JP2002131473A - Water-quality control method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a water-quality control method which restrains a radioactive substance from being stuck to a reactor core internal structure and to the surface of a pipe. SOLUTION: The radioactive substance which is stuck to at least a face coming into contact with reactor water in the reactor core internal structure or a face coming into contact with reactor water in the pipe is removed while a nuclear heating operation is stopped. Then, at least a metal organic compound complex or a metal oxide organic compound complex which has at least the adhesion suppression effect of the radioactive substance to the reactor core internal structure or the corrosion reduction effect of the reactor core internal structure is added to nuclear reactor water in a nuclear power plant before a rated output operation is performed after the radioactive substance has been removed. After that, the organic compound complex is decomposed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for controlling water quality, and more particularly, to the attachment of radioactive material to at least one of a reactor internal structure and piping in which radioactive material has been removed from a surface in contact with reactor water. The present invention relates to a water quality control method for reducing water quality.

[0002]

2. Description of the Related Art A water-cooled nuclear power plant (hereinafter referred to as L
It is called a WR plant. In), reducing radiation exposure of workers during maintenance and inspection is an important issue for safety.
The main radiation source is Co that is taken in from the reactor water into the oxide film during the growth of the oxide film on the reactor internals and piping surfaces.
-60, Co-58, Mn-54, etc. (Co-60, Co-58, Mn in these reactor waters).
The -54 is produced by neutron irradiation of nuclear fuel such as Co, Ni, and Fe brought into the reactor water or feedwater due to corrosion and elution of structures inside and outside the reactor.) Therefore, radioactive substances taken into the oxide film on the surfaces of furnace structures and pipes by chemically or physically removing the oxide film on the surfaces of the furnace structures and pipes (hereinafter referred to as decontamination). To reduce radiation exposure of workers.

[0003] As a method for suppressing the incorporation into the oxide film on the surface of the reactor internals and pipes after decontamination, Zn is contained in the reactor water during operation after decontamination at a reactor water concentration of 5%.
It has been reported on page 1090 of the Proceedings of the Atomic Energy Society of Japan "Spring 2000 Annual Meeting" that the injection of radioactive materials can be suppressed by injecting so that the pressure becomes about 10 ppb. Japanese Patent Application Laid-Open No. 09-133784 discloses a method of exposing to a high-temperature oxidizing gas to form an oxide film to suppress the adhesion of radioactive substances. Japanese Patent Application No. Showa 6 shows a method of controlling the adhesion of radioactive substances by forming an oxide film with a low growth rate on the surface after exposure to water for several hundred hours.
It is disclosed in Japanese Patent Application Laid-Open No. 2-24195.

[0004]

Since the radioactive material of the radiation source is removed by the decontamination, the radiation exposure of the workers is suppressed during the maintenance and inspection work immediately after the removal. However, since the rate of incorporation of radioactive substances into the oxide film on the furnace internals and piping surface and the growth rate of the oxide film are related by the formulas 1 and 2, respectively, when the oxide film is removed by decontamination, As a result, the growth rate of the oxide film increases, and the radioactive substance is rapidly incorporated into the oxide film on the surface of the furnace internals and pipes.

DA / dt = α · (dm / dt) · C (Equation 1) dm / dt = β · (1 / t ^1/2 ) (Equation 2) A: radioactivity adhesion amount, α: constant , M: amount of oxide film, t: time, C: amount of radioactive material in reactor water, β: constant (if t ₁ > t ₂ , 1 / t ₁ ^1/2 <1 / t ₂ ^1/2 Therefore, since dm ₁ / dt <dm ₂ / dt, dA ₁ / dt
dt <dA ₂ / dt. If rapid reattachment of radioactive materials after this decontamination occurs, the dose rate of the radiation source rapidly increases, so that the effect of decontamination during the next maintenance and inspection work on reducing radiation exposure is reduced.

[0006] On the other hand, it is conceivable to perform decontamination again, but the cost for the reduced amount of exposure increases.

[0007] In the method reported on page 1090 of the Proceedings of the Atomic Energy Society of Japan, "Annual Meeting of the Spring of 2000", the activation of Zn causes the radioactive Zn-
65, which becomes a new radiation source, that the operation of removing Zn-64, which is the parent nuclide, in order to suppress the production of Zn-65 increases costs, and that the implanted Zn ions cause reactor water purification. There is a problem that the load on the ion exchange resin of the system is increased, and the performance of the resin is deteriorated earlier, which leads to an increase in the exchange cost.

The method disclosed in Japanese Patent Application Laid-Open No. 9-133784 has a problem that the size of a high-temperature gas supply facility when applied to a wide area is increased. Also, Japanese Patent Application Laid-Open No. Sho 62-2419
The method disclosed in Japanese Patent Publication No. 5 has a problem that high-concentration ions cannot be implanted during plant operation, and a heater facility for maintaining high-temperature and high-pressure water becomes large when the method is performed other than during plant operation. Was.

[0009] An object of the present invention is to provide a water quality control method for suppressing the adhesion of radioactive substances to the reactor internal structure and the pipe surface after decontamination.

[0010]

An embodiment for solving the problem is that at least the surface of the reactor internal structure that is in contact with the reactor water or the surface of the pipe that is in contact with the reactor water during the stop of nuclear heating. After the removal of the radioactive material attached to any of the reactor water of the nuclear power plant before the rated output operation after the removal is performed, the radioactive material is prevented from adhering to the reactor internal structure. Decomposing the organic compound complex after adding at least one of an organic compound complex of a metal and an organic compound complex of an oxide of the metal having at least one of the effect and the effect of reducing corrosion of the reactor structure. I do.

Thus, it is possible to deposit a metal having at least one of the effect of suppressing the adhesion of the radioactive material and the effect of reducing the corrosion of the nuclear reactor structure. Can be suppressed. Further, by depositing the metal oxide, generation of metal ions as a source of the radioactive substance can be suppressed, and by reducing the amount of the radioactive substance in the reactor water, the deposition of the radioactive substance can be suppressed.

Another embodiment for solving the problem is that, during the stop of the nuclear heating, at least one of the surface of the reactor internal structure which is in contact with reactor water and the surface of piping which is in contact with reactor water. After the removal of the radioactive material, the effect of suppressing the adhesion of radioactive material to the reactor structure and the effect of the An organic complex of iron and at least one of metal ions or colloids having at least one of the effects of reducing corrosion are injected to decompose the organic compound complex of iron.

[0013] Thus, iron can be deposited by decomposing the organic compound complex of iron, and the effect of suppressing the adhesion of radioactive substances to the reactor structure injected into the reactor water and reducing the corrosion of the reactor structure. At least one of metal ions or colloids having at least one of the effects can be co-deposited with iron. Thereby, a metal having at least one of the effect of suppressing the adhesion of the radioactive material and the effect of reducing the corrosion of the nuclear reactor structure can be attached, and the re-adhesion of the radioactive material to the nuclear reactor structure can be suppressed.

The decomposition of the organic compound complex of the metal ion organic compound complex can be carried out by irradiating ultraviolet rays while circulating water to which the metal ion organic compound complex has been added, or by passing water through a heterogeneous catalyst. An example of the heterogeneous catalyst is an activated carbon catalyst supporting a noble metal such as Ru or Pt.

As the organic compound complex of iron ions, an oxalic acid complex is preferable. Because oxalic acid is used in decontamination to remove radioactive substances by chemical methods, the integrity of the material after oxalic acid is used has been investigated. When performing the operation of decomposing the oxalic acid in the furnace during the decontamination step, the same operation is performed, so that the adhesion operation can be performed during the decontamination step, and extra time is spent on the adhesion operation This is because there is no need.

The initial concentration of iron oxalate complex is 0.5 ppm in terms of iron concentration from the viewpoint that the amount of waste generated is reduced and that if the concentration is too low, precipitation of Fe oxides is difficult to occur. To 100 ppm is desirable.

The precipitation of iron ions is carried out by using Na ₂ CO ₃ , KOH,
It can be promoted by adding an alkali such as NaOH so that the pH does not become 5.5 or more. This is because the solubility of iron ions decreases when an alkali is added. Since the added alkali becomes a waste, the amount of waste generated can be suppressed by adding it so that the pH does not become 5.5 or more.

The decomposition of an organic compound such as oxalic acid as a ligand can be accelerated by adding hydrogen peroxide as an oxidizing agent.

In the case of performing an adhesion operation using an oxalic acid complex of iron ions, in particular, performing decontamination using oxalic acid, and performing an operation of decomposing the oxalic acid in the decontamination step in a furnace. Can be repeated in the step of decomposing oxalic acid in the decontamination step.

At the start of the operation, the concentration of oxalic acid is 1
It is desirable that the time is not more than 00 ppm and the pH is not less than 4.0. At that time, the amount of radioactive substance dissolved by decontamination has become sufficiently small.

Pt, Rh, Pd, Zr, Tr are metals or metal oxides that have the effect of suppressing the adhesion of radioactive substances.
There are i, Al, Zn and the like, and it is desirable to use them alone or as a mixture. Since Pt, Rh, and Pd have the effect of decomposing hydrogen and lowering the dissolved oxygen concentration in an H ₂ injection environment, the effect of suppressing the growth of an oxide film, thereby suppressing the attachment of radioactive substances. Can be expected. Zr, Ti, and Al are made of ZrO ₂ , T
By covering as a compound such as iO ₂ and Al ₂ O _3, it is possible to suppress the diffusion of oxygen into the base material, thereby suppressing the growth of the oxide film, thereby exerting the effect of suppressing the adhesion of radioactive substances. Can be expected. Zn is the base material Fe or C
By forming an oxide film in a form that is difficult to dissolve by reacting with r, it is expected that the growth of the oxide film is suppressed and an effect of suppressing the attachment of a radioactive substance is exerted.

As a metal having at least one of the effect of suppressing the adhesion of radioactive materials to the reactor structure and the effect of reducing corrosion of the reactor structure, Zn can be cited. Reactor water concentration is 0.1 ppb
It is desirable to add so as to be at least 2 ppb or less.
This is because, when the Zn water in the reactor water is injected so as to have a concentration of 2 ppb, the amount of radioactive substances attached can be reduced to about １ ／ as compared with the case where no Zn is added. Further, by adjusting the concentration, the amount of Zn to be implanted can be reduced.
5 can be ignored and the parent substance Zn-64
There is no need to perform operations other than. Further, the load on the ion exchange resin of the reactor water purification system can be reduced.

[0023]

DESCRIPTION OF THE PREFERRED EMBODIMENTS First, an experiment performed by the inventors to find out the conditions for implementation will be described. In this experiment, F
This is an experiment performed to find out the conditions for decomposition of the oxalic acid organic compound complex of e and precipitation of Fe accompanying the decomposition.

In the experiment, as shown in FIG. 9, an adhesion processing apparatus 210 for adhering a metal or metal oxide having an effect of suppressing the adhesion of radioactive substances or an effect of reducing corrosion is attached to a Teflon tube 2 which is an object part to be subjected to the adhesion processing. This is an experiment in which a connection is made through the connection portions X1 and X2 to perform an adhesion process. First, the device will be described. The Teflon pipe 2 has a circulation pump 3
Water quality measuring device 1 for measuring pH and conductivity of system water
5, a piping 1 so as to form a closed loop in series with a heating / cooling device 16 for raising system water to a predetermined temperature or cooling to room temperature, and a surge tank 17 for adjusting system water flow.
2 connected. In this experiment, the predetermined temperature of the system water is 90 ° C. The adhesion processing apparatus 210 installs the valve 6 on the pipe 12, installs the pipe 13 so as to connect the upstream side and the downstream side, and installs the valve 4 on the pipe 13 from the upstream side.
a, A water purification device 5 and a valve 4b for purifying system water after the completion of the adhesion treatment are installed. Also, piping 1
2, a flow control valve 8 is installed, a pipe 14 is installed so as to connect the upstream side and the downstream side, and an organic compound decomposer 10 using an activated carbon catalyst carrying a valve 9a, Ru is installed in the pipe 14 from the upstream side. And a valve 9b, and an H ₂ O ₂ tank 2 between the valve 9a and the organic compound decomposing device 10.
1, consists of H ₂ O ₂ injection pump 22 and valve 23 H ₂
The O ₂ injection device 20 is connected. In addition, Fe
, An Fe oxalate complex injection device 30 comprising a tank 31 containing an oxalic acid complex solution, a chemical solution injection pump 32 and a valve 33, and a tank 41 containing a pH adjuster, a pH adjustment comprising a chemical solution injection pump 42 and a valve 43. The agent injection device 40 is connected. In this experiment, KOH is used as a pH adjuster. Other pH adjusters include Na
OH or Na ₂ CO ₃ can be used.

In addition, a pipe 11 is provided with a vent 11 for removing gas generated at the time of decomposition of organic compounds,
After the sampling of the solution for the analysis of the water quality of the solution flowing through the pipe 12 and the completion of the adhesion treatment, the supply / drainage valve 7 used for the wastewater of the system solution is connected. The water purification device 5
Uses an ion exchange resin tower filled with a mixture of a cation exchange resin and an anion exchange resin.

In this experiment, using this apparatus, the amount of Fe oxalate complex added to the system and the pH value of the system water were changed multiple times by changing the amount of the pH adjusting agent. By conducting experiments, the relationship between the Fe concentration of the system water, the pH value of the system water, the oxalic acid concentration of the system water, and the presence or absence of Fe precipitation in the system water was examined. The presence or absence of Fe precipitation was determined by sampling the system water from the feed / wastewater valve 7.

The operation of the adhesion processing apparatus 210 will be described. (1-1) Water is supplied to the system from the supply / wastewater valve 7. (1-2) Valves 4a, 4b, 9a, 9b, 33, 4
The system water is circulated by the circulation pump 3 by closing the valves 3 and 23 and the valves 6 and 8 are opened, and the temperature of the system water is raised to 90 ° C. by the heating / cooling device 16. (1-3) When the temperature of the system water reaches 90 ° C., the valve 33 is opened in the Fe oxalate complex injection device 30,
The chemical liquid injection pump 32 is started, the oxalic acid complex of Fe is added to the system, and after the addition is completed, the chemical liquid injection pump 32 is stopped and the valve 33 is closed. Thereby, the oxalic acid concentration of the system water is adjusted. The oxalic acid concentration of the system water is measured by the water quality measuring device 15. Similarly, KOH as a pH adjuster is injected from the pH adjuster injection device 40 to adjust the pH of the system water. The pH of the system water is measured by the water quality measuring device 15. (1-4) When the various reagents are uniformly mixed in the system, the valves 9a and 9b are opened, the flow rate is adjusted by the flow rate adjusting valve 8, and the system water is passed through the organic compound decomposer 10. The determination as to whether or not they are uniformly mixed is made based on the change in the conductivity measured by the water quality measuring device 15. Further, the valve 23 of the H ₂ O ₂ injection device 20 is opened, the H ₂ O ₂ injection pump 22 is started, and H ₂ O ₂ is added to decompose oxalic acid. (1-5) When the decomposition of the oxalic acid is completed, stop the H ₂ O ₂ injection pump 22, closing the valve 23. The progress of oxalic acid decomposition is monitored by sampling and analyzing the system water from the feed / wastewater valve 7. Further, the system water is sampled and analyzed to determine the presence or absence of Fe precipitation. (1-6) The system water is cooled to a normal temperature (about 30 ° C.) by the heating / cooling device 16. (1-7) After cooling, the valves 4a and 4b are opened, the valve 6 is closed, and the system water is passed through the water purification device 5 to purify the system water to an impurity concentration level at which wastewater can be generated.
In this experiment, the oxalic acid concentration was purified to below the detection limit. (1-8) After the purification is completed, the system water is drained from the supply and waste water valve 7. (1-9) The Teflon tube 2 is removed, and the state of adhesion of Fe to the water contact surface is visually inspected.

FIG. 2 shows the relationship between the Fe concentration and the pH, and FIG. 3 shows the relationship between the Fe concentration and the oxalic acid concentration. In FIGS. 2 and 3, the case where precipitation of Fe was observed is indicated by “●”, and the case where precipitation of Fe was not observed is indicated by “○”. From FIGS. 2 and 3, F
It can be seen that e was deposited when the Fe concentration was 0.5 ppm or more, the pH was 5.7 or more, and the oxalic acid concentration was 100 ppm or less. Therefore, when operating the adhesion processing apparatus 1, Fe
It is desirable to add the oxalic acid complex such that the Fe concentration of the oxalic acid complex becomes 0.5 ppm or more. Further, from the viewpoint of reducing the amount of waste generated and shortening the time, the Fe concentration is desirably 100 ppm or less. When the pH does not reach 5.7 or higher, the pH of system water can be increased by adding an alkaline aqueous solution such as an aqueous KOH solution or an aqueous NaOH solution, so that precipitation of Fe can be started more quickly.

The end of the adhesion treatment can also be determined by actually measuring the amount of metal ions having a corrosion reducing effect or the amount of colloid containing a metal having a corrosion reducing effect. In this case, a line is constructed separately from the adhesion processing apparatus 1 or separately, a test piece in a state similar to the part to be subjected to the adhesion processing is installed, and it is sequentially taken out during the execution of the adhesion processing, and the amount of the adhesion is analyzed. Can be determined directly. According to this, since the amount of adhesion can be directly determined, if the amount of adhesion is insufficient at the time of (1-5) of the operation method in the above-described operation method, the process returns to (1-3) and returns to (1-3). Processing can be performed. If the amount of adhesion exceeds a predetermined amount, or if there is a particular time constraint, (1-1-
5) By performing the following steps, it is possible to prevent the amount of adhesion from being exceeded.

From the above experiments, it was confirmed that when oxalic acid complex of Fe was added to water and oxalic acid was decomposed, Fe was deposited and adhered to the water-contact surface of the pipe. This gives Z
When a metal having an effect of suppressing the attachment of a radioactive substance such as n is added as an oxalic acid complex, it is conceivable that the metal adheres to the water contact surface in the same manner. Further, a metal having an effect of suppressing the adhesion of radioactive substances such as Zn is added to the oxalic acid complex of Fe and water in the form of metal ions or metal colloids,
It is conceivable that metal ions or metal colloids can be co-precipitated by precipitating Fe from the oxalic acid complex of (1).

Embodiments will be described below based on the above experiments. (Embodiment 1) In this embodiment, a process of using oxalic acid as a decontamination agent and decomposing the oxalic acid in a boiling water nuclear power plant (hereinafter, referred to as a BWR plant) which is one of LWR plants is described. This is an example in which, after a certain chemical decontamination operation, the adhesion treatment is performed on the piping of the BWR plant after the chemical decontamination using the adhesion treatment device 1. The adhesion processing device 1
As shown in FIG. 1, this is an apparatus in which a radioactive substance adhesion suppressing reagent injection device 50 including a tank 51 containing a radioactive substance adhesion suppressing reagent, a chemical solution injection pump 52 and a valve 53 is further connected to the adhesion processing device 210. This adhesion processing device 1
Is used to inject a metal ion and an oxalic acid complex of Fe having an effect of suppressing the adhesion of radioactive substances to reactor water of a nuclear power plant.

First, the device will be described. The attachment processing apparatus 1 is the same as the attachment processing apparatus 210 except for the radioactive substance attachment processing apparatus 50, and thus the description is omitted here.
As shown in FIG. 4, the adhesion processing apparatus 1 is connected to the recirculation pipe 108 and the recirculation pump 105 of the BWR plant, which is the target area where the adhesion processing is performed, via the connection parts X1 and X2. The pressure vessel 10 is controlled by the valve 114 and the valve 115.
1 and close the valves 110 and 11
1, 18, 19 are opened, the adhesion processing apparatus 1 and the recirculation pipe 1 are opened.
08 and the recirculation pump 105.

In this embodiment, the predetermined temperature of the system water is 9
0 ° C. In this example, as the pH adjuster,
Use KOH. In the present embodiment, Zn is used as a reagent for suppressing radioactive substance adhesion. As the radioactive substance adhesion suppressing reagent, in addition to Zn, metals or metal oxides having an effect of suppressing the adhesion of radioactive substances include Pt, R
There are h, Pd, Zr, Ti, Al and oxides thereof, and these can be used alone or as a mixture. Zn forms an oxide film in a form that is hardly dissolved by reacting with Fe or Cr of the base material, thereby suppressing the growth of the oxide film and has an effect of suppressing the adhesion of radioactive substances. Since Pt, Rh, and Pd have the effect of decomposing hydrogen and lowering the concentration of dissolved oxygen in an H ₂ injection environment, they suppress the growth of an oxide film and thereby have the effect of suppressing the attachment of radioactive substances. Zr, Ti, Al
Is to cover the base material surface with a compound such as ZrO ₂ , TiO ₂ , Al ₂ O ₃ to suppress diffusion of oxygen into the base material, thereby suppressing the growth of an oxide film, thereby adhering radioactive substances. Has the effect of suppressing

Next, an implementation method will be described. First,
Conduct chemical decontamination. Chemical decontamination equipment includes a pump that circulates the decontamination agent between the chemical decontamination device and the decontamination site, a heating / cooling device that heats and cools the decontamination agent to a predetermined temperature, and water purification that removes dissolved radioactive materials. It comprises a device (cation exchange resin tower and a mixed bed resin tower in which cation exchange resin and anion exchange resin are mixed), a device for injecting oxidative decontamination agent, and a device for injecting reduction decontamination agent. This is the same apparatus as the adhesion processing apparatus 1 except that a chemical solution to be injected is different from the adhesion processing apparatus. Therefore, in the embodiment, the adhesion treatment device 1 is used as a chemical decontamination device. That is, each part of the adhesion processing apparatus 1 is used as a chemical decontamination apparatus as described below. The pump 3 is a pump, the heating / cooling device 16 is a heating / cooling device, and the water purification device 15
Is installed in the water purification system,
0 is diverted to the device for injecting the oxidative decontamination agent, and the oxalate complex injection device 30 and the pH adjusting agent injection device 40 are used for the device for injecting the reduced decontamination agent. In addition, a chemical decontamination apparatus may be provided separately from the adhesion processing apparatus 1.

In chemical decontamination, potassium permanganate is used as an oxidative decontamination agent, and oxalic acid and hydrazine are used as reductive decontamination agents. Chemical decontamination is performed in the following procedure. (2-1) The system water is heated to a predetermined temperature by the heating / cooling device 16. (2-2) Potassium permanganate is injected into the system from the radioactive substance adhesion suppressing reagent injection device 50 so as to have a predetermined concentration, and is exposed to the decontamination site for a predetermined time. (2-3) By adding oxalic acid from the oxalic acid complex injection device 30, potassium permanganate is reduced to divalent manganese ions, and the oxidative decontamination agent is decomposed. (2-4) Hydrazine is injected into the system from the pH adjusting agent injection device 40 so as to have a predetermined concentration, and is exposed to the decontamination site for a predetermined time. During the exposure, system water is circulated through the water purification device 5 to remove dissolved radioactive materials. (2-5) The reduced decontamination agent is decomposed by the decontamination agent decomposer. During this period, the system water is circulated through a purification device (cation exchange resin tower) that takes in radioactive substances to remove dissolved radioactive substances. (2-6) After the decomposition of the reducing decontaminant is completed, the system water is circulated through the water purification device 5 to remove the remaining ions. (2-7) The operations from (2-2) to (2-6) are performed in 2 to 3
Repeat several times. (2-8) In (2-7), from (2-2) to (2-
(6) is repeated, (2-
(2-9) is performed from the middle of 5). In (2-5), there is a possibility that the pH is lowered due to carbonic acid generated by the decomposition of oxalic acid. Therefore, from (2-5) when oxalic acid becomes 100 ppm or less or the pH becomes 4.0 or more ( 2-9) is started.

This is for the following reason. When the adhesion treatment is performed, radioactive ions in the water also adhere, so that the concentration thereof needs to be sufficiently low. In the chemical decontamination method shown in the present embodiment, when the reducing agent is decomposed, the concentration of radioactive ions in the water decreases approximately in proportion to the concentration of the reducing agent. According to the waste receiving standard at the waste management facility, oxalic acid is a chelating agent, and there is a rule that when oxalic acid is removed by ion exchange resin, water must be passed at 10 ppm or less. Decomposition of 10pp
It is necessary to disassemble it to m or less. The time required for the decomposition is (time required) {ln} (initial concentration) / (final concentration), assuming that the amount of the solution to be decomposed per unit time is constant. For example, the initial concentration of oxalic acid is 2000 pp.
Assuming m, the time to decompose from 2000 ppm to 200 ppm is the same as the time to decompose from 200 ppm to 20 ppm.

From the above, it is desirable that the radioactivity concentration in the system water be 1/10 or less from the viewpoint of preventing reattachment of radioactive substances, and it is necessary to decompose all oxalic acid from the viewpoint of shortening the decomposition treatment. It is desirable to carry out the adhesion treatment in a period of か ら to の of the time. This is the time when the concentration of oxalic acid in the system water is between 100 and 200 ppm. When the concentration of oxalic acid is 100 to 200 ppm, the pH becomes about 4.

In (2-5), the system water has already been heated to a temperature (predetermined temperature) sufficient to perform the adhesion treatment. By overlapping the last step of chemical decontamination with the first step of adhesion treatment, the processing time can be reduced. Further, the injection amount of the oxalic acid complex of iron ions can be reduced. What is different from the case of decontamination is
In the step (2-5), system water is circulated through a purification device (cation exchange resin tower) for removing radioactive substances to remove dissolved radioactive substances. The point is not to do so. That is, when the predetermined time comes, the operation after (2-9) is performed. (2-9) In the oxalic acid complex injection device 30 for Fe,
Open the valve 33, start the chemical injection pump 32, and
The oxalic acid complex of e is added to the system, and after the addition is completed, the chemical solution injection pump 32 is stopped and the valve 33 is closed. Thereby, the oxalic acid concentration of the system water is adjusted. The oxalic acid concentration of the system water is measured by the water quality measuring device 15. Similarly, KOH as a pH adjuster is injected from the pH adjuster injection device 40 to adjust the pH of the system water. The pH of the system water is measured by the water quality measuring device 15. Similarly, Zn as a radioactive substance adhesion suppressing reagent is added to the system from the radioactive substance adhesion suppressing reagent injection device 50. (2-10) When the various reagents are uniformly mixed in the system, the valves 9a and 9b are opened, the flow rate is adjusted by the flow rate adjusting valve 8, and the system water is passed through the organic compound decomposer 10. The determination as to whether or not they are uniformly mixed is made based on the change in the conductivity measured by the water quality measuring device 15. Further, the valve 23 of the H ₂ O ₂ injection device 20 is opened, the H ₂ O ₂ injection pump 22 is started, and H ₂ O ₂ is added to decompose oxalic acid. (2-11) When the decomposition of oxalic acid is completed, the H ₂ O ₂ injection pump 22 is stopped, and the valve 23 is closed. The progress of oxalic acid decomposition is monitored by sampling and analyzing the system water from the feed / wastewater valve 7. Further, the system water is sampled and analyzed to determine the presence or absence of Fe precipitation. (2-12) Cool the system water to normal temperature (about 30 ° C.) with the heating / cooling device 16. (2-13) After the cooling is completed, the valves 4a and 4b are opened, the valve 6 is closed, and the system water is passed through the water purification device 5,
Purify system water to an impurity concentration level that allows wastewater. In this experiment, the oxalic acid concentration was purified to below the detection limit. (2-14) After the purification is completed, the system water is drained from the supply / drain valve 7.

FIG. 4 shows a recirculation pipe 108 of a boiling water reactor.
And the recirculation pump 105 as the target site,
The above-mentioned operation can be carried out by forming a circulation loop in the same manner for other piping and reactor internals.

When the chemical decontamination described in Example 1 is performed, the oxide film on the surface of the base material is dissolved and removed. After that, when a metal or metal oxide that exerts a corrosion inhibiting effect is applied under the conditions found in the experiment, a corrosion inhibiting effect is exerted on the base metal surface as shown in the upper left diagram of FIG. Metals and metal oxides can be attached.

The details of the phenomenon shown in FIG. 5 will be described below.
First, it is considered that ions or colloids of metals and metal oxides which exert a corrosion inhibiting effect are accompanied by precipitation of iron oxides, and ions co-precipitate as metals, oxides or hydroxides. Zn, which is a metal having a corrosion inhibiting effect,
Al, Zr, Ti, Pt, Rh, and Pd are Zn ²⁺ ion, Al ³⁺ ion, ZrO ²⁺ ion, TiO ²⁺ ion, respectively.
Pt (OH) ₆ ²⁺ ions, Rh (NO _{2) 6} ³⁺ ions, Pd ²⁺
When added as ions, ZnO or Zn (OH) ₂ , Al (OH) ₃ or Al
OOH, ZrO (OH) ₂ or ZrO ₂ , TiO (OH) ₂
Or TiO ₂ , Pt or PtO ₂ , Rh or Rh ₂
It is believed that they co-precipitate as O ₃ , Pd or PdO.

After the adhesion treatment, it is considered that the metal and the metal oxide exerting the corrosion inhibitory effect when exposed to high-temperature and high-pressure water upon starting the plant are dissolved and reprecipitated.
Metals and metal oxides having a corrosion inhibiting effect are considered to exert a corrosion inhibiting effect on the base material in the following three types. (1) A dense oxide film is formed only with the metal or metal oxide to exert a corrosion inhibiting effect. (2) During the growth of the oxide film on the base material, a fine oxide film is formed by a chemical reaction with Fe or Cr to exert a corrosion inhibiting effect. (3) During the growth of the oxide film on the base material, it undergoes an oxidation-reduction reaction with Fe or Cr and adheres as a metal, acts as a catalyst for oxidizing hydrogen under a hydrogen injection environment, and exerts a corrosion inhibiting effect by lowering the corrosion potential. . Al, Z as the case of (1)
r and Ti (upper right in FIG. 5). It is considered that these metal oxides deposited by the deposition process are dissolved and redeposited to form oxide films of Al ₂ O ₃ , ZrO ₂ , and TiO _{2 on} the surface of the base material, respectively. It is considered that the diffusion of oxygen into the base material is suppressed by covering the surface with these oxides, and the corrosion of the base material is suppressed. The case (2) includes Zn (lower left of FIG. 5). Zn deposited by the deposition process dissolves as Zn ions, and chemically reacts with Fe ions and Cr ions generated by corrosion of the base material to form ZnF.
It is considered that oxides such as e ₂ O ₄ and ZnCr ₂ O ₄ are generated and deposited. It is considered that diffusion of oxygen to the base material is suppressed by covering the surface with these compounds, and corrosion of the base material is suppressed. Pt, R as case (3)
h and Pd (lower right of FIG. 5). Pt, Rh, and Pd deposited by the deposition process are Pt ions, Rh ions,
Fe dissolved as Pd ions and produced by corrosion of the base material
Pt, R
It is considered that they are reprecipitated as h and Pd metals. It is known that these metals greatly reduce the corrosion potential in a hydrogen implantation environment, particularly in an environment where the molar ratio of H ₂ / O ₂ is 2 or more. It is considered that the base material surface is less likely to corrode as the corrosion potential decreases.

Since the radioactive metal ions in the reactor water adhere with the progress of the base material, it is considered that when the corrosion of the base material is suppressed as described above, the amount of the radioactive substance attached is suppressed.

After the adhesion treatment, the LWR plant is restarted,
When exposed to high-temperature and high-pressure water, a metal or metal oxide (in this embodiment, Zn or
Dissolves and re-deposits, ferrite-forms, redox-reacts, etc., covers the surfaces of the reactor internal structures and pipes that have been subjected to adhesion treatment, suppresses the growth of oxide films, and emits radiation. Suppress the capacity accumulation. (Embodiment 2) The present embodiment is an example in which an oxalic acid complex of Fe is added while being decomposed to perform an adhesion treatment. FIG. 6 shows an adhesion processing apparatus 80 used in this embodiment. The adhesion treatment device 80 includes the adhesion treatment device 1, the oxalic acid complex injection device 30 for Fe, the valve 9a and the organic compound decomposition device 10
It has a different configuration in that it is connected to the piping between Other parts are the same as those of the adhesion processing apparatus 80. The configuration of the apparatus in the present embodiment is similar to that of the adhesion processing apparatus 1 shown in FIG. 4 except that the adhesion processing apparatus 80 is connected to the recirculation pipe 108 of the boiling water reactor and the recirculation pump 105 as connection points. Connect to the target site via X1 and X2. The configuration of each part of the boiling water reactor is the same as that of the second embodiment. After performing chemical decontamination in the same manner as in Example 2, the adhesion treatment device 80 is operated in the following procedure. (3-1) Water is supplied to the system from the supply / wastewater valve 7. (3-2) Valves 4a, 4b, 9a, 9b, 33, 4
The system water is circulated by the circulation pump 3 by closing the valves 3, 53 and 23, the valves 6 and 8 are opened, and the system water is heated to a predetermined temperature by the heating / cooling device 16. (3-3) When the temperature of the system water reaches 90 ° C., the valve 9
a, 9b are opened, and the flow rate is adjusted by the flow rate adjusting valve 8, so that the system water is passed through the organic compound decomposing device 10. (3-4) In the Fe oxalate complex injection device 30,
Open the valve 33, start the chemical injection pump 32, and
The oxalic acid complex of e is added to the system, and a predetermined amount of the oxalic acid complex of Fe is added to the system. Further, the valve 23 of the H ₂ O ₂ injection device 20 is opened, the H ₂ O ₂ injection pump 22 is started, and H ₂ O ₂ is added to decompose oxalic acid. Similarly, Zn as a radioactive substance adhesion suppressing reagent is added to the system from the radioactive substance adhesion suppressing reagent injection device 50. (3-5) The quality of the system water is analyzed by sampling the system water from the water quality measuring device 15 and the supply / drainage valve 7. Thus, the state of attachment of oxalic acid is determined. In addition, KOH as a pH adjuster is injected from the pH adjuster injection device 40 to adjust the pH of the system water within a range where the pH does not become 5.5 or more. (3-6) When the addition of each reagent is completed, the injection pump for each reagent is stopped, and each valve is closed. (3-7) The system water is cooled to a normal temperature (about 30 ° C.) by the heating / cooling device 16. (3-8) After cooling is completed, the valves 4a and 4b are opened, the valve 6 is closed, and the system water is passed through the water purification device 5 to purify the system water to an impurity concentration level at which wastewater can be generated.
Purify the oxalic acid concentration below the detection limit. (3-9) After the purification is completed, the system water is drained from the supply and waste water valve 7.

Example 1 is an example in which each reagent is added to a system in advance, mixed uniformly, and then decomposed to perform an adhesion treatment. In contrast, this example sequentially provides a corrosion reducing effect. This is an example in which the oxalic acid complex of Fe, which is added for coprecipitating a metal ion or a colloid containing a metal having a corrosion reducing effect, is added while being decomposed, thereby performing an adhesion treatment. In particular, according to the present embodiment, each reagent has an effect of suppressing the adhesion of radioactive substances or having an effect of reducing corrosion, according to the present embodiment, when each of the reagents reaches a predetermined amount. Can be stopped, so that the amount of reagent to be added can be reduced as compared with the case of Example 1. (Embodiment 3) This embodiment is an embodiment in which a reagent for suppressing radioactive substance adhesion is added to reactor water during the operation period of a nuclear power plant after decontamination. As shown in FIG. 7, the apparatus configuration is such that a radioactive substance adhesion suppression reagent injection device 50 is connected to a water supply pipe of a boiling water reactor, and a sampling valve 113 for sampling reactor water is provided to a recirculation pipe 108. Connected. The radioactive substance adhesion suppressing reagent injection device 50 may be connected to the recirculation pipe 108. Further, the sampling valve 113 may be connected upstream of a purification device (not shown) of the reactor water purification system pipe. The apparatus 50 for injecting a radioactive substance adherence suppressing reagent so that the concentration of Zn ion or colloid sampled from the sampling valve becomes a predetermined concentration.
To adjust the injection amount of Zn ions or Zn colloid. FIG. 8 shows the results of an experiment in which the effect of suppressing the adhesion of radioactive substances by Zn ions under these conditions was measured. This is a water quality simulating reactor water (dissolved oxygen (DO) 200 ppb, temperature 288
C), a Co-58 ion is added to the high-temperature and high-pressure water circulation loop adjusted to have a constant concentration, and Zn ion is further added to the solution.
As two types of conditions, with and without ppb addition, the amounts of Co-58 adhered when stainless steel was immersed therein for 1000 hours were compared. The adhesion amount is Z
Approximately 1 when adding only 2 ppb of n ions and not adding
It can be seen that it decreases to / 2. Therefore, by adjusting the amount of Zn added so that the Zn concentration of the reactor water becomes 2 ppb, the deposition of radioactivity can be suppressed.

According to each of the embodiments described above, a metal or metal oxide having the effect of suppressing the adhesion of radioactive substances or the effect of reducing corrosion to the surface of a reactor internal structure or the surface of a pipe subjected to decontamination. Can be suppressed, rapid re-attachment of radioactive material can be suppressed, and radiation of workers can be suppressed during maintenance and inspection work.

According to the embodiment in which oxalic acid is used as a decontaminating agent and the adhesion treatment is performed in the chemical decontamination with the step of decomposing the oxalic acid, the chemical decontamination and the adhesion treatment can be performed by the same apparatus. Furthermore, it can overlap with the step of chemical decontamination. Therefore, the time required for the adhesion process can be reduced as compared with the case where the overlap is not performed.

The metal or metal oxide P, which has the effect of suppressing the adhesion of radioactive substances or the effect of reducing corrosion,
Since noble metals such as t, Rh, and Pd have the effect of lowering the corrosion potential, they can be expected to exhibit the effect of suppressing stress corrosion cracking (SCC).

By adding metal ions or metal colloids to the reactor water, which have the effect of suppressing the adhesion of radioactive substances or the effect of reducing corrosion during operation after decontamination, rapid re-adhesion of radioactive substances Can be suppressed. Further, during maintenance and inspection work, radiation exposure of workers can be suppressed.

Since the amount of Zn ion or Zn colloid added is small, the cost of the reagent can be reduced and the load on the ion exchange resin of the reactor water purification system can be reduced.

[0051]

According to the present invention, it is possible to provide a water quality control method for suppressing the adhesion of radioactive substances to the reactor internals and the piping surface after decontamination.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating an adhesion processing apparatus used in a first embodiment.

FIG. 2 shows the Fe concentration regarding the presence or absence of Fe precipitation when oxalic acid in an oxalic acid complex solution of Fe is catalytically decomposed, and
The figure showing the relationship of pH.

FIG. 3 shows the Fe concentration regarding the presence or absence of Fe precipitation when oxalic acid in an oxalic acid complex solution of Fe is catalytically decomposed, and
The figure showing the relationship of oxalic acid concentration.

FIG. 4 is a diagram showing a first embodiment.

FIG. 5 is a view showing the behavior of an attached matter after applying an attaching treatment.

FIG. 6 is a diagram showing a second embodiment.

FIG. 7 is a diagram showing a third embodiment.

FIG. 8 is a graph showing the Zn injection effect of Co-58 adhesion to stainless steel in high-temperature, high-pressure water.

FIG. 9 is a diagram illustrating an adhesion processing apparatus used in an experiment.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Adhesion processing apparatus, 2 ... Teflon (registered trademark) tube, 3 ...
Circulation pump, 4a ... piping valve, 4b, 6, 9a, 9
b, 18, 19, 23, 33, 43, 53, 106, 1
07, 110, 111, 112, 114, 115 ... valve, 5, 15 ... water purification device, 7 ... supply and waste water valve, 8 ...
Flow control valve, 10: Organic compound decomposer, 11: Vent, 12, 13, 14: Piping, 16: Heating / cooling device, 1
7 ... surge tank, 20 ... H ₂ O ₂ injection apparatus, 21 ... H ₂
O ₂ tank, 22 ... H ₂ O ₂ injection pump, 30 ... oxalate complexes implanter of Fe, 31 ... oxalate complex solution tank containing, 32, 42, 52 ... liquid injection pump, 40 ... p
H adjusting agent injection device, 41: tank containing a pH adjusting agent,
50: radioactive substance adhesion treatment device, 51: tank containing a radioactive substance adhesion suppressing reagent, 101: pressure vessel, 102:
Main steam piping, 103: water supply piping, 104: nuclear fuel,
105 ... recirculation pump, 108 ... recirculation piping, 109 ...
Jet pump, 113 ... sampling valve.

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Hideyuki Hosokawa 7-2-1, Omika-cho, Hitachi City, Ibaraki Prefecture Inside Power and Electricity Research Laboratory, Hitachi, Ltd. (72) Inventor Naoto Uetake Omika-cho, Hitachi City, Ibaraki Prefecture 7-2-1, Hitachi, Ltd. Power and Electricity Research Laboratory (72) Inventor Kazumi Anazawa 3-1-1, Sakaimachi, Hitachi, Ibaraki Pref. Hitachi, Ltd. Nuclear Power Division

Claims (14)

[Claims] 1. After the removal of radioactive substances adhered to at least one of the surface of reactor internals in contact with reactor water and the surface of pipes in contact with reactor water while nuclear heating is stopped. At least one of the effect of suppressing the adhesion of radioactive substances to the reactor internal structure and the effect of reducing the corrosion of the reactor structure is added to the reactor water of the nuclear power plant before performing the rated output operation after the removal. A water quality control method comprising decomposing the organic compound complex after adding at least one of an organic compound complex of a metal having the above effect and an organic compound complex of an oxide of the metal. 2. After the removal of radioactive substances adhered to at least one of the surface of reactor internals in contact with reactor water and the surface of pipes in contact with reactor water while nuclear heating is stopped. After the removal, at least one of the effect of suppressing the adhesion of radioactive materials to the reactor structure and the effect of reducing the corrosion of the reactor structure in the reactor water of the nuclear power plant before the rated output operation is performed A method for controlling water quality, comprising injecting at least one of a metal ion or a colloid having an organic compound of iron and an organic compound of iron to decompose the organic compound complex of iron. 3. The method according to claim 2, wherein iron is precipitated as iron hydroxide or iron oxide by decomposing said organic complex, and coprecipitated with ions or colloids of said metal.
A method for controlling water quality, comprising attaching the metal or an oxide of the metal to the nuclear reactor structure. 4. The method for controlling water quality according to claim 2, wherein the organic compound complex of iron is an oxalic acid complex. 5. The method according to claim 4, wherein the concentration of the oxalic acid complex in the reactor water is not less than 0.5 ppm and not more than 100 ppm as iron concentration.
Water quality control method characterized by being below ppm. 6. The method according to claim 2, wherein Na ₂
A water quality control method, wherein at least one of CO ₃ , KOH and NaOH is added to the reactor water in a range where the pH of the reactor water is 5.5 or less. 7. A method for controlling water quality according to claim 1, wherein the organic compound complex added to the reactor water is decomposed by irradiating ultraviolet rays or passing water through a heterogeneous catalyst. 8. The water quality control method according to claim 1, wherein hydrogen peroxide is added to the reactor water to decompose an organic compound. 9. The method according to claim 1, wherein the method for removing a radioactive substance includes a step of decomposing the oxalic acid by using oxalic acid as a decontaminant, and A method for controlling water quality, comprising a step of performing at least partially overlapping a step of decomposing a compound complex. 10. The reactor according to claim 9, wherein the step of performing the overlapping is performed when the oxalic acid concentration of the reactor water is 100 ppm.
A method for controlling water quality, wherein the method is performed at the time when the pH of the solution satisfies at least one of the conditions of 4 or more. 11. The method according to claim 1, wherein the metal having at least one of the effect of suppressing the adhesion of radioactive materials to the reactor structure and the effect of reducing corrosion of the reactor structure is Pt, A method for controlling water quality, comprising at least one metal selected from the group consisting of Rh, Pd, Zr, Ti, Al and Zn. 12. After the removal of radioactive material attached to at least one of the surface of the reactor internal structure that is in contact with reactor water and the surface of the pipe that is in contact with reactor water while nuclear heating is stopped. It has at least one of the effect of suppressing the adhesion of radioactive materials to the reactor structure and the effect of reducing the corrosion of the reactor structure in the reactor water of the nuclear power plant that is performing the operation following the removal. A method for controlling water quality, comprising adding at least one of a metal ion and a colloid. 13. The method according to claim 12, wherein said metal is P
A water quality control method comprising at least one metal selected from the group consisting of t, Rh, Pd, Zr, Ti, Al and Zn. 14. The water quality control method according to claim 12, wherein the Zn concentration in the reactor water is 0.1 ppb or more and 2 ppb or less.