JP2002156487A - Piping exchanging method for core spray system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enable workers going in a reactor in a state that a core shroud is put and exchanging core spray system piping easily, surely and in a short time and improve the reliability of the reactor power plant. SOLUTION: For a core spray sparger placed on the inner surface of upper shell of a core shroud on the nearly whole circle in a pressure vessel of a boiling water reactor, a core spray system pipe arranged by penetrating the upper shroud wall of the core shroud is replaced by a new core spray piping in a reactor work. After removing a reactor upper structure in the reactor pressure vessel, the core spray system piping is cut and removed and the new core spray system piping is introduced in the reactor pressure vessel to place in the state that the core shroud is left.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a technology for replacing a reactor internal structure installed in a reactor pressure vessel of a boiling water reactor during a service period, and particularly to a piping outside the reactor pressure vessel. The present invention relates to a core spray system pipe replacement method for replacing a core spray system pipe in a reactor, which is provided for guiding suppression pool water to a core sparger installed on an inner surface of an upper part of a core shroud, only by operation in the reactor.

[0002]

2. Description of the Related Art Among the reactor internals of a reactor pressure vessel in a boiling water reactor, a core spray system pipe is used to supply fuel when the core is exposed due to a coolant loss accident such as a recirculation pipe break. In order to prevent the fuel cladding tube from melting due to overheating, it is installed as an in-furnace pipe that guides water in the suppression pool from an external pipe to a core sparger.

[0003] The core spray system piping is composed of pipes surrounding the core in a range of approximately 180 degrees, and two systems are installed at 180-degree symmetric positions.

[0004] The core sparge system piping is connected to a thermal sleeve welded to the safe end of the core spray nozzle of the reactor pressure vessel, branches right and left through a junction box, and connects the pressure vessel in a direction of about 90 degrees. They are arranged in a semi-annular shape along the inner wall. The end of this semi-annular portion has a vertical tube that bends vertically and hangs down, this vertical tube bends further horizontally through the sleeve,
It is connected to the core sparger pipe that protrudes from the upper outer wall of the core shroud.

[0005] A ring bracket is attached to a pipe of the core sparger that protrudes from the upper outer wall of the core shroud to prevent leakage of reactor water flowing inside the shroud, and a pump for the core sparger is used in an emergency. The core has a role of relieving thermal stress between the core spray sparger and the core spray system piping and the shroud mounting portion when spraying is performed.

[0006] The internal structure of the reactor pressure vessel is constructed by welding stainless steel members.

[0007] In stainless steel having a high carbon content,
It is known that stress corrosion cracking occurs in the heat affected zone near the weld in a high temperature water environment, and there is a concern that this may occur in core spray piping used in contact with high temperature reactor coolant. ing.

When such an event occurs, it is necessary to repair or replace the internal structure of the reactor in order to ensure reactor safety.

However, the furnace internals used for a long time are
Since it is embrittled due to neutron irradiation, and welding may cause defects in the welded metal, repair by welding becomes difficult. Therefore, replacement of the furnace internals may be considered as a desirable solution in the case where cracks occur in the irradiated portion due to stress corrosion cracking or the like.

[0010] Various methods have conventionally been considered as a method of replacing the core spray system piping installed in the reactor pressure vessel during the service period, but most of them are almost all in the reactor pressure vessel. Are replaced at the same time, and there is no known example of replacement of the core spray system piping alone.

[0011]

In the construction method in which almost all of the reactor internal structures are removed and replaced with new structures, the entire reactor interior is cleaned and removed in an empty state after removing all the reactor internal structures. Since there is no existing structure with a high radiation dose, the radiation dose equivalent rate inside the reactor can be reduced by laying a shield inside the reactor pressure vessel, making it easier for workers. It is possible to enter the furnace.

On the other hand, when only the structure located on the upper part of the core shroud is replaced alone, the entire interior of the reactor can be easily cleaned and decontaminated because other existing structures are installed. In addition, since there is an existing structure having a high irradiated radiation dose, it is difficult to reduce the radiation dose equivalent rate in the furnace to a level at which a worker can work in the furnace.

[0013] Accordingly, such an environment is improved even a little, and removal of the existing core spray piping, installation of a new structure, and the like can be performed by a worker entering the furnace.
It is necessary to consider a method of replacing the core spray system piping and the work accompanying it easily and in a short time.

The present invention has been made in view of such circumstances, and even in a state where the core shroud is present, an operator can enter the furnace and the replacement work of the core spray system piping can be performed easily and in a short time. An object of the present invention is to provide a core spray system piping replacement method that can be performed.

[0015]

In order to achieve the above object, according to the first aspect of the present invention, an inner peripheral surface of an upper shell of a core shroud in a reactor pressure vessel of a boiling water reactor extends over substantially the entire circumference. Core place sparger
A replacement method for replacing a core spray system pipe, which is piped through the upper shell wall of the core shroud, with a new core spray pipe by in-furnace work, wherein the in-core upper structure in the reactor pressure vessel is replaced. After removal, cut and remove the core spray system piping, with the core shroud remaining,
A method for replacing a core spray system piping of a reactor internal structure, wherein the new core spray system piping is introduced into the reactor pressure vessel and installed therein.

According to a second aspect of the present invention, in the replacement method of the core spray system piping according to the first aspect, the new core spray system piping is made of a material and a structure which are subjected to measures against stress corrosion cracking and crevice corrosion. A method for replacing a core spray system piping, wherein the core spray system piping is attached to the upper body of the core sprung sparger and the core shroud by mechanical fastening.

In the invention according to claim 3, in the core spray system pipe replacement method according to claim 1 or 2, after the existing core spray system pipe is cut and removed, the inside of the reactor pressure vessel above the core shroud is removed. Locally decontaminating by chemical cleaning, mechanical cleaning or both, then lowering the water level in the reactor pressure vessel to the top of the core shroud, placing the working platform on the top of the core shroud,
Provided is a method of replacing a core spray system pipe, which is characterized in that a new core spray system pipe is installed by work in a furnace.

According to a fourth aspect of the present invention, in the core spray system pipe replacement method according to the third aspect, the step of chemically cleaning the inside of the reactor pressure vessel includes removing the upper surface of the core shroud in the reactor pressure vessel. A dyeing tank is installed, and a space between the outer peripheral portion of the decontamination tank and the inner peripheral portion of the reactor wall of the reactor pressure vessel is formed by an upper and lower double sealing mechanism and purge water therebetween, thereby forming an upper portion of the core shroud. A method for replacing a core spray system piping, comprising isolating reactor water below a ring from reactor water above and circulating the reactor water above into the decontamination tank.

According to the fifth aspect of the invention, the first to fourth aspects are described.
In the core spray system pipe replacement method described in any one of the above, the installation of the new core spray system pipe and the replacement of the reactor internal structure installed above the core shroud are performed by piping provided outside the reactor pressure vessel. The present invention also provides a core spray system piping replacement method, which is carried out entirely by work inside the furnace in a state where ancillary facilities are kept.

In the invention according to claim 4, claims 1 to 3 are provided.
In the core spray system pipe replacement method described in any one of the above, the installation of the new core spray system pipe and the replacement of the reactor internal structure installed above the core shroud are performed by piping provided outside the reactor pressure vessel. The present invention also provides a core spray system piping replacement method, which is carried out entirely by work inside the furnace in a state where ancillary facilities are kept.

According to a fifth aspect of the present invention, in the core spray system pipe replacement method according to the fourth aspect, the step of chemically cleaning the inside of the reactor pressure vessel includes removing the upper surface of the core shroud in the reactor pressure vessel. A dyeing tank is installed, and a space between the outer peripheral portion of the decontamination tank and the inner peripheral portion of the reactor wall of the reactor pressure vessel is formed by an upper and lower double sealing mechanism and purge water therebetween, thereby forming an upper portion of the core shroud. A method for replacing a core spray system piping, comprising isolating reactor water below a ring from reactor water above and circulating the reactor water above into the decontamination tank.

In the invention according to claim 6, claims 1 to 5 are provided.
In the existing core spray system piping replacement method according to any one of the above, after cutting the core spray system piping, cutting the remaining thermal sleeve in the core spray nozzle to which the junction box of the core spray system piping was connected Remove and cut and remove the remaining part of the clamp for mounting the core spray piping, insert a safe-end beveling machine into the core spray nozzle, and insert a safe-end groove to connect with the new core spray piping. Provided is a method of replacing a core spray system piping, wherein the processing is performed from the inside of the furnace.

In the invention according to claim 7, according to claims 1 to 6,
In the core spray system pipe replacement method according to any one of the above, as a step of restoring a new inlet pipe for connecting the new core spray system pipe and the core sparger, the vicinity of the inlet pipe connection portion on the outer surface of the core shroud. By forming a flange seal surface and a stud bolt hole in the portion, joining a flange provided at the tip of the new inlet pipe to the flange seal surface, and fastening the flange with a stud bolt embedded in the stud bolt hole. The present invention provides a core spray system piping replacement method characterized by fixing the core shroud to the core shroud by non-welding.

In the invention according to claim 8, in the core spray system pipe replacement method according to claim 7, the flange of the new inlet pipe is a ring bracket for fixing the remaining pipe of the existing core sparger and the core shroud. It is assumed that the whole is covered, a material for preventing stress corrosion cracking is used for a connection part of the new inlet pipe including this flange, and the connection part is positioned and fixedly connected to a remaining pipe of the core sparger. To provide a new core spray system piping replacement method.

[0025]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a core spray system piping replacement method according to the present invention will be described below with reference to the drawings.

First Embodiment (FIGS. 1 to 20) FIG. 1 is a process chart showing a procedure for replacing a core spray system piping, and FIG. 2 is a configuration of a reactor pressure vessel of a boiling water reactor to be worked. FIG. 3 to 20 are explanatory diagrams showing the state of the furnace equipment in each step.

As shown in FIG. 2, a reactor core shroud 2 is disposed in a reactor pressure vessel 1.
Are supported by the shroud support cylinder 3. The shroud support cylinder 3 is supported by a shroud support leg 4 on the bottom of the reactor pressure vessel 1. An upper lattice plate 5 is provided at an upper portion of the core shroud 2, and a core support plate 6 is provided at a lower portion. A jet pump 7 is provided on the outer peripheral side of the core shroud 2, and the jet pump 7 is roughly divided into a jet pump diffuser 7a, a jet pump riser pipe 7b, and a jet pump inlet mixer 7c. A baffle plate 8 is provided below the jet pump 7.

In the core shroud 2, control rods 9 are provided.
And a fuel 10. Above the core shroud 2, a control rod guide tube 11, a core spray system piping 12, a core sparger 13, a differential pressure detection / boric acid water injection pipe 14, and a steam dryer (dryer) 15. , A steam-water separator (separator) and a shroud head 16 are provided. The core spray system piping 12 is the core spray nozzle 3
Connected to 0.

In the present embodiment, after the reactor pressure vessel 1 having such a configuration is filled with water and the upper lid 17 is removed,
The replacement work proceeds according to the process shown in FIG.

Generally, first, a steam dryer (dryer)
15. Steam-water separator (separator) and shroud head 1
6 and the fuel 10 are removed (S1). Next, the fall prevention cover described later is attached (S2), and the guide rod and the core spray system piping clamp are cut and removed (S3). Then, the core spray system piping 12 is cut and removed (S4), and local chemical decontamination of the upper part of the reactor pressure vessel 1 is performed (S5).

Next, the work table to be described later is installed (S
6), cutting and removing the remaining members (S7), etc.
Stud bolt hole processing and stud mounting (S
After performing 8), the dimension is measured using the template (S9), and a new inlet tube is attached (S10).

Thereafter, a new core spray system pipe is attached (S11), and a guide rod restoring step and a work stand detaching step (S12) are performed to restore fuel loading and a dryer separator (S13).

Hereinafter, each step will be described in detail with reference to FIGS.

The first step (S1) is a preparation step for cutting the core spray system piping 12, in which the steam dryer 15 and the steam / water separator / shroud head 16 are removed, and these are transferred to a dryer / separator pool (not shown). Transfer and store.
Further, all the fuel 10 is transferred and stored in a fuel pool (not shown).

FIGS. 3 and 4 show the second to fourth steps (S
2 shows the state inside the furnace in (S4).

As shown in FIG. 3, in the fall prevention lid attaching step (S2), which is the second step, a wire mesh for preventing the equipment from falling into the core shroud 2 is provided on the upper surface of the upper ring 2a of the core shroud 2. The fall prevention cover 23 is attached.
In the third step of cutting and removing the guide rod and the core spray system piping clamp (S3), the guide rod 24 that interferes with the removal and installation of the core spray system piping 12 is cut by an underwater diver (not shown). Remove it.
When the furnace is full, the diver can work because the furnace water functions as a shielding material.

The core spray system piping 12 which is the fourth step
In the cutting and removing step (S4) of FIG.
As shown in (C), the clamp 25 fixing the core spray system piping 12 to the reactor wall of the reactor pressure vessel 1 and the riser pipe 26 of the core spray system piping 12 are cut by a diver.

Then, as shown in FIG. 4 (A), a hanger 27 is attached to the annular portion of the core spray system piping 12 and a part of the riser pipe 26.

In this state, an electric discharge machining (EDM) device (not shown) is introduced into the furnace, and is positioned on the lid (cover plate) 28a of the junction box 28 by a diver, and the lid 28a is removed by EDM cutting by remote control. Further, the EDM device is installed at the position of the thermal sleeve 29 in the core spray nozzle 30, and the thermal sleeve 29 is cut by EDM. The thermal sleeve 29
Will be described later in detail with reference to FIG. Then, the core spray pipe 12 that has become free due to the cutting of the thermal sleeve 29 is separated from the core spray nozzle 30, and is removed outside the furnace by the hanging tool 27.

An EDM device is attached to the base of the inlet tube 31 by remote control, and the inlet tube 31 is also cut off from the core shroud 2.

After removing the equipment above the core shroud 2 by the above steps, a local chemical cleaning is performed as a fifth step (S5).

In this local chemical cleaning step, as shown in FIGS. 5 and 6, the inner surface of the furnace wall in the upper part 1a of the reactor pressure vessel 1 is locally chemically decontaminated by a CORD method or the like. That is, as shown in FIG. 5, the reactor water level 33 is lowered to about the normal operation water level, and the upper part of the core shroud 2 (about 5 cm from the upper surface of the core shroud 2 where the work is performed on a work platform (platform) described later). The decontamination tank 32 is installed on the upper surface of the upper ring of the core shroud 2 (a range above a meter). As shown in FIG. 6, a flow pump 34 and a pipe 35 are provided inside the decontamination tank 32.
This allows the reactor water to circulate inside and outside the decontamination tank 32.

The double seal mechanism 36 provided at the lower part on the outer peripheral side of the decontamination tank 32 and the purge water (seal water) supplied to the double seal mechanism 36 lower the upper ring 2 a of the core shroud 2. Is separated from the reactor water above, and the reactor water above the seal is decontaminated by the decontamination tank 3.
By circulating between the inside 2 and the decontamination device 37, chemical decontamination of the furnace upper part 1a is performed.

After completion of the chemical decontamination, the decontamination tank 32 is carried out of the furnace, and mechanical decontamination such as partially jetting jet water into the furnace is performed to complete the cleaning. As a result, the radiation level in the reactor pressure vessel 1 is reduced, and aerial work becomes possible.

Therefore, as a sixth step after the completion of the cleaning,
The work stand is installed (S6). FIG. 7A shows a state in which a work platform (platform) 38 is installed on the upper flange portion of the core shroud 2 in this step (S6). The work stand 38 is installed by being suspended from above the furnace by, for example, a hanging tool (not shown). An outer wall shield 38a is provided around the work gantry 38 to shield radiation from the furnace wall. As a result, the worker can enter the reactor pressure vessel 1 and the preparation for performing the recovery work of the core spray system piping is completed.

Next, as a seventh step (S7), the worker enters the work platform 38 and cuts and removes the remaining members.
The remaining members to be removed here include, for example, the thermal sleeve 29 (not shown in FIG. 7; see FIG. 13) and the piping remaining in the core spray nozzle 30 when the existing core spray piping 12 is cut. There is a remaining portion of the fixed clamp 25 (see FIG. 3). In this process,
Perform these cutting and removal.

Next, as an eighth step, stud bolt holes for mounting a new inlet pipe and stud mounting (S8) are performed. 7 (A), (B), FIGS. 8 to 1
0 indicates this step.

As shown in FIGS. 7A and 7B, when the existing core spray system piping 12 is completely removed, the remaining pipe 40 of the core sparger projects on the outer surface of the core shroud 2. ing. In this embodiment,
In order to connect an inlet pipe (new inlet pipe) of a new core spray system pipe to the remaining pipe 40, the remaining pipe 40 is formed in advance.

FIG. 8 shows how the EDM machine 42 forms the cut surface of the remaining pipe 40 and the flange seal surface 41 as the forming means.
That is, the EDM processing machine 42 has a remaining pipe tip surface processing portion 42a and a flange seal surface processing portion 42b.
And the outer surface of the core shroud 2 is finished.

FIG. 9 shows a state in which a stud bolt hole 44 is further formed on the outer surface of the core shroud 2 by using another EDM processing machine 43. That is, the EDM machine 43 has a plurality of hole processing portions 43a, and the stud bolt holes 44 are formed around the remaining pipe 40, that is, around the connection portion of the new inlet pipe by the hole processing portions 43a. To form.

FIG. 7B shows the stud bolt hole 4
FIG. 4 shows a state in which the stud bolt 45 is embedded.
10 (A), (B) and FIG. 11 (A),
(B) shows a state where the new inlet pipe 111 is mounted.

As shown in these figures, in this embodiment, a flange 112 integrally provided at the tip of the new inlet pipe 111 is joined to the flange sealing surface 41 shown in FIG. 8, and the flange 112 is connected to a stud. By fastening with the stud bolt 45 and the nut 48 embedded in the bolt hole 44, the core shroud 2 is not welded.
, And mechanically connected to the core sparger 13. As a result, the entire remaining pipe 40 of the existing core sparger 13 and the ring bracket 49 fixing the core shroud 2 are connected to the flange 1.
It is considered that all the water supplied to the core spray system piping is guided to the core sparger 13 in a state covered by the core 12.

At the same time, in this step (S8), a safe-end beveling machine is inserted into the core spray nozzle 30 to perform safe-beveling of a safe end to be fitted with a new core spray pipe. FIG. 12 shows a state of the groove processing, and FIG. 13 shows an existing junction box and a tee instead of the junction box in an up-down direction.

That is, as shown in FIG. 12, a safe end 50 is
1, the safe end 52 has a safe end side thermal sleeve remaining portion 52 left by the cutting in the step (S4). To connect the thermal sleeve 102 of the new core spray system piping 100 to be described later by butt welding to the thermal sleeve residual portion 52 on the safe end side, the thermal sleeve residual portion 5 is connected.
In 2, beveling is performed by a beveling machine 53.

The beveling machine 53 has a shaft 54 provided with a processing blade 55 for rotational molding and the like, and also has a camera 56 and an illuminator 57. The processing blade 55 is driven by remote control to provide a safe end. The tip of the remaining thermal sleeve portion 52 is machined.

FIG. 13 shows the connection of the thermal sleeves of the new and old core spray system pipes connected in the core spray nozzle 30 after such groove processing in a vertical direction. The existing (old) shown in the upper half of FIG.
In the case of the core spray system piping 12, the large-diameter thermal sleeve 29 protruded from the junction box 28 closed by the lid 28a, but as shown in the lower half of FIG. In the case of the new core spray system piping 100, the tee 101 is formed integrally with an annular portion, and a lid 101a is provided at an end of the tee 101 on the center side in the furnace, and the other end of the tee 101 is provided. A new thermal sleeve 102 is joined to the portion via a welded portion 103. The new thermal sleeve 102 has a smaller diameter than that of the old type, and its tip is located at the grooved portion of the thermal sleeve remaining portion 52 on the safe end 50 side.
It is joined by the welding part 104 in the state of the same diameter.

The installation and the like of the new core spray system piping 100 having the new thermal sleeve 102 and the new inlet pipe 111 are specifically performed according to the following procedure.

That is, before introducing the new core spray system piping 100, it is necessary to form a curved pipe corresponding to the installation site, and as described above in the ninth step (S9), the reactor pressure vessel 1, a template (not shown) for restoring the core spray system piping was used, based on the length of the new thermal sleeve 102 to be installed in the core spray nozzle 30 and the position of the remaining pipe 40 of the core sparger 13. Measure the bend dimensions etc. of the core spray system piping.

While the core spray system piping is being bent outside the reactor building based on the measured values, the new core spray piping 100 is set in the reactor pressure vessel 1.
The inlet pipe 111 is fastened and fixed to a stud bolt 45 attached to the existing core shroud 2 with a nut 48 and connected to the existing core sparger 13.

The tee 10 of the new inlet tube 111
For the connection portion such as 1, a material for preventing stress corrosion cracking (SCC) such as SUS316L is adopted, and a structure for preventing crevice corrosion is considered. In addition, at the time of attachment, the flange 112 and the like are provided so that the remaining pipe 40 of the core sparger 13 can be positioned using the guide as a guide and the new inlet pipe 111 can be easily connected to the existing core sparger 13. There is a structure.

At the time of installing the new core spray system piping 100 in the tenth step (S10), FIG.
As shown in the figure, the new core spray system piping 100 with the new thermal sleeve 102 is tilted, suspended while avoiding interference with the remaining water supply sparger 109, stopped at a predetermined mounting position, and The new thermal sleeve 102 is inserted into the inside, and the groove of the new thermal sleeve 102 is aligned and welded to the groove of the safe end 50 described above.

FIGS. 15 and 16 show an operation of hanging the new core spray system piping 100 without contacting the water supply sparger 109. That is, in the present embodiment, the maximum diagonal length L1 of the semi-annular pipe portion of the new core spray system piping 100 is set to be smaller than the inner dimension L2 of the existing water supply sparger 109, so that FIGS. As shown in the figure, since the semi-circular annular pipe portion of the new reactor core spray system pipe 100 can be lowered into the furnace through the inner peripheral side of the water supply sparger 109 in a state where it is inclined, the water supply sparger 109 is attached. In this state, replacement with the new core spray system piping 100 is possible.

The new core spray system piping 1 suspended in this manner
00 riser pipe 108 is connected to the new inlet pipe 111 via a sleeve 110, and the riser pipe 108 and the sleeve 110 and the new inlet pipe 111 and the sleeve 1
10 and each is welded.

After the new core spray system piping 100 is connected as a system, a clamp (see clamp 25 in FIG. 3) for holding the new core spray system piping 100 is attached, and finally, the lid 101 is attached to the tee 101 by welding.

After the restoration by the new core spray system piping 100 is completed, in the twelfth step (S12), the guide rod 2
4 is attached to the guide pin bracket of the core shroud 2, and the work platform 38 and the fall prevention lid 23 are removed.

Thereafter, in a thirteenth step (S13),
Load fuel 10 and restore steam dryer 15 and steam separator / shroud head 16.

The furnace internal structure cut and removed in the furnace is as follows:
Temporarily place in a dryer / separator pool, shred after completion of core spray pipe replacement work, fill in cask, and store in side bunker pool or solid waste disposal storage.

In the present embodiment, in the above-described fourth step (S4), after the existing core spray system piping 12 is cut, as shown in FIGS. From the residual pipe 40 to the inner surface welded portion of the existing core sparger 13, construction for removing residual stress and improving the material is performed by a surface reforming device 201 such as peening or desensitization heat treatment. That is, the material of the existing core sparger 13 is
Since it is not a material for countermeasure against stress corrosion cracking (SCC), the surface modification for stress corrosion cracking is performed from the inner side of the core sparger 13.

FIG. 17 shows the mounted state of the surface reforming device 201. As shown in FIG. 17, the surface reforming apparatus 201 includes an inlet pipe 13 a of the core sparger 13.
Is inserted into the core sparger 13 through the opening. In this case, water, dust and the like remaining in the core sparger 13 are wiped and cleaned by a cleaning device such as a water suction cleaner (not shown) in advance, and after the inner surface is dried by the drying device, the cleaning device is removed. Further, the polishing apparatus is inserted into the core sparger 13 through the opening of the inlet pipe 13a, and taking into account the positional accuracy of the surface reforming apparatus 201,
The hard clad or the like adhering to the inner surface of the core sparger 13 in the vicinity of the working area is polished and removed.

Thereafter, the surface reforming device 201 is attached to the opening of the inlet pipe 13a of the core sparger 13.
After attaching the surface reforming apparatus 201, the surface condition of the construction range is confirmed by remote image observation using a camera (not shown) attached to the surface modifying apparatus 201.

The surface reforming apparatus 201 is provided with a head 20 for construction.
The head 202 is inserted into the core sparger 13 through the opening of the inlet pipe 13a.
The surface reforming apparatus 201 is connected to a laser oscillator 204 installed on an operation floor 203 via a guide tube 205 including an optical fiber or the like.

In this embodiment, the surface reforming apparatus 201
The surface modification is performed by desensitizing the inner surface of the core sparger 13 as a surface modification target, or transferring the residual stress on the surface opposite to the surface to the compression side. In this case, as a surface modification method, rapid heating and rapid cooling of the construction target portion surface by laser irradiation from the oscillator 204 are performed.

As the laser heating, for example, a method using a YAG laser is applied. That is, in this method, the surface of the sensitized region of stainless steel is irradiated with a YAG laser to form a surface treatment layer (a fusion solidified layer and a fusion treatment layer). By moving the focused laser beam at a high speed, the surface of the construction target portion is rapidly heated / cooled, and the chromium carbide is eliminated.
In addition, when the laser is irradiated to the pipe inner construction target portion, the molten portion on the inner surface contracts with cooling, and the residual stress on the pipe outer surface side of the construction target portion becomes in the compression direction. By such an action, a modification work capable of preventing stress corrosion cracking is performed.

As the conditions for the surface modification by the desensitization method, the laser irradiation output and the processing speed are set in advance so that the penetration depth is about 0.2 mm. As the shielding gas, for example, an inert gas such as an argon gas is used.

FIGS. 18 to 20 show examples of the modification work.

FIG. 18 is a side view showing a reforming work site, and FIG. 19 is a cross-sectional view taken along line AA of FIG.
FIG. 20A is a cross-sectional view taken along the line BB of FIG. 18, and FIG. 20B is a cross-sectional view taken along the line CC of FIG.

In this example, the working range of the surface modification is limited to the inlet pipe 13 a of the core sparger 13 and the header pipe 13.
This is for the case where the welded portion 13d of the lid 13c arranged at the joint with b and the vicinity of the welded portion.

That is, the surface modification work range is the welded portion 13d between the lid 13c and the inlet pipe 13a and the heat affected zone + α, for example, about 10 mm from the outer peripheral end of the lid 13c.
mm or more, and about 25 mm from the welded end of the inlet pipe 13a at the inner portion near the center (portion indicated by "204" in 19).
The portion up to the distant position ("206" in FIG. 20A)
Part indicated by).

By performing the above-described reforming work on such a portion, surface reforming is performed from the inner surface of the core sparger 13 to the vicinity of the welded portion, and the molten portion on the inner surface shrinks during cooling in this work. Then, the residual stress on the outside of the core sparger 13 in the construction target portion shifts to the compression side. In addition, the surface of the inner surface of the core sparger 13 is subjected to rapid heating / cooling, so that chromium carbide disappears and becomes a desensitized layer.

Note that, as shown in FIG.
Since b is attached to the cylindrical inlet pipe 13a, the welded portion 13d between the header pipe 13b and the inlet pipe 13a has a saddle shape. Therefore, the surface modification working range of this portion is such that, when the core sparger 13 is viewed from the core shroud center, the center line O1 of the header pipe 13a and the inlet pipe 1
A range of about 25 mm or more from the intersection O2 with the outer peripheral surface of the inlet pipe 3a in the direction opposite to the center of the inlet pipe 13a (see "20" in FIG. 19).
5 ").

In the above modification example, surface modification is performed from the inner surface of the core sparger 13 to the vicinity of the welded portion, and the melted portion on the inner surface shrinks during cooling in this process, so that the core spray of the target portion is constructed. The residual stress outside the sparger 13 shifts to the compression side. In addition, the surface of the inner surface of the core sparger 13 is subjected to rapid heating / cooling, so that chromium carbide disappears and becomes a desensitized layer.

Further, a welding portion 203a between the header tube 13b and the end plate 203 and the vicinity of the welding portion, which is a heat affected zone, are added as a surface modification working range. The surface modification range in this modification example is about 25 mm or more from the joint surface between the end face of the header tube 13b and the end plate 203, and the end plate 20
3 (the portion indicated by “203b” in FIG. 19) and about 10 mm from the outer peripheral end of the end plate 203.
As described above, the inner portion closer to the center ("207" in FIG. 20B)
(The part indicated by).

In such a modification example, the surface modification is performed from the inner surface of the core sparger 13 to the vicinity of the welded portion, and the molten portion of the inner surface shrinks during cooling in this process, so that the core of the portion to be processed is cooled. Residual stress outside the sparger 13 shifts to the compression side. Also,
Since the surface is rapidly heated / cooled, the chromium carbide disappears in the surface reforming section on the inner surface of the core sparger 13 to form a desensitized layer.

According to the first embodiment described above, the structure above the core shroud 2 which has conventionally been considered difficult to replace alone is replaced due to problems such as interference of surrounding structures and a high radiation environment. It becomes possible.

That is, the existing core spray system piping 12 installed above the core shroud in the reactor pressure vessel 1 was cut and removed by a simple operation, and the new core spray system piping 100 was installed on the upper surface of the core shroud 2. Work stand 38
By the above operation, it can be attached to the existing structure. The mounting portion between the new core spray system piping 100 and the core shroud 2 and the remaining pipe 40 of the core sparger 13 can be easily restored by a mechanical fastening structure without a welded portion.

In this case, the existing core spray system piping 12
Are mechanically cut by a submersible diver in a full state of the reactor pressure vessel 1 and ED by submersible remote control.
After cutting and removing using the M apparatus and decontaminating the reactor pressure vessel 1 above the core shroud 2 by local chemical and mechanical cleaning, the water level in the reactor pressure vessel 1 is adjusted to the upper surface of the core shroud 2. By lowering the work platform 38 to the upper surface of the core shroud 2, the operator can easily enter the reactor pressure vessel 1 and install the new core spray system piping 100. And, such a core spray system pipe replacement work can be performed entirely inside the reactor without having to remove the outer pipe and the auxiliary equipment of the reactor pressure vessel 1, and the work can be performed extremely easily.

Also, during the replacement work, after the existing core spray system piping 12 is cut, the core spray sparger 13 which is not a measure against stress corrosion cracking (SCC) inscribed in the core shroud 2 from the cut portion is provided. The integrity of the equipment can be maintained by removing residual stress or performing peening or desensitization heat treatment for material improvement as preventive maintenance for the inner surface welded portion and the like.

For chemical cleaning to provide an environment in which workers can enter and work in the reactor pressure vessel 1, a decontamination tank 32 is installed on the upper surface of the core shroud 2 in the reactor pressure vessel 1. Then, the double seal mechanism 36 and the purge water provided at the lower part of the decontamination tank 32 separate the reactor water below the upper ring of the core shroud 2 from the reactor water above and remove the reactor water above. By circulating in the dye tank 32, chemical decontamination of the upper part of the reactor can be performed with high efficiency and certainty.

Further, after the existing core spray system piping 12 is cut, the thermal sleeve remaining part 52 in the core spray nozzle 30 and the remaining part of the pipe mounting clamp 25 are cut and removed, or the core is sprayed safely into the core spray nozzle 12. The groove processing of the safe end 50 to be engaged with the new core spray system piping 100 by inserting the groove processing machine 53 of the end 50 can be efficiently performed from the inside of the furnace.

The EDM machine is used to form the flange seal surface 41 for mounting the new inlet pipe and the cut surface of the remaining pipe 40 on the outer surface of the existing core shroud 2 and to process the stud bolt hole 44 for mounting the new inlet pipe. In addition to being able to perform efficiently, mounting the tod bolt 45,
Restoration of the new inlet pipe 111 can be reliably performed.

Further, with the installation of the new core spray system piping 100, the length of the new thermal sleeve 102 required for connecting the core spray nozzle 30 to the core spray sparger 13 and the bending dimensions of the core spray system piping. Can be easily measured using a template. The connection portion of the new inlet pipe 111 can be effectively used for a long period of time by adopting a material against stress corrosion cracking (SCC). In addition, the new inlet pipe 111 can be easily connected to the core sparger 13 by positioning using the remaining pipe 40 of the core sparger 13 as a guide.

Further, the connecting portion of the new inlet pipe 111 has a flange structure, and the existing core sparger 13
By covering the entire ring bracket that fixes the remaining pipe 40 and the core shroud 2, all the water supplied to the new core spray system piping 100 can be guided to the core sparger 13.

Second Embodiment (FIG. 21) This embodiment relates to a method of replacing the water supply sparger 109 simultaneously with the core spray system piping 12.

FIG. 21 is a process chart showing a procedure for implementing this method. As shown in FIG. 21, in this embodiment, a step of cutting and removing the existing water supply sparger 109 (S4-1) and a step of attaching a new water supply sparger (S11-2) are added to the steps of the first embodiment. .

That is, the steam dryer (dryer) 15, the steam / water separator (separator) / shroud head 16, the fuel 10, etc. are removed by the same method as in the first embodiment (S1). Next, the fall prevention cover 23 is attached (S
2), guide rod 24 and core spray system piping clamp 2
5 is removed (S3).

Thereafter, the water supply sparger 109 installed above the core spray system piping 12 is first cut and removed (S4-1), and then the core spray system piping 12 is cut and removed as in the first embodiment (S4-1). S4-2).

Thereafter, local chemical decontamination of the upper part of the reactor pressure vessel 1 is performed (S5), and the work stand 38 is installed (S6).
After the remaining members are cut and removed (S7), the stud bolt holes 44 are processed and the stud bolts 45 are attached (S8), the dimensions are measured using a template (S9), and the new inlet pipe 111 is attached. . (S
10).

After the installation of the new core spray system piping 100 (S11-1), a new water supply sparger 109 is installed above the new core spray system piping 100, and then the guide rod is restored and the work platform is removed (S12). Recovery of the fuel loading and the dryer separator (S13) is performed.

According to the second embodiment, the replacement operation of the water supply sparger 109 can be performed easily and efficiently, and interference can be caused during the operation as compared with the case where the core spray system piping 12 is replaced alone. The absence of the water supply sparger 109 having the property provides an advantage that the core spray system piping 12 can be easily cut and suspended, and the new core spray system piping 100 can be easily suspended.

Third Embodiment (FIG. 22) This embodiment relates to a construction method in which the water supply sparger 109 is independently replaced.

FIG. 22 is a process chart showing a procedure for implementing this method. As shown in FIG. 22, in the present embodiment, the water supply sparger 109 is cut, removed, and restored in place of the core spray system piping 12.

That is, the steam dryer (dryer) 15, the steam / water separator (separator) / shroud head 16, the fuel 10, etc. are removed by the same method as in the first embodiment (S1). Next, the fall prevention cover 23 is attached (S
2), the guide rod 27 is cut and removed (S3 ').

Thereafter, the water supply sparger 109 installed above the core spray system piping 12 is cut and removed (S4 ') (S4-2).

Thereafter, as in the first embodiment, local chemical decontamination of the upper part of the reactor pressure vessel 1 is performed (S5), installation of a work platform (S6), cutting and removal of remaining members (S7), and the like. Do. In this embodiment, it is not necessary to machine the stud bolt hole and attach the stud. After that, the dimensions for mounting a new water supply sparger using the template are measured (S8 ').

Thereafter, a new water supply sparger 109 is introduced into the furnace and attached thereto, thereby performing restoration (S
9 '). In addition, as a structure of the new water supply sparger 109, a lid is attached similarly to the tee of the thermal sleeve for introduction into the spray nozzle of the core spray system piping.

After installing the new water supply sparger 109, the guide rod is restored and the work platform is removed (S10 '), and the fuel loading and the dryer separator are restored (S1).
Perform 1 ').

According to the third embodiment, the work of restoring the water supply sparger can be performed in a procedure that is easier than the procedure for replacing the core spray system piping 12.

[0108]

As described in detail above, according to the present invention, it is possible to allow a worker to enter the furnace with the core shroud in place, and to easily replace the core spray system piping. Can be performed reliably in a short time.

[Brief description of the drawings]

FIG. 1 is a process chart showing a core spray system pipe replacement procedure according to a first embodiment of the present invention.

FIG. 2 is an overall sectional view showing a furnace internal structure to which the first embodiment of the present invention is applied.

FIG. 3 is an explanatory view showing a fall prevention cover attaching step and the like according to the first embodiment of the present invention.

FIG. 4A is an explanatory view showing a hanging tool attaching step according to the first embodiment of the present invention, and FIGS. 4B and 4C are explanatory views showing a pipe cutting state.

FIG. 5 is an explanatory view showing a decontamination tank installation state according to the first embodiment of the present invention.

FIG. 6 is an explanatory view showing a decontamination step of the first embodiment of the present invention.

FIG. 7A is an explanatory view showing a state in which the work platform is mounted according to the first embodiment of the present invention, and FIG. 7B is an enlarged view of a virtual line part of FIG.

FIG. 8 is an explanatory view showing a remaining pipe forming step according to the first embodiment of the present invention.

FIG. 9 is an explanatory view showing a stud bolt hole forming step according to the first embodiment of the present invention.

FIG. 10A is an explanatory view showing a new inlet pipe connection state according to the first embodiment of the present invention, and FIG. 10B is an enlarged view of a virtual line part of FIG.

11A is an enlarged view showing a new inlet pipe connection state according to the first embodiment of the present invention, and FIG. 11B is an XI view of FIG.
-XI sectional drawing.

FIG. 12 is an enlarged sectional view showing a groove processing state in the spray nozzle according to the first embodiment of the present invention.

FIG. 13 is an enlarged sectional view showing a new thermal sleeve joining state according to the first embodiment of the present invention.

FIG. 14 is an explanatory diagram showing a new core spray pipe suspension process according to the first embodiment of the present invention.

FIG. 15 is a longitudinal sectional view showing a new core spray pipe suspended state according to the first embodiment of the present invention.

FIG. 16 is a cross-sectional view showing a new core spray pipe suspended state according to the first embodiment of the present invention.

FIG. 17 is an explanatory view showing a surface modification step according to the first embodiment of the present invention.

FIG. 18 is an explanatory diagram showing a surface modification range according to the first embodiment of the present invention.

FIG. 19 is a sectional view taken along line AA of FIG. 18;

20A is a sectional view taken along line BB of FIG. 18, and FIG. 20B is a sectional view taken along line CC of FIG.

FIG. 21 is a process chart showing a replacement procedure according to the second embodiment of the present invention.

FIG. 22 is a process chart showing a replacement procedure according to the third embodiment of the present invention.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 reactor pressure vessel 2 core shroud 5 upper lattice plate 7 jet pump 12 core spray system piping 13 core sparger 15 steam dryer (dryer) 16 steam separator (separator) and shroud head 17 top lid 23 fall prevention lid 24 guide Rod 25 Clamp 26 Rise pipe 27 Hanging tool 28 Junction box 28a Lid (cover plate) 29 Thermal sleeve 30 Core spray nozzle 31 Inlet pipe 32 Decontamination tank 38 Work platform (platform) 38a Outer wall shield 40 Remaining pipe 41 Flange seal surface 42 EDM Processing machine 43 EDM processing machine 44 Stud bolt hole 45 Stud bolt 50 Safe end 52 Remaining part of thermal sleeve 53 Groove processing machine 100 New core spray system piping 101 Tee 101a Lid 102 New thermal sleeve 103 Rise pipe 109 Water supply sparger 111 New inlet pipe 201 Surface reformer

Claims (8)

[Claims] 1. A piping penetrating through an upper shell wall of a core shroud to a core sparger installed on the inner surface of an upper shell of a core shroud in a reactor pressure vessel of a boiling water reactor over substantially the entire circumference. The core spray system piping is replaced with a new core spray piping by in-core operation, after removing the upper structure inside the reactor in the reactor pressure vessel, cutting and removing the core spray system piping. A method of replacing a core spray system piping of a reactor internal structure, wherein the new core spray system piping is introduced into the reactor pressure vessel and installed with the core shroud remaining. 2. The core spray system piping replacement method according to claim 1, wherein the new core spray system piping is made of a material and a structure which has been subjected to a stress corrosion cracking and crevice corrosion countermeasure. A method of replacing a core spray system piping in which the sparger and the core shroud are attached to the upper body by mechanical fastening. 3. The core spray system piping replacement method according to claim 1, wherein the existing reactor spray system piping is cut and removed, and then the inside of the reactor pressure vessel above the core shroud is locally chemically cleaned. Then, decontamination by mechanical washing or both, and then lowering the water level in the reactor pressure vessel to the upper surface of the core shroud, installing a working platform on the upper surface of the core shroud, and performing new core spray system piping by in-core operation Core spray system piping replacement method characterized by performing installation. 4. The core spray system pipe replacement method according to claim 3, wherein in the step of chemically cleaning the inside of the reactor pressure vessel, a decontamination tank is installed on an upper surface of a core shroud in the reactor pressure vessel, The upper and lower double sealing mechanisms and purge water between the outer peripheral part of the decontamination tank and the inner peripheral part of the reactor wall of the reactor pressure vessel make the furnace lower than the upper ring of the core shroud. Isolate the water from the reactor water above,
A method for replacing a core spray system piping, wherein upper furnace water is circulated in the decontamination tank. 5. The core spray system piping replacement method according to any one of claims 1 to 4, wherein the installation of the new core spray system piping and the replacement of the core internal structure installed above the core shroud are performed by: A core spray system pipe replacement method, wherein the pipes and auxiliary equipment provided outside the reactor pressure vessel are kept and all the work is performed inside the reactor. 6. The existing core spray system piping replacement method according to claim 1, wherein after cutting the core spray system piping, the junction box of the core spray system piping is connected. Cut and remove the residual thermal sleeve in the core spray nozzle, cut and remove the remaining part of the clamp for mounting the core spray system piping, insert a safe-end beveling machine into the core spray nozzle and insert a new core. A method of replacing a core spray system piping, in which a safe end groove processing for the spray piping is performed from inside the furnace. 7. The core spray system pipe replacement method according to any one of claims 1 to 6, wherein the step of restoring a new inlet pipe for connecting the new core spray system pipe and the core sparger is performed. A flange seal surface and a stud bolt hole are formed around the inlet pipe connection site on the outer surface of the core shroud, and a flange provided at the tip of the new inlet tube is joined to the flange seal surface, and the flange is connected to the stud bolt hole. By fastening with stud bolts embedded in the
A method of replacing a core spray system piping, comprising fixing the core shroud to the core shroud by non-welding. 8. The core spray system piping replacement method according to claim 7, wherein the flange of the new inlet pipe covers the entire ring bracket fixing the remaining pipe of the existing core sparger and the core shroud. A core spray system piping system, characterized in that a stress corrosion cracking preventive material is adopted for a connection part of the new inlet pipe including the flange, and the connection part is positioned and fixedly connected to a remaining pipe of a core sparger. Alternative construction method.