JPH02102494A - Method for repairing reactor pressure vessel - Google Patents

Abstract

PURPOSE:To automate welding operations and to allow convenient repair welding by executing cutting of the weld zone between cracked cylindrical pipe and a reactor pressure vessel and working of a groove to a through-hole by the operation in the circumference. CONSTITUTION:The pipe in the region from the position nearer the inside part side of the reactor pressure vessel than the weld zone 3 of the cylindrical pipe and the pressure vessel to the outside par of the through-hole 1B is cut away and the groove 5 is provided circumferentially to the inside wall of the through-hole 1B. A build-up weld zone is provided to the groove 5. The fresh 1st pipe is thereafter inserted to the inner part side of the pressure vessel than the build-up weld zone. The insertion front end of this pipe and the pipe remaining in the pressure vessel are joined by welding, by which the 1st pipe 2 and the 2nd pipe are build-up welded. The pipe of the region from the position nearer the inside part side of the pressure vessel than the weld zone 3 of the cylindrical pipe and the pressure vessel to the outside part of the through-hole 1B is cut away and the groove 5 is provided in the circumferential direction of the region of the inside wall of the through-hole 1B communicating with the outside part of the pressure vessel. The build-up weld zone provided to the groove 5 and the fresh pipe inserted into the through-hole 1B then welded.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention provides a method for repairing a weld between a cylindrical pipe penetrating the pressure vessel and a pressure vessel in a nuclear reactor pressure vessel during the service life of a nuclear power plant. Regarding.

[Conventional technology]

FIG. 17 shows a pressure vessel of a boiling water reactor as an example of a penetration part of a cylindrical pipe of a reactor pressure vessel.

The reactor pressure vessel 1 is composed of a fuselage, a lower mirror, and an upper M (not shown), and is fixed on the pedestal of the reactor pressure vessel 1 by a support skirt. The reactor pressure vessel 1 includes a reactor core consisting of a fuel assembly 14 and a core support structure 1.
5, a control rod 16, a steam separator 17, a steam dryer 18, etc. are built in.

[Problem to be solved by the invention]

During regular inspections, the steam separator 17 and steam dryer 18 at the top of the core are removed, and the fuel assembly 14 is also removed and replaced, so the core support is removed as shown in Figure 18(A). Internal structures such as the structure 15 and the control rod through-hole housing tube 19 are connected to the reactor pressure vessel 1 by welding, so that when attempting to approach the lower part of the reactor pressure vessel 1 from above, there is no interference. There are many parts that are difficult to access.

Furthermore, the reactor pressure vessel is a highly radioactive environment, and during periodic inspections it is usually filled with water to reduce the radiation dose, making it increasingly difficult to access equipment to be repaired, as well as for welding machines, etc. Equipment that cannot be used underwater must be drained before use. If water is drained from the reactor pressure vessel 1, the radiation dose will increase, making it impossible for humans to enter the upper part of the reactor pressure vessel 1 and its surroundings, even if the equipment is operated remotely. The conditions become worse.

FIG. 18(B) is an enlarged view of the main part of FIG. 18(A), and shows the through hole of CM housing 2, which is an example of the target structure of the present invention. The ICM housing 2 is a cylindrical tube that vertically passes through the lower mirror IA of the reactor pressure vessel 1, and is intended for measuring neutrons in the reactor core region, and has a small outer diameter of about 50 mm. Such TCM
For a structure such as a through hole in the housing 2 that is welded to the lowest part of the lower mirror IA of the reactor pressure vessel 1, it is difficult to repair it by approaching from above.

Another way to approach the weld is to approach the weld from the bottom of the lower mirror IA and repair it, but in this case, the number of penetration pipes at the bottom of the lower mirror IA poses an obstacle, but radiation Compared to the upper part, the level is in the atmosphere, so it is relatively easy to access the welding area. However, the biggest obstacle is that all repair work must be carried out in a narrow through-hole because the repair is carried out from outside the container.

An object of the present invention is to accomplish the purpose of repair by utilizing a narrow through hole from the outside of the vessel, which is relatively easy to access, when repairing a welded portion where an ICM housing penetrates a reactor pressure vessel. The purpose of the present invention is to provide a method for repairing a nuclear reactor pressure vessel.

[Means to solve the problem]

The above purpose is to cut and remove the pipe in the area from the inside of the reactor pressure vessel to the outside of the through-hole than the welded part between the 10M housing and the reactor pressure vessel, and to cut and remove the pipe from the inside of the through-hole of the reactor pressure vessel. After forming a groove in the circumferential direction and forming an overlay weld in the groove, a new first pipe is inserted inside the reactor pressure vessel from the overlay weld, and the first pipe is Welding and joining the insertion tip of the pipe remaining in the reactor pressure vessel, and welding and joining the first pipe and the second pipe to be inserted into the through hole at the overlay welding part, and Cut and remove the pipe in the area from the welded part of the 10M housing and the reactor pressure vessel to the outside of the through hole from a position on the inside of the reactor pressure vessel, and remove the pipe on the inner wall of the through hole of the reactor pressure vessel. This is achieved by forming a groove in the circumferential direction of a region that communicates with the outside, and joining an overlay weld formed in the groove and a new pipe inserted into the through hole using the weld.

[Effect]

Generally, the boundary line where the container and the cylindrical tube intersect becomes a complicated three-dimensional trajectory, making welding complicated. It is difficult to insert and operate a remote automatic welding machine capable of such complicated operations into a narrow through hole.

In such a narrow area, welding efficiency is greatly improved by a two-dimensional welding operation such as welding on the top of a pipe.

In addition, cylindrical pipes (10M) with cracks, etc.
cutting of the weld between the housing) and the reactor pressure vessel,
The processing of grooves for the through-holes can be performed on a substantially circumferential surface, thereby avoiding the difficulty of conventional work.

(Example) Hereinafter, an example of the present invention will be described with reference to FIG. 1 and FIGS. 2 to 4.

Figure 1 shows the ECM housing through hole IB, which is a cylindrical tube attached to the lower mirror IA of the boiling water reactor pressure vessel.
shows a cross-sectional view before repair. During manufacture, the 10M housing (hereinafter simply referred to as housing) 2 is partially melt-welded (welded part 3
) is welded from inside the reactor pressure vessel 1 and joined to the neutron monitor guide tube 4. However, this type of welding is a welding method that requires access to the inside of the furnace without radiation, and there are many factors that make it difficult to repair the welded portion during operation.

Fig. 2 shows that in order to repair the welded part 3', a part of the existing housing 2 is removed, the welded part 3 and a part of the overlay seat ID are removed, a welded part 6 is formed, and the welded part 6 is penetrated. A groove 5 for overlay welding is provided in the hole IB by machining. In Fig. 2, 2B is the cutting position of the housing;
Two people show the housing remaining in the weld. FIG. 3(A) shows the state after Inconel overlay welding 7 has been applied to the groove 5 by temper bead welding using a remote automatic welding machine 8. Overlaying is performed in multiple layers using limited low heat input welding, and as shown in Figure 3 (B), the heat-affected zone of the container low-alloy steel material created by overlaying the first layer 7A is sequentially As the second layer 7B and third layer 7C are built up, they are softened again, and there is no need to perform post-weld heat treatment as an annealing treatment for stress relief. The overlay welding by temper bead welding is usually performed up to the 6th to 7th layers.

Moreover, since this overlay welding can be performed on the inner wall circumference of the groove 5 of the through hole IB, it is easy to apply the remote automatic welding machine 8 to narrow areas.

Furthermore, this groove 5 is also useful for setting the position of the remote automatic welding machine 8.

FIG. 4 is a sectional view after new housings 9A and 9B are welded to the overlay welded portion 7 formed in FIG. 3. The new housing is divided into two parts, an upper housing 9A and a lower housing 9B.
After welding the lower housing 9B to the upper housing 9
Weld with A.

As a result, the remaining housing 2A connected to the neutron monitor guide tube 4 has a welded portion 10.11.1.
2 to the new upper housing 9A and lower housing 9B. Since the welding for all new housings shown in FIG. 4 is perpendicular to the axis of the cylindrical tube, the tubes can be welded together two-dimensionally, and the remote automatic welding machine 8 can be used in narrow spaces. It's easy.

Next, an example of the repair method of the present invention will be explained based on FIGS. 5 to 13.

In Figure 5, the reactor pressure vessel lower mirror IA is made of low alloy steel.
IC is stainless steel or Inconel overlay
(clad), the weld overlay ID is made of stainless steel or Inconel welded, the housing 2 is made of stainless steel, the welded part 3 is made of stainless steel or Inconel welded metal, and the neutron monitor guide tube 4 is made of stainless steel.

First, as shown in FIG. 5, a portion of the existing housing 2 to be repaired below the welded portion 3 is cut by a remote machining machine 13, and a part of the existing housing 2 is removed. Next, the remote machining machine 13 descends to machine a groove 5 in the wall of the through hole IB of the reactor pressure vessel in the circumferential direction of the tube in a plane perpendicular to the tube axis direction, as shown in FIG. Thereafter, after the remote machining machine 13 inside the through hole IB is lowered, the remote automatic welding machine IMB is inserted into the through hole IB, and as shown in FIG. give, 8th
The figure shows a state in which the surface of the built-up portion 7 is finished by machining after overlay welding.

Next, in order to remove the existing housing welded part 3, first, as shown in FIG. 9, the existing housing attached to the welded part 3 is machined to remove the portion shown by the dashed line.

Next, as shown in FIG. 10, the existing housing welded portion 3 is removed by machining to form a welded portion 6.

Next, a new upper housing 9A is inserted and Inconel welded to the existing housing 2A (welding portion 10). This state is shown in FIG. 11. In this case, the existing housing 2A side is machined into a groove shape by remote machining 13, and the insertion tip of the upper housing 9A is previously machined into a groove shape. The length of the new upper housing 9A is the upper housing 9A.
The lower end of the upper housing 9A is adjusted in advance so that when the upper housing 9A is welded to the existing housing 2A, the lower end of the upper housing 9A is located at the overlay welding part 7 formed inside the through hole IB.

Next, as shown in FIG. 12, the newly installed upper housing 9A is fillet welded to the Inconel built-up part 7 formed in the through hole IB of the reactor pressure vessel (weld part 11). Since this welding is not directly applied to the pressure vessel, which is made of low-alloy steel, no post-weld heat treatment is required. Next, as shown in Figure 13,
The new lower housing 9B is inserted into the through hole IB and welded by the weld 11 between the new upper housing upper part 9A and the build-up weld 7 or the weld 12 between the build-up weld 7 and the build-up weld 7.

In this way, even in the unlikely event that a crack occurs in or near the welded part of the existing housing and a problem such as leakage occurs, it can be replaced and repaired with a new housing relatively easily by following the repair procedure described above. becomes.

When performing repair work in the steps shown in FIGS. 5 to 13, the grooves 5 and 5 shown in FIGS.
During overlay welding, the existing housing 2 remains above the through hole IB, which has the advantage of preventing dust containing radioactive materials from entering the through hole IB from the lower part of the furnace. .

It is possible to perform the above steps in a different order. For example, it is possible to cut and remove the short tubes of the existing housing as shown in Figures 9 and 10, and to work on the welds and overlay welds between the existing housing and the container. It is possible to cut and remove a part of the housing in the step after removing the lower part of the existing housing shown in FIG.

In this case, since the cutting and removing work can be performed all at once, there is an advantage that the number of times the machining cutting machine is set is reduced and work efficiency is improved.

FIGS. 14 to 16 show other embodiments.

In Fig. 14, when the existing housing is removed by machining, a groove communicating with the welded part 10 side is provided in the upper part of the through hole IB as shown in the figure, and a groove in the direction perpendicular to the axis of the housing is added to the groove. A temper bead overlay welding section 7 is provided along the direction of use, and the tempering bead overlay welding section 7 connects the upper housing 9A and the lower housing 9B to the welding section 11.
It is joined by 12.

In addition, in FIG. 15, after removing the existing housing by machining, a groove is provided that continues the through hole IB on the outside of the pressure vessel, and this groove is tempered along the direction between the grooves in the direction perpendicular to the axis of the housing. A bead overlay welding part 7 is provided,
This temper bead overlay welding part 7 connects the upper housing 9A.
The lower housing 9B is joined to the lower housing 9B by a welded portion 11.12.

In the embodiment described above, the temper bead overlay welding part 7
, two-dimensional circumferential welding perpendicular to the axis of the cylindrical housing is possible no matter where the welding portions 11, 12 are located in the thickness direction of the container.

Furthermore, depending on the environmental conditions around the inside or outside of the existing nuclear reactor pressure vessel, the embodiments shown in FIGS. 14 and 15 may have improved workability.

Furthermore, in FIG. 16, a groove is provided on the outside of the pressure vessel of the through hole IB, and a temper bead build-up welding part 7 is provided in this groove to connect the new housing 9C to the existing housing 2A.
are joined to the welding part 10 by a welding part 12A by fillet welding by welding from the outside of the container. In this embodiment, there is an advantage that the number bead overlay welding portion can be welded to the newly installed housing from outside the housing.

Since low-alloy steel materials are used in the reactor pressure vessel, post-weld heat treatment is required when directly welding the vessel and the cylindrical tube. However, it is not only difficult to heat-treat existing reactor pressure vessels after welding during periodic inspections, but also because it may have an adverse effect on surrounding equipment, such as reactor internal structures, for which heat treatment is not recommended. It is preferable.

If temper bead welding is used as in the embodiments described above, it is possible to overlay low alloy steel without performing post-weld heat treatment. This temper bead method originally requires heat treatment after welding, and the hardened area of the material in the heat affected zone of low alloy steel is sequentially cured by performing low heat input overlay welding with sufficient control of the heat input. It is meant to soften it. As the overlay welding material, welding material such as stainless steel or high nickel alloy that does not require post-weld heat treatment when welding the overlay part and the cylindrical tube, which will be performed later, is used to overlay the groove part with a temper bead. implement.

In particular, if the groove is machined perpendicular to the axis of the through-hole, welding by the temper bead method can also be performed by the operation of a remote automatic welding machine on a two-dimensional plane. It is also relatively easy to weld the parts. The subsequent welding between the end of the cylindrical tube and the overlay weld can also be performed at right angles to the axis of the welded portion and the cylindrical tube, making it possible to perform welding by operating the remote automatic welding machine on a two-dimensional plane. Welding is relatively easy even in narrow areas within a cylindrical pipe.

In the embodiment described above, an example was shown in which the overlay welded portion 7 was formed in the groove 5 by the temper bead method, but the present invention
After forming an overlay weld, local post-weld heat treatment using an induction heating coil can be performed to perform stress relief annealing of the overlay.

Heating with an induction heating coil is a method of passing an alternating current through the coil and heating it by the fluctuations in the magnetic field generated by it. By adjusting the frequency and current, any part near the outside of the coil can be heated at the peak of the fluctuation of the magnetic field. In other words, it can be set as a heat generating part. This means that in the case of overlay welding on the surface of a nuclear reactor pressure vessel or a tube, the overlay part is limited to the surface, so using the above characteristics of the induction heating coil has the following advantages.

When welding low-alloy steel, post-weld heat treatment is generally required because part of the heat-affected zone of the low-alloy steel, which is the base metal near the weld, hardens and the toughness of the hardened part decreases. This is to prevent the phenomenon in which cracks are likely to occur. The hardened heat-affected zone can be reheated in a post-weld heat treatment to transform the hardened zone into a softened zone. Here, since build-up welding involves applying welding material to the surface of low-alloy steel, the hardened region of the heat-affected zone in low-alloy steel is necessarily located at a certain depth from the surface. . Therefore, by using an electromagnetic induction coil, it is possible to heat the hardening region of the heat affected zone under build-up welding, and it is possible to minimize unnecessary heat supply to other parts.

When heating a part of the reactor pressure vessel, heat is inevitably transferred to the surrounding area by thermal conduction, and by heating the surrounding area, the temperature also increases at the joints with harmful reactor internals. become. However, for portions where temperature rise is undesirable, the temperature rise can be suppressed using cooling means such as water.

The heating by the induction heating coil is performed after forming the build-up weld part 7 in the groove 5, so as to locally heat the build-up weld part 7. Therefore, heating by the induction heating coil is performed after the overlay welding operation shown in FIG. 7. The hardened area due to the heat effect of the reactor pressure vessel material caused by overlay is limited to the area below the overlay, so conditions such as the frequency and current of the electromagnetic induction coil are set so that this area becomes the heat generating area. Ru.

The groove in the present invention may be in any direction in the axial direction of the through hole IB, as long as the welded portion in this groove can seal the gap between the housing and the through hole IB.

Further, in the present invention, the groove 5 and the overlay welding part 7 formed in the through hole IB do not necessarily have to be formed in a direction strictly perpendicular to the tube axis of the housing, and the remote automatic welding machine in the housing, It also includes a range formed in the circumferential direction with the remote machining machine slightly eccentric from the tube axis direction.

According to the repair method according to the present invention, all repair work such as removal of the existing housing, insertion of a new housing, machining, welding, etc. can be performed from outside the lower part of the reactor pressure vessel lower mirror IA. Repair work is basically carried out by draining the reactor water, but even in this case, the upper part of the pressure vessel becomes a highly radioactive environment, making it impossible for humans to approach quite far away. Radiation levels are not so high below the container, and humans can access directly below the housing for a short period of time.This greatly facilitates work when handling repair equipment or replacing parts. It means becoming.

Furthermore, when working from the bottom of the pressure vessel, the existing housing can be removed or the repair part can be accessed in a straight line from inside the housing bore. On the other hand, when working from the upper side, the reactor internals become an obstacle and the repaired area cannot be approached in a straight line, making it necessary to take a detour.

Being able to approach the repair area in a straight line is important when working in a radiation environment such as a nuclear reactor vessel, and it improves workability when inserting and removing parts, or when carrying in and out of remote automated equipment, and when operating remote automated equipment. The design and manufacture of equipment becomes significantly easier.

Therefore, according to the present invention, a repair method has been developed that overcomes the narrowness of the penetration part, which was a problem when working from the bottom side, so that the above-mentioned effects can be obtained. Specifically, the total repair work time is reduced. It is possible to reduce the radiation exposure dose of workers, rationalize the design and cost of remote automated equipment, jigs, and tools, and increase safety margins by improving workability.

〔Effect of the invention〕

As described above, according to the present invention, cutting of the welded part between the cylindrical tube (tcM housing) and the reactor pressure vessel in which cracks have occurred, and processing of the groove for the through hole are both carried out approximately on the circumference. The difficulty of conventional work can be avoided, and repair welding can be easily performed by automating the welding work.

[Brief explanation of the drawing]

Fig. 1 is a sectional view showing the state before repair by the repair method of the present invention, Figs. 2 to 4 show an overview of an embodiment of the repair method of the present invention, and Fig. 2 shows a part of the existing housing. Fig. 3 is a sectional view showing a state in which a groove is formed in the through-hole by removing the groove, Fig. 3 is a cross-sectional view showing a state in which an overlay welded part is formed in the groove by the temper bead method, and Fig. 4 is an overlay welded part by the temper bead method. Sectional view showing the state where the new housing is welded in the fifth section.
Figure, Figure 6, Figure 7, Figure 8, Figure 9, Figure 10! 11th
12 and 13 are cross-sectional views showing an embodiment of the repair method of the present invention in the order of steps, FIG. 14, FIG. 15, and FIG.
6 is a schematic diagram showing other embodiments of the repair method of the present invention, FIG. 17 is a sectional view of the reactor pressure vessel during periodic inspection, and FIG. 18 (A) is an enlarged view of the main part of FIG. 17. , Figure 18(B)
is an enlarged view of the main part of FIG. 18(A).

Claims (10)

[Claims] (1) In a method for repairing a reactor pressure vessel in which a cylindrical pipe that penetrates the reactor pressure vessel via a through hole and the reactor pressure vessel are joined at a welded portion to form a pressure boundary, the Cutting and removing the pipe in the area from the inside of the reactor pressure vessel to the outside of the through hole, forming a groove in the circumferential direction on the inner wall of the through hole of the reactor pressure vessel, and forming an overlay weld in the groove. After forming, a new first pipe is inserted inside the reactor pressure vessel from the overlay welded part, and the first pipe is
The insertion tip of the tube and the tube remaining in the reactor pressure vessel are welded together, and the first tube and the second tube inserted into the through hole are welded together.
A method for repairing a nuclear reactor pressure vessel, characterized in that the pipe is welded to the pipe at the overlay welding part. (2) The method for repairing a nuclear reactor pressure vessel according to claim (1), characterized in that an overlay weld is formed in the groove by a temper bead method. (3) The method for repairing a nuclear reactor pressure vessel according to claim (1), wherein the groove is formed in a direction perpendicular to the axis of the cylindrical tube. (4) Inside the reactor pressure vessel from the position where the groove is formed in the through hole and outside the reactor pressure vessel from the weld between the cylindrical pipe and the reactor pressure vessel. 2. The method for repairing a nuclear reactor pressure vessel according to claim 1, wherein the groove is formed in the through hole after the pipe is cut and removed, and then overlay welding is applied to the groove. (5) The method for repairing a nuclear reactor pressure vessel according to claim (1), wherein the overlay weld formed in the groove is locally subjected to post-heat treatment by induction heating. (6) In a method for repairing a reactor pressure vessel in which a cylindrical pipe that penetrates the reactor pressure vessel via a through hole and the reactor pressure vessel are joined at a weld to form a pressure boundary, the Cutting and removing the pipe in the area from the inside of the reactor pressure vessel to the outside of the through hole, and forming a groove in the circumferential direction of the area of the inside wall of the through hole of the reactor pressure vessel that communicates with the outside of the reactor pressure vessel. A method for repairing a nuclear reactor pressure vessel, characterized in that a welded portion formed in the groove and a new pipe inserted into the through hole are joined by a welded portion. (7) The method for repairing a nuclear reactor pressure vessel according to claim (6), characterized in that an overlay weld is formed in the groove by a temper bead method. (8) The method for repairing a nuclear reactor pressure vessel according to claim (6), wherein the groove is formed in a direction perpendicular to the axis of the cylindrical tube. (9) Inside the reactor pressure vessel from the position where the groove is formed in the through hole and outside the reactor pressure vessel from the weld between the cylindrical pipe and the reactor pressure vessel. 7. The method for repairing a nuclear reactor pressure vessel according to claim 6, wherein the groove is formed in the through hole after the pipe is cut and removed, and then overlay welding is applied to the groove. (10) The method for repairing a nuclear reactor pressure vessel according to claim (6), wherein the overlay weld formed in the groove is locally subjected to post-heat treatment by induction heating.