JPH08220287A - Method and device for repairing structure in reducing liquid - Google Patents

Abstract

PURPOSE: To repair the defect of a structure in contact with a reducing liquid without any relocation thereof. CONSTITUTION: For repairing the defect 10 of the inner wall of a structure 2 in contact with a reducing liquid contained therein, a sealed space 14 is formed to cover the defect 10, and purged of the reducing liquid under the spray of a shield gas 8. Then, the gas 8 is recovered through a passage 20, and the defect 10 is repaired in the space 14. In this case, the defect 10 is repaired by welding or applying compression stress to the surrounding area thereof.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and apparatus for repairing a structural material containing liquid by welding or the like, and is particularly suitable for repairing an inner wall of a reactor vessel of a fast breeder reactor containing liquid sodium. Repair method and apparatus therefor.

[0002]

2. Description of the Related Art A fast breeder reactor uses liquid sodium as a medium for transmitting energy generated from a nuclear reactor. Sodium has the advantages that it has a good heat transfer property, has a high boiling point, can retain a liquid at atmospheric pressure at the operating temperature of a nuclear reactor, and has a small nuclear absorption of neutrons.

On the other hand, since sodium is chemically active and acts as a reducing substance, various reactions occur on the surface of the material, and as a result, the material properties are also affected. Phenomena that occur in materials in sodium include corrosion, mass transfer, wear and self-fusion, and as a result, the material strength such as creep and fatigue changes. The form of corrosion in sodium is general corrosion, and the amount of corrosion of the material depends on impurities in sodium, temperature, etc., but the largest factor is oxygen or carbon in sodium. The mass transfer phenomenon is a phenomenon in which a component element in a material is eluted into sodium, or conversely, an element dissolved in sodium is diffused and penetrated into the material. The wear / self-fusion phenomenon is accelerated by the fact that the base material of the material itself comes into contact as a result of the removal of the oxide film on the material surface by sodium. The above phenomenon in sodium changes the material strength such as tensile strength, creep strength, and fatigue strength.

Since the fast breeder reactor is operated at a high temperature of 500 ° C. or higher, it is necessary to grasp the high temperature strength characteristics of the material and design the structure in order to secure the safety and reliability of the plant. is there. As described above, the material strength characteristics can be mainly classified into tensile strength characteristics, creep strength characteristics, fatigue strength characteristics, etc.When designing a structure, these basic material strength characteristics data are acquired to determine the strength. Shape to satisfy
Dimensions etc. are determined.

Of these material strengths, the most important one is fatigue strength. Repeated loads, so-called fatigue loads, are applied to the structure of the fast breeder reactor due to thermal expansion that occurs during start-up and shutdown during the life of the plant, and hydrodynamic vibration and thermal shock that occur during steady operation. In particular, since fast breeder reactors operate at high temperatures, measures against thermal shock tend to be an issue when designing.

A furnace vessel is an example of a site where the thermal shock phenomenon occurs. During transient operation such as scramming a nuclear reactor, the density of sodium changes as the sodium flowing out from the core changes from a high temperature to a low temperature. This causes a so-called thermal stratification phenomenon in which high-density low-density sodium stays in the upper part of the hot plenum. Thermal striping occurs at the interface between the high temperature and low temperature sodium layers generated at this time. When thermal striping occurs in the hot plenum, temperature fluctuations are added to the reactor vessel and the upper core mechanism, which causes thermal fatigue.

Further, there is a reactor upper part mechanism as an example of a portion where the thermal shock phenomenon occurs, in which low temperature and high temperature sodium flowing out from the core are mixed. The coolant flowing out of the control rod assembly or the blanket fuel assembly in the core that generates a small amount of heat has a lower temperature than the coolant flowing out of the fuel assembly. The control rod assembly is a strong neutron absorber, and has functions such as nuclear reactivity adjustment and reactor shutdown. In the fast breeder reactor, blanket fuel assemblies are loaded in the reactor in order to produce more plutonium than it has consumed. Since the blanket fuel assembly uses depleted uranium, the temperature rise from the inlet nozzle to the handling head is small in the early stage of use when the production of plutonium is low. It flows above the fuel assembly.

In the upper part of the core, the high temperature and low temperature coolants are mixed and rise toward the upper structure of the reactor. The reactor upper structure has a function of supporting various instrumentation mechanisms such as thermocouples for core monitoring, and a function of rectifying coolant.
The thermocouple measures the coolant outlet temperature in each assembly during reactor operation. The rectifying device consists of a guide rod for the control rod drive mechanism and a rectifying cylinder supported by a lattice plate arranged on the lattice around the control pipe. The rectifying device is exposed to high-temperature and low-temperature coolants of the reactor superstructure. Near the surface, a high-frequency thermal shock of about several hertz is applied, and fatigue damage increases. The stress generated by the high-frequency thermal shock becomes maximum on the surface, and the stress is rapidly attenuated as it goes inward. Furthermore, the higher the thermal shock frequency, the more the fatigue damage is limited to the surface. Further, in thermal shock, the larger the temperature difference between the high temperature and the low temperature, the greater the damage.

The thermal shock phenomenon can also occur in piping systems other than the furnace vessel. For example, when the coolants of the main pipe and the branch pipe merge at the joint between the main pipe and the branch pipe, if there is a temperature difference between the coolants, thermal shock occurs in the downstream region of the joint.

As described above, in the fast breeder reactor, the fatigue load such as thermal shock is applied to the equipment / structure used in sodium. In designing equipment and structures, the shapes and dimensions are determined by fully considering their fatigue loads. However, if a defect occurs in the equipment / structure due to some cause, the conventional method for repairing the defect in the structural material is to drain sodium in the structure, then divide / disassemble the structure to remove sodium on the surface of the material. Had been cleaned and then repaired.

However, it is necessary to set up necessary work steps before repair, such as sodium drain, division / disassembly and cleaning of the structure, and further it is necessary to reassemble after repair, so that it takes a long time to restart the plant. There is a problem of cost. Also, since sodium is chemically active and causes a rapid reaction with water, it is necessary to give sufficient consideration to safety when cleaning the structure taken out. In particular, when radioactive substances are attached to the surface of the structure, it is necessary to take measures against exposure to radiation and cleaning waste liquid treatment. in this way,
The above-mentioned repair method is not preferable from the viewpoints of period, safety and economical efficiency.

[0012] Therefore, it is preferable to repair the structure with sodium still contained without draining sodium, but this could not be realized conventionally. For example, as shown in FIG. 15, using a general underwater welding apparatus,
When the defect 10 formed inside the furnace vessel 2 is repaired by welding, it is possible to apply it to a fast breeder reactor simply by injecting a shielding gas from the tip of the welder 1 to shield sodium from the defect 10 and perform welding. I can't.

Incidentally, as a conventional technique related to a general underwater welding apparatus, there are JP-A-3-258462 and JP-A-54-54.
35840, JP-A-54-35841, Shoukai 58
-85483, SAIkai Sho 57-204875, SAIKAI HEI 4-80664, etc.

[0014]

The reason why the conventional underwater welding technique cannot be applied to the fast breeder reactor is that, first of all, there is a problem that the work cannot be visually performed because liquid sodium is opaque. Further, if the welding slag scatters into the liquid sodium and is not collected, the operation of the breeder reactor may be hindered. Furthermore, it is necessary to inject the shield gas to isolate the welded part from the liquid sodium as in the conventional method, but if the shield gas is not recovered, the shield gas will be mixed into the atmosphere inside the reactor and various instruments will detect it. There is also a possibility that it may cause a false detection during operation of the breeder reactor.

An object of the present invention is to provide a repairing method and an apparatus therefor, which does not require visual work, collects welding slag and shielding gas, and enables repairing of a structure in a shorter period, safely and at low cost. To provide.

[0016]

The above object is to provide a closed space for covering a defect formed on the liquid side inner wall of a structure containing a reducing liquid and to provide a closed space in the closed space. This is accomplished by removing the liquid from and repairing the defect in the enclosed space.

The above object can also be achieved by injecting a shield gas into the closed space and collecting the shield gas without discharging the shield gas to the outside of the closed space.

The above object is also achieved by detecting the position of the defect with an ultrasonic sensor.

The above object is also achieved by performing the repair by welding.

The above object is also achieved by performing the repair by applying a compressive stress to the periphery of the defect to bond the defect.

The above-mentioned object is also to carry out the repair by cutting the defective portion with a cutting tool having a large radius of curvature,
Achieved.

The above-mentioned object is also to repair a defect formed on the liquid contact side of a structure that contacts a reducing liquid by applying a compressive stress to the periphery of the defect from the side opposite to the liquid contact side. This is achieved by joining the defects.

The above object is also achieved by applying the thermal stress to generate the compressive stress.

[0024]

[Function] Since the reducing liquid in the closed space is removed for repair, it is not necessary to construct the necessary working steps before and after the repair, such as draining the reducing liquid, dividing / disassembling the structure, cleaning and reassembling. The period until the plant is restarted can be shortened. Further, it is possible to save the trouble of cleaning the chemically active sodium adhering to the structure taken out.
Further, there is no problem of exposure to radioactive substances adhering to the surface of the structure and treatment of cleaning waste liquid.

[0025]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a configuration diagram of a repair device according to an embodiment of the present invention. The liquid in the furnace vessel 2 is sodium. The repairing device 1 has a covered arc welding device as a joining device 3 which is joined by an electric method inside. Furthermore, the repair device 1 has a casing 14 for isolating sodium from the joining device 3. The repair device 1 is inserted from the upper part of the furnace vessel 2 using a maintenance hole or the like. After inserting the repairing device 1 into the sodium of the furnace vessel 2, an inert shield gas 8 such as argon gas is blown into the sodium from the inside of the repairing device 1 to form a joining device 3 inside the repairing device 1. And move while isolating sodium. At the tip of the repair device 1, a sealing material 12 is brought into close contact with the inner surface of the furnace container 2, and a space is formed by the inner surface of the furnace container 2 and the casing of the repair device 1.

When the repair apparatus 1 and the inner surface of the furnace vessel 2 are brought into contact with each other, the shielding gas 8 blows off the sodium adhering to the inner surface of the furnace vessel 2 to remove it. Further, by attaching a relatively soft sealing material 12 to the tip of the repair apparatus 1 and pressing the repair apparatus 1 toward the furnace vessel 2, the adhesion between the inner surface of the furnace vessel 2 and the tip of the repair apparatus 1 is maintained. . Here, the shielding gas 8 such as argon gas is continuously blown from the inside of the repair device 1 so that sodium does not enter the inside of the repair device 1 through a slight gap in the contact portion. The blown argon gas passes through the passage 20.
Recovered through. It should be noted that the welding location is cooled by blowing argon gas to the welding location.

A small ultrasonic sensor (not shown) is attached to the tip of the welding device 3, and the welding location is found by the output of this sensor. After the welding device 3 and the welding spot are positioned to face each other, the welding device 3 inside the repair device 1 is positioned.
Repair the welded part (defective part). In this example,
Although a welding method is adopted as the repair method, the slag generated by this welding is recovered along with the argon gas through the passage 20. The example shown in FIG. 1 is a repair method in the case of a relatively small defect, and at this time, repair can be performed only with weld metal.

FIG. 2 shows a case where the reinforcing member 4 is attached to the inner surface of the furnace vessel 2 by using a covered arc welding apparatus, which is suitable for repairing relatively large defects. In this case, the reinforcing member 4
Is held from inside the repair device 1. When moving the repair device 1 in sodium, the repair device 1 is moved in the same manner as above.
The shield gas 8 such as argon gas is continuously blown from the inside. When the repair device 1 and the inner surface of the furnace vessel 2 are brought into contact with each other, the shielding gas 8 blows off the sodium adhering to the inner surface of the furnace vessel 2 to remove it.

The embodiment shown in FIGS. 1 and 2 is joined by covered arc welding. In the arc welding, an arc is generated between the base material and the metal electrode by a low voltage and a large current, and the heat causes the base material and the metal electrode in the welding rod to be melted and joined. The arc generated between the material and the welding rod produces intense light and heat. A shield gas 8 is flown around the arc to keep the arc stable. In order to maintain this protective effect, the shield gas 8 needs to be stable, and therefore the arc is shortened.

Joining methods by arc welding other than the covered arc welding include TIG welding method, MIG welding method and submerged arc welding method. TIG welding is a method in which an arc is generated between a material and a tungsten electrode in argon or helium gas, a filler rod is inserted into the arc, and the material and the filler rod are melted and welded. . TIG welding is used for welding relatively thin plates and welding pipes. MIG welding, like TIG welding, produces an arc between itself and the electrode, but there is no filler rod and the electrode itself is the filler material. Submerged arc welding uses a bare welding wire as an electrode and supplies flux to the material,
It is a method of generating an arc in the flux and continuously welding. Generally suitable for welding medium to thick plates.

Further, as electric joining methods other than arc welding, resistance welding method, plasma welding method, electrogas welding method, electroslag welding method, high frequency welding method, electron beam welding method, laser welding method, light beam welding method, etc. There is. Resistance welding utilizes the electric resistance of two metals to be joined and the contact resistance between the two metals, and is a welding performed by passing an electric current and converting electric energy into thermal energy. Resistance welding includes spot welding, seam welding, projection welding and butt welding. Resistance welding is suitable for joining relatively thin plates, round bars and pipes.

When the material is repaired by using the electrical method as described above, sodium on the surface of the material and the inside of the defect is cleaned and removed as much as possible. When joining materials using an electrical method, the material temperature near the joining can be heated up to around 2000 ° C. At this time, the residual sodium vaporizes and remains inside the material. In addition to sodium vapor, it is easy to absorb oxygen, nitrogen, hydrogen and other gases in the space. Therefore, the sodium vapor can be removed using the shield gas 8 and the absorption of these gases can be reduced.

Austenitic stainless steel is mainly used as the structural material of the fast reactor. A point to be noted in the welding of this austenitic stainless steel is grain boundary precipitation of chromium carbide in the heat affected zone. Grain boundary precipitation of chromium carbides increases as the heating time increases in the temperature range of 550 ° C to 850 ° C. If there is a possibility that grain boundary precipitation of chromium carbide will occur during welding, the time to cool in the critical temperature range where grain boundary precipitation occurs by limiting the welding heat input amount or concentrating the welding heat as much as possible. To shorten.

In the embodiment shown in FIGS. 1 and 2, by appropriately selecting the cooling process by the shield gas 8,
The above problems can be solved. In addition, when grain boundary precipitation of chromium carbide is unavoidable, there is a method of performing a solution heat treatment after welding to decompose and solidify the chromium carbide. Also, by using low carbon stainless steel as the material itself, the precipitation of chromium carbide can be suppressed.

FIG. 3 is a diagram showing an embodiment to which a method of repairing a structure in a space in sodium by a friction welding method which is a mechanical method is applied. The repair device 1 is inserted from the upper part of the furnace container 2, the tip of the repair device 1 is in close contact with the inner surface of the furnace container 2, and the inner surface of the furnace container 2 and the repair device 1 form a space. The repair device 1 is inserted from the upper part of the furnace vessel 2 using a maintenance hole or the like. After inserting the repairing device 1 into the sodium of the furnace vessel 2, an inert shield gas 8 such as argon gas is blown into the sodium from the inside of the repairing device 1 to form a joining device 3 inside the repairing device 1. And move while isolating sodium. A reinforcing member 4 and a rotary load device 5 having a function of driving the reinforcing member 4 to rotate and a function of pressing the reinforcing member 4 toward the furnace vessel are loaded in this space.

Here, the reinforcing member 4 is attached to the defective portion on the inner surface of the furnace vessel.
When pressed against the furnace vessel while rotating at a high speed, both materials are softened and fused by the frictional heat generated between the furnace vessel and the reinforcing member 4 to join them. During bonding, the surrounding material is cooled by continuing to blow the shield gas 8. As described above, in the present embodiment, the friction welding method is adopted, the joining end faces are abutted with a constant pressing force while the materials to be joined are relatively moved, and the friction heat generated at that time is used as a welding heat source. .

As a method of joining by a mechanical method other than friction welding, there is an ultrasonic welding method and the like. The ultrasonic welding method
This is a method in which ultrasonic vibration is applied to the bonding interface under pressure to rub the bonded portions together to obtain a contact surface between metals and bonding. At this time, due to the friction phenomenon on both interfaces accompanying the ultrasonic vibration, the oxide film on the surface is destroyed and the adherence is facilitated. Further, due to the local temperature rise due to the frictional heat, the diffusion and recrystallization of atoms are promoted, and a strong adhesion surface is formed.

When the materials are joined by the above mechanical method,
The distance between the surfaces should be as short as possible in order to bring the two surfaces of the materials to be bonded into close contact with each other. Therefore, the groove processing of the material required in the case of the above electrical connection is not particularly required, and there is an advantage that repair can be performed in a short time.

In FIG. 4, the peripheral portion of the defective portion generated on the inner surface of the furnace vessel 2 is heated by the heating device 6, and the cooling device 11 blows an inert gas to cool the defective portion to apply compressive stress to the defective portion. It is a figure of the Example which adopted the repair method of making it press-contact. The repair device 1 having a heating device 6 such as a heater therein is inserted from the upper portion of the furnace container 2, and the tip of the repair device 1 is inserted into the furnace container 2.
The inner surface of the furnace container 2 and the repair device 1 form a space. Here, the tip of the repair device 1 is strongly pressed toward the inner surface of the furnace vessel 2 to maintain adhesion, and deformation of the member around the defect that is about to thermally expand is suppressed so that the thermal stress of compression is applied to the defect. Generate.

In the embodiment shown in FIG. 4, the joining points are strongly pressed by thermal stress to cause plastic deformation of the materials and joining is performed.
In the case of such pressure welding, when the bonding surfaces are brought close to each other to the lattice constant of the crystal, free electrons are shared with the metal ions belonging to each and metal bonding occurs. Here, there is also a means for facilitating deformation by increasing the temperature of the defective portion without cooling with the cooling device 11. At this time, atoms are easily diffused, and a stronger joint surface can be obtained. When strong plastic deformation is applied to the joint surface, the oxide film is destroyed and it becomes possible to adhere clean new metal surfaces to each other.

FIG. 5 is a diagram showing an embodiment to which a repairing method is applied in which a sharp defect tip portion generated on the inner surface of the furnace vessel 2 is cut so as to have a large radius of curvature. The repair device 1 has a cutting device 7 inside. When a defect having a sharp tip portion is generated on the inner surface of the furnace vessel 2, stress is likely to be concentrated on the defect tip portion. For example, there is an elliptical defect having a length 2a and a radius of curvature ρ in the major axis direction in an infinite flat plate,
It is assumed that the tensile stress σ acts uniformly in the minor axis direction of the ellipse. At this time, the stress σMAX generated in the portion having the radius of curvature ρ of the elliptical defect is σMAX = 2σ (a / ρ) ^1/2 (1) assuming that ρ is sufficiently small.

Therefore, by increasing the radius of curvature ρ, the stress σMAX can be reduced and the progress of defects can be suppressed. In the embodiment of FIG. 5, the shape of the cutting blade attached to the cutting device 7 can be selected and processed into a shape having an arbitrary radius of curvature. Further, by blowing the shield gas during cutting, it is possible to suppress the rise of the surrounding material temperature.

In the embodiment shown in FIG. 5, a method of repairing a sharp defect tip portion generated on the inner surface of the furnace vessel 2 by cutting is shown. However, even when a defect occurs in the internal structure of the furnace vessel 2, The generated stress can be reduced by the same method. Further, in this case, the stress generated can be reduced by cutting a hole such as a so-called stop hole at the tip of the defect.

FIG. 6 is a diagram showing an example in which a repair method in sodium is applied by a friction welding method which is a mechanical method. The difference from the embodiment of FIG. 3 is that repair is performed without providing a space in sodium. At the tip of the repair device 1, a reinforcing member 4 having a shape similar to that of the defective portion and rotating at high speed is attached. The repair device 1 has a function of rotating the repair member 4 and a function of pressing the repair member 4 toward the furnace vessel. The sodium seal of the rotary drive shaft and the main body of the repair device 1 is maintained by an oil seal or the like. In addition, repair device 1
Is inserted from the top of the furnace vessel 2. Repair device 1 is furnace container 2
When the inner surface of the furnace is approached, the reinforcing member 4 is rotated at high speed and pressed toward the furnace vessel 2. Furnace vessel and reinforcing member 4
Both materials are softened and fused by the frictional heat generated between them to join them. In this example, the materials are joined in sodium. According to the fusion test of the material in sodium, the fusion phenomenon is observed even at the temperature of 550 ° C. Therefore,
Friction welding in sodium is possible by setting the temperature during friction welding to 882 ° C or lower, which is the boiling point of sodium.

In FIG. 7, the periphery of the defective portion 10 generated on the inner surface of the furnace vessel 2 is heated by the heating device 6 attached to the outer surface of the furnace vessel 2, and the outer surface corresponding to the central portion of the defective portion 10 is cooled. FIG. 11 is a diagram showing an example in which a repair method in which cooling is performed by the device 11 and a compressive stress is applied to the defective portion to press-contact the defective portion is applied. This example was made based on the characteristics obtained in the material strength experiment in sodium, which will be described in detail later, and effectively utilizes the reducibility of sodium.

Here, in order to suppress the thermal expansion of the peripheral material of the defective portion 10 and generate the thermal stress, the deformation suppressing member 13 is installed in the furnace vessel 2 around the heating device 6 by spot welding or the like.
In the embodiment shown in FIG. 7, it is not necessary to insert the repair device into the sodium. In this embodiment, the joining points are strongly pressed by thermal stress to cause plastic deformation of the materials and joining. In the case of such pressure welding, when the bonding surfaces are brought close to each other to the lattice constant of the crystal, free electrons are shared with the metal ions belonging to each and metal bonding occurs.
Here, there is also a means for stopping the cooling by the cooling device 11 and increasing the temperature to make it easier to deform. At this time, diffusion of atoms is likely to occur, and a stronger joint surface can be obtained. When strong plastic deformation is applied to the joint surface, the oxide film is destroyed and it becomes possible to adhere clean new metal surfaces to each other.

In the embodiment shown in FIG. 7, the defect surface is to be bonded while being in contact with sodium. In this case, the reducing property of sodium can be utilized to perform the bonding more easily and firmly. Since sodium has a reducing property, the oxide film on the material surface is removed by sodium and a clean material surface is obtained. For example, a clean surface can be obtained even on the fracture surface of the defect.

In the region including the defective portion surrounded by the heating device 6, the surrounding material is heated to a high temperature, so that the compressive stress acts. Therefore, as shown in FIG. 8, compressive stress also acts on the defective portion, and as shown in FIG. 9, the opening amount of the defective portion is gradually reduced and repair can be performed. As described above, since sodium has a reducing property, the fracture surface of the defective portion is stored relatively cleanly and is likely to be recombined.

Next, the material behavior of sodium invented by the present invention will be described. The characteristic of the sodium environmental effect on the growth and retention of cracks (hereinafter, laboratory-worked defects are called cracks) generated in the material can be explained by the reducibility of sodium. FIG. 10 is a schematic representation of the environmental effects on crack propagation and retention behavior in air and sodium. In sodium, (1) oxide formation on the fracture surface is less than in air, and recombination between fracture surfaces is more likely to occur, so the crack growth rate decreases. (2) Oxide formation on the fracture surface is small, and the wedge effect between fracture surfaces generated during compression is small.

Therefore, the closing angle (angle formed by two fracture surfaces) at the time of closing the crack is small, the compressive strain generated at the tip of the crack is large, and the crack is less likely to stay. Hereinafter, the sodium environmental effect will be described based on conventional experimental data.

FIG. 11 shows the relationship between the crack length a and the crack growth rate da / dN obtained from an experiment on a minute crack. The test piece is a SUS304 plate with a central notch, and the experimental temperature is 550.
Fatigue load is maximum and minimum stress σ = ± 50MPa.
From this, the crack growth rate in sodium is affected by the frequency, and becomes slower at higher frequencies. Furthermore, the crack growth rate in sodium is slower than in air when the frequency is 0.07Hz. It can be inferred that this is due to the tendency of recombination between fracture surfaces in sodium. That is, the fracture surface is not easily oxidized in sodium, and recombination between fracture surfaces is likely to occur in the compression process of repeated loading. On the other hand, when a crack develops and a fracture surface is formed in the air, the fracture surface is oxidized and recombination between both fracture surfaces is difficult.

Such recombination between fracture surfaces in sodium has also been observed from fracture surfaces in fatigue crack growth experiments using Inconel. In the experiment, inconel was used to perform fatigue tests in sodium and air at a temperature of 427 ° C to compare striations. Striation is a wavy pattern formed on the fracture surface by repeated loading, and one wavy pattern is formed in one cycle. As a result, the continuous striations clearly observed in air were not observed in sodium, leaving a trace that the striations were removed, which was attributed to the recombination between the fracture surfaces. Think

FIG. 12 is obtained from a thermal striping experiment in sodium. The stress intensity factor range ΔK and the crack growth rate da / dN in a low stress field where the crack stays.
Shows the relationship. In the thermal striping experiment in sodium, hot and cold sodium jets flowing from a fixed nozzle were made to collide with a rotating flat plate made of SUS304 alternately. Here, the temperatures of hot and cold sodium are 550 ° C. and 250 ° C., respectively. If the stress intensity factor ranges ΔK are equal, it means that the stress amplitudes at the crack tip are equal even if the shape of the object, the applied load, and the shape of the crack are different. The ΔKth shown in FIG. 11 is a value in the stress intensity factor range ΔK at which a crack does not propagate below this value, and normally, ΔK when the crack growth rate is around 10 to ⁷ mm / cycle is used. Therefore,
Lower critical stress intensity factor range ΔKth in Natliu is about 8MP
It becomes am ^1/2 .

FIG. 12 also shows in-air data obtained by a fatigue test under load control at a temperature of 550 ° C. using a flat plate specimen with a central notch of SUS304. From FIG. 11, the lower limit stress intensity factor range ΔKth at which cracks stay is about 18 MPam ^1/2 in air, while it is about 8 MPam ^1/2 in sodium, which is smaller in sodium. From this, it can be seen that the cracks are more likely to propagate in sodium even in low stress than in air. This is because oxides are less likely to be generated in reducing sodium and the wedge effect is smaller than that in air. In other words, in sodium during repeated compression process, oxides do not intervene between the fracture surfaces, so the distance between the fracture surfaces is long and crack closure that closes the fracture surfaces does not occur easily. As a result, in sodium, the compressive strain at the tip of the crack increases, and the crack easily propagates. On the other hand, in high temperature air, there is an oxide on the fracture surface, and due to its wedge effect, crack closure that closes the fracture surface easily occurs,
Damage to the crack tip is mitigated. It is considered that the characteristic of the crack in sodium as compared with that in air is that the oxide is less likely to be generated on the material surface or fracture surface in each process.

The embodiment shown in FIG. 7 is for repairing the material in the above-mentioned reducing sodium by utilizing the characteristics obtained from various experiments, and can obtain a strong adhesion surface. . Further, in this embodiment, since it is not necessary to insert a repair device into sodium, it is possible to repair the defect easily and promptly.

Although the above embodiments have been described for the reactor vessel, the repairs according to the above-described embodiments can be applied to other devices and structures of the fast breeder reactor such as the intermediate heat exchanger and the piping system. Further, it can be applied not only to repairing sodium but also to repairing materials used in a liquid having a reducing property.

FIG. 13 is a diagram showing an embodiment to which a repairing method for the pipe 15 is applied. A high frequency induction heating device 16 is installed around the pipe 15 to heat the outer surface of the pipe.
The sodium 9 in the pipe 15 is flowing to cool the inner surface of the pipe. In such a case, a large temperature difference occurs between the inner and outer surfaces of the pipe. When this temperature difference is linear and a sufficiently wide range is heated, the thermal stress generated on the inner and outer surfaces of the tube is approximately represented by the following equation.

Σ = ± EαΔT / 2 (1−ν) (2) where α: linear expansion coefficient E: Young's modulus ΔT: temperature difference between the inner and outer surfaces of the tube ν: Poisson's ratio, and the positive sign is The cooling surface is shown, and the negative sign shows the heating surface.

FIG. 14 shows a schematic diagram of the stress-strain relationship on the inner surface during the heating and cooling process. The stress σ increases as ΔT increases, and the yield stress σy of the material becomes point 1
Reach When the temperature difference is further increased, thermal strain increases and reaches point 2. From this point, if the temperature difference ΔT is made smaller, the load up to point 3 is unloaded, and compressive residual stress occurs. 14
In the example shown in (1), since the reducing sodium is repaired in the state where it exists in the pipe, the surface of the defect 10 can be kept clean. In this way, a compressive residual stress is generated on the inner surface of the pipe, and the defects 10 on the inner surface of the pipe can be recombined and repaired.

[0060]

EFFECTS OF THE INVENTION According to the present invention, it is not necessary to construct necessary work steps before and after repair, such as draining a reducing liquid such as sodium, dividing / disassembling a structure, cleaning and reassembling, and even restarting a plant. The period can be shortened. Further, it is possible to save the trouble of cleaning the chemically active sodium adhering to the structure taken out. Furthermore, there are no problems such as exposure to radioactive substances adhering to the surface of the structure and treatment of cleaning waste liquid.

[Brief description of drawings]

FIG. 1 is a configuration diagram of a repair device according to a first embodiment of the present invention.

FIG. 2 is a configuration diagram of a repair device according to a second embodiment of the present invention.

FIG. 3 is a configuration diagram of a repair device according to a third embodiment of the present invention.

FIG. 4 is a configuration diagram of a repair device according to a fourth embodiment of the present invention.

FIG. 5 is a configuration diagram of a repair device according to a fifth embodiment of the present invention.

FIG. 6 is a configuration diagram of a repair device according to a sixth embodiment of the present invention.

FIG. 7 is a configuration diagram of a repair device according to a seventh embodiment of the present invention.

FIG. 8 is a diagram showing an open state of a defect portion before repairing in sodium.

FIG. 9 is a diagram showing an open state of a defect portion due to repair in sodium.

FIG. 10 is a schematic diagram of air and sodium environmental effects on crack growth and retention behavior.

FIG. 11 is a diagram showing a relationship between a crack length and a crack growth rate in air and sodium.

FIG. 12 is a diagram showing a relationship between a stress intensity factor range and a crack growth rate in air and sodium.

FIG. 13 is an explanatory diagram of repair according to the eighth embodiment of the present invention.

FIG. 14 is a diagram showing a stress-strain relationship on the inner surface of a pipe.

FIG. 15 is an explanatory diagram of a conventional general underwater welding apparatus.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Repair device, 2 ... Furnace vessel, 3 ... Joining device, 4 ... Reinforcing member, 5 ... Rotation load device, 6 ... Heater, 7 ... Cutting device, 8
… Shield gas, 9… Sodium, 10… Defect, 11…
Cooling device, 12 ... Sealing material, 13 ... Deformation suppressing member, 14
... casing, 15 ... piping, 16 ... high frequency induction heating device.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Hiromi Tokoi, 7-2-1, Omika-cho, Hitachi-shi, Ibaraki Hitachi, Ltd. Energy Research Laboratory, Hitachi, Ltd. (72) Inventor Kiyoshi Harada 3-chome, Saiwai-cho, Hitachi-shi, Ibaraki No. 1 No. 1 Stock Company Hitachi Ltd. Hitachi factory

Claims (16)

[Claims] 1. A repairing method for repairing a defect formed on a liquid-side inner wall of a structure containing a reducible liquid, wherein a closed space for covering the defect is provided and the liquid is removed from the closed space. A method for repairing a structure in a reducing liquid, which comprises repairing the defect in a closed space. 2. The method for repairing a structure in a reducing liquid according to claim 1, wherein a shield gas is injected into the closed space and the shield gas is recovered without being discharged to the outside of the closed space. 3. The method for repairing a structure in a reducing liquid according to claim 1, wherein the position of the defect is detected by an ultrasonic sensor. 4. The method for repairing a structure in a reducing liquid according to claim 1, wherein the repair is performed by welding. 5. The structure repair in a reducing liquid according to claim 1, wherein the repair is performed by applying a compressive stress to the periphery of the defect to bond the defect. Method. 6. The method for repairing a structure in a reducing liquid according to claim 1, wherein the repair is performed by cutting a defective portion with a cutting tool having a large radius of curvature. 7. A repair method for repairing a defect formed on a liquid contact side of a structure contacting a reducing liquid, comprising:
A method for repairing a structure in a reducing liquid, which comprises applying a compressive stress to the periphery of the defect from the side opposite to the liquid contact side to bond the defect. 8. The method for repairing a structure in a reducing liquid according to claim 5, wherein compressive stress is generated by applying thermal stress. 9. A repair device for repairing a defect formed on a liquid-side inner wall of a structure containing a liquid having a reducing property, a cover forming a sealed space for covering the defect, and the liquid from the sealed space. An apparatus for repairing a structure in a reducing liquid, comprising: a shield gas injecting means for eliminating the above; and a repairing means for repairing the defect in the closed space. 10. The structure in a reducing liquid according to claim 9, further comprising a passage for injecting the shield gas into the sealed space and collecting the shield gas without discharging the shield gas to the outside of the sealed space. Repair device. 11. The method according to claim 9 or 10,
An apparatus for repairing a structure in a reducing liquid, comprising an ultrasonic sensor for detecting the position of the defect. 12. The structure repairing apparatus in a reducing liquid according to claim 9, wherein the repairing means is welding means. 13. The reducing liquid according to claim 9, wherein the repairing means is a compressive stress generating means that applies a compressive stress to the periphery of the defect to bond the defect. Structure repair equipment. 14. The structure repairing apparatus in a reducing liquid according to claim 9, wherein the repairing means is a means for cutting a defective portion with a cutting tool having a large radius of curvature. . 15. A repair device for repairing a defect formed on a liquid contact side of a structure contacting a reducing liquid, wherein a compressive stress is applied to the periphery of the defect from the side opposite to the liquid contact side to remove the defect. A structure repairing device in a reducing liquid, characterized in that a compressive stress generating means for joining is provided. 16. The structure repairing device in a reducing liquid according to claim 13 or 15, wherein the compressive stress generating means is a thermal stress generating means by applying a thermal stress.