JP2018004291A - Stress corrosion crack suppression method for atomic power plant constitution member - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a stress corrosion crack suppression method for an atomic power plant constitution member that can suppress radioactive nuclides from sticking on a surface of the atomic power plant constitution member and suppress a stress corrosion crack made in the atomic plant constitution member from developing.SOLUTION: A BWR plant has an RPV 2, recirculation system piping 6 connected to the RPV 2, water supply piping 11, and purification system piping 17. A graphene injection device 25 is connected to the water supply piping 11. In actuation of the BWR plant in which steam begins to be introduced into a condenser 10 from the RPV 2 through bypass piping 33, graphene is injected into supplied water in the water supply piping 11 from the graphene injection device 25. The supplied water including the graphene is fed to the RPV 2 to inject the graphene into furnace water. The furnace water including the injected graphene contacts the RPV 2 and inner surfaces of the recirculation system piping 6 or the like, so that the graphene sticks on those inner surfaces.SELECTED DRAWING: Figure 2

Description

  The present invention relates to a method for suppressing stress corrosion cracking of nuclear plant components, and more particularly, to a method for suppressing stress corrosion cracking of nuclear plant components suitable for application to a boiling water nuclear power plant.

  In a nuclear power plant such as a boiling water nuclear power plant (hereinafter referred to as a BWR plant) and a pressurized water nuclear power plant (hereinafter referred to as a PWR plant), main components such as a reactor pressure vessel suppress corrosion. In addition, stainless steel, nickel-base alloy, or the like is used for the water contact portion in contact with water. In addition, components such as the reactor coolant purification system, residual heat removal system, reactor isolation cooling system, core spray system, feed water system, and condensate system are used from the viewpoint of reducing the required manufacturing costs of the plant, Carbon steel members are mainly used from the viewpoint of avoiding stress corrosion cracking of stainless steel caused by high-temperature water flowing in the water system.

  In addition, since corrosion products that are the source of radioactive corrosion products are also generated from water contact parts such as RPV and recirculation piping, the primary primary components are made of stainless steel and nickel bases with low corrosion. Stainless steel such as alloy is used. In addition, the low alloy steel RPV has a stainless steel overlay on the inner surface, preventing the low alloy steel from coming into direct contact with the reactor water (cooling water present in the RPV). Reactor water is cooling water present in the nuclear reactor. Furthermore, a part of the reactor water is purified by a filter demineralizer of the reactor purification system to positively remove metal impurities that are slightly present in the reactor water.

  However, even if the above-described corrosion countermeasures are taken, the presence of very few metal impurities in the reactor water is inevitable, so some metal impurities are converted into metal oxides to the fuel rods contained in the fuel assembly. Adhere to the surface. The metal element contained in the metal impurity adhering to the surface of the fuel rod causes a nuclear reaction by irradiation of neutrons emitted from the nuclear fuel in the fuel rod, and becomes a radionuclide such as cobalt 60, cobalt 58, chromium 51, manganese 54, etc. . Most of these radionuclides remain attached to the fuel rod surface in the form of oxides, but some radionuclides elute as ions in the reactor water depending on the solubility of the incorporated oxides. Or re-released into the reactor water as an insoluble solid called clad. Radioactive material in the reactor water is removed by the reactor purification system. However, the radioactive material that has not been removed accumulates on the surface of the component that contacts the reactor water while circulating in the recirculation system together with the reactor water. As a result, radiation is radiated from the surface of the component member, which causes radiation exposure of workers during regular inspection work. The exposure dose of the employee is managed so that it does not exceed the prescribed value for each person. In recent years, this regulation value has been lowered, and it has become necessary to make the exposure dose of each person as low as economically possible.

  Thus, various methods for reducing the adhesion of radionuclides to piping and methods for reducing the concentration of radionuclides in the reactor water have been studied. For example, by injecting metal ions such as zinc into the reactor water, and forming a dense oxide film containing zinc on the inner surface of the recirculation piping that contacts the reactor water, cobalt 60 and cobalt 58 in the oxide film, etc. Has been proposed (see Japanese Patent Laid-Open No. 58-79196).

  Further, a chemical decontamination method has been proposed in which radioactive nuclides such as cobalt 60 and cobalt 58 once taken into the oxide film formed on the pipe surface are dissolved and removed from the pipe surface using chemicals (specialty). Kaihei 11-344597).

  Further, a method for suppressing the attachment of radionuclides to the surface of a constituent member after the operation of the plant by forming a magnetite film as a ferrite film on the surface of the constituent member of the nuclear power plant after chemical decontamination is disclosed in Japanese Patent Application Laid-Open No. 2006-2006. No. 38483 is proposed. In this method, a formic acid aqueous solution containing iron (II) ions, hydrogen peroxide and hydrazine, and a treatment liquid heated to a temperature ranging from room temperature to 100 ° C. are brought into contact with the surface of the component member to form a ferrite film on the surface. To form.

  JP2013-237602A describes a manufacturing method of an industrial product using a graphene bonded body. The graphene bonded body is obtained by bonding graphene to each other by supporting iron fine particles on the surface of graphene and metal-bonding the iron fine particles. Japanese Patent Application Laid-Open No. 2013-237602 also describes an example of a graphene bonded body in which Pd and Pt are attached to the surface of iron fine particles. In the manufacturing method of the industrial product, a pipe made of SUS having a film of a graphene bonded body formed on the inner surface is also manufactured. Since the coating of the graphene joined body formed on the inner surface of the pipe blocks contact between the reactor water and the inner surface of the pipe, stress corrosion cracking of the SUS pipe can be prevented.

  WO2013 / 058383 describes a porous material containing carbon nanophones. Carbon nanophone has a catalytic action.

  Japanese Patent Laid-Open No. 2006-312783 describes a method for reducing stress corrosion cracking of structural materials. In this stress corrosion cracking mitigation method, dielectric nanoparticles containing carbon are attached to the surface of a structural member of a nuclear power plant that is in contact with reactor water. The adhesion of dielectric nanoparticles reduces stress corrosion cracking of nuclear plant structural components.

JP 58-79196 A Japanese Patent Laid-Open No. 11-344597 JP 2006-38483 A JP 2013-237602 A WO2013 / 058383 Publication JP 2006312783 A

Proceeding of water chemistry 2004, p1054-1059

  The graphene bonded film formed on the inner surface of a pipe described in JP2013-237602A prevents the corrosion corrosion of the pipe by blocking the contact between the reactor water and the pipe. This graphene bonded film does not function as a catalyst. In addition, since the iron fine particles joining the graphenes are ionized and eluted into the reactor water in the graphene joined film, the graphene may be separated from the pipe.

  The carbon nanophone described in WO2013 / 058383 cannot reduce the corrosion potential of nuclear plant components to such an extent that the progress of stress corrosion cracking in the nuclear plant components can be suppressed. Moreover, carbon forming the dielectric nanoparticles described in JP-A-2006-312783 has no catalytic action.

  An object of the present invention is to provide a method for suppressing stress corrosion cracking of a nuclear plant constituent member, in which the attachment of radionuclides to the surface of the nuclear plant constituent member is suppressed, and the progress of stress corrosion cracking occurring in the nuclear plant constituent member can be suppressed. It is in.

The feature of the present invention that achieves the above object is that graphene is injected into the reactor water during operation of the nuclear power plant, and the reactor water containing the graphene is brought into contact with the surface of the nuclear plant component that contacts the reactor water. In addition, the graphene contained in the reactor water is adhered to the surface of the constituent member by 0.01 μg / cm ² or more.

Since the graphene contained in the reactor water adheres to the surface of the structural member by 0.01 μg / cm ² or more, the adhesion of radionuclides to the surface of the structural member of the nuclear power plant is suppressed, and the stress corrosion cracking that has occurred in the nuclear power plant structural member Progress can be suppressed.

Preferably, graphene is attached to the surface of the constituent member in the range of 0.01 μg / cm ^{2 to} 10 μg / cm ² . As a result, it is possible to prevent other graphene from adhering to the graphene adhering to the structural member, and the catalytic ability to promote the recombination reaction of hydrogen and oxygen in the reactor water is reduced and wasted. The amount of graphene formed can be reduced.

  ADVANTAGE OF THE INVENTION According to this invention, adhesion of the radionuclide to the nuclear power plant structural member surface is suppressed, and also the progress of the stress corrosion crack which arose in the nuclear power plant structural member can be suppressed.

It is a flowchart which shows the procedure which makes a graphene adhere to the surface of a nuclear power plant structural member in the stress corrosion cracking suppression method of the nuclear power plant structural member of Example 1 which is one suitable Example of this invention. It is a block diagram of the boiling water nuclear power plant to which the stress corrosion cracking suppression method of the nuclear power plant structural member of Example 1 is applied. It is a detailed block diagram of the graphene injection apparatus shown in FIG. It is a characteristic view which shows the electric potential dependence of the Co-60 adhesion amount in a stainless steel test piece. It is a characteristic view which shows the electric potential dependence of the Co-60 adhesion amount in a carbon steel test piece. It is explanatory drawing which shows the corrosion potential of each test piece in the reactor water environment in a nuclear reactor. It is explanatory drawing which shows the experimental result of the Co-60 adhesion amount of each stainless steel test piece in the environment in a nuclear reactor. It is explanatory drawing which shows the experimental result of the Co-60 adhesion amount of each carbon steel test piece in the environment in a nuclear reactor. It is explanatory drawing which shows the catalyst efficiency of each of a graphene, carbon nanophone, and a nanotube. It is a block diagram of the boiling water nuclear power plant to which the stress corrosion cracking suppression method of the nuclear power plant structural member of Example 2 which is another suitable Example of this invention is applied. It is a detailed block diagram of the graphene injection apparatus shown in FIG.

  The inventors investigated the effects of water quality and materials on the adhesion of Co-60 to nuclear plant components in a water quality environment simulating the operating conditions of a nuclear plant. As a result, it has been found that Co-60 adheres to the surface of the constituent member when Co-60 is taken into the oxide film formed on the surface of the constituent member, and Co-60 is taken into the oxide film. In order to suppress, it turned out that what is necessary is to control the corrosion potential of a structural member which controls the formation amount of an oxide film. Based on this consideration, the inventors controlled the corrosion potential under the operating conditions of the atomic plant and conducted a Co-60 adhesion experiment.

  The result of the Co-60 adhesion experiment on the stainless steel specimen is shown in FIG. 4, and the result of the Co-60 adhesion experiment on the carbon steel specimen is shown in FIG. In each figure, the horizontal axis indicates the corrosion potential, and the vertical axis indicates the amount of Co-60 adhesion. As is clear from these figures, in each of the stainless steel test piece and the carbon steel test piece, the adhesion amount of Co-60 increased as the corrosion potential decreased.

  On the other hand, the structural member made of stainless steel has a problem that stress corrosion cracking occurs. In order to suppress the progress of stress corrosion cracking in the components of the nuclear power plant, there is a technique for injecting hydrogen and platinum into the reactor water and controlling the corrosion potential of the components to −0.23 V / SHE or less. This platinum injection technique is described in Proceeding of water chemistry 2004, p1054-1059.

  That is, in order to suitably suppress the adhesion of Co-60 to the components of the nuclear power plant, it is necessary to control the corrosion potential of the nuclear plant components to be as high as possible at −0.23 V / SHE or less. is there. By controlling this corrosion potential, it is possible to suppress the amount of Co-60 adhesion and to suppress the development of stress corrosion cracking in the constituent members.

  Therefore, the inventors examined a method of controlling the corrosion potential in the reactor water environment of the BWR plant to a potential as high as possible at −0.23 V / SHE or less.

FIG. 6 shows the corrosion potential of each test piece immersed in simulated water simulating reactor water in the rated operation of the BWR plant. Here, test piece A is a test piece made of stainless steel, test piece B is a test piece made of carbon steel, test piece C is a test piece made of stainless steel with graphene attached to the surface, and test piece D is a test piece made of carbon steel with graphene attached to the surface. Each of the test pieces A and B has no graphene attached to the surface. Graphene is a sheet of sp ² bonded carbon atoms with a thickness of 1 atom, and has a honeycomb hexagonal lattice structure made of carbon atoms and their bonds. The length of one side of the graphene is in the range of 1 nm to 1 μm (1 nm to 1 μm).

  The corrosion potentials of the test pieces C and D are lower than the corrosion potentials of the test pieces A and B, and are −0.23 V / SHE to −0.27 V / SHE. That is, by attaching graphene to the surface of the test piece, it was confirmed that the corrosion potential of the test piece surface could be controlled in the range of −0.23 V / SHE to −0.27 V / SHE.

  Furthermore, the inventors conducted an experiment to confirm the effect of graphene on Co-60 adhesion using a stainless steel specimen and a carbon steel specimen. In this experiment, each test piece was immersed in the aforementioned simulated water containing Co-60. The results of these experiments are shown in FIGS. As apparent from FIG. 7, the Co-60 adhesion amount of the stainless steel test piece having graphene attached to the surface was significantly reduced as compared to that of the stainless steel test piece having no graphene attached to the surface. Further, as is apparent from FIG. 8, in the carbon steel test piece, the Co-60 adhesion amount when graphene was adhered to the surface was remarkably reduced as compared with the case where graphene was not adhered to the surface. .

  The catalytic efficiencies of graphene, carbon nanophones, and nanotubes are shown in FIG. The catalytic efficiency of graphene is the highest, and the catalytic efficiency of carbon nanophones and nanotubes is significantly lower than that of graphene. Even if carbon nanophones and nanotubes with low catalytic efficiency are attached to the surfaces of the nuclear plant components that contact the cooling water, the effect of reducing the corrosion potential of the carbon nanophones and nanotubes is small. The progress of stress corrosion cracks occurring in the plant components cannot be suppressed. Moreover, even if each of the carbon nanophones and the nanotubes is attached to the surface of the constituent member of the nuclear power plant that contacts the cooling water, the attachment of the radionuclide to the surface of the constituent member cannot be suppressed.

  Examples of the present invention reflecting the above examination results will be described below.

  A method for suppressing stress corrosion cracking of a nuclear plant component according to embodiment 1, which is a preferred embodiment of the present invention, will be described below with reference to FIGS. 1, 2, and 3. FIG. The method for suppressing stress corrosion cracking of nuclear plant components according to this embodiment is applied to a BWR plant.

  As shown in FIG. 2, the BWR plant includes a nuclear reactor 1, a turbine 3, a condenser 4, a recirculation system, a nuclear reactor purification system, a water supply system, and the like. The nuclear reactor 1 is installed in a nuclear reactor containment vessel 7 disposed in a nuclear reactor building (not shown). The nuclear reactor 1 has a nuclear reactor pressure vessel (hereinafter referred to as RPV) 2 in which a core 3 is built, and a jet pump 4 is installed in the RPV 2. A number of fuel assemblies (not shown) loaded on the core 3 include a plurality of fuel rods filled with a plurality of fuel pellets made of nuclear fuel material. The core 3 is surrounded by a cylindrical stainless steel core shroud (not shown) disposed in the reactor pressure vessel 2. The recirculation system includes a stainless steel recirculation system pipe 6 and a recirculation pump 5 installed in the recirculation system pipe 6. One end of the recirculation piping 6 is connected to the RPV 2 and communicates with a downcomer that is an annular cooling water passage formed between the RPV 2 and the core shroud. The other end of the recirculation pipe 6 is connected to a nozzle (not shown) of the jet pump 4 disposed in the downcomer.

  The main steam pipe 8 connected to the RPV 2 is connected to the turbine 9. A steam control valve 34 is provided in the main steam pipe 8. A bypass pipe 33 connected to the main steam pipe 8 on the upstream side of the steam control valve 34 and having a bypass valve 35 is connected to the condenser 10 disposed below the turbine 9.

  In the water supply system, a condensate pump 12, a condensate purification device (for example, a condensate demineralizer) 13, a low pressure feed water heater 14, a feed water pump 15 and a high pressure feed water heater 16 are directed from the condenser 10 to the RPV 2. In this order, they are installed in a water supply pipe 11 made of carbon steel that connects the condenser 10 and the RPV 2. In the reactor purification system, a purification system pump 18, a regenerative heat exchanger 19, a non-regenerative heat exchanger 20, and a reactor water purification device 21 are made of carbon steel that communicates the recirculation system pipe 6 and the feed water pipe 11 in this order. It is installed in the purification system pipe 17. In the purification system pipe 17, as shown in FIG. 2, an on-off valve 22 is provided between the purification system pump 18 and the recirculation system pipe 6. The purification system pipe 17 is connected to the recirculation system pipe 6 upstream of the recirculation pump 5.

  The recirculation system pipe 6, the water supply pipe 11 and the purification system pipe 17 are pipe systems connected to the RPV 2.

  Cooling water (hereinafter referred to as “reactor water”) in the RPV 2 is boosted by the recirculation pump 5 and jetted into the jet pump 4 through the recirculation piping 6. Reactor water existing around the nozzle of the jet pump 4 in the downcomer is also sucked into the jet pump 4 and supplied to the core 3. The reactor water supplied to the core 3 is heated by the heat generated by the nuclear fission of the nuclear fuel material in the fuel rod, and a part of the reactor water becomes steam. When the steam control valve 34 is opened and the bypass valve 35 is closed, the steam is guided from the RPV 2 through the main steam pipe 8 to the turbine 9 to rotate the turbine 9. A generator (not shown) connected to the turbine 9 rotates to generate electric power. The steam discharged from the turbine 9 is condensed by the condenser 10 to become water. This water is supplied into the RPV 2 through the water supply pipe 11 as water supply. The feed water flowing through the feed water pipe 11 is boosted by the condensate pump 12, impurities are removed by the condensate purification device 13, and further boosted by the feed water pump 15. The feed water is heated by the low pressure feed water heater 14 and the high pressure feed water heater 16 and guided into the RPV 2. The extraction steam extracted from the turbine 9 by the extraction piping is supplied to the high-pressure feed water heater 16 and the low-pressure feed water heater 14, respectively, and becomes a heating source of the feed water.

  Part of the reactor water flowing in the recirculation system pipe 6 flows into the purification system pipe 17 of the reactor purification system by driving the purification system pump 18 and is cooled by the regenerative heat exchanger 19 and the non-regenerative heat exchanger 20. Then, it is purified by the reactor water purification device 21. The purified reactor water is heated by the regenerative heat exchanger 19 and returned to the RPV 2 through the purification system pipe 17 and the water supply pipe 11.

  The graphene injection device 25 is connected to a sampling pipe (not shown) connected to the feed water pipe 11 between the condensate purification device 13 and the low-pressure feed water heater 14. As shown in FIG. 3, the graphene injection device 25 includes a graphene tank 26, an injection pump 27, and an injection pipe 28. One end of an injection pipe 28 provided with an injection pump 27 is connected to the graphene tank 26, and the other end of the injection pipe 28 is connected to the above-described sampling pipe. The graphene tank 26 is filled with water containing graphene. As described above, the length of one side of each graphene in the graphene tank 26 is in the range of 1 nm to 1 μm. An on-off valve 29 is provided on the injection pipe 28 on the downstream side of the injection pump 27, and an on-off valve 30 is provided on the injection pipe 28 on the upstream side of the injection pump 27.

  A method for suppressing stress corrosion cracking of nuclear plant components will be described based on the procedure shown in FIG. First, the graphene injection device is connected to the piping system of the nuclear power plant (step S1). In the case of a BWR plant that has experienced operation, when the operation of the BWR plant is stopped, or in the case of a newly installed BWR plant, before the operation is started, the injection pipe 28 of the graphene injection device 25 is Connected to the sampling pipe.

  The nuclear power plant is activated (step S2). In a state where both the steam control valve 34 and the bypass valve 35 are closed, the recirculation pump 5 of the BWR plant is driven. The reactor water in the RPV 2 is increased in pressure by driving the recirculation pump 5, jetted into the jet pump 4 through the recirculation system pipe 6, and the reactor water present around the nozzle of the jet pump 4 in the downcomer, It is discharged from the jet pump 4 and supplied to the core 3. The reactor water discharged from the reactor core 3 flows into the downcomer and is supplied to the reactor core 3 again. With the reactor water being supplied to the core 3, a plurality of control rods (not shown) are withdrawn from the core 3, and the reactor 1 eventually changes from a subcritical state to a critical state. By further pulling out the control rod, the reactor water is heated by the fission of the fissile material contained in each fuel rod in each fuel assembly loaded in the reactor core 3, the temperature of the reactor water rises, and the pressure in the RPV 2 rises. To do.

  After the reactor water temperature rises to the rated temperature and the internal pressure of the RPV 2 rises to the rated pressure, the bypass valve 35 is opened with the steam control valve 34 closed, and the control rod is further pulled out of the core 3 to increase the reactor power. Let The steam generated in the reactor core 3 is led to the condenser 10 through the main steam pipe 8 and the bypass pipe 33 and is condensed in the condenser 10 to become water. When the bypass valve 35 is opened, the condensate pump 12 and the feed water pump 15 are driven. The rotation speed of each of the condensate pump 12 and the feed water pump 15 is the rotation speed at which the amount of water generated by the condensation of the steam flowing into the condenser 10 through the bypass pipe 33 can be supplied to the RPV 2 as feed water. For this reason, the water produced in the condenser 10 by the condensation of the steam flowing into the condenser 10 is supplied into the RPV 2 through the water supply pipe 11 as water supply. As the reactor power increases, the flow rate of steam flowing into the condenser 10 from the bypass pipe 33 increases, so that the number of revolutions of the condensate pump 12 and the feed water pump 15 also increases as the steam flow rate increases. The flow rate of feed water supplied into the RPV 2 increases.

  For example, when the reactor power increases to about 10%, the steam control valve 34 is opened and the bypass valve 35 is closed. For this reason, all the steam generated in the RPV 2 is supplied to the turbine 9 through the main steam pipe 8. A generator (not shown) connected to the turbine 9 also rotates to generate electricity. Eventually, the reactor power increases to 100%, and the BWR plant enters the rated operating state.

  Graphene is injected (step S3). During the operation of increasing the reactor power of the BWR plant, specifically, after opening the bypass valve 35 to introduce the steam generated in the RPV 2 to the condenser 10, each of the on-off valves 29 and 30 is opened and injected. The pump 27 is driven. Water containing graphene in the graphene tank 26 is injected into the water supply pipe 11 through which water is supplied through the injection pipe 28 by driving the injection pump 27. The amount of graphene injected into the water supply in the water supply pipe 11 through the injection pipe 28 is 0.1 ppb with respect to the flow rate of the water supply.

  Since the reactor output increases until the rated operation state (100% output operation state) of the BWR plant is started after the introduction of the steam generated in the RPV 2 to the condenser 10 by the bypass pipe 33 is started, the RPV 2 The flow rate of the steam discharged from the main steam pipe 8 to the main steam pipe 8 increases, and accordingly, the flow rate of the feed water supplied to the RPV 2 through the feed water pipe 11 also increases. In order to inject graphene in an amount of 0.1 ppb with respect to the water supply flow rate, the concentration of graphene contained in the water in the graphene tank 26 is uniform, and therefore, from the graphene tank 26 to the water supply pipe 11 through the injection pipe 28. It is necessary to increase the flow rate of the supplied water containing graphene in accordance with the increase in the feed water flow rate in the feed water pipe 11.

  Such an increase in the flow rate of water containing graphene is performed by controlling the number of revolutions of the infusion pump 27 by a control device (not shown). This control device was measured with a feed water flow rate measured by a first flow meter (not shown) provided in the feed water pipe 11 and a second flow meter (not shown) provided in the injection pipe 28. Each of the flow rates of water to be injected is input, and 0.1 ppb of graphene is injected with respect to the water supply flow rate measured by the first flow meter. Control the number of revolutions. For this reason, even if the feed water flow rate increases as the reactor power increases, the graphene concentration of the feed water supplied to the RPV 2 can be maintained at 0.1 ppb.

  The graphene injected into the feed water is supplied into the RPV 2 together with the feed water through the feed water pipe 11 and is injected into the reactor water in the RPV 2. The reactor water containing the injected graphene flows through the inside of the recirculation system pipe 6 and the RPV 2 which are constituent members of the BWR plant, and contacts the inner surfaces thereof. For this reason, the graphene is composed of the inner surfaces of the recirculation system pipe 6, the RPV 2 and the reactor purification system pipe 17, the inner and outer surfaces of the core shroud that is installed in the RPV 2 and surrounds the core 3, and the fuel assembly loaded in the core 3. It adheres to the contact surface with the reactor water. In the furnace purification system piping 17, graphene adheres to the inner surface of the furnace purification system piping 17 upstream of the reactor water purification device 21. In the fuel assembly, graphene is placed on the outer surface of the fuel rod, the contact surface of the fuel spacer with the reactor water, the contact surface of the upper tie plate and the lower tie plate with the reactor water, and the inner and outer surfaces of the channel box. Adhere to. Since the heat conduction of graphene is good, the graphene adhering to the outer surface of the fuel rod does not hinder the heat removal of the nuclear fuel material in the fuel rod.

  Since the graphene contained in the reactor water flowing into the reactor purification system piping 17 from the recirculation system piping 6 is removed by the reactor water purification device 21, the inside of the reactor purification system piping 17 is located downstream of the reactor water purification device 21. Not included in flowing reactor water. Although not shown, in the reactor water purification apparatus 21, a filter is disposed upstream and an ion exchange resin layer is disposed downstream of the filter. Graphene contained in the reactor water is removed by the filter, and ions contained in the reactor water are removed by the ion exchange resin of the ion exchange resin layer after passing through the filter. The amount of graphene injected from the injection pipe 28 into the water supply pipe 11 is determined in consideration of the amount of graphene removed by the reactor water purification device 21.

The injection of the water containing graphene from the graphene tank 26 into the water supply pipe 11 is performed, for example, for about 10 days with the above-described graphene injection amount. Graphene is injected after the bypass valve 35 is opened to guide the steam generated in the RPV 2 to the condenser 10 until the reactor power reaches 100% and after the reactor power reaches 100%. It is carried out over about 10 days including the period. By injection of the graphene, graphene, in the range of ^{0.01μg / cm 2 ~10μg / cm 2} (0.01μg / cm 2 or more 10 [mu] g / cm ² or less), the recirculation pipe 6, the RPV2 and the core 3 It adheres to the surface of a BWR plant component, such as a fuel assembly, that is, the surface in contact with the reactor water.

When the amount of graphene attached to the surface of the constituent member is less than 0.01 μg / cm ² , the effect of suppressing the attachment of the radionuclide to the surface of the constituent member in contact with the reactor water is significantly reduced. The progress of stress corrosion cracking that has occurred in the BWR plant components cannot be suppressed. When the amount of graphene attached to the surface of the component becomes 0.01 μg / cm ² or more, the attachment of the radionuclide to the surface of the BWR plant component is remarkably suppressed, and the stress corrosion cracking generated in the BWR plant component Progress can be suppressed. However, when the amount of graphene attached to the surface of the constituent member exceeds 10 μg / cm ² , the probability that another graphene adheres on the graphene directly attached to the surface of the constituent member increases. For this reason, the hydrogen contained in the reactor water is less likely to come into contact with the graphene covered with the other graphene and directly attached to the surface of the component, and the hydrogen due to the action of the graphene directly attached to the surface of the component The recombination reaction of oxygen contained in the reactor water is less likely to occur. This means that the catalytic ability of graphene directly attached to the surface of the constituent member is not utilized, and from the viewpoint of catalytic action, the graphene covered with other graphene is useless graphene. In order to reduce useless graphene that cannot utilize the catalytic capacity and efficiently suppress the development of stress corrosion cracking that has occurred in the BWR plant component, the amount of graphene adhering to the surface of the component is 10 μg / cm ² or less It is necessary to.

The injection of graphene is stopped (step S4). Components of the BWR plant, on the surface in contact with the reactor water, a predetermined amount of graphene adhering the graphene in the range of ^{0.01μg / cm 2 ~10μg / cm 2} , the injection into the reactor water in the reactor 1 After completion, the driving of the infusion pump 27 is stopped and the on-off valves 29 and 30 are closed. Thereby, the injection of graphene into the nuclear reactor 1 is stopped.

According to the present embodiment, graphene is injected into the reactor water, and the graphene adheres to the surface of the BWR plant component that contacts the reactor water in an amount of 0.01 μg / cm ² or more. The adhesion of the radionuclide to the contacting surface is suppressed, and the development of stress corrosion cracks generated in the constituent members can be suppressed.

In this embodiment, components of the BWR plant, since adhering the graphene surface in contact with the reactor water in 0.01 [mu] g / cm ² or more 10 [mu] g / cm ² or less in the range of the radionuclide (e.g., Co-60) It can suppress that the oxide film to contain is formed in the surface which contacts the reactor water of the structural member. By causing graphene to adhere to the surface of the constituent member in contact with the reactor water in the range of 0.01 μg / cm ^{2 to} 10 μg / cm ² , the corrosion potential of the constituent member is lowered. This decrease in the corrosion potential can suppress the attachment of radionuclides to the surface of the constituent member that contacts the reactor water, and can suppress the development of stress corrosion cracks that have occurred in the constituent member.

In this embodiment, the amount of graphene attached to the constituent member is set to 10 μg / cm ² or less, so that other graphene can be prevented from attaching onto the graphene attached to the constituent member. The amount of adhering graphene that is wasted by reducing the catalytic ability to promote the recombination reaction between hydrogen and oxygen can be reduced.

  During operation of the BWR plant, the reactor water in the BWR plant flows in the piping system connected to RPV2 and RPV2. In this embodiment, graphene is injected into the reactor water during the operation of the BWR plant. Therefore, the graphene is supplied to the surface of all the components in contact with the reactor water in the BWR plant by the flowing reactor water. Can be attached. For this reason, in a wide range of constituent members of the BWR plant, adhesion of radionuclides to the surface can be suppressed, and further, the progress of the generated stress corrosion cracking can be suppressed.

  In this embodiment, after starting the introduction of the steam generated in the RPV 2 into the condenser 10 at the start of the BWR plant, that is, during the operation of increasing the reactor power, graphene is injected into the reactor water. The graphene can be attached to the surface of the component that contacts the reactor water at an early stage of startup. For this reason, it is possible to suppress the attachment of the radionuclide to the constituent member at the time of starting the BWR plant, and it is possible to suppress the attachment of the radionuclide to the constituent member even during the rated operation of the BWR plant. . The surface dose rate of the structural member is remarkably reduced, and the exposure of workers during maintenance inspections performed when the BWR plant is shut down can be significantly reduced.

  In addition, the graphene adhering to the surface which contacts the reactor water of the structural member of a BWR plant does not peel from the surface of the structural member. The graphene that has once adhered to the surface of the constituent member normally remains attached to the surface of the constituent member even when the operation cycle of the BWR plant changes. However, when chemical decontamination is performed on the BWR plant, the graphene adhering to the surface of the component member is removed from the surface by this chemical decontamination. For this reason, in the next operation cycle after the completion of chemical decontamination, in the above-mentioned period when the BWR plant is started up, the above-described injection of graphene into the reactor water is carried out, and the components that have been subjected to chemical decontamination Graphene adheres to the surface in contact with the reactor water. In this way, since graphene is attached to the surface of the component that has been subjected to chemical decontamination, the surface contacting the reactor water, adhesion of radionuclides to the component that has been subjected to chemical decontamination is further suppressed, It is possible to suppress the development of stress corrosion cracks generated in the constituent members.

Further, all the fuel assemblies loaded in the core 3 are taken out from the core 3 as spent fuel assemblies at the time of the fuel replacement operation when the operation of the BWR plant is stopped, for example, 1/4 each year. A new fuel assembly having a burnup of 0 GWd / t and having the same number as that of the removed bodies is loaded into the core 3. Since graphene is not attached to the surface of these new fuel assemblies loaded in the core 3, as described above, graphene is injected into the reactor water when the BWR plant is started, and the core 3 is newly loaded. Graphene is adhered to the surface of each fuel assembly that comes into contact with the reactor water. Graphene adheres to the surface of the new fuel assembly in contact with the reactor water in the range of 0.01 μg / cm ^{2 to} 10 μg / cm ² .

  The graphene injection device 25 may be always connected to the water supply pipe 11 (permanent), or may be temporarily connected to the water supply pipe 11 in an operation cycle in which graphene is injected into the reactor water. The temporary graphene injection device 25 is connected to the water supply pipe 11 during the operation stop period of the BWR plant immediately before the operation cycle for injecting graphene, and the BWR after the operation of the BWR plant in the operation cycle for injecting graphene is stopped. It is removed from the feed water pipe 11 during the plant shutdown period.

  A method for suppressing stress corrosion cracking of nuclear plant components according to embodiment 2, which is another preferred embodiment of the present invention, will be described below with reference to FIGS. The method for suppressing stress corrosion cracking of nuclear plant components according to this embodiment is applied to a BWR plant.

  The configuration of the graphene injection device 25A used in the method for suppressing stress corrosion cracking of nuclear plant components according to this embodiment will be described with reference to FIG. A graphene injection device 25A having a configuration different from that of the graphene injection device 25 includes a graphene tank 26 and an injection pipe 28B. One end of the injection pipe 28B provided with the on-off valve 32 is connected to the graphene tank 26, and the other end of the injection pipe 28B is connected to the water supply pipe 11 between the condensate purification device 13 and the low-pressure feed water heater 14. . One end of the feed water supply pipe 28A provided with the on-off valve 31 is connected to the graphene tank 26, and the other end of the feed water supply pipe 28A is between the connection point of the injection pipe 28B and the feed water pipe 11 and the condensate purification device 13. , Connected to the water supply pipe 11. A valve 36 is provided in the water supply pipe 11 between a connection point between the water supply pipe 28 </ b> A and the water supply pipe 11 and a connection point between the injection pipe 28 </ b> B and the water supply pipe 11.

  Also in the method for suppressing stress corrosion cracking of the nuclear plant component according to the present embodiment, the steps S1 to S4 performed by the method for suppressing stress corrosion cracking of the nuclear plant component according to the first embodiment are performed. The graphene injection device is connected to the piping system of the nuclear power plant (step S1). When the operation of the BWR plant is stopped, the injection pipe 28B is connected to the water supply pipe 11 and the water supply pipe 28A is connected to the water supply pipe 11 as described above. As a result, the graphene injection device 25A is connected to the water supply pipe 11 by two pipes (an injection pipe 28B and a water supply pipe 28A).

Similar to the first embodiment, the nuclear power plant is activated (step S2). Thereafter, graphene is injected (step S3). The injection of graphene into the reactor water is performed by opening the on-off valves 31 and 32 and slightly closing the opened valve 36. Since the valve 36 is slightly closed, a pressure difference is generated between the connection point of the feed water supply pipe 28A and the feed water pipe 11 and the connection point of the injection pipe 28B and the feed water pipe 11, and the pressure at the former connection point is the latter connection. Higher than the pressure at the point. For this reason, a part of the feed water flowing in the feed water pipe 11 upstream from the valve 36 flows into the graphene tank 26 through the feed water supply pipe 28A. Water containing graphene in the graphene tank 26 is injected into the water supply pipe 11 through the injection pipe 28B. The water supply into which graphene is injected is supplied into the RPV 2 through the water supply pipe 11. In this way, graphene is injected into the reactor water in the RPV2. The opening degree of the valve 36 is adjusted so that the graphene concentration of the feed water becomes 0.1 ppb by injecting the graphene from the injection pipe 28B. Consequently, as with Example 1, the components of the BWR plant, on the surface in contact with the reactor water, the graphene in the range of 0.01μg / cm ² ~10μg / cm ² is deposited. After the predetermined amount of graphene is injected, the graphene injection is stopped (step S4).

  In the present embodiment, each effect produced in the first embodiment can be obtained. Furthermore, in this embodiment, the graphene injection device 25A that does not include the injection pump 27 is used, so that the graphene injection device can be made compact.

  The graphene injection device 25 used in the first embodiment and the graphene injection device 25A used in the second embodiment may be connected to the purification system pipe 17 downstream of the reactor water purification device 21.

  The method for suppressing stress corrosion cracking of each nuclear plant component in Examples 1 and 2 may be applied to a pressurized water nuclear plant. When applied to a pressurized water nuclear power plant (PWR plant), each of the graphene injectors 25 and 25A is connected to a reactor pressure vessel containing a core and a steam generator instead of a feed water pipe, and is heated in the core. It is connected to the primary cooling system piping that guides the reactor water to the steam generator. Graphene is injected into the reactor water flowing through the primary cooling system piping from the graphene injection device 25 or 25A, and the injected graphene is a reactor pressure vessel, a primary cooling system piping, a steam generator, and a core that are components of the PWR plant It adheres to the inner surface of the fuel assembly in contact with the reactor water. In the PWR plant, graphene is injected into the reactor water when the reactor power is increased. The primary cooling system piping is a piping system connected to the reactor pressure vessel.

  DESCRIPTION OF SYMBOLS 1 ... Reactor, 2 ... Reactor pressure vessel, 3 ... Core, 6 ... Recirculation system piping, 8 ... Main steam piping, 10 ... Condenser, 11 ... Feed water piping, 17 ... Purification system piping, 21 ... Reactor water Purification device, 25, 25A ... graphene injection device, 26 ... graphene tank, 27 ... injection pump, 28, 28B ... injection pipe, 28A ... water supply pipe.

Claims (4)

During operation of a nuclear power plant, graphene is injected into reactor water, the reactor water containing graphene is brought into contact with a surface of the nuclear plant component that contacts the reactor water, and the graphene contained in the reactor water is A method for suppressing stress corrosion cracking of a nuclear plant component member, wherein 0.01 μg / cm ² or more is adhered to the surface of the component member. The method for stress corrosion cracking of a nuclear plant component according to claim 1, wherein the graphene is adhered to the surface of the component in a range of 0.01 µg / cm ^{2 to} 10 µg / cm ² .   The method for suppressing stress corrosion cracking of a nuclear plant component according to claim 1 or 2, wherein the graphene is injected into the reactor water when the nuclear power plant is started.   When chemical decontamination is performed on the component, the graphene is injected into the reactor water after the chemical decontamination, and the graphene adheres to the surface of the component where the chemical decontamination is performed The method for suppressing stress corrosion cracking of a nuclear plant component according to any one of claims 1 to 3, wherein:

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