JP2018173391A - Decontamination processing water processing method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a processing method of decontamination processing water capable of preventing obstruction of piping and/or devices.SOLUTION: The processing method of decontamination processing water includes: an oxidation step in which decontamination object adhered with metal oxide is immersed in processing water which contains oxidant derived permanganate ion to allow a metal element constituting the metal oxide to elute into the processing water; a pH adjustment step of adjusting the pH of the processing water to be 7 to 13 by adding a pH modifier to the processing water after the oxidation step; and a first reduction process of reducing the permanganate ion contained in the processing water by adding a first reductant to the processing water after the pH adjustment step.SELECTED DRAWING: Figure 2

Description

  The present disclosure relates to a decontamination water treatment method.

In a nuclear power plant or the like, when a radioactive substance adheres to a member constituting the plant equipment, chemical decontamination may be performed to remove the radioactive substance from the member.
For example, Patent Document 1 discloses a method for eluting and removing a radioactive substance from an object to be decontaminated with an oxide film containing the radioactive substance using an oxidizing agent or the like. In this method, an object to be decontaminated is immersed in treated water to which permanganic acid is added as an oxidizing agent to elute radioactive substances together with components contained in the oxide film, and then the treated water is brought into contact with an ion exchange resin. Then, the radioactive material contained in the treated water is adsorbed on the ion exchange resin and removed.
Further, in Patent Document 1, in order to remove the oxidizing agent from the treated water, a reducing agent is added to the treated water after elution of the radioactive substance as described above, and precipitation is caused by the reaction between the oxidizing agent and the reducing agent. After forming the product, it is disclosed to remove the precipitate from the treated water.

JP 2014-92442 A

By the way, if the treatment water used for chemical decontamination of a plant or the like contains an oxidant, the plant equipment immersed in the treatment water may be corroded by the oxidant, for example, which may affect the plant equipment. . In order to suppress such an influence on plant equipment, it is necessary to inject pure water. Since pure water is injected, surplus water containing an oxidizing agent is generated.
As described in Patent Document 1, for example, the oxidizing agent in the treated water can be removed as a precipitate by adding a reducing agent to the treated water containing the oxidizing agent to generate a precipitate. However, the precipitate produced by the reaction between the oxidizing agent and the reducing agent may have low fluidity, and in this case, there is a possibility that piping and equipment constituting the plant are blocked by the precipitate.
In this regard, Patent Document 1 does not specifically disclose a measure for suppressing blockage of equipment due to precipitates generated when the oxidizing agent is removed from the treated water.

  In view of the above circumstances, at least one embodiment of the present invention aims to provide a method for treating decontaminated water that can suppress blockage of piping and equipment.

(1) A decontamination treatment water treatment method according to at least one embodiment of the present invention includes:
An oxidation step of immersing the decontamination object to which the metal oxide is attached in treated water containing permanganate ions derived from an oxidant, and eluting the metal element constituting the metal oxide in the treated water;
A pH adjusting step of adjusting the pH of the treated water to 7 or more and 13 or less by adding a pH adjuster to the treated water;
A first reduction step of adding a first reducing agent to the treated water after the pH adjustment step to reduce the permanganate ions contained in the treated water;
Is provided.

As a result of intensive studies by the inventors, when the treated water containing permanganate ions is acidic, when a reducing agent is added to the treated water, a reaction between the permanganate ions contained in the treated water and the reducing agent results. It was revealed that the generated precipitate has a relatively low fluidity, whereas when the treated water containing permanganate ions has a relatively high pH, the generated precipitate has a relatively high fluidity.
In this regard, according to the method of (1) above, after eluting the metal element from the decontamination object with permanganate ions, the pH of the treated water containing the permanganate ions is adjusted to 7 or more and 13 or less. Therefore, since the permanganate ions in the treated water are reduced, a precipitate having a relatively high fluidity is likely to be generated by the reaction between the permanganate ions and the reducing agent. Therefore, blockage of piping and equipment (for example, blockage of an evaporator used in a concentration step described later) caused by a precipitate generated by a reaction between permanganate ions and a reducing agent can be suppressed.

(2) In some embodiments, the method of (1) further includes a heating step of heating the treated water after the first reduction step.

  According to the method (2), the fluidity of the precipitate generated by the reaction between the permanganate ion and the reducing agent can be further increased by heating the treated water after the first reduction step. Therefore, it is possible to effectively suppress blockage of piping and equipment due to the deposit.

(3) In some embodiments, the method of (1) or (2) further includes a concentration step of concentrating the treated water after the first reduction step.

  According to the method of (3) above, the treated water after the first reduction step is concentrated, and even if the concentration of the precipitate in the treated water becomes high, the fluidity of the precipitate is kept relatively high. And blockage of piping and equipment due to sediment can be suppressed.

(4) In some embodiments, in the method of (3) above, the concentration step includes the heating step.

  According to the method (4), since the heating step is performed as the concentration step for concentrating the treated water, the treatment efficiency of the treated water can be improved.

(5) In some embodiments, in the method of any one of (1) to (4) above, in the pH adjustment step, the pH of the treated water is adjusted to 10 or more and 12 or less.

  According to the method of (5) above, the permanganate ion in the treated water is reduced after the pH of the treated water containing the permanganate ion is adjusted to 10 or more and 12 or less in the pH adjustment step. The reaction between the ions and the reducing agent makes it easier to produce a precipitate having a relatively high fluidity. Therefore, blockage of piping and equipment caused by precipitates generated by the reaction between permanganate ions and a reducing agent can be effectively suppressed.

(6) In some embodiments, in any of the methods (1) to (5), the oxidizing agent includes potassium permanganate.

  According to the method of said (6), the metal element which comprises the metal oxide which adhered to the decontamination target object by immersing a decontamination target object in the treated water to which potassium permanganate was added as an oxidizing agent ( For example, chromium) can be effectively eluted in the treated water.

(7) In some embodiments, in the methods (1) to (6), the pH adjuster includes at least one alkali metal hydroxide.

  According to the method of (7), since the alkali metal hydroxide that is a strongly basic compound is used as the pH adjuster, the treated water can be used even when the pH of the treated water before pH adjustment is relatively low. It is easy to adjust pH of 7 to 13 or less.

(8) In some embodiments, in any of the methods (1) to (7), the first reducing agent includes at least one of bisulfite, sulfite, and hydrazine.

  According to the method (8), since at least one of sodium bisulfite or hydrazine is used as the first reducing agent, the permanganate ion in the treated water is reduced under the condition that the pH of the treated water is 7 or more and 13 or less. It can be reduced appropriately.

(9) In some embodiments, in any of the above methods (1) to (8),
In the first reduction step, the first reducing agent in an amount of 1.1 to 1.3 molar equivalents is added to the treated water with respect to the oxidizing agent.

  According to the method of (9) above, since 1.1 mol equivalent or more of the first reducing agent is added to the treated water with respect to the oxidizing agent, a part of the first reducing agent is caused by oxygen dissolved in the treated water. Even if it is consumed, permanganate ions derived from the oxidizing agent can be appropriately reduced. Further, according to the method (9), since the first reducing agent having a molar equivalent of 1.3 or less with respect to the oxidizing agent is added to the treated water, an increase in cost due to an increase in the amount of the first reducing agent used is suppressed. be able to.

(10) In some embodiments, the method of any one of (1) to (9) above is
The method further includes a second reduction step of adding a second reducing agent to the treated water after the pH adjustment step to reduce the metal element dissolved in the treated water.

  According to the method of (10) above, the second reducing agent can be added to the treated water after the pH adjustment step to reduce the metal element dissolved in the treated water and convert it to another form. . For example, the treated water can be made easier to handle by reducing hexavalent chromium dissolved in the treated water to trivalent chromium by the second reducing agent.

(11) In some embodiments, in the method of (10) above,
In the second reduction step, 1.0 molar equivalent or more and 2.0 molar equivalent or less of the second reducing agent is added to the treated water with respect to the oxidizing agent.

  According to the method of (11) above, since 1.0 mol equivalent or more of the second reducing agent with respect to the oxidizing agent is added to the treated water, the metal element dissolved in the treated water can be appropriately reduced. it can. Moreover, according to the method (11), since the second reducing agent having a molar equivalent of 2.0 or less relative to the oxidizing agent is added to the treated water, an increase in cost due to an increase in the amount of second reducing agent used is suppressed. be able to.

  According to at least one embodiment of the present invention, a method for treating decontaminated water that can suppress blockage of piping and equipment is provided.

It is a schematic structure figure of a nuclear power plant concerning one embodiment. It is a flowchart of the treated water processing method which concerns on one Embodiment.

  Hereinafter, some embodiments of the present invention will be described with reference to the accompanying drawings. However, the dimensions, materials, shapes, relative arrangements, etc. of the components described in the embodiments or shown in the drawings are not intended to limit the scope of the present invention, but are merely illustrative examples. Absent.

  A treated water treatment method according to some embodiments is a method of treating treated water for chemical decontamination of plant equipment constituent members to which radioactive substances have adhered in a nuclear power plant. First, a nuclear power plant to which treated water treatment methods according to some embodiments are applied will be described.

  FIG. 1 is a schematic configuration diagram of a nuclear power plant according to an embodiment. As shown in FIG. 1, a nuclear power plant 1 includes a nuclear reactor 2 for generating steam by thermal energy generated in a fission reaction, a steam turbine 4 driven by the steam generated in the nuclear reactor 2, and a steam turbine. The generator 6 driven by rotation of the rotating shaft 4 is provided. Note that the nuclear reactor 2 shown in FIG. 1 is a pressurized water reactor (PWR: Pressurized Water Reactor). In other embodiments, the reactor 2 may be a boiling water reactor (BWR) or, unlike a light water reactor including a pressurized water reactor and a boiling water reactor, a moderator or It may be a reactor of a type using a substance other than light water as a coolant.

A nuclear reactor 2 includes a primary cooling loop 10 through which primary cooling water (primary coolant) flows, a reactor vessel (pressure vessel) 11 provided in the primary cooling loop 10, a pressurizer 14, a steam generator 16, and a primary coolant pump. (Coolant pump) 18. The primary coolant pump 18 is configured to circulate primary cooling water in the primary cooling loop 10. The pressurizer 14 is configured to pressurize the primary cooling water in the primary cooling loop 10 so that the primary cooling water does not boil. Note that the reactor vessel 11, the pressurizer 14, the steam generator 16, and the primary coolant pump 18 constituting the reactor 2 are stored in a reactor containment vessel 19.
The reactor vessel 11 contains fuel rods 12 containing pellet-like nuclear fuel (for example, uranium fuel, MOX fuel, etc.), and the primary energy in the reactor vessel 11 is generated by the thermal energy generated by the fission reaction of this fuel. The cooling water is heated. The reactor vessel 11 is provided with a control rod 13 for absorbing and adjusting the number of neutrons generated in the core containing nuclear fuel in order to control the reactor power. The primary cooling water heated in the reactor vessel 11 is sent to the steam generator 16, and the secondary cooling water (secondary coolant) flowing through the secondary cooling loop 20 is heated to generate steam by heat exchange.

  The steam generated in the steam generator 16 is sent to the steam turbine 4 including the high-pressure turbine 21 and the low-pressure turbine 22 to rotate the steam turbine 4. The steam turbine 4 is connected to a generator 6 through a rotating shaft, and the generator 6 is driven by the rotation of the rotating shaft to generate electric energy. A moisture separator / heater 23 is provided between the high-pressure turbine 21 and the low-pressure turbine 22 so that the steam after working in the high-pressure turbine 21 is heated again and then sent to the low-pressure turbine 22. ing.

  The secondary cooling loop 20 is provided with a condenser 24 and a heater (not shown), and steam after working in the low-pressure turbine 22 is condensed and heated in the process of passing through the condenser 24 and the heater. And return to the steam generator 16. The secondary cooling loop 20 is provided with a pump such as a condensate pump 25, and the secondary cooling water is circulated in the secondary cooling loop 20 by these pumps. The condenser 24 is supplied with cooling water (for example, seawater) for cooling the steam from the low-pressure turbine 22 by heat exchange via the pump 15.

The treated water treatment method according to some embodiments is applied to decontaminated treated water for performing chemical decontamination of a primary cooling system in which a primary coolant flows in the nuclear power plant 1 having the above-described configuration.
In the primary cooling system, the surface of the member constituting the equipment such as the reactor vessel 11, the pressurizer 14, the steam generator 16 or the primary coolant pump 18 provided on the primary cooling loop 10 in contact with the primary coolant. In some cases, an oxide film containing a radioactive substance (for example, a metal oxide such as chromium, iron, nickel, etc.) may adhere due to factors such as metal corrosion. The treatment method according to some embodiments can be applied to the treatment of surplus water (treated water) used when performing chemical decontamination of the above-described member (decontamination target).

Next, a case where the treated water treatment method according to some embodiments is applied to the above-described nuclear power plant 1 will be described as an example.
FIG. 2 is a flowchart of a treated water treatment method according to an embodiment. As shown in the flowchart of FIG. 2, the treated water treatment method according to one embodiment includes an oxidation step S2, a pH adjustment step S4, a first reduction step S6, a second reduction step S8, a heating step S10, A concentration step S12.
In some embodiments, the second reduction step S8, the heating step S10, and the concentration step S12 are not necessarily performed, and these steps may be performed as necessary.

(Oxidation process)
First, in the oxidation step S2, the object to be decontaminated with the metal oxide attached is immersed in treated water containing permanganate ions derived from the oxidizing agent, and the metal elements constituting the metal oxide are eluted in the treated water. Let
For example, treated water to which an oxidizing agent has been added is introduced into the primary cooling loop 10, and a decontamination object (for example, the reactor vessel 11, the pressurizer 14, steam, etc.) to which an oxide film (metal oxide) containing a radioactive material has adhered. Generator 16 or primary coolant pump 18 etc.) may be immersed in the treated water.

  The treated water used in the oxidation step S2 may be an aqueous solution of an oxidizing agent.

The oxidizing agent used in the oxidation step S2 includes permanganate ions (MnO ₄ ⁻ ). The cation constituting the oxidizing agent together with the permanganate ion may be, for example, a hydrogen ion (H ⁺ ) or an alkali metal ion such as potassium. The oxidizing agent may be, for example, a permanganate such as potassium permanganate, or permanganic acid. By using treated water containing permanganate ions, metal oxides (for example, oxides of chromium, iron, nickel, etc.) attached to the decontamination target can be effectively eluted.
For example, in the oxidation step S2, the poorly water-soluble chromium (III) oxide contained in the oxide film (metal oxide) is oxidized with permanganate ions in the treated water to form water-soluble hexavalent chromium (HCrO ₄ ⁻ or CrO ₄ ²⁻ etc.) can be eluted together with radioactive substances attached to the oxide film.

  In the oxidation step S2, the primary coolant pump 18 may be used to circulate treated water containing an oxidizing agent (permanganate ions). In this case, the primary coolant pump 18 is operated while supplying water (pure water or the like) to the primary coolant pump 18 so that the chemical such as an oxidant contained in the coolant does not contact the primary coolant pump 18. May be.

  The process described below (the process after the pH adjustment process S4) may be performed on the treated water in which the decontamination target is immersed in the primary cooling loop 10 after the oxidation process S2 is performed, or After the oxidation step S2, the treated water discharged from the primary cooling loop 10 (for example, treated water stored in a tank or the like) may be performed.

(PH adjustment step)
In pH adjustment process S4, a pH adjuster is added to the treated water after performing oxidation process S2, and the pH of treated water is adjusted to 7 or more and 13 or less. In some embodiments, in the pH adjustment step S4, a pH adjuster may be added to the treated water after the oxidation step S2 to adjust the pH of the treated water to 10 or more and 12 or less.

  The pH adjusting agent used in the pH adjusting step S4 may contain at least one alkali metal hydroxide. The alkali metal oxide may be sodium hydroxide, lithium hydroxide or potassium hydroxide. By using an alkali metal hydroxide that is a strongly basic compound as a pH adjuster, the pH of the treated water is 7 or more, 13 or less, or 10 or more even when the pH of the treated water before pH adjustment is relatively low. Easy to adjust to 12 or less.

(First reduction step)
In 1st reduction process S6, a 1st reducing agent is added to the treated water after performing pH adjustment process S4, and the permanganate ion contained in treated water is reduced.

  In the oxidation step S2 that oxidizes the metal oxide adhering to the decontamination target, the entire amount of permanganate ions (oxidant) contained in the treated water is not used up, and surplus permanganate ions are treated after the oxidation step S2. May remain in water. In this case, permanganate ions are contained in the treated water after performing the oxidation step S2 and the pH adjustment step S4. Thus, if permanganate ions remain in the treated water, these components may be affected, such as oxidizing the constituent materials of the devices that come into contact with the treated water. Therefore, by reducing the permanganate ions in the treated water in the first reduction step S6, the oxidizing power of the treated water can be reduced, and the influence on the equipment in contact with the treated water can be suppressed.

Here, according to the knowledge of the present inventors, when the treated water after the oxidation step S2 is acidic, if a reducing agent is added to the treated water without performing the pH adjustment step S4, Due to the reaction between the permanganate ions contained and the reducing agent, precipitates having low fluidity such as manganese dioxide are generated. A half reaction formula in which manganese dioxide is generated by reducing permanganate ions is represented by the following formula (A).
MnO ₄ ⁻ + 4H ⁺ + 3e ⁻ → MnO ₂ + 2H ₂ O (A)
On the other hand, when the reducing agent is added to the treated water after adjusting the pH of the treated water after the oxidation step S2 to a relatively large value (for example, alkaline), the permanganic acid contained in the treated water By reaction of the ions with the reducing agent, for example, manganese hydroxide (Mn (OH) ₂ ), manganese oxide (II, III) (Mn ₂ O ₃ ) or manganese oxide (III) (Mn ₂ O ₃ ), A relatively fluid precipitate is produced. The half reaction formula in which manganese hydroxide is generated by reducing permanganate ions is represented by the following formula (B).
MnO ₄ ⁻ + 6H ⁺ + 5e ⁻ → Mn (OH) ₂ + 4H ₂ O (B)

  Therefore, like the above-mentioned embodiment, after adjusting the pH of the treated water to 7 to 13 or 10 to 12 in the pH adjustment step S4, the permanganate ions in the treated water in the first reduction step S6. Is reduced, it becomes easy to produce a precipitate having relatively high fluidity due to the reaction between the permanganate ion and the reducing agent. Therefore, blockage of piping and equipment (for example, blockage of an evaporator used in the concentration step S12 described later) due to the precipitate generated by the reaction between the permanganate ion and the reducing agent can be suppressed.

The first reducing agent used in the first reduction step S6 is, for example, bisulfite (for example, sodium bisulfite (NaHSO ₃ )), sulfite (for example, sodium sulfite (Na ₂ SO ₃ )), or hydrazine ( N ₂ H ₄ ) may be included.
In this case, permanganate ions in the treated water can be appropriately reduced under the condition that the pH of the treated water is 7 or more and 13 or less or 10 or more and 12 or less.
In addition, the half reaction formula in the case of using sulfite (sulfite ion) as a reducing agent is represented by the following formula (C).
SO ₃ ²⁻ + H ₂ O → SO ₄ ²⁻ + 2H ⁺ + 2e ⁻ (C)

The amount of the first reducing agent added in the first reduction step S6 may be 1.1 molar equivalent or more and 1.3 molar equivalent or less with respect to the oxidizing agent used in the oxidation step S2.
It is a case where a part of the first reducing agent is consumed by the oxygen dissolved in the treated water by adding 1.1 mole equivalent or more of the first reducing agent to the treated water with respect to the oxidizing agent. In addition, permanganate ions derived from the oxidizing agent can be appropriately reduced. Moreover, the cost increase by the usage-amount increase of a 1st reducing agent can be suppressed by adding the 1st reducing agent below 1.3 molar equivalent with respect to an oxidizing agent to treated water.

(Second reduction process)
In some embodiments, after performing pH adjustment process S4, you may perform 2nd reduction process S8 which adds a 2nd reducing agent to treated water, and reduces the metallic element dissolved in treated water. .

By adding the second reducing agent to the treated water after the pH adjustment step S4, the metal element dissolved in the treated water can be reduced and converted into another form. For example, the treated water can be made easier to handle by reducing hexavalent chromium dissolved in the treated water to trivalent chromium by the second reducing agent. An example of a half reaction formula in which trivalent chromium is generated by reducing hexavalent chromium in the treated water is represented by the following formula (D).
HCrO ₄ ⁻ + 3e ⁻ + 4H ⁺ → Cr (OH) ₃ + H ₂ O (D)

Note that the second reduction step S8 may be performed simultaneously with the first reduction step S6.
The second reducing agent used in the second reducing step S8 may be the same type of reducing agent as the first reducing agent used in the first reducing step S6.

The addition amount of the second reducing agent in the second reduction step S8 may be 1.0 molar equivalent or more and 2.0 molar equivalent or less with respect to the oxidizing agent used in the oxidation step S2.
By adding 1.0 mole equivalent or more of the second reducing agent to the treated water with respect to the oxidizing agent, the metal element dissolved in the treated water can be appropriately reduced. Moreover, the cost increase by the usage-amount increase of a 2nd reducing agent can be suppressed by adding to a treated water the 2nd reducing agent below 2.0 molar equivalent with respect to an oxidizing agent.

(Heating process)
In some embodiments, after performing 1st reduction process S6, you may perform heating process S10 which heats treated water.
By heating the treated water after the first reduction step S6, the fluidity of the precipitate generated by the reaction between the permanganate ions and the reducing agent can be further increased. Therefore, it is possible to effectively suppress blockage of piping and equipment due to the deposit.

  In addition, when performing 2nd reduction | restoration process S8, you may perform heating process S10 after performing 2nd reduction | restoration process S8, or simultaneously with 2nd reduction | restoration process S8.

(Concentration process)
In some embodiments, after performing 1st reduction process S6, you may perform concentration process S12 which concentrates treated water.
Concentrating the treated water after the first reduction step S6 increases the concentration of precipitates in the treated water, but even in this case, the oxidation step S2, the pH adjustment step S4, and the first reduction step S6 are performed. Thereby, the fluidity | liquidity of the deposit produced | generated by 1st reduction process S6 can be maintained comparatively high. Therefore, blockage of piping and equipment due to the deposit can be suppressed.

Concentration process S12 may be performed simultaneously with the above-mentioned heating process S10. Alternatively, the concentration step S12 may include a heating step S10 (that is, the heating step S10 may be performed as part of the concentration step S12). For example, you may concentrate by heating the treated water after performing 1st reduction process S6 (heating process S10 and concentration process S12).
Thus, the treatment efficiency of treated water can be improved by performing concentration process S12 and heating process S10 simultaneously, or performing heating process S10 as a part of concentration process S12.

In the concentration step S12, the treated water after the first reduction step S6 may be concentrated using an evaporator. At this time, using an evaporator, the treated water may be concentrated (concentration step S12) while heating the treated water after the first reduction step S6 (heating step S10).
Thus, even if it is a case where concentration process S12 (and heating process S10) is performed using an evaporator, by the above-mentioned oxidation process S2, pH adjustment process S4, and 1st reduction process S6, the 1st reduction process The fluidity of the precipitate produced in S6 can be kept relatively high. Therefore, the obstruction | occlusion of the evaporator resulting from a deposit can be suppressed.

In addition, by passing the treated water subjected to the oxidation step S2 to the first reduction step S6 (and optionally the second reduction step S8 to the concentration step S12) through a filter or the like, it is contained in the treated water. A precipitate may be collected.
Further, the radioactive water contained in the treated water is obtained by bringing the treated water subjected to the oxidation step S2 to the first reduction step S6 (and optionally the second reduction step S8 to the concentration step S12) into contact with the ion exchange resin. The radioactive substance may be removed from the treated water by adsorbing the substance to the ion exchange resin.

Next, the effects of the treated water treatment method according to some embodiments will be described with test examples.
(Test Example 1)
_3. Mix 20 L of pure water simulating the water in the primary cooling loop 10 of the nuclear power plant 1 with 30 mg of chromium (III) oxide (Cr ₂ O ₃ ) and use potassium permanganate (KMnO ₄ ) as an oxidizing agent. 0 g was dissolved (oxidation step S2) to obtain test treated water 1.
Next, 1.0 g of sodium hydroxide (NaOH) as a pH adjuster was added to the test treated water 1 and stirred (pH adjustment step S4). It was pH 11-12 when the pH of this test water 1 was measured.
Next, when 395 mg / L of sodium bisulfite (NaHSO ₃ ) (1.2 molar equivalents relative to the oxidizing agent KMnO ₄ ) was added to the test treated water 1 as a reducing agent and stirred (first reduction step S6). ), A precipitate formed. When the treated water for testing 1 containing the precipitate is tilted together with the container, the precipitate is deformed so as to collect in the lower part of the container according to the shape of the container at a position inclined at least about 70 ° from the initial position. (I.e., deformed by gravity) was visually confirmed.
Next, the test treatment water 1 containing the precipitate was concentrated at 100 ° C. until the volume of the test treatment water 1 became 1/100 to 1/360 (heating step S10 and concentration step S12). When the test treated water 1 containing the precipitate is tilted together with the container, the precipitate is deformed so as to collect in the lower part of the container in accordance with the shape of the container at a position inclined at least about 20 ° from the initial position ( That is, it was visually confirmed that the material was deformed by gravity.

(Test Example 2)
Test Example 2 differs from Test Example 1 in that the type of oxidizing agent used and the pH adjustment step S4 were not performed.
That is, in Test Example 2, 30 mg of chromium (III) oxide (Cr ₂ O ₃ ) was mixed with 20 L of pure water simulating water in the primary cooling loop 10 of the nuclear power plant 1, and permanganic acid ( HMnO ₄ ) solution was added to obtain test treated water 2 of 150 mg / L. It was pH 2-3 when the pH of this test water 2 was measured.
Next, 395 mg / L of sodium bisulfite (NaHSO ₃ ) (1.2 molar equivalents relative to the oxidizing agent, HMnO ₄ ) was added to the test treated water 1 as a reducing agent, and a precipitate was formed. . When the test treated water 2 containing the precipitate was tilted together with the container, it was visually confirmed that the precipitate was not deformed (ie, not deformed by gravity) even when tilted by about 70 ° from the initial position. .
Next, the test water 2 containing the precipitate was concentrated at 100 ° C. until the volume of the test water 2 was 1/100 to 1/360. When the test treated water 2 containing the precipitate was tilted together with the container, it was visually confirmed that even if the test treatment water 2 was tilted by about 70 ° from the initial position, the precipitate was not deformed (that is, not deformed by gravity).

Regarding the precipitate generated by adding the reducing agent to the test water, the precipitate was deformed at a position where the container was inclined by about 70 ° in Test Example 1, whereas in Example 2, the container was inclined by 70 °. The precipitate was not deformed even after the treatment. That is, the fluidity of the precipitate after addition of the reducing agent and before heating and concentration is higher in Test Example 1 than in Test Example 2.
In Test Example 2, the pH was 2 to 3 before the addition of the reducing agent, whereas in Test Example 2, the reducing agent was added after the pH adjusting agent was adjusted to about pH 11 before the addition of the reducing agent. Therefore, it is considered that the fluidity of the precipitate formed in the reaction of the oxidizing agent (permanganate ion) and the reducing agent in Test Example 1 was relatively high.

  Moreover, about the deposit after a heating and concentration, in Test Example 1, the deposit deform | transformed in the position which inclined the container about 70 degrees. That is, in Test Example 1, the fluidity of the precipitate after heating and concentrating the test treated water is higher than that before heating and concentrating. Thereby, it was confirmed that the fluidity | liquidity of a precipitate can be made higher by heating and concentrating the treated water after precipitation production.

  As mentioned above, although embodiment of this invention was described, this invention is not limited to embodiment mentioned above, The form which added the deformation | transformation to embodiment mentioned above and the form which combined these forms suitably are included.

In this specification, an expression representing a relative or absolute arrangement such as “in a certain direction”, “along a certain direction”, “parallel”, “orthogonal”, “center”, “concentric” or “coaxial”. Represents not only such an arrangement strictly but also a state of relative displacement with tolerance or an angle or a distance to obtain the same function.
For example, an expression indicating that things such as “identical”, “equal”, and “homogeneous” are in an equal state not only represents an exactly equal state, but also has a tolerance or a difference that can provide the same function. It also represents the existing state.
In this specification, expressions representing shapes such as quadrangular shapes and cylindrical shapes not only represent shapes such as quadrangular shapes and cylindrical shapes in a strict geometric sense, but also within a range where the same effects can be obtained. In addition, a shape including an uneven portion or a chamfered portion is also expressed.
In this specification, the expression “comprising”, “including”, or “having” one constituent element is not an exclusive expression for excluding the existence of another constituent element.

DESCRIPTION OF SYMBOLS 1 Nuclear power plant 2 Reactor 4 Steam turbine 6 Generator 10 Primary cooling loop 11 Reactor vessel 12 Fuel rod 13 Control rod 14 Pressurizer 15 Pump 16 Steam generator 18 Primary coolant pump 19 Reactor containment vessel 20 Secondary cooling loop 21 High pressure turbine 22 Low pressure turbine 23 Moisture separation heater 24 Condenser 25 Condensate pump

Claims (11)

An oxidation step of immersing the decontamination object to which the metal oxide is attached in treated water containing permanganate ions derived from an oxidant, and eluting the metal element constituting the metal oxide in the treated water;
A pH adjusting step of adjusting the pH of the treated water to 7 or more and 13 or less by adding a pH adjusting agent to the treated water after the oxidation step;
A first reduction step of adding a first reducing agent to the treated water after the pH adjustment step to reduce the permanganate ions contained in the treated water;
A decontamination water treatment method.   The decontamination treatment water treatment method according to claim 1, further comprising a heating step of heating the treatment water after the first reduction step.   The decontamination treatment water treatment method according to claim 1 or 2, further comprising a concentration step of concentrating the treated water after the first reduction step.   The decontamination treatment water treatment method according to claim 3, wherein the concentration step includes the heating step.   The decontamination treatment water treatment method according to any one of claims 1 to 4, wherein in the pH adjustment step, the pH of the treatment water is adjusted to 10 or more and 12 or less.   The decontamination water treatment method according to any one of claims 1 to 5, wherein the oxidizing agent contains potassium permanganate.   The decontamination treatment water treatment method according to any one of claims 1 to 6, wherein the pH adjuster contains at least one alkali metal hydroxide.   The decontamination water treatment method according to any one of claims 1 to 7, wherein the first reducing agent contains at least one of bisulfite, sulfite, and hydrazine.   In the first reduction step, the first reducing agent having a molar ratio of 1.1 to 1.3 molar equivalents is added to the treated water with respect to the oxidizing agent. The decontamination treatment water treatment method according to any one of the above.   The second reducing step of reducing the metal element dissolved in the treated water by adding a second reducing agent to the treated water after the pH adjusting step is further provided. The decontamination treatment water treatment method according to any one of the above.   11. The removal according to claim 10, wherein, in the second reduction step, a 1.0 to 2.0 molar equivalent of a second reducing agent is added to the treated water with respect to the oxidizing agent. Dyed water treatment method.

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