KR20080077505A - Method for surface treatment of pwr piping materials by platinum powder doping - Google Patents

Abstract

A surface treatment method of PWR(Pressurized Water Reactor) piping material using platinum powder doping is provided to reduce corrosion of carbon steel by doping a surface of the carbon steel with precious metal or oxide thereof. In a surface treatment method of PWR piping material, a surface of the PWR piping material is doped with platinum or platinum oxide. The piping material is carbon steel having a magnetite layer on a surface. A dissolved oxygen content of a PWR nuclear power plant water chemistry system is less than 5 ppb. The surface of the PWR piping material is doped with platinum oxide particles. A platinum or platinum oxide dispersion is directly injected into the PWR nuclear power plant water chemistry system at a concentration of 1 to 5000 ppb so that the platinum or platinum oxide particles are doped on the surface of the PWR piping material.

Description

Method for surface treatment of PWR piping materials by platinum powder doping}

1 is a diagram showing the electrochemical potential according to pH in Fe-H ₂ O system,

2 is a photograph of a PtO ₂ supported carbon steel specimen according to an embodiment of the present invention,

3 is a schematic diagram showing an apparatus for evaluating FAC (Flow-Accelerated Corrosion) according to a test example of the present invention,

4 is a graph showing the specific weight loss of a sample after FAC evaluation.

The present invention relates to a method of suppressing corrosion of a hydraulic water pipe system of a PWR type nuclear power plant.

Nuclear power is divided into boiling water type (BWR) and pressurized water type (PWR), and there is a big difference in the structure of converting water into steam using heat generated in the reactor. In the BWR type, the water heated in the core is boiled in the reactor pressure vessel to generate steam, which is completely separated from the water and sent to the turbine. On the other hand, in the PWR type, the primary system water heated in the core is not boiled there but leaves the reactor pressure vessel with high temperature and high pressure water and is sent to the adjacent steam generator. Secondary system water stored in the steam generator is heated by the high temperature and high pressure water (primary system water) sent from the reactor to generate steam.

Comparing the pressure vessel of the reactor, in the BWR type, the direct flow path of steam communicates with the turbine. On the other hand, in the PWR, the high temperature and high pressure water goes to the steam generator and back again. In addition to this, the steam and the moving path of the water and the steam flow through the turbine. That is, it has two roads that are not connected to each other, which is called a primary system and a secondary system, respectively.

In addition, in the case of the BWR type, the corrosion products of the reactor pressure vessel and the pipe are radiated by neutrons, and since they are included in water vapor, radioactivity is managed from a nuclear reactor building to a turbine building. In the case of the PWR type, the primary system and the secondary system are completely separated by the steam generator boundary, so the radioactive primary system does not reach the turbine building. While advantageous in this respect, the steam generator consists of a number of thin heat pipes which can cause corrosion or other cracks or breaks.

In addition, BWR type and PWR type have very different hydrochemical conditions. In particular, BWR maintains dissolved oxygen within 100ppb, whereas PWR type keeps dissolved oxygen below 10ppb, more preferably less than 5ppb. There is this.

On the other hand, the hydroelectric system of a nuclear power plant consists of numerous pipes. These pipes cause Flow-Accelerated Corrosion (FAC) by the fast flowing fluid. Accumulation of this FAC leads to a thinner pipe, which ultimately causes a big accident, such as a pipe rupture, leading to enormous losses.

Piping material used mainly for economic reasons is carbon steel (CS). Carbon steels are more vulnerable to FAC than nickel alloys (Inconel / Alloy-600) or stainless steels. However, the surface of the carbon steel is covered with an oxide film, which protects the surface from FAC. The main component of this oxide film is magnetite (Fe ₃ O ₄ ). 1 is a diagram showing the electrochemical potential (ECP, Electrochemical Potential) of the Fe-H ₂ O system with pH change at 300 ℃ or E-pH diagram as a magnetite stable electrochemical potential or surface corrosion potential (Surface Corrosion Potential) ) Region corresponds to a region of pH 5-10 and a reduction potential of -1.2 to -0.5V. In addition, the ECP is higher than the potential value of the carbon steel under certain environmental conditions such as temperature, pH, dissolved oxygen (DO) concentration. If the surface potential of the carbon steel is changed to the magnetite potential value under certain conditions, the magnetite may be well formed on the surface, and at the same time, the magnetite may be well maintained. If the surface of a material having the same potential value as that of magnetite is doped on the surface, the potential value of the carbon steel surface will be changed to the potential value of the material.

In the prior art, Korean Patent Nos. 264466 and 264467 disclose a method of doping a platinum group material such as palladium in stainless steel in a BWR type hydrochemical system. However, as described above, since the BWR reactor and the PWR reactor have different hydrochemical conditions, it is difficult to apply the corrosion protection technology applied to the conventional BWR reactor to the PWR hydrochemical system as it is. Therefore, it is necessary to develop a corrosion resistance method for piping materials suitable for the PWR hydrochemical system.

It is an object of the present invention to provide a method for suppressing corrosion of a hydrostatic piping system for a PWR type nuclear power plant. More specifically, it is an object of the present invention to provide a method of suppressing corrosion of piping material in a secondary system using carbon steel (CS, Carbon Steel) as a piping material in a PWR-type hydrochemical system.

In addition, the present invention is another object to provide a piping material having a corrosion inhibitive performance of carbon steel as a base material suitable for PWR-type nuclear power plant hydrochemical system.

The present invention relates to a method of suppressing corrosion of a hydrostatic piping system for a PWR-type nuclear power plant, and a piping material based on carbon steel.

Hydrogen system of PWR type nuclear power plant is operated with less than 10ppb of dissolved oxygen, more preferably less than 5ppb, so it has different hydrochemistry from BWR type of chemical system, and primary system and secondary system are separated. It is. Particularly, as the piping material of these systems, carbon steel (CS) is mainly used for economic reasons, but it is vulnerable to FAC (Flow-Accelerated Corrosion), and a corrosion inhibiting method for effectively controlling it and There is a need for the development of new piping materials for this purpose.

Corrosion suppression method of the piping material according to the present invention relates to the corrosion suppression method of the piping material of the pressurized water reactor (PWR) nuclear power plant, in particular the secondary system using carbon steel as a base material, and also has a corrosion inhibiting performance It relates to the piping material using the base material.

The present invention provides a method for suppressing corrosion of a hydrostatic piping system for a pressurized water reactor (PWR) type nuclear power plant, characterized in that at least one member selected from a noble metal or an oxide thereof is supported on a surface of a piping material.

The present invention also provides a piping material in which precious metal or precious metal oxide particles are dispersed and bonded on carbon steel, a magnetite layer formed on the surface of the carbon steel, and the magnetite layer.

Hereinafter, the present invention will be described in more detail.

At this time, if there is no other definition in the technical terms and scientific terms used, it has a meaning commonly understood by those of ordinary skill in the art.

In addition, repeated description of the same technical configuration and operation as in the prior art will be omitted.

The present invention relates to a method for suppressing corrosion of a hydrostatic piping system of a pressurized water reactor (PWR) type nuclear power plant characterized in that at least one member selected from a noble metal or an oxide thereof is formed on a surface of a piping material. The hydrochemical piping material is preferably carbon steel, and more preferably carbon steel having a magnetite (Fe ₃ O ₄ ) layer formed on its surface. PWR hydrochemical piping materials are mainly carbon steel, and the surface of carbon steel has magnetite, a protective oxide film. Hydrochemical conditions of the PWR secondary system are specifically, for example, dissolved oxygen is less than 5ppb, temperature is 35 ~ 288 ℃, hydrazine (N ₂ H ₄ ) concentration is 100 ~ 200ppb, pH is 9 ~ 10 and pH control Zero ammonia or ethanolamine (ETA, Ethanolamine) is used. Corrosion potential (Ecorr, Corrosion Potential), or electrochemical potential (ECP) of the surface of the carbon steel without magnetite under the PWR hydrochemical conditions is about -680mV, magnetite corrosion potential is about -530mV. By inducing the corrosion potential of the carbon steel surface into the magnetite corrosion potential region (see FIG. 1), since the protective oxide film magnetite is more stably present, the corrosion resistance of the carbon steel is greatly increased. Therefore, as described above, the material having the corrosion potential contained in the magnetite corrosion potential region is supported on the surface of the carbon steel (Doping) to create a corrosion inhibitory effect.

As a material supported on the surface of the carbon steel, a noble metal or an oxide thereof is suitable, and the noble metal or an oxide thereof is a noble metal selected from Pt, Pd, Rh, Ir, etc. or an oxide of the noble metal, and platinum as a material supported on the carbon steel piping material. Or platinum oxide (PtO ₂ ) is more preferred and platinum oxide (PtO ₂ ) is most preferred. The precious metal or an oxide thereof may be immersed in the dispersion using a particulate matter having a mean particle size of 0.01 to 10 μm or a dispersion thereof, or sprayed with the dispersion. In addition, a method of injecting a noble metal or an oxide dispersion thereof into the hydrochemical system by in-situ may be adsorbed or deposited on the surface of the pipe material while moving according to the flow of the fluid. If the average particle diameter of the particulate matter is less than 0.01 μm, the production cost of the particulate material increases, so it is economically disadvantageous. If the average particle diameter of the particulate matter is too large, exceeding 10 μm, the dispersibility decreases and the concentration is supported. There is a problem that is lowered.

The amount of the precious metal or oxide thereof is preferably 0.01 to 30 atomic% based on the precious metal component on the surface of the piping material. When the supporting amount is less than 0.01 atomic%, the effect of increasing the electrochemical potential of the carbon steel is insignificant and the supporting amount may increase. It is preferable to increase the FAC reduction effect, but when the content exceeds 30 atomic%, the amount of noble metal or oxide thereof increases, which is disadvantageous economically.

In the case of using the method of directly injecting the noble metal or oxide dispersion thereof into the PWR-type nuclear power plant hydration system water, the amount of the noble metal or its oxide in the hydrochemical plant water is 1 to 5000 ppb based on the precious metal component. It is preferable to make it possible to achieve the supporting amount as described above.

In addition, the particulate matter may be prepared by pulverizing the large particles, or may be prepared in the form of a colloid, the dispersion containing the particulate matter may further contain a dispersion stabilizer for improving the dispersibility of the particulate matter. In addition, the dispersion may contain methanol (Methanol) or ethanol (Ethanol) does not affect the secondary system hydrochemical conditions.

In addition, when the ultrasonic treatment during the production of the noble metal or noble metal oxide particle dispersion, the dispersibility is improved and a higher concentration of the dispersion may be prepared, and the noble metal or oxide particles thereof supported on the piping material are clustered. There is an advantage to suppress. In addition, there is an advantage that the particle distribution density on the surface of the piping material may be larger when doping using a dispersion having a relatively small average particle diameter and highly dispersed.

The present invention also provides a piping material in which precious metal or precious metal oxide particles are dispersed and bonded on carbon steel, a magnetite layer formed on the surface of the carbon steel, and the magnetite layer, and more specifically 0.01 to 30 atoms based on platinum (Pt). It provides a PWR-type nuclear power plant hydrochemical piping material in which% platinum oxide (PtO ₂ ) particles are dispersed and supported on the surface of the piping material.

Hereinafter, preferred embodiments of the present invention will be described in detail. The following embodiments are provided as examples to sufficiently convey the spirit of the present invention to those skilled in the art. Accordingly, the invention is not limited to the embodiments described below and may be embodied in other forms.

<Example 1>

Carbon steel specimens (width 9.30mm X length 9.00mm X thickness 1.18mm) were analyzed by SEM-EDX (manufactured by JEOL Ltd., product name: Scanning Electron Microscope) to analyze the surface composition of 85.51 atomic% Fe and carbon (C). ) Represents 14.49 atomic%.

3.04 mg of PtO ₂ xH ₂ O powder (manufacturer: Merck, product no .: 807346, 80% Pt) was added to 1000 g of distilled water, followed by sonication, to prepare a PtO ₂ dispersion having a PtO ₂ dispersion of 2.43 ppm. The dispersion was added to a reaction vessel, the carbon steel specimen was added thereto, and reacted at 80 ° C. for 12 hours so that PtO ₂ was supported on the surface of the carbon steel specimen. After the supporting treatment, the carbon steel specimen was dried to prepare a carbon steel specimen carrying PtO ₂ as shown in the photograph of FIG. 2. The PtO ₂ -carrying carbon steel specimen was surface-analyzed by SEM-EDX at any 10 points, and the average content of 0.7 atomic% (maximum 2.33 atomic%) was found, and no carbon (C) component was detected. It can be seen that the iron oxide film was formed.

<Test Example 1>

The PtO ₂ loaded carbon steel specimen prepared in Example 1 was evaluated using the FAC test apparatus as shown in FIG. Referring to the FAC test apparatus of FIG. 3 in detail, an aqueous solution satisfying hydrochemical requirements is injected into the pressurizer, and the aqueous solution is introduced into the autoclave via a damper (buffer) and a preheater by a pump. The autoclave is provided with a columnar specimen-support (or specimen loader) and a rotary vane, and the specimens mounted on the specimen-support are provided with the required flow rates by rotating vanes therein. The aqueous solution which passed the autoclave which is a high temperature part falls to room temperature by a cooler, and a back pressure regulator (BPR) maintains the required pressure of a high temperature part. A sample part is collected for use in analysis by collecting a portion of the aqueous solution at room temperature, and a DO measuring device is provided so that DO, which seriously affects the FAC, is controlled by real time measurement. The autoclave is a magnetically driven autoclave. In general, when a mechanically connected rotary shaft is used in a high temperature and high pressure state, leakage occurs easily in a minute gap between the rotary shaft and the support, but the inside of the container rotates. Linking the wing and external rotational force with magnetic force has the advantage of preventing leakage.

3 carbon steel specimens without PtO ₂ (CS-B1, CS-B2, CS-B3) and 3 PtO ₂ supported carbon steel specimens prepared in Example 1 (CS-D1, CS-D2, CS-D3) ) Were prepared and mounted on specimen-supports of the autoclave, respectively. At this time, the hydrochemical conditions were similar to those of the PWR hydrochemical system. The pH was 8.5, the DO was less than 5 ppb, and the temperature was 150 ° C. The rotation speed of the inner rotor provided on the surface of the specimen-support of the autoclave was measured. It was performed at 1500 rpm for 62 hours.

After the test, the specific weight loss (μg / cm ² ) of the sample was measured and shown in FIG. 4. Referring to the results of Figure 4 it can be seen that the non-weight loss value is significantly reduced in the PtO ₂ supported carbon steel specimen.

Corrosion suppression method of the PWR-type nuclear power plant hydrochemical piping material according to the present invention can significantly reduce the corrosion of carbon steel by supporting a precious metal or oxide thereof on the surface of the carbon steel mainly used in PWR-type hydrochemical system. Has the effect.

Claims (8)

In the corrosion suppression method of the pressurized water reactor (PWR) type nuclear power plant hydrochemical piping materials, A method of suppressing corrosion of a pressurized water reactor (PWR) -type hydroelectric power plant piping material, characterized by supporting platinum or platinum oxide on the surface of the piping material. The method of claim 1, The piping material is a method of suppressing corrosion of a hydrostatic system piping material of a pressurized water reactor (PWR) type nuclear power plant, characterized in that the carbon steel with a magnetite (Fe ₃ O ₄ ) layer formed on the surface. The method of claim 1, Method for suppressing corrosion of the PWR-type nuclear power plant hydrochemical piping material, characterized in that the dissolved oxygen content of the PWR-type nuclear power plant hydrochemical system is less than 5ppb. The method of claim 1, A method of inhibiting corrosion of a PWR-type nuclear power plant hydrochemical piping material, characterized in that platinum oxide (PtO ₂ ) particles are supported on a surface of the piping material. The method of claim 4, wherein The platinum oxide is a corrosion suppression method of a hydrostatic piping system of a pressurized water reactor (PWR) -type nuclear power plant, characterized in that the surface of the pipe material is loaded in a content of 0.01 to 30 atomic% based on platinum. The method according to any one of claims 1 to 5, The supported platinum or platinum oxide dispersion is directly injected into the PWR-type nuclear power plant hydrochemical system so that the concentration of platinum or platinum oxide is 1 to 5000 ppb so that the platinum or platinum oxide particles are supported on the surface of the piping material. A method of suppressing corrosion of a hydraulic water pipe of a pressurized water reactor (PWR) type nuclear power plant. The method of claim 6, The platinum or platinum oxide dispersion is a method for suppressing corrosion of a hydrostatic system piping material of a pressurized water reactor (PWR) type nuclear power plant, characterized in that finely dispersed platinum oxide powder by ultrasonic waves. Pressurized water reactor (PWR) -type nuclear power plant hydrochemical system in which 0.01 to 30 atomic% of platinum oxide (PtO ₂ ) particles are loaded on carbon steel, a magnetite layer formed on the surface of the carbon steel, and the magnetite layer on a basis of platinum (Pt). Plumbing materials.

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