JP2013057591A - Method for processing activation concrete - Google Patents

Abstract

PROBLEM TO BE SOLVED: To efficiently and certainly remove Co, Eu of a target nuclide from activation concrete, to make an installation space of a processor small by improving dewaterability, to suppress process costs, and to reduce a labor and costs of pH management.SOLUTION: The present invention provides a processing method including: an extraction process 3 of immersing a ground product S consisting of activation concrete 1 obtained in a grinding process 2 in nitric acid solution M1; a neutralization process 4 of immediately raising the nitric acid solution M1 to an alkali region of ph7-12 to precipitate metal salt consisting of components of a target nuclide K1 of Co, Eu, and a non-target nuclide K2 such as Fe and Al contained in the ground product S; a washing process 5 of washing a precipitate T1 obtained in the neutralization process 4 with water W1; and an ether extraction process 6 of collecting the non-target nuclide K2 in a precipitate T2 after washing after the washing process 5 by ether extraction, after solving the precipitate T2 after the washing washed in the washing process 5 in hydrochloric acid.

Description

  The present invention relates to a method for treating activated concrete in which the target nuclide is removed from the activated concrete to treat the activated concrete.

  2. Description of the Related Art Conventionally, in a nuclear facility such as a nuclear power plant, a structural frame is constructed of concrete because it has sufficient strength and is excellent in radiation shielding. Since the concrete of such nuclear facilities is exposed to radiation and activated, there is a need for storage management as radioactive waste when the facility is replaced (decommissioned). For this reason, in recent years, the processing method of activation concrete has been proposed (for example, refer nonpatent literature 1).

By the way, although various elements are contained in concrete, the target nuclide to be activated in this is Co (cobalt) and Eu (europium). Concrete also contains non-target nuclides such as Fe (iron) and Al (aluminum).
In the method for treating activated concrete of Non-Patent Document 1, the concrete is dissolved and heated with an acidic treatment liquid such as nitric acid, and the metals (Co, Eu, Fe, Al, etc.) extracted in the treatment liquid are recovered. Yes.

  In such a volume reduction technology for activated concrete, the target nuclide is extracted from the aggregate with nitric acid, and the target nuclide is recovered through a neutralization step. And since the extracted nitric acid contains a lot of metal (iron) outside the target nuclide, the non-target nuclide component mainly composed of iron and the target nuclide component are separated and disposed of by performing a two-step neutralization process. To be done. In other words, in the first stage of the two-stage neutralization method, the target nuclide is neutralized at about pH 4 to precipitate and collect iron (Fe or Al) and further precipitated in the second stage due to the pH (about pH 4) by the precipitation. Is kept in the supernatant, and the pH is raised to about 7 to promote the solidification of the target nuclides Co and Eu.

“Developed the world's first technology to reduce the activity of activated concrete”, [online], March 2, 2010, Shimizu Corporation, [Search September 8, 2011], Internet <URL: http: // / Www. shimz. co. jp / news_release / 2010/770. html>

However, the conventional activation concrete processing method has the following problems.
That is, in the first-stage precipitation in the conventional two-stage neutralization method, a trace amount of target nuclides (Co, Eu) is mixed into the precipitate mainly composed of iron, so that the target performance may not be exhibited. Further, there is a problem that the dewaterability is poor and the space for the processing apparatus becomes excessive.
In addition, when the first-stage supernatant is processed at a higher pH of about 7, the target nuclide does not precipitate and accumulates in the liquid as it is, so that the target nuclide remaining in the liquid can be recovered. Furthermore, there is a concern that a process may be required, and there has been a concern of further cost increase.
Furthermore, it is very difficult to control the pH value of the nitric acid solution at 4 or 7 at the time of neutralization, and the labor and cost for this pH control are increased, and there is room for improvement in that respect.

The present invention has been made in view of the above-described problems, and can efficiently and reliably remove target nuclides of Co and Eu from activated concrete, and can improve the dehydrability and install a processing apparatus. An object of the present invention is to provide a method for treating activated concrete capable of reducing the space.
Another object of the present invention is to provide a method for treating activated concrete that can reduce the process cost and reduce the labor and cost for pH control.

  In order to achieve the above object, in the method for treating activated concrete according to the present invention, a pulverizing step of pulverizing the activated concrete, an extraction step of immersing the pulverized material obtained in the pulverizing step in a nitric acid solution, and a nitric acid solution having a pH of 7 The neutralization process which raises at a stretch to the alkaline region of -12, and precipitates the metal salt which consists of the component of the target nuclide of cobalt, europium, and a non-target nuclide contained in a ground material, and the precipitate obtained by the neutralization process. And a washing step of washing with water.

  In the present invention, in the neutralization step, the nitric acid solution that has undergone the extraction step in which the pulverized product obtained in the pulverization step is immersed is raised to an alkaline region of pH 7 to 12 at a stretch, so that non-target nuclides such as Fe (iron) and Al ( Aluminum) and the like precipitate as hydroxides, and the target nuclides Co (cobalt) and Eu (europium) also become hydroxides and coprecipitate. That is, since the target nuclide and non-target nuclide components contained in the extract co-precipitate, precipitation and removal can be performed reliably and efficiently. Then, at least the target nuclide is not left in the neutralized nitric acid neutralized solution, and this nitric acid neutralized solution can be appropriately treated as a general waste solution. Further, in the washing step, the precipitate obtained in the neutralization step is washed with water, so that neutralized salts (for example, sodium nitrate and ammonium nitrate) dissolved in a high concentration in the moisture retained in the precipitate are removed. Can be removed from sediment. Further, the target nuclide is not dissolved in the washed water after washing.

As described above, in the method for treating activated concrete according to the present invention, the precipitate that is disposed of as the radioactive waste obtained by drying and solidifying the precipitate that has been washed in the washing step includes iron content of non-target nuclides. It becomes possible to reduce the volume to 10% or less by weight ratio of the original aggregate and the like.
Further, in the method for treating activated concrete according to the present invention, the neutralization step with nitric acid solution is performed once, so that the removal operation can be performed efficiently, and two-step neutralization is performed as in the past. The process cost can be reduced as compared with the method. In addition, since there is no need to manage the pH of about 4 at the first stage, which is difficult to control in the two-step neutralization method, the pH can be easily controlled, and the cost can be reduced.
Moreover, the conventional two-stage neutralization method has poor dewaterability of the first-stage precipitate, and requires a large facility cost for solid-liquid separation. However, in the present invention, the dewaterability is also excellent and simple. It is possible to cope with equipment with a simple structure.

  In the method for treating activated concrete according to the present invention, it is preferable to recover the non-target nuclide in the precipitate by ether extraction after dissolving the precipitate washed in the washing step in hydrochloric acid.

  In this case, the iron content occupying a high concentration in the precipitate washed in the washing step can be further dissolved in hydrochloric acid, and then the non-target nuclide (iron) in the washed precipitate can be recovered by ether extraction. Thus, all the target nuclides contained in the original nitric acid are present in the hydrochloric acid, and only iron content can be eliminated almost 100%.

  Moreover, in the processing method of the activated concrete which concerns on this invention, it is more preferable that the water used at a washing | cleaning process is hot water.

  In this case, the neutralized salt can be reliably removed from the precipitate by washing the precipitate using hot water in the washing step.

According to the method for treating activated concrete of the present invention, the nitric acid solution in which the pulverized material is soaked is rapidly raised to the alkaline region of pH 7 to 12, so that the target nuclides Co and Eu are efficiently and reliably obtained from the activated concrete. Can be removed. Moreover, the installation space of a processing apparatus can be made small by improving dehydrating property.
Furthermore, in the activation concrete processing method of the present invention, the process cost can be suppressed by using a one-step neutralization step, and the pH value is difficult to manage as in the conventional two-step neutralization method. Since it is not necessary to manage the pH to a certain extent, there is an effect that it is possible to reduce labor and cost for pH management.

It is a flowchart which shows the processing method of the activated concrete by embodiment of this invention. It is a flowchart which shows the processing method of the activated concrete by other embodiment of this invention.

  Hereinafter, the processing method of activated concrete by embodiment of this invention is demonstrated based on drawing.

  As shown in FIG. 1, the activated concrete processing method according to the present embodiment is, for example, an activated waste concrete lump (solid waste generated as a result of renovation or dismantling of a nuclear facility such as a nuclear power plant). It relates to a method for treating activated concrete 1).

  As shown in FIG. 1, the activated concrete processing method includes a pulverization step 2 for pulverizing the activated concrete 1, an extraction step 3 for immersing the pulverized material S obtained in the pulverization step 2 in a nitric acid solution M1, and its The nitric acid solution M1 is raised to an alkaline region of pH 7 to 12 at a stretch, and the target nuclides K1 of Co (cobalt) and Eu (europium) contained in the pulverized product S, and non-such as Fe (iron) and Al (aluminum) Neutralization step 4 for precipitating the metal salt (precipitate T1) composed of the component of the target nuclide K2, washing step 5 for washing the precipitate T1 obtained in the neutralization step 4 with water W1, and washing in the washing step 5 After the obtained precipitate (washed precipitate T2) is dissolved in hydrochloric acid, ether extraction step 6 for recovering the non-target nuclide K2 in the washed precipitate T2 after the washing step 5 by ether extraction, and after the ether extraction step 6 Deposit ( And a recovery step 7 for drying and solidifying the precipitate T3) after extraction.

(Crushing process 2)
As shown in FIG. 1, in the pulverization step 2, the activated concrete 1 is pulverized using a pulverizer so as to have a particle diameter of, for example, 8 mm or less. At this time, it is desirable to pulverize the activated concrete 1 in a flake form so that a pulverized product S having a surface area as large as possible can be obtained by using a pulverizer such as a roll crusher. Then, it is confirmed that the particle size of the pulverized product S is 8 mm or less with a sieve or the like. In addition, as long as the particle size of the pulverized material S is 8 mm or less, each particle size may be uneven.

(Extraction process 3, neutralization process 4)
Next, after performing the extraction step 3 in which the pulverized product S obtained in the pulverization step 2 is immersed in the nitric acid solution M1, the nitric acid solution M1 is raised to the alkaline region at once, and the purpose of cobalt and europium contained in the pulverized product S The neutralization process 4 which precipitates the metal salt (precipitate T1) which consists of a component of the nuclide K1 and the non-target nuclide K2 is performed. The concentration of the nitric acid solution M1 is 30% by weight or more and 70% by weight or less. By raising the nitric acid solution M1 at once to an alkaline region of pH 7 to 12 at an arbitrary time, the target nuclide K1 and the non-target nuclide K2 components are co-precipitated and extracted. In this neutralization process, Fe, Al, and the like of the non-target nuclide K2 become hydroxides and precipitate, and Co and Eu of the target nuclide K1 become hydroxides and coprecipitate together. Here, the extraction time for immersing the pulverized material S in the nitric acid solution M1 is 12 to 48 hours, although it varies depending on the size and material of the aggregate, for example. Then, at least the target nuclide K1 does not remain in the neutralized nitric acid neutralized solution M2, and the nitric acid solution M2 is appropriately treated.

(Washing process 5)
Then, the washing | cleaning process 5 which isolate | separates the deposit T1 obtained by the neutralization process 4 from a nitric acid neutralization liquid, and wash | cleans with the water W1 is performed.
Specifically, the nitric acid neutralization liquid is introduced into a solid-liquid separation apparatus such as a centrifugal separator or a filter filtration apparatus, and solid-liquid separation is performed. Water W1 is supplied to the precipitate to wash the precipitate T1. Thereby, the neutralized salt (for example, sodium nitrate and ammonium nitrate) dissolved in the water | moisture content hold | maintained at the precipitate T1 at high concentration can be removed from the precipitate T1. At this time, Co and Eu are not redissolved in the wash water. In addition, this water W1 can perform more reliable washing | cleaning, for example by using hot water of 40-90 degreeC.

(Ether extraction step 6)
Next, with respect to the iron content occupying a high concentration in the washed precipitate T2 washed in the washing step 5, after further dissolving in hydrochloric acid, ether for recovering the non-target nuclide K2 in the washed precipitate T2 by ether extraction Extraction step 6 is performed. As a result, 100% of the target nuclide K1 contained in the original nitric acid is present in the hydrochloric acid, and only about 100% of the iron content can be eliminated.

(Recovery process 7)
Subsequently, after extraction of the target nuclide K1 and the hydroxide of Co and Eu and the non-target nuclide K2 such as Al, which are precipitated after the ether extraction step 6, with respect to the precipitate T3 after extraction. Then, a recovery step 7 for drying and solidifying and recovering is performed. These recovered hydroxides are sent to a metal component drying step (not shown), dried, and then disposed of as radioactive waste. At this time, since the neutralized salt has been removed from the dried solid content by the washing step 5, it is disposed in a state where the neutralized salt is low.
Further, the treatment liquid W2 in which the neutralized salt is dissolved in the washing step 5 to become high salt water is diluted and discharged.

Next, the effect | action of the processing method of the activated concrete mentioned above is demonstrated based on drawing.
As shown in FIG. 1, in the neutralization step 4, the nitric acid solution M1 that has passed through the extraction step 3 in which the pulverized product S obtained in the pulverization step 2 is immersed is raised to an alkaline region of pH 7 to 12 at a stretch. The non-target nuclide K2 such as Fe and Al precipitates as hydroxides, and the target nuclide K1 Co and Eu form hydroxides and coprecipitate.
That is, since the target nuclide K1 and the non-target nuclide K2 components co-precipitated in the extract are co-precipitated, precipitation and removal can be performed reliably and efficiently. Then, at least the target nuclide K1 does not remain in the neutralized nitric acid neutralized liquid M2, and the nitric acid neutralized liquid M2 can be appropriately treated as a general waste liquid.

  Further, in the washing step 5, the precipitate T1 obtained in the neutralization step 4 is washed with water W1, so that the neutralized salt dissolved at a high concentration in the water retained in the precipitate T1 is precipitated. It can be removed from T1. Further, the target nuclide K1 is not dissolved in the cleaning water W2 after the cleaning.

As described above, the post-extraction precipitate T3 that is disposed of as the radioactive waste obtained by drying and solidifying the post-cleaning precipitate T2 in the cleaning step 5 includes the iron content of the non-target nuclide K2. The volume can be reduced to 10% or less (7% in the examples described later) by weight.
Furthermore, since the neutralization step 4 with the nitric acid solution M1 is performed once, the removal operation can be performed efficiently, and the process cost is reduced as compared with the conventional two-step neutralization method. be able to. In addition, since there is no need to manage the pH of about 4 at the first stage, which is difficult to control in the two-step neutralization method, the pH can be easily controlled, and the cost can be reduced.
Moreover, the conventional two-stage neutralization method has poor dewaterability of the first-stage precipitate, and requires a large facility cost for solid-liquid separation. However, in this embodiment, the dewaterability is also excellent. It is possible to cope with equipment with a simple structure.

  Further, the iron content occupying a high concentration in the washed precipitate T2 washed in the washing step 5 is further dissolved in hydrochloric acid, and then the non-target nuclide K2 in the washed precipitate T2 is recovered by ether extraction. As a result, all of the target nuclide K1 contained in the original nitric acid is present in the hydrochloric acid, and only iron content can be eliminated almost 100%.

As described above, in the method for treating activated concrete according to the present embodiment, the nitric acid solution in which the pulverized material S is soaked is raised at a stretch to the alkaline region of pH 7 to 12, so that from the activated concrete 1 to Co of the target nuclide K1, Eu can be efficiently and reliably removed. Moreover, the installation space of a processing apparatus can be made small by improving dehydrating property.
Furthermore, by setting it as the neutralization process 4 of 1 step | paragraph, since process cost can be suppressed, pH management of about 4 difficult pH values like the conventional 2 step | paragraph neutralization method becomes unnecessary, There is an effect that it is possible to reduce labor and cost for pH control.

As mentioned above, although embodiment of the processing method of the activated concrete by this invention was described, this invention is not limited to said embodiment, It can change suitably in the range which does not deviate from the meaning.
For example, in this embodiment, the ether extraction step 6 is performed after the washing step 5 and then the precipitate T3 is recovered after the extraction. However, the present invention is not limited to such a processing step, and FIG. As shown, the ether extraction step 6 can be omitted. In this case, it becomes the method of performing the collection | recovery process 7 which dries, solidifies, and collect | recovers with respect to the precipitate T2 after washing | cleaning wash | cleaned by the washing | cleaning process 5.

In the present embodiment, hot water is used in the cleaning step 5, but it is not limited to hot water, and water at normal temperature may be used.
In addition, it is possible to appropriately replace the components in the above-described embodiments with known components without departing from the spirit of the present invention.

1 Activation concrete 2 milling step 3 HNO ₃ extraction step 4 neutralization step 5 washing step 6 ether extraction step 7 recovery step K1 object species K2 non-target species M1 nitrate solution M2 nitrate neutralization solution S pulverized material T1 precipitate T2 washed Precipitate T3 Precipitate after extraction W1 Water W2 Treatment liquid

Claims (3)

A crushing process for crushing the activated concrete;
The pulverized product obtained in the pulverization step is immersed in a nitric acid solution, and the nitric acid solution is raised to an alkaline region of pH 7 to 12 at a stretch. From the components of cobalt, europium target nuclides, and non-target nuclides contained in the pulverized product. A neutralization step of precipitating a metal salt,
A step of separating the precipitate obtained in the neutralization step from the nitric acid neutralization solution and washing with water;
A method for treating activated concrete, comprising:   The method for treating activated concrete according to claim 1, wherein after the precipitate washed in the washing step is dissolved in hydrochloric acid, non-target nuclides in the precipitate are recovered by ether extraction. The method of treating activated concrete according to claim 1 or 2, wherein the water used in the washing step is hot water.

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