KR100579399B1 - Method of making laboratory degraded heat transfer tubes for steam generator - Google Patents

Abstract

Preparing the heat exchanger tube for specimen formation, subjecting the heat transfer tube to sensitizing heat treatment, and contacting the heat exchanger tube surface with an oxidizing solution with application of a radial denting load that stresses the heat transfer tube from the outside to the center of the heat transfer tube Disclosed is a method for fabricating a specimen of a steam generator heat pipe comprising a cracking step. Subsequent to the cracking step, the step of corrosion in a hydrothermal environment, usually high temperature and high pressure, is further provided.

According to the present invention, since it is possible to produce a crack specimen with the steam generator heat transfer having the same shape as the actual shape, by using it more precisely to study the safety and life extension of the pressurized water light reactor, and non-destructive inspection of the steam generator heat pipe Can increase the reliability.

Description

Method of making laboratory degraded heat transfer tubes for steam generator

1 is a flow chart showing a crack specimen manufacturing method according to an embodiment of the present invention,

Fig. 2 is a front view showing an example in which a window for generating cracks is formed on a part of the surface of the heat pipe tube;

3 is a side view showing a pressure applying device (tension tester) for applying pressure to a heat pipe tube according to an embodiment of the present invention;

Fig. 4 is a front view showing a part of the pressure applying device and the device for bringing the oxidizing solution into contact with the tube surface and check the appearance of the crack.

* Explanation of symbols for the main parts of the drawings

1,101: tube tube 2: circular focus microscope

3: probe 4: spring

5: wire 6: wall

7: (container) bottom 8: oxidizing solution

9: copper plate 10, 14: rectangular plate

11,153: synthetic resin 15: support

22: insulator 23: upper terminal

24: lower terminal 130: hole

151: tube surface 153: synthetic resin

155: window

The present invention relates to a method for fabricating a specimen of a steam generator heat pipe of a pressurized light-water reactor nuclear power plant, and more particularly, to a method for forming grain boundary cracks in a heat pipe specimen.

In the steam generator, the reactor coolant on the primary circulation side of a pressurized water reactor (PWR) type nuclear power plant transfers heat to the secondary circulation side cooling water to convert the secondary circulation side cooling water into steam. At this time, the heat transfer is made through the heat transfer tube which is in contact with the coolant in the primary circulation side and the outside is in contact with the coolant in the secondary circulation side. That is, the heat transfer tube forms a pressure boundary between the primary circulation side and the secondary circulation side. At this time, since the primary circulation side has radioactivity, but the secondary circulation side should not have radioactivity, the steam generator including the heat transfer tube is the main safety to prevent the radioactive material from the primary circulation side from entering or transmitting radiation to the secondary circulation side. It becomes facilities.

Therefore, as the material of the heat transfer tube tube of the steam generator currently in operation, an excellent corrosion resistance and mechanical properties such as 'Alloy 600', which is a nickel-chromium alloy, are used. However, during operation of a nuclear power plant, the heat transfer tubes are placed under high temperature and high pressure on both the primary and secondary sides. Done.

If the primary cooling water leaks to the secondary side through the steam generator tube due to such damage, the secondary side circulation, which is not protected against the external leakage of radioactivity, causes the radioactivity to leak out, contaminating the environment and impairing the safety of the power plant. have. In addition, depending on the degree of radioactive outflow, the radioactive outflow may cause the power plant to be shut down, and the downtime of the power plant may mean a decrease in the operation rate and an extension of the maintenance air, resulting in enormous economic losses.

Therefore, maintenance activities and studies are needed to secure the integrity of the heat transfer tube of the steam generator in order to secure safety and extend the life of the pressurized water-type light water reactor in operation. Nondestructive testing, leak rate measurement and break pressure prediction through the eddy current technique (ECT) are considered to play an important role in determining the integrity of the heat pipe. In order to verify and verify the reliability of the studies, first of all, a specimen of a steam generator tube having a crack similar in shape and characteristics to a crack generated in a steam generator tube of a nuclear power plant is required.

Some of the existing research institutes have succeeded in producing crack specimens for eddy current test verification. Recently, the Argonne National Laboratory (ANL) and the Atomic Energy Research Institute of the United States have established a procedure for producing room temperature intergranular cracks using alloy 600 heat pipe tubes. They conducted the study by applying the pressure-bearing method and the tensile load method, respectively, to create the axial crack and the circumferential crack. In addition, 0.1 M (mol) of Na ₂ O ₆ S ₄ .2H ₂ O (sodium tetrathionate) aqueous solution was used as an oxidizing solution to make the surface damage by corrosion.

However, the loading method used in these studies is convenient and economical in making intergranular cracks, but the cracks produced are typical of high 10 or higher aspect ratios occurring in the heat pipes of a steam generator. It is different from cracks. The step ratio is the ratio of the length of the crack to the depth of the crack. The higher the step ratio, the longer and shallower the crack is formed in the heat pipe.

As a result, the study through the specimens obtained by these methods has a problem that only limited availability.

The present invention is to solve the above problems, to provide a method for producing a specimen of the steam generator tube for more accurate research to increase the safety and life of the pressurized water reactor, and to increase the reliability of non-destructive inspection for the steam generator tube. For the purpose of

An object of the present invention is to provide a method for forming a specimen having a grain boundary crack similar to the crack of an actual steam generator heat pipe of a nuclear power plant.

The specimen manufacturing method of the steam generator heat transfer tube of the present invention for achieving the above object comprises the steps of preparing a heat transfer tube tube for the formation of the specimen, performing a sensitization heat treatment for the heat transfer tube tube, the center direction of the heat transfer tube tube outside the heat transfer tube And a cracking step of contacting the heat pipe tube surface with the oxidizing solution together with the application of a stressed radial denting load.

In the present invention, the cracked heat pipe tube is usually further provided with a step of corroding in a high temperature and high pressure hydrochemical environment in order to make conditions such as cracks of the actual steam generator heat pipe.

In the present invention, in the cracking step of contacting the tube surface with an oxidizing solution, it is preferable to expose only a predetermined portion in a narrow and long form in a slit form so as to selectively obtain only a crack of a desired shape, and the slit may be formed in the circumferential direction or the axial direction. Can be.

In the present invention, it is preferable that the monitoring of the occurrence and growth of the crack also be performed in conjunction with the cracking step in order to determine whether a desired crack is obtained in the cracking step.

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

1 is a flow chart showing a crack specimen manufacturing method according to an embodiment of the present invention.

Prior to the sensitization heat treatment step, first, a predetermined length of the same heat pipe tube as the steam generator heat pipe is prepared (S10) and subjected to a tensile test to determine the tensile properties (S20). In addition, the finite element analysis method is used to predict the stress distribution and strain at each position of the heat transfer tube when applying pressure to the heat transfer tube by considering the specifications and materials of the given heat transfer tube. This is to determine the pressure to be applied to the tube in order to obtain the desired crack, and to give a pressure of a suitable size and direction according to the calculation.

In order to easily generate cracks in the heat pipe tube, a heat treatment is performed on the heat pipe tube (S30). Sensitization heat treatment is generally intended to form a state susceptible to grain boundary corrosion by heating the object to a temperature of about 450 to 850 degrees Celsius in order to test the grain boundary corrosion of the ostate stainless steel. The sensitization heat treatment allows for faster and easier cracking in the tube tube. Specific sensitization heat treatment conditions can be obtained through a Huey test (Huey test).

An operation is carried out so that the oxidizing solution contacts only a portion of the heat pipe to obtain a crack at a desired position, for example, at a position where the stress is easy to analyze and where a crack of the desired shape is likely to occur. That is, a narrow and narrow window (slit) is formed in the circumferential direction or the axial direction at a desired position of the heat pipe tube (S40).

FIG. 2 is a front view showing an example in which a window 155 for causing a crack is formed on a portion of the surface 151 of the heat pipe tube 101. The window 155 may be formed using synthetic resin or anticorrosive paint, and preferably, the synthetic resin 153 with the window 155 is attached and the synthetic resin 153 is attached only around the site where the crack is to be generated. Replenish the area with paint to prevent oxidizing solutions.

On the other hand, in order for the cracking pattern of the specimen to be similar to the cracking of the heat pipe of the steam generator of the nuclear power plant, a means for accurately inspecting the cracking pattern of the heat pipe and the crack of the specimen is also required.

FIG. 3 is a side view showing a pressure applying device (tensile tester) for applying pressure (partially tensile force) to a heat pipe tube according to an embodiment of the present invention, and FIG. 4 shows a portion of the pressure applying device and an oxidizing solution on the tube surface. It is a front view showing a device that touches and checks the aspect of the crack together. At this time, the pressure applying device may be considered as a tensile force applying device because the heat transfer and the inner surface of the tube partially serves to give a tensile force.

3 and 4, a predesigned jig portion is mounted to the tensile tester. The jig is placed on the stainless steel support (15) symmetrically up and down on the stainless steel rectangular plate (10,14), and the copper plate (9) is installed in the rectangular plate to contact the heat pipe tube (1) and bolt them (12,13) Is made by tightening. An upper terminal 23 and a lower terminal 24 are formed in the upper support and the lower support, respectively. The tension tester has a combination of right and left screws 16, 17, 18, 19, 20 and 21, so care must be taken when handling. The tensile tester and jig are preferably designed in consideration of the results of the stress analysis on the load applied to the heat pipe tube 1 through the finite element analysis method. The probes (probes: 3) mounted to identify the cracking properties measure the voltage between the top and bottom of the crack by the current flowing through the tube (1). To this end, the jig mounted in the tensile tester is connected to the upper terminal 23, the negative electrode is connected to the lower terminal 24, the direct current flows. Since high current flows through the test apparatus, the tensile tester is designed to interpose an insulator 22, such as acrylic, in the middle of the connection for complete insulation.

And the heat exchanger tube 1 is attached between jig | tools. The heat pipe tube 1 is formed to a length of about 10 to 20 cm, jig is formed long in the longitudinal direction of the heat pipe tube (1). The copper plate (9) forming the jig surface in contact with the heat pipe tube is one flat surface, and the heat pipe tube (1) is cylindrical, so that the part where the jig and the heat pipe tube (1) outside are ideally ideally centered on the heat pipe tube (1). It becomes a straight line parallel to. Where the jig and the heat pipe tube (1) is in contact with the insulation is not made so that the current flows through the heat pipe. The window is formed of synthetic resin so that the exposed part is located in the middle of the jig. It is preferable to make the part where the upper and lower ends of the copper plate 9 and the heat transfer tube 1 contact each other in parallel with the axis of the heat transfer tube 1 in order to equalize the stress.

Referring to FIG. 4, a probe is formed on the left circumference of the heat transfer tube 1 in the axial direction of a window or slit formed in the axial direction of the steam generator tube 1 using a synthetic resin 11. 3) is in contact. The probe 3 has one end fitted into an egg hole 130 on one wall 6 of the oxidizing solution container provided on the left side of the heat pipe tube 1 and connected to the electric wire 5. A force is applied toward the tube 1 using the spring 4 to maintain contact with the tube 1. 5 pairs of probes 3 are provided in the axial direction of the tube 1 by pairing two installed in the upper and lower sides. The number of probe pairs or spacing can be changed as needed.

The oxidizing solution container has the surface of the heat pipe tube (1) removed from the container when the solution is contained in a state in which the upper and lateral one faces are removed from the rectangular parallelepiped, that is, the sidewall faces (6) and the bottom face (7). It is installed outside the tube 1 to form one side wall. At this time, the oxidizing solution container is adhered well to the surface of the heat pipe tube (1) so as not to leak the oxidizing solution (8) filled in the container to contain the oxidizing solution (8). The oxidizing solution 8 acts on the exposed part of the tube 1 through the slit to generate and grow cracks in the sensitized heat-treated tube 1. Probe or oxidizing solution container should be removed after the desired type of heat pipe crack occurs, so spring pressure, adhesive means, etc. should be designed so as not to leave traces on the specimen upon contact.

On the left side of the oxidizing solution container, a focal microscope 2 is provided to observe the exposed portion between the slits. In order to observe the heat transfer tube 1 accurately, it is preferable to install the original focal microscope 2 on the exact left side of the exposed part, so that the container of the oxidizing solution is preferably formed of a transparent acrylic plate or the like.

At the end of the probe and at the end of the focal microscope, a digital multimeter, a switch current unit, a power supply, a charge couppled device (CCD), etc., are connected through signal lines to prevent cracking. Allows you to measure your growth.

3 and 4, when a device for applying stress to the heat pipe tube and a means for acting an oxidizing solution and a means for checking a crack state are prepared (S50), the pressure against the tube is acted through a tensile tester, The crack is generated and progresses (S60). Pressure or tensile force is applied based on finite element analysis. For example, a tube about 15 cm long and 1.2 mm thick can be subjected to a force of 3 to 4 N (Newton) through a linear contact with a vertical jig. . The state of a crack can be determined by arranging a plurality of pairs of probes located above and below a predetermined crack in the axial direction, measuring voltage difference, resistance, etc. at the end of the probe, or by observing the crack state under a microscope. The stress application device and the oxidizing solution container are removed.

In this embodiment, only the radial denting load is applied to push the outer surface of the tube from the outside of the tube to the center, but in the present invention, in addition to or with the radial denting load in order to create a more realistic cracking, withstand pressure and tension Combining the load method, applying an external force, can produce cracks.

In addition, in order to damage the surface by corrosion, 0.1 M (mole) of Na ₂ O ₆ S ₄ .2H ₂ O (sodium tetrathionate) aqueous solution may be used as an oxidizing solution, but other oxidizing solutions are not excluded. .

On the other hand, the generation of cracks alone does not form cracks, such as cracks in the heat pipes of the nuclear power plant steam generator. In order to make crack specimens of the same shape as actual ones, corrosion must be formed at the grain boundary where cracks have occurred. Proceed (S70).

For the cracked specimen of the heat exchanger tube formed through the above process, it is judged whether the desired high step ratio crack has been formed through eddy current test (ECT) and the like (S80). Research will be used, for example, to determine how many more cracked heat pipes can be used in real nuclear power plant conditions without problems and when they need to be replaced.

According to the present invention, since it is possible to produce a crack specimen with the steam generator heat transfer having the same shape as the actual shape, by using it more precisely to study the safety and life extension of the pressurized water light reactor, and non-destructive inspection of the steam generator heat pipe Can increase the reliability.

Claims (7)

Preparing a heat pipe tube for specimen formation; Subjecting the heat transfer tube tube to sensitization heat treatment; And And a cracking step of contacting the surface of the heat pipe tube with an oxidizing solution together with a radial denting load applied to the center of the heat pipe tube from the outside of the heat pipe tube. . The method of claim 1, Subsequent to the cracking step, the method of producing a specimen of steam generator tube, characterized in that further comprising the step of corroding the heat pipe tube in a high temperature and high pressure hydrochemical environment. The method of claim 2, And a step of checking a crack state by an eddy current test (ECT) after the corroding step is further provided. The method of claim 1, And a window forming step of narrowing and exposing only a predetermined portion of the steam generator heat pipe and shielding a peripheral surface with an oxidizing solution cover prior to the cracking step. The method of claim 1, In the cracking step, the specimen production method of the steam generator tube, characterized in that the monitoring is carried out to perform a crack observation to determine whether the desired crack is obtained. The method of claim 1, Before the step of subjecting the sensitizing heat treatment, using the tensile test and the finite element analysis method for the heat pipe tube to analyze the stress applied to the heat pipe tube for the tensile force, and extracting the tensile force to be applied to the heat pipe tube Specimens manufacturing method of the steam generator heat pipe. The method of claim 1, Steam generator tube specimen manufacturing method characterized in that the external force is applied by combining the pressure resistance method and the tensile load method with the radial denting load applied to the heat pipe tube in the cracking step.

Images