Chemical injection piping and method for manufacturing the same

Abstract

To provide a chemical injection piping capable of suppressing the thermal decomposition of an injected metal compound and the reduction of metal ions when injecting a chemical to the system piping of a plant to prevent passage resistance due to the excess deposition of metal from increasing and a passage from being blocked, and a method for manufacturing the same.SOLUTION: A chemical injection piping 100 connected to the system pipe 1 of a plant includes: a body part 3 constituting the main body of the piping; a first coating 4 provided in a part or all of the inner surface of the body part 3; and a second coating 5 provided on the first coating 4. The first coating 4 is formed of a material having a thermal conductivity smaller than that of the body part 3; and the second coating 5 is formed of a material having an electrical resistivity larger than that of the body part 3. A method for manufacturing the chemical injection piping comprises the steps of: forming the first coating 4 with the material having a thermal conductivity smaller than that of the body part 3 in a part or all of the inner surface of the body part 3; and forming the second coating 5 with the material having an electrical resistivity larger than body part 3 on the first coating 4.SELECTED DRAWING: Figure 1B

Description

[Technical Field]

[0001] The present invention relates to a chemical injection pipe used for injecting precious metals into reactor cooling water, and a method for manufacturing the chemical injection pipe. [Background technology]

[0002] In a boiling water reactor (BWR), it is necessary to suppress stress corrosion cracking (SCC) in the reactor internals installed inside the pressure vessel and in the system piping connected to the pressure vessel. The reactor internals and system piping are made of stainless steel, low-alloy steel, carbon steel, nickel-based alloys, etc. Although these materials have excellent corrosion resistance, there is a risk of SCC initiation and progression due to the combination of mechanical and environmental factors.

[0003] When a nuclear reactor is operating, high-temperature, high-pressure cooling water comes into contact with reactor internal structures and system piping. The cooling water contains oxygen and hydrogen peroxide, which are produced by radiolysis of water. It is known that the higher the oxygen and hydrogen peroxide concentrations in the cooling water, the more pronounced the occurrence and progression of SCC. Reducing the oxygen and hydrogen peroxide concentrations in the cooling water alleviates environmental factors, and is therefore known to be effective in suppressing SCC.

[0004] Measures to suppress SCC include hydrogen injection and precious metal injection. Hydrogen injection is a technology in which hydrogen gas is injected into the cooling water, causing a recombination reaction between oxygen and hydrogen peroxide and hydrogen, turning it back into water. Precious metal injection is a technology in which a solution of a precious metal compound is injected into the cooling water, causing the precious metal to adhere to the surface of materials that come into contact with the cooling water. Precious metals such as platinum, rhodium, and palladium catalyze the recombination reaction.

[0005] Patent Document 1 describes a method for suppressing the initiation and progression of SCC. In this method, a solution or suspension of a compound containing a catalytic metal is injected into the reactor water. Examples of compounds containing catalytic metals include palladium acetylacetonate and palladium nitrate.

[0006] In BWRs, precious metal injection may be performed while the reactor is in operation. For precious metal injection during operation, a low-concentration platinum compound solution is used. The platinum compound used is sodium hexahydroxoplatinate (Na2Pt(OH)6). The platinum compound solution is injected into the cooling water through chemical injection piping. The chemical injection piping is connected to the system piping of the feedwater system.

[0007] A solution of precious metal compounds is injected into the cooling water through the chemical injection pipe, and then supplied to the pressure vessel, etc. together with the cooling water. The solution of precious metal compounds is turned into a colloidal solution of oxides by irradiating it with gamma rays, and the precious metals are deposited on the surfaces of the reactor internals and system piping. When the precious metals are injected, hydrogen is also injected. Hydrogen gas is injected into the cooling water upstream of the chemical injection pipe, and then supplied to the pressure vessel, etc. together with the cooling water.

[0008] When hydrogen is injected, oxygen and hydrogen peroxide are consumed by recombination reactions inside the pressure vessel and in the system piping. As the oxygen concentration and hydrogen peroxide concentration in the cooling water decrease, intergranular corrosion becomes less likely to progress, and SCC of the reactor internal structures and system piping is suppressed. When precious metals are injected, the recombination reaction is catalyzed, so SCC can be suppressed with a small amount of hydrogen. Generally, 0.1 μg / cm of precious metals are injected onto the surface of the material. 2 If the platinum content is above this level, a sufficient suppression effect can be obtained.

[0009] It is known that when precious metals are injected, excessive reduction and precipitation of the precious metals occurs near the outlet of the chemical injection pipe. If the cooling water into which a solution of precious metal compounds has been injected is at a high temperature, thermal decomposition of the precious metal compounds occurs. Furthermore, if the cooling water has a high hydrogen concentration, reduction of the precious metal ions occurs. The area near the outlet of the chemical injection pipe is prone to precious metal precipitation because the cooling water is prone to high temperatures and high hydrogen concentrations. If unintended excessive reduction and precipitation of precious metals occurs, there is a problem of a decrease in the amount of precious metal supplied to pressure vessels, etc. Furthermore, there are problems such as increased flow resistance in the chemical injection pipe and blockage of the chemical injection pipe.

[0010] Patent Document 2 describes a technique in which a precious metal injection device is installed in the piping between the outlet of a reactor coolant purification device and a heat exchanger. It is said that the temperature of the reactor water at the injection point of the precious metal is desirably 30 to 70°C. Since the temperature is low between the outlet of the reactor coolant purification device and the heat exchanger, it is said that the risk of precious metal deposition and piping blockage is reduced.

[0011] Patent Document 3 describes a technology for injecting a precious metal compound into water in a system where the concentration of oxygen or hydrogen peroxide exceeds the equivalent of the concentration of hydrogen that chemically reacts to form water. Injecting an aqueous solution of sodium hexahydroxoplatinate into such water is said to reduce the amount of platinum compound deposition that occurs due to reduction reactions and thermal decomposition reactions caused by hydrogen in the water supply system piping and in the vicinity of the joint between the chemical injection piping and the system piping. [Prior art documents] [Patent documents]

[0012] [Patent Document 1] Japanese Patent Application Publication No. 7-311296 [Patent Document 2] Japanese Patent Application Laid-Open No. 2017-181351 [Patent Document 3] Japanese Patent Application Laid-Open No. 2017-181350 Summary of the Invention [Problem to be solved by the invention]

[0013] Chemical injection piping is used for applications such as injecting precious metals into liquids flowing through plant system piping, such as injecting precious metals in nuclear power plants. The chemical injection piping has a relatively small diameter and is connected to a larger system piping. This type of chemical injection piping has a problem of excessive reduction and precipitation of metals near the outlet connected to the system piping.

[0014] Excessive reduction and precipitation of metals occurs in high-temperature environments where metal compounds thermally decompose, or in reducing environments where metal ions are easily reduced. When unintended excessive reduction and precipitation of metals occurs near the outlet of the chemical injection pipe, problems such as a decrease in the supply amount of metal compounds, an increase in flow resistance of the chemical injection pipe, and blockage of the chemical injection pipe occur.

[0015] In the case of a nuclear power plant, the temperature rise near the outlet of the chemical injection pipe occurs when high-temperature cooling water flows into the chemical injection pipe from the system piping. The inflow of high-temperature cooling water can be prevented by changing the installation location of the chemical injection pipe. As in Patent Document 2, installing the chemical injection pipe in a low-temperature location can prevent the temperature rise near the outlet of the chemical injection pipe. However, even if the installation location of the chemical injection pipe is changed, there is still the problem of heat conduction through the pipe itself.

[0016] On the other hand, in the case of nuclear power plants, the reducing property near the outlet of the chemical injection pipe increases due to the hydrogen injection carried out upstream of the chemical injection pipe. When the chemical injection pipe is used for the injection of precious metals, the reducing property problem is difficult to prevent by simply changing the installation location of the chemical injection pipe, because the hydrogen injection is carried out in conjunction with the chemical injection pipe. Another countermeasure is to increase the flow rate of the chemical injection pipe. However, there is a limit to the effectiveness of increasing the flow rate.

[0017] When injecting precious metals in a nuclear power plant, the flow rate of the chemical injection pipe is generally on the order of several cm / s. In contrast, the flow rate of the system pipe of the feedwater system is on the order of several m / s. Because the difference in flow rates is extremely large, even if the flow rate of the chemical injection pipe is increased, the cooling water with a high hydrogen concentration flowing through the system pipe will enter the chemical injection pipe as a vortex. Furthermore, even if oxygen or hydrogen peroxide is injected as in Patent Document 3, it is difficult to suppress the reducing environment near the outlet of the chemical injection pipe. From the perspective of suppressing SCC, it is also not appropriate to stop hydrogen injection when injecting precious metals.

[0018] Therefore, an object of the present invention is to provide a chemical injection pipe and a method for manufacturing the chemical injection pipe that suppresses thermal decomposition of injected metal compounds and reduction of metal ions when injecting a chemical into a plant's system piping, thereby preventing an increase in flow path resistance and flow path blockage due to excessive metal precipitation. [Means for solving the problem]

[0019] In order to solve the above problems, the chemical injection pipe according to the present invention comprises: nuclear power Connected to the plant's system piping It is used to inject precious metals into reactor cooling water. a chemical liquid injection pipe comprising: a main body constituting a main body of the chemical liquid injection pipe; a first coating provided on a part or all of an inner surface of the main body; and a second coating provided on the first coating, wherein the first coating is formed of a material having a lower thermal conductivity than the main body; The thermal conductivity is 10W / m·K or less and the thickness is 1mm or more. The second coating is made of a material having a higher electrical resistivity than the main body.

[0020] Further, a method for manufacturing a chemical injection pipe according to the present invention includes the steps of: nuclear power Connected to the plant's system piping It is used to inject precious metals into reactor cooling water. The method for manufacturing a chemical liquid injection pipe includes the steps of: forming a first coating on a part or all of an inner surface of a main body constituting the main body of the chemical liquid injection pipe, the first coating being made of a material having a lower thermal conductivity than the main body; and forming a second coating on the first coating being made of a material having a higher electrical resistivity than the main body, the first coating being The thermal conductivity is 10W / m·K or less and the thickness is 1mm or more. The main body is formed by at least one of a thermal oxidation method, a physical vapor deposition method, a chemical vapor deposition method, a thermal spraying method, a sol-gel method, a metal organic decomposition method, and a coating method, and the second coating is formed by at least one of a physical vapor deposition method, a chemical vapor deposition method, a thermal spraying method, a sol-gel method, a metal organic decomposition method, and a coating method. [Effects of the Invention]

[0021] According to the present invention, it is possible to provide a chemical injection pipe and a method for manufacturing the chemical injection pipe that suppresses thermal decomposition of injected metal compounds and reduction of metal ions when injecting a chemical into a plant's system piping, thereby preventing an increase in flow path resistance and flow path blockage due to excessive metal precipitation. [Brief explanation of the drawings]

[0022] [Figure 1A] FIG. 10 is a cross-sectional view showing the structure of a conventional chemical injection pipe. [Figure 1B] 1 is a cross-sectional view showing a structure of a chemical liquid injection pipe according to an embodiment of the present invention. [Figure 2] FIG. 10 is a diagram showing heat transfer paths around the chemical injection pipe. [Figure 3] FIG. 10 is a diagram showing the relationship between the distance from the outer surface of the chemical injection piping main pipe and the temperature. [Figure 4] FIG. 10 is a diagram showing the relationship between the thermal conductivity of a coating provided on a chemical injection pipe and the temperature of the inner surface of the chemical injection pipe. [Figure 5] FIG. 10 is a diagram showing the relationship between the distance from the outer surface of the chemical injection piping main pipe and the temperature. [Figure 6] FIG. 10 is a diagram showing the relationship between the temperature inside the chemical injection pipe and the rate at which platinum adheres to the inner surface of the chemical injection pipe. [Figure 7] FIG. 10 is a diagram showing the relationship between the distance from the outer surface of the chemical injection piping main pipe and the temperature. [Figure 8] 1A to 1C are diagrams illustrating an example of a method for installing chemical liquid injection piping according to an embodiment of the present invention. [Figure 9] 1A to 1C are diagrams illustrating an example of a method for installing chemical liquid injection piping according to an embodiment of the present invention. [Figure 10] 1A to 1C are diagrams illustrating an example of a method for installing chemical liquid injection piping according to an embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0023] Hereinafter, a chemical liquid injection pipe and a method for manufacturing the chemical liquid injection pipe according to one embodiment of the present invention will be described. Note that the same reference numerals are used to designate common components in the following figures, and redundant explanations will be omitted. In each figure, the outline arrow indicates the direction of liquid flow.

[0024] The chemical injection piping according to this embodiment is a piping for chemical injection that is connected to the system piping of a plant. The chemical injection piping is used to inject a solution of a metal compound into a liquid flowing through the system piping of the plant. In the following explanation, the chemical injection piping and a method for manufacturing the chemical injection piping will be described using an example in which a precious metal is injected into reactor cooling water flowing through the system piping of a nuclear power plant.

[0025] FIG. 1A is a cross-sectional view showing the structure of a conventional chemical injection pipe. As shown in FIG. 1A, conventional chemical injection piping 3 is inserted into chemical injection piping header 2, which is connected to the middle of system piping 1 of a plant. Chemical injection piping header 2 is joined to system piping 1 by welding or the like. Chemical injection piping 3 is used to inject a chemical, which is a solution of a metal compound, into the liquid flowing through system piping 1. Conventional chemical injection piping 3 is a single-layered pipe made of metal.

[0026] In a nuclear power plant, precious metals are injected through chemical injection piping 3. Examples of system piping 1 include piping for a feedwater system and piping for a reactor coolant purification system. The chemical injection piping 3 injects a solution of a precious metal compound into the cooling water flowing through the system piping 1 while the nuclear power plant is in operation. An example of the solution of a precious metal compound is an aqueous solution of sodium hexahydroxoplatinate.

[0027] A solution of precious metal compounds is injected into the cooling water and supplied to the inside of the reactor pressure vessel, etc. The solution of precious metal compounds becomes a colloidal solution of oxides when irradiated with gamma rays, and the precious metals are deposited on the surfaces of reactor internal structures and system piping. Precious metals such as platinum, rhodium, and palladium catalyze the recombination reaction between oxygen and hydrogen peroxide produced by radiolysis of water and the injected hydrogen.

[0028] When noble metals are injected, the recombination reaction with the injected hydrogen reduces the oxygen and hydrogen peroxide concentrations in the coolant. Factors involved in the occurrence of stress corrosion cracking (SCC) include mechanical factors such as tensile stress and residual stress applied to the material, environmental factors to which the material is exposed, and material factors such as the chemical composition of the material. Oxygen and hydrogen peroxide are environmental factors that increase the susceptibility to intergranular corrosion. Therefore, combining hydrogen injection with noble metal injection can suppress SCC in reactor internal structures and piping.

[0029] FIG. 1B is a cross-sectional view showing the structure of a chemical liquid injection pipe according to an embodiment of the present invention. 1B, chemical liquid injection piping 100 according to this embodiment is inserted into chemical liquid injection piping header 2 connected to an intermediate portion of system piping 1 of a plant, similar to conventional chemical liquid injection piping 3. Chemical liquid injection piping 100 is used to inject a chemical liquid into a liquid flowing through system piping 1, but unlike conventional chemical liquid injection piping 3, it is a pipe with a multi-layer structure.

[0030] The chemical solution injection piping 100 according to this embodiment includes a main body 3 that constitutes the main body of the piping, a first coating 4 provided on part or all of the inner surface of the main body 3, and a second coating 5 provided on the first coating 4. The main body 3 is formed in a cylindrical shape or the like. The first coating 4 and the second coating 5 coat the entire inner circumferential surface of the main body 3, at least on the tip side of the main body 3 connected to the system piping 1.

[0031] The main body 3 is made of a metal for piping, similar to conventional chemical injection piping 3. On the other hand, the first coating 4 is made of a material with a lower thermal conductivity than the main body 3. The second coating 5 is made of a material with a higher electrical resistivity than the main body 3. By forming the first coating 4 and the second coating 5, it is possible to suppress unintended excessive reduction and deposition of metal near the outlet of the chemical injection piping 100.

[0032] 2 is a diagram showing the heat transfer path around the chemical liquid injection pipe. The black arrows in Fig. 2 indicate the heat transfer path from the liquid flowing through the system pipe 1 to the liquid flowing through the chemical liquid injection pipe 3. As shown in Figure 2, when a high-temperature liquid flows through system piping 1, heat is transferred from the liquid flowing through system piping 1 to the liquid flowing through chemical injection piping 3. The liquid flowing through chemical injection piping 3 is subject to not only convective heat transfer from system piping 1 but also heat conduction via the piping.

[0033] In a nuclear power plant, high-temperature, high-pressure cooling water exceeding 200°C flows through the feedwater system piping and purification system piping connected to the reactor pressure vessel in order to improve the thermal efficiency of the reactor core. When high-temperature liquid flows through system piping 1, the heat of the liquid flowing through system piping 1 is mainly transferred to the vicinity of the outlet of chemical injection piping 3. Therefore, the chemical liquid injected through chemical injection piping 3 is heated to a high temperature near the outlet of chemical injection piping 3.

[0034] Metal compounds contained in chemical solutions may undergo thermal decomposition when exposed to high temperatures. For example, sodium hexahydroxoplatinate, which is used in the injection of precious metals, undergoes thermal decomposition at approximately 180°C. When metal compounds undergo thermal decomposition, unstable metal compounds and metal ions are produced. Unstable metal compounds and metal ions are components that are easily reduced to metals.

[0035] Furthermore, a highly reducing liquid may flow through the system piping 1. In the case of a nuclear power plant, hydrogen is injected into the cooling water flowing through the system piping 1 on the upstream side of the system piping 1 to which the chemical injection piping 3 is connected. When hydrogen is injected, the dissolved hydrogen concentration in the cooling water flowing through the system piping 1 increases, and the reducing property increases.

[0036] When a highly reducing liquid is flowed through the system piping 1, unstable metal compounds and metal ions generated in the chemical solution by thermal decomposition cause excessive reduction and precipitation of metals. Excessive reduction and precipitation mainly occurs near the outlet of the chemical solution injection piping 3, which is a high-temperature and reducing environment. When excessive metals are precipitated near the outlet of the chemical solution injection piping 3, problems arise such as a decrease in the supply amount of metal compounds, an increase in the flow path resistance of the chemical solution injection piping 3, and clogging of the chemical solution injection piping 3.

[0037] Even if the flow rate of the chemical liquid is increased near the outlet of the chemical liquid injection piping 3, it is difficult to prevent the accumulation of unstable metal compounds, metal ions, etc., and the intrusion of the liquid flowing through the system piping 1. This is because the pipe diameters of the system piping 1 and the chemical liquid injection piping 3 are significantly different, resulting in a large difference in flow rate. Because of the large difference in flow rate, the liquid flowing through the system piping 1 easily intrudes into the chemical liquid injection piping 3 as a vortex.

[0038] Therefore, in order to suppress excessive reduction and precipitation of metal near the outlet of chemical injection piping, a first coating 4 formed from a material with a lower thermal conductivity than the main body 3 and a second coating 5 formed from a material with a higher electrical resistivity than the main body 3 are effective.

[0039] Figure 3 shows the relationship between the distance from the outer surface of the chemical injection piping header and the temperature. In Figure 3, the horizontal axis represents the distance [mm] from the outer surface of the chemical injection piping header to the inside of the chemical injection piping, and the vertical axis represents the temperature [°C] of the chemical injection piping header and the chemical injection piping. The plots of ● and ▲ show the results of theoretical heat transfer calculations.

[0040] The plots marked with ● show the results when the chemical injection piping is composed of only the main body, as in conventional chemical injection piping. The plots marked with ▲ show the results when the chemical injection piping is composed of the main body and a coating with low thermal conductivity. Carbon steel, which has a thermal conductivity of approximately 40 W / m·K, was assumed to be used for the chemical injection piping header and the main body of the chemical injection piping. The temperature of the outer surface of the chemical injection piping header was assumed to be 215°C. This is because the temperature of the cooling water in the feedwater system is approximately 215°C when a BWR is operating.

[0041] As shown in Figure 3, if the chemical injection piping consists of only the main body, when a liquid at approximately 215°C flows through the system piping, the temperature of the inner surface of the chemical injection piping will reach approximately 205°C. At such high temperatures, when a solution of metal compounds is injected through the chemical injection piping, the metal compounds will thermally decompose. There is a risk that unstable metal compounds and metal ions produced by thermal decomposition will be reduced and precipitated in excess near the outlet of the chemical injection piping.

[0042] In order to prevent the thermal decomposition of the metal compounds injected through the chemical injection pipe, it is thought to be effective to provide the chemical injection pipe with a structure with low thermal conductivity. For example, as shown in Figure 3, if the inner surface of the main body of the chemical injection pipe is coated with a 1 mm thick film of zirconium oxide, which has a thermal conductivity of approximately 30 W / m K, the temperature of the inner surface of the chemical injection pipe can be reduced to below 180°C.

[0043] Figure 4 shows the relationship between the thermal conductivity of the coating applied to the chemical injection pipe and the temperature of the inner surface of the chemical injection pipe. In Figure 4, the horizontal axis represents the thermal conductivity [W / m K] of the coating applied to the chemical injection pipe, and the vertical axis represents the temperature [°C] of the inner surface of the chemical injection pipe. The curves show the results of theoretical heat transfer calculations. The coating thickness is fixed at 1 mm, and the thermal conductivity of the coating is varied.

[0044] As shown in Figure 4, when the coating applied to the inside of the chemical injection piping is 1 mm thick and has a thermal conductivity of approximately 3 W / m K or less, the temperature of the inner surface of the chemical injection piping falls below approximately 180°C. Because the temperature of the inner surface of the chemical injection piping falls below the thermal decomposition temperature of sodium hexahydroxoplatinate, excessive generation of platinum ions and other substances near the outlet of the chemical injection piping can be prevented.

[0045] According to the results shown in Figure 4, the thermal conductivity of the coating applied to the inside of the chemical injection pipe should preferably be 10 W / m K or less, taking into account the thermal conductivity of the main body of the chemical injection pipe and the actual thickness of the coating.

[0046] Figure 5 shows the relationship between temperature and distance from the outer surface of the chemical injection piping header. In Figure 5, the horizontal axis represents the distance [mm] from the outer surface of the chemical injection piping header to the interior of the chemical injection piping, and the vertical axis represents the temperature [°C] of the chemical injection piping header and chemical injection piping. The dotted lines and the dotted lines represent the results of theoretical heat transfer calculations.

[0047] The dotted circles represent the results when the chemical injection piping is composed of only the main body, as in conventional chemical injection piping. The dashed lines represent the results when the chemical injection piping is composed of the main body and coating. Carbon steel, which has a thermal conductivity of approximately 40 W / m·K, was assumed for the chemical injection piping header pipe and the main body of the chemical injection piping. The thermal conductivity of the coating was assumed to be 20 W / m·K.

[0048] As shown in Figure 5, when a coating with a thermal conductivity of 20 W / m K is formed on the inner surface of the main body of the chemical injection piping, if the coating thickness is approximately 10 mm or more, the temperature of the inner surface of the chemical injection piping will fall below approximately 180°C. Because the temperature of the inner surface of the chemical injection piping will be lower than the thermal decomposition temperature of sodium hexahydroxoplatinate, it is possible to prevent the excessive generation of platinum ions and other substances near the outlet of the chemical injection piping.

[0049] According to the results shown in Figure 5, the heat transfer rate (heat flux) per unit area of ​​the coating provided inside the chemical injection pipe is 700 kW / m, taking into account the temperature difference between the liquid flowing through the system pipe and the liquid flowing through the chemical injection pipe, as well as the heat conduction and heat transfer of each part. 2 It is preferable to suppress the temperature to below this value. This is because the temperature of the liquid flowing through the system piping is expected to be 215°C, and the temperature of the liquid flowing through the chemical injection piping is expected to be 25°C.

[0050] Figure 6 shows the relationship between the temperature inside the chemical injection piping and the rate at which platinum deposits on the inner surface of the chemical injection piping. In Figure 6, the horizontal axis represents the temperature [°C] of the inner surface of the chemical injection piping, and the vertical axis represents the rate [m / day] at which platinum deposits on the inner surface of the chemical injection piping when an aqueous solution of sodium hexahydroxoplatinate is injected. The dots represent the results of a simulation test that simulated a liquid flowing through the chemical injection piping.

[0051] The platinum deposition rate was determined by measuring the fluid pressure in a simulation test simulating the liquid flowing through the chemical injection piping and converting the change in fluid pressure into the platinum deposition rate. The main body of the chemical injection piping was made of carbon steel with a thermal conductivity of approximately 40 W / m K. The liquid flowing through the chemical injection piping was an aqueous solution of sodium hexahydroxoplatinate with a dissolved hydrogen concentration adjusted to 160 ppb.

[0052] As shown in Figure 6, a certain rate of platinum deposition was observed even when the temperature of the inner surface of the chemical injection piping was below approximately 180°C. Even if the temperature of the inner surface of the chemical injection piping was lower than the thermal decomposition temperature of sodium hexahydroxoplatinate, it is estimated that reduction and precipitation of platinum would occur if the dissolved hydrogen concentration was high.

[0053] In order to prevent the reduction of unstable metal compounds and metal ions generated in the chemical solution by thermal decomposition, it is considered effective to provide the chemical solution injection pipe with a structure with high electrical resistivity. Unstable metal compounds and metal ions generated by thermal decomposition are reduced by electron exchange with reducing chemical species such as hydrogen. If the inner surface of the chemical solution injection pipe is insulated, electron donation to reducing chemical species such as hydrogen can be suppressed, and therefore reduction and precipitation of metals can be prevented.

[0054] In general, in nuclear power plants, system piping connected to pressure vessels and chemical injection piping used for injecting precious metals are made of carbon steel. When high-temperature cooling water or the like flows through carbon steel piping, an oxide film forms on the inner surface. The oxide film is formed of hematite (Fe2O3), magnetite (Fe3O4), etc. depending on the dissolved oxygen concentration, etc. It is estimated that an oxide film was also formed on the inner surface of the piping in the simulation test shown in Figure 6.

[0055] According to the results shown in Figure 6, the volume resistivity of the coating on the inside of the chemical injection pipe is 10 6It can be said that a resistance of Ω·cm or more is preferable.

[0056] Figure 7 shows the relationship between temperature and distance from the outer surface of the chemical injection piping header. In Figure 7, the horizontal axis represents the distance [mm] from the outer surface of the chemical injection piping header to the inside of the chemical injection piping, and the vertical axis represents the temperature [°C] of the chemical injection piping header and the chemical injection piping. The plots of ■ and ▲ show the results of theoretical heat transfer calculations.

[0057] The plot ■ shows the results when the main body of the chemical injection piping is made of zircaloy. The plot ▲ shows the results when the main body of the chemical injection piping is made of carbon steel. For zircaloy, a material with a thermal conductivity of approximately 14 W / m·K was assumed. For carbon steel, a material with a thermal conductivity of approximately 40 W / m·K was assumed.

[0058] As shown in Figure 7, when the main body of the chemical injection piping is made of zircaloy, the temperature of the main body of the chemical injection piping and the temperature of the coating can be significantly reduced compared to when it is made of carbon steel. From the perspective of preventing thermal decomposition of the metal compound injected by the chemical injection piping, it is preferable that the main body of the chemical injection piping itself has low thermal conductivity.

[0059] In the chemical solution injection pipe 100 according to this embodiment, the main body 3 can be made of at least one of carbon steel, stainless steel, zircaloy, low-alloy steel, and nickel-based alloy. As long as at least one of these materials is used, the main body 3 may be formed as a single pipe or a multiple pipe.

[0060] Carbon steel can improve the cost performance of the main body 3. Stainless steel can improve the corrosion resistance of the main body 3. Zircaloy can improve the thermal insulation of the main body 3. Zircaloy has a thermal conductivity of approximately 14 W / m·K and is a material with superior thermal insulation properties compared to carbon steel and the like. Low alloy steel is an alloy steel with a total of alloy elements of 5 mass % or less. Low alloy steel and nickel-based alloys can improve the corrosion resistance, high-temperature strength, etc. of the main body 3.

[0061] The inner diameter, outer diameter, length, shape, etc. of the main body 3 can be set to any suitable conditions. Typically, the inner diameter of the system piping 1 is about several tens of centimeters. The inner diameter of the main body 3 can be set to about 1 to 3 cm. There is a large difference in flow rate between the system piping 1 and the chemical injection piping 100, which makes it easy for vortex currents to enter the inside of the chemical injection piping 100. However, the first coating 4 and the second coating 5 can prevent excessive reduction and precipitation of metal.

[0062] The first coating 4 can be formed of any suitable material to achieve an appropriate thermal conductivity, as long as the material has a lower thermal conductivity than the main body 3. The first coating 4 is preferably provided as an independent coating that is different from the second coating 5. The first coating 4 can be provided with any suitable relative density and packing ratio.

[0063] First coating 4 preferably has a thermal conductivity of 10 W / m·K or less. A thermal conductivity of 10 W / m·K or less can sufficiently prevent the temperature on the inner surface of the chemical injection piping from rising too high when the coating has a thickness of 1 mm or more. Since the thermal decomposition of the metal compound injected by chemical injection piping 100 is suppressed, an increase in flow path resistance and flow path blockage due to excessive reduction and precipitation of metal near the outlet of chemical injection piping 100 can be prevented.

[0064] The first coating 4 can be formed to contain at least one of zirconium oxide (zirconia: ZrO2), yttria-stabilized zirconia (YSZ), partially stabilized zirconia (PSZ), titanium oxide (titania: TiO2), and aluminum titanate (TiO2·Al2O3). These materials can provide high thermal insulation with a small film thickness.

[0065] The first coating 4 can be provided to any appropriate thickness as long as heat insulation is ensured between the main body 3 and the chemical solution. From the viewpoint of suppressing thermal decomposition of the metal compound injected through the chemical solution injection pipe 100, the first coating 4 is preferably provided to a thickness of 1 mm or more.

[0066] The second coating 5 can be formed of any suitable material so as to have an appropriate electrical resistivity, as long as the material has a higher electrical resistivity than the main body 3. The second coating 5 is preferably provided as an independent coating that is different from the first coating 4. The second coating 5 can be provided with any suitable relative density and packing rate, but from the perspective of ensuring electrical insulation, it is preferable that the second coating 5 be provided with a higher relative density and packing rate than the first coating 4.

[0067] The second coating 5 has a volume resistivity of 10 6 It is preferable that the volume resistivity is 10 Ω·cm or more. 6 A resistivity of Ω·cm or more can sufficiently suppress electron transfer on the inner surface of the chemical injection pipe, compared to conventional carbon steel pipes that develop an oxide film on their inner surface under operating conditions. Since the reduction of unstable metal compounds and metal ions generated in the chemical solution by thermal decomposition is suppressed, an increase in flow path resistance and flow path blockage due to excessive reduction and precipitation of metals near the outlet of the chemical injection pipe 100 can be prevented.

[0068] The second coating 5 can be formed to contain at least one of aluminum oxide (alumina: Al2O3), chromium oxide (chromia: Cr2O3), zirconium oxide (zirconia: ZrO2), yttria-stabilized zirconia (YSZ), partially stabilized zirconia (PSZ), and aluminum titanate (TiO2·Al2O3). These materials can provide high electrical insulation with a small film thickness.

[0069] The second coating 5 may be provided to any appropriate thickness as long as electrical insulation is ensured between the main body 3 and the chemical solution. From the viewpoint of suppressing reduction of unstable metal compounds and metal ions generated in the chemical solution by thermal decomposition, the second coating 5 is preferably provided to a thickness of 0.5 μm or more.

[0070] The first coating 4 and the second coating 5 are preferably provided at least on the inner surface of the main body 3, at the tip end side connected to the system piping 1. This is because a high heat flux enters the tip end side of the chemical injection piping 100 due to convective heat transfer from the liquid flowing through the system piping 1 and thermal conduction via the system piping 1 and the chemical injection piping header pipe 2. Providing the first coating 4 and the second coating 5 on the tip end side of the chemical injection piping 100 is highly effective in suppressing excessive reduction and precipitation of metal.

[0071] It is more preferable that the first coating 4 and the second coating 5 are provided on the inner surface of the main body 3 in a region extending from the tip connected to the system piping 1 in the longitudinal direction of the main body 3 to at least 10 cm. In the region near the outlet of the chemical injection piping 100, extending approximately 30 cm from the tip, the liquid flowing through the system piping 1 may enter as a vortex. Providing the first coating 4 and the second coating 5 in a region extending up to 10 cm from the tip of the chemical injection piping 100 is highly effective in suppressing an increase in temperature and high reduction caused by the vortex.

[0072] The chemical liquid injection pipe 100 according to this embodiment can be manufactured using an appropriate film forming method using the main body portion that constitutes the main body of the pipe as the material.

[0073] The manufacturing method of the chemical solution injection pipe according to this embodiment includes the steps of forming a first coating on part or all of the inner surface of the main body portion constituting the main body of the chemical solution injection pipe, using a material having a lower thermal conductivity than the main body portion, and forming a second coating on the first coating formed on part or all of the inner surface of the main body portion, using a material having a higher electrical resistivity than the main body portion.

[0074] The first coating can be formed using at least one of a thermal oxidation method in which the main body is heat-treated, a physical vapor deposition (PVD) method, a chemical vapor deposition (CVD) method, a thermal spraying method, a sol-gel method, a metal organic decomposition (MOD) method, and a coating method.

[0075] The second coating can be formed by at least one of physical vapor deposition (PVD), chemical vapor deposition (CVD), thermal spraying, sol-gel, metal organic decomposition (MOD), and coating. The method for forming the second coating may be the same as or different from the method for forming the first coating.

[0076] The thermal oxidation method can be a method of thermally oxidizing the main body that constitutes the main body of the chemical injection pipe by heat treatment. The heat treatment can be performed in an air atmosphere or an oxidizing gas atmosphere. When a main body made of an appropriate material is thermally oxidized, an inorganic oxide coating with low thermal conductivity can be formed on the inner surface of the main body. For example, when a main body made of zircaloy is thermally oxidized, a zirconium oxide coating can be formed. The thermal oxidation method allows the formation of a first coating with low thermal conductivity through simple operations without the need to prepare a separate coating material.

[0077] Physical vapor deposition (PVD) methods include vacuum deposition using resistance heating, electron beam heating, and high-frequency induction heating, as well as reactive sputtering. Chemical vapor deposition (CVD) methods include thermal CVD, plasma CVD, and metal organic CVD. PVD and CVD can form precise coatings with high adhesion.

[0078] The thermal spraying method may be a flame thermal spraying method, a plasma thermal spraying method, an arc thermal spraying method, a cold spraying method, etc. Since the thermal spraying method does not limit the atmosphere, a coating with high adhesion can be easily formed on-site.

[0079] The sol-gel method can be, for example, a method of carrying out hydrolysis and polycondensation reactions using metal alkoxides or the like as raw materials. The organometallic decomposition method (MOD) can be, for example, a method of drying and baking using citrates, carboxylates, oxalates, acetates, or the like as raw materials. The coating method can be a method of applying a liquid or fluid raw material solution and then drying and baking the raw material solution. The sol-gel method, MOD method, and coating method do not limit the atmosphere or piping shape, so coatings can be easily formed on-site. Furthermore, the relative density and packing rate of the coating can be easily adjusted by using additives in combination.

[0080] The step of forming the first coating and the step of forming the second coating may be performed at either the stage before connecting the main body 3 of the chemical liquid injection piping 100 to the system piping 1 or the stage after connecting the main body 3 of the chemical liquid injection piping 100 to the system piping 1. However, from the viewpoint of the workability of the film formation process, it is preferable to perform the steps before connecting the main body 3 of the chemical liquid injection piping 100 to the system piping 1.

[0081] According to the chemical injection piping 100 and the method for manufacturing the chemical injection piping described above, a first coating made of a material with a lower thermal conductivity than the main body and a second coating made of a material with a higher electrical resistivity than the main body are formed on the inner surface of the main body that constitutes the main body of the chemical injection piping. This suppresses thermal decomposition of injected metal compounds and reduction of unstable metal compounds and metal ions produced by thermal decomposition when chemicals are injected into the system piping of a plant. This prevents an increase in flow resistance of the chemical injection piping due to excessive metal precipitation and clogging of the flow path of the chemical injection piping. Furthermore, metal compounds flow more easily toward the system piping and are less likely to become immobilized near the outlet of the chemical injection piping, ensuring a high supply rate to the system piping.

[0082] FIG. 8 is a diagram showing an example of a method for installing chemical liquid injection piping according to an embodiment of the present invention. As shown in FIG. 8, the chemical liquid injection piping 100 according to this embodiment can be installed by being inserted into and fixed to a chemical liquid injection piping main pipe 2 connected to an intermediate portion of a system piping 1.

[0083] The chemical injection piping header 2 is connected as an existing pipe to the middle of the system piping 1 of the plant. The chemical injection piping header 2 can be provided with a connection flange 6 on the opposite side of the system piping 1. The main body 3 of the chemical injection piping 100 can be provided with a flange 7 in advance that can be flange-connected to the flange 6 of the chemical injection piping header 2. The flange 7 is provided in the middle part on the tip side of the main body 3 that corresponds to the length of the chemical injection piping header 2 so as to protrude radially outward.

[0084] When installing chemical liquid injection piping 100, chemical liquid injection piping 100 is first inserted into chemical liquid injection piping header 2, which is connected to the middle section of system piping 1. It is preferable that the outer diameter of chemical liquid injection piping 100 and the inner diameter of chemical liquid injection piping header 2 are set to be similar to each other. A small gap between chemical liquid injection piping header 2 and chemical liquid injection piping 100 makes it easier to prevent liquid leakage.

[0085] Next, packing 8 to prevent liquid leakage is sandwiched between flange 6 of chemical liquid injection piping header 2 and flange 7 of chemical liquid injection piping 100. Then, flange 6 of chemical liquid injection piping header 2 and flange 7 of chemical liquid injection piping 100 are fastened together with bolts 9 and nuts 10. With this flange connection, chemical liquid injection piping 100 can be installed within the system of the plant.

[0086] The first coating 4 and the second coating 5 may be formed either before or after inserting the chemical liquid injection piping 100 into the chemical liquid injection piping main pipe 2. However, from the viewpoint of the workability of the film formation process, it is preferable to form the coatings before inserting the chemical liquid injection piping 100 into the chemical liquid injection piping main pipe 2.

[0087] 8, chemical liquid injection piping 100 is installed to chemical liquid injection piping main pipe 2 by flange connection with packing 8 sandwiched therebetween. However, chemical liquid injection piping 100 may also be installed by a shaft seal method without using a flange connection.

[0088] In the case of the shaft seal system, the chemical injection pipe 100 can be fixed by inserting a sealing material such as packing into the chemical injection pipe main pipe 2. The sealing material is interposed between the chemical injection pipe and the chemical injection pipe main pipe 2. In addition to packing, gaskets, O-rings, sealing materials, etc. may also be used as the sealing material. Examples of packing and sealing materials that can be used include graphite-based gland packing, labyrinth packing, sealing gland, etc.

[0089] 8, it is possible to use the existing chemical injection piping header 2 connected to the system piping 1. This makes it possible to reduce the amount of construction work.

[0090] FIG. 9 is a diagram showing an example of a method for installing chemical liquid injection piping according to an embodiment of the present invention. As shown in FIG. 9, the chemical liquid injection piping 100 according to this embodiment can be installed by being inserted into and fixed to a chemical liquid injection piping main pipe 2 connected to the middle part of a system piping 1.

[0091] The chemical injection piping header 2 is connected as an existing pipe to the middle of the system piping 1 of the plant. The chemical injection piping header 2 may have a threaded portion formed on the outer circumferential surface on the side opposite the system piping 1. The threaded portion is provided so as to be able to screw into the threaded portion of the cap 14. The cap 14 is prepared as a fixture and is attached so as to cover the chemical injection piping header 2.

[0092] When installing chemical liquid injection piping 100, first, chemical liquid injection piping 100 is inserted into chemical liquid injection piping header 2, which is connected to the middle of system piping 1. Next, sealant 12 is sandwiched between chemical liquid injection piping header 2 and chemical liquid injection piping 100 to prevent liquid leakage. Furthermore, follower 13 is inserted between chemical liquid injection piping header 2 and chemical liquid injection piping 100.

[0093] Then, cap 14, which has a hole with a diameter approximately the same as the outer diameter of chemical injection piping 100, is passed through chemical injection piping 100, and the threaded portions of cap 14 and chemical injection piping mother pipe 2 are engaged with each other. This causes sealant 12 and follower 13 to be pushed into and fixed in place on system piping 1. By fixing chemical injection piping 100 with this sealing gland, chemical injection piping 100 can be installed within the plant system.

[0094] The first coating 4 and the second coating 5 may be formed either before or after inserting the chemical liquid injection piping 100 into the chemical liquid injection piping main pipe 2. However, from the viewpoint of the workability of the film formation process, it is preferable to form the coatings before inserting the chemical liquid injection piping 100 into the chemical liquid injection piping main pipe 2.

[0095] 9, it is possible to use the existing chemical injection piping header 2 connected to the system piping 1. This reduces the amount of construction work required. For example, graphite, tetrafluoroethylene, silicone, fluororubber, etc. can be used as the sealant 12.

[0096] FIG. 10 is a diagram showing an example of a method for installing chemical liquid injection piping according to an embodiment of the present invention. As shown in Figure 10, the chemical injection piping 100 of this embodiment can also be installed by forming a first coating 4 and a second coating 5 on the inner surface of the main body 3, which is the chemical injection piping main pipe 2 connected to the middle part of the system piping 1, as the main body 3.

[0097] The first coating 4 and the second coating 5 can be formed on the inner surface of the chemical injection piping header 2 by any suitable film-forming method, such as thermal oxidation, which heat-treats the main body, physical vapor deposition (PVD), chemical vapor deposition (CVD), thermal spraying, sol-gel processing, metal organic decomposition (MOD), or coating. However, when using an existing chemical injection piping header 2 connected to the system piping 1, it is preferable to use a film-forming method that does not affect the water quality of the liquid flowing through the system piping 1. Examples of such film-forming methods include the sol-gel method, MOD, and coating.

[0098] In the sol-gel method, MOD, and coating method, a highly viscous slurry liquid can be used as the raw material for forming the coating. Because the highly viscous liquid is less likely to drip, it can be applied to the inner surface of the chemical injection piping header 2 without mixing with the liquid flowing through the system piping 1. In the case of a nuclear power plant, this prevents the formation of scale and radioactive contamination from scale and impurities, reducing the load on the purification system.

[0099] 10, it is possible to use the existing chemical injection piping header pipe 2 connected to the system piping 1. This reduces the amount of construction work. Since there is no need to insert the main body 3 of the chemical injection piping 100, it is easy to ensure the piping diameter and reduce material costs.

[0100] FIG. 11 is a diagram showing an example of a method for installing chemical liquid injection piping according to an embodiment of the present invention. As shown in FIG. 11, the chemical liquid injection piping 100 according to this embodiment can also be installed by forming an opening in the system piping 1 and inserting and fixing it into the opening.

[0101] An opening can be formed in the system piping 1 of the plant by cutting, such as mechanical cutting or laser cutting, during shutdown of the plant. The main body 3 of the chemical injection piping 100 can be inserted into such an opening and then joined via a weld 11 by welding. Any suitable welding method can be used. In FIG. 11, the weld 11 is provided as a fillet, but various welding methods such as butt welding and socket welding can also be used.

[0102] 11, the chemical injection piping 100 can be connected to the system piping 1 without using the chemical injection piping header 2. Because an existing chemical injection piping header 2 is not used, there is greater freedom in the location of the connection of the chemical injection piping 100. Compared to conventional chemical injection piping 3, the chemical injection piping 100, which has been designed to suppress excessive reduction and deposition of metals, can also be connected to a section of the system piping 1 through which a higher temperature liquid flows or a section of the system piping 1 through which a more reducing liquid flows.

[0103] The chemical injection piping 100 according to this embodiment can be used in various plants where a solution of a metal compound is injected into system piping. Examples of such plants include nuclear power plants, thermal power plants, chemical plants, and petroleum plants. The chemical injection piping 100 can be used when the plant is shut down or during operation.

[0104] The system piping of a plant is piping through which a liquid carrying the main functions of the plant flows. The system piping is not particularly limited in terms of inner diameter, outer diameter, length, shape, etc. The system piping is preferably piping through which a high-temperature liquid or a liquid with a high concentration of reducing chemical species flows. The chemical liquid injection piping 100 can be connected to such system piping.

[0105] A specific example of an application of the chemical injection piping 100 according to this embodiment is the injection of precious metals in a nuclear power plant such as a boiling water reactor (BWR). Examples of precious metal compounds used for the injection of precious metals include compounds of platinum, palladium, rhodium, ruthenium, osmium, and iridium. In a BWR, the chemical injection piping 100 is preferably connected to system piping of a feedwater system through which high-temperature cooling water flows. The chemical injection piping 100 may be connected to a section where the temperature of the cooling water exceeds 200°C.

[0106] Furthermore, the chemical solution injection piping 100 according to this embodiment can be used for a process of injecting a solution of a metal compound in a nuclear power plant such as a pressurized water reactor (PWR), a thermal power plant, etc. Examples of a process of injecting a solution of a metal compound include a process of injecting a corrosion inhibitor, a radionuclide adhesion inhibitor, an oxygen scavenger, a pH adjuster, etc.

[0107] Although the embodiments of the present invention have been described above, the present invention is not limited to the above-described embodiments, and various modifications are possible within the scope of the present invention. For example, the present invention is not necessarily limited to those having all of the configurations of the above-described embodiments. It is possible to replace part of the configuration of an embodiment with another configuration, add part of the configuration of an embodiment to another form, or omit part of the configuration of an embodiment. [Explanation of symbols]

[0108] 100 Chemical injection piping 1 system piping 2. Chemical injection piping main pipe 3 Main body (chemical injection piping) 4 First coating 5 Second coating 6 flange 7 flange 8 Packing, gaskets, O-rings or sealants 9 volts 10 nuts 11 Welded parts 12. Sealant 13 Followers 14 Cap

Claims

1. A chemical injection pipe connected to the system piping of a nuclear power plant and used to inject precious metals into reactor cooling water, comprising: a main body portion constituting the main body of the chemical liquid injection pipe; a first coating provided on a part or all of the inner surface of the main body; a second coating provided on the first coating, the first coating is formed of a material having a thermal conductivity lower than that of the main body, the thermal conductivity being 10 W / m K or less and a thickness of 1 mm or more; The second coating is formed of a material having a higher electrical resistivity than the main body of the chemical injection pipe.

2. The chemical injection pipe according to claim 1, The first coating has a heat transfer rate per unit area of ​​700 kW / m ２ is as follows: The second coating has a volume resistivity of 10 ６ Chemical injection piping with a resistance of Ω·cm or more.

3. The chemical injection pipe according to claim 1, The chemical injection pipe, wherein the first coating is provided on at least an area of ​​the inner surface of the main body portion from the tip connected to the system piping up to 10 cm in the longitudinal direction of the main body portion.

4. The chemical injection pipe according to claim 1, The chemical injection pipe, wherein the main body is formed from at least one of carbon steel, stainless steel, zircaloy, low alloy steel, and nickel-based alloy.

5. The chemical injection pipe according to claim 1, The first coating includes at least one of zirconium oxide, yttria-stabilized zirconia, partially stabilized zirconia, titanium oxide, and aluminum titanate.

6. The chemical injection pipe according to claim 1, The second coating film contains at least one of aluminum oxide, chromium oxide, zirconium oxide, yttria-stabilized zirconia, partially stabilized zirconia, and aluminum titanate.

7. A method for manufacturing a chemical injection pipe that is connected to a system pipe of a nuclear power plant and is used to inject precious metals into reactor cooling water, comprising: forming a first coating on a part or all of an inner surface of a main body constituting the main body of the chemical liquid injection pipe, the first coating being made of a material having a lower thermal conductivity than the main body; forming a second coating on the first coating, the second coating being made of a material having a higher electrical resistivity than the main body; The first coating has a thermal conductivity of 10 W / m·K or less and a thickness of 1 mm or more, and is formed by heat-treating the main body using at least one of a thermal oxidation method, a physical vapor deposition method, a chemical vapor deposition method, a thermal spraying method, a sol-gel method, an organic metal decomposition method, and a coating method.

8. The method for manufacturing a chemical injection pipe according to claim 7, The second coating is formed by at least one of physical vapor deposition, chemical vapor deposition, thermal spraying, sol-gel, metal organic decomposition, and coating.

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