JPH0886896A - Shroud in nuclear reactor, and method for installing and replacing it - Google Patents

Abstract

PURPOSE: To provide a shroud in nuclear reactor, and a method for installing and replacing it which make it possible to install a core shroud in nuclear reactor so that it can be mounted or removed freely, ensure the soundness of it and enable the effective preventive maintenance. CONSTITUTION: A shroud support cylinder 30 is placed on a shroud support leg 31 erected on a lower end plate part 10a of a nuclear reactor pressure vessel 10. A fitting bracket 48 is fixed to the shroud support cylinder 30. A shroud flange 36 of a core shroud 11 is placed on the fitting bracket 48, and the core shroud 11 is mounted freely removably on the shroud support cylinder 30 with a shroud fastening means 57.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an in-reactor shroud that is detachably installed in a reactor pressure vessel, and a method of installing and replacing the shroud, and more particularly to an in-reactor shroud that is replaceable with an existing core shroud. The present invention relates to a shroud and a method of installing and replacing the shroud.

[0002]

2. Description of the Related Art In a boiling water reactor as a light water reactor, a stainless steel core shroud is housed and installed in a reactor pressure vessel. The core is housed in this core shroud, and a large number of fuel assemblies are loaded. The core shroud is fixed on the shroud support cylinder by welding, and is formed into an integral tubular structure by circumferential and longitudinal welding. The shroud support cylinder is fixed on a shroud support leg that is erected on the lower mirror portion of the reactor pressure vessel.

On the other hand, a metallic material such as austenitic stainless steel which constitutes the core shroud, when placed in high temperature water, undergoes stress corrosion cracking (IGSC) at or near the weld.
It is generally known that C) occurs.

It is known that stress corrosion cracking occurs under the condition in which three factors, that is, material, stress and environment, are superposed. As a material factor, chromium (Cr) carbide is precipitated at grain boundaries, and a Cr-deficient layer with poor corrosion resistance is formed around it, which increases the sensitivity of the material. The tensile residual stress remaining in the steel is increased. Further, as an environmental factor, the amount of dissolved oxygen existing in high temperature water can be raised. Since stress corrosion cracking occurs under the condition in which three factors, that is, material, stress and environment, are superposed, it is possible to prevent the occurrence of stress corrosion cracking by removing one factor from these three factors.

The core shroud is a stainless steel member formed into a cylindrical structure by circumferential welding and vertical welding. If the core shroud has a high carbon content in stainless steel, cracks due to stress corrosion cracking or the like may occur at or near the weld.

Nuclear reactors are generally provided with triple, quadruple or higher safety, and have a complete system for ensuring safety. If an event such as a crack occurs in the core shroud of the reactor, it is necessary to repair or replace the core shroud for the safety of the reactor. As a method for repairing the welded portion of the core shroud, there is one disclosed in Japanese Patent Laid-Open No. 5-323078.

On the other hand, the core shroud of a nuclear reactor that has been used for a long period of time is fragile due to neutron irradiation from the core,
Welded core shroud is welded metal (welded part)
It is difficult to repair the core shroud by welding, because finer cracks may occur around the core.

A method of bolting a reinforcing member to repair the core shroud is also conceivable. However, in a nuclear reactor installed in a high earthquake zone like Japan, fine cracks may occur near the bolt coupling, or handling work may be required. Due to the difficulties involved, their adoption is limited.

[0009]

The most desirable method for reactor safety is to replace the core shroud with a new core shroud.

However, the lower end of the core shroud is fixed to the shroud support cylinder by welding,
In addition, the problem of interference with the dry tube of the in-core housing stabilizer and neutron flux monitor (neutron measurement tube),
Due to the problem of high radiation dose in the reactor, the difficulty of adjusting the position of the upper lattice plate and the core support plate installed in the core shroud, and the difficulty of processing the removed core shroud, It was extremely difficult to remove the core shroud installed in the reactor and install a new core shroud.

In the conventional nuclear reactor, it was judged that the core shroud itself could not be replaced, and replacement of the core shroud was not considered. When a defect such as a crack occurs in the core shroud, it is disclosed in JP-A-5-32307.
As described in Japanese Patent Publication No. 8, the defective portion is targeted for repair using a polishing device, an electric discharge machining device, and an underwater welding device to locally repair the welded portion. However, in this repair, new fine cracks are likely to occur around the welded part that is brittle (material deterioration) due to neutron irradiation. In this core shroud repair, measures against material deterioration of the core shroud were sufficiently taken. However, it was difficult to ensure the integrity of the core shroud.

The present invention has been made in consideration of the above-mentioned circumstances, and a reactor capable of detachably installing the core shroud in the reactor, ensuring the soundness of the core shroud, and effectively performing preventive maintenance. It is an object to provide an inner shroud and a method of installing and replacing the shroud.

Another object of the present invention is to replace the core shroud in the reactor with a new core shroud without welding, to ensure the integrity of the core shroud and to ensure the safety and reliability of the reactor. It is an object of the present invention to provide a shroud in a reactor, an installation method and a replacement method thereof.

[0014]

According to the present invention, there is provided a shroud in a nuclear reactor for solving the above-mentioned problems.
As described in, the shroud support cylinder is installed on the shroud support leg that is erected on the lower mirror part of the reactor pressure vessel, the mounting bracket is fixed to this shroud support cylinder, and the shroud of the core shroud is mounted on this mounting bracket. The flange is installed, and the core shroud is detachably installed on the shroud support cylinder by the shroud fastening means.

Further, in order to solve the above-mentioned problems, the shroud in the nuclear reactor according to the present invention has a plurality of mounting brackets fixed to the inner side of the shroud support cylinder over the entire circumference as described in claim 2. Then, install the inner peripheral flange formed on the shroud flange of the core shroud together on this mounting bracket, and the shroud fastening means consisting of stud bolts and tightening nuts enables the core shroud to be attached to and detached from the shroud support cylinder. It has been installed.

Further, in order to solve the above-mentioned problems,
In the nuclear reactor shroud according to the present invention, as described in claim 3, the core shroud has a tubular structure in which a ring-shaped upper shroud, an intermediate shroud and a lower shroud are integrally welded in the circumferential direction, and A shroud flange is integrally provided on the lower end of the shroud by welding in the circumferential direction, and the shroud flange has an inner peripheral flange having a large number of insertion holes, and a cutout is formed in the inner peripheral flange so as not to interfere with the in-core equipment. It was done.

Further, in order to solve the above-mentioned problems, the shroud in the nuclear reactor according to the present invention has a core shroud, a shroud support cylinder, and a core shroud on the shroud support cylinder. The shroud fastening means that is detachably installed in the core is made of the same metal material such as a heat-resistant and corrosion-resistant alloy so as not to cause a difference in thermal expansion between the metal materials, or as described in claim 5, the core shroud and the shroud support. The shroud fastening means for mounting the core shroud on the shroud support cylinder, while forming the cylinder with the same metal material, uses a material having a smaller coefficient of thermal expansion than the core shroud and the shroud support cylinder.

In order to solve the above-mentioned problems, in the nuclear reactor shroud according to the present invention, as described in claim 6, the core shroud includes an upper shroud, an intermediate shroud, a lower shroud and a shroud flange. While forming the joint part into an integral tubular structure by welding joining, the welding part of each joint part has a curved surface on the welding surface,
According to a seventh aspect of the present invention, the sealing means for waterproofing the reactor water leak is incorporated in the engaging portion between the core shroud and the shroud support cylinder.

On the other hand, the method for installing a shroud in a nuclear reactor according to the present invention is intended to solve the above-mentioned problems.
As described in, in the installation method of the reactor shroud in which the shroud support cylinder is installed on the shroud support leg erected on the lower mirror part of the reactor pressure vessel, a mounting bracket is provided on the side surface of the shroud support cylinder. Fix, then install the factory manufactured core shroud on the shroud support cylinder, align the shroud flange of the core shroud and fasten by the shroud fastening means, and removably install the core shroud on the shroud support cylinder Is.

In order to solve the above-mentioned problems, a method for installing a shroud in a nuclear reactor according to the present invention provides a method according to claim 9.
As described above, after fixing the mounting bracket to the shroud support cylinder, seal welding is performed over the entire circumference of the shroud support cylinder in order to prevent crevice corrosion.

On the other hand, the method for replacing a shroud in a nuclear reactor according to the present invention is intended to solve the above-mentioned problems.
As described in No. 0, at the time of periodic inspection of the reactor, after removing the core shroud installed in the reactor pressure vessel from the shroud support cylinder by underwater cutting, the inside of the reactor pressure vessel is washed, and after this washing While installing a work platform at the bottom of the reactor pressure vessel, install a shielded elevator that can be elevated up and down from the reactor well to this work platform, then fix the mounting bracket to the shroud support cylinder, and mount it on this mounting bracket. A new factory-made core shroud is suspended in the reactor pressure vessel and seated on the shroud support cylinder, and then the new core shroud is detachably fastened to the mounting bracket of the shroud support cylinder by the shroud fastening means. , Then take out the work platform installed in the reactor pressure vessel It is the law.

In order to solve the above-mentioned problems, the method for replacing a shroud in a nuclear reactor according to the present invention is defined in claim 1.
As described in 1, when a new core shroud is manufactured in a factory, the upper shroud, the intermediate shroud, the lower shroud and the shroud flange are circumferentially welded to form an integral tubular structure while the new core shroud is A method of forming an insertion hole in a shroud flange in accordance with a hole position of a mounting bracket fixed to a shroud support cylinder, and further, as described in claim 12, in a mounting bracket fixed to the shroud support cylinder. This is a method in which the hole positions are copied to a template and insertion holes are drilled in the shroud flange of a new core shroud at the factory according to the hole positions copied in the template.

[0023]

[Function] Since the shroud support cylinder is detachably fixed on the support cylinder, the shroud support cylinder is reinforced by the mounting bracket, and the reinforced mounting bracket is used to removably install the core shroud in the reactor by the shroud fastening means. The integrity of the core shroud can be secured and preventive maintenance can be effectively performed.

Since the core shroud of this in-reactor shroud can be removably installed on the shroud support ring by using the shroud fastening means, cracks and the like occur, and the defective core shroud is replaced with a sound core shroud. Since they can be replaced, the integrity of the core shroud can be secured, and the safety and reliability of the nuclear reactor can be improved.

Since a plurality of mounting brackets are fixed to the inside of the shroud support cylinder according to claim 2 over the entire circumference, the mechanical rigidity and strength of the shroud support cylinder are improved, while the core shroud is mounted on the mounting bracket. The inner peripheral flange can be easily, easily and detachably installed by the shroud fastening means including the stud bolt and the fastening nut.

In the in-reactor shroud according to claim 3, the core shroud has a ring-shaped upper shroud,
The intermediate shroud, lower shroud, and further shroud flanges can be integrally manufactured at the factory by welding in the circumferential direction, improving the manufacturing accuracy, while preventing the inner peripheral flange of the shroud flange from interfering with the in-core equipment. Since the notch is formed, it is possible to install the in-reactor shroud without contacting the inner peripheral flange during the installation work of the in-reactor shroud, and the handling work of the in-reactor equipment becomes easy.

In the nuclear reactor shroud of claim 4, since the core shroud, the shroud support cylinder, and the shroud fastening means are made of the same metal material, a difference in thermal expansion due to temperature change occurs between the materials. There is no. Therefore, it is possible to eliminate the adverse effect due to the difference in thermal expansion on the installation portion of the core shroud.

In the nuclear reactor shroud according to claim 5, the core shroud and the shroud support cylinder are made of the same metal material, while the shroud fastening means is made of a material having a smaller coefficient of thermal expansion than the core shroud and the shroud support cylinder. During operation of the nuclear reactor, a tightening force resulting from a difference in thermal expansion can be applied to the shroud fastening means, and the core shroud can be firmly and stably fastened and installed by the shroud support cylinder.

In the in-reactor shroud of the sixth aspect, since the welded portions of the joint portions of the upper shroud, the intermediate shroud, the lower shroud and the shroud flange are formed so that the welding surfaces form a curved surface, A crack or the like is unlikely to enter the heat-affected zone, and a highly reliable welded structure can be obtained.

In the reactor shroud of the seventh aspect, since the sealing means is incorporated in the engaging portion between the core shroud and the shroud support cylinder, leakage of reactor water can be effectively and surely prevented.

In the method of installing the shroud in the nuclear reactor according to claim 8, since the core shroud can be removably fastened and installed by the shroud fastening means on the shroud support cylinder, the soundness of the core shroud is ensured. While the preventive maintenance can be effectively performed, the soundness of the core shroud can be secured by replacing with a sound core shroud, so that the safety and reliability of the reactor can be improved.

In the method for installing the shroud in the nuclear reactor according to the ninth aspect, since the gap between the shroud support cylinder and the mounting bracket is filled with seal welding over the entire circumference, crevice corrosion is effectively prevented. be able to.

In the method for replacing the shroud in the nuclear reactor according to the tenth aspect, the core shroud having cracks and the like generated in the existing reactor can be removed, while the new shroud is removed and then the new shroud is removed. The core shroud can be removably installed by the shroud fastening means. Therefore, if stress corrosion cracking (SCC) etc. occurs in the core shroud, the defective core shroud can be replaced with a sound core shroud, and the new core shroud is sound, so preventive maintenance is required. This can be effectively achieved, the safety and reliability of the reactor can be improved, and the operation rate can be improved.

In the method for replacing a shroud in a nuclear reactor according to claim 11, since the insertion hole is formed in the shroud flange of the new core shroud in accordance with the hole position of the mounting bracket of the shroud support cylinder, the new core shroud is formed. The shroud support cylinder can be easily aligned.

In the method for replacing a shroud in a nuclear reactor according to a twelfth aspect, the hole position of the mounting bracket fixed to the shroud support cylinder is copied (copied) to a template, and the hole position copied to the template is copied. Since the through hole is formed in the shroud flange of the new core shroud at the factory, the through hole can be accurately and accurately formed in the shroud flange of the core shroud, and the assembling work of the new core shroud becomes easy.

[0036]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the accompanying drawings.

FIG. 1 is a vertical sectional view showing a boiling water reactor in which the shroud in the reactor according to the present invention is installed. In this boiling water reactor, a tubular core shroud 11 is housed in a reactor pressure vessel 10. Core shroud 11
A core 12 is formed inside, and a large number of fuel assemblies 13 are mounted by a core support plate 14 and an upper lattice plate 15.

A plurality of control rod guide tubes 18 are provided in a forested state in a lower core plenum 17 formed below the core 12, and control rods 19 housed in the respective control rod guide tubes 18 are control rod drive mechanisms 20. Driven by. This control rod drive mechanism 2
0 is hung vertically on the lower mirror portion 10a of the reactor pressure vessel 10.
By controlling the control rod 19 to be moved in and out of the reactor core 12 by the control rod drive mechanism 20, the starting and stopping of the nuclear reactor and the power control operation are performed. Reference numeral 21 is a neutron measuring tube (neutron flux monitor).

On the other hand, the upper part of the core shroud 11 is covered with a shroud head 23, and a steam separator 24 is installed on the shroud head 23. The steam-water separator 24 separates the reactor water (coolant) whose temperature has risen through the core 12 into a gas-liquid, and the separated steam is the upper steam dryer 2
5 and is dried by passing through the steam dryer 25 to become dry steam. This dry steam is the main steam system 26
Through which the steam turbine (not shown) is guided to drive the steam turbine to perform work.

The liquid separated by the water-water separator 24 is guided to an annular downcomer portion 28 formed by the reactor pressure vessel 10 and the core shroud 11, and provided in the downcomer portion 28. It is sent to the lower core plenum 17 by the jet pump 29 and is guided to the core 12 again. A plurality of jet pumps 29 are installed in the reactor pressure vessel 10 to forcibly circulate the reactor water.

By the way, the core shroud 11 is integrally formed with a cylindrical or sleeve-shaped cylindrical body and is supported on the shroud support cylinder 30. The shroud support cylinder 30 is arranged on the shroud support leg 31 and detachably supports the core shroud 11 on the upper part thereof. The shroud support leg 31 is a reactor pressure vessel 1
It is erected around the lower mirror part of 0 and fixed.

As shown in FIG. 2, the core shroud 11 includes a ring-shaped upper shroud 33 and an intermediate shroud 3.
4 and a lower shroud 35, and these upper, middle and lower shrouds 33, 34, 35 are integrally joined by circumferential welding (circumferential welding) a to form a sleeve-like cylindrical structure. is there. The upper, middle and lower shrouds 33, 34, 35 are formed by joining shroud members integrally by vertical welding (longitudinal welding) b to form a ring shape.

Lower shroud 35 of core shroud 11
3 and 4, a shroud flange 36 is integrally joined to the lower end by circumferential welding, and an inner circumferential flange 36a is formed inside the lower shroud 35.
Welding of the lower shroud 35 and the shroud flange 36 is J-shaped on the inner peripheral side of the shroud or circumferential welding such as single-edged groove and fillet welding, and U-shaped or V-shaped on the outer peripheral side of the shroud.
It is integrally joined by circumferential welding such as die groove welding, and the welded part has a curved structure without being aligned. That is, the lower shroud 35 and the shroud flange 36 are formed in a curved structure so that the welding surfaces are not aligned on the inner circumference side and the outer circumference side of the shroud, and the heat-affected zone due to welding is formed by a curved line. The heat-affected zone has a curved surface structure so that cracks are less likely to occur in the welded portion. The cracks are likely to enter the heat affected zone in a straight line.

Lower shroud 35 of core shroud 11
The outer peripheral joint between the shroud flange 36 and the shroud flange 36 may have another welding shape, and the weld overlay 3 is formed on the outer peripheral joint.
8 can also be applied to force the heat affected zone to bend approximately 90 °. The weld overlay 38 has a width of, for example, several cm in the circumferential direction, and the height (thickness) of the weld overlay 38 is formed to be about 1 mm to several mm, for example, 3 mm.

The core shroud 11 has an upper shroud 33.
And the intermediate shroud 34 and the intermediate shroud 34 and the lower shroud 35 are welded to both U-shapes, X-shapes so that the welding surfaces are not located on a straight line between the inner peripheral side and the outer peripheral side of the shroud.
It is formed into a curved structure by die and double V-shaped groove welding.
Further, the heat-affected zone may be forcibly bent by applying weld overlay on the inner or outer periphery of the shroud.

The shroud flange 36 of the core shroud 11 has an inner peripheral flange 36a formed in a ring shape in the circumferential direction as shown in FIG. The inner peripheral flange 36a is provided with a plurality of notches 39 that are partially notched so that the notches 39 do not interfere with the control rod guide tubes 18 of the in-core equipment. Reference numeral 40 is a pressure sensor,
The pressure sensor 40 detects the pressure difference between the upper and lower parts of the diffuser 29a of the jet pump 29.

Further, as shown in FIG. 3, a circumferential groove extending in the circumferential direction is formed on the lower surface of the shroud flange 36, and a sealing means 44 for preventing reactor water leak is provided in the circumferential groove. The sealing means 44 is, for example, a metal O-ring 45.
Are fixed by mounting bolts 64. Sealing means 4
No. 4 has a structure for sealing the upper surface of the shroud support cylinder 30 after removing the old core shroud.

Further, the shroud support cylinder 30
As shown in FIGS. 3 and 5, a plurality of mounting brackets 48 are provided on the inner side of the bracket over substantially the entire circumference thereof.
Is detachably fastened. The bracket fastening means 49 is configured by combining a fastening bolt 50 and a nut 51, for example. Shroud support cylinder 30 mounting hole 52
The tightening bolt 50 is inserted through the sleeve-shaped spacer 53, the tightening nut 51 is attached to the tightening bolt 50 from the inner peripheral side of the shroud support cylinder 30, and the tightening nut 51 is tightened to attach the mounting bracket 48. Are fixed to the shroud support cylinder 30. A spacer 53 is attached to the mounting hole 52 of the shroud support cylinder 30.
By inserting, it has a sealing property.

After mounting the mounting bracket 48 to the shroud support cylinder 30 with the bracket fastening means 49 and fixing the mounting bracket 48, the shroud support cylinder 30 is covered over the entire circumference thereof in order to prevent crevice corrosion between the shroud support cylinder 30 and the mounting bracket 48. Seal welding may be applied. Further, the mounting bracket 48 may be fixed by welding. The top surfaces of the mounting brackets 48 mounted on the inner peripheral side of the shroud support cylinder 30 are substantially flush with each other.

A chamfer or notch 55 for preventing interference with the control rod guide tube 18 of the in-core equipment is formed on the mounting bracket 48 which is mounted on the inside of the shroud support cylinder 30 over substantially the entire circumference. The chamfer or notch 55 is formed on the inner peripheral flange 3 of the core shroud 11.
6a is formed at a position corresponding to the notch 39.

The inner peripheral flange 36a of the core shroud 11 is superposed on the mounting bracket 48 fixed to the shroud support cylinder 30, and the core shroud 11 is detachably fastened by the shroud fastening means 57.
Fixed. The shroud fastening means 57 is composed of, for example, a stud bolt 58 planted in the mounting bracket 48 and a tightening nut 59 that screw-connects the stud bolt 58.

Therefore, the core shroud 11 is detachably mounted on the shroud support cylinder 30 by mounting a large number of stud bolts 58 on the mounting bracket 48 of the shroud support cylinder 30 and by mounting the core shroud on the stud bolts 58. The core shroud 11 is detachably installed by guiding and inserting the through hole 60 formed in the inner peripheral flange 36a of 11 and fastening the stud bolt 58 with the fastening nut 59.

The shroud in the reactor is the core shroud 1
1 lower shroud 35, shroud flange 36, shroud support cylinder 30, mounting bracket 48,
The stud bolt 58, the tightening nut 59, and the like are made of the same metal material, for example, a heat-resistant and corrosion-resistant alloy (NCF), so that the joint between the core shroud 11 and the shroud support cylinder 30 is not affected by loosening due to the difference in thermal expansion. .

Instead of constructing the core shroud 11, the shroud support cylinder 30 and the shroud fastening means 57 of the same metal material, the core shroud 11 and the shroud support cylinder 30 are made of the same metal material such as Inconel material while the shroud fastening is performed. For the means 57, a material having a smaller thermal expansion than the core shroud 11 and the shroud support cylinder 30 is used, and when the reactor is at a high temperature, the shroud fastening means 57 applies a tightening force due to a difference in thermal expansion to the core shroud 11 to reduce the heat. It may be firmly mounted by the mounting bracket 48 of.

Next, a method of replacing the shroud in the reactor will be described.

When the core shroud 11 is damaged by cracks or the like due to a periodic inspection of the boiling water reactor, the core shroud 11 is replaced for the safety of the reactor. In the existing boiling water reactor, the core shroud 1
Since No. 1 is fixed on the shroud support cylinder 30 by welding, underwater cutting of the core shroud 11 is required to replace the core shroud 11.

Replacement of the core shroud 11 is usually performed at the time of regular inspection. During a reactor shutdown inspection, the reactor pressure vessel upper lid 16 is removed from the reactor pressure vessel 10 using an overhead crane of a reactor building (not shown), transferred to a temporary equipment pool, and temporarily placed. Then, steam dryer 25
Is removed by an overhead crane and transferred to a temporary equipment pool for temporary storage. At this time, the reactor water is maintained below the flange 10b of the reactor pressure vessel 10.

Top cover 16 of reactor pressure vessel and steam dryer 25
The reactor well is filled with water to remove the shroud head 23 with the ceiling crane, and the shroud head 23 is moved to the temporary equipment pool for temporary placement. At this time, the steam separator 24 is removed together with the shroud head 23.

Subsequently, the fuel assemblies 13 are removed from the core 12, and all the fuel assemblies 13 are transferred to and stored in a fuel storage pool (not shown). After that, the control rod 19, the fuel support fitting, the control rod guide tube 18, and other in-core devices are all removed, while the neutron measuring tube (neutron flux monitor) 21 is removed to empty the core 12.

After that, the inlet mixer 29a of the jet pump 29 arranged in the downcomer unit 28 is removed, and it is moved to and stored in the fuel storage pool or the equipment temporary storage pool by using an overhead crane or the like.

Next, the wear-resistant material provided on the upper end of the diffuser 29b of the jet pump 29 is covered with a neutron shield to reduce the radiation exposure dose. This is because the member used as the wear resistant material contains cobalt and the radiation dose is extremely high.

Subsequently, the core spray pipe 62 is cut to secure a shroud removing space for removing the core shroud 11 upward when removing the core shroud 11. The upper lattice plate 15 fixed to the core shroud 11 can be lifted above the core shroud 11 by removing the lattice plate fastening means. Similarly, the core support plate 14 can be lifted above the core shroud 11 by removing the support plate fastening means. The upper lattice plate 15 and the core support plate 14 removed from the core shroud 11 are stored in a fuel storage pool or the like, and can be reused depending on the inspection result.

When the upper grid plate 15 and the core support plate 14 cannot be reused, they may be removed while being cut into small pieces by an underwater cutting method such as electric discharge machining or plasma cutting. In addition, the neutron measuring tube 21 and the in-core stabilizer for mutual restraint of the neutron measuring tube 21 are partially cut and removed as necessary. At this time, the differential pressure detection / boric acid water injection pipe that penetrates the lower mirror portion (bottom portion) 10a of the reactor pressure vessel 10 and rises along the inner wall of the core shroud 11 is also partially cut.

Next, the core shroud 11 fixed by welding on the shroud support cylinder 30 is circumferentially cut by using an underwater cutting machine (not shown) such as electric discharge machining or plasma cutting, and the shroud support cylinder 36 is cut. Separated from the reactor and using an overhead crane, etc., the reactor pressure vessel 1
Remove from within 0. The final cutting position of the core shroud 11 is the upper part of the shroud support cylinder 30, but the core shroud 11 may be cut into several pieces and removed.

When all the core shrouds 11 are removed from the reactor pressure vessel 10, the inside of the reactor pressure vessel 10 is cleaned by chemical cleaning or the like to reduce the radiation exposure dose.

After the inside of the reactor pressure vessel 10 is cleaned, a work platform 64 is placed inside the reactor pressure vessel 10 as shown in FIG.
Are installed almost horizontally. Below the work platform 64,
A plurality of support legs 65 are provided, and the support legs 65 are engaged with the upper end portion of the control rod drive mechanism (CRD) housing 66,
Fix it. At this time, the water level in the reactor pressure vessel 10 is positioned below the work platform 64 so that the work platform 64 is not submerged.

Next, a shielded elevator 68 for transporting the worker from above the reactor well 67 to the work platform 64 is installed. At this time, a shield is installed inside the reactor pressure vessel 10 if necessary.

After that, the cutting surface of the shroud support cylinder 30 is machined horizontally and precisely with high precision by a machining device by electric discharge machining or machining. Since the processed surface constitutes the reactor water seal, inspection is performed so that there are no irregularities or damage.

Subsequently, the shroud support cylinder 30
A hole for fastening the mounting bracket 48 is formed on the side surface of the. This hole machining is performed by electrical discharge machining or machining, and a plurality of mounting holes are formed in the shroud support cylinder 3.
Drill on the 0 side.

After the hole processing for forming the mounting hole on the side surface of the shroud support cylinder 30 is completed, the mounting bracket 48 is fixed by using the bracket fastening means 49. The bracket fastening means 49 uses, for example, a tightening bolt 50 and a nut 51.
Thus, the plurality of mounting brackets 48 are fixed to the inner peripheral side of the shroud support cylinder 30 so that the upper surfaces of the brackets are substantially flush with each other over substantially the entire circumference.

After fixing the plurality of mounting brackets 48,
The positions of the screw holes formed on the upper surface of the mounting bracket 48 are copied on the template. After copying the screw hole position and making a replica, the template is brought back to the manufacturing plant, the hole forming position formed on the inner peripheral flange 36a of the new core shroud 11 is determined, and the insertion hole 60 is formed at this hole forming position. Precise and accurate drilling at the factory.

The new core shroud 11 is one in which the upper shroud 33, the intermediate shroud 34, the lower shroud 35 and the shroud flange 36 are manufactured at the factory by circumferential welding a into an integral cylindrical structure. The lower shroud 34 and the lower shroud 35 are formed in a ring shape by joining shroud members by vertical welding b.

The new core shroud 11 is precisely pre-manufactured in the factory to have substantially the same shape except for the conventional core shroud and the shroud flange 36, while the shroud flange 36 of the manufactured new core shroud 11 has many The insertion hole 60 is formed in the inner peripheral flange 36a. This drilling is also done at the factory.

The new core shroud 11 manufactured in the factory is transferred to the reactor building and suspended in the reactor pressure vessel 10 by using an overhead crane or the like, and the installation work of the new core shroud 11 is performed.

In the installation work of the new core shroud 11, first, the new core shroud 11 is suspended in the reactor pressure vessel 10 using an overhead crane or the like, and seated on the shroud support cylinder 30. At this time, the sealing means 44 incorporating the metal O-ring 45 is previously attached to the shroud flange 36 of the new core shroud 11.

Instead of the sealing means 44, the sealing means 70 shown in FIG. 7 may be used. The sealing means 70 may be formed by holding a metal having a large thermal expansion, for example, stainless steel 71, in the circumferential groove with a mounting bolt 72.

The new core shroud 11 seated on the shroud support cylinder 30 is aligned so that the insertion hole 60 formed in the inner peripheral flange 36a of the shroud flange 36 matches the screw hole of the mounting bracket 48. The shroud flange 36 of the new core shroud 11 is fastened and fixed to the mounting bracket 48 of the shroud support cylinder 30 by using the shroud fastening means 57.

In this case, the shroud support cylinder 3
The stud bolt holes 58 of the shroud fastening means 57 are previously planted in the mounting bracket 48 of No. 0, and when the new core shroud 11 is suspended, the shroud flange 36
Each of the insertion holes 60 may be guided and suspended so as to be inserted into the stud bolt 58. In this case, by suspending the new core shroud 11, the new core shroud 11 is automatically aligned with each stud bolt 58. Then, by tightening the tightening nut 59, the new core shroud 11 can be installed and installed accurately and accurately.

After installing the new core shroud 11, the cut neutron flux monitor guide tube and differential pressure detection /
While connecting a new joint pipe to the boric acid water injection pipe,
The work platform 64 and the like installed in the reactor pressure vessel 10 are removed.

After the new core shroud 11 is installed, the core support plate 14 and the upper lattice plate 15 are suspended and installed. First, the core support plate 14 is suspended in the reactor pressure vessel 10, and the upper ends of tens of neutron flux monitor guide tubes are inserted into the through holes at the corresponding positions of the new core support plate 14. After adjusting the alignment between the hole for the control rod guide tube 18 of the core support plate 14 and the upper end of the CRD housing 66,
It is fixed to the lower ring (inner peripheral ring formed on the lower shroud 35) 72 (see FIG. 2) of the new core shroud 11 by bolting.

Next, the upper lattice plate 15 is attached to the reactor pressure vessel 1
In the same way, suspend the new core shroud 11
Is seated on the intermediate ring (stepped ring formed on the upper shroud 33) 73 of. And the upper lattice plate 15
Is aligned with the hole for the control rod guide tube 18 of the core support plate 14, and then fixed by bolt fastening.

In this way, after the core support plate 14 and the upper grid plate 15 are installed on the core shroud 11 installed in the reactor pressure vessel 10, the core spray pipe 6 is installed.
2. Install the guide rod 74 and the water supply sparger. This attachment is performed by welding or the like.

After that, the reactor water level in the reactor pressure vessel 10 is raised, returned to the lower part of the flange of the reactor pressure vessel 10, and the jet pump inlet mixer 29a stored in the fuel storage pool is hung on the downcomer section 28,
Install it in its original position.

The work after the jet pump inlet mixer 29a is attached is carried out in accordance with the procedure of the returning work during the regular inspection. In this restoration work, the reactor well 67
(See FIG. 6) is filled with water, and the control rod guide tube 18, the control rod 19, the fuel support fitting and the fuel assembly 13 are successively suspended in the fuel storage pool and moved into the reactor pressure vessel 10 while being filled with water. And set them to their respective predetermined positions.

Next, the overhead crane is operated to operate the shroud head 23 and the steam dryer 2 stored in the temporary equipment pool.
5 are successively hung in the reactor pressure vessel 10 and fixed by bolts. A steam separator 24 is attached to the shroud head 23.

Finally, the reactor pressure vessel upper lid 16 is aligned with the flange 10b of the reactor pressure vessel 10 from the equipment temporary storage pool and attached by bolt fastening. Then, the water in the reactor well 67 is drained, a well cover (not shown) is installed, and the reactor pressure vessel 1 is installed in the reactor containment vessel.
0 is stored, and the restoration work is completed.

In this in-reactor shroud, the core shroud of the boiling water reactor can be replaced with a new core shroud to restore the same structure as the original reactor.

[0088]

As described above, in the in-reactor shroud according to claim 1 of the present invention, the mounting bracket is fixed to the shroud support cylinder, and the shroud flange of the core shroud is installed on the mounting bracket. Since the core shroud is detachably fixed to the shroud support cylinder by the shroud fastening means, the shroud support cylinder is reinforced by the mounting bracket, and the core shroud is reinforced by the shroud fastening means using the reinforced mounting bracket. It can be detachably installed inside, the integrity of the core shroud can be secured, and preventive maintenance can be effectively performed.

Since the core shroud of this in-reactor shroud can be removably installed on the shroud support ring by using the shroud fastening means, cracks and the like occur, and the defective core shroud is replaced with a sound core shroud. Since they can be replaced, the integrity of the core shroud can be secured, and the safety and reliability of the nuclear reactor can be improved.

Since the plurality of mounting brackets are fixed to the inside of the shroud support cylinder according to claim 2 over the entire circumference, the mechanical rigidity and strength of the shroud support cylinder are improved, while the core shroud is mounted on the mounting bracket. The inner peripheral flange can be easily, easily and detachably installed by the shroud fastening means including the stud bolt and the fastening nut.

In the in-reactor shroud according to claim 3, the core shroud has a ring-shaped upper shroud,
The intermediate shroud, lower shroud, and further shroud flanges can be integrally manufactured at the factory by welding in the circumferential direction, improving the manufacturing accuracy, while preventing the inner peripheral flange of the shroud flange from interfering with the in-core equipment. Since the notch is formed, it is possible to install the in-reactor shroud without contacting the inner peripheral flange during the installation work of the in-reactor shroud, and the handling work of the in-reactor equipment becomes easy.

In the in-reactor shroud according to claim 4, since the core shroud, the shroud support cylinder, and the shroud fastening means are formed of the same metal material, a difference in thermal expansion due to temperature change occurs between the materials. There is no. Therefore, it is possible to eliminate the adverse effect due to the difference in thermal expansion on the installation portion of the core shroud.

In the nuclear reactor shroud of claim 5, the core shroud and the shroud support cylinder are made of the same metal material, while the shroud fastening means is made of a material having a smaller coefficient of thermal expansion than the core shroud and the shroud support cylinder. During operation of the nuclear reactor, a tightening force resulting from a difference in thermal expansion can be applied to the shroud fastening means, and the core shroud can be firmly and stably fastened and installed by the shroud support cylinder.

In the nuclear reactor shroud according to claim 6, since the welded portions of the joint portions of the upper shroud, the intermediate shroud, the lower shroud and the shroud flange are formed so that the welding surface forms a curved surface, A crack or the like is unlikely to enter the heat-affected zone, and a highly reliable welded structure can be obtained.

In the nuclear reactor shroud according to the seventh aspect, since the sealing means is incorporated in the engaging portion between the core shroud and the shroud support cylinder, leakage of reactor water can be effectively and surely prevented.

In the method for installing the shroud in the reactor according to the eighth aspect, since the core shroud can be detachably fastened and installed on the shroud support cylinder by the shroud fastening means, the integrity of the core shroud can be secured. While the preventive maintenance can be effectively performed, the soundness of the core shroud can be secured by replacing with a sound core shroud, so that the safety and reliability of the reactor can be improved.

In the method of installing the shroud in the reactor according to claim 9, since the gap between the shroud support cylinder and the mounting bracket is filled with seal welding over the entire circumference, crevice corrosion is effectively prevented. be able to.

In the method of replacing the shroud in the reactor according to the tenth aspect, the core shroud having cracks and the like generated in the existing reactor can be removed, while a new shroud is removed and then new shroud is removed. The core shroud can be removably installed by the shroud fastening means. Therefore, if stress corrosion cracking (SCC) or the like occurs in the core shroud, the defective core shroud can be replaced with a sound core shroud, and the new core shroud is sound, so preventive maintenance is required. This can be effectively achieved, the safety and reliability of the reactor can be improved, and the operation rate can be improved.

In the method for replacing a shroud in a nuclear reactor according to claim 11, since the through hole is formed in the shroud flange of the new core shroud in accordance with the hole position of the mounting bracket of the shroud support cylinder, the new core shroud is formed. The shroud support cylinder can be easily aligned.

In the method of replacing the shroud in the reactor according to claim 12, the hole position of the mounting bracket fixed to the shroud support cylinder is copied (copied) to the template, and the hole position copied to the template is copied. Since the through hole is formed in the shroud flange of the new core shroud at the factory, the through hole can be accurately and accurately formed in the shroud flange of the core shroud, and the assembling work of the new core shroud becomes easy.

[Brief description of drawings]

FIG. 1 is a vertical cross-sectional view of a boiling water reactor equipped with an in-reactor shroud according to the present invention.

FIG. 2 is an overall view showing an assembled state of a shroud in a nuclear reactor according to the present invention.

FIG. 3 is a partial cross-sectional view showing an enlarged part A of FIG.

4 is a plan sectional view taken along line IV-IV in FIG.

5 is a plan sectional view taken along line VV of FIG.

FIG. 6 is a state diagram in which a work platform and a shielded elevator are installed after removing the old core shroud from the reactor.

FIG. 7 is a partial sectional view corresponding to FIG. 3, showing another modified example of the sealing means provided in the reactor shroud.

[Explanation of symbols]

 10 Reactor Pressure Vessel 11 Core Shroud 12 Core 13 Fuel Assembly 14 Core Support Plate 15 Upper Lattice Plate 17 Lower Core Plenum 18 Control Rod Guide Tube 19 Control Rod 20 Control Rod Drive Mechanism 23 Shroud Head 24 Steam Separator 25 Steam Drying Unit 26 Main steam system 28 Downcomer part 29 Jet pump 30 Shroud support cylinder 31 Shroud support leg 33 Upper shroud 34 Intermediate shroud 35 Lower shroud 36 Shroud flange 38 Weld build-up 39 Notch 44 Sealing means 45 Metal O-ring 46 Mounting bolt 48 Mounting Bracket 49 Bracket fastening means 50 Tightening bolt 51 Tightening nut 55 Notch or chamfer 57 Shroud fastening means 58 Stud bolt 59 Fastening bolt 60 Insertion hole 64 Work platform 67 Large metal child reactor well 68 shielded with elevator 70 sealing means 71 thermal expansion

Claims (12)

[Claims] 1. A shroud support cylinder is provided on a shroud support leg erected on a lower mirror portion of a reactor pressure vessel, a mounting bracket is fixed to the shroud support cylinder, and a shroud flange of a core shroud is mounted on the mounting bracket. Is installed, and the core shroud is detachably installed on the shroud support cylinder by the shroud fastening means. 2. A plurality of mounting brackets are fixed to the inside of the shroud support cylinder over the entire circumference, and an inner peripheral flange formed on the shroud flange of the core shroud is installed together on the mounting bracket, and a stud bolt and The nuclear reactor shroud according to claim 1, wherein the core shroud is detachably installed on the shroud support cylinder by a shroud fastening means including a fastening nut. 3. The core shroud comprises a ring-shaped upper shroud, an intermediate shroud, and a lower shroud which are integrally formed into a tubular structure by circumferential welding, and a shroud flange is integrally welded to the lower end of the lower shroud by circumferential welding. The shroud flange is provided with an inner peripheral flange having a large number of insertion holes, and a cutout is formed in the inner peripheral flange so as not to interfere with internal reactor equipment.
The shroud in the reactor described in. 4. The core shroud, the shroud support cylinder, and the shroud fastening means for removably installing the core shroud on the shroud support cylinder are made of the same metal material such as heat resistant corrosion resistant alloy, and have a thermal expansion difference between the metal materials. The nuclear reactor shroud according to claim 1, wherein the shroud has a structure that does not occur. 5. The shroud fastening means for mounting the core shroud on the shroud support cylinder while forming the core shroud and the shroud support cylinder with the same metal material uses a material having a coefficient of thermal expansion smaller than that of the core shroud and the shroud support cylinder. The shroud in the reactor according to claim 1. 6. The core shroud has a tubular structure in which each joint portion of an upper shroud, an intermediate shroud, a lower shroud, and a shroud flange is welded to form an integral tubular structure, and a welding surface of each joint portion has a curved surface structure. The nuclear reactor shroud according to claim 1. 7. The in-reactor shroud according to claim 1, wherein a sealing means for waterproofing a reactor water leak is incorporated in an engaging portion between the core shroud and the shroud support cylinder. 8. A method for installing an in-reactor shroud in which a shroud support cylinder is installed on a shroud support leg erected on a lower mirror portion of a reactor pressure vessel,
Fix the mounting bracket on the side surface of the shroud support cylinder, then install the core shroud manufactured in the factory on the shroud support cylinder, align the shroud flange of the core shroud and fasten with the shroud fastening means, A method for installing a shroud in a nuclear reactor, which is detachably installed on a shroud support cylinder. 9. The method of installing a shroud in a nuclear reactor according to claim 8, wherein after the mounting bracket is fixed to the shroud support cylinder, seal welding is performed over the entire circumference of the shroud support cylinder to prevent crevice corrosion. 10. A reactor pressure vessel is cleaned after the core shroud installed in the reactor pressure vessel is removed from the shroud support cylinder by underwater cutting at the time of periodic inspection of the reactor. While installing a work platform at the bottom of the container, install a shielded elevator that can be elevated up and down from the reactor well to this work platform, then fix the mounting bracket to the shroud support cylinder, and install it on the mounting bracket at the factory. The manufactured new core shroud is suspended in the reactor pressure vessel and seated on the shroud support cylinder, and then the new core shroud is detachably fastened to the mounting bracket of the shroud support cylinder by the shroud fastening means, and then installed. , Take out the work platform installed in the reactor pressure vessel. Characteristic method of replacing shroud in reactor. 11. When manufacturing a new core shroud in a factory, the upper shroud, the intermediate shroud, the lower shroud and the shroud flange are circumferentially welded to form an integral tubular structure, while the shroud flange of the new core shroud is formed. 11. The method of replacing a shroud in a nuclear reactor according to claim 10, wherein an insertion hole is formed at a position corresponding to a hole position of a mounting bracket fixed to the shroud support cylinder. 12. A copy of the hole position of the mounting bracket fixed to the shroud support cylinder is copied to a template,
12. The method for replacing a shroud in a nuclear reactor according to claim 11, wherein an insertion hole is drilled at a factory in a shroud flange of a new core shroud according to a hole position copied in this template.