JPH09133784A - Repair method for reactor primary piping - Google Patents

Abstract

PROBLEM TO BE SOLVED: To restrain radioactive nuclide to be again deposited on the piping where the radioactive nuclide of a nuclear power plant under operation is already deposited. SOLUTION: The primary piping of a nuclear power plant is cut at the area where a coolant containing radioactive nuclide is made to flow and a dose is already high at a step S2, and a device to collect radioactive waste liquid generated with a decontamination device and at a decontamination process is connected thereto at a step S3. Then, the inner surface of the piping is decontaminated at steps S4 and S5. Subsequently, a heating device is installed on the piping at steps S6 for the heating thereof in a gaseous phase containing 0.1% or more of oxygen, thereby forming a dense oxidized film having thickness between 1nm and 100nm at a step S7. After the heating device and the radioactive waste liquid collection device are demounted at steps S8 and S9, the piping is restored to an original state at a step S10. According to this construction, a coolant containing radioactive nuclicle can be prevented from being deposited directly on the metal surface of the piping, and the deposition thereof after reuse on the metal surface can be restrained.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a primary system piping for a boiling water nuclear power plant (hereinafter abbreviated as “BWR”) and a pressurized water nuclear power plant (hereinafter abbreviated as “PWR”). Regarding repair methods.

[0002]

BWR removes heat generated in a core, so that cooling water in a reactor pressure vessel (hereinafter referred to as "reactor water") is forcedly circulated by a recirculation pump and generated in a reactor. The steam is sent to a turbine after removing moisture with a separator and a dryer provided in the upper part of the core. Some of this steam is extracted as turbine bleed air and used as the heat source for the high and low pressure heaters, while most of the other steam is condensed in the condenser back to water. Condensate is almost completely degassed in the condenser, while oxygen and hydrogen generated by radiolysis of water in the core are almost completely removed.

Condensate is generally heated up to about 200 ° C. by multi-stage low-pressure and high-pressure heaters and supplied to the reactor again. However, in order to suppress the generation of radioactive corrosion products in the reactor, the condensate is mainly metal. For the purpose of removing impurities and maintaining high purity, an ion exchange resin filtration device for debasing or the like is provided between the condenser and the low-pressure heater, and the entire amount of condensate is treated with this debasing. At that time, in order to reduce the amount of metal impurities generated by corrosion of the primary structural material, stainless steel, stellite steel or other stainless steel is generally used as the main structural material. Further, in a carbon steel reactor pressure vessel, stainless steel is used to build up the inner surface of the pressure vessel to prevent the carbon steel from directly contacting the reactor water.
In addition to the consideration of the material, a part of the reactor water is purified by the reactor water purifying device to positively remove a very small amount of metallic impurities generated in the reactor water.

[0004]

However, in spite of such material and water quality control measures, the presence of a very small amount of metallic impurities in the reactor water is unavoidable, and some of them are fuel cladding tubes. It adheres to the surface as an oxide. The adhered metal element undergoes a nuclear reaction upon receiving neutron irradiation from the fuel. As a result, cobalt 60 on the surface of the fuel cladding tube,
It produces radionuclides such as cobalt 58, chromium 51, and manganese 54. Most of these radionuclides remain attached to the fuel cladding tube in the form of oxides, but some of them are again eluted as ions in the reactor water or re-emitted into the reactor water as insoluble solids called clad. It Some of these radioactive substances are removed by the reactor water purification system, but those that cannot be removed are accumulated on the surface of the water contact part of the structural material such as pipes while circulating through the recirculation system. For this reason, the surface dose of the structural material increases, and the radiation exposure of the inspection workers during the periodic inspection work becomes a problem. Therefore, various methods for preventing the radionuclide from adhering to the pipe have been studied.

As one of such methods, there is a technique of forming a so-called preliminary oxide film on the inner surface of the pipe in high temperature water before the full-scale operation, as disclosed in JP-A-62-24195 and JP-A-63-103999. It is described in Japanese Patent Publication No. However, these methods are intended for a new plant, and the radionuclide is already present in the reactor water in the existing plant, so the radionuclide will be incorporated into the preliminary oxide film. It should be noted that, in addition to this, a method of forming a preliminary oxide film by using high temperature steam is disclosed in JP-A-60-
The technique described in Japanese Patent No. 53897 is also known.

[0006] On the other hand, decontamination by chemical agents and polishing is performed for pipes and the like whose radionuclides have adhered and whose dose has increased. However, in this method, since the new surface of the metal with a fast oxide film contact with the reactor water containing the radionuclide, the deposition rate of the radionuclide becomes faster than that in the non-decontaminated area, and the decontamination effect Has the drawback that it will quickly become smaller.

The present invention has been made in view of the above problems of the prior art, and an object thereof is to prevent reattachment of a radionuclide to a pipe to which the radionuclide of an operating nuclear power plant is attached. To provide a method for repairing primary reactor primary piping. Another object of the present invention is to provide a method for repairing a primary reactor piping which can keep the dose low even after replacing the piping to which the radionuclide is attached in the operating nuclear power plant.

[0008]

In order to achieve the above object, the present invention provides a pipe after decontamination of a pipe to which a radionuclide is attached in an operating nuclear power plant or a pipe in an operating nuclear power plant. When replacing the pipe to which the radionuclide is attached, heat the pipe to be replaced in the gas phase containing oxygen before or after connecting it to each system of the nuclear power plant to form an oxide film on the inner surface of the pipe. did.

More specifically, the first means is a method of repairing a primary system piping of a nuclear reactor for repairing a primary system piping of a nuclear reactor, wherein an inner surface of the primary system piping to which radionuclides of a nuclear power plant in operation are attached. Is decontaminated, and then an oxide film is formed on the inner surface of the pipe in a gas phase containing oxygen.

The second means is to remove the pipe at a preset position of the primary system to which the radionuclide of the operating nuclear power plant is attached, decontaminate the inner surface of the removed pipe, and then contain oxygen. It is characterized in that the pipe having an oxide film formed on the inner surface thereof is connected in a gas phase.

A third means is to remove the pipe at a preset position of the primary system to which the radionuclide of the operating nuclear power plant is attached, connect a new pipe in place of the removed pipe, and then add oxygen. An oxide film is formed on the inner surface of the pipe in a gas phase containing

A fourth means is to remove the pipe at a preset position of the primary system to which the radionuclide of the operating nuclear power plant is attached, and form an oxide film on the inner surface of the pipe in a gas phase containing oxygen. It is characterized in that the new pipe is connected instead of the removed pipe.

In these cases, the thickness of the oxide film formed in the vapor phase is preferably 1 nm or more and 100 nm or less. Further, the oxygen concentration in the gas phase containing oxygen is required to be 0.1% or more.

When forming the oxide film, the pipe is covered with a heat insulating material having a heating means for heating the pipe, and the pipe is heated in the gas phase by the heating means before water is passed through the pipe. As a result, an oxide film can be formed on the inner surface of the pipe. It is also possible to cause a heated gas to flow inside the pipe to heat the inner surface of the pipe to form an oxide film. It is also possible to install a movable heating device inside the pipe and move the inside while heating the inner surface of the pipe to form an oxide film. In this case, a high frequency induction heating device can be used as the heating device. Further, before forming an oxide film on the inner surface of the pipe, the surface of the inner surface of the pipe is polished to have a surface roughness of 10
It may be less than or equal to μm. This can reduce the attachment surface area of the radionuclide. Further, the inner surface of the pipe is heated by the frictional heat due to the polishing, and the oxide film is formed. In addition, in the second or third means, a device for circulating heated gas is previously attached to both ends of the new pipe, and the heated gas is circulated after the pipe is attached to clean the inner surface of the pipe. Heat
You may make it form an oxide film.

As the primary system piping of the reactor,
At least one piping of a reactor coolant recirculation system, a reactor coolant purification system, and a residual heat removal system is applied.

Before specifically describing the embodiments, the mechanism of radionuclide attachment to the reactor piping will be described. FIG. 8 is an explanatory view schematically showing the mechanism of radionuclide attachment to the reactor piping.

Of the radioactive nuclides in the reactor water, the ones that are problematic for periodic inspections are cobalt 60, cobalt 58, chromium 51, manganese 54, etc. Among them, the most problematic is the radioactive isotope of cobalt, which has a relatively half-life. Long cobalt 60. Most of these radionuclides of cobalt exist as divalent cobalt ions in reactor water. On the other hand, under the reactor water condition, wet corrosion that occurs with the interposition of water in stainless steel and the like and dry corrosion that occurs due to diffusion of oxygen, electrons, and ions in the material in a high temperature atmosphere occur at the same time. Of these, it is the wet eating process that mainly takes in radionuclides. In the wet corrosion process, iron is eluted from a base material such as stainless steel through an oxide film formed by dry etching to become iron divalent ions. This divalent iron ion is oxidized by dissolved oxygen in water to become a trivalent iron ion, but since the trivalent iron ion has a very low solubility, it precipitates again as an oxide solid. At this time, if divalent metal ions are present in the vicinity, a part thereof is precipitated as ferrite which is a spinel type oxide containing divalent metal ions, and if no divalent metal is present, it is a corundum type oxide. Precipitates as hematite. The ferrite is mainly in the form of nickel ferrite formed with nickel ions, which are the divalent metals that are most abundant in reactor water, but cobalt ions are also contained in this, and as a result, radionuclide piping Causes sticking. In particular, the pipe after decontamination which is the subject of the present invention, or the new pipe has a high corrosion rate because the inner surface is a new surface of the metal, and since radionuclides are present in the reactor water of the existing plant, the adhesion of radionuclides It is easy to happen.

Then, the inventors proceeded with the study and found that the thickness of the inner surface of the pipe after decontamination of the existing plant or the new pipe to be replaced has a thickness of 1 nm in the gas phase containing oxygen before contacting with the reactor water. It has been found that formation of a 100 nm oxide film can suppress the attachment of radionuclides.

FIG. 9 shows the experimental results of the inventors. The experiment was carried out by buffing a SUS316 plate-shaped test piece and then heating it in an oxygen-containing gas phase at 500 ° C., 700 ° C., and 900 ° C. for 8 hours to form an oxide film, and to form an oxide film at 280 ° C. containing cobalt ions. Was immersed in high temperature water, and the amount of cobalt adhering to the test piece was examined. From this result, 500 ° C and 7
It can be seen that the adhesion of cobalt is suppressed by the oxide film formed by the heat treatment at 00 ° C.

The surface of the test piece was observed at 500 ° C. and 70
The surface of the test piece subjected to the heat treatment at 0 ° C. was maintained in a mirror state when the interference film was formed. On the other hand, 900
As for the surface condition of the test piece heated at ℃, the mirror-like condition was destroyed and fine irregularities were visible. Furthermore, when the surface after adhesion was observed with a scanning electron microscope, it was found that the number of adhered substances on the test piece subjected to the 900 ° C. heat treatment increased by about 8 times as compared with that at the 700 ° C. heat treatment. Also,
When the thickness of the oxide film was measured by the secondary ion mass spectrometer, the oxide films of 40 nm, 100 nm and 900 nm were formed at the processing temperatures of 500 ° C., 700 ° C. and 900 ° C., respectively.

In most cases, when the metal becomes an oxide, the volume expands, so that a compressive stress is generated in the oxide film. But 900
In the heat treatment at ℃, since the growth of the oxide film is fast, the oxide film is destroyed by the compressive stress, the denseness of the oxide film is lost, and the mirror state is also destroyed. Then, it is considered that the specific surface area was increased due to the gap formed by the destruction, and the amount of cobalt deposited was increased. On the other hand, the oxide film formed on the test piece at 500 ° C and 700 ° C, which kept the mirror surface state, has not been destroyed yet, and the dense oxide film causes the adhesion of cobalt from the base material of the iron ion to the water side. It is considered that the amount of cobalt ions deposited was small because it hindered the migration.

The reason why the oxygen concentration in the gas phase is set to 0.1% or more is as follows. That is, oxygen must be adsorbed on the metal surface in order to form an oxide film, and the frequency depends on the volume molar concentration of oxygen. This is true not only in the gas phase but also in the liquid phase. On the other hand, the inventors conducted an experiment to change the dissolved oxygen concentration to form an oxide film in high temperature water, and found that the densest oxide film could be formed at 400 ppb. This is expressed as a volume molar concentration of about 13 μmol / l. On the other hand, in the case of gas at 500 ° C., for example, the volume of 1 mol is about 63.5 [l], so the number of moles per 1 [l] is 16 mmol / l. Therefore, dissolved oxygen 4 on the metal surface
The oxygen concentration of (13 μmol / l) / (16 mmol / l) ≈0.1 [%] is necessary for oxygen to be adsorbed at the same frequency as the high temperature water of 00 ppb. Therefore, the lower limit of the oxygen concentration is set to 0.
It was set to 1%.

As described above, the heating device is attached to the inside of the heat insulating material of the pipe to heat the pipe, whereby an oxide film can be formed at an arbitrary position of the pipe. as a result,
It is possible to effectively and selectively form an oxide film at the most effective place to reduce the exposure and to suppress the attachment of radionuclides. Further, once the heater is attached to the inside of the heat insulating material, thereafter, it is possible to form an oxide film in the gas phase every time decontamination is performed to reduce the adhesion of radionuclides.

If a device for circulating a high temperature gas is attached to both ends of the pipe to be connected in advance, the high temperature gas containing oxygen is circulated in the attached pipe to heat the pipe after connecting the pipe to the system. Thus, a uniform oxide film can be formed on the metal surface. Moreover, once the device for circulating this high-temperature gas is installed, it is also possible to circulate the liquid decontamination material using this device. After reducing the dose by decontamination, the metal after decontamination can be used. A high temperature gas can be circulated on the surface to form an oxide film that suppresses the attachment of radionuclides.

If a heating device is installed inside the pipe and is moved to heat the inner surface of the pipe, only the surface layer can be heated in a short time. In that case, an oxide film can be selectively formed particularly in a place where adhesion is desired to be suppressed, which is very efficient. In particular, when high frequency induction heating is used as the heating method, it is possible to easily heat to a desired depth by changing the frequency of the high frequency, and to efficiently heat the surface layer to form an oxide film.

Further, according to the experiments conducted by the inventors, it has been found that when the oxide film is formed after the surface roughness is set to 10 μm or less, the adhesion of cobalt ions is suppressed more effectively. FIG. 10 shows the result. In this figure, after the surface of stainless steel was washed with an acid, an oxide film was formed in the vapor phase on a test piece whose surface roughness was changed by surface polishing, and then the amount of adhesion was examined by a cobalt immersion test. As shown in the figure, by setting the surface roughness to 10 μm or less, the adhesion amount is 50% or less as compared with the case of untreated.

When dry polishing is performed when polishing the inner surface of the pipe, the polishing portion is heated by utilizing the heat generated during polishing,
An oxide film can be formed in the gas phase. If this method is applied to pipes whose dose has risen in an existing plant, it will decontaminate radionuclides that have already adhered, and at the same time,
It is possible to form an oxide film that can suppress reattachment of radionuclides.

Further, in the BWR, radionuclides accumulate on the metal surface with which the reactor water contacts, but the main sources of radiation to workers during periodic inspections are the reactor coolant recirculation system and the reactor coolant purification. System and residual heat removal system piping equipment. By applying the present invention to the piping equipment of these parts, it is possible to continuously reduce the radiation exposure of the worker at the time of periodic inspection.

[0029]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a flow chart showing the outline of the procedure of the repair process of the reactor coolant piping according to the present invention. In this repair procedure, first, in step S1, the dose rate of the pipe and the amount of the radionuclide attached are measured, and the predetermined pipe, that is, the portion of the pipe to be decontaminated is cut (step S2). Then, a decontamination device, for example, a device for rotating the abrasive material 22 such as the grinder 21 shown in FIG. 2 is installed in the reactor coolant recirculation pipe 23 in the cut pipe (step S
3), the radionuclide-containing layer 24 attached to the inner surface of the pipe is removed by moving the inner surface of the pipe 23 while polishing (step S5). At this time, a drain line is connected to the opening of the pipe 23 cut in step S2 (step S4), water is caused to flow out from the grinder 21, and polishing debris generated by polishing is washed off to the drain line. In addition, the surface roughness of the polishing surface can be set to 10 μm or less by changing the type of the polishing material [first decontamination method].

Alternatively, as shown in the explanatory view of FIG. 3, the reactor coolant recirculation pipe 32 from which the reactor coolant recirculation pump 31 has been removed during the periodic inspection is cut off from the reactor pressure vessel 33, and this reactor coolant An abrasive circulating device 34 is attached to the recirculation pipe 32 to circulate abrasive particles at high speed inside. Thereby, the layer containing the radionuclide attached to the inner surface of the pipe can be scraped off. Further, instead of the abrasive particles, a chemical solution may be circulated to dissolve and remove the layer containing the radionuclide [second decontamination method].

When the decontamination is completed in this way, in step S7, heating is performed to form an oxide film on the inner surface of the pipe. This heating connects the reactor coolant recirculation pipe 32 to the reactor coolant recirculation pump 31 and the reactor pressure vessel 33 to restore the reactor coolant recirculation system, as shown in FIG.
Thereafter, a pipe heat insulating material 41 having a built-in pipe heater 42 is attached to the outer periphery of the reactor coolant recirculation pipe 32 as shown in the figure (step S6), and in the vapor phase before passing water to the pipe 32. After heating and holding the inner surface of the pipe at 500 ° C. for 1 minute or more, the pipe is gradually cooled [first oxide film forming method].
As a result, an oxide film effective for suppressing the attachment of radionuclides can be formed on the inner surface of the pipe 32.

As a second oxide film forming method, as shown in FIG. 5, heating is performed so that the inside of the reactor coolant recirculation pipe 23 from which the layer having the radionuclide attached is removed can be moved. The container 51 is installed (step S6). Then, the atmosphere is used as a gas phase containing 0.1% or more of oxygen. That is, the inner surface of the pipe is moved while being heated to 500 ° C. by the heater 51 in the atmosphere. As a result, an oxide film 52 capable of suppressing the attachment of radionuclides when contacted with reactor water can be formed on the inner surface of the pipe 23 (step S7).

As a third oxide film forming method, the same oxidation can be performed by heating the inner surface of the pipe 23 by blowing a gas of 500 ° C. containing 0.1% or more of oxygen in place of the heater 51. A film can be formed (step S7). Further, as the fourth oxide film forming method, when the heater 51 is a device capable of performing high frequency induction heating, in other words, a high frequency induction heater, the pipe 23 can be heated to an arbitrary depth. This makes it possible to form an oxide film by heating only the surface without heating an unnecessary portion (step S7).

As a second method, the heater 51 shown in FIG. 5 is used.
It is not always easy to form a uniform oxide film on the inner surface of the pipe by the method of moving. However, in the present invention, it is sufficient that the material is heated in the gas phase to form an oxide film having a thickness of 1 nm or more, which suppresses the adhesion of radionuclides to the portion where the oxide film exists. It does not necessarily have to be formed uniformly on the inner surface of the pipe. Further extremely, depending on the piping portion, the portion where the oxide film is formed and the portion where the oxide film is not formed may be mixed. Therefore, an oxide film is formed on the reactor coolant recirculation pipe in the vicinity of the reactor coolant recirculation pump, which is the main source of radiation due to workers approaching during regular inspection work The reactor coolant recirculation pipe near the entrance and exit of the plant can suppress work exposure without special treatment.

FIG. 6 shows a fifth method for forming an oxide film on the inner surface of the pipe. In this method, heated gas is circulated in a pipe, and a valve 61 is installed at an inlet and an outlet of a core of a reactor coolant circulation system, and this is connected by a bypass pipe 62. The gas injection device 6 is provided in the bypass pipe 61.
3, a gas heating device 64, and a gas circulation pump 65 are attached. By operating the valve 61, a circulation system closed by the reactor recirculation system and the bypass system is formed without passing through the core (pressure vessel 33). Subsequently, a gas containing oxygen is introduced into the circulation system constituted by the gas injection device 63, and this is heated by the gas heater 64 to 500 ° C. and the gas circulation pump 65.
To circulate. As a result, the inner surface of the pipe 32 in contact with the heated gas can be heated to form an oxide film. Further, the circulation system constituted by the bypass pipe 62 constructed here can be used for decontamination of the pipe 32 by circulating the decontamination material. Furthermore, once installed, this equipment can be used to facilitate the subsequent removal of the radiation source by decontamination and the formation of an oxide film effective for suppressing the attachment of radionuclides.

As a sixth method of forming an oxide film,
The high temperature gas is circulated by utilizing the circulation system (reference numerals 32 and 34) constructed for decontamination by cutting off the reactor coolant recirculation pipe 32 shown in FIG. An oxide film may be formed on the inner surface of the pipe 32 before restoration, and the pipe 32 may be connected again.

As a seventh oxide film forming method, as shown in FIG.
The polishing may be performed dry without using water to generate frictional heat between the polishing surface and the polishing agent, and the polishing surface may be heated to 500 ° C. to form an oxide film.

After forming the oxide film by each method as described above, the detachable apparatus used for heating is removed (step S8), and when the drain line is used, the drain line is further removed (step S9). , The pipes are restored to the operable state (step S10).

These first to seventh oxide film forming methods are not limited to the decontaminated pipe 23, but when replacing a pipe contaminated with a radionuclide with a new pipe, the new pipe is oxidized in the gas phase. It can also be applied when forming a film.

FIG. 7 shows an example in which the present invention is applied to a PWR. In the pressurized water reactor, the primary system cooling water 701 is the pressurizer 7
It is pressurized by 02 so as not to boil. The primary cooling water 701 is heated by the nuclear fuel 703,
The heated primary system cooling water 701 is heat-exchanged in the steam generator 704 to turn the secondary system cooling water into steam, and then the primary system cooling water 701 returns to the pressure vessel 710 again. After the secondary cooling water that has become steam passes through the turbine 705 to generate electricity,
Returned to water by condenser 706. On the other hand, the heat exchanger 7
Part of the primary cooling water 701 that has passed through 04 is guided to the reactor water purification system, and impurities are removed by the purification device 707. Further, in the pressurized water reactor, the reaction of the nuclear fuel 703 is controlled not only by the flow rate of the primary cooling water but also by the boric acid concentration of the primary system cooling water, so that after the purifying device 707, the boric acid water injection system 708 and the dilution water injection system 709. Is equipped with. Due to such a structure, in the pressurized water reactor, the radionuclide attaches to the pipe that is in contact with the primary system cooling water 701 and causes radiation exposure.

Therefore, in order to suppress this adhesion, the present patent application is applied to the piping of the primary system. That is, the inlet and outlet of the reactor pressure vessel 710 of the primary system piping are connected to the bypass piping 7
A valve 712 is provided in the illustrated portion so that the system can be switched at 11 (corresponding to steps S2 and S3). Next, the valve 712 is operated to allow the circulation pump 713 to pass through the bypass pipe 711 without passing through the reactor pressure vessel 710.
The decontamination material is circulated to decontaminate the primary system piping such as the heat exchanger 704 (corresponding to steps S4 and S5). Then, a gas including 0.1% or more of oxygen, for example, air is introduced into the newly constructed circulation system passing through the bypass pipe 711 using the gas injection device 714. The introduced air is heated to 500 ° C. by the heater 715 and circulated in the system by the circulation pump 713. As a result, the heat exchanger 7
It is possible to form an oxide film effective in suppressing the adhesion of radionuclides on the primary piping such as 04 (corresponding to steps S6 and S7).

As described above, according to these embodiments, the decontamination of the inner surface of the pipe and the formation of an oxide film in the gas phase suppress the increase in the radiation dose rate after the repair to 1/4 or less. be able to. Further, in these embodiments, the temperature of the gas phase containing oxygen is set to 500 ° C. This is because the deposition of cobalt was most suppressed when the oxidation treatment was performed at 500 ° C. in FIG. Before and after, it is fully effective, about 500-700 ℃, or 300
Even at about 500 ° C, the effect of the present application can be sufficiently exerted.

[0044]

As is apparent from the above description, according to the present invention, the primary system pipes of the boiling water nuclear power plant and the pressurized water nuclear power plant that are already in operation, that is, already in operation, are removed. After dyeing, the redeposition of radionuclides can be suppressed by forming an oxide film in the gas phase. At that time, since an oxide film is formed in the gas phase,
No large-scale equipment is required, and repair of primary reactor system piping is possible at low cost.

[0045]

[Brief description of the drawings]

FIG. 1 is a flowchart showing an example of a processing procedure of a method for repairing a reactor primary system piping according to an embodiment of the present invention.

FIG. 2 is an explanatory view showing a first radionuclide removing method of removing a radionuclide by polishing an inner surface of a pipe on which the radionuclide is attached with a polishing machine.

FIG. 3 is an explanatory diagram showing a second radionuclide removing method of removing the radionuclide by causing a decontamination material to flow through the inner surface of the pipe to which the radionuclide is attached.

FIG. 4 is an explanatory view showing a first oxide film forming method for forming an oxide film by placing a heater in a heat insulating material and heating it.

FIG. 5 is an explanatory view showing a second oxide film forming method of forming an oxide film by moving a heater in the reactor primary system piping.

FIG. 6 is an explanatory view showing a fifth oxide film forming method of flowing a heating gas to form an oxide film in a gas phase after the reactor primary system piping is restored.

FIG. 7 is an explanatory diagram showing a decontamination method and an oxide film forming method in PWR.

FIG. 8 is a schematic diagram for explaining a mechanism of attaching a radionuclide to a reactor coolant pipe.

FIG. 9 is a diagram showing the amount of cobalt deposited by in-gas oxidation treatment with the oxidation treatment temperature as a parameter.

FIG. 10 is a diagram showing the amount of cobalt deposited by vapor-phase oxidation treatment using the surface roughness as a parameter.

[Explanation of symbols]

 21 Grinder 22 Abrasive 23 Reactor Coolant Recirculation Pipe 24 Radionuclide-Containing Layer 31 Reactor Coolant Recirculation Pump 32 Reactor Coolant Recirculation Pipe 33 Reactor Pressure Vessel 34 Abrasive Circulator 41 Pipe Heat Insulation 42 Pipe Heater 51 Heater 52 Oxide film 61 Valve 62 Bypass pipe 63 Gas injection device 64 Gas heating device 65 Gas circulation pump 701 Primary system cooling water 702 Pressurizer 710 Reactor pressure vessel 711 Bypass pipe 712 Valve 713 Circulation pump 714 Gas injection device 715 heater

Continuation of the front page (51) Int.Cl. ⁶ Identification code Office reference number FI Technical display location G21F 9/28 521 G21F 9/28 521D

Claims (14)

[Claims] 1. A method for repairing a primary system piping of a nuclear reactor for repairing a primary system piping of a nuclear reactor, comprising decontaminating an inner surface of a primary system piping to which radionuclides of an operating nuclear power plant adhere, and then deoxidizing the oxygen. An oxide film is formed on the inner surface of the pipe in a gas phase containing the following: a method for repairing a reactor primary system pipe. 2. A method for repairing a primary system piping of a reactor for repairing a primary system piping of a nuclear reactor, comprising removing a piping at a preset position of a primary system to which radionuclides of an operating nuclear power plant are attached, A method for repairing a primary reactor system pipe, comprising decontaminating an inner surface of a removed pipe, and then connecting the pipe having an oxide film formed on the inner surface in a gas phase containing oxygen. 3. A method of repairing a primary system piping of a nuclear reactor for repairing a primary system piping of a nuclear reactor, comprising removing a piping at a preset position of a primary system to which radionuclides of an operating nuclear power plant are attached, A method for repairing a primary reactor system piping, comprising connecting a new piping in place of the removed piping, and then forming an oxide film on the inner surface of the piping in a gas phase containing oxygen. 4. A method of repairing a primary system piping of a nuclear reactor for repairing a primary system piping of a nuclear reactor, wherein a pipe at a preset position of a primary system to which radionuclides of an operating nuclear power plant adhere is removed, and oxygen is removed. A method for repairing a primary reactor system pipe, wherein a new pipe having an oxide film formed on the inner surface of the pipe is connected in place of the removed pipe in a gas phase containing 5. The reactor primary system piping according to claim 1, wherein the oxide film formed in the vapor phase has a thickness of 1 nm or more and 100 nm or less. Repair method. 6. The oxygen concentration in the gas phase containing oxygen is 0.
It is 1% or more, The repair method of the nuclear reactor primary system piping according to any one of claims 1 to 4. 7. The inner surface of the pipe is obtained by coating the pipe with a heat insulating material having heating means for heating the pipe, and heating the pipe in a gas phase by the heating means before passing water through the pipe. 5. The method for repairing a primary reactor system piping according to any one of claims 1 to 4, wherein an oxide film is formed. 8. The nuclear reactor according to claim 1, wherein a heated gas is circulated inside the pipe to heat the inner surface of the pipe to form an oxide film. Repair method for primary piping. 9. A device for circulating a heated gas is previously attached to both ends of the new pipe, and the heated gas is circulated after the pipe is attached to heat the inner surface of the pipe to form an oxide film. The method for repairing primary reactor system piping according to claim 2 or 3, wherein 10. A heating device that is movable inside the pipe is installed, and while moving the inside of the pipe while heating the inner surface of the pipe, an oxide film is formed. The method for repairing the primary piping of the reactor described in. 11. The method for repairing primary system piping of a nuclear reactor according to claim 10, wherein the heating device comprises a high frequency induction heating device. 12. The surface roughness of the inner surface of the pipe is polished to form a surface roughness of 10 μm or less before the oxide film is formed on the inner surface of the pipe. Repair method for primary reactor piping. 13. The method for repairing a primary reactor system pipe according to claim 12, wherein an inner surface of the pipe is heated by frictional heat generated by the polishing to form an oxide film. 14. The reactor primary system pipe is at least one system of a reactor coolant recirculation system, a reactor coolant purification system, and a residual heat removal system. The method for repairing the primary reactor system piping according to any one of items.