JP2001349979A - Method and structure for replacing core spray sparger - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for replacing a core spray sparger, capable of being executed even in a radioactive environment and a structure for replacing the core spray sparger. SOLUTION: Two existing reactor spray spargers 13 installed along approximately the overall periphery of the inner surface of the upper shell of a core shroud 2 installed within the reactor pressure vessel 1 of a boiling water reactor, for injecting cooling water into the reactor in an accident or the like, are replaced with new ones by the method of replacing the reactor spray spargers. After in-reactor upper equipment, reactor fuel and upper reactor plates are removed, the intermediate shell of the core shroud is cut and the existing spray spargers are taken outside of the core, together with the upper part of t core shroud. Thereafter, a new in-reactor structure having new core spray spargers and upper grid plates integrally assembled into a new core shroud upper structure is suspended inside the reactor pressure vessel and mounted to the lower part of the intermediate shell of the existing core shroud through a remotely- controlled underwater operation without being welded thereto.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and a structure for replacing a core sparger installed in a reactor pressure vessel.

[0002]

2. Description of the Related Art A core sparger discharges water from a suppression pool in a fuel assembly so as to prevent melting of a fuel cladding tube due to overheating of fuel when the core is exposed due to a coolant loss accident such as a recirculation pipe break. Installed to inject into. The core sparger is installed on the upper shell inner surface above the upper end of the fuel assembly of the core shroud so that cooling water can be uniformly injected into the nuclear fuel assembly.

[0003] This core sparger is almost 18
It is composed of pipes in a range of 0 degrees, has two spargers per system at 180-degree symmetric positions, and is installed in a shroud with two systems. The core sparger is fixed by a bracket so that the outer circumferential portion of the pipe is in contact with the inner surface of the upper portion of the shroud.

[0004] The upper grid plate, which is installed on the upper surface of the intermediate ring of the core shroud and supports the fuel assembly in the horizontal direction, is close to the core sparger and is attached to the shroud by wedges or other in-core structural components. In contact with the upper torso inner surface. The inner diameter of the shroud upper ring is smaller than the outer diameter of the core sparger.

[0005]

The internal structure of the reactor pressure vessel of a boiling water reactor is constructed by welding stainless steel members. Stainless steel with high carbon content is known to cause stress corrosion cracking (SCC) in the weld heat affected zone near the weld in a high temperature water environment, and is used in contact with high temperature reactor coolant. There is a concern about the occurrence of this in core spargers.

When such an event occurs, it is necessary to repair or replace the internal structure of the reactor in order to ensure the safety of the reactor. However, furnace internal structures that have been used for a long period of time are embrittled by neutron irradiation, and when welded, finer cracks may occur around the deposited metal, making repair by welding difficult. Become.

[0007] Therefore, in a case where a crack is generated due to stress corrosion cracking or the like in the irradiated portion, replacement of the furnace internal structure can be considered. However, since the core sparger is fixed by a bracket so that the outer circumferential portion of the core sparger is in contact with the inner surface of the upper body of the shroud, and is installed close to the upper lattice plate, the working space is almost limited. Therefore, it is difficult to remove the core sparger alone.

For this reason, a method of removing the upper lattice plate, which is an obstacle to the removal of the core sparger, prior to the removal of the core sparger can be considered, but has the following problems.

(1) The same applies when the upper lattice plate is not removed. However, since the outer diameter of the core sparger is larger than the inner diameter of the upper ring of the core shroud, it is necessary to carry out the core sparger out of the core. However, since the core sparger is inscribed in the upper part of the core shroud, it is difficult to cut without damaging the core shroud side.

(2) It is difficult to position a junction box to be fitted with a core shroud and to mount and weld a ring bracket when restoring a core sparger.

(3) Further, when the upper lattice plate is removed, the operation is performed under a high dose, so that it is difficult to perform operations such as alignment of the upper lattice plate and mounting of mounting parts.

The present invention has been made in order to solve such a problem, and an object of the present invention is to provide a method and a structure for replacing a core sparger which can be performed even in a radiation environment. I do.

[0013]

In order to achieve the above object, according to the first aspect of the present invention, substantially the entire circumference of an inner surface of an upper shell of a core shroud installed in a reactor pressure vessel of a boiling water reactor is provided. A method of replacing a core sparger that replaces an existing core sparger with a new core sparger for injecting cooling water into the reactor in the event of an accident, for example, comprising: After removing the core fuel and the upper lattice plate, the intermediate shroud of the core shroud is cut and the existing sparger is taken out of the furnace together with the upper part of the core shroud, and then a new core sparger and upper lattice plate are removed. Of the existing core shroud is integrated into a new core shroud upper structure and suspended in the reactor pressure vessel. The underwater remote work on The inter cylinder bottom, provides a replacement method of the core spray sparger, characterized in that installing a non-welded connection.

According to a second aspect of the present invention, in the method of replacing the core sparger according to the first aspect, the new internal structure is attached to the existing shroud by a plurality of tapered pins and a lower surface of an intermediate ring of the core shroud. The present invention provides a method for replacing a core sparger, which is a mechanical fastening method using a skirt provided in the core.

According to a third aspect of the present invention, in the method of replacing the core sparger according to the first or second aspect, the core of the upper lattice plate is aligned with the internal structure of the new furnace. Provides a method for replacing spargers.

According to a fourth aspect of the present invention, in the method of replacing the core sparger according to the third aspect, the tapered pin and the skirt are used to eliminate a gap between the tapered pin and the skirt which is generated for alignment of the upper lattice plate. A method of replacing a core sparger, wherein an eccentric sleeve is applied between the core and the sparger.

According to a fifth aspect of the present invention, in the method for replacing a core sparger according to any one of the second to fourth aspects, a taper pin is inserted from the inside of an existing shroud to fix the taper pin and the eccentric sleeve. And a method of replacing the core sparger, wherein the fixing of the eccentric sleeve and the skirt is fixed by welding from the outside of the skirt.

According to a sixth aspect of the present invention, in the method for replacing a core sparger according to any one of the first to fifth aspects, after removing the upper lattice plate and the mounting parts, cutting and removing other existing in-furnace equipment. The present invention provides a method of replacing a core sparger, which comprises performing chemical cleaning of the upper part of the furnace.

According to a seventh aspect of the present invention, in the method of replacing a core sparger according to any one of the first to sixth aspects, the conversion to an existing structure for mounting a new in-furnace structure is performed underwater and remote. Provided is a method of replacing a core sparger, which is characterized by being constructed.

According to an eighth aspect of the present invention, in the method for replacing a core sparger according to any one of the first to seventh aspects, a new in-furnace structure other than the upper shroud, the upper grid plate and the core sparger is mounted. A method for replacing a core sparger is provided, wherein a platform having a shielding function is carried into the furnace integrally with the upper part of the shroud, the upper lattice plate, and the core sparger.

According to the ninth aspect of the present invention, two systems are installed on the inner surface of the upper shell of the core shroud installed in the reactor pressure vessel of the boiling water reactor over almost the entire circumference. Replacement structure for replacing a core sparger for injecting cooling water with an existing core sparger, wherein a new core sparger and an upper lattice plate are integrated with a new core shroud upper structure. And a replacement structure for a spar purger.

According to a tenth aspect of the present invention, in the structure for replacing a sparger according to the ninth aspect, at least a structure or a material which has been subjected to measures against stress corrosion cracking or clevis is applied to the new furnace internal structure. A structure for replacing a core sparger is provided.

In the above invention, when cutting or removing the existing structure, it is desirable to construct the structure with a diver and an underwater remote device.

The internal structure of the furnace cut and removed in the furnace is as follows:
It is preferable to temporarily store the waste in a DS pool, shred it after replacing the core sparger, and pack it in a cask before storing it in a side bunker pool or a solid waste disposal storage.

[0025]

Embodiments of the present invention will be described below with reference to the drawings.

1 to 19 show one embodiment of the present invention.

FIG. 1 is a sectional view showing the overall structure of the reactor pressure vessel. Core shroud 2 in reactor pressure vessel 1
The core shroud 2 is supported by a 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. The jet pump 7 is roughly divided into jet pump diffusers 7a,
It comprises a jet pump riser pipe 7b and a jet pump inlet mixer 7c. Jet pump 7
A baffle plate 8 is provided below.

In the core shroud 2, control rods 9 are provided.
And a fuel 10. Above the core shroud 2, a control rod guide pipe 11, a core spray pipe 12, a core sparger 13, a differential pressure detection / boric acid water injection pipe 1.
4, steam dryer 15, steam-water separator and shroud head 1
6 etc. are provided.

Reference numeral 17 denotes an upper cover of the reactor pressure vessel 1, 1
9 is an installation space, 20 is a control rod drive mechanism, 21 is a control rod drive mechanism housing (CRD housing), and 22 is a dry tube / LPRM detector assembly.

FIG. 2 shows a state in which the new reactor internal structure replaced according to the present invention is connected to an existing core shroud.

The existing core shroud 2 is cut off at the middle section of the core shroud 2 after removing the in-furnace upper equipment, the core fuel and the upper lattice plate, and a new core sparger 103 is added to that part.
And a new furnace internal structure in which the upper lattice plate 104 is integrally incorporated into a new core shroud upper structure (new shroud upper portion 102). That is, the skirt 108 at the lower end of the new shroud upper portion 102 is
5 and is mechanically connected to the existing core shroud 2 via the eccentric sleeve 116. This configuration will be described later in detail.

FIG. 3 is a process chart showing the procedure of the replacement method according to the present embodiment.

As shown in FIG. 3, in the present embodiment, as the preparatory steps, a step of removing the dryer, the steam separator, the fuel and the like (step S101), a step of attaching a fall prevention lid (step S102), Step of cutting and removing the guide rod and the core spray pipe clamp (Step S103), Step of cutting and removing the core spray pipe (Step S10)
4), a step of removing the structural attachment parts and the upper lattice plate (Step S105), a step of chemically decontaminating the furnace upper part (Step S106), a step of loading a shroud cutting device (Step S107), and cutting the upper shroud. Step (step S108), removing the upper shroud and core sparger (step S109),
It has a step of finishing the cut surface and performing pin hole processing (step S110), a step of carrying out the shroud cutting device (step S111), and the like.

Further, as this step, a step of suspending the new structure (step S112), a step of aligning the new structure (step S113), a step of fastening the new structure and welding the taper pin (step S114) Having.

Further, a post-process includes a core spray pipe restoration preparation step (step S115), a new inlet pipe mounting step (step S116), a new core spray pipe mounting step (step S117), and the like.

Next, a method of replacing the core sparger 13 will be described in detail in the order of steps.

(Steps S 101 to S 104: FIGS. 1, 4)
In replacing the core sparger 13, the core spray system piping 12 is removed by the following procedure (see FIG. 4).

In preparation for cutting the core spray system piping 12, the steam dryer 15 and the steam-water separator (shroud head) 16 are removed and transferred to a DS pool for storage. Further, all the fuel assemblies 10 are transferred and stored in the fuel pool. Remove the inlet mixer and store it, since the inlet mixer may interfere with subsequent operations.

A fall prevention lid 52 for preventing the core shroud 2 from falling into the core shroud 2 is attached to the upper surface of the upper ring.

Core spray system piping 1 by underwater diver
The guide rod 53 which interferes with the removal and installation of 2 is cut and removed, the clamp 54 of the core spray pipe 12 is cut and removed, and the core spray system riser pipe 55 is cut. Also,
A hanger is attached to the annular portion of the core spray system piping 12 and a part of the riser pipe 55 to be removed by a diver.

The electric discharge machining device (EDM device) is attached to the junction box 56 lid by a diver, the lid is removed, and then the core spray nozzle thermal sleeve is cut by the EDM device, and the nozzle and the core spray pipe 12 are separated. Remove outside the furnace.

Remotely, at the base of the inlet tube 57, E
The DM device is attached, and the inlet pipe 57 is cut and removed from the core shroud 2.

(Step S 105: FIG. 5) Following the removal of the core spray system piping 12, the upper lattice plate mounting parts (wedges, hold downs, etc.) are cut by underwater remote work while the water level 100 is in a well-filled state. Remove it. After removing the mounting parts, the upper lattice plate 5 is carried out of the furnace, and D
It is temporarily placed in the S pit (see FIG. 5).

(Step S106: FIGS. 6 and 7) Next, the RPV1 wall (furnace upper portion 65) in a range approximately 5 meters above the upper surface of the shroud, which is a range where the work is performed on the platform installed on the upper portion of the shroud, is subjected to the CODE method. (See FIG. 6).

The chemical decontamination of the upper part of the furnace can be carried out even before the upper lattice plate 5 is removed.
It is necessary to temporarily reduce 0 to about the normal operating water level of the reactor. On the other hand, when carrying the upper lattice plate 5 out of the furnace, the water level 100 needs to be filled with wells in order to suppress the dose. Therefore, by carrying out the upper lattice plate 5 before chemical decontamination, the step of raising and lowering the water level can be reduced.

After removing the upper grid plate 5, the water level of the reactor 10
0 is lowered to about the normal operation water level, and a cylindrical decontamination tank 62 including a flow pump 61 therein is installed on the upper surface of the upper ring of the shroud 2.

The double seal mechanism 63 provided at the lower part of the decontamination tank 62 and the purge water separate the reactor water below and above the upper ring of the core shroud 2,
By circulating the upper furnace water into the decontamination tank 62, chemical decontamination of the furnace upper part 65 is performed.

After the completion of the chemical decontamination, the decontamination tank 62 is carried out of the furnace, and mechanical decontamination by partially jetting jet water or the like is performed to complete the cleaning.

(Steps S107 to S111: FIGS. 7 to 1)
2) Next, the upper shroud is cut and removed.

The water level 100 when cutting the shroud is slightly higher than the upper surface of the core shroud 2.

The shroud cutting device is installed on the upper surface of the core support plate 6 in the shroud 2 (see FIG. 7). The shroud cutting device includes a cutting unit 66 and a cutting device base 67.
It is composed of

The cutting device base 67 engages with the core support plate 6. The joint between the core support plate 6 and the shroud cutting device is connected to the furnace support so that the weight of the shroud cutting device is transmitted and supported by the rim cylinder, the shroud lower ring, the shroud lower body, the shroud support cylinder 3 and the shroud port leg 4 of the core support plate 6. A hole for CRGT on the outer periphery of the plate 6.

The cutting unit 66 includes a centering function of the shroud cutting device, a leveling mechanism of the shroud cutting device,
Each has a plurality of shroud cylinder cutting heads 70, shroud cutting end face finishing heads 72, and pin hole processing and finishing heads 73 (see FIGS. 8 to 11).

After the shroud cutting device is installed in the core shroud 2, a work table 68 is mounted on the upper surface of the cutting unit 66 (see FIG. 8).

The leveling and centering of the shroud cutting device are performed, and the shroud cutting device is fixed to the core shroud 2. For the core adjustment, a laser type core measuring device is used.

Several jigs 69 are provided between the upper shell of the core shroud 2 and the wall of the RPV 1 to prevent lateral slippage of the upper shroud. The side slip prevention jig is removed after cutting the shroud.

The shroud 2 is hung by using the upper shroud hanging tool 71, and the shroud cutting head 70 prevents the shroud cutting head 70 from being caught between the upper shroud 2a and the remaining shroud 2 while the shroud is being cut.

The cutting position of the shroud is set at the intermediate ring 2.
In order to remove the heat-affected zone at the time of welding of the b and the middle part shell, the core shroud 2 is made about 100 mm below the lower surface of the middle part ring 2b (see FIG. 8).

After the core shroud 2 intermediate cylinder has been cut all around, the upper part of the shroud 2a and the core sparger 13
Is taken out of the furnace together and temporarily placed in the DS pit. At this time, since the upper shroud 2a is activated, the water level 100 is raised to the well full position in order to reduce the exposure (see FIG. 9).

After the shroud upper portion 2a has been carried out, the water level 100
To the water level when the shroud is cut.

Finishing is performed by the end face finishing head 72 attached to the cutting unit 66 so that the cut surface of the existing intermediate shroud cylinder is horizontal (see FIG. 10).

A tapered hole for a taper pin used for fixing an upper part of a new shroud in which a core sparger and an upper lattice plate are integrally assembled to the existing shroud 2 is formed at a predetermined position of the existing shroud intermediate cylinder. The shape of the tapered hole is such that the inner surface of the shroud has a larger diameter than the outer surface of the shroud (see FIG. 11).

After a predetermined number of tapered holes have been formed, the work platform 68 and the shroud cutting devices (66, 67) are carried out of the furnace (see FIG. 12).

(Step S112: FIGS. 13 and 14) Next, the new internal furnace structure is installed in the furnace.

The structure inside the new furnace is the upper part 10 of the new shroud.
2. New core sparger 103, new upper lattice plate 1
04. As the material, an SCC countermeasure material is adopted (see FIG. 14).

The upper part 102 of the new shroud is the upper ring 1
05, an upper body 106 and an intermediate ring 107, and the upper ring 105 is the same as the existing one, but the upper body 10
6 is provided with a female thread for mounting a new inlet pipe. The intermediate part ring 107 is used when the new furnace internal structure 101 is installed on the existing shroud 2 intermediate part body.
04, so that the elevation of the upper surface is the same as that of the existing one, it is made thicker by the length of the existing middle trunk. Further, on the lower surface of the intermediate ring 107, a skirt 108 for fastening to an existing shroud is installed all around.

The skirt 108 is provided with a hole 109 at a predetermined position for engaging with a tapered pin for fastening. In order to avoid interference between the skirt 108 and the jet pump 7, a notch 110 is provided near the jet pump 7. Since the annulus formed by the existing shroud 2 and the skirt 108 may become an air pocket after installation, an air vent hole 111 is provided at the upper end of the skirt 108.

In the new core sparger 103, the connecting portion between the inlet pipe and the header pipe 103a has a reducing tee structure (103c) as a measure against clevis. The welded portion between the end plate 103b and the header tube 103a has a butt structure.

The new upper lattice plate 104 adopts a wedge 104a method reflecting the latest design. In addition, a hold-down structure is provided to prevent lifting in the event of a coolant loss accident (LOCA).

The new upper lattice plate 104 is attached to the shroud upper part 102 in advance so as to match the core of the new shroud upper part 102. The new core shroud sparger 103 also uses the bracket 112 in the same manner as before to
Is mounted in the upper trunk 106. At this time, the sparger nozzle is attached and fixed in consideration of the spray distribution.

Before the new in-furnace structure 101 is suspended, a temporary suspension guide rod is attached to the RPV 1.

The working platform 113 is superimposed on the new core structure 101 including the new shroud upper portion 102, the new core sparger 103, and the new core support plate 104, and is carried into the furnace using temporary guide rods (see FIG. 13).

(Step S 113: FIG. 15) Using the laser core measuring device 114, the core aligning operation of the new furnace internal structure is performed. At the time of core alignment, the new furnace internal structure 101 is integrally moved while the weight of the new furnace internal structure is being received by the hanging tool 120, and the core of the new upper lattice plate matches the core of the CRD stub and the core support plate. (See FIG. 15).

(Step S 114: FIGS. 16 to 18) When the alignment of the new upper lattice plate is completed, the new furnace internal structure is seated on the upper surface of the existing intermediate shroud body, and separated from the overhead crane.

Next, the new furnace internal structure 101 and the existing shroud 2 are fastened by taper pins (see FIG. 16).

The tapered pin 115 has a tapered structure at a portion where the tapered pin 115 is engaged with the existing shroud 2. New furnace internal structure 1
The portion that mates with the skirt 108 provided on the circumstance 01 has a cylindrical structure. Further, the axis of the tapered portion and the axis of the cylindrical portion are eccentric, and the skirt 108 provided on the new reactor internal structure 101 is provided.
Between the taper hole 121 provided in the intermediate body of the existing shroud 2 and the fastening hole 109 of the skirt 108 provided in the new furnace internal structure 101 by absorbing the misalignment. Has become.

The taper pin 115 is inserted from the inner side of the existing shroud 2 into the taper pin hole provided in the intermediate body of the existing shroud 2 using a taper pin insertion device. On the other hand, the skirt 108 from the outside of the skirt 108
The eccentric sleeve 116 is inserted into the hole 109 for fastening provided in the above. The taper pin 115 and the eccentric sleeve 116 are respectively rotated, and are mounted at positions where there is no gap between the hole 109 of the skirt, the outer diameter of the eccentric sleeve 116, the inner diameter of the eccentric sleeve 116, and the outer diameter of the cylindrical portion of the taper pin 115.

When the positions of the taper pin 115 and the eccentric sleeve 116 are determined, the water level is lowered so that the taper pin 115 is above the water surface, a taper pin welding machine 117 is installed in the annulus, and the skirt 108 and the eccentric sleeve 116 are positioned.
Also, the first layer welding of the eccentric sleeve 116 and the taper pin 115 is performed in the air.

The water level 100 is set to the shroud upper ring 105.
It rises to the upper side and the next taper pin 115 is attached.

The operation up to the first layer welding of the taper pins 115 is repeated by the number of the taper pins 115. When all the taper pins 115 have been mounted, the skirt 108 and the eccentric sleeve 116 and the eccentric sleeve 116 and the taper pin 115 are fully welded to all the taper pins. (See FIGS. 17 and 18).

(Step S 115: FIGS. 18 and 19) By welding the above-described tapered pin 115 to the skirt 108 from outside the skirt 108, welding shrinkage occurs and the tapered portion of the tapered pin 115 is tapered to the tapered hole of the existing shroud 2. To reduce the gap at the tapered joint.

Next, restoration work of the new core spray system piping is performed (see FIGS. 18 and 19).

The remaining portion of the clamp 54 and the bolt are removed. Further, an unmeasured material portion of the remaining thermal sleeve of the RPV nozzle is cut, and a groove portion to be fitted with the new core spray system piping 63 is processed.

Using the template, the dimensions required for processing the thermal sleeve 64 and the piping are measured.

Attach the new inlet pipe 65 to the shroud with bolts. An annular pipe with a thermal sleeve is suspended, and the RPV nozzle groove and thermal sleeve 64 are suspended.
Groove welding / welding.

The rising pipe 6 is inserted between the rising pipe 66 of the annular pipe and the new inlet pipe 65 via the sleeve 67.
6 and the new inlet pipe 65 are welded.

A clamp for holding the annular pipe is attached, and a junction box lid for the core spray system piping is attached by welding.

Attach the guide rod to the guide pin bracket of the shroud.

The work platform 61 and the fall prevention lid 52 are removed.

The internal structure cut and removed in the furnace is as follows:
They are temporarily placed in a DS pool, shredded after core replacement sparger replacement work is completed, packed in a cask, and stored in a side bunker pool or solid waste disposal storage.

Another Embodiment (FIG. 20) The configuration of this embodiment is different from that of the skirt 1 of the taper pin 115 shown in FIG.
Except for the fixing method to 08, it is the same as the first embodiment. A method and structure for fixing the taper pin 115 to the skirt 108 according to the second embodiment will be described below (see FIG. 20).

The shape of the tapered portion of the tapered pin 115 of this embodiment is the same as that of the embodiment, but an external thread is provided at the end of the cylindrical portion which is attached to the shaft of the tapered portion slightly eccentrically.

The taper pin 115 is inserted into the taper pin hole 121 provided in the intermediate body of the existing shroud 2 from the inner surface side of the existing shroud 2 using a taper pin insertion device. On the other hand, the eccentric sleeve 11 is inserted into the fastening hole 109 provided in the skirt 108 from the outside of the skirt 108 of the new furnace internal structure 101.
Insert 6. Taper pin 115 and eccentric sleeve 116
Are rotated, and the skirt hole 109 and the eccentric sleeve 1 are rotated.
16 outer diameter and eccentric sleeve 116 inner diameter and taper pin 1
15 Attach it to a position where there is no gap in the outer diameter of the cylindrical portion.

When the positions of the tapered pin 115 and the eccentric sleeve 116 are determined, the male screw provided at the end of the tapered pin 115 is fastened with a nut 118.

After the fastening of the predetermined number of taper pins 115 is completed, the water level is lowered so that the taper pins 115 are above the water surface, and a taper pin welding machine is installed in the annulus portion.
Non-rotating weld 119 between taper pin 115 and nut 118
Is performed in the air.

The present invention can be embodied in other forms besides the above embodiments. For example, the tapered structure on the existing shroud side in another embodiment may be a bolted structure, and the tapered structure on the existing shroud side in the one embodiment may be a bolted structure.

According to the above-described embodiment, it is possible to replace the core sparger, which has been difficult to replace by itself due to interference of surrounding structures.

[0098]

According to the present invention, when a problem occurs or when a problem may occur,
By replacing the target part, the defective part or the cause of anxiety can be completely removed, so that the reliability of the plant is improved and the life of the plant can be prolonged.

[Brief description of the drawings]

FIG. 1 is an overall cross-sectional view showing a furnace internal structure according to an embodiment of the present invention.

FIG. 2 is an enlarged view showing a configuration after replacement according to an embodiment of the present invention.

FIG. 3 is a flowchart showing a construction procedure according to an embodiment of the present invention.

FIG. 4 is a schematic diagram of removing a core spray system piping according to an embodiment of the present invention.

FIG. 5 is a process diagram of removing an upper lattice plate according to an embodiment of the present invention.

FIG. 6 is a schematic diagram of local chemical cleaning according to an embodiment of the present invention.

FIG. 7 is a process chart for carrying in a shroud cutting device according to an embodiment of the present invention.

8A is a view showing a process of cutting the upper part of the shroud according to an embodiment of the present invention, and FIG. 8B is an enlarged view of a portion b of FIG.

FIG. 9 is a view showing a core displaced sparger and a shroud upper unloading process according to an embodiment of the present invention.

FIG. 10A is an end face finishing process diagram according to one embodiment of the present invention, and FIG. 10B is an enlarged view of a portion b of FIG.

11A is a process drawing of a tapered pin hole according to an embodiment of the present invention, and FIG. 11B is an enlarged view of a portion b of FIG.

FIG. 12 is a view showing a process of unloading the shroud cutting device according to the embodiment of the present invention.

FIG. 13 is a process chart of a process for suspending a structure inside a new furnace integrally according to an embodiment of the present invention.

FIG. 14 is a structural diagram of a structure inside a new furnace according to an embodiment of the present invention.

FIG. 15 is a process chart of aligning a new in-furnace structure according to an embodiment of the present invention.

16A is a view showing a process of attaching a taper pin and an eccentric sleeve according to an embodiment of the present invention, and FIG.
Part enlarged view.

17A is a welding process diagram of a taper pin and an eccentric sleeve according to an embodiment of the present invention, and FIG. 17B is a drawing b of FIG.
Part enlarged view.

FIG. 18 is a diagram showing a tapered pin fastening structure according to an embodiment of the present invention.

FIG. 19 is a schematic diagram of a new core spray system pipe restoration according to an embodiment of the present invention.

FIG. 20 is a diagram showing a tapered pin fastening structure according to another embodiment of the present invention.

[Explanation of symbols]

 Reference Signs List 1 reactor pressure vessel 2 core shroud 3 shroud support cylinder 4 shroud support leg 5 upper lattice plate 6 core support plate 7 jet pump 7a jet pump diffuser 7b jet pump riser pipe 7c jet pump inlet mixer 8 baffle plate 9 control rod 10 fuel 11 Control rod guide tube 12 Core spray pipe 13 Core sparger 14 Differential pressure detection / boric acid water injection pipe 15 Steam dryer 16 Steam separator / shroud head 17 Top lid 19 Installation space 20 Control rod drive mechanism 21 Control rod drive mechanism housing (CRD housing) 22 Dry tube / LPRM detector assembly 52 Fall prevention cover 53 Guide rod 54 Clamp 55 Core spray system piping riser tube 56 Junction box 57 Inlet tube 61 Flow pump 62 Decontamination tank 63 Double sealing mechanism 65 Furnace upper part 66 Cutting unit 67 Cutting device base 68 Work table 69 Side slip prevention jig 70 Shroud barrel cutting head 72 Shroud cutting end face finishing head 73 Finishing head 100 Water level 102 New shroud upper part 103 New core sparger 104 New upper lattice plate 105 Upper ring 106 Upper trunk 107 Intermediate ring 108 Skirt 109 Notch hole 110 Notch 111 Air vent hole 112 Bracket 113 Work platform 114 Laser core measuring device 115 Taper pin 116 Eccentricity Sleeve 115 Tapered pin 116 Eccentric sleeve 117 Taper pin welder 118 Nut 119 Non-rotating welding 120 Hanging tool 121 Tapered hole

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) G21D 1/00 G21D 1/00 X (72) Inventor Masahiro Kobayashi 2-4 Suehirocho, Tsurumi-ku, Yokohama-shi, Kanagawa Address: Toshiba Keihin Works Co., Ltd. (72) Inventor Kazuo Sudo 2-4, Suehirocho, Tsurumi-ku, Yokohama-shi, Kanagawa Prefecture Toshiba Keihin Works Co., Ltd.

Claims (10)

[Claims] 1. Two systems are installed on the inner surface of the upper shell of a core shroud installed in a reactor pressure vessel of a boiling water reactor over almost the entire circumference, and cooling water is injected into the reactor in the event of an accident or the like. A method of replacing a core sparger that replaces an existing core sparger with a new core sparger, the method including removing an upper device, a core fuel, and an upper lattice plate in a furnace, and then removing an intermediate body of the core shroud. Cutting out the existing sparger and taking it out of the furnace together with the upper part of the core shroud, and then a new core structure in which a new core sparger and an upper lattice plate are integrally incorporated into a new core shroud upper structure. It is suspended in the reactor pressure vessel and installed as a non-weld connection by underwater remote work on the lower part of the middle part of the existing core shroud. A method for replacing a core sparger. 2. A method of replacing a core sparger according to claim 1, wherein the new internal structure is attached to an existing shroud by using a plurality of tapered pins and a skirt provided on a lower surface of an intermediate ring of the core shroud. A method of replacing a core sparger, which is characterized by using a mechanical fastening method. 3. The method for replacing a core sparger according to claim 1 or 2, wherein the alignment of the upper lattice plate is performed integrally with the internal structure of the new furnace. . 4. A method of replacing a core sparger according to claim 3, wherein an eccentric sleeve is provided between the tapered pin and the skirt to eliminate a gap between the tapered pin and the skirt which is generated for centering of the upper lattice plate. A method of replacing a core sparger, characterized by applying the following. 5. The method of replacing a core sparger according to claim 2, wherein a taper pin is inserted from the inside of an existing shroud to fix the taper pin to the eccentric sleeve and to fix the tapered pin to the eccentric sleeve. A method of replacing a core sparger, wherein the core is fixed to the skirt by welding from the outside of the skirt. 6. The method for replacing a core sparger according to claim 1, wherein after removing the upper grid plate and the mounting parts, and before cutting and removing other existing in-furnace equipment. A method for replacing a core sparger, comprising performing chemical cleaning of the upper part. 7. A method for replacing a core sparger according to any one of claims 1 to 6, wherein remodeling to an existing structure for mounting a new in-furnace structure is performed underwater remotely. How to replace core sparger. 8. A method for replacing a core sparger according to any one of claims 1 to 7, further comprising a shielding function for mounting a new in-furnace structure other than the upper shroud, the upper grid plate and the core sparger. A method for exchanging a core sparger, comprising: loading a platform having a shroud upper part, an upper lattice plate, and a core sparger into a furnace. 9. Two systems are installed on the inner surface of the upper shell of the core shroud installed in the reactor pressure vessel of the boiling water reactor over almost the entire circumference, and cooling water is injected into the reactor in the event of an accident or the like. Replacement structure for replacing a core sparger to be replaced with an existing core sparger, wherein a new core sparger and an upper lattice plate are integrally incorporated into a new core shroud upper structure. A structure for replacing a sparger. 10. A structure for replacing a sparger according to claim 9, wherein the internal structure of the new furnace is formed by applying at least a structure or a material which has been subjected to measures against stress corrosion cracking or clevis. Replacement structure for core sparger.