JP2014048231A - Decontamination waste liquid processing method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a decontamination waste liquid processing method capable of suppressing a usage amount of an anion exchange resin and a cation exchange resin while using an organic acid containing a nitrogen and reducing an ion exchange resin as a secondary waste.SOLUTION: A decontamination waste liquid processing method includes: a decomposition step S30 of decomposing at least an oxalic acid by heating a treated water which contains the oxalic acid, an organic acid containing a nitrogen and a nickel eluted from an object to be decontaminated by the organic acid at the decomposition starting temperature or higher of the oxalic acid and the decomposition starting temperature or lower of the organic acid containing the nitrogen; and a removal step S40 of removing the organic acid containing the nitrogen and the nickel in the treated water by a cation exchange resin and an anion exchange resin after the decomposition step S30.

Description

  The present invention relates to a decontamination waste liquid treatment method 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 small amount of 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, a dry type organic acid decontamination waste liquid that removes radioactive substances attached to an object to be decontaminated using a chemical solution containing an organic acid and treats the remaining decontamination waste liquid containing an organic acid. By the thermal decomposition method, waste liquid can be treated without using an ion exchange resin, and the amount of waste can be reduced.

However, since ion exchange resins have been used in nuclear power plants and the like, they are still widely used in general chemical cleaning.
Here, not only stainless steel containing a large amount of iron but also nickel-based alloys such as nickel-based inconel are used as members of nuclear power plant pipes to be decontaminated. It consists of a plurality of members made of material. In chemical decontamination using oxalic acid, if the object to be decontaminated contains a lot of nickel as in these members, oxalic acid for reducing and eluting iron from the oxide film and nickel contained in the member Reacts to produce nickel oxalate, which is deposited on the surface of the stainless steel and inhibits the reaction between the oxide film adhering to the stainless steel and oxalic acid. Therefore, the efficiency of reductive elution gradually decreases, and the decontamination target cannot be sufficiently decontaminated. Therefore, there is a method of maintaining and improving the decontamination performance by promoting the dissolution of nickel by adding an organic acid containing nitrogen such as picolinic acid.

JP 2003-19495 A

  However, organic acids containing nitrogen are difficult to dispose of because ammonia remains even after pyrolysis after chemical decontamination, increasing the amount of high-dose cation exchange resin used to remove it. Secondary waste increases. On the other hand, if it is attempted to remove without thermal decomposition, there is a problem that the amount of a large amount of anion ion resin used increases and the amount of secondary waste increases significantly.

  The present invention has been made in order to solve the above-mentioned problems, and suppresses the use amount of anion exchange resin and cation exchange resin while using an organic acid containing nitrogen, thereby reducing the amount of ion exchange resin that becomes secondary waste. A decontamination waste liquid treatment method that can be reduced is provided.

In order to solve the above problems, the present invention proposes the following means.
In the decontamination waste liquid treatment method according to one embodiment of the present invention, oxalic acid, nitrogen-containing organic acid, and treated water containing nickel eluted from the decontamination target by the organic acid are used to start decomposition of the oxalic acid. A decomposition step of decomposing at least oxalic acid by heating the treated water at a temperature equal to or higher than the temperature and equal to or lower than a decomposition start temperature of the organic acid containing nitrogen, and after the decomposition step, by a cation exchange resin and an anion exchange resin A removal step of removing the organic acid containing nitrogen and the nickel in the treated water.

  According to such a configuration, oxalic acid contained in the treated water can be decomposed into carbon and water by heating at or above the decomposition start temperature at which only oxalic acid begins to significantly start decomposition. Most of the oxalic acid in the water can be removed. This eliminates the need to remove oxalic acid with an anion exchange resin, thereby reducing the amount of anion exchange resin used. Further, since the heating temperature is lower than the decomposition start temperature of the organic acid containing nitrogen, the decomposition of the organic acid containing nitrogen does not proceed and hardly generates ammonia. Thereby, the usage-amount of the cation ion resin used as a high dose secondary waste is not increased. In other words, by reducing the amount of low-dose secondary waste anion exchange resin without increasing the amount of high-dose cation exchange resin used, it is used for decontamination and becomes secondary waste. The amount of ion exchange resin used can be reduced.

  The decontamination waste liquid treatment method according to another aspect of the present invention is characterized in that the organic acid containing nitrogen is picolinic acid.

  According to such a configuration, since the decomposition start temperature of oxalic acid and the decomposition start temperature of picolinic acid are far apart, it is possible to easily set the temperature at which only oxalic acid is thermally decomposed. Only the decomposition can be carried out efficiently.

  Furthermore, in the decontamination waste liquid treatment method according to another aspect of the present invention, an oxygen concentration increasing step for increasing the oxygen concentration in the treated water after the decomposition step, and heating the treated water again after the oxygen concentration increasing step. And a re-decomposing step for decomposing.

  According to such a configuration, by increasing the oxygen concentration in the treated water and then performing thermal decomposition again, most of the oxalic acid that could not be thermally decomposed in the decomposition step can be decomposed. As a result, most of the oxalic acid in the treated water can be thermally decomposed, and there is almost no oxalic acid to be removed by the anion exchange resin, so that the amount of the anion exchange resin used can be reduced.

  Furthermore, the decontamination waste liquid treatment method according to another aspect of the present invention includes an oxalic acid reduction step of adding oxalic acid to treated water to reduce and elute iron adhering to a decontamination target, and the oxalic acid reduction step. Then, after the decomposition start temperature of oxalic acid or higher, the treated water is heated to decompose the oxalic acid, and after the oxalic acid decomposition step, an organic acid containing nitrogen is added to the treated water. And an organic acid reducing step for reducing and eluting nickel adhering to the decontamination object.

  According to such a configuration, treated water that does not contain nitrogen-containing organic acid is thermally decomposed by performing the oxalic acid decomposition step after adding oxalic acid and carrying out reductive elution of iron. Thus, picolinic acid is not decomposed together with oxalic acid and ammonia is not generated, and decomposition can be performed only for oxalic acid. Therefore, since the treated water does not contain ammonia, the amount of cation exchange resin used can be reliably reduced.

  Moreover, the decontamination waste liquid treatment method according to another aspect of the present invention includes a cation exchange resin containing treated water containing oxalic acid, an organic acid containing nitrogen, and nickel eluted from the decontamination object by the organic acid. A radionuclide removal step for removing the radionuclide by passing water through, and a decomposition step for decomposing the organic acid containing oxalic acid and nitrogen by heating the treated water after the radionuclide removal step And a removal step of removing ammonia generated from the organic acid containing nitrogen by passing water through a cation exchange resin after the decomposition step.

  According to such a configuration, the radionuclide is previously removed from the treated water in the radionuclide removal step, and then oxalic acid and the organic acid containing nitrogen are both decomposed by thermal decomposition. As a result, oxalic acid is decomposed into carbonic acid and water and can be removed without using an ion exchange resin. Moreover, the organic acid containing nitrogen generates ammonia by decomposition and is removed by the cation exchange resin. Since the radionuclide is removed in advance, a cation exchange resin that removes ammonia that is slightly contaminated by radiation is low in dose. Accordingly, the amount of anion exchange resin used can be reduced without increasing the amount of cation exchange resin used at a high dose, and the amount of ion exchange resin as secondary waste can be reduced.

  According to the decontamination waste liquid treatment method of the present invention, an anion exchange resin and a cation can be used while using an organic acid containing nitrogen by removing only oxalic acid by thermal decomposition without thermally decomposing the organic acid containing nitrogen. The present invention provides a decontamination waste liquid treatment method that can reduce the amount of exchange resin used and reduce ion exchange resin as secondary waste.

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 1st 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.

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, and a pressurizer 52 that pressurizes the primary cooling water in order to suppress boiling of the primary cooling water (light water) in the pressurized water reactor 50. A steam generator 53 that turns the secondary cooling water into steam by the heat of the primary cooling water, a coolant pump 54 that returns the primary cooling water from the steam generator 53 to the pressurized water reactor 50, and the steam generator 53 A steam turbine 56 driven by the generated steam, 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 water from the condenser 58 are generated by steam. The water supply pump 59 which returns to the vessel 53 is provided.

  The pressurized water reactor 50 and the steam generator 53 are connected by primary cooling water pipes 55a and 55b, the steam generator 53 and the steam turbine 56 are connected by a steam pipe 55c, and the condenser 58 and the steam turbine 56 are connected to each other. Are connected by a water supply pipe 55d.

  In the nuclear power plant P configured as described above, the pressurized water reactor 50 is used as a primary cooling system member (hereinafter referred to as “decontamination target Z”) that is a member in contact with the reactor water, that is, the primary cooling water. , A pressurizer 52, a steam generator 53, a coolant pump 54, primary cooling water pipes 55a and 55b connecting them, various valves provided in the primary cooling water pipes 55a and 55b, and the like. 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 undergoes a nuclear reaction when irradiated with neutron rays from the fuel, and becomes a radionuclide such as chromium, nickel, and cobalt. 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 into 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 decontaminating the treated water W from which the oxide film containing the radionuclide adhering to the inner surface of the decontamination target Z is removed while circulating the water W.

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

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 W, and the treated water W added with the oxidizing agent is supplied to the inside of the decontamination target Z and circulated. By circulating the treated water W to which the oxidizing agent is added inside the decontamination target Z, chromium in the oxide film as the decontamination target Z is oxidized and eluted as Cr ⁶⁺ and contains chromium which is this radionuclide. Primary treated water W10 is generated.
In addition, what is used as an oxidizing agent is not limited to permanganic acid. For example, any additive that can oxidize and elute chromium, such as ozone and potassium permanganate, may be used.
Moreover, what is necessary is just to determine suitably the addition amount of permanganic acid according to the scale of the nuclear power plant P used as the decontamination object.

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（２）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（３）式で表すことができる。

これらの反応により、一次処理水Ｗ１０に放射性核種である鉄やニッケルを含有させた二次処理水Ｗ２０が生成される。 Next, reduction process S20 is implemented.
That is, in the reduction step S20, the primary treated water W10 is obtained by adding oxalic acid and picolinic acid as reducing agents to the primary treated water W10 after the oxidation step S10 and adding these reducing agents inside the decontamination target Z. Supply and circulate. And reduction process S20 pressurizes with a pressure pump, heats decontamination subject Z, and carries out primary treatment water W10 as high temperature. The heating temperature is preferably set to 80 ° C to 100 ° C, and more preferably set to 90 ° C.
By circulating the primary treated water W10 with a reducing agent added inside the decontamination target 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 (1).

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 (2).

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 (3).

By these reactions, secondary treated water W20 in which iron or nickel that is a radionuclide is contained in primary treated water W10 is generated.

Next, the decomposition step S30 is performed.
That is, decomposition | disassembly process S30 is implemented by pressurizing and heating the secondary treated water W20 after implementing reduction process S20 with a pressure pump. The heating temperature is set to 110 ° C. in consideration of the decomposition start temperature and decomposition end temperature of oxalic acid, and the secondary treated water W20 heated inside the decontamination target Z while continuously heating for 24 hours. Supply and circulate.
Here, the decomposition start temperature is a temperature at which the additive remarkably starts to decompose from the solution. For example, in the case of oxalic acid, 2000 ppm of oxalic acid has a temperature rising rate of 55 ° C./hour. Of these, 110 ° C., which is a temperature at which decomposition of 5% or more was observed. On the other hand, the decomposition end temperature is a temperature at which the additive ends decomposition in the solution and becomes undetectable. For example, when the temperature rising rate is 55 ° C./hour, all of 2000 ppm of oxalic acid is decomposed and detected. It is 280 ° C., which is the temperature at which it cannot be performed.
As the secondary treated water W20 is heated, oxalic acid contained in the secondary treated water W20 is thermally decomposed. The chemical reaction formula at this time can be expressed by the following formula (4).
2C ₂ H ₂ O ₄ + O ₂ → 4CO ₂ + 2H ₂ O (Formula 4)
As shown in Table 1, the heating temperature of 110 ° C. is a temperature lower than the decomposition start temperature of picolinic acid, and picolinic acid remains in the secondary treated water W20 with almost no decomposition. Thereby, the tertiary treated water W30 from which most of the oxalic acid has been removed from the secondary treated water W20 is generated.

Finally, the removal step S40 is performed.
That is, in removal process S40, the radionuclide of chromium, iron, and nickel contained in the tertiary treated water W30 is removed using a cation exchange resin that is an ion exchange resin. At the same time, an anion exchange resin that is an ion exchange resin is used to remove permanganic acid, picolinic acid and the like contaminated with the radionuclide remaining in the tertiary treated water W30, thereby decontaminating the tertiary treated water W30. . The decontaminated tertiary treated water W30 is used again as treated water W 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 performing the decomposition step S30 while heating for 24 hours at 110 ° C., which is equal to or higher than the decomposition start temperature at which only oxalic acid starts to start remarkably, About 80% of the oxalic acid in the treated water W20 can be pyrolyzed into carbon and water to produce tertiary treated water W30 from which most of the oxalic acid in the treated water W has been removed. By removing the tertiary treated water W30 with an anion exchange resin, there is almost no oxalic acid to be removed with the anion exchange resin, so the amount of anion resin used can be reduced by about 40% compared to the case where oxalic acid is not decomposed. .
Further, since the heating temperature does not reach 170 to 190 ° C. which is the decomposition start temperature of picolinic acid, it is hardly decomposed, and ammonia generated by pyrolyzing an organic acid containing nitrogen such as picolinic acid is hardly generated. . Normally, ammonia cannot be removed unless it is a cation exchange resin. Therefore, ammonia is removed together with radionuclides such as chromium and nickel by the cation exchange resin in the decontamination waste liquid, resulting in a high-dose secondary waste. However, since picolinic acid itself can be removed with an anion exchange resin, chemical decontamination without thermally decomposing picolinic acid does not increase the amount of high-dose cation exchange resin used.
By decomposing only oxalic acid without decomposing picolinic acid, the amount of secondary waste by low-dose anion exchange resin can be reduced without increasing secondary waste by high-dose cation exchange resin. The amount of ion exchange resin used for decontamination and becoming secondary waste can be greatly reduced.
Furthermore, by performing chemical decontamination using oxalic acid and picolinic acid, it is possible to improve the decontamination performance of the decontamination object Z including stainless steel and nickel-based alloy.

  Moreover, high decontamination performance can be maintained by using picolinic acid as an additive for an organic acid containing nitrogen for eluting nickel. Furthermore, since the decomposition start temperature is far away from oxalic acid, the temperature at which only oxalic acid is thermally decomposed can be easily set in the decomposition step S30, and the decomposition of only oxalic acid can be carried out efficiently. it can.

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 is different from the first embodiment in that the oxygen concentration raising step S50 and the re-decomposition step S31 are performed after the decomposition step S30.

  That is, in 2nd embodiment, after performing decomposition | disassembly process S30 similarly to 1st embodiment, oxygen concentration raising process S50 which raises the oxygen concentration of the tertiary treated water W30 and makes high oxygen concentration treated water W50 is implemented. Thereafter, the high oxygen concentration treated water W50 is heated again, and after performing the re-decomposition step S31 in which thermal decomposition is performed, the removal step S40 is performed as in the first embodiment.

In the oxygen concentration increasing step S50, after the thermal decomposition is performed in the decomposition step S30, the tertiary treatment water W30 is stirred and supplied with oxygen to increase the oxygen concentration of the tertiary treatment water W30, thereby increasing the oxygen concentration treatment water W50. Is generated.
In the re-decomposition step S31, the high oxygen concentration treated water W50 having an increased oxygen concentration is again pressurized with a pressure pump and heated. The heating temperature is set to 110 ° C. as in the decomposition step S30, and the heated high oxygen concentration treated water W50 is supplied and circulated inside the decontamination target Z while continuously heating for 24 hours. When the high oxygen concentration treated water W50 is heated, thermal decomposition of oxalic acid is performed again. Thereby, the oxalic acid-removed treated water W31 from which more oxalic acid has been removed from the high oxygen concentration treated water W50 is generated.

  According to the decontamination waste liquid treatment method of the second embodiment as described above, the tertiary treatment water W30 is stirred and the surrounding air is taken in to increase the oxygen concentration in the tertiary treatment water W30, thereby increasing the oxygen concentration treatment water W50. It can be. Most of the oxalic acid can be decomposed by heating again to this high oxygen concentration treated water W50 and performing thermal decomposition. That is, normally, decomposition is promoted in the decomposition step S30, and when about 80% of the oxalic acid is thermally decomposed, a reducing atmosphere is obtained, and the oxygen concentration in the tertiary treated water W30 is reduced. Therefore, the thermal decomposition reaction of oxalic acid in the tertiary treated water W30 stops. However, the high oxygen concentration treated water W50 having an increased oxygen concentration is heated again and subjected to thermal decomposition, so that the remaining about 20% of the remaining oxalic acid that could not be decomposed in the decomposition step S30 is further reduced. About 80% can be pyrolyzed. Thereby, it becomes possible to thermally decompose oxalic acid by 95% or more together with the decomposition step S30, and there is almost no oxalic acid to be removed by the anion exchange resin in the removal step S40, thereby further reducing the use amount of the anion exchange resin. be able to.

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. In the decontamination waste liquid treatment method according to the third embodiment, the step performed between the oxidation step S10 and the removal step S40 is not the reduction step S20 and the decomposition step S30, but is performed by adding only oxalic acid. It differs from the first embodiment in that it is S21, an oxalic acid decomposition step S32 for thermally decomposing oxalic acid, and an organic acid reduction step S22 performed by adding picolinic acid.

  That is, in the third embodiment, after the oxidation step S10 is performed as in the first embodiment, the oxalic acid reduction step S21 in which only the oxalic acid is added to reduce and elute iron is performed, and the oxalic acid reduction step S21. After the execution, an oxalic acid decomposition step S32 performed in the same manner as in the first embodiment is performed. Thereafter, after performing the organic acid reduction step S22 in which only nickel picolinic acid is added and nickel is reduced and eluted after the oxalic acid decomposition step S32, the removal step S40 is performed as in the first embodiment.

In the oxalic acid reduction step S21, first, oxalic acid is added as a reducing agent to the primary treated water W10, and the inside of the decontamination target Z is circulated. And it pressurizes with a pressurization pump, the decontamination target Z is heated, and the primary treated water W10 is made into high temperature, and it implements. The heating temperature is preferably set to 80 ° C to 100 ° C, and more preferably set to 90 ° C. By circulating the primary treated water W10 added with oxalic acid inside the decontamination target Z, iron in the oxide film adhering to the stainless steel is reduced and eluted by oxalic acid. On the other hand, nickel and oxalic acid contained in the oxide film of Inconel react and nickel oxalate is eluted. Owing to these reactions, unlike the secondary treated water W20 in the first embodiment, the primary treated water W10 not only contains iron or nickel as radionuclides but also oxalic acid reduced treated water W21 not containing picolinic acid at all. Is generated.
In addition, in order to prevent nickel and oxalic acid from reacting and elution of nickel oxalate, oxalic acid added as a reducing agent is about 200 ppm in the case of decontamination target Z that requires 2000 ppm. It is preferable to carry out in a small amount.

The oxalic acid decomposition step S32 is performed by heating at 110 ° C. for 24 hours after the oxalic acid reduction step S21 as in the first embodiment. Thereby, unlike the tertiary treated water W30 in the first embodiment, oxalic acid-decomposed tertiary treated water W32 not only containing most of oxalic acid but also containing no picolinic acid is generated.
In addition, since picolinic acid is not included in the oxalic acid decomposition step S32, if the decomposition start temperature of oxalic acid is about 110 ° C. or higher, the temperature is set within a temperature that can be handled by equipment for chemical decontamination. be able to. In this case, the heating time may be 24 hours, and it may be set to a time at which oxalic acid is sufficiently decomposed according to the heating temperature and the amount of oxalic acid added.

  In the organic acid reduction step S22, first, picolinic acid is added as a reducing agent to the oxalic acid decomposition tertiary treated water W32, and the inside of the decontamination target Z is circulated. And it pressurizes with a pressure pump, the decontamination target Z is heated, and the oxalic acid decomposition | disassembly tertiary treated water W32 which added picolinic acid is made into high temperature, and it implements. The heating temperature is preferably set to 170 ° C. or lower, which is the decomposition start temperature of picolinic acid, and more preferably set to 90 ° C., which is the same as in the oxalic acid reduction step S21. By circulating the oxalic acid decomposition tertiary treated water W32 to which picolinic acid has been added inside the decontamination target Z, nickel in the oxide film adhering to Inconel, which is a nickel-based alloy, is reduced and eluted by picolinic acid. By this reaction, organic acid reduction treated water W22 in which picolinic acid and nickel are added to oxalic acid decomposition tertiary treated water W32 is generated.

  According to the decontamination waste liquid treatment method of the third embodiment as described above, nitrogen is contained by performing the oxalic acid decomposition step S32 after the oxalic acid returning step in which only oxalic acid is added and iron is reduced and eluted. The oxalic acid reduction treated water W21 containing no picolinic acid, which is an organic acid, is thermally decomposed. Thereby, in the oxalic acid decomposition step S32, picolinic acid is not decomposed together with oxalic acid and ammonia is not generated, and decomposition can be performed exclusively for oxalic acid. Therefore, since ammonia is not contained in the oxalic acid decomposition tertiary treated water W32 that has finished the oxalic acid decomposition step S32, the amount of cation exchange resin used can be reliably reduced.

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. In the decontamination waste liquid treatment method according to the fourth embodiment, the step performed between the reduction step S20 and the removal step S40 includes a radionuclide removal step S41 for removing the radionuclide, and then thermal decomposition of oxalic acid and picolinic acid simultaneously. It differs from the first embodiment in that it is an oxalic acid organic acid decomposition step S33.

  That is, in 4th embodiment, after performing reduction process S20 like 1st embodiment, radionuclide removal process S41 which removes a radionuclide from secondary treated water W20 using only cation exchange resin was implemented. Thereafter, an oxalic acid organic acid decomposition step S33 for thermally decomposing oxalic acid and picolinic acid at the same time is performed, and then a removal step S40 similar to that of the first embodiment is performed.

In the radionuclide removal step S41, cation exchange resin is added to the secondary treated water W20 after the reduction step S20, and the secondary treated water W20 is allowed to flow therethrough, so that chromium, nickel, iron, etc. contained in the secondary treated water W20, etc. The radionuclide is removed, and radionuclide removal water W41 is generated.
In the oxalic acid organic acid decomposition step S33, after performing the radionuclide removal step S41, the oxalic acid and picolinic acid are both heated and heated at 180 ° C. for 24 hours at which thermal decomposition starts. Thereby, oxalic acid and picolinic acid are removed, and oxalic acid organic acid-removed water W33 containing ammonia is generated.

  In the removal step S40, similarly to the first embodiment, ammonia contained in the oxalic acid organic acid removal water W33 is removed using a cation exchange resin that is an ion exchange resin. At the same time, an anion exchange resin that is an ion exchange resin is used to remove permanganic acid and the like contaminated with radionuclides remaining in the oxalic acid organic acid-removed water W33, thereby removing the oxalic acid organic acid-removed water W33. Dye.

  According to the decontamination waste liquid treatment method of the fourth embodiment as described above, the radioactive nuclide removal step S41 removes the radionuclide using the cation exchange resin, so that the secondary waste having a high dose is firstly removed. Can be removed. Thereafter, oxalic acid and picolinic acid are heated and thermally decomposed, whereby oxalic acid is decomposed into carbon and water, and can be removed without requiring the ion exchange resin itself. Since picolinic acid is decomposed into ammonia, it needs to be removed with a cation exchange resin. However, since the radionuclide has been removed first, even if ammonia is removed with a cation exchange resin, the dose is not high and low. Can be treated as a secondary waste dose. In addition, since oxalic acid and picolinic acid are decomposed, the amount of anion exchange resin can be reduced without increasing the amount of high-dose cation exchange resin used, and the amount of ion exchange resin that becomes secondary waste Can be 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.

In addition, this invention is not limited to system decontamination, When decomposing the decontamination target Z decomposed | disassembled with the large sized decontamination equipment etc., when nuclear power plant P etc. are made into a decommissioning furnace. Can also be used.
Further, the organic acid containing nitrogen used in the present embodiment is not limited to picolinic acid, and for example, EDTA or aspartic acid can be used. In that case, since the decomposition start temperature and the decomposition end temperature are slightly different for each organic acid used, it is necessary to select appropriately depending on the organic acid used. Generally, there is a decomposition start temperature around 170 to 200 ° C., which is a temperature at which an organic acid containing nitrogen does not cause decarboxylation, and similarly there is a decomposition end temperature around 220 to 250 ° C. For example, in the case of EDTA, as shown in Table 1 above, when the rate of temperature rise is 55 ° C./hour, the decomposition start temperature is 170 to 190 ° C., and the decomposition end temperature is 220 to 240 ° C.

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 55a ... Primary cooling Water piping 55b ... Primary cooling water piping 55c ... Steam piping 55d ... Feed water piping Z ... Decontamination object S10 ... Oxidation process S20 ... Reduction process S30 ... Decomposition process S40 ... Removal process W ... Treated water W10 ... Primary treated water W20 ... Second Next treated water W30 ... Tertiary treated water S50 ... Oxygen concentration increasing process W50 ... High oxygen concentration treated water S31 ... Re-decomposition process W31 ... Oxalic acid removing treated water S21 ... Oxalic acid reducing process W21 ... Oxalic acid reducing treated water S32 ... Oxalic acid Decomposition process W32 ... Oxalic acid decomposition tertiary treatment water S22 ... Organic acid reduction process W22 ... Organic acid reduction treatment water S4 ... radionuclide removal step W41 ... radionuclides free water S33 ... oxalate organic acid degradation step W33 ... oxalic acid organic acid removal Water

Claims (5)

Oxalic acid, organic acid containing nitrogen, and treated water containing nickel eluted from the object to be decontaminated by the organic acid, not less than the decomposition start temperature of the oxalic acid and not more than the decomposition start temperature of the organic acid containing nitrogen A decomposition step of decomposing at least oxalic acid by heating the treated water at a temperature of
After the decomposition step, a removal step of removing the organic acid containing nitrogen and the nickel in the treated water by a cation exchange resin and an anion exchange resin;
A decontamination waste liquid treatment method comprising:   2. The decontamination waste liquid treatment method according to claim 1, wherein the organic acid containing nitrogen is picolinic acid. After the decomposition step,
An oxygen concentration increasing step for increasing the oxygen concentration in the treated water;
The decontamination waste liquid treatment method according to claim 1, further comprising a re-decomposition step of heating and decomposing the treated water again after the oxygen concentration increasing step. An oxalic acid reduction step of adding oxalic acid to the treated water and reducing and eluting iron adhering to the decontamination target
After the oxalic acid reduction step, the oxalic acid decomposition step of heating the treated water to decompose the oxalic acid at a decomposition start temperature of oxalic acid, and after the oxalic acid decomposition step, the organic acid containing nitrogen is A decontamination waste liquid treatment method comprising an organic acid reduction step of adding to treatment water and performing reductive elution of nickel adhering to the decontamination target. Treated water containing oxalic acid, an organic acid containing nitrogen, and nickel eluted from the object to be decontaminated by the organic acid,
A radionuclide removal step of removing the radionuclide by passing water through the cation exchange resin;
A decomposition step of decomposing the oxalic acid and the organic acid containing nitrogen by heating the treated water after the radionuclide removal step;
After the decomposition step, by removing the ammonia generated from the organic acid containing nitrogen by passing water through a cation exchange resin,
A decontamination waste liquid treatment method comprising:

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