JP2003194984A - Repair method for reactor structure - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To perform repair-welding without requiring preprocess of welding for welded material in reactor structures irradiated by neutron and prevent weld cracking. <P>SOLUTION: The vicinity of crack type defect 10 caused on a welded material 9 of reactor structure irradiated by neutron is cut (a), a new welding material 12 is provided to the cut surface (a) and contact surfaces are welded with a laser welder 13. During the welding, annular heat radiation jigs 11 are arranged to each of welding member 9 and a new member 11. By arranging the heat radiation jigs 11 to the welding members 9 and 12, the weld part is quickly cooled after welding, and growth of helium bubbles in grain boundary is suppressed and generation of weld cracking is prevented. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of repairing a neutron-irradiated nuclear reactor structure for ensuring the integrity of a nuclear reactor structure such as a light water cooled reactor.

[0002]

2. Description of the Related Art The internal structure of a boiling water reactor will be schematically described with reference to FIG. FIG. 7 schematically shows the internal structure of a boiling water reactor. In FIG. 7, reference numeral 1 is a core, and a reactor pressure vessel 2 containing the core 1 has a core as a reactor structure. A core shroud 3 surrounding 1 is installed. Further, a core support plate 4 and an upper lattice plate 5 are provided above and below the core 1, and a jet pump 6, a diffuser 7, a shroud support plate 8 and the like are provided between the core shroud 3 and the reactor pressure vessel 2. The structure is installed.

Among these internal structures, a core shroud 3, a core support plate 4, an upper lattice plate 5, a jet pump 6
Etc. are mostly made of stainless steel. Other diffusers 7, shroud support plates 8
Etc., a Ni-based alloy is used.

The reactor pressure vessel 2 is made of low alloy steel, and the inner surface of the reactor pressure vessel 2 is buttered with stainless steel or Ni-based alloy. In some light water nuclear power plants, austenitic stainless steel having a high carbon content is used as the stainless steel forming the reactor structure.

When austenitic stainless steel having a high carbon content is welded during the construction of a nuclear reactor,
Grain boundary precipitation of chromium carbide occurs in the heat-affected zone to sensitize the material. Therefore, if high tensile stress is present in the material, stress corrosion cracking may occur in high temperature water. Also, N
It is known that the i-based alloy can also cause stress corrosion cracking according to the same principle as stainless steel.

On the other hand, the core shroud 3, the core support plate 5,
The reactor structure such as the upper lattice plate 6 and the reactor pressure vessel 2 receive neutron irradiation during the operation of the nuclear power plant. For this reason,
Deterioration of the material of the reactor structure, such as a decrease in ductility and an increase in susceptibility to irradiation-induced stress corrosion cracking, occurs. Also,
The neutron irradiation causes a nuclear reaction of constituent elements such as stainless steel and Ni-based alloy forming the reactor structure, and gas components such as helium slightly exist in the material.

The gas component in the above-mentioned material is agglomerated at the grain boundaries in the vicinity of the molten metal by heating during welding to form bubbles, and the bubbles grow until almost adjacent bubbles come into contact with each other. It is known to cause cracks along the.

[0008] Therefore, when repair welding is performed on a nuclear reactor structure or the like that has undergone neutron irradiation for the purpose of improving the safety and reliability of a nuclear power plant, the occurrence of welding cracks caused by helium bubbles generated by welding. In addition, it is necessary to apply a construction method that avoids a decrease in the strength of the welded joint.

As a repair welding method for preventing welding cracks in a nuclear reactor structure that has been irradiated with neutrons, for example, the concept of suppressing the growth of helium bubbles by reducing the amount of welding heat input and preventing welding cracks is described in WRKanne, Jr. et al .: Welding Jou
rnal, 67 (1988) p33.

Further, for example, JP-A-6-234070, JP-A-8-254595, JP-A-8-29580, and JP-A-6-289.
No. 183, JP 8-15481 JP, JP 6-289184 JP, JP 8-1344 JP, JP 8-57637 JP, JP 2
A conventional example is disclosed in Japanese Patent Publication No. 000-230996.

That is, Japanese Unexamined Patent Publication No. 6-234070 discloses heating the whole or a predetermined portion of a SUS304 steel furnace internal structure deteriorated by neutron irradiation to a designated temperature not exceeding the melting point,
After cooling, this is a repairing method that avoids cracks by welding the heating area.

Japanese Unexamined Patent Publication (Kokai) No. 8-254595 discloses that irradiation material containing an inert gas atom is preheated to generate trap site nuclei in which gas atoms are bubbled and then welded to avoid cracking. It is a repair method.

Japanese Unexamined Patent Publication No. 8-29580 discloses that a metal material deteriorated by neutron irradiation is heat-treated before welding to release an inert gas such as helium from the metal material, and then cracked by repair welding. Is a way around.

Japanese Unexamined Patent Publication No. 6-289183 discloses 0 to 5.0 × 10 ^27.
For a structure with a crack-like defect that has been irradiated with neutrons of n / m ² , a plate material is covered in the area including the defect part, and the edge of the plate material is fillet-welded. In, in the surface of the structure side is melted before coating the plate,
After that, it is a repair method that avoids cracks by performing fillet welding on the edges of the plate material.

Japanese Unexamined Patent Publication No. 8-15481 discloses 0 to 5.0 × 10 ²⁷ n
After removing the region containing the crack-like defect occurrence part in the structure where the crack-like defect has been generated by irradiation with high energy particle beam of / m ² , spot welding is continuously performed on the removed part surface. Alternatively, it is a repairing method in which cracking is avoided by intermittently performing half-wrapping of each spot weld to form a first layer weld and then performing welding of two or more layers.

Japanese Unexamined Patent Publication (Kokai) No. 6-289184 discloses a method of cooling a material surrounding a repair welding portion of a reactor internal structure material, which has been subjected to neutron irradiation, to an ambient temperature or a temperature lower than a temperature of the reactor internal structure. Alternatively, it is a repairing method in which a tensile residual stress caused by welding is offset by releasing the compressive strain caused by precooling by cooling by covering with a cooling medium to avoid cracking due to welding.

Japanese Unexamined Patent Publication No. 8-1344 discloses a reactor internal structural material that has been irradiated with high-energy particle beams and has a defect. This is a repair method for avoiding cracks by joining the plate material and the structural material while applying pressure.

Japanese Unexamined Patent Publication (Kokai) No. 8-57637 discloses that a member that has been irradiated with neutrons is subjected to heat treatment after applying stress above the yield point to increase dislocations in the vicinity of a portion to be welded and then performing heat treatment. This is a repair method that avoids cracking by doing.

Japanese Unexamined Patent Publication No. 2000-230996 discloses cracking by controlling the welding heat input and the cross-sectional shape of the weld metal within specific ranges according to the helium content of the reactor structure and avoiding cracking. It is a repair method.

[0020]

Among the above-mentioned known examples, JP-A-6-234070, JP-A-8-254595, and JP-A-8-254595
In JP-A-29580 and JP-A-6-289183, since it is necessary to heat or melt the weld before repairing the weld, it takes an enormous amount of work time as compared with the case where only repair welding is performed, and the heat treatment is performed. A separate construction device is required to perform the melting process.

In the method disclosed in Japanese Patent Laid-Open No. 8-15481, it is necessary to perform spot welding on the entire removed surface before filling the removed portion by overlay welding. It takes time and requires a separate construction device for spot welding.

The method disclosed in Japanese Patent Laid-Open No. 6-289184 is a method of preliminarily cooling the surrounding area of the repaired welded portion to a temperature lower than the atmospheric temperature or the temperature of the internal structure of the furnace. Equipment is required separately.

The method disclosed in Japanese Patent Laid-Open No. 8-1344 requires a separate device for applying a pressure to the plate material covering the working portion. The method disclosed in Japanese Patent Laid-Open No. 8-57637 requires a huge amount of work time because a stress is added to the vicinity of the planned welding portion to propagate dislocations, and further heat treatment is required. It is required separately.

The method disclosed in Japanese Unexamined Patent Publication No. 2000-230996 is performed by controlling the welding heat input amount and the cross-sectional shape of the weld metal within specific ranges in accordance with the helium content of the reactor structure to perform welding. This is an effective method because it can suppress the occurrence of cracks. However, for a material having a large helium content, it is necessary to reduce the welding heat input amount and the cross-sectional shape of the weld metal to some extent, and the construction conditions may be limited.

The present invention has been made to solve the above-mentioned problems, and repair welding can be performed on a nuclear reactor structure that has been irradiated with neutrons, and the life of the nuclear reactor can be extended and preventive maintenance can be achieved. Moreover, it is an object of the present invention to provide a method for repairing a nuclear reactor structure in a nuclear power plant that improves the reliability of the nuclear reactor.

[0026]

In order to achieve the above-mentioned object, the invention of claim 1 is to cover a nuclear reactor structure made of stainless steel, Ni-base alloy or low alloy steel containing helium by neutron irradiation. For the welded member, after deleting a region including a portion where a crack-like defect has occurred or a portion where the material of the welded member has deteriorated due to the neutron irradiation, a new welded member is brought into contact with the deleted portion. The heat dissipating jig is disposed on each of the contacted members to be welded, and welding is performed.

According to the present invention, by disposing the heat radiation jig in the welded portion, the welded portion is rapidly cooled immediately after welding, so that the growth of the grain boundary helium bubbles is greatly suppressed,
The occurrence of welding cracks can be prevented.

According to the second aspect of the present invention, crack-like defects are generated in the welded member of the reactor structure made of helium-containing stainless steel, Ni-base alloy or low alloy steel, which is irradiated with neutrons. Place heat radiating jigs on both sides of the area where the material is deteriorated by neutron irradiation.
It is characterized in that a molten layer is formed by welding to remove the crack-like defects, or the molten layer is coated with the molten layer. According to this invention, weld cracking can be suppressed.

The invention of claim 3 is characterized in that overlay welding is applied instead of the molten layer. According to this invention,
Weld cracks can be further suppressed as compared with the invention of claim 2.

According to a fourth aspect of the present invention, a crack-like defect occurs in a welded member of a reactor structure made of stainless steel containing Ni, helium, a Ni-base alloy or a low-alloy steel by neutron irradiation. Part, or after removing a region including a part where the material is deteriorated by neutron irradiation by cutting or electrical discharge machining, a heat dissipation jig is arranged on the welding member, and the removed part is welded by overlay welding and filled. To do. According to the present invention, weld cracking can be further prevented.

In a fifth aspect of the present invention, crack-like defects are generated in a welded member of a reactor structure made of helium-containing stainless steel, Ni-base alloy or low-alloy steel under neutron irradiation. Characterized in that the plate material is coated on a region including a portion where the material is deteriorated by neutron irradiation, or a radiating jig is arranged on the member to be welded and the edge of the plate member is welded to the member to be welded. . According to this invention,
Weld cracks can be further prevented.

The invention of claim 6 is characterized in that, in any one of claims 1 to 5, the material of the heat radiation jig is at least one metal or alloy selected from copper, aluminum or iron. According to the present invention, by using a metal or an alloy having excellent thermal conductivity as the material of the heat radiating jig, the welding heat can be easily dissipated and the welded portion can be rapidly cooled.

The invention of claim 7 is characterized in that, in any one of claims 1 to 5, the heat dissipating jig is provided with a coolant cooling mechanism. According to the present invention, welding cracks can be suppressed by welding while cooling with a refrigerant.

An eighth aspect of the present invention is characterized in that, in the first to fifth aspects, the heat radiating jig is provided with a cooling fin. According to the present invention, the cooling effect of the heat radiating jig is improved, so that welding cracks can be suppressed.

According to a ninth aspect of the present invention, in the first aspect, the members to be welded are welded while applying a pressing force. According to the present invention, when a pressing force is applied, the growth of helium bubbles during welding is suppressed, and the occurrence of welding cracks can be prevented.

The invention of claim 10 relates to claims 1, 6, 8 and
9. In the invention according to any one of 9 above, the welding is laser, T
One of IG arc, MIG arc, plasma arc, friction welding, and electric heating is used as the thermal energy source. According to the present invention, the welding method is simple and can be easily implemented.

[0037]

BEST MODE FOR CARRYING OUT THE INVENTION A first embodiment of a method for repairing a nuclear reactor structure according to the present invention will be described with reference to FIGS. In this embodiment, as shown in FIG. 1A, when a crack-like defect 10 is generated in a welded member 9 of a nuclear reactor structure that has been irradiated with neutrons, a region including the defect 10 is indicated by a dotted line a. Remove by cutting or EDM as shown in. Next, as shown in FIGS. 1 (b) and 1 (c), a new welding member 12 is provided in contact with the deleted portion of the dotted line a deleted in FIG. 1 (a), and the welding target member 9 and the new welding target member are provided. An annular heat radiating jig 11 is arranged in each of 12 and a laser welding machine 13 is installed. Then, as shown in FIG. 1D, the periphery of the contact surface between the member to be welded 9 and the new member to be welded 12 is welded by a laser welding machine 13 to form a weld metal layer 14.

Through the steps shown in FIGS. 1 (a) to 1 (d), the repair portion of the reactor structure can be repaired by providing a heat radiating jig 11 and welding. As the member 9 to be welded, a tubular body or an empty rod can be used.

Here, the reason for disposing the heat radiation jig 11 on the members 9 and 12 to be welded will be described. Specimen (material to be welded)
As a result, a welding test was performed on stainless steel containing helium under the conditions shown in Table 1, and the presence or absence of weld cracks was evaluated by observing the cross-section metallurgical phase of the welded portion. As a result, as shown in Table 2,
When the heat radiating jig was not arranged, the occurrence of weld cracks along the grain boundaries was observed in the weld heat affected zone. On the other hand, when the heat radiating jig was arranged, the occurrence of welding cracks was not observed, and the formation of sound welds was confirmed.

[0040]

[Table 1]

[0041]

[Table 2]

The reason why welding cracks are less likely to occur when a heat radiation jig is placed on a member to be welded and then welded is that the welded portion is rapidly cooled immediately after welding, so that the growth of grain boundary helium bubbles is extremely suppressed. Because it is done.

Therefore, according to the first embodiment, repair welding satisfying the strength of the welded joint can be performed, the occurrence of weld cracks can be avoided, and a sound welded joint can be obtained.

By using at least one kind of metal or alloy selected from copper, aluminum or iron as the material of the heat radiating jig 11, the heat conductivity is excellent, the welding heat can be easily dissipated, and it can be rapidly cooled. Target.

Next, a second embodiment of the method for repairing a nuclear reactor structure according to the present invention will be described with reference to FIG. In FIG. 2, the same parts as those in FIG. 1B are designated by the same reference numerals and overlapping description will be omitted.

This embodiment is different from the first embodiment in that as shown in FIG. 2, a heat radiating jig to be placed on a welded member 9 and a new welded member 12 of a nuclear reactor structure which has been irradiated with neutrons. In FIG. 11, a water cooling tube 15 is provided as a refrigerant cooling mechanism, and the other parts are the same as in the first embodiment.

According to the present embodiment, the laser welding machine 13 welds while cooling water is flown through the water cooling tube 15 serving as the refrigerant cooling mechanism to cool the heat radiation jig 11. Water circulates or circulates in the heat dissipation jig 11 through the cooling tube 15. As a result, the members to be welded 9 and 12 are cooled and welding cracks can be suppressed.

Next, a third embodiment of the method for repairing a nuclear reactor structure according to the present invention will be described with reference to FIG. In the present embodiment, in the second embodiment, a cooling fin 16 is provided in the heat radiating jig 11 instead of the water cooling tube 15.
That is, the heat radiation jig 11 provided with the cooling fins 16 is arranged in the welded member 9 and the new welded member 12 of the nuclear reactor structure that have been irradiated with neutrons, and the other portions are the same as those in the first embodiment. It is similar to the form. According to this embodiment,
Since the cooling effect of the heat radiation jig 11 is improved, it is possible to suppress welding cracks.

In addition, in the second and third embodiments, when a pressing force is applied to the welded member 9 and the new welded member 12 of the nuclear reactor structure which have been irradiated with neutrons, the welding is performed during welding. Since the growth of helium bubbles is suppressed, welding cracks are less likely to occur, and welding cracks can be prevented.

A fourth embodiment of a method for repairing a nuclear reactor structure according to the present invention will be described with reference to FIGS. 4 (a) to 4 (c).
This embodiment differs from the first to third embodiments in that the cutting a shown in FIG. 1A and the new welded member 12 shown in FIGS. 1B, 2 and 3 are obtained. Without
As shown in FIG. 4 (a), the welded member 9 of the nuclear reactor structure having the crack-like defect 10 that has been irradiated with neutrons has the same structure as that shown in FIG. 4 (b). Welding after disposing the heat radiating jigs 11 on both sides apart and installing the laser welder 13 and then removing the crack-like defects 10 by non-filler welding with the laser welder 13 as shown in FIG. 4 (c). Metal layer 14
Then, the molten layer 17 is formed.

According to the present embodiment, the heat radiating jigs 11 are arranged on both sides of the crack-like defect 10 as the center, and the molten layer 17 is formed on the weld metal layer 14 from which the crack-like defect 10 is removed by welding. Form and repair reactor structures. Thereby, weld cracking can be suppressed. In place of the molten layer 17, for example, a crack-like defect 10 of the member 9 to be welded may be welded while supplying a filler rod, and overlay welding processing may be performed.

A fifth embodiment of a method for repairing a nuclear reactor structure according to the present invention will be described with reference to FIGS.
In this embodiment, as shown in FIG. 5A, the crack-like defect 10 is surrounded by the welded plate-like member 9a of the nuclear reactor structure having the crack-like defect 10 that has been irradiated with neutrons. As shown by the dotted line a, a substantially bottomed V-shaped cutting removal region is defined, and the region of the dotted line a is removed by cutting or electric discharge machining as shown in FIG. A substantially V-shaped groove 18 is formed. In this case, the plate member 9a to be welded
The plate-shaped heat radiation jigs 11a to 11c are arranged on the upper and lower surfaces of the above. After that, as shown in FIG. 5C, a weld metal layer 14 is formed in the groove 18 by overlay welding to repair the crack-like defect 10. According to the present embodiment, repair welding can be performed without the need for welding pretreatment, and weld cracking can be prevented.

A sixth embodiment of the method for repairing a nuclear reactor structure according to the present invention will be described with reference to FIGS. 6 (a) to 6 (c).
The present embodiment does not form the groove 18 in the fifth embodiment, but the welded plate-like member of the reactor structure having the crack-like defect 10 which has been subjected to the neutron irradiation shown in FIG. 6A. 9
As shown in FIG. 6 (b), the plate material 19 is coated on the area including the portion where the defect 10 is generated, and the plate-shaped heat radiation jigs 11a to 11c are formed on the upper and lower surfaces of the plate-shaped member 9a to be welded. To place. Thereafter, as shown in FIG. 6C, the edge portion of the plate material 19 is welded to the plate-shaped member 9a to be welded to form the weld metal layer 14.

According to the present embodiment, the member to be welded of the nuclear reactor structure which has been irradiated with neutrons can be repaired by welding without requiring pretreatment. In each of the above embodiments, a laser, a TIG, etc. are used as the heat energy source during welding.
Arc, MIG arc, plasma arc, friction welding, electrical heating can be used.

The above-mentioned respective embodiments are not limited to boiling water reactors, but also pressurized water reactors and liquid metal cooling reactors,
It is also applicable to fusion reactors. Further, by applying each of the embodiments described above, it is effective for extending the life of the nuclear reactor and for preventive maintenance, and it is possible to improve the reliability of the nuclear reactor.

[0056]

According to the present invention, a nuclear reactor structure that has been irradiated with neutrons can be repaired by welding without the need for welding pretreatment, and welding cracks in the welded member can be prevented.

[Brief description of drawings]

1A and 1B are views for explaining a first embodiment of a method for repairing a nuclear reactor structure according to the present invention, in which FIG. 1A is a side view showing a state before repair, and FIG. Side view showing the state,
(C) is a sectional view taken along the line A-A of (b), and (d) is a side view showing a state after repair.

FIG. 2 is a side view for explaining a second embodiment of the nuclear reactor structure according to the present invention.

FIG. 3 is a side view for explaining a third embodiment of a nuclear reactor structure according to the present invention.

4A and 4B are views for explaining a fourth embodiment of a method for repairing a nuclear reactor structure according to the present invention, FIG. 4A is a side view showing a state before repair, and FIG. Side view showing the state,
(C) is a side view showing a state after repair.

5A and 5B are views for explaining a fifth embodiment of a method for repairing a nuclear reactor structure according to the present invention, in which FIG. 5A is a longitudinal sectional view showing a state before repair, and FIG. 2C is a vertical cross-sectional view showing a part of the state in FIG. 3C, and FIG.

6A and 6B are views for explaining a sixth embodiment of a method for repairing a nuclear reactor structure according to the present invention, in which FIG. 6A is a longitudinal sectional view showing a state before repair, and FIG. 2C is a vertical cross-sectional view showing a part of the state in FIG. 3C, and FIG.

FIG. 7 is a schematic elevational view for explaining the structure of a boiling water reactor.

[Explanation of symbols]

1 ... Reactor core, 2 ... Reactor pressure vessel, 3 ... Reactor shroud,
4 ... Core support plate, 5 ... Upper lattice plate, 6 ... Jet pump, 7 ... Diffuser, 8 ... Shroud support plate, 9 ... Welded member of nuclear reactor structure that has been irradiated with neutrons, 9a ... Plated member to be welded , 10 ... Crack-like defects, 11 ... Heat dissipation jig, 12 ... New welded member, 13 ... Laser welding machine, 14
… Weld metal layer, 15… Water cooling tube, 16… Cooling fin,
17 ... molten layer, 18 ... groove, 19 ... plate material.

Claims (10)

[Claims] 1. A portion in which a crack-like defect is generated in a welded member of a reactor structure made of stainless steel, Ni-base alloy or low alloy steel containing helium upon irradiation with neutrons or the neutrons. After deleting the region including the part where the material of the welded member has deteriorated by irradiation, a new welded member is provided in contact with the deleted location, and a heat dissipation jig is arranged on each of the contacted welded members. A method for repairing a nuclear reactor structure, which comprises welding by welding. 2. A portion in which a crack-like defect is generated in a welded member of a reactor structure made of stainless steel, Ni-base alloy or low alloy steel containing helium upon neutron irradiation, or neutrons. Atoms characterized by disposing heat radiating jigs on both sides of a region including a portion where the material is deteriorated by irradiation, and removing the crack-like defects by forming a molten layer by welding or coating with the molten layer. Method of repairing furnace structure. 3. The method for repairing a nuclear reactor structure according to claim 2, wherein overlay welding is applied instead of the molten layer. 4. A portion in which a crack-like defect is generated in a welded member of a reactor structure made of stainless steel, Ni-base alloy or low alloy steel containing helium under neutron irradiation, or neutrons. A reactor structure characterized in that after a region including a portion whose material is deteriorated by irradiation is removed by cutting or electric discharge machining, a heat radiation jig is arranged on the member to be welded, and the removed portion is welded by overlay welding and filled. How to repair things. 5. A portion in which a crack-like defect has occurred in a welded member of a reactor structure made of stainless steel, Ni-base alloy or low alloy steel containing helium upon neutron irradiation, or neutrons. A reactor structure characterized by covering a plate material in a region including a portion whose material is deteriorated by irradiation, arranging a heat radiation jig on the member to be welded, and welding an edge portion of the plate material to the member to be welded. Repair method. 6. The repair of the nuclear reactor structure according to claim 1, wherein the material of the heat radiation jig is at least one metal or alloy selected from copper, aluminum or iron. Method. 7. The method for repairing a nuclear reactor structure according to claim 1, wherein the heat dissipation jig is provided with a coolant cooling mechanism. 8. The method for repairing a nuclear reactor structure according to claim 1, wherein the heat radiation jig is provided with a cooling fin. 9. The method for repairing a nuclear reactor structure according to claim 1, wherein the members to be welded are welded while applying a pressing force. 10. The welding is laser, TIG arc, M
The method for repairing a nuclear reactor structure according to any one of claims 1 to 5 and 9, wherein any one of IG arc, plasma arc, friction welding, and electric heating is used as a thermal energy source.