JP2000249791A - Replacing method for reactor core shroud - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a reactor core shroud replacing method for integrating a reactor core shroud in a nuclear reactor pressure container. SOLUTION: This replacing method for a reactor core shroud is carried out in the following procedure; the reactor core shroud is cut off in a reactor core pressure container so as to be removed from the reactor core pressure container, divided bodies of a new reactor core shroud divided into a plurality of pieces are conveyed into the reactor core pressure container, at least one of the plurality of the divided bodies is mounted in the reactor core pressure container, other divided bodies are sequentially installed to the mounted divided body, and consequently, the new reactor core shroud is assembled.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for replacing a reactor internal structure installed in a nuclear reactor such as a boiling water reactor during a service period, and more particularly to a method for replacing an overhead crane installed on an operation floor. The present invention relates to an exchanging method suitable for exchanging a core shroud of a nuclear power plant having a limited head or the like.

[0002]

2. Description of the Related Art Conventionally, when a core shroud of a boiling water reactor or the like is replaced during a service period, the core shroud must be carried in as a unit because of the size of the entrance of a reactor building. No, it is divided into several parts and transported to the reactor building.

[0003] For the purpose of reducing the work in the reactor pressure vessel and reducing the exposure, a split body of the core shroud carried into the reactor building is assembled on an operation floor or the like. The assembled and integrated core shroud is suspended in a reactor pressure vessel with a shield installed, and then welded to a shroud support cylinder.

However, this method can be applied to a nuclear power plant having a space for integrating a core shroud, but cannot be applied to a nuclear power plant having no such space. In addition, it could not be applied to a nuclear power plant where there is no head to lift the core shroud integrally with the overhead crane on the operation floor.

[0005] Regarding the shield, patent number: 2766
There is a method for exchanging the internal structure of a reactor known from Japanese Patent No. 195. The technique relating to the shield described here is effective when the recovery work of the jet pump diffuser is efficiently performed near the baffle plate. However, when an operator enters the reactor pressure vessel and performs a work such as installation of a new core shroud, it is insufficient from the viewpoint of reducing exposure from the core region of the reactor pressure vessel.

For example, an opening or a notch is provided in the shield for mounting the jet pump, but in order to reduce the exposure of the worker, this opening is set to be small as long as workability can be ensured. Is preferred. However,
In the shield and the like described in Japanese Patent No. 2766195, a notch is formed in the shield so that the shield can be pulled out and removed after installing a new internal structure such as a new jet pump and a new core shroud. It has been opened toward the lower end of the notch, and it has been desired to further reduce the notch. It has also been desired that the thickness of the shield can be sufficiently ensured.

[0007]

As described above, the above-described conventional method is applicable to a nuclear power plant having a space for integrating a core shroud, but a nuclear power plant having no such space is required. There is a problem that it cannot be applied to power plants.

Further, the shield is not sufficient from the viewpoint of reducing exposure when an operator enters the reactor pressure vessel and performs work such as installation of a core shroud. There is a problem that it takes a long time to remove the shield.

The present invention has been made in view of such a conventional situation, and has as its object to provide a method of exchanging a core shroud that integrates a core shroud in a reactor pressure vessel.

[0010]

In order to achieve the above object, a method for exchanging a core shroud according to the present invention comprises the steps of cutting a core shroud in a reactor pressure vessel and removing the core shroud from the reactor pressure vessel. Assembling a new core shroud by installing at least one of the divided parts of the new core shroud divided in the reactor pressure vessel, and sequentially attaching other divided bodies to the installed divided body. Features.

According to a second aspect of the present invention, in the method for exchanging a core shroud according to the first aspect, the divided body first installed in the reactor pressure vessel is a divided body including the lowermost part of the core shroud. It is characterized by.

According to a third aspect of the present invention, there is provided a method of cutting a core shroud in a reactor pressure vessel and removing the core shroud from the reactor pressure vessel, and separating a plurality of divided new core shrouds into the reactor pressure vessel. Loading into the
A step of assembling a new core shroud from the plurality of divided bodies in the reactor pressure vessel; and a step of installing the assembled new core shroud in the reactor pressure vessel.

According to a fourth aspect of the present invention, in the method for exchanging a core shroud according to any one of the first to third aspects,
A step of mounting a shield in the reactor pressure vessel, a step of draining reactor water in the reactor pressure vessel, and a step of removing the shield, wherein the shield is provided by the reactor pressure vessel. It is a divided shape arranged so as to cover a range including a core region, has a mounting hole corresponding to a joint between the reactor pressure vessel and the jet pump, and corresponds to an adjustment screw bracket of the jet pump and its vicinity. The thickness below the set height position is smaller than the thickness above the set height position.

According to a fifth aspect of the present invention, in the method for exchanging a core shroud according to any one of the first to third aspects,
A step of mounting a shield in the reactor pressure vessel, a step of draining reactor water in the reactor pressure vessel, and a step of removing the shield, wherein the shield is provided by the reactor pressure vessel. It is a divided shape arranged so as to cover a range including a core region, has a mounting hole corresponding to a joint between the reactor pressure vessel and the jet pump, and corresponds to an adjustment screw bracket of the jet pump and its vicinity. The thickness at the corresponding height position is configured to be thinner than the thickness below the height position.

According to a sixth aspect of the present invention, in the method of replacing a core shroud according to the fourth aspect, the shield is configured such that a thickness of the adjusting screw bracket and a portion corresponding to the vicinity thereof is thinner than other portions. It is characterized by having.

According to a seventh aspect of the present invention, in the method for exchanging a core shroud according to any one of the first to sixth aspects,
It is characterized in that the plurality of divided bodies are two.

According to an eighth aspect of the present invention, in the method for exchanging a core shroud according to any one of the first to sixth aspects,
The number of the plurality of divided bodies is three.

According to a ninth aspect of the present invention, in the method for exchanging a core shroud according to any one of the first to eighth aspects,
The assembling of the new core shroud is performed by welding or bolting the plurality of divided bodies.

According to the present invention, the core shroud carried in a divided state can be integrated in the reactor pressure vessel. 2 and 3 show an example of a method for dividing and assembling a new core shroud.

FIG. 2 shows an example in which the divided new core shroud is welded and integrated. FIG. 2A shows a case where the upper torso divided body and the intermediate torso / lower trunk divided body are divided and carried in, and FIG. FIG. 2C shows a case where the body is divided into three parts: an upper body divided body, an intermediate body divided body, and a lower body divided body.

FIG. 3 shows an example in which the divided new core shroud is integrated with bolts. FIG. 3A shows a case where the upper torso divided body and the intermediate torso / lower trunk divided body are divided and carried in, and FIG. FIG. 3C shows a case where the body is divided into three parts, namely, an upper body divided body, an intermediate body divided body, and a lower body divided body.

Of course, the present invention is not limited to the examples shown in FIGS. 2 and 3, and four or more divided bodies may be carried in, or vertically divided bodies may be used. Welding and bolt fastening may be used together.

After one of the divided bodies is installed in the reactor pressure vessel, the other divided bodies are sequentially attached to the installed divided body to assemble a new core shroud, or It is desirable to select whether to install the new core shroud after integrating it in consideration of the type and structure of the target reactor.

Further, by installing a shield inside the reactor wall of the reactor pressure vessel and reducing the radiation level in the reactor to a level below a reference value that allows personnel work in the reactor, a new core shroud or the like can be obtained. Installation of the furnace internals can be performed manually by an operator. In this case, it is preferable to add a step of reducing the radiation level in the reactor by performing chemical decontamination in the reactor pressure vessel in the presence of the core shroud and the jet pump.

The opening provided in the shield for mounting the jet pump or the like is preferably set as small as possible within a range where the workability can be ensured in order to reduce the exposure of the worker.

If the dividing line of the block of the shield is set so as to pass through such a mounting hole as the opening, the shield can be easily removed even if the opening is not opened toward the lower end of the shield. Can be performed. That is, first, the block next to the shield block including the mounting hole is removed, and then the shield block including the mounting hole is slid sideways and then pulled up.

The size of the mounting hole is set in consideration of the type of the reactor, the size of the reactor pressure vessel and the jet pump, etc., so that the workability is good and the exposure of the workers can be reduced as much as possible.

Since the radiation dose varies depending on the years of operation of the reactor, the thickness of the shield is set so that the dose equivalent rate in the reactor can be reduced to a desired range.

Of course, in order to reduce the radiation exposure, the thickness of the shield in the core region of the reactor pressure vessel should be as thick as possible. However, since the adjustment screw bracket portion of the jet pump has a small distance from the reactor pressure vessel, the thickness of the adjustment screw bracket and the shield at a height corresponding to the vicinity thereof are less than the height position. It is desirable that the thickness be smaller than the thickness of the shield.

Since the shield is formed in a block shape, when the shield is removed after the installation of a new core structure such as a core shroud, the shield block disposed between the jet pumps is removed. The shield block in which the portion at the height position corresponding to the adjustment screw bracket is formed thin can be removed by sliding it sideways and pulling it upward. By doing so, the portion where the thickness of the shield is reduced can be reduced, and the exposure of the worker can be further reduced.

The thickness of the shield at the portion corresponding to the adjusting screw bracket may be smaller than at other portions. in this case,
If a portion corresponding to the adjustment screw bracket (that is, a portion having a smaller thickness than other portions) is completely included in one shield block, the shield block cannot be removed after the jet pump is mounted.

However, if the dividing line of the shielding block is set so as to pass through a portion corresponding to the adjusting screw bracket, it can be easily removed. First, the block adjacent to the shield block including the portion corresponding to the adjustment screw bracket may be removed, and then the shield block including the portion corresponding to the adjustment screw bracket may be slid sideways and then pulled up.

By doing so, the portion where the thickness of the shield is reduced can be further reduced, and the exposure of the worker can be further reduced.

[0034]

DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described below with reference to FIGS. In the figure below,
The same components are denoted by the same reference numerals, and redundant description will be omitted. The present invention is not limited to the embodiments described below, but can be implemented with appropriate modifications without departing from the scope of the invention.

FIG. 4 is a sectional view showing the structure of a reactor pressure vessel to which a core shroud replacement method according to the present invention is applied. FIGS. 5 to 16 and FIGS. FIG. FIG. 17 shows a shield used in the core shroud replacement method according to the present invention.

First, the configuration of the reactor pressure vessel will be described with reference to FIG. A core shroud 2 is disposed in the reactor pressure vessel 1, and the core shroud 2 is supported by a shroud support cylinder 3. The shroud support cylinder 3 is supported at the bottom of the reactor pressure vessel 1 by a shroud support leg 4.

Above the core shroud 2, a core spray pipe 12, a steam dryer 15, a steam / water separator / core shroud head 16, and a control rod guide tube 11 below the core shroud 2, differential pressure detection and boric acid water injection. Equipment such as a pipe 14 is provided.

A jet pump 7 is provided on the outer peripheral side of the core shroud 2. The jet pump 7 is roughly composed of 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.

An upper grid plate 5 is provided above the core shroud 2.
Is provided, and a core support plate 6 is provided below.
Fuel 10 and control rods 9 are arranged in the core shroud 2.

Next, the reactor pressure vessel 1 having such a configuration will be described.
The method of exchanging the in-furnace structure including the core shroud 2 will be described in the order of steps.

(1) Removal of Steam Dryer and Core Shroud Head, and Fuel Transfer Process (FIGS. 4 and 5) In this process, as in the ordinary periodic inspection, FIG.
The reactor pressure vessel upper lid 17 and the steam dryer 15 are removed from the reactor pressure vessel 1 in the state shown in (1) by an overhead crane (not shown) in the reactor building (not shown). At this time,
Reactor water is held below the flange of the reactor pressure vessel 1.

Next, the reactor well 18 is filled with water, and the steam / water separator / core shroud head 1 is filled with an overhead crane.
Remove 6. Thereafter, all the fuel 10 is moved from the core to the fuel pool, and the reactor water level is returned to the lower part of the flange of the reactor pressure vessel 1.

In this step, the steam dryer 15 and the steam / water separator / core shroud head 16 are moved to a normal installation location in the reactor well. In this case, a steam dryer temporary mounting base (not shown) is installed above the steam / water separator / core shroud head 16, and the steam dryer 15 is moved and stacked. A shield is provided on the steam dryer 15.

As described above, by laying the steam / water separator / core shroud head 16 and the steam dryer 15 on top of each other, a wide working space can be secured, and the working efficiency can be improved.

When the steam dryer 15 is placed above the steam-water separator / core shroud head 16, the height and the concentricity are substantially the same as those in the reactor, due to the support member incorporated in the equipment storage pool. It is desirable to adopt a strategic arrangement. This is because the steam dryer 15 is in the same supporting state as the installed state in the nuclear reactor, and damage prevention and the like can be effectively achieved.

(2) Removal of dry tube / LPRM detector assembly, control rod drive mechanism, control rod, control rod guide tube, and fuel support bracket (FIGS. 5 and 6) The dry tube / LPRM detector assembly 22 occupying the space between the upper grid plate 5 and the core support plate 6 is removed, and the space between the upper grid plate 5 and the core support plate 6 is emptied. The above procedure is performed to secure a space to be removed upward after the core shroud 2 is removed, and the order may be changed.

From this state, the fuel support 10a, the control rod 9 and the control rod guide tube 11 are removed by a simultaneous gripping tool (not shown) and moved to the fuel pool. When removing the control rod guide tube 11, it is necessary to remove the control rod drive mechanism 20 of the pedestal chamber 19 and to pull out a thermal sleeve (not shown) from the control rod drive mechanism housing 21.
The removed control rod drive mechanism 20 and thermal sleeve are stored in a storage box, and are moved from the pedestal chamber 19 to a storage area such as a refueling work floor and stored there. Alternatively, the control rod guide tube 11 may be removed and then returned to the control rod drive mechanism housing 21.

(3) Chemical decontamination step in the furnace (FIG. 7) In this step, a chemical agent is injected into the reactor pressure vessel 1 and circulated in the furnace by using a jet pump 7 to perform work. Reduce the radiation dose rate to a level that allows personnel to enter the furnace. In other words, in order to reduce radiation exposure when the core shroud 2 is removed and the reactor water level is lowered, the inside and outside of the core shroud 2, the inside surface of the reactor pressure vessel 1, the bottom of the reactor pressure vessel 1, and the like are reduced. Perform cleaning.

A spray ring 6 is provided on the upper part of the reactor pressure vessel 1.
In the state in which the reactor 4 is mounted, the chemical is injected from the chemical injection device 65 connected to the reactor pressure vessel 1, and the chemical is introduced into the furnace by the jet pump 7 from the recirculation inlet nozzle and circulated in the furnace. As the chemical, permanganic acid and oxalic acid are alternately circulated.

In this manner, the activated oxides and the like existing in the reactor pressure vessel 1 are dissolved and removed, discharged from the control rod drive mechanism housing 21 to the outside of the reactor, and circulated by the circulation pump 66 attached to the outside. Is done. Then, it is returned into the furnace again through the spray ring 64. The radioactive material discharged from the control rod drive mechanism housing 21 to the outside of the furnace and circulated by the purification system pump 69 is removed by the ion exchange resin device 67.

By repeating this process several times, it is possible to safely remove the radioactive substance adhering to each device in the furnace and the inner surface of the pressure vessel, and drastically reduce the radiation dose in the furnace.
The waste gas is processed by a waste gas device 68. In addition, in order to reduce the dose of the radiation atmosphere in the furnace, brush cleaning or cladding suction cleaning of the surface of the furnace internal structure may be appropriately performed.

For example, a certain amount of time is required for groove preparation and manual welding at the level of the shroud support ring 3. Atmospheric dose equivalent rate of this level is 1 mSv /
In the case of h, work for about 1 hour is possible.

By performing chemical decontamination in the furnace and then shielding the internal structure of the activation furnace with a shield or the like, the atmospheric dose equivalent rate at the furnace bottom can be reduced to 0.1 mSv / h or less. Work exposure in the furnace is kept low, and long-term work is possible. Further, the activated corrosion products are removed, the problem of dust that dries and pollutes the atmosphere is reduced, and the safety is enhanced from the viewpoint of protection of workers from internal exposure.

In chemical decontamination, it is not necessary to install large-scale pumps by mainly using an existing reactor recirculation pump system and jet pump. Further, the entire reactor water can be easily circulated, and the working efficiency can be improved. Thus, the exposure of the worker in the furnace can be reliably reduced, and the worker can access the inside of the furnace.

(4) Cutting and removing the safe end of the recirculating water inlet nozzle and the core spray nozzle and the thermal sleeve, and removing the water supply sparger, the core spray pipe and the guide rod (FIG. 8) The safe end 71 and the thermal sleeve 72 of the recirculation inlet nozzle 70 and the safe end and the thermal sleeve of the core spray nozzle are cut from outside the furnace. After cutting, the recirculation inlet nozzle 70 has a temporary closing lid 80
The temporary closing lid 80 is attached to the core spray nozzle by welding.

As described above, the safe end 71 of the recirculation inlet nozzle 70 and the thermal sleeve 72
Is cut off to release the lower end of the riser tube 7b. Therefore, when cutting and removing the riser pipe 7b,
Only the riser brace arm 73 from inside the furnace needs to be cut, and the working efficiency can be improved. The provision of the temporary closing lid 80 makes it possible to fill the furnace with water, thereby shortening the process.

As a cutting method, for example, the efficiency of the cutting operation can be improved by simultaneously cutting every five recirculation inlet nozzles 70 provided from the outside of the furnace.

Next, after filling the reactor well with water, the water supply sparger 26 installed above the core shroud 2 is removed, the core spray system piping 12 is cut and removed, and a bracket on the inner wall of the reactor pressure vessel 1 is removed. The guide rod 27 which is suspended and inserted into the hole of the bracket of the core shroud is cut and removed. These detachment and cutting / removal operations are performed using a remote control device and a diver in combination.

(5) Step of Removing Upper Lattice Board and Jet Pump Inlet Mixer (FIG. 9) In this step, as shown in FIG.

The upper lattice plate 5 is mounted and fixed on a stepped portion of the upper end ring of the core shroud 2 via an upper lattice plate mounting plate 5a, and its periphery is fixed by brackets and wedges. Further, an L-shaped stopper is fixed to a bolt screwed to a stud fixed to the upper surface of the upper lattice plate 5 via a welded portion.

When removing the upper lattice plate 5, the bolts of the upper lattice plate are threaded from the fuel exchange device on the operation floor using a threading jig, and the bolts and wedges are collected. 5 is lifted above the core shroud 2.

The removed upper lattice plate 5 is moved to the equipment storage pool adjacent to the reactor well 18 via the reactor well 18 which has been filled with water. After being cut into small segments by a method such as electric discharge machining or plasma cutting, they are packed in a storage container and stored in a storage place.

In this step, the inlet mixer 7c of the jet pump 7 is also removed.

(6) Cutting Stud Bolt of Core Support Plate and Cutting Upper Part of Core Shroud (FIG. 10) In this step, the stud bolt of the core support plate 6 is cut. The core support plate 6 is fixed to a flange of a lower step portion of the core shroud 2 via a stud bolt and a nut, and a U-shaped cap covering the nut is fixed to a bolt end portion by a welded portion via a block.

Therefore, in this step, in order to remove the core support plate 6, the stud bolt is threaded by a threading jig or cut by an electric discharge machine by an operation on the refueling machine.

Thereafter, the upper part of the core shroud is cut. For example, by machining (roll-type tooth cutting technology, etc.), electric discharge machining or water jet machining,
The core shroud 2 is cut in order from the top, for example, into two short cylindrical segments. You may shred finely.

FIG. 10 shows a core shroud cutting device for performing such a cutting operation. As shown in FIG. 10, the core shroud cutting device includes a core shroud hanging tool 104, machining (push-off technique using roll-type teeth), electric discharge machining or a high-pressure water jet type upper shroud cutting device 106, and a shroud upper cutting platen. 108
Etc. are provided. In the case of electric discharge machining or a high-pressure water jet method, it is preferable to provide a cutting powder collecting device.

The upper shroud cutting device 106 (and the cutting powder collecting device, if installed), cuts the upper part of the core shroud 2 (and the cutting powder collection) while running in the circumferential direction on the shroud upper cutting platen 108. ). The shroud upper cutting device 106 (and the cutting powder recovery device if installed) is remotely operated to cut the upper part of the core shroud 2.

(7) Unification of core shroud and core support plate, removal of incore guide tube and incore stabilizer, and differential pressure detection / cutting and removal of boric acid water injection pipe (FIG. 11) In this step, (6) Upper cut portion 2a of core support plate 6 and core shroud 2 cut and separated in the process
Is lifted by the lifting tool 104.

Cut core shroud upper cut part 2
a and the core support plate 6 are stored and stored in an equipment storage pool or the like. The storage state can be appropriately selected from a dispersion state, a stacked state, and the like.

Next, the in-core guide tube 81 and the in-core stabilizer 28 are removed. In this case, the upper part of the in-core housing 25 in the furnace and all or part of the in-core stabilizer 28 are cut and removed, and the in-core guide tube 81 is removed.

Further, the differential pressure detection / boric acid water injection pipe 14 that penetrates through the bottom of the reactor pressure vessel 1 and rises along the inner wall of the core shroud 2 is cut and removed.

(8) Core Shroud Lower Cutting / Removing Step (FIG. 12) In this step, a core shroud hanging tool 104, a lower shroud cutting device 111, a cutting powder collecting device 112, a shroud lower cutting surface plate 113 and the like are used. Then, the lower part of the core shroud 2 is cut and removed.

At the time of cutting the core shroud 2, the cutting near the welded portion between the core shroud 2 and the shroud support cylinder 3 is performed in consideration of the possibility that the vicinity of the welded portion of the shroud support cylinder 3 is deteriorated by the influence of heat. Set the position. It is desirable that the cutting position be a height position excluding the upper end side portion of the shroud support leg 4 that is affected by heat due to welding, for example, a height position excluding within 5 mm from the upper end. As a result, the core shroud 2 after replacement
Can be obtained with high reliability.

For example, the core shroud 2 is made of SUS304
When the steel and the shroud support cylinder 3 are made of Inconel, there is a possibility of stress corrosion cracking in the heat-affected zone (about 5 mm) of the welded portion of the shroud support cylinder 3 remaining without being removed by welding different materials. is there. By removing all of the parts that are likely to undergo the stress corrosion cracking, for example, the heat effect due to reheating when the new core shroud 2 is fixed by welding can be prevented, and the useful life of the new core shroud can be extended.

At the time of cutting the core shroud 2, the support cylinder 3 is considered in consideration of the possibility that the vicinity of the welded portion of the shroud support cylinder 3 is deteriorated by the influence of heat.
Set the cutting position in the vicinity of the welded part. It is desirable to set the height of the shroud support leg 4 excluding the upper end side portion, for example, 30 to 150 mm from the upper end, which is affected by heat due to welding. Thereby, the strength reliability of the core shroud after replacement can be obtained.

The cut core shroud 2 segments are accommodated in the removed internal structure, equipment storage pool, and the like. The space in the equipment storage pool is effectively used to make use of the steam dryer 15, steam-water separator and core shroud head 16.
The cut core shroud 2 and the like can be stored efficiently.

If the core shroud 2 and the shroud support cylinder 3 are cut with high precision, the beveling of the shroud support cylinder in the step (19) to be described later can be omitted, and the process can be shortened and the exposure of workers can be reduced. .

(9) Cutting and removing the riser brace of the jet pump, and removing the riser pipe (FIG. 13) In this step, the riser pipe 7b and the riser brace 73 of the jet pump 7 are cut and removed by remote control underwater.
After being temporarily placed on a temporary storage rack installed at the bottom of the furnace by the hanging tool 114, it is transferred outside the furnace.

In this step of removing the jet pump, for example, after cutting 10 riser tubes and 20 diffusers,
It is stored in a storage rack previously installed in the furnace, and after all the riser pipes and diffusers have been cut, the whole storage rack is lifted out of the furnace in a later step. As a result, the moving time can be reduced, and the removal work in the storage pool for devices and the like can be smoothly performed.

(10) Step of Cutting and Removing Sensing Line and Diffuser (FIG. 14) In this step, for example, 20 pieces of diffuser 7a are used by using the suspender 115 and the diffuser cutting device 116.
Is cut, and a plurality of 20 diffusers 7a are cut at the same time and removed outside the furnace in a later step.

The cutting of the diffuser 7a of the jet pump 7 is performed by inserting a cutting device from the lower end of the diffuser remotely underwater and cutting the vicinity of the base of the jet pump. Further, by simultaneously cutting a plurality of diffusers 7a and temporarily storing the cut diffusers 7a in the furnace bottom, the working time can be reduced.

(11) Movement of riser pipe and diffuser outside furnace, cleaning inside furnace, and all drain flushing step (FIG. 15) In this step, riser pipe 7b temporarily stored at the furnace bottom is used.
And the diffuser 7a is removed. For example, 10 riser tubes and 20 diffusers are moved at once to an equipment storage pool for removal. Thus, the process can be shortened by moving the riser tube and the diffuser temporarily stored in the furnace bottom part at once by using the storage rack.

Since all cutting is completed in the above steps,
The inside of the furnace is cleaned by water washing, and the inside of the furnace is flushed while draining the furnace water.

(12) Water Filling to Reactor Pressure Vessel Flange Level and Mounting Step of Reactor Pressure Vessel Inner Wall Shield (FIGS. 16 and 17) In this step, installation and recovery work of a new reactor internal structure is started. First, when the inside of the furnace is underwater, the shield 117 is installed on the entire surface of the furnace wall near the core. Fine adjustment of the installation position can be performed by remote control underwater and by disposing a diver at the bottom of the furnace.

Since the radiation dose varies depending on the number of years of operation of the reactor, the thickness of the shield 117 needs to be determined in advance so that the dose equivalent rate in the reactor can be 1 mSv / h or less.

When the shield 117 is provided and the dose equivalent rate in the furnace is set to 1 mSv / h or less, the exposure of workers to the furnace can be reliably reduced, and the workers can access the furnace. It becomes possible. The effect of installing the new furnace internal structure can be realized.

FIGS. 17A, 17B, 17C and 17D show details of the shield. The shield 117 is configured in a block shape so that it can be removed after the jet pump 7 and the core shroud 2 are installed.

As shown in FIG. 17A, around the riser brace arm attachment portion of the shield 117, the shield 11 is used to install a riser brace pad surface finishing device and a riser brace pad and a riser brace arm welder.
7 is provided with a riser brace attachment hole 85 that can be opened by removing a part of the same.

In the vicinity of the recirculation inlet nozzle 70,
In order to install the riser pipe 7b, a mounting hole 86 for a recirculation inlet nozzle is provided which can be opened by removing a part of the shield 117. Neither of the openings of the mounting holes 85, 86 reaches the lower end of the shield 117.

Since the shield 117 is formed in the shape of a block, as shown in FIG. 17A, if the dividing line of the block is set so as to pass through the mounting hole 85 or the mounting hole 86, when the shield is removed, First, the block next to the shield block including the mounting holes 85 or 86 may be removed, and then the shield block including these mounting holes may be slid sideways and then pulled up.

According to such a configuration, the mounting holes 85, 8
Even if the opening 6 does not reach the lower end of the shield 117, the shield 117 can be removed after the new core shroud 2 and the jet pump 7 are installed. Therefore, the opening area of the shield 117 can be reduced, and the exposure of the worker can be reduced.

The sizes of the mounting holes 85 and 86 are set in consideration of the type of the reactor, the size of the reactor pressure vessel and the jet pump, etc., so that the workability is good and the exposure of the workers can be reduced as much as possible. I do.

To reduce the exposure, it is very effective to increase the thickness of the shield 117 in the core region of the reactor pressure vessel. However, as shown in FIG.
The distance between the adjustment screw bracket 7d and the reactor pressure vessel 1 is small. Therefore, in the present embodiment, as shown in FIGS. 17B and 17D, when the shield 117 is arranged on the furnace wall, the thickness of the shield 117 near the height position corresponding to the adjusting screw bracket 7d is set to: The thickness is smaller than the thickness of the shield 117 at the height position corresponding to the top and bottom of the adjustment screw bracket 7d.

Since the shield 117 is formed in a block shape, the new core shroud 2 and the jet pump 7
When removing the shield after installation, remove the shield block disposed between the jet pumps 7,
The shield block in which the portion near the height position corresponding to the adjustment screw bracket 7d is formed thin can be removed by sliding it sideways and pulling it upward. By doing this, the part where the thickness of the shield becomes thinner is reduced,
Exposure of workers can be further reduced.

The thickness of the portion of the shield 117 corresponding to the adjusting screw bracket 7d may be smaller than the thickness of the other portions.

If the dividing line of the shield block is set so as to pass through a portion corresponding to the adjustment screw bracket 7d (that is, a portion having a smaller thickness than the other portions), first, when removing the shield, the adjustment is performed first. Remove the block adjacent to the shield block including the portion corresponding to the screw bracket 7d,
Next, the block including the portion corresponding to the adjustment screw bracket 7d may be slid sideways and then pulled up.

In this manner, the portion where the thickness of the shield is reduced can be further reduced, and the exposure of the worker can be further reduced.

The thickness of the shield 117 below the height position corresponding to the adjusting screw bracket 7d is smaller than the thickness of the shielding body 117 above the height position corresponding to the adjusting screw bracket 7d. May be.

In this way, when the shield 117 is to be removed after the new core shroud 2 and the jet pump 7 have been installed, the shield block may be pulled up, and the working time can be reduced.

As described above, by installing the shield 117, an operator enters the furnace as an aerial work, and can easily perform installation, fine adjustment, surface finishing, welding work, and the like of devices and the like described later. Therefore, workability can be improved.

(13) Draining the furnace, installing a scaffold in the furnace,
(FIG. 18) In this step, as shown in FIG. 18, after draining water in the furnace to bring it into the air, a scaffold 119 is installed in the furnace in advance, and a worker enters the furnace with the elevating device 120 and works. Create an environment to do.

(14) Installation of riser pipe, safe end of recirculating water inlet nozzle and welding recovery of thermal sleeve (FIG. 19) In this step, installation of riser pipe 7b is performed in parallel with installation of diffuser 7a. . That is, the above-described shield 1
Then, the lower end of the riser pipe 7b suspended in the furnace is inserted into the recirculation water inlet nozzle 70, and the thermal sleeve 72 and the safe end 71 are welded outside the furnace.

For example, every 10 riser tubes 7b are grouped into groups of 5 every other, and the riser tube mounting operation is performed in air in a furnace in parallel with the operation of installing the diffuser 7a. Can be shortened.

(15) Groove adjustment of riser brace,
Attachment of the riser brace arm and attachment of the riser brace yoke (FIG. 20) In this step, the pad surface is finished using a pad surface finisher, and the weld is inspected using a weld inspector. After confirming the thickness and adjusting the groove, etc., the riser brace arm 73 is attached and welded using the riser brace arm welding device 121. In this step, the mounting holes 8 of the shield 117 described above are used.
5 is opened and work is performed.

In this step, since the worker performs the work in the furnace using the pad surface finishing device, the riser brace arm welding device 121, etc., the fine adjustment and the work are performed reliably, and the reliability of the work is improved. And the process can be shortened.

In this operation, a welding operation is simultaneously performed on a plurality of riser tubes 7b, for example, on ten riser tubes 7b. This is because the process can be shortened.

(16) Baffle Plate Groove Processing and Diffuser Installation Step (FIG. 21) In this step, a groove processing machine is installed on the baffle plate 8 and grinding is performed.

Next, the diffuser 7a is welded to the baffle plate 8 using the diffuser welding machine 123.

The attachment of the diffuser 7a is carried out by sequentially suspending 20 bodies in a furnace, and after installation and adjustment, successively welding. In parallel with this operation, every 10 riser tubes are divided into two groups every other, and when the recirculation outlet nozzle is restored,
Install riser pipes in groups.

With this configuration, the installation efficiency can be improved. In addition, a worker operates the diffuser welding machine 123 in the furnace.
By performing the installation, the installation accuracy can be improved. Since a plurality of diffusers 7a are welded at the same time, the process can be shortened.

(17) Attaching / adjusting the inlet mixer of the jet pump and attaching the sensing line (FIG. 22) In this step, the inlet mixer 7c is connected to the above (1).
6) The upper end of the diffuser 7a installed in the process and (14)
It is suspended from the upper end of the riser pipe 7b installed in the process, and these are connected.

Next, after all the diffusers 7a of the 20 jet pumps 7, for example, are installed, a sensing line, which is an instrumentation system pipe, is installed in the furnace by manual welding or automatic welding by an operator. Automatic welding by machine. With such a configuration, the mounting of the sensing line can be performed efficiently and reliably.

With the above steps, the installation of the jet pump is completed.

(18) Removal of the jet pump inlet mixer, installation of the diffuser seal plug, and removal of the scaffold in the furnace (FIG. 23) In this step, the inlet mixer 7c attached in the above-mentioned step (17) is removed, and the upper end of the diffuser 7a is sealed. The plug 122 is attached. Seal plug 122
If a new core shroud (lower portion) 2c is attached in step (21) described later, water can be filled between the reactor pressure vessel 1 and the core shroud 2.
It is possible to further reduce the exposure of workers in the furnace.

Next, in order to suspend the new core shroud, the in-core scaffold 119 used for installing the jet pump was used.
From the reactor pressure vessel 1.

(19) Shroud Support Cylinder Groove Processing Step (FIG. 24) In this step, the groove processing machine 118 of the shroud support cylinder 3 is set in a furnace to perform grinding.

(20) Preparation in the furnace before hanging the new core shroud (lower part), hanging in the new core shroud (lower part), and fitting up step (FIG. 25) In this step, the guide pole 1 for hanging the new shroud is used.
24, new core shroud hanging tool 125, core measuring device 12
6. Use a jack 127 or the like. Core measuring device 126
For example, a laser beam radiated vertically downward from a laser device built in the core measuring device is applied to a target on the level of the control rod drive mechanism housing 21 to measure the core of the core shroud.

The divided lower core 2c of the new core shroud is suspended in the furnace by a new core shroud suspender 125 guided by a new shroud suspension guide pole 124. The suspended lower divided body 2c is received by the jack 127 installed on the furnace bottom, and is gently seated on the groove of the shroud support cylinder 3 to fit up.

In this step, since the jack 127 temporarily receives the lower divided body 2c of the new core shroud and gently seats it on the shroud support cylinder 3, the welding groove of the lower divided body 2c can be protected.

(21) New Core Shroud (Lower) Outer Welding Step (FIG. 26) In this step, the lower split body 2c of the new core shroud and the shroud support cylinder 3 are welded from the outer side of the core shroud. Welding is performed using a new shroud outer welding machine 128 that is simultaneously suspended while being attached to the lower split body 2c.

In this step, the welding operation can be performed efficiently in the circumferential direction along the groove formed in the above step.

After the outer welding of the new core shroud is completed, the new shroud outer welding machine 128 and the jack 127 are removed, and water is filled in an area sandwiched between the reactor pressure vessel 1 and the lower divided body 2c. It is possible to further reduce the exposure of the workers inside.

(22) Inner Welding of New Core Shroud (Lower) and Inspection Step after Welding (FIG. 27) In this step, a worker enters the furnace and firstly installs the shroud inner welding machine 130. After the installation of the shroud inner welding machine 130, automatic welding is performed by remote control.
Then, after welding, a worker enters the furnace again to inspect the welded portion and remove the welder.

Thus, the lower divided body 2c of the core shroud is fixed by welding from the inner and outer peripheral sides.

(23) Preparing the new core shroud (upper) in the furnace before suspension, hanging the new core shroud (upper), and fitting up (FIG. 28) This step was used in the above step (20). Guide pole 124 for suspending new shroud, new core shroud suspender 125, lead measuring device 126, and jack 127
Use a or the like. Upper core split 2a of new core shroud
Is suspended in the furnace by a new core shroud suspender 125 guided by a new shroud suspension guide pole 124. The suspended upper core 2a of the new core shroud is received by the jack 127a installed on the lower core 2c, and is gently seated on the groove of the lower core 2c to fit up.

In this step, the upper core 2a of the new core shroud can be temporarily received by the jack 127a and can be quietly seated on the lower core 2c, so that the welding groove of the upper core 2a can be protected. I can do it.

(24) New Core Shroud (Upper) Inside Welding Step (FIG. 29) In this step, an operator enters the furnace and firstly install the shroud inner welding machine 130. After the installation of the shroud inner welding machine 130, the lower end of the upper split body 2a and the upper end of the lower split body 2c of the new core shroud are remotely controlled by:
Automatic welding from the inner peripheral side of the new core shroud.

After welding, an operator enters the furnace again to inspect the welded portion and remove the welder. Thus, the core shroud 2 is entirely fixed by welding.

(25) Recovery of differential pressure detection / boric acid water injection pipe, recovery of incore guide pipe and incore stabilizer (FIG. 30) In this step, beveling machine 131, automatic welding device 132
The operator enters the furnace and installs the differential pressure detection / boric acid water injection pipe 14, the incore guide pipe 81, and the incore stabilizer 28 by using the method. After such restoration work, the in-furnace scaffold will be removed.

Thus, the core shroud lower structure is restored.

(26) Hanging the new core support plate, connecting the incore guide tube insertion guide, and attaching the new core support plate (FIG. 31) In this process, the work platform 134 on the shroud is installed in the furnace. The new core support plate 6 is hung by the hanger 135. For example, the core support plate 6 to which the in-core guide tube insertion guide 136 is attached in advance is suspended in the furnace by the suspender 135, and the in-core guide tube insertion guide 13 is provided.
6 is inserted into the in-core guide tube 81, and the core support plate 6 is suspended.

Next, using a core support plate core adjusting jig or the like,
The new core support plate 6 is centered. Then, the stud is tightened using the stud tensioner and the tack weld device, and the new core support plate 6 is attached.

(27) New upper lattice plate installation process (FIG. 3)
2) In this step, a hanging tool 135, a new upper lattice plate alignment jig,
Use a tack weld device, a wedge mounting device, a core measuring device, and the like.

A new upper lattice plate 5 is suspended in the furnace and placed on the core shroud 2. Next, an operator enters the furnace and tightens the wedge of the new upper lattice plate to perform installation.

As a result, the upper lattice plate can be restored.
If the integrity of the removed upper lattice plate and / or core support plate is maintained, a shield is installed below the working platform 134 above the shroud, and a remote automatic stud tensioner, wedge mounting device, The upper lattice plate and / or the core support plate may be used again by using a tack weld device, a core measuring device, or the like. This is preferable because cost reduction and waste reduction can be achieved.

(28) Removing the inner wall shield of the reactor pressure vessel, removing the diffuser seal plug, installing the inlet mixer, and installing the upper part shield of the core shroud (FIG. 33). Remove the shield 117 installed on the inner wall of the container 1, remove the diffuser seal plug 122,
Attach the inlet mixer 7c.

Thereafter, a shielding member 146 for shielding is installed on the upper part of the core shroud in order to reduce the exposure in the next (29) step operation.

(29) Attachment of core spray pipe and water supply sparger, and removal of core shroud upper part shield (FIG. 34) In this step, the shroud upper work platform 13 is used.
4. Use a shielding member 146 for the upper part of the core shroud, an automatic welding machine, a restraining jig, a beveling machine, and the like.

Using these devices, workers
The core spray pipe 12 and the water supply sparger 26 are attached, and after the work is completed, the shield member 146 for the upper part of the core shroud is removed.

(30) Attaching Step of Guide Rod (FIG. 35) In this step, the worker attaches the guide rod 27 using the work scaffold 151 and a tack weld device.

(31) Installation of control rod guide tube, control rod, fuel support bracket and control rod drive mechanism, dry tube
Installation of LPRM detector assembly, confirmation of core shroud head installation in furnace, control rod drive mechanism venting, fuel loading, and normal restoration work process (Fig. 36) This process is the final process, and the above (30) process After the installation of the main equipment accompanied by welding etc., the control rod guide tube 11, the control rod 9, the fuel support fitting 10a, and the control rod drive mechanism 20, which were removed first, are installed. Also, the installation of the dry tube / LPRM detector assembly 22, the confirmation of the installation of the core shroud head 16 in the furnace, the control rod drive mechanism vent, the loading of fuel, and the normal recovery work are performed.

[0143]

As described above, in the core shroud replacement method of the present invention, since the core shroud is integrated in the reactor pressure vessel, even in a nuclear power plant having a limited head lift of an overhead crane or the like. The core shroud can be replaced.

Further, by installing the shield in the reactor pressure vessel, it is possible to surely reduce the exposure of workers when the core shroud is integrated in the reactor, and to enable the workers to access the inside of the reactor. , Each work can be realized.

[Brief description of the drawings]

FIG. 1 is a flow chart showing one embodiment of a method for replacing a core shroud of the present invention.

FIG. 2 is a view showing an example of a method of assembling a new core shroud by splitting and welding in a core shroud replacement method of the present invention.

FIG. 3 is a diagram showing an example of a method of assembling a new core shroud by splitting and bolting in a core shroud replacement method of the present invention.

FIG. 4 is an explanatory view showing one embodiment of a method of exchanging a core shroud of the present invention, and is an overall sectional view showing a furnace internal structure.

FIG. 5 is a cross-sectional view of the in-furnace structure showing a step (1) of one embodiment of a method for exchanging a core shroud of the present invention.

FIG. 6 is a sectional view of an in-furnace structure showing a step (2) of an embodiment of a method for exchanging a core shroud of the present invention.

FIG. 7 is a sectional view of an in-furnace structure showing a step (3) of an embodiment of a method for exchanging a core shroud of the present invention.

FIG. 8 is a sectional view of the in-furnace structure showing step (4) of the embodiment of the method for exchanging a core shroud of the present invention.

FIG. 9 is a sectional view of the in-furnace structure showing step (5) of the embodiment of the method for exchanging a core shroud of the present invention.

FIG. 10 is a sectional view of the in-furnace structure showing step (6) of the embodiment of the method for exchanging a core shroud of the present invention.

FIG. 11 is a cross-sectional view of the in-furnace structure showing step (7) of the embodiment of the method for replacing a core shroud of the present invention.

FIG. 12 is a cross-sectional view of the in-furnace structure showing step (8) of the embodiment of the method for replacing a core shroud of the present invention.

FIG. 13 is a sectional view of the in-furnace structure showing step (9) of the embodiment of the method for exchanging a core shroud of the present invention.

FIG. 14 is a sectional view of the in-furnace structure showing a step (10) of the embodiment of the method for exchanging a core shroud of the present invention.

FIG. 15 is a sectional view of the in-furnace structure showing a step (11) of the embodiment of the method for replacing a core shroud of the present invention.

FIG. 16 is a cross-sectional view of the in-furnace structure showing a step (12) of the embodiment of the core shroud replacement method of the present invention.

17A is a perspective view showing a state before a jet pump is installed, and FIG. 17B is a perspective view showing a state after the jet pump is installed, of a shield used in an embodiment of the core shroud replacement method of the present invention. FIG. 17C is a view in the direction of the arrow X in FIG. 17B, and FIG. 17D is a view in the direction of the arrow Y in FIG. 17B.

FIG. 18 is a sectional view of the in-furnace structure showing a step (13) of the embodiment of the method for replacing a core shroud of the present invention.

FIG. 19 is a sectional view of the in-furnace structure showing a step (14) of the embodiment of the method for replacing a core shroud of the present invention.

FIG. 20 is a cross-sectional view of the in-furnace structure showing a step (15) of the embodiment of the core shroud replacement method of the present invention.

FIG. 21 is a sectional view of the in-furnace structure showing a step (16) of the embodiment of the method for exchanging the core shroud of the present invention.

FIG. 22 is a sectional view of an in-furnace structure showing a step (17) of the embodiment of the method for exchanging a core shroud of the present invention.

FIG. 23 is a sectional view of an in-furnace structure showing a step (18) of the embodiment of the method for exchanging a core shroud of the present invention.

FIG. 24 is a sectional view of the in-furnace structure showing a step (19) of the embodiment of the method for replacing a core shroud of the present invention.

FIG. 25 is a sectional view of the in-furnace structure showing a step (20) of the embodiment of the method for replacing a core shroud of the present invention.

FIG. 26 is a sectional view of the in-furnace structure showing a step (21) of the embodiment of the method for exchanging a core shroud of the present invention.

FIG. 27 is a cross-sectional view of the in-furnace structure showing a step (22) of the embodiment of the core shroud replacement method of the present invention.

FIG. 28 is a sectional view of an in-furnace structure showing a step (23) of one embodiment of a method of exchanging a core shroud of the present invention.

FIG. 29 is a sectional view of an in-furnace structure showing a step (24) of one embodiment of a method of exchanging a core shroud of the present invention.

FIG. 30 is a sectional view of an in-furnace structure showing a step (25) of the embodiment of the core shroud replacement method of the present invention.

FIG. 31 is a sectional view of an in-furnace structure showing a step (26) of the embodiment of the core shroud replacement method of the present invention.

FIG. 32 is a cross-sectional view of the in-furnace structure showing a step (27) of the embodiment of the method for replacing a core shroud of the present invention.

FIG. 33 is a cross-sectional view of the in-furnace structure showing a step (28) of the embodiment of the core shroud replacement method of the present invention.

FIG. 34 is a sectional view of an in-furnace structure showing a step (29) of the embodiment of the method for exchanging a core shroud of the present invention.

FIG. 35 is a sectional view of an in-furnace structure showing a step (30) of an embodiment of a method for exchanging a core shroud of the present invention.

FIG. 36 is a sectional view of an in-furnace structure showing a step (31) of the embodiment of the method for exchanging a core shroud of the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Reactor pressure vessel, 2 ... Core shroud, 2a ... Core shroud (upper part), 2b ... Core shroud (middle part), 2c ... Core shroud (lower part), 2d ... Connection bolt, 3 ... Shroud support cylinder, 4 ... Shroud support leg, 5: upper grid plate, 5a: upper grid plate mounting plate, 6: core support plate, 7: jet pump, 7a: jet pump diffuser, 7b: jet pump riser tube, 7c: jet pump inlet mixer, 7d …
Jet pump adjusting screw bracket, 8: baffle plate, 9: control rod, 10: fuel, 10a: fuel support bracket, 11: control rod guide tube, 12: core spray system piping,
14 ... Differential pressure detection / boric acid water injection pipe, 15 ... Steam dryer, 16 ... Gas-water separator / core shroud head, 17 ...
Reactor pressure vessel head, 18 ... Reactor well, 19 ... Pedestal chamber, 20 ... Control rod drive mechanism, 21 ... Control rod drive dynamic mechanism housing, 22 ... Dry tube / LPRM detector assembly, 25 ... In core housing, 26 ... water supply sparger, 27 ... guide rod, 28 ... incoa stabilizer,
63: Reactor recirculation pump, 64: Spray ring, 6
5 ... chemical liquid injection device, 66 ... circulation pump, 67 ... ion exchange resin device, 68 ... waste gas device, 69 ... purification system pump,
70 ... recirculation inlet nozzle, 71 ... safe end, 72 ...
Thermal sleeve, 73 ... riser brace arm, 80
... Temporary closing lid, 81 ... In-core guide tube, 85, 86 ... Mounting hole, 100 ... Hanging tool, 104 ... Core shroud hanging tool, 106 ... Shroud upper cutting device, 108 ... Shroud upper cutting surface plate, 111 ... Shroud lower cutting apparatus,
112: cutting powder collecting device, 113: shroud lower cutting surface plate, 114, 115: hanging tool, 116: diffuser cutting device, 117: shielding body, 118: groove processing machine, 11
9: Scaffolding, 120: Lifting device, 121: Riser brace arm welding device, 122: Seal plug, 123: Diffuser welding machine, 124: Guide pole for hanging a new shroud, 125: New core shroud hanging tool, 126 ...
Core measuring device, 127, 127a jack, 128 new shroud outer welding machine, 130 shroud inner welding machine, 131 groove preparation machine, 132 automatic welding device, 13
4 ... Working platform on shroud, 135 ... Hanging tool, 136 ... In-core guide tube insertion guide, 146 ... Shielding member, 147 ... Work scaffold, 148 ... Automatic welding machine, 149
... Restriction jig, 150 ... Bevel processing machine, 151 ... Work scaffold.

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Kenichi Ueno 8 Shinsugitacho, Isogo-ku, Yokohama-shi, Kanagawa Prefecture Inside the Toshiba Yokohama Office (72) Inventor Toshihiro Yasuda 2--4 Suehirocho, Tsurumi-ku, Yokohama-shi, Kanagawa Address Toshiba Keihin Works Co., Ltd. (72) Inventor Masahiro Kobayashi 2-4 Suehirocho, Tsurumi-ku, Yokohama-shi, Kanagawa Prefecture Toshiba Keihin Works Co., Ltd.

Claims (9)

[Claims] 1. A step of cutting a core shroud in a reactor pressure vessel and removing the core shroud from the reactor pressure vessel; and placing at least one of a plurality of divided new core shrouds in the reactor pressure vessel. Installing a new core shroud by sequentially attaching another split body to the installed split body, and assembling a new core shroud. 2. The method for exchanging a core shroud according to claim 1, wherein the first segment installed in the reactor pressure vessel is a segment including a lowermost portion of the core shroud. 3. A step of cutting the core shroud in the reactor pressure vessel and removing the core shroud from the reactor pressure vessel, and a step of carrying a plurality of divided new core shrouds into the reactor pressure vessel. A step of assembling a new core shroud from the plurality of divided bodies in the reactor pressure vessel; and a step of installing the assembled new core shroud in the reactor pressure vessel. Exchange method. 4. A method comprising: attaching a shield in the reactor pressure vessel; draining reactor water in the reactor pressure vessel; and removing the shield. An adjusting screw bracket for the jet pump, having a divided shape arranged to cover a range including a core region of the reactor pressure vessel, the mounting hole corresponding to a joint between the reactor pressure vessel and the jet pump, 4. The core shroud according to claim 1, wherein a thickness below a height position corresponding to the vicinity of the core shroud is smaller than a thickness above the height position. 5. Exchange method. 5. A step of attaching a shield in the reactor pressure vessel, draining reactor water in the reactor pressure vessel, and removing the shield, wherein the shield comprises: An adjusting screw bracket for the jet pump, having a divided shape arranged to cover a range including a core region of the reactor pressure vessel, the mounting hole corresponding to a joint between the reactor pressure vessel and the jet pump, 4. The method for exchanging a core shroud according to any one of claims 1 to 3, wherein the thickness of the core shroud is smaller than the thickness below the height position. 6. The core shroud replacement according to claim 4, wherein the shield is configured such that a thickness of a portion corresponding to the adjustment screw bracket and its vicinity is thinner than other portions. Method. 7. The method for exchanging a core shroud according to claim 1, wherein the plurality of divided bodies are two. 8. The method for exchanging a core shroud according to claim 1, wherein the number of the plurality of divided bodies is three. 9. The method for exchanging a core shroud according to claim 1, wherein the assembly of the new core shroud is performed by welding or bolting the plurality of divided bodies.