JP6049404B2 - Decontamination waste liquid treatment method - Google Patents

Description

  The present invention relates to a decontamination waste liquid treatment method using precipitation applied to system decontamination and the like.

  In general, a nuclear power plant such as a nuclear reactor is composed of a large number of devices and members such as piping. When these members are used over a long period of time, an oxide film containing a radionuclide such as cobalt may adhere to the surface of the member due to factors such as corrosion of the metal constituting the member. For this reason, the radiation dose may increase around these members. Therefore, it is necessary to remove the oxide film from the surface of the member at the time of periodic inspection, for example, chemical decontamination of the member is performed.

The following techniques are known as chemical decontamination methods. That is, the member is immersed in a permanganic acid aqueous solution, and chromium in the chromium-based oxide contained in the oxide film attached to the surface of the member is oxidized and eluted from Cr ³⁺ to Cr ⁶⁺ . Next, an organic acid such as oxalic acid is added to reduce and elute iron in the iron-based oxide, which is the main component of the oxide film, as Fe ²⁺ . At this time, the radionuclide is also eluted simultaneously. Then, the radioactive substance can be removed by contacting the ion exchange resin containing ions and eluting the radioactive substance from the aqueous solution into the treated water. At this time, if the radioactive substance eluted in the treated water is adsorbed and removed by the ion exchange resin, the ion exchange resin becomes secondary waste.

  Depending on the type of radioactive material to be removed, the types of ion exchange resins used can be broadly classified into two. A cation exchange resin used for removing metal ions and the like, and an anion resin used for removing additives such as oxalic acid contained in the treated water. Cation exchange resin is used to remove a few metal ions in the treated water, so the amount used is small and the amount of waste does not increase so much, but metal ions etc. often contain radionuclides, so the treatment is very Difficult high-dose secondary waste. On the other hand, anion exchange resins are used to remove additives that occupy most of the treated water, so the amount used is large and the amount of waste is enormous. It becomes waste. As a method for reducing the amount of secondary waste as described above, for example, a method described in Patent Document 1 is disclosed.

  In the method described in Patent Document 1, treated water containing oxalic acid is sent to the reaction layer, and after irradiation with ultraviolet rays while blowing an oxygen-containing gas, calcium hydroxide is added and stirred. As a result, oxalic acid, which is an organic acid, is changed into a calcium salt, and metal ions are changed into a hydroxide, thereby causing coprecipitation. Radionuclide is also precipitated by coprecipitation to form solid sludge. Then, the radionuclide is removed from the treated water by filtering the radionuclide together with the solid sludge through a filter. Thereby, oxalic acid and radionuclide in the treated water can be removed in advance, and the amount of ion exchange resin used can be suppressed.

JP 2003-202396 A

  However, it is difficult to remove all the radionuclides, and the radionuclides that have not been removed remain in a state of being dispersed in the treated water. In addition to oxalic acid, treated water contains many oxidizing agents containing permanganic acid used to elute radionuclides, so even if you try to remove a few radionuclides, a large amount of treated water generated from permanganic acid. Therefore, there is a problem that the amount of ion exchange resin to be used cannot be sufficiently reduced.

  The present invention has been made in order to solve the above-described problems, and provides a decontamination waste liquid treatment method capable of reducing the amount of ion exchange resin used as secondary waste.

In order to solve the above problems, the present invention proposes the following means.
The decontamination waste liquid treatment method according to one aspect of the present invention is an oxidation step in which chromium is oxidized and eluted from the decontamination object by adding an oxidizing agent containing permanganic acid to the treated water in which the decontamination object is immersed. A precipitation step of adding a reducing agent that precipitates permanganic acid in the treated water after the oxidation step, a precipitate removal step of removing the permanganic acid precipitate after the precipitation step, After the precipitate removing step, an organic acid is added to the treated water to reduce and elute iron from the decontamination target, and after the reducing step, the radionuclide eluted in the treated water is removed. And a removing step.

  According to such a configuration, by adding a reducing agent for precipitating permanganic acid to the treated water, the permanganic acid contained in the oxidizing agent used when oxidizing and eluting chromium in the oxidation step is changed to permanganic acid. It turns into a precipitate containing. By removing such permanganic acid as a precipitate, it is possible to remove several times as much manganese as in the case of removing with an ion exchange resin. As a result, manganese is reduced in the treated water that is simultaneously removed when the radionuclide is removed in the removal step, and the amount of ion exchange resin used can be reduced.

  In the decontamination waste liquid treatment method according to another aspect of the present invention, the oxidizing agent containing permanganic acid is potassium permanganate, and the treated water is disposed between the precipitate removing step and the reducing step. It is further characterized by further comprising a resin water passing step for passing water through the ion exchange resin.

According to such a configuration, permanganic acid, sodium ions, and potassium ions are eluted in the treated water by performing oxidation elution using potassium permanganate on the treated water exhibiting alkalinity. Then, permanganic acid is precipitated as manganese dioxide in the precipitation step and removed in the precipitate removal step. By precipitating and removing permanganate ions in advance, manganese in the treated water containing the radionuclide can be greatly reduced. As a result, manganese is reduced in the treated water that is simultaneously removed when the radionuclide is removed in the removal step, and the amount of ion exchange resin used can be reduced.
Furthermore, sodium ion and potassium ion can be removed in advance by passing the treated water through the ion exchange resin in the resin water passing step. Until the reduction step is carried out, almost no radionuclide is eluted in the treated water, so even if an ion exchange resin is used, it does not become a high dose and can be treated as a low-dose secondary waste.

  Furthermore, in the decontamination waste liquid treatment method according to another aspect of the present invention, the pH of the treated water is set to 1 or more and 5 or less by adding a pH adjuster between the precipitation step and the precipitate removal step. It further comprises a pH adjusting step for adjusting.

  According to such a configuration, since the isoelectric point of the precipitate containing permanganic acid is around 3, the cohesiveness of the precipitate is improved by setting the pH of the treated water to be around 3, and the precipitate becomes larger. can do. Thereby, a deposit becomes large and the repair efficiency in a deposit removal process improves, and it becomes possible to remove manganese from the treated water by precipitation more efficiently in a short time.

  Further, in the decontamination waste liquid treatment method according to another aspect of the present invention, the precipitation step includes a reducing agent that precipitates the permanganic acid in accordance with the concentration of the oxidizing agent containing the permanganic acid in the treated water. The addition amount is adjusted.

  According to such a configuration, the equivalent amount of the reducing agent necessary for precipitating permanganic acid from the treated water is grasped, and hydrogen peroxide is treated in a small amount less than a sufficient amount necessary for precipitating permanganic acid. Can be added to water. For this reason, it is possible to prevent a phenomenon in which precipitation occurs after the precipitation removing step is completed without excessively supplying the reducing agent and completing the precipitation in the precipitation step. Thus, the precipitation is completed by the precipitate removing step, and the precipitate can be surely removed.

  Furthermore, the decontamination waste liquid treatment method according to another aspect of the present invention includes, after the oxidation step, a decomposition step of decomposing the permanganic acid by adding an organic acid to the treated water, and after the decomposition step The treated water is further provided with an inorganic ion exchanger water passing step for passing water through the inorganic ion exchanger adsorbing manganese.

  According to such a configuration, the organic acid was added to the treated water to decompose permanganic acid, and then adsorbed and removed with the inorganic ion exchanger, so that the precipitate removal step could not be sufficiently removed. Manganese can be removed from the treated water. Therefore, it is possible to remove manganese, which has not been completely removed in the precipitation step and the precipitate removal step, from the treated water. As a result, almost no manganese in the treated water is removed at the same time when the radionuclide is removed in the removal step, and the amount of ion exchange resin used can be further reduced.

  According to the decontamination waste liquid treatment method of the present invention, it is possible to reduce the amount of ion-exchange resin used as secondary waste by reducing manganese in the treated water by preliminarily removing permanganic acid and removing it. A decontamination waste liquid treatment method is provided.

It is a figure which shows the example of the decontamination target object used as the object of the chemical cleaning method which concerns on embodiment of this invention. It is a flowchart explaining the process of the chemical cleaning method which concerns on 1st embodiment of this invention. It is a flowchart explaining the process of the chemical cleaning method which concerns on 2nd embodiment of this invention. It is a flowchart explaining the process of the chemical cleaning method which concerns on 3rd embodiment of this invention. It is a flowchart explaining the process of the chemical cleaning method which concerns on 4th embodiment of this invention. It is a flowchart explaining the process of the chemical cleaning method which concerns on 5th embodiment of this invention.

Hereinafter, a decontamination method using the decontamination apparatus according to the present embodiment will be described with reference to the drawings.
First, the decontamination target Z that is an object of the present embodiment will be described.
The decontamination target Z that is the target of this embodiment is a part such as piping, containers, and various devices that constitute a nuclear power plant, and is a part that makes contact with reactor water.

  Here, as the nuclear power plant, for example, as shown in FIG. 1, there is a nuclear power plant P including a pressurized water reactor 50.

  The nuclear power plant P includes a pressurized water reactor 50 in which fuel rods 51 and the like are accommodated, a pressurizer 52 that pressurizes primary cooling water to suppress boiling of the primary cooling water in the pressurized water reactor 50, a primary A steam generator 53 that turns the secondary cooling water into steam by the heat of the cooling water, and a coolant pump 54 that returns the primary cooling water from the steam generator 53 to the pressurized water reactor 50 are provided. And the ion-exchange resin tower 60 which returns to the pressurized water reactor 50 after taking in and purifying the primary cooling water which flows from the steam generator 53 is provided. Furthermore, a steam turbine 56 driven by steam generated by the steam generator 53, a generator 57 that generates electric power by driving the steam turbine 56, a condenser 58 for returning steam from the steam turbine 56 to water, and a condenser And a water supply pump 59 for returning the water from 58 to the steam generator 53.

  The pressurized water reactor 50 and the steam generator 53 are connected by primary cooling water pipes 55a and 55b to form a primary cooling system. The condenser 58 and the steam turbine 56 are connected by a water supply pipe 55d to form a secondary cooling system. Furthermore, the chemical volume control pipes 55e and 55f are connected between the steam generation and the coolant pump 54, and between the coolant pump 54 and the reactor, and the chemical volume control pipes 55e and 55f are connected to the solenoid valve 61. The chemical volume control system is formed so that the internal treated water can be circulated by being connected to each other. The steam generator 53 and the steam turbine 56 are connected by a steam pipe 55c.

  In the nuclear power plant P configured as described above, the reactor water, that is, the primary cooling system member (hereinafter referred to as the decontamination target Z) that is a member in contact with the primary cooling water, is a pressurized water reactor 50, There are a pressurizer 52, a steam generator 53, a coolant pump 54, primary cooling water pipes 55a and 55b connecting these, various valves provided in the primary cooling water pipes 55a and 55b, and the like. The ion exchange resin tower 60 and the chemical volume control pipes 55e and 55f, which are chemical volume control systems, are also primary cooling system members. These decontamination objects Z are formed of stainless steel containing iron as a main component and chromium or nickel, inconel that is a nickel-based alloy, or the like.

  The metal element constituting the decontamination object Z is slightly eluted in the reactor water, and a part thereof adheres to the surface of the fuel rod 51 in the pressurized water reactor 50. The metal element adhering to the surface of the fuel rod 51 is irradiated with neutron beams from the fuel rod 51 to cause a nuclear reaction to become a radionuclide such as chromium, nickel, cobalt and the like. Most of these radionuclides remain attached to the surface of the fuel rod 51 in the form of oxides, but some of them are eluted in the reactor water or released as insoluble solids. The radionuclide eluted or released in the reactor water adheres to the reactor water contact surface of the decontamination object Z, and forms an oxide film mainly composed of iron on the reactor water contact surface. For this reason, the worker who works in the vicinity of the decontamination target Z is exposed to radiation from the radionuclide in the oxide film formed on the part.

  The present embodiment relates to the system decontamination of the nuclear power plant P described above, and is a treatment that is a chemical solution so that the primary cooling water circulates in the nuclear power plant inside the piping that is the decontamination target Z. This is a decontamination waste liquid treatment method for decontamination of treated water from which an oxide film containing a radionuclide adhering to the inner surface of the decontamination target Z is removed while circulating water.

  As shown in FIG. 2, the decontamination waste liquid treatment method of the first embodiment includes an oxidation step S10, a precipitation step S20, a precipitate removal step S30, a reduction step S40, and a removal step S50.

First, the oxidation step S10 is performed.
That is, in the oxidation step S10, permanganic acid is added as an oxidizing agent to the treated water, and the treated water with the oxidizing agent added is supplied to the inside of the decontamination target Z and circulated. By circulating the treated water with permanganic acid added inside the decontamination object Z, the chromium in the oxide film of the decontamination object Z is oxidized and eluted as Cr ⁶⁺ , and contains the primary radionuclide chromium. Treated water W1 is generated. Permanganate ions added as an oxidizing agent also remain in the primary treated water W1. The chemical reaction formula at this time can be expressed by the following formula (1).
Cr ³⁺ + MnO ₄ ⁻ + 4H ⁺ → Cr ⁶⁺ + MnO ₂ + 2H ₂ O (Formula 1)

Next, the precipitation step S20 is performed.
That is, in the precipitation step S20, the primary treated water W1 after the oxidation step S10 is performed is circulated through the chemical volume control pipe 55e, and hydrogen peroxide as a reducing agent is added to the primary treated water W1. Permanganate ions remaining in the primary treated water W1 in the chemical volume control pipe 55e react with hydrogen peroxide and precipitate as manganese dioxide. The chemical reaction formula at this time can be expressed by the following formula (2).
MnO ₄ ⁻ + 2H ₂ O ₂ → MnO ₂ + 2O ₂ + 2H ₂ O (Formula 2)
When the permanganate ion becomes manganese dioxide and becomes the precipitate P1, it is removed from the primary treated water W1 and the secondary treated water W2 is generated. The secondary treated water W2 flows into the ion exchange resin tower 60 together with the precipitate P1.

Next, the precipitate removing step S30 is performed.
That is, in the precipitate removing step S30, first, a filter is installed in the ion exchange resin tower 60. By passing the secondary treated water W2 flowing into the ion exchange resin tower 60 through the filter, the precipitate P1 mixed in the secondary treated water W2 is collected by the filter. The filter that collects the precipitate P <b> 1 is removed from the ion exchange resin tower 60. The secondary treated water W2 from which the precipitate P1 has been removed is circulated from the chemical volume control pipe 55f to the primary cooling water pipe 55b.

一方で、インコネルの酸化被膜に含まれるニッケルとシュウ酸とが反応しシュウ酸ニッケルが溶出される。この際の化学式は、以下（４）式で表すことができる。

そして、ピコリン酸がニッケルの溶出を促進し、シュウ酸ニッケルからニッケルを分解する。この際の化学反応式は、以下（５）式で表すことができる。

これらの反応により、二次処理水Ｗ２に放射性核種である鉄やニッケルを含有させた三次処理水Ｗ３が生成される。 Next, reduction process S40 is implemented.
That is, in the reduction step S40, after the sediment removal step S30 is performed, the chemical volume control pipe 55e returns to the primary cooling water pipe 55b which is the primary cooling system, and oxalic acid and picolinic acid are used as reducing agents in the secondary treated water W2. The secondary treated water W2 to which these reducing agents have been added is added and circulated inside the decontamination object Z.
By circulating the secondary treated water W2 added with a reducing agent inside the decontamination object Z, iron in the oxide film adhering to the stainless steel is reduced and eluted by oxalic acid. The chemical formula at this time can be expressed by the following formula (3).

On the other hand, nickel and oxalic acid contained in the oxide film of Inconel react and nickel oxalate is eluted. The chemical formula at this time can be expressed by the following formula (4).

And picolinic acid promotes elution of nickel and decomposes nickel from nickel oxalate. The chemical reaction formula at this time can be expressed by the following formula (5).

By these reactions, tertiary treated water W3 in which iron or nickel that is a radionuclide is contained in the secondary treated water W2 is generated.

Finally, the removal step S50 is performed.
That is, in the removal step S50, first, the ion exchange resin is installed in the ion exchange resin tower 60 from which the filter has been removed. Then, the tertiary treated water W3 is caused to flow into the ion exchange resin tower 60 from the chemical volume control pipe 55e. By passing the tertiary treated water W3 through the ion exchange resin in the ion exchange resin tower 60, the radionuclides of chromium, iron and nickel contained in the tertiary treated water W3 are adsorbed and removed. Further, using the ion exchange resin, picolinic acid contaminated with the radionuclide remaining in the tertiary treated water W3 is simultaneously adsorbed and removed to decontaminate the tertiary treated water W3. The decontaminated tertiary treated water W3 is used again as treated water after the next cycle.

Next, the effect | action of the chemical decontamination method by 1st embodiment of the said process is demonstrated.
According to the decontamination waste liquid treatment method as described above, by adding hydrogen peroxide, which is a reducing agent for precipitating permanganic acid, to the primary treated water W1, the permanganese remaining in the primary treated water W1 after the oxidation step S10. The acid ion becomes manganese dioxide and changes to the precipitate P1. By collecting and removing permanganate ions as a precipitate P1 on the filter, about several hundred g / L of manganese in the secondary treated water W2 can be removed. This is a collection efficiency several times higher than 50 g / L when manganese is removed together with permanganate ions by an ion exchange resin. Further, when the radionuclide is adsorbed and removed by the ion exchange resin, manganese is contained more in the tertiary treated water W3 than the radionuclide, so that the ion exchange resin is often used to remove manganese. The However, by precipitating and removing permanganate ions in advance, manganese in the tertiary treated water W3 in which radionuclides are present can be significantly reduced. As a result, the amount of manganese in the tertiary treated water W3 that is simultaneously removed when the radionuclide contained in chromium, iron, or the like is removed using the ion exchange resin in the removal step S50 is reduced, and the amount of ion exchange resin used is reduced. Can be reduced.

Next, the decontamination waste liquid treatment method of the second embodiment will be described with reference to FIG.
In the second embodiment, the same components as those in the first embodiment are given the same reference numerals, and detailed description thereof is omitted. The decontamination waste liquid treatment method of the second embodiment performs the alkaline oxidation step S11 instead of the oxidation step S10, and further performs the resin water passing step S60 after the precipitate removing step S30 with the first embodiment. Is different.

  That is, the oxidation step S10 in the first embodiment is not carried out, but instead of the alkaline oxidation step S11, the precipitation step S20 and the precipitate removal step S30 are carried out. Then, after performing resin water flow process S60, reduction process S40 and removal process S50 are implemented.

Alkaline oxidation process S11 is implemented when sodium hydroxide etc. are added to treated water and treated water shows alkalinity. Potassium permanganate is added as an oxidizing agent to the alkaline treated water, and the treated water is supplied into the decontamination target Z and circulated. By circulating the treated water with potassium permanganate added inside the decontamination target Z, chromium in the oxide film, which is the decontamination target Z, is oxidized and eluted as Cr ⁶⁺ and contains chromium, which is a radionuclide. Primary treated water W11 is generated. In the primary treated water W11 in the second embodiment, not only permanganate ions but also potassium ions (K ⁺ ) and sodium ions (Na ⁺ ) remain. The chemical reaction formula in which hexavalent chromium elutes in the basic aqueous solution at this time can be represented by the following formula (6).
Cr ³⁺ + MnO ₄ ⁻ + 2H ₂ O → Cr ⁶⁺ + MnO ₂ + 4OH ⁻ (formula 6)

Next, when the precipitation step S20 is performed in the same manner as in the first embodiment, potassium permanganate becomes the precipitate P11. And the sediment removal process S30 is implemented, the deposit P11 is removed, and the secondary treated water W21 is produced | generated. In the secondary treated water W21 in the second embodiment, permanganate ions are removed by the precipitation step S20 and the precipitate removal step S30, but potassium ions (K ⁺ ) and sodium ions (Na ⁺ ) remain. It remains.

Next, resin water flow process S60 is implemented.
In the resin water passing step S60, an ion exchange resin is installed in the ion exchange resin tower 60. Even after the sediment removal step S30 is performed, the secondary treated water W21 is not returned to the primary cooling water pipe 55b, but the electromagnetic valve 61 is opened and the chemical volume control system is circulated. Then, by passing the secondary treated water W21 through the ion exchange resin, potassium ions (K ⁺ ) and sodium ions (Na ⁺ ) present in the secondary treated water W21 are adsorbed on the ion exchange resin. The ion exchange resin that adsorbs potassium ions (K ⁺ ) and sodium ions (Na ⁺ ) is removed from the ion exchange resin tower 60. The secondary treated water W21 from which potassium ions (K ⁺ ) and sodium ions (Na ⁺ ) have been removed is circulated from the chemical volume control pipe 55f to the primary cooling water pipe 55b.
Then, reduction process S40 etc. are implemented in a primary cooling system.

According to the decontamination waste liquid treatment method of the second embodiment as described above, secondary treatment is performed by performing oxidation elution using potassium permanganate in the alkaline oxidation step S11 on the treated water exhibiting alkalinity. Permanganic acid, potassium ions (K ⁺ ) and sodium ions (Na ⁺ ) are eluted in the water W21. Then, permanganate is precipitated as potassium permanganate in the precipitation step S20, and is removed by a filter in the precipitate removal step S30. By precipitating and removing permanganate ions in advance, manganese in the tertiary treated water W3 in which radionuclides are present can be significantly reduced. As a result, the amount of manganese in the tertiary treated water W3 that is simultaneously removed when the radionuclide contained in chromium, iron, or the like is removed using the ion exchange resin in the removal step S50 is reduced, and the amount of ion exchange resin used is reduced. Can be reduced.

Further, by passing the secondary treated water W21 through the ion exchange resin in the resin water passing step S60, potassium ions (K ⁺ ) and sodium ions (in the secondary treated water W21 after the precipitate removing step S30) ( Na ⁺ ) can be removed in advance. Until the reduction step S40 is carried out, almost no radionuclide is eluted in the secondary treated water W21. Therefore, even if ion-exchange resin is used, the dose is not high, and it is treated as a low-dose secondary waste. Is possible.

Next, the decontamination waste liquid treatment method of the third embodiment will be described with reference to FIG.
In the third embodiment, the same components as those in the first embodiment are given the same reference numerals, and detailed description thereof is omitted. The decontamination waste liquid treatment method of the third embodiment is different from the first embodiment in that the pH adjustment step S70 is performed on the secondary treated water W2 between the precipitation step S20 and the precipitate removal step S30. .

  That is, in 3rd embodiment, after implementing to precipitation process S20 similarly to 1st embodiment, pH adjustment process S70 which adds a pH adjuster and adjusts pH in the secondary treated water W2 is implemented. Thereafter, the precipitate removing step S30, the reducing step S40, and the removing step S50 are performed as in the first embodiment.

  The pH adjustment step S70 does not return the secondary treated water W2 to the primary cooling water pipe 55b after the precipitation step S20 is performed by the chemical volume control pipes 55e and 55f, which are chemical volume control systems, and the ion exchange resin tower 60. Then, the electromagnetic valve 61 is opened and circulated in the chemical volume control system. And the pH adjuster is added to the secondary treated water W2 in the chemical volume control piping 55e, and it is set as the secondary treated water W22 which changed pH. The pH adjuster may be added until the pH of the secondary treated water W22 falls within the range of 1 to 5, and is preferably added until it falls within the range of 2 to 4, and is added until it becomes 3. Is more preferable.

In addition, what is necessary is just to select suitably the pH adjuster added according to the environment to be used, for example, when the secondary treated water W2 shows basicity, oxalic acid is used, and when it shows acidity Hydrazine is used.
Thereafter, the precipitate removing step S30 is performed in the ion exchange resin tower 60, and the reducing step S40 and the like are performed in the primary cooling system.

  According to the decontamination waste liquid treatment method of the third embodiment as described above, since the isoelectric point of manganese dioxide, which is the precipitate P1 containing permanganic acid, is around 3, the pH of the secondary treated water W2 is 3 By bringing it closer to the vicinity, the cohesiveness of the precipitate P1 is improved, and the aggregated precipitate P2 larger than the precipitate P1 can be obtained. In particular, the cohesiveness is further improved by setting the pH of the secondary treated water W22 to 3. As a result, the manganese dioxide that is the precipitate P1 becomes larger and is easily collected by the filter, so that the repair efficiency in the precipitate removing step S30 is improved, and the secondary by precipitation more efficiently in a short time. It is possible to remove manganese from the treated water W2.

Next, the decontamination waste liquid treatment method of the fourth embodiment will be described with reference to FIG.
In the fourth embodiment, the same components as those in the first embodiment are given the same reference numerals, and detailed description thereof is omitted. The decontamination waste liquid treatment method according to the fourth embodiment performs a concentration measurement step S80 for measuring the concentration of permanganate ions contained in the primary treated water W1 and adjusts the amount of hydrogen peroxide to be added. It differs from the first embodiment in that step S21 is performed.

  That is, in 4th embodiment, after implementing oxidation process S10 like 1st embodiment, concentration measurement process S80 which measures the density | concentration of the permanganate ion in the primary treated water W1 with a sensor is implemented. After carrying out the concentration measurement step S80, an adjustment precipitation step S21 is carried out in which the amount of hydrogen peroxide is added while adjusting the equivalent amount of permanganate ions. Thereafter, a precipitate removing step S30, a reducing step S40, and a removing step S50 are performed.

In the concentration measurement step S80, the concentration of permanganate ions in the primary treated water W1 generated in the oxidation step S10 is measured by sensors in the primary cooling water pipes 55a and 55b. Normally, the sensor used for the steady operation of the nuclear power plant P is used.
In addition, when the concentration of permanganate ions in the primary treated water W1 is known in advance, the concentration measurement step S80 can be omitted.

In the adjustment precipitation step S21, the primary treated water W1 after the concentration measurement step S80 is passed through the chemical volume control pipe 55e, and permanganate ions are precipitated from the concentration of permanganate ions measured in the concentration measurement step S80. Calculate the equivalent amount of hydrogen peroxide required for the reaction. The calculated amount of permanganate ions is adjusted to an amount of about 90% with respect to the equivalent amount of hydrogen peroxide required for complete precipitation, and added to the primary treated water W1. Permanganate ions remaining in the primary treated water W1 in the chemical volume control pipe 55e react with hydrogen peroxide and precipitate as manganese dioxide. When the permanganate ion becomes manganese dioxide and becomes the precipitate P3, it is removed from the primary treated water W1 and the secondary treated water W23 is generated. The amount of the precipitate P3 is smaller than the amount of the precipitate P1 in the first embodiment. The secondary treated water W23 flows into the ion exchange resin tower 60 together with the precipitate P3.
Thereafter, the precipitate removing step S30 is performed in the ion exchange resin tower 60, and the reducing step S40 and the like are performed in the primary cooling system.

  According to the decontamination waste liquid treatment method of the fourth embodiment as described above, the equivalent of hydrogen peroxide that is a reducing agent necessary for precipitating permanganic acid from the secondary treated water W23 is obtained by the sensor. Can do. By adjusting and adding the addition amount to about 90% with respect to the equivalent amount of hydrogen peroxide in the adjustment precipitation step S21, an amount of hydrogen peroxide that is a little smaller than the necessary and sufficient amount for precipitating permanganic acid is reduced. It can be added to the next treated water W23. When the precipitation is performed completely, the precipitation rate gradually decreases and it takes a long time to precipitate the last 10%. However, by suppressing the amount of hydrogen peroxide added, precipitation occurs in a range where permanganese reacts immediately. Therefore, hydrogen peroxide is supplied excessively, and precipitation is not completed in the chemical volume control pipe 55e which is the precipitation process S20, but precipitation is generated in the primary cooling water pipe 55a after the precipitate removal process S30 is completed. Can be prevented. Thus, the precipitation is completed by the precipitate removing step S30, and the precipitate P3 can be reliably removed.

Next, the decontamination waste liquid treatment method of the fifth embodiment will be described with reference to FIG.
In the fifth embodiment, the same components as those in the first embodiment are given the same reference numerals, and detailed description thereof is omitted. The decontamination waste liquid treatment method of the fifth embodiment includes a decomposition step S90 in which permanganic acid is decomposed with oxalic acid after performing the precipitate removal step S30, and inorganic ion exchange for removing the decomposed permanganic acid. It differs from the first embodiment in that the body water passing step S91 is performed.

That is, in the fifth embodiment, after performing the precipitation step S20 as in the first embodiment, oxalic acid that is an organic acid is added to decompose the permanganate ions into manganese ions (Mn ₂ ⁺ ) S90. To implement. Then, to implement the inorganic ion exchanger water passage step S91 of removing manganese ions (Mn 2 ^₊₎ an inorganic ion exchanger. Then, similarly to 1st embodiment, reduction process S40 and removal process S50 are implemented.

In the decomposition step S90, the electromagnetic valve 61 is opened and the chemical volume control system is opened without returning the secondary treated water W2 in which the precipitate removal step S30 is performed and the permanganate ions slightly remain to the primary cooling water pipe 55b. Circulate.
About 100 to 200 ppm of oxalic acid is added to the secondary treated water W2 through the chemical volume control pipe 55e. In the secondary treated water W24 to which oxalic acid is added, permanganate ions become manganese ions (Mn ₂ ⁺ ). The chemical reaction formula at this time can be expressed by the following formula (7).
2MnO ₄ ⁻ + 5C ₂ O ₄ H ₂ + 6H ⁺ → 2Mn ₂ ⁺ + 10CO ₂ + 8H ₂ O (formula 7)
Then, the secondary treated water W24 flows into the ion exchange resin tower 60 together with manganese ions (Mn ₂ ⁺ ).

In the inorganic ion exchanger water passing step S91, first, the inorganic ion exchanger is installed in the ion exchange resin tower 60 in which the precipitate removing step S30 is completed and the filter is removed. As the secondary treated water W24 flows into the ion exchange resin tower 60, the secondary treated water W24 containing manganese ions (Mn ₂ ⁺ ) in the inorganic ion exchanger flows. Manganese ions (Mn ₂ ⁺ ) are adsorbed on the inorganic ion exchanger and removed from the secondary treated water W24.
In addition, as an inorganic ion exchanger, a zeolite and a clay mineral can be used, for example.
Then, reduction process S40 etc. are implemented in a primary cooling system.

According to the decontamination waste liquid treatment method of the fifth embodiment as described above, oxalic acid, which is an organic acid, is added to the secondary treated water W2, so that it is slightly secondary even after the precipitate removing step S30 is performed. Permanganic acid remaining in the treated water W2 can be decomposed into manganese ions (Mn ₂ ⁺ ). Then, in the inorganic ion exchanger water passing step S91, the secondary treated water W24 containing manganese ions (Mn ₂ ⁺ ) is passed through the inorganic ion exchanger, whereby the manganese ions (Mn ₂ ⁺ ) are passed through the inorganic ion exchanger. It can be adsorbed and removed. Therefore, it is possible to remove manganese that has not been completely removed in the precipitation step S20 and the precipitate removal step S30 from the secondary treated water W24. Thereby, when the radionuclide contained in chromium, iron, etc. is removed using the ion exchange resin in the removal step S50, the manganese in the tertiary treated water W3 removed at the same time is almost eliminated, and the amount of the ion exchange resin used is reduced. This can be further reduced.

  Although the embodiments of the present invention have been described in detail with reference to the drawings, the configurations and combinations of the embodiments in the embodiments are examples, and the addition and omission of configurations are within the scope not departing from the gist of the present invention. , Substitutions, and other changes are possible. Further, the present invention is not limited by the embodiments, and is limited only by the scope of the claims.

The present invention is not limited to system decontamination. When the nuclear power plant P or the like is decommissioned, the decontamination object Z decomposed by a large decontamination equipment or the like is immersed and removed. It can also be used when dyeing.
Moreover, each process is not limited to being implemented by a primary processing system or a chemical volume control system as in this embodiment, and can be implemented by all systems.
Furthermore, a known filter is used as the filter, for example, a submicron filter is used. The roughness of the filter may be appropriately selected depending on the size of the precipitate to be removed.

P ... Nuclear power plant 51 ... Fuel rod 50 ... Pressurized water reactor 52 ... Pressurizer 53 ... Steam generator 54 ... Coolant pump 56 ... Steam turbine 57 ... Generator 58 ... Condenser 59 ... Feed water pump 60 ... Ion exchange Resin tower 61 ... Solenoid valve 55a ... Primary cooling water piping 55b ... Primary cooling water piping 55c ... Steam piping 55d ... Water supply piping 55e ... Chemical volume control piping 55f ... Chemical volume control piping Z ... Decontamination object S10 ... Oxidation process S20 ... Precipitation step S30 ... precipitate removal step S40 ... reduction step S50 ... removal step S11 ... alkaline oxidation step S60 ... resin water flow step S70 ... pH adjustment step S80 ... concentration measurement step S21 ... adjustment precipitation step S90 ... decomposition step S91 ... inorganic ions Exchanger water passing process W1 ... primary treated water W2 ... secondary treated water W3 ... tertiary treated water P ... precipitate P2 ... aggregate precipitate

Claims (5)

An oxidation step for oxidizing and elution of chromium from the decontamination object by adding an oxidizing agent containing permanganic acid to the treated water in which the decontamination object is immersed,
A precipitation step of adding a reducing agent that precipitates permanganic acid in the treated water after the oxidation step;
A precipitate removing step for removing the permanganic acid precipitate after the precipitation step;
A reduction step of reducing and eluting iron from the decontamination object by adding an organic acid to the treated water after the precipitate removal step;
A decontamination waste liquid treatment method comprising: a removal step of removing the radionuclide eluted in the treated water after the reduction step. The oxidizing agent containing permanganic acid is potassium permanganate,
The decontamination waste liquid treatment method according to claim 1, further comprising a resin water-passing step of passing the treated water through an ion exchange resin between the precipitate removing step and the reducing step.   The pH adjusting step of adjusting the pH of the treated water to 1 or more and 5 or less by adding a pH adjusting agent between the precipitation step and the precipitate removing step is further provided. The decontamination waste liquid processing method according to claim 2.   The said precipitation process adjusts the addition amount of the reducing agent which precipitates the said permanganic acid according to the density | concentration of the oxidizing agent containing the said permanganic acid in the said treated water. The decontamination waste liquid processing method as described in any one of these. A decomposition step of decomposing the permanganic acid by adding an organic acid to the treated water after the oxidation step;
5. The method according to claim 1, further comprising an inorganic ion exchanger water passing step of passing the treated water through the inorganic ion exchanger adsorbing manganese after the decomposition step. The decontamination waste liquid processing method as described in claim | item.

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