KR100822035B1 - Method for manufacturing heat tube with oxide layer of steam generator - Google Patents

Abstract

A method for manufacturing a heat tube with an oxide layer of a steam generator is provided to improve reliability of an eddy current test and integrity of the steam generator and extend a lifetime of a pressurized water reactor. A method for manufacturing a heat tube with an oxide layer of a steam generator includes the steps of: manufacturing an oxide layer generation system including a chamber(S100); installing steam generator laboratory degraded tubes inside the chamber(S200); generating an oxide layer on the steam generator laboratory degraded tubes by simulating steam generator environment of a pressurized water reactor inside the chamber receiving the steam generator laboratory degraded tubes(S300); and measuring a thickness of the oxide layer formed on the steam generator laboratory degraded tubes by mounting a wire for measuring impedance of the oxide layer generated on the steam generator laboratory degraded tubes(S400).

Description

TECHNICAL FIELD METHOD OF MANUFACTURING STEAM GENERATOR HEADER TUBES SPECIFICATION WITH CRACK OXIDE

1 is a view showing a high temperature oxide film production system for producing a steam generator heat pipe specimen according to an embodiment of the present invention,

2 is a flow chart showing a steam generator heat pipe specimen manufacturing method according to an embodiment of the present invention,

3 shows an equivalent circuit of the measured alternating current impedance for calculating the oxide capacitance.

<Description of Symbols for Main Parts of Drawings>

100: oxide film generating system 110: chamber

120: hydrochemical control unit 130: environmental control unit

140: oxide film measuring unit 150: eddy current test unit

The present invention relates to a method for producing a steam generator specimen, and more particularly to a method for manufacturing a steam generator heat pipe specimen formed with a crack oxide film.

In general, the steam generator converts the secondary circulating coolant into steam by allowing the primary circulating coolant of the PWR (Pressurized Water Reactor) to transfer heat to the secondary circulating coolant. The heat transfer tube of the steam generator has a structure in which the inner circumferential coolant is in contact with the outer circulating coolant and the outer circumferential coolant is transferred to the secondary circulating coolant.

On the other hand, since the first circulating coolant is heated by nuclear fuel, it is radioactive, but the second circulating coolant is not radioactive because it receives heat through the heat exchanger tube of the steam generator. In other words, the heat transfer tube of the steam generator is a part that forms a pressure boundary between the primary circulation side and the secondary circulation side, and is a main safety facility for preventing radioactive material from the primary circulation side into the secondary circulation side.

Therefore, the heat generator tube of the steam generator is formed of a material having excellent corrosion resistance and mechanical properties such as 'Alloy 600', a nickel-chromium alloy. However, in the case of nuclear power generation, the heat generator tube of the steam generator is in a state of high temperature and high pressure on both sides of the primary circulation side and the secondary circulation side, and when the nuclear power generation progresses for a long time, IGA / IGSCC (InterGranular Attack / InterGranular Stress Corrosion Cracking) It can be damaged by

Damage to the heat transfer tube of the steam generator may leak the primary cooling water to the secondary circulation side to leak the radiation contained in the primary cooling water to the outside. Radioactive spills have a direct impact on safety and also cause serious environmental pollution. In addition, the disruption of nuclear power for repairs leads to enormous economic losses.

Therefore, maintenance activities and studies are needed to secure the integrity of the steam generator heat pipes in order to secure safety and extend the life of the pressurized water reactors in operation. Eddy Current Technique (ECT) is a method of evaluating the integrity of steam generator tubes, and it is recognized that non-destructive testing, leak rate measurement and break pressure prediction play an important role.

However, in order to secure the verification and reliability of these studies, first of all, in the case of actual nuclear power generation, it is necessary to precede the production of laboratory degraded tubes that simulate the mechanical and chemical properties similar to the natural cracks generated in the steam generator tube. do.

Some of the existing research institutes have succeeded in fabricating steam generator tube specimens for eddy current test validation. In particular, the Argonne National Laboratory (ANL) and the Atomic Energy Research Institute (ARL) of the United States have established a method of creating grain boundary cracks at room temperature using the Alloy 600 tube. This method creates a corrosive environment by using Na ₂ O ₆ S ₂ · 2H ₂ O (Sodoum Tetrathionate) aqueous solution at room temperature, and uses specimens with axial cracks and circumferential cracks by pressure-bearing and tensile load application. Fabrication and eddy current test (ECT).

In general, nickel, chromium, iron oxide film is formed on the surface of the steam generator tube made of nickel (Ni) alloy because it is in direct contact with the first and second circulating coolant of the pressurized water reactor in which nuclear power generation proceeds. Since the oxide film formed on the surface has conductivity, it is a major factor influencing the accuracy of the eddy current test, which is a non-destructive inspection means.

However, the steam generator heat pipe specimen for verifying the conventional eddy current test has a problem in the reliability of the eddy current test by the oxide film because the oxide film distributed at the crack boundary and the surface oxide film actually seen in the crack of the steam generator heat pipe is not considered.

An object of the present invention is to provide a method for manufacturing a steam generator heat pipe specimen having a surface oxide film as seen in natural cracking in an environment that simulates a hydrochemical environment with pressurized hard water.

In order to solve the above technical problem, the present invention provides a method for manufacturing an oxide film production system including a chamber; A specimen mounting step of installing a steam generator heat pipe specimen in the chamber; An environment simulation step of generating an oxide film on the steam generator heat pipe specimen by simulating the inside of the chamber in which the steam generator heat pipe specimen is installed in a steam generator environment of a pressurized water reactor; And an oxide film measuring step of measuring a thickness of the oxide film generated on the steam generator heat pipe specimen.

Here, the oxide film measuring step includes attaching a wire for measuring the impedance of the oxide film generated on the steam generator heat pipe specimen.

The measuring of the oxide layer may include measuring an impedance of the oxide layer, calculating a capacitance of the oxide layer using the impedance, and calculating a thickness of the oxide layer using the capacitance of the oxide layer.

In addition, the oxide film impedance measurement step is preferably using an electrochemical impedance spectroscopy (Electrochemical Impedance Spectroscopy).

In the oxide capacitance calculation step, it is preferable to use an equivalent circuit of the oxide impedance.

을 이용하여 상기 산화막 두께를 산출하며, 상기 수학식에서 C는 상기 산화막의 커패시턴스이며, A는 상기 산화막의 면적이며, d는 상기 산화막의 두께이며,ε는 유전 상수(dielectric constant)이며, ε₀는 상수 8.854 x 10^-12 F/M인 것이 바람직하다.In addition, the oxide film thickness calculating step,

The thickness of the oxide film is calculated by using C, wherein C is the capacitance of the oxide film, A is the area of the oxide film, d is the thickness of the oxide film, ε is the dielectric constant, and ε ₀ is It is preferred that the constant is 8.854 x 10 ^-12 F / M.

In the environmental simulation step, the dissolved hydrogen concentration in the chamber is maintained at 25 to 35 cc / Kg, the dissolved oxygen concentration is maintained at 5 ppb or less, and the temperature of the steam generator heat pipe specimen at a temperature of 320 ° C. or higher and a pressure of 150 atm or higher. Maintaining for at least 40 hours.

Hereinafter, the present invention will be described in more detail with reference to the accompanying drawings.

1 is a diagram illustrating a high temperature oxide film formation system for fabricating a steam generator heat pipe specimen according to an embodiment of the present invention. Referring to FIG. 1, the high temperature oxide film generating system 100 for fabricating a steam generator heat pipe specimen includes a chamber 110, a hydrochemical control unit 120, an environmental control unit 130, an oxide film measuring unit 140, and a eddy current It includes a test unit 150,

The chamber 110 simulates a high temperature and high pressure steam generator environment of a pressurized water reactor (not shown) by the hydrochemical control unit 120 and the heater 122 controlled by the environmental control unit 130. The interior of the chamber 110 communicates with the hydrochemical control unit 120 and is equipped with a specimen and measurement electrode 116 electrically connected to the oxide film measuring unit 140 or the eddy current test unit 150. Here, the specimen includes a specimen 114 for measuring the eddy current and the specimen 112 for measuring the AC impedance, and the measuring electrode 116 is formed of AUEN (AU PH Electrode-Non PTFE) or CU / CU ₂ O / ZrO _2. An electrode. The outside of the chamber 110 surrounds the chamber 110 and a heater 122 is installed to make the inside of the chamber 110 at a high temperature.

The hydrochemical control unit 120 is in communication with the interior of the chamber 110 and under the control of the environmental control unit 130 to adjust the chemical composition of the water flowing into the chamber 110 by the steam generator of the pressurized water reactor in the chamber 110 Artificially create the internal environment. In addition, the hydrochemical control unit 120 maintains a constant hydrochemical environment inside the chamber 110 while the oxide film is generated in the specimens 122 and 114 installed inside the chamber 110.

To this end, the hydrochemical control unit 120 includes a charging pump, a accumulator for maintaining a high pressure, a heat exchanger, and the like.

The environmental control unit 130 controls the hydrochemical control unit 120 and the heater 122 so that an oxide film may be formed on the specimens 112 and 114 in the chamber 110. Allow it to be simulated into a steam generator environment.

The oxide film measuring unit 140 measures the oxide film generated in the specimen 112 for measuring the AC impedance mounted in the chamber 110 in real time. The oxide film measuring unit 140 uses a frequency response analyzer for measuring impedance spectra in order to measure the thickness of the oxide film in real time, an electrochemical impedance measuring program, and an impedance spectra analysis program for impedance spectra analysis. Can be used. Here, the impedance scan frequency range is preferably set to 10 ⁶ to 10 ⁻² .

The eddy current test unit 150 measures the eddy current and the like through the eddy current measurement specimen 114 and the measurement electrode 116 mounted inside the chamber 110, and based on the eddy current test unit 150 Maintain stability of chemical conditions. In addition, the eddy current test unit 150 is the temperature and pressure inside the chamber 110, the eddy current measured through the specimen inside the chamber 110, dissolved hydrogen (DH) and dissolved oxygen (DO), conductivity (conductivity) Measure and store the lights in real time.

2 is a flowchart illustrating a method for manufacturing a steam generator heat pipe specimen according to an embodiment of the present invention. Referring to FIG. 2, the steam generator heat pipe specimen manufacturing method includes a high temperature oxide film production system manufacturing step (S100), a specimen mounting step (S200), an environmental simulation step (S300), and an oxide film measuring step (S400).

In the manufacturing of the high temperature oxide film production system (S100), the high temperature oxide film production system described with reference to FIG. 1 is manufactured for fabricating a steam generator heat pipe specimen according to an embodiment of the present invention.

After fabrication of the high temperature oxide film production system, the chamber is washed with ultra pure water. After tightening the connection part of the chamber by a predetermined torque, the pressure is increased to check whether the connection part is leaked. After the pressure test, it is advisable to further increase the temperature to check for leaks in the connection.

The thermometer and manometer used in the high temperature oxide film formation system are calibrated using calibration equipment. On the other hand, if you use a calibrated thermometer and pressure gauge, you can skip the calibration process.

The specimen mounting step (S200) is attached to a fixture prepared in advance by preparing a specimen for measuring the eddy current and the specimen for measuring the AC impedance, and is mounted in the chamber.

Here, the specimen for measuring AC impedance serves as a working electrode when measuring the eddy current. Specimens for ac impedance measurement can be obtained by the following steps: First, the specimen is processed to have an area of 1 cm ² and polished step by step using an abrasive, for example, SiC Paper of Grit Size 400, 600, or 1000, or 3 μm of Alumina. . After each step, the wafer is cleaned by ultrasonic cleaning in a distilled water environment and then dried in air. In addition, a 0.5 mm diameter wire (Alloy 600) is spot welded to the edge of the specimen for impedance measurement, and then insulated with a heat shrinkable Teflon tube.

The environmental simulation step (S300) is a step of artificially forming the environment in the primary circulation side by pressurized hard water in the chamber in which the specimen is mounted.

In this embodiment, the conditions of the high temperature oxide film formation system for simulating the primary circulation side environment of the pressurized light water reactor are as follows. Dissolved hydrogen concentration 25 to 35 cc / Kg Preferably 30 cc / Kg, dissolved oxygen concentration 5ppb or less, boron (B) 1200ppm, lithium (Li) 2ppm, chlorine and fluorine ion concentrations respectively 0.05ppm or less, pH 7.0 ± 25 ℃ 0.2, electrical conductivity of 21 to 22 us / cm, temperature of 320 ° C. or higher at the specimen position, pressure of 150 atm at the specimen position, experiment duration of 40 hours.

Here, when boron boric acid (H ₃ BO ₃ ) is 1200ppm concentration, lithium hydroxide (LiOH) is adjusted so that the pH of the reference 300 ℃ 7.0. In addition, gas purging using high purity argon (Ar) or nitrogen (N ₂ ) gas is performed to remove oxygen in the chamber, and then the temperature and pressure inside the chamber are raised to a set temperature and pressure. Through this environment simulation step (S300), an oxide film generated in the pressurized water reactor primary circulation side environment is formed on the specimen mounted in the chamber.

The oxide film thickness calculating step (S400) measures the impedance between two impedance measurement specimens at appropriate time intervals and calculates the thickness of the oxide film formed using the same. Oxide film thickness calculating step (S400) preferably further comprises the step of confirming the stability of the hydrochemical conditions by performing a eddy current test while maintaining a high temperature of 320 ℃ and a high pressure of 150 atm.

In this embodiment, electrochemical impedance spectroscopy (ESI) using an alternating current impedance between specimens for impedance measurement as a function of time is used for real-time measurement of oxide thickness.

The method of calculating the thickness of an oxide film using the measured AC impedance specifically, is demonstrated. This includes calculating an oxide capacitance using the measured alternating current impedance and calculating an oxide thickness using the oxide capacitance.

First, the step of calculating the oxide capacitance using the measured AC impedance will be described. The oxide capacitance may be calculated by substituting an appropriate constant value using an equivalent circuit of the measured AC impedance and then fitting. 3 illustrates an equivalent circuit of the measured alternating current impedance for calculating the oxide capacitance.

Where R _s is the solution resistance, C _ox is the capacitance of the oxide, R _ox is the resistance of the oxide, and C _dl is the double layer capacitance, R _corr Is the corrosion resistance, and L is the inductance effect of lead wire.

Next, the process of obtaining an oxide film thickness using the calculated oxide film capacitance will be described. The oxide film thickness can be obtained by substituting the oxide capacitance calculated in Equation 1 below.

In Equation 1, C is the capacitance of the oxide film [farad], A is the oxide film area [m ² ], d is the thickness of the oxide film, ε is a dielectric constant, ε ₀ is a constant 8.854 x 10 ^-12 F / M means each.

Table 1 exemplifies a case where the thickness of the oxide film is calculated by measuring the impedance between two impedance measurement specimens at appropriate time intervals and using the equivalent circuit of the measured impedance and Equation (1).

Primary measurement Secondary measurement 3rd measurement Oxidation Resistance (R _ox ) 62.61 Ω 76.13 Ω 87.01 Ω Oxide Capacitance (C _ox ) 0.47087 uF 0.45558 uF 0.45249 uF Oxide thickness (d) 0.18803 um 0.19435 um 0.19567 um

In Table 1, the primary, secondary, and tertiary measurements are impedance measurements taken sequentially at regular intervals. It can be seen that as the measurement time elapses, the resistance of the oxide film increases and the capacitance decreases. In addition, the thickness of the oxide film is gradually increased.

Next, when the formation of the oxide film having a desired thickness is finally confirmed, the process of fabricating the steam generator heat pipe specimen according to the embodiment of the present invention is completed, and the surface and the cross-section of the steam generator heat transfer and the oxide film of the specimen are optical microscopes. In addition, it is confirmed by Scanning Electron Microscopy (SEM) and the information of the oxide film formed by observing by Auger Electron Spectroscopy (Auger Electron Microscopy).

According to the present invention, since it is possible to provide a steam generator heat pipe specimen having a surface oxide film as seen in natural cracking in an environment that simulates a hydrochemical environment with pressurized hard water, it improves the reliability of the eddy current test, improves the integrity of the steam generator, and It has the effect of extending the life of pressurized water reactor.

Claims (7)

delete Fabricating an oxide film production system comprising a chamber; A specimen mounting step of installing a steam generator heat pipe specimen in the chamber; An environment simulation step of generating an oxide film on the steam generator heat pipe specimen by simulating the inside of the chamber in which the steam generator heat pipe specimen is installed in a steam generator environment of a pressurized water reactor; And An oxide film measuring step of attaching a wire for measuring impedance of an oxide film generated on the steam generator heat pipe specimen and measuring a thickness of the oxide film formed on the steam generator heat pipe specimen; Steam generator heating tube specimen generation method comprising a. The method of claim 2, wherein the measuring oxide film, Measuring an impedance of the oxide film, calculating a capacitance of the oxide film using the impedance, and calculating a thickness of the oxide film using the capacitance of the oxide film; Method of generating steam generator tube specimens. The method of claim 3, wherein the oxide impedance measurement step is performed. Using electrochemical impedance spectroscopy Method of generating steam generator tube specimens. The method of claim 3, wherein the oxide capacitance calculation step, Using an equivalent circuit of the oxide film impedance Method of generating steam generator tube specimens. The method of claim 5, wherein the oxide film thickness calculating step, Equation

The thickness of the oxide film is calculated by using C, wherein C is the capacitance of the oxide film, A is the area of the oxide film, d is the thickness of the oxide film, ε is the dielectric constant, and ε ₀ is Constant 8.854 x 10 ^-12 F / M Method of generating steam generator tube specimens. The method of claim 6, wherein the environment simulation step, Maintaining a dissolved hydrogen concentration of 25 to 35 cc / Kg in the chamber, maintaining a dissolved oxygen concentration of 5 ppb or less, and maintaining a temperature of at least 320 ° C. and a pressure of at least 150 atm for 40 hours at a position of the steam generator tube. Containing Steam generator heat transfer and specimen creation method.

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