, and a waste adsorbent after adsorption (hereinafter, also referred to as “radioactive waste”) is converted into zeolite or the like. After being mixed with an adsorbent consisting of and compressed, and then calcined, a stable solidified substance from which radioactive strontium is hardly eluted is formed.

  As shown in FIG. 2, the radioactive waste treatment apparatus used in the present embodiment includes a waste container 1 in which radioactive waste containing radioactive strontium is stored and an adsorption container in which an adsorbent made of, for example, zeolite or the like is stored. Material container 2, a mixing device 3 for stirring and mixing the radioactive waste and the adsorbent, a compression device 4 for compressing the mixture mixed by the mixing device 3, and firing the mixture compressed by the compression device 4. And a firing device 5 for obtaining a solidified body 10.

(Action)
The processing flow of the radioactive waste will be described with reference to FIG.
First, an adsorbent made of radioactive waste containing radioactive strontium and zeolite (for example, A-type zeolite) is dehydrated in the waste container 1 and the adsorbent container 2 (dehydration step; S1).

  In the dehydration step S1, a drying means is generally used, the drying temperature is, for example, 60 ° C. or more, and the drying time is about 24 hours, depending on the processing amount. As the drying means, a heater, a dryer, or the like is used.

Next, the dewatered radioactive waste and the adsorbent are mixed by the mixing device 3 (mixing step; S3), and then the mixture of the radioactive waste and the adsorbent is compressed by the compression device 4 (compression step; S4). ). As the compression device 4, a molding device such as a press machine is used. The pressing pressure is, for example, 300 kg / cm ² or more. By passing through this compression step, it is possible to prevent the mixture from scattering in the subsequent firing step (S5).

Next, the mixture compressed in S4 is fired by the firing device 5 (firing step; S5), and the solidified body 10 is formed. As the firing device 5, an electric furnace, a firing furnace, a firing kiln, or the like can be used.
The firing temperature is set to 800 ° C. or higher, preferably about 1100 ° C. By setting the firing temperature to 800 ° C. or higher, the adsorption performance of radioactive strontium on the adsorbent is improved, so that the radioactive strontium is fixed in the fired solid. Thereby, elution of radioactive strontium from the solidified body 10 after firing can be suppressed.

If the firing temperature is 800 ° C. or higher, the components of the adsorbent and the radioactive strontium generate a mineral (slowsonite: SrAl ₂ Si ₂ O ₈ ), so that the radioactive strontium can be firmly incorporated into the mineral. it can.

Thereby, the solidified body 10 in which the radioactive strontium is immobilized for a long time and stably can be obtained.
In the firing step S5, fixation is performed during firing.

(Dissolution test 1)
The dissolution test result of the solid obtained based on the above processing flow will be described below.
The solids used in this dissolution test 1 are as follows.

<Example 1> A solidified product 1 of a titanate-based adsorbent (about 50 wt%) adsorbing radioactive strontium fired at 1100 ° C and A-type zeolite (about 50 wt%).
<Comparative Example 1> A solid 2 of only a titanate-based adsorbent adsorbing radioactive strontium, which was calcined at 1100 ° C.
In the firing step (S5), the temperature was raised to 1100 ° C. at a rate of 20 ° C./min, and then maintained at that temperature for 1 hour.

In the dissolution test, the solidified body was immersed in pure water at a liquid-solid ratio of 10 ml / g for 6 hours, and the immersion liquid was passed through a 0.45 μm filter, followed by ICP-AES (ICP emission spectroscopy; Inductively Coupled Plasma). Strontium concentration was measured by Atomic Emission Spectroscopy). Table 1 shows the results.

As shown in Table 1, the eluted strontium concentration in Comparative Example 1 was 18 mg / l, whereas in Example 1, it was 0.1 mg / l or less, which was below the detection limit.
From this, it was found that the solidified body formed by adding the adsorbent to the radioactive waste can suppress the elution of radioactive strontium more than the solidified body formed without adding the adsorbent.

FIG. 2 is a diagram obtained by analyzing the solidified body 1 of Example 1 with an X-ray diffractometer, and a certain amount of SrAl ₂ Si ₂ O ₈ was detected. This indicates that radioactive strontium is present in the solidified body 1 in the mineral form of SrAl ₂ Si ₂ O ₈ , and that radioactive strontium is a strong and stable form in the solidified body for a long period of time. That is, it is understood that the elution of radioactive strontium from the solidified body is suppressed for a long time.

(effect)
According to the present embodiment, the easily soluble radionuclide contained in the waste adsorbent can be firmly fixed to the adsorbent made of zeolite or the like. It can be suppressed in the long term.

[Second embodiment]
A method and an apparatus for treating radioactive waste according to the second embodiment will be described with reference to FIGS.

(Constitution)
In this embodiment, an example of treating contaminated soil containing radioactive strontium (hereinafter, also referred to as “radioactive waste”) will be described.
The processing apparatus and processing conditions are basically the same as those in the first embodiment, and a duplicate description will be omitted.

(Action)
The processing flow of radioactive waste (contaminated soil) according to the second embodiment will be described with reference to FIG.
First, an adsorbent made of zeolite (for example, A-type zeolite) is dehydrated in the adsorbent container 2 (dehydration step; S1), and a radioactive waste made of contaminated soil containing radioactive strontium is dehydrated and classified ( Dehydration / classification step; S2).

  In the classification process of S2, organic substances such as plants and small organisms, debris, and the like contained in the contaminated soil are removed, and the classification process is performed so that the particle size of the soil is, for example, 2 mm or less. An air separator, a sieve, or the like is used as a classifier (not shown).

  Next, the radioactive waste and the adsorbent are mixed by the mixing device 3 (mixing process; S3), and then the mixture of the radioactive waste and the adsorbent is compressed by the compression device 4 (compression step; S4), and then fired. Firing is performed by the apparatus 5 (firing step; S5). Thereby, the solidified body 10 in which the radioactive strontium is fixed stably for a long time can be obtained.

(Dissolution test 2)
The dissolution test result of the solid obtained based on the above processing flow will be described below.
The solids and the like used in this dissolution test 2 are as follows.

<Example 2> Solidified body 3 of contaminated soil containing radioactive strontium (about 50 wt%) and A-type zeolite (about 50 wt%) fired at 1100 ° C.
<Example 3> Solidified body 4 of contaminated soil (about 50 wt%) containing mordenite (about 50 wt%), which is one kind of zeolite fired at 1100 ° C, and radioactive strontium.

<Example 4> Solidified body 5 of contaminated soil containing titanium oxide adsorbent and radioactive strontium fired at 100 ° C.
<Example 5> Solidified body 6 of contaminated soil (about 50 wt%) containing chabazite (IE-96), which is one type of zeolite, calcined at 1100 ° C (about 50 wt%) and radioactive strontium.

Comparative Example 2 Contaminated soil contaminated with unfired radioactive strontium.
Comparative Example 3 Solidified contaminated soil 7 containing radioactive strontium fired at 1100 ° C.

In the dissolution test 2, as shown in Table 2, the strontium concentrations detected in Examples 2 to 5 were 0.1, 17, 16, and 31 mg / l, whereas in Comparative Examples 2 to 3, They were 2462 and 43 mg / l, respectively.
The measuring method is the same as in the above-mentioned dissolution test 1. Table 2 shows the dissolution test results.

  From the results of the dissolution test 2, the solidified bodies (Examples 2 to 5 and Solidified bodies 3 to 6) prepared by adding an adsorbent to radioactive waste as contaminated soil are more radioactive waste only (Comparative Example). 2) Or it can be seen that the amount of radioactive strontium eluted from the solidified bodies 3 to 6 is lower than that of the solidified body prepared without adding an adsorbent to radioactive waste (Comparative Example 3, solidified body 7).

In particular, in the solid 3 of Example 2, the amount of radioactive strontium eluted was below the detection limit, and was hardly detected.
Further, when the solidified body 3 of Example 2 was analyzed with an X-ray diffractometer, the result shown in FIG. 2 was obtained as in the first embodiment. That is, according to FIG. 2, a certain amount of SrAl ₂ Si ₂ O ₈ was detected from the solidified body 3. This indicates that radioactive strontium is present in the solidified body 2 in the mineral form of SrAl ₂ Si ₂ O ₈ , and elution of radioactive strontium from the solidified body is suppressed for a long time.

Similarly, it is considered that radioactive strontium also exists in the solid form in the mineral form of SrAl ₂ Si ₂ O ₈ in the solid forms 3 to 6 of Examples 2 to 5, and the elution of radioactive strontium from the solid form is It is thought to be suppressed in the long term.

(effect)
According to the present embodiment, even in a contaminated soil containing a readily soluble radionuclide, the easily soluble radionuclide can be firmly fixed to the adsorbent made of zeolite or the like, so that the easily radioactive nuclide can be easily removed from the solidified body. Elution of soluble radionuclides can be suppressed for a long time.

  Although some embodiments of the present invention have been described above, these embodiments are presented as examples and are not intended to limit the scope of the invention. These new embodiments can be implemented in other various forms, and various omissions, replacements, and changes can be made without departing from the spirit of the invention. These embodiments and their modifications are included in the scope and gist of the invention, and are also included in the invention described in the claims and their equivalents.

DESCRIPTION OF SYMBOLS 1 ... Waste container, 2 ... Adsorbent container, 3 ... Mixing device, 4 ... Compression device, 5 ... Baking device, 10 ... Solidified body

Claims (6)

A mixing step of mixing a radioactive waste containing a readily soluble radionuclide and an adsorbent containing titanium oxide adsorbing the readily soluble radionuclide, and a compression step of compressing the mixture obtained in the mixing step,
Method of processing radioactive waste that have a, a firing step of firing the compressed product obtained in the compression step. The method for treating a radioactive waste according to claim 1, wherein the radioactive waste containing the easily soluble radionuclide is contaminated soil containing radioactive strontium . The method according to claim 1, wherein in the mixing step, the radioactive waste containing the easily soluble radionuclide and the adsorbent are mixed at a ratio of about 50 wt%, respectively.   The method for treating radioactive waste according to any one of claims 1 to 3, wherein in the firing step, the firing temperature is a set temperature of 800 to 1100 ° C.   The method for treating a radioactive waste according to any one of claims 1 to 4, further comprising a classifying step of classifying the radioactive waste before the mixing step. A radioactive waste treatment apparatus for performing the radioactive waste treatment method according to any one of claims 1 to 5,
A mixing device for mixing a radioactive waste containing a readily soluble radionuclide and an adsorbent containing a titanium oxide adsorbing the readily soluble radionuclide , a compression device, and a baking device, Radioactive waste treatment equipment.

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