JP6982412B2 - Radioactive waste treatment method and treatment equipment - Google Patents

Description

The present invention relates to a method and a treatment apparatus for treating radioactive liquid waste.

Radioactive waste liquid generated from nuclear facilities contains various radionuclides, and in order to remove the nuclides, radioactive waste liquid to be treated (hereinafter referred to as "treatment target") is used as an adsorbent that can adsorb and remove nuclides. There is a way to pass water.

When the water to be treated is acidic or neutral, it is known that the performance of some adsorbents is deteriorated, and it may not be possible to sufficiently adsorb and remove nuclides. Further, when the water to be treated is acidic, the pH does not fall within the range of the general wastewater standard of the nuclear facility even after the nuclides are adsorbed and removed, and the water cannot be discharged.

In order to solve the above-mentioned problems, if the water to be treated is acidic or neutral, the pH may be adjusted to an appropriate pH (neutral to weakly alkaline). There are several methods for adjusting the pH, but the method of injecting an alkaline agent into the water to be treated to adjust the pH to a predetermined pH is mainly used. As the alkaline agent, sodium hydroxide or the like is used.

However, when a highly alkaline alkaline agent such as sodium hydroxide is directly injected into the acidic or neutral water to be treated, a portion that becomes highly alkaline locally occurs in the water to be treated and exists in the water to be treated. There is a problem that metal ions such as Ca ²⁺ and Mg ^{2+ are precipitated as carbonates and hydroxides.}

When precipitates are generated in the radioactive effluent, radioactive nuclides may coprecipitate with the precipitates, making it difficult to adsorb and remove them, or the precipitates may block the adsorbent and make it difficult for the radioactive effluent to pass through. ..

On the other hand, when a relatively low alkaline alkaline agent that does not generate a precipitate is injected, a large amount of the alkaline agent solution to be injected is required, and the amount of radioactive liquid waste flowing through the adsorbent may increase.

Under these circumstances, a method of injecting an alkaline agent to adjust the pH is not desirable for adsorbing and removing nuclides.

As a method of adjusting the pH without using an alkaline agent, a method of using a carbonate mineral or the like as a solid material for adjusting the pH (hereinafter referred to as "pH buffering material") is known. For example, Patent Document 1 describes a method for treating pesticide wastewater by contacting pesticide wastewater with a carbonate mineral acting as a pH buffer and then removing the pesticide with a biological carrier.

Patent Document 2 describes a treatment method for removing iodide ions by passing water to be treated, which has been adjusted to be acidic, through an activated carbon filter.

Japanese Unexamined Patent Publication No. 6-15285 Japanese Unexamined Patent Publication No. 57-205304

The carbonate mineral described in Patent Document 1 is intended for pesticide wastewater, and may not be an appropriate material when targeting radionuclides. That is, Patent Document 1 is different from the technical field of the present invention.

Since the waste liquid generated in the treatment described in Patent Document 2 is acidic, there is a problem that it cannot be directly drained. Further, when the treatment step of other nuclides is used in combination after the treatment of Patent Document 2, there is a problem that the performance of the adsorbent in the latter stage may be deteriorated.

The present invention is to adjust the acidic or neutral water to be treated (radioactive waste liquid) to an appropriate pH (neutral to weakly alkaline) evenly without generating precipitates such as carbonates and hydroxides. With the goal.

The present invention is a method for treating acidic or neutral radioactive liquid waste generated from a nuclear facility, and pH adjustment for adjusting the pH of the radioactive liquid waste with a solid compound (hereinafter referred to as a pH buffer material) that elutes an alkaline component. It includes a step and a treated liquid storage step of storing the liquid treated in the pH adjusting step.

According to the present invention, the acidic or neutral water to be treated (radioactive waste liquid) is evenly adjusted to an appropriate pH (neutral to weakly alkaline) without generating precipitates such as carbonates and hydroxides. can do.

Further, according to the present invention, since the treated liquid is neutral or weakly alkaline, it can be discharged from a nuclear facility, and even if it is not discharged, it can be discharged into a relatively inexpensive stainless steel container without worrying about corrosion of the container. The treated liquid can be stored in.

When not discharged, the above-mentioned container can be used for long-term storage without worrying about corrosion of the container, so that nuclides having a short half-life such as iodine can be reduced in the process.

It is a flow chart which shows the treatment method of the radioactive waste liquid of Example 1. FIG. It is a schematic block diagram which shows the radioactive waste liquid treatment apparatus of Example 1. FIG. It is a graph which shows the test result of Example 1. FIG. It is a flow chart which shows the treatment method of the radioactive waste liquid of Example 2. It is a graph which shows the test result of Example 2. FIG. It is a flow chart which shows the treatment method of the radioactive waste liquid of Example 3. FIG. It is a schematic block diagram which shows the radioactive waste liquid treatment apparatus of Example 3.

The present invention raises the pH of acidic or neutral water to be treated (radioactive waste liquid) evenly and appropriately using a pH buffer material, and is liquid without generating precipitates such as carbonates and hydroxides. It relates to a treatment method and a treatment apparatus for adjusting the pH to neutral or weakly alkaline.

The radioactive waste liquid treatment method and treatment apparatus according to the embodiment of the present invention are as follows.

Radioactive waste liquid is generated from nuclear facilities and is acidic or neutral.

The method for treating the radioactive waste liquid includes a pH adjusting step of adjusting the pH of the radioactive waste liquid with a pH buffer material that elutes an alkaline component, and a treated liquid storage step of storing the liquid treated in the pH adjusting step. Storage has the effect of reducing nuclides with a short half-life, such as iodine-131. Further, since the treated liquid is neutral or weakly alkaline, the treated liquid can be stored in a relatively inexpensive stainless steel container without worrying about corrosion of the container. In other words, since it is not necessary to coat the inner wall of the stainless steel container or the like in order to suppress corrosion, an inexpensive container can be used.

When the radioactive waste liquid contains radioactive Sr, the method for treating the radioactive waste liquid further includes an Sr removing step of removing Sr from the stored liquid using an Sr adsorbent after the treated liquid storage step. Is desirable. The Sr adsorbent is preferably a silicate-based compound, a titanium acid compound, or a zeolite.

In the method for treating radioactive waste liquid, when the radioactive waste liquid contains radioactive Cs, radioactive Ru, and radioactive I, at least one of Cs, Ru, and I is removed from the stored liquid by using an adsorbent. It is desirable to include an adsorption removal step. This removes radionuclides other than Sr. Since the pH of the liquid is adjusted, it is possible to prevent the performance of the adsorbent in the subsequent stage from deteriorating.

Further, in the method for treating radioactive waste liquid, the pH of the radioactive waste liquid can be adjusted evenly and appropriately in the pH adjusting step, so that the wastewater standards of nuclear facilities (generally pH 6 to 9 or pH 6 to 8) are satisfied. The treated liquid can be discharged to the outside. The process of discharging the treated liquid to the outside (outside the nuclear facility) will be referred to as the "treated liquid discharge process".

In the method for treating radioactive waste liquid, an adsorption removal step of removing at least one of Cs, Ru and I using an adsorbent may be provided from the liquid treated in the pH adjusting step. The adsorption removal step may be performed without providing the treated liquid storage step.

Further, an acid addition step of adjusting the pH may be provided by adding an acid to the liquid treated in the pH adjusting step. As a result, the pH that has become too high can be lowered, and an appropriate pH can be obtained. The acid used here preferably contains at least one of hydrochloric acid and sulfuric acid. Further, carbon dioxide gas (carbon dioxide) may be injected into the liquid in order to lower the pH of the liquid. In the present specification, carbon dioxide gas is also treated as a kind of acid.

Examples of the pH buffer material include magnesium oxide, magnesium hydroxide, dolomite, hydrotalcite, iron hydroxide and the like. These may be used alone or in combination.

As a specific example, the action when magnesium oxide (MgO) is used as the pH buffer material is shown. The following shows the reaction formula in which MgO comes into contact with water and releases an alkaline component.

(Equation 1) MgO (s) + H ₂ O → Mg ^{2 +} + 2OH ⁻
(Equation 2) 2OH ⁻ + 2H ⁺ → 2H ₂ O
Equation 1 shows the dissolution of MgO. Equation 2 shows a reaction in which the ^{acid (H +} ) is neutralized following the dissolution of MgO in Equation 1 when the water to be treated is acidic. Further, the amount of MgO dissolved in neutral water is 9.8 × 10 ^-3 g / L (in _{terms of Mg (OH) 2} ), and the pH of the aqueous solution in which MgO is saturated and dissolved is 10.3, so that MgO is dissolved. The alkaline component (OH ⁻ ) released from the water does not cause the pH of the water to be treated to be high even locally, and even if the water to be treated contains Ca, Mg, or carbonate ions, the precipitate or scale It becomes possible to prevent the occurrence.

The pH adjusted by MgO, which is a pH buffering material, is maintained for a long period of time as long as MgO is dissolved.

The radioactive waste liquid treatment apparatus includes a pH adjustment unit that mixes the radioactive liquid waste and a pH buffer material, and a treated liquid storage container that stores the liquid sent from the pH adjustment unit. The pH adjusting unit may have any configuration as long as the radioactive liquid waste and the pH buffer material are brought into contact with each other.

In the radioactive waste liquid treatment apparatus, it is further desirable to provide a container containing an Sr adsorbent on the downstream side of the treated liquid storage container.

In the radioactive waste liquid treatment apparatus, it is further desirable to provide a container containing an adsorbent for removing at least one of Cs, Ru and I on the downstream side of the treated liquid storage container.

The pH adjusting unit may include a buffer tank, and the pH buffer material may be configured to be supplied to the buffer tank.

Further, the pH adjusting unit may include a container containing a pH cushioning material filled with the pH buffering material.

The pH buffer material filled in the container containing the pH buffer material may be taken out from the container containing the pH buffer material, and the pH buffer material for replacement may be filled in the container containing the pH buffer material. This has the advantage that it is not necessary to perform a large-scale work such as replacing the container containing the pH cushioning material together with the container.

The radioactive waste treatment device includes a pH adjustment unit that mixes the radioactive liquid and a pH buffer material, and a container containing an adsorbent that removes at least one of Cs and Ru and I on the downstream side of the pH adjustment unit. It may be provided.

Hereinafter, examples of the present invention will be described with reference to the drawings.

The following examples are presented as examples and do not limit the scope of the present invention. These examples can be added, omitted, replaced, changed, or the like without departing from the gist of the present invention.

FIG. 1 is a flow chart showing a method for treating radioactive waste liquid according to Example 1.

As shown in this figure, first, the radioactive liquid waste, which is the water to be treated, is acidic. This waste liquid shall include a waste liquid that has become acidic due to the addition of an acid and a waste liquid that has become acidic due to the addition of an acid and a reducing agent.

Then, the acidic radioactive liquid waste is passed through a pH buffer material to make it weakly alkaline. As a result, treated water is obtained.

FIG. 2 is a schematic configuration diagram showing a radioactive liquid waste treatment apparatus of Example 1.

In this figure, the treatment apparatus includes a water collection tank 1 to be treated, a supply pump 2, a container 4 containing a pH buffer material, and a treated water receiving tank 5. The container 4 containing the pH buffer material is a container filled with the solid pH cushioning material. The pH buffer is magnesium oxide.

The water S to be treated is injected into the water collection tank 1 to be treated and sent to the container 4 containing the pH buffer material by the supply pump 2. The liquid that has passed through the container 4 containing the pH buffer material becomes weakly alkaline and is stored in the treated water receiving tank 5 (treated liquid storage container).

An actual treatment test of radioactive liquid waste was conducted using the treatment device shown in this figure.

In this test, the pH of the water to be treated was adjusted to about 3.5 with hydrochloric acid. Then, the flow rate of the water to be treated ^{was set to the space velocity (SV) 15 (hr -1} ) and introduced into the container 4 containing the pH buffer material to change the liquid property to weak alkaline.

FIG. 3 is a graph showing the test results of Example 1.

As shown in this figure, the water to be treated has a pH of 3.5 before being introduced into the container 4 containing the pH buffer material, and has a pH of 8.9 (at the outlet of the container 4 containing the pH buffer material). It was weakly alkaline).

As described above, by using the solid pH buffer material, it is possible to discharge weakly alkaline water which is a liquid in which no precipitate is formed from the outlet of the container 4 containing the pH buffer material.

On the other hand, in the case of the method of continuously injecting a chemical solution such as a NaOH solution, the water to be treated and the chemical solution are not completely mixed instantly, so that the pH is locally increased and a precipitate is generated. There was a possibility that it would be done.

In this embodiment, it was confirmed that the pH of the precipitate can be adjusted to be lower than the pH produced by passing water to be treated through a container filled with magnesium oxide as a pH buffer material (container 4 containing a pH buffer material). did.

Examples of the pH buffer material include magnesium hydroxide, iron hydroxide and the like, in addition to magnesium oxide. The pH buffer material can be selected according to the water quality of the water to be treated.

FIG. 4 is a flow chart showing a method for treating the radioactive liquid waste of Example 2.

This figure differs from FIG. 1 (Example 1) in that the liquid to be treated is neutral. It is the same as in Example 1 in that the flow velocity of the water to be treated is the space velocity (SV) 15 (hr ^{-1) and the pH buffer material is magnesium oxide.}

FIG. 5 is a graph showing the test results of Example 2.

As shown in this figure, the water to be treated has a pH of 7.2 (neutral) before being introduced into the container 4 containing the pH buffer material, and has a pH at the outlet of the container 4 containing the pH buffer material. It was 9.2 (weakly alkaline).

Also in this example, it was possible to prevent the formation of precipitates.

Depending on the water quality of the radioactive liquid waste, the pH after passing water through the pH buffer material may be higher than expected even if the same treatments as in Examples 1 and 2 are performed. In that case, the pH may be adjusted by adding a small amount of acid after passing water through the pH buffer material. Examples of the acid include hydrochloric acid, sulfuric acid and the like. Further, carbon dioxide gas (carbon dioxide) may be injected into the liquid in order to lower the pH of the liquid.

FIG. 6 is a flow chart showing a method for treating the radioactive liquid waste of Example 3.

The difference from Example 2 in this figure is that when the pH of the neutral treatment target water in contact with the pH buffer material reaches about 10, the liquid property is adjusted to neutral by adding an acid. Is.

FIG. 7 is a schematic configuration diagram showing the radioactive waste liquid treatment apparatus of Example 3.

In this figure, since hydrochloric acid is added to the treated water on the downstream side of the treated water receiving tank 5, the hydrochloric acid in the acid container 3 can be supplied by the acid supply pump 7. The liquid whose liquidity has been adjusted to neutral by adding hydrochloric acid is stored in the pH-adjusted waste liquid tank 6.

In Examples 1 to 3, the pressure-fed water was passed through the container 4 containing the pH buffer as shown in FIG. 2, but in Example 4, the water storage container (buffer tank) to be treated was used instead of the pressure-fed water. Add the pH buffer and immerse. This eliminates the need for a powerful pump to pump and pass water through the container. As a result, the pump can be miniaturized or can be configured without a pump, and the equipment cost can be reduced.

In Example 5, when the pH cushioning material used in Examples 1 to 3 deteriorates and the pH is out of the target range, the entire container is not replaced and only the used pH cushioning material is taken out. Then, the operation of filling the container with a new pH buffer material is performed. As a result, the container can be reused and the running cost can be reduced.

In Examples 1 to 3, the liquid property was made weakly alkaline or neutral by using a pH buffer material, but in Example 6, a case where radionuclides other than Sr are removed will be described.

Radionuclides other than Sr include cesium (Cs), ruthenium (Ru), iodine (I) and the like.

Of these, Cs can be adsorbed and removed by an adsorbent such as strontium (Sr), which is an adsorbent capable of adsorbing strontium (Sr).

On the other hand, Ru can be adsorbed and removed by using an adsorbent such as silica gel, activated carbon, or iron oxide.

Iodine is mainly present in the form of ^{I −} and IO ^3-. When ^{removing I −} , it can be adsorbed and removed by using an adsorbent such as silver-impregnated zeolite. When ^{removing IO 3-} , it can be adsorbed and removed by using an adsorbent such as a cerium oxide-based adsorbent.

1: Treatment target water collection tank 2: Supply pump 3: Acid container 4: Container containing pH buffer material 5: Treatment water receiving tank, 6: pH-adjusted waste liquid tank, 7: Acid supply pump.

Claims (18)

A method for treating acidic or neutral radioactive liquid waste generated from nuclear facilities.
A pH adjusting step of adjusting the pH of the radioactive liquid by passing water through the pH buffer material that elutes the alkaline component, and a pH adjusting step.
A method for treating radioactive waste liquid, which comprises a treated liquid storage step of storing the liquid treated in the pH adjusting step. The method for treating radioactive liquid waste according to claim 1.
Further, a method for treating radioactive waste liquid, which comprises a Sr removing step of removing Sr from the liquid using an Sr adsorbent after the treated liquid storage step. The method for treating radioactive liquid waste according to claim 2.
The method for treating radioactive liquid waste, wherein the Sr adsorbent is a silicate-based compound, a titanium acid compound, or a zeolite. The method for treating radioactive waste liquid according to any one of claims 1 to 3.
Further, a method for treating radioactive waste liquid, which comprises an adsorption removal step of removing at least one of Cs, Ru and I from the liquid using an adsorbent. A method for treating acidic or neutral radioactive liquid waste generated from nuclear facilities.
A pH adjusting step of adjusting the pH of the radioactive liquid by passing water through the pH buffer material that elutes the alkaline component, and a pH adjusting step.
A method for treating radioactive waste liquid, which comprises a treated liquid discharge step of discharging the liquid treated in the pH adjusting step to the outside. A method for treating acidic or neutral radioactive liquid waste generated from nuclear facilities.
A pH adjusting step of adjusting the pH of the radioactive liquid by passing water through the pH buffer material that elutes the alkaline component, and a pH adjusting step.
A method for treating radioactive waste liquid, which comprises an adsorption removal step of removing at least one of Cs, Ru and I from the liquid treated in the pH adjusting step using an adsorbent. The method for treating radioactive liquid waste according to any one of claims 1 to 6.
Further, a method for treating radioactive waste liquid, which comprises an acid addition step of adjusting the pH by adding an acid to the liquid treated in the pH adjusting step. The method for treating radioactive liquid waste according to claim 7.
A method for treating radioactive liquid waste, wherein the acid contains at least one of hydrochloric acid and sulfuric acid. The method for treating radioactive liquid waste according to any one of claims 1 to 8.
The method for treating radioactive liquid waste, wherein the pH buffer material is magnesium oxide, magnesium hydroxide, dolomite, hydrotalcite or iron hydroxide. It is a treatment device for radioactive liquid waste generated from nuclear facilities.
A pH adjustment unit that allows the radioactive liquid waste to pass through the pH cushioning material, and
A device for treating radioactive liquid waste, comprising a treated liquid storage container for storing the liquid sent from the pH adjusting unit. The radioactive waste liquid treatment apparatus according to claim 10.
Further, a radioactive waste liquid treatment apparatus provided with a container containing an Sr adsorbent on the downstream side of the treated liquid storage container. The radioactive waste liquid treatment apparatus according to claim 10 or 11.
Further, a radioactive liquid waste treatment apparatus provided with a container containing an adsorbent for removing at least one of Cs, Ru and I on the downstream side of the treated liquid storage container. The radioactive waste liquid treatment apparatus according to any one of claims 10 to 12.
The pH adjusting unit includes a buffer tank.
The pH buffer material is a device for treating radioactive liquid waste, which is configured to be supplied to the buffer tank. The radioactive waste liquid treatment apparatus according to any one of claims 10 to 13.
The pH adjusting unit is a device for treating radioactive liquid waste, which comprises a container containing the pH buffer material filled with the pH buffer material. The radioactive waste liquid treatment apparatus according to claim 14.
A device for treating radioactive waste liquid, wherein the pH buffer material filled in the pH buffer material container is taken out from the pH buffer material container, and a replacement pH buffer material is filled in the pH buffer material container. It is a treatment device for radioactive liquid waste generated from nuclear facilities.
A pH adjustment unit that allows the radioactive liquid waste to pass through the pH cushioning material, and
A radioactive liquid waste treatment device provided with a container containing an adsorbent for removing at least one of Cs and Ru and I on the downstream side of the pH adjustment unit. The method for treating radioactive liquid waste according to any one of claims 1 to 9.
The pH adjusting step is a method for treating radioactive waste liquid, which prevents the formation of precipitates when the pH is adjusted. The radioactive waste liquid treatment apparatus according to any one of claims 10 to 16.
A device for treating radioactive liquid waste, which can prevent the formation of precipitates when the water is passed through the pH adjusting unit.

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