JPH0580187A - Intra-reactor structure maintaining method - Google Patents

Abstract

PURPOSE:To secure the soundness of an intra-reactor structure comparatively easily by employing the replacement, partical repair, and preventive maintenance mothods in proper combination according to the degree of difficulty of the dismantling and remounting works from/to the intra-reactor structure. CONSTITUTION:The intra-reactor structure of a nuclear reactor is installed in a pressure vessel 3 and is composed of such apparatus as a shroud 1, shroud supporting cylinder 2, upper grating plate 5, core supporting plate 6, jet pump diffuser 8a, jet pump riser 8b, jet pump mixer 8c, shroud support leg 9, shroud support plate 12, fuel supporting metal piece 21, vapor dryer 22, air/water separator and shroud head 23, control rod 24, control rod guide pipe 25, core spray sparger/piping 26, low pressure water injection piping 27, differential pressure sensing/boric acid water infection piling 28, etc.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a core support plate, an upper lattice plate, a core sparger / pipe, a low pressure water injection pipe, a jet pump riser, a jet pump mixer in a reactor pressure vessel during a service period of a nuclear power plant. Etc., ICM
Guideline, ICM stabilizer and other internal structures are replaced with newly manufactured products, and shrouds, shroud supports and jet pump diffusers are subjected to surface modification, residual stress improvement, heat treatment, etc. In particular, the present invention relates to a method for maintaining the internal structure of a reactor, which has high reliability after maintenance work and is suitable for reducing exposure of workers.

[0002]

2. Description of the Related Art It is generally known that when a metallic material such as austenitic stainless steel is placed in high temperature water, stress corrosion cracking (hereinafter abbreviated as IGSCC) occurs at or near the welded portion. IGSCC is said to be generated under the condition that material, stress, and environmental factors are superposed. The material factor is sensitization due to the precipitation of Cr carbide at the grain boundaries and the formation of a Cr-deficient layer with inferior corrosion resistance around the grain boundary. The stress factor is the tensile residual stress remaining inside the material due to welding or working, and the environmental factor. Is the amount of dissolved oxygen in high temperature water. Since IGSCC occurs under the condition in which these three factors are superposed, it can be prevented by removing one factor from these three factors. Similarly, it is generally known that SCC also occurs in the Inconel material under a certain condition, and it is particularly remarkable in a gap environment.

In order to prevent such SCC of the welded portion, a method of desensitizing only the surface portion of the portion related to corrosion by surface modification is adopted, and the member surface is irradiated by irradiating a high energy beam. A method has been devised to measure the desensitization by heating the sensitized part of the solution above the solution temperature.
A laser beam is regarded as a promising energy source because it can suppress the precipitation of carbides in the cooling process by a thermal cycle of rapid heating and rapid cooling. Similar surface modification is effective for Inconel material, but elimination of the gap structure can be said to be one means of preventing SCC.

Known examples are cases in which the surface of a member is heated above the solutionizing temperature, as described in JP-A-60-165323, JP-A-61-52315 and JP-A-61-96025. Or
As described in JP-A-61-177325, there is a case where the surface is remelted. In each case, the carbide deposited on the surface of the sensitizing member is dissolved to form a solid solution by heating, and the subsequent rapid cooling suppresses the precipitation of the carbide, thereby desensitizing the material.

Further, in the conventional reactor internal structures such as shroud, upper lattice plate and core support plate, the shroud is mounted via a shroud support cylinder which is an installation member as described in JP-A-54-35589. It is attached to the reactor pressure vessel by welding. Regarding the replacement of the internal structure of the furnace, see JP-A-57-8490 and JP-A-57-12394.
Control rod drive mechanism housing replacement method known from Japanese Patent Laid-Open No. 2-118499, neutron flux monitor housing repair method known from Japanese Patent Laid-Open No. 2-118499, and known from Japanese Patent Laid-Open No. 63-36195. There is a method for replacing internal reactor internal structures.

[0006]

The prior arts disclosed in JP-A-57-8490, JP-A-57-12394, and JP-A-2-118499 target individual internal reactor structures. It is not directly applicable to equipment such as upper grid plate, core support plate, core sparger / piping, low pressure water injection pipe, jet pump diffuser, jet pump riser, jet pump mixer, ICM guide pipe, ICM stabilizer, etc. Also, in Japanese Patent Laid-Open No. 63-36195, the shroud is also replaced in a large scale, and it takes a long time for the replacement work, and when IGSCC occurs in these devices, replacement work or repair work becomes necessary. There was a problem that it took a long time.

Further, JP-A-60-165323 and JP-A-61
-52315, JP 61-96025, JP 61-17
When performing the preventive maintenance for IGSCC by applying the surface modification using the laser beam described in 7325 gazette and the like, in the reactor internal structure, there is a narrow part such as a connecting part between devices,
It cannot be said that these devices can be applied to all areas covered by the IGSCC preventive maintenance method. Furthermore, there is a problem that it takes a long time to apply the preventive maintenance method using a laser beam to all areas of the preventive maintenance method of the internal structure of the reactor.

Therefore, an object of the present invention is to provide a core support plate, an upper lattice plate, a core sparger / pipe, a low pressure water injection pipe, a jet pump diffuser, a jet pump riser, a jet pump mixer, an ICM guide pipe, an ICM stabilizer shroud, By using the replacement method and the partial repair / preventive maintenance method for the equipment in the furnace such as a shroud support and the like in consideration of the arrangement and arrangement of the equipment, it is relatively easy and in a short period of time.
An object of the present invention is to provide a method for maintaining the internal structure of a reactor in which the reliability of the equipment after application of the partial repairing method and the preventive maintenance method is high, and the reduction of radiation exposure of workers engaged in the work is taken into consideration.

Further, the welded portion of the jet pump diffuser and the shroud support plate and the welded portion of the shroud and the shroud support can be relatively easily and in a short period of time, and in consideration of reduction of exposure of workers engaged in the work, Provide a preventive maintenance method with high equipment reliability.

[0010]

In order to achieve the above object, a method for maintaining a reactor internal structure according to the present invention is a remote operation in which reactor water is retained after a device to be removed by a normal periodic inspection is removed. Type equipment, upper lattice plate, core support plate, core sparger / pipe, low pressure water injection pipe, jet pump riser, jet pump mixer, ICM guide pipe, I
Remove the CM stabilizer and other devices in sequence, and then
Surface modification of shroud, shroud support and jet pump diffuser, improvement of residual stress and heat treatment, etc., and then core support plate, upper lattice plate, core sparger / pipe, low pressure injection pipe, jet pump riser, jet This can be achieved by replacing pump mixers, ICM guide tubes, ICM stabilizers, etc. with newly manufactured products.

For the welded portion of the jet pump diffuser and the shroud support plate and the welded portion of the shroud and the shroud support, the outer surface of the welded portion is removed at a constant depth by mechanical means or thermal means, After that, the removed portion is subjected to overlay welding by using Inconel welding material having excellent chemical resistance such as C, Ti, Nb and other chemical components adjusted, and surface modification and residual stress improvement in the heat affected zone of overlay welding. This can be achieved by performing the process of.

[0012]

According to the method for maintaining the internal structure of the present invention, the core support plate, the upper lattice plate, the core sparger / piping,
For low pressure water injection pipes, jet pump risers, jet pump mixers, ICM guide tubes, ICM stabilizers, etc., which are relatively easy to remove and re-install, replace them with newly manufactured ones, such as shrouds, shroud supports and jets. Partial repair and surface modification for internal structures that are difficult to remove and re-install such as pump diffusers
Applying preventive maintenance methods such as residual stress improvement and heat treatment can improve the stress corrosion cracking resistance and soundness of the internal structure.

Further, for the welded portion of the jet pump diffuser and the shroud support plate and the welded portion of the shroud and the shroud support, the outer surface of the welded portion is removed at a constant depth by mechanical means or thermal means. , Or the portion removed afterwards, is subjected to overlay welding with Inconel welding material with excellent corrosion resistance in which chemical components such as C, Ti, Nb are adjusted, and surface modification and residual stress improvement in the heat affected zone of overlay welding. It is possible to improve the stress corrosion cracking resistance and the soundness of the internal structure by performing such treatments.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT An embodiment of the present invention will be described below with reference to FIGS.
Will be explained.

FIG. 7 shows a reactor pressure vessel and a reactor internal structure of a boiling water reactor. The reactor internal structure is installed in the reactor pressure vessel 3, and the shroud 1 and the shroud support cylinder are installed. 2, upper grid plate 5, core support plate 6, jet pump diffuser 8a, jet pump riser 8b, jet pump mixer 8c, shroud support leg 9, shroud support plate 12, fuel support fitting 21, steam dryer 22, steam separation It comprises equipment such as a vessel / shroud head 23, a control rod 24, a control rod guide pipe 25, a core sparger / pipe 26, a low pressure water injection pipe 27, and a differential pressure detection / boric acid water injection pipe 28.

3 to 6 are views showing the installation of the shroud 1, the upper lattice plate 5, and the core support plate 6 on the reactor pressure vessel 3 during the construction of the plant. The shroud 1 is a shroud which is an installation member. It is mounted by welding in the reactor pressure vessel via the support cylinder 2. Inside the shroud 1, an upper lattice plate 5 for loading the fuel assembly 4 and a core support plate 6 are incorporated, whereby the fuel assembly 4 is supported from the up and down direction. The lower end of the shroud 1 is joined to the upper end of the shroud support cylinder 2 by welding 7. The lower end of the shroud support cylinder 2 and the upper end of the shroud support leg 9 are connected by welding 10, and the lower end of the shroud support leg 9 is fixed to the reactor pressure vessel 3 by welding 11. In this way, the shroud 1 is fixedly integrated with the reactor pressure vessel 3 via the welded portion. Further, between the outside of the shroud 1 and the reactor pressure vessel 3, a shroud support plate 12 is connected to the reactor pressure vessel 3 and the shroud support cylinder 2 by welding 14 and welding 14 ', respectively. The shroud support plate 12 has a jet pump diffuser 8
a is fixed by welding 13. The upper lattice plate 5 is fixed to the shroud 1 by a wedge 15, a stopper 16 and a bolt 17. The core support plate 6 is fixed to the shroud 1 with bolts 18. The upper lattice plate 5 and the core support plate 6 enable smooth insertion and extraction of control rods for controlling the output of the reactor, and also enable high-speed insertion of control rods during an emergency reactor shutdown. , The stub tube 20 attached by welding 19 to the lower mirror of the reactor pressure vessel 3 is required to be installed within a very tight tolerance (0.76 Dia). Fig. 6 shows the core support plate 6 at the time of plant construction.
Shows the installation status of. The target 7 is provided in each of the control rod guide tube through holes of the stub tube 20 and the core support plate 6.
1, 72 are installed, and core measurement is performed by the core measuring device 73 set on the core support plate 6. Detailed steps of core measurement are
As described in JP-A-63-36195.

FIG. 1 shows a procedure diagram of a method for maintaining a core internal structure according to the present invention, and FIG. 2 shows another procedure diagram of a method for maintaining a core internal structure according to the present invention. FIG. 8 to FIG. 12 show maintenance work of each internal structure of the reactor. JP-A-63-3619
Regarding the work step diagram described in Japanese Patent Publication No. 5, although not shown, as shown in FIG. 1, first, the reactor pressure vessel upper lid (RPV upper lid) 42 and the steam dryer to be detached from the reactor pressure vessel 3 at the time of a regular periodical inspection. 22 is removed by the overhead crane of the reactor building. The removal of the RPV upper lid 42 and the steam dryer 22 is performed in consideration of reduction of worker's exposure to radiation.
Perform with the reactor water held under the flange. Next, the reactor well 36 is filled with water in order to reduce the exposure of the worker, and the steam-water separator / shroud head 23 is removed by an overhead crane. Next, the fuel is moved to the total fuel pool, and then the control rod 24 and the control rod guide pipe 25 are removed.
Next, although not shown, the control rod drive mechanism and the thermal sleeve are removed. Next, the core spray sparger / pipe 26, which is connected to the shroud 1 by welding, and the low-pressure water injection pipe 27 are removed by a remote control cutting device. Next, the wedges 15, the stoppers 16 and the bolts 17 fixing the upper grid plate 5 shown in FIG. 4 to the shroud 1 are removed to remove the upper grid plate 5 as described in JP-A-63-36195. Remove from shroud 1. Next, the bolt 1 for fixing the core support plate 6 shown in FIG. 5 to the shroud 1
8 is removed, and the core support plate 6 is removed from the shroud 1 as described in JP-A-63-36195. Next, the support 29 supporting the differential pressure detection / boric acid water injection pipe 28 on the shroud 1 is cut in water by a remote control cutting device. Next, the ICM guide tube 30 and the ICM stabilizer 31 are cut in water by a remote control cutting device. All of the above removal of the upper lattice plate 5 and the core support plate 6 is performed with a dedicated gripping jig. Furthermore, cutting of the jet pump riser 8b and the jet pump mixer 8c,
Removal is performed in water by a remote control cutting device. All of the above operations are performed in a state where the reactor well 36 is filled with water in consideration of the reduction of radiation exposure of workers.

The above can be carried out in the same manner as described in JP-A-63-36195. In this way, most of the reactor internals in the reactor pressure vessel 3 are carried out of the reactor pressure vessel 3, and then the shroud 1, the shroud support leg 9, the shroud support plate 12, the shroud support cylinder 2, and the jet pump are used. Preventive maintenance of the diffuser 8a and partial repair as necessary, and then the jet pump riser 8b, the jet pump mixer 8c, the ICM guide pipe 30, the ICM stabilizer 31, the differential pressure detection / boric acid water injection pipe, which are replacement devices. 28, the core support plate 6, the upper lattice plate 5, the low pressure water injection pipe 27, and the core spray sparger / pipe 26 are restored. Reinstallation of the upper lattice plate 5 and the core support plate 6 is described in JP-A-63-
The centering and installation method described in Japanese Patent No. 36195 shall be adopted. All the above replacement devices are SCC resistant
Newly manufactured with excellent properties. Further, when the ICM guide tube 30 or the like is restored and installed, a coupling means such as a shape memory alloy is also used.

FIG. 8 shows an example in which the preventive maintenance method is applied to the shroud 1 after all the replacement devices have been removed. The example of FIG. 8 shows an example of performing heat treatment as a preventive maintenance method.

In this embodiment, induction heating is performed from the inner surface of the shroud 1, and after heating, cooling water is sprayed on the inner and outer surfaces of the shroud 1 to rapidly cool the shroud 1. In the same figure, the reactor pressure vessel 3 is shown as a cross section. It is a thing. The heat treatment apparatus of this embodiment includes a heat treatment apparatus head 32 for induction heating and cooling after heating, and an opening / closing mast 3 for holding the heat treatment apparatus head 32.
1, an upper mast 30 that holds the open / close mast 31, a drive device 43 that vertically and rotationally moves the upper mast 30, a transformer 44 for induction heating, a power supply control device 45 and a cable 46, a cooling water supply for cooling after induction heating It is composed of a pump 47 and a cooling water supply hose 48. Further, the water seal chamber includes a disc-shaped body 39, a seal 4 for sealing the shroud flange portion and the water seal chamber body 39.
A seal 41 for sealing the water seal chamber body 39 is provided on the inner surface of the reactor pressure vessel. The water seal chamber has a carry-in port for carrying in the heat treatment apparatus head 32,
It has a structure in which a gas supply port and a cooling water supply port for providing an atmosphere in the air below the water seal chamber are provided. After setting the water seal chamber main body 39 to the shroud flange portion, although not shown, drain the reactor water below the water seal chamber main body 39 from the drain nozzle and the recirculation water outlet nozzle, and dry it from the dry gas supply nozzle 34 via the dry gas supply line 35. Gas is supplied to make the inner and outer surfaces of the core shroud into an air atmosphere. Next, the heat treatment apparatus head 3 of the core shroud heat treatment apparatus is introduced from the carry-in port for carrying in the heat treatment apparatus provided in the water seal chamber body 39.
2. The open / close mast 31 and the upper mast 30 are carried in. The opening / closing mechanism 33 of the opening / closing mast 31 has the water seal chamber body 3
After passing 9, the opening / closing mast 31 is opened as shown in the figure. A detailed description of the opening / closing mechanism 33 is omitted, but the purpose can be achieved by adopting a structure such as an umbrella. After opening the opening / closing mast 31, induction heating is performed. Induction heating
By rotating the heat treatment device head 32 up and down by the drive device 43, it is possible to heat an arbitrary heat treatment target portion of the shroud 1. After heating, the cooling water is sprayed from the cooling water spray nozzle 38 through the heat treatment device head 32 and the cooling water spray line 37 to the inner and outer surfaces of the shroud 1 to perform rapid cooling. By controlling the heating time, temperature and cooling rate, solution treatment and surface residual stress can be improved. The drive device 43 is
It is installed on the service platform 49 installed on the reactor pressure vessel flange, and all operations are performed remotely. Since the heat treatment is performed after removing the core sparger / pipe 26, the upper lattice plate 5, and the core support plate 6, the main heat treatment can be applied to the entire surface of the shroud 1. If the core sparger / pipe 26, the upper grid plate 5, and the core support plate 6 are not removed, it is difficult to apply these devices in the vicinity of them.

FIG. 9 shows an example in which the preventive maintenance method is applied to the shroud 1 after all the replacement devices have been removed. The example of FIG. 9 shows an example in which surface modification is performed by using high-density energy irradiation such as a laser beam as a preventive maintenance method. In this figure, an example of performing solution treatment by irradiating a laser beam in water is shown. The surface of the shroud 1 is coated with a powder of Cr, Nb, Mo, Ti or the like having excellent corrosion resistance, and the coated surface is irradiated with the laser beam. It is also possible to form an alloy layer that is melted by the high-density energy irradiation used and has excellent corrosion resistance. It is also possible to carry out the work in an air atmosphere by means such as removing the reactor water in the reactor pressure vessel 3 and installing a shield on the flange portion of the reactor pressure vessel. In the surface modification according to the present embodiment, the Zervis platform 49 is installed on the flange portion of the reactor pressure vessel, the laser beam oscillator 54, the laser torch moving mechanism 50, the laser torch holding mast 51,
A laser torch moving mechanism 50 is used at an arbitrary heat treatment target portion of the shroud 1 by using a laser device including a fluid jet forming water supply pump 55, a shield gas supply cylinder 56, a cable 58, a hose 59, and the like.
After that, the high-speed fluid jet 52 is used to locally make the heat treatment target part an atmospheric atmosphere and irradiate the laser beam 53.

FIG. 10 shows an example in which the preventive maintenance method is applied to the shroud 1 after the removal of the replacement device is completed. The example of FIG. 10 shows an example of improving residual stress by using a water jet as a preventive maintenance method.

In order to improve the residual stress according to the present embodiment, the Zervis platform 49 is installed on the flange of the reactor pressure vessel, the drive mechanism 64 is installed on the Zervis platform 49, the upper mast 60, the opening / closing mast 61, and the opening / closing mechanism 6 are installed.
2, an example of using a water jet peening device including a water jet jet head 63, a water jet control device 68, a high pressure pump 67, a control signal cable 66, a high pressure hose 65, and the like will be shown. The opening / closing mast 61 is opened in the shroud 1 by the opening / closing mechanism 62 as illustrated, and the water jet jet head 63 is moved up and down and rotated by the drive mechanism 64 to enable peening at any position in the shroud 1.

Although the examples of FIGS. 8 to 10 are all directed to the shroud 1, the application to the shroud support cylinder 2, the shroud support leg 9, and the shroud support plate 12 is basically possible.

FIG. 11 shows an example in which water jet peening is performed on the outer surface of the shroud 1 and the outer surface of the jet pump diffuser 8a to improve the residual stress. Figure 1
Similar to the application example to the inner surface of the shroud 1 shown in FIG. 0, the device configuration is basically the same, and in this embodiment as well, the Zervis platform 49 is installed on the flange portion of the reactor pressure vessel, and the drive mechanism 64 is mounted on the Zervis platform 49. Install and install. In the present embodiment, the lower mast 69 is moved up and down by the lower drive mechanism 70 and the water jet ejection head 6 is moved.
3 is brought close to the peening target site and construction is performed. In this embodiment, the application to the outer surface of the shroud 1 and the outer surface of the jet pump diffuser 8a is shown. However, the water jet jet head 63 is closer to the inner surface side of the jet pump diffuser 8a than the inner surface of the shroud 1 and the shroud support leg 9. It is also possible to carry out construction.

The example of FIG. 11 shows an example of water jet peening, but surface modification by using a laser for the jet pump diffuser 8a is also applicable.

FIG. 12 shows an embodiment in which the shroud 1 is partially repaired. The main procedures for partial repair are confirmation of partial repair points by inspection, removal of defects, repair welding, finishing of repair welds, and inspection of repair parts. In FIG. 12, defect removal is shown. That is, this is an example in which the processing machine main body 74 is carried in from above the reactor pressure vessel and installed in the repair target portion to mechanically remove defects. In this example, only the vicinity of the processed portion is shown,
The processing machine main body 74 is installed on the service platform installed on the flange part of the reactor pressure vessel, and the lower end is installed and positioned on the stub tube. Although a mechanical processing method is shown in this example, an electric discharge processing method or a processing method using other thermal means can also be applied. Inspection, repair welding, finishing of repair welds, and inspection of repair parts can be performed with the same equipment. In addition, regarding the heat affected zone of the repair weld toe, treatment such as improvement of the sensitized area by low heat input, surface modification of the sensitized area by using laser beam, or improvement of residual stress by using water jet is performed. I will do it.

The examples shown in FIGS. 8 to 12 are all upper lattice plate 5, core support plate 6, core spray sparger /
After removing the pipe 26, the low-pressure water injection pipe 27, the differential pressure detection / boric acid water injection pipe 28, the jet pump riser 8b, the jet pump mixer 8c, and ICM guide pipes / stabilizers (not shown), the shroud 1 and the shroud. Since the preventive maintenance method and the partial repair method are applied to the support plate 12, the shroud support leg 9, the shroud support cylinder 2, and the jet pump diffuser 8a, the applicable range is expanded compared to the case where these devices are not removed. I can.

FIGS. 2 and 13 to 18 show an embodiment of the second invention, which is a welded portion 7 of the shroud 1 and the shroud support cylinder 2 and a jet pump diffuser 8a.
And the preventive maintenance method is applied to the welded portion 13 of the shroud support plate 12.

FIG. 2 is a flow chart showing the reactor pressure vessel upper lid 42, steam dryer 22, steam separator / shroud head 23, fuel assembly, control rod 24, control rod guide tube 25, control rod drive mechanism. / The devices such as the thermal sleeve are sequentially removed, and then the welded portion 7 of the shroud 1 and the shroud support cylinder 2 and the jet pump diffuser 8
The welding and the welding portion 13 of the shroud support plate 12 are repaired, the preventive maintenance method is applied, and the detached device is restored to complete the process.

FIGS. 13 to 15 show a preventive maintenance method for the welded portion 7 of the shroud 1 and the shroud support cylinder 2. As shown in FIG. 13, shroud 1
The backing ring 75 is used for the welded portion 7 of the shroud support cylinder 2 and the welded portion 7 of the shroud support cylinder 2 has a structure in which it cannot be said that no gap is left in the joint portion of the shroud support cylinder 2 and the backing ring 75. The shroud support cylinder 2 and the welded portion 7 are made of Inconel material, and in the case of Inconel material, the gap is not preferable in terms of SCC resistance. Therefore, as preventive maintenance, it can be said that it is effective to remove a portion where a gap may remain as shown in FIG. 14 by a mechanical means or a thermal means. In FIG. 15, a material having excellent SCC resistance in which components have been adjusted is subjected to overlay welding 76 in the removed portion in FIG. 14, and although not shown, surface modification of laser beam irradiation on the heat-affected zone by overlay welding 76 is not shown. ,
This is an example of performing residual stress improvement processing by water jet peening. Although FIG. 14 and FIG. 15 show an example of construction for preventive maintenance, the construction can be performed in the same manner in the case of repair.

16 to 18 show a preventive maintenance method for the welded portion 13 of the jet pump diffuser 8a and the shroud support plate 12. As shown in FIG. As shown in FIG. 16, the welded portion 13 of the jet pump diffuser 8a and the shroud support plate 12 has a butt welded structure, and basically there is no gap, but in case of emergency, preventive maintenance is assumed. As shown in FIG. 17, it is effective to remove a portion where a gap may remain by mechanical means or thermal means. In FIG. 18, a material having excellent SCC resistance in which components are adjusted in the removed portion in FIG. 17 is subjected to overlay welding 77. Further, although not shown, surface modification of laser beam irradiation on the heat affected zone by overlay welding 77 is performed. This is an example of performing residual stress improvement processing by water jet peening. Although FIG. 17 and FIG. 18 show an example of construction as preventive maintenance, it can be constructed in the same manner in the case of repair.

[0033]

EFFECTS OF THE INVENTION According to the present invention, the soundness of all in-core structures can be improved by adopting a combination of removal, re-installation, replacement, partial repair, and preventive maintenance construction methods for the in-core structures. It is relatively easy to secure the sex. Moreover, the application of the preventive maintenance method to narrow spaces can also be applied by constructing after removing some equipment.

Basically, all construction is performed by remote control under water, so that the worker can be reduced in exposure to radiation.

[Brief description of drawings]

FIG. 1 is a work procedure diagram.

FIG. 2 is a work procedure diagram.

FIG. 3 is a vertical cross-sectional view of a reactor pressure vessel and a reactor internal structure.

FIG. 4 is a shroud / upper lattice plate diagram.

FIG. 5 is a shroud / core support plate engagement diagram.

FIG. 6 is a core support plate core measurement diagram.

FIG. 7 is a vertical cross-sectional view of a reactor pressure vessel and a reactor internal structure.

FIG. 8 is an explanatory diagram for heat-treating the shroud.

FIG. 9 is an explanatory diagram for performing surface modification of the shroud.

FIG. 10 is an explanatory diagram for improving the residual stress of the shroud.

FIG. 11 is a cross-sectional view for improving the residual stress of the jet pump diffuser.

FIG. 12 is a perspective view showing an example of repairing the shroud.

FIG. 13 is a cross-sectional view showing the connection between the shroud and the shroud support cylinder.

FIG. 14 is a preventive maintenance cross-sectional view of a shroud and a shroud support cylinder weld.

FIG. 15 is a preventive maintenance cross-sectional view of the shroud and the shroud support cylinder weld.

FIG. 16 is a cross-sectional view showing the connection between the jet pump diffuser and the shroud support plate.

FIG. 17 is a preventive maintenance cross-sectional view of a jet pump diffuser and a shroud support plate weld.

FIG. 18 is a preventive maintenance sectional view of the jet pump diffuser and the shroud support plate welded portion.

[Explanation of symbols]

1 ... Shroud, 2 ... Shroud support cylinder, 3
... Reactor pressure vessel, 5 ... Upper lattice plate, 6 ... Core support plate,
8a ... Jet pump diffuser, 8b ... Jet pump riser, 8c ... Jet pump mixer, 9 ... Shroud support leg, 12 ... Shroud support plate, 20 ... Stub tube, 21 ... Fuel support fitting, 22
… Steam dryer, 23… Steam separator and shroud head,
24 ... Control rod, 25 ... Control rod guide pipe, 26 ... Core sparger purger / pipe, 27 ... Low pressure water injection pipe, 28 ... Differential pressure detection / boric acid water injection pipe, 29 ... Support, 36 ... Reactor well.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Kinya Aota 4026 Kujicho, Hitachi City, Hitachi, Ibaraki Prefecture Hitachi Research Laboratory, Hitachi, Ltd. (72) Inventor Michiyoshi Yamamoto 3-1-1, Saiwaicho, Hitachi City, Ibaraki Hitachi Ltd., Hitachi Plant (72) Inventor Yasukata Tamai 3-1-1, Sachimachi, Hitachi City, Ibaraki Hitachi Ltd., Hitachi Ltd. (72) Inventor Isao Nemezawa Yuchi, Hitachi City, Ibaraki Prefecture 3-1-1, Machi Hitachi Ltd., Hitachi factory (72) Inventor Keiichi Nomura 3-1-1, Saiwaicho, Hitachi City, Ibaraki Hitachi Ltd. Hitachi factory

Claims (11)

[Claims] 1. A cylindrical core shroud formed on the inner surface of an existing reactor pressure vessel via a shroud support leg and a shroud support cylinder, and fixed to the upper end of the shroud support cylinder by a circumferential welding portion by circumferential welding and vertical welding. , A core support plate and an upper lattice plate fixed to the core shroud by mechanical means, a core sparger / pipe connected to the core shroud by welding, and a low pressure water injection pipe, an outer periphery of the shroud support cylinder Jet pump diffuser welded to a shroud support plate welded to the inner wall of the shroud support cylinder and the reactor pressure vessel on the side, to the jet pump diffuser and the reactor pressure vessel for mechanical means and welding Fixed by joining Jet pump riser and a jet pump mixer or the like, IC mounted by welding to the ICM housing joined by welding to said reactor pressure vessel under mirror
In a method for preserving internal structures of an ICM stabilizer or the like, in which the M guide pipe and the ICM guide pipes are fixed by welding and mechanical means, in a state where reactor water is held in the reactor pressure vessel, Steam dryer attached on the core shroud in the reactor pressure vessel, equipment such as shroud head and steam separator are sequentially removed, and further fuel assemblies in the core shroud, control rod guide tubes, etc. are removed, Next, the core sparger / pipe and the low-pressure water injection pipe are cut and removed from the core shroud and the reactor pressure vessel by mechanical means or thermal means, and then the upper lattice plate is mechanically or thermally removed. And remove the core support plate from the core shroud by mechanical means, thermal means, or the like. To the ICM guide tube and ICM
The stabilizer is removed from the ICM housing by mechanical means or thermal means, and the jet pump riser and jet pump mixer are removed from the reactor pressure vessel and jet pump diffuser by mechanical means or thermal means. , The shroud, shroud support, jet pump diffuser surface modification, residual stress improvement and preventive maintenance such as heat treatment, and then the core support plate, upper grid plate,
Core sparger / piping, low-pressure water injection piping, jet pump diffuser, jet pump riser, jet pump mixer, ICM guide tube, ICM stabilizer, etc. are replaced with newly manufactured ones, respectively. .. 2. The method for maintaining an internal reactor structure according to claim 1, wherein the existing internal reactor structure is removed and a new internal reactor structure is installed in water by a remote control device. 3. The shroud, and the surface modification of the shroud support and the jet pump diffuser according to claim 1, wherein the surface treatment of the shroud and the shroud support is performed by a solution treatment by irradiation with high-density energy such as a laser beam. Excellent Cr, Nb, Mo,
A method for preserving the internal structure of a furnace, which comprises applying a powder of Ti or the like and melting the applied surface by irradiation with high-density energy such as a laser beam to form an alloy layer having excellent corrosion resistance. 4. The shroud, shroud support and jet pump diffuser according to claim 1, wherein residual stress is improved by peening using a water jet, or rapid heating by electromagnetic induction heating, cooling water spraying, or the like.
Preservation method of reactor internals using rapid cooling method. 5. The method of claim 1, wherein the shroud is heat-treated by using electromagnetic induction heating or the like. 6. A method for preserving the internal structure of a reactor, characterized in that the outer surface of the welded portion of the jet pump diffuser and the shroud support plate is removed at a constant depth by mechanical means or thermal means. 7. The outer surface of the welded portion of the jet pump diffuser and the shroud support plate is removed at a certain depth by mechanical means or thermal means, and then the removed portion is covered with C, Ti, Nb, etc. Internal structure characterized by performing build-up welding with Inconel welding material with adjusted chemical composition and excellent corrosion resistance, and further subjecting the heat-affected zone of the build-up welding to surface modification, residual stress improvement, etc. Conservation method. 8. A method for maintaining the internal structure of a reactor, wherein the outer surface of the welded portion of the shroud and the shroud support cylinder is removed at a constant depth by mechanical means or thermal means. 9. An outer surface of a welded portion of a shroud and a shroud support cylinder is removed at a constant depth by a mechanical means, a thermal means, or the like, and then the removed portions are C, T.
It is characterized in that overlay welding is performed using Inconel welding material having excellent corrosion resistance in which scientific components such as i and Nb are adjusted, and further, the heat-affected zone of the overlay welding is subjected to surface modification, residual stress improvement, and the like. Method for maintaining internal furnace structure. 10. The surface modification according to claim 7, wherein the surface treatment is solution treatment by irradiation with high-density energy such as a laser beam, or Cr, Nb, Mo having excellent corrosion resistance on the surfaces of the shroud and the shroud support. , Ti or the like is applied, and the applied surface is melted by high-density energy irradiation such as a laser beam to form an alloy layer having excellent corrosion resistance. 11. A method for preserving the internal structure of a reactor using a peening method using a water jet, a rapid heating method such as electromagnetic induction heating, a cooling water spray method, or a rapid cooling method for improving the residual stress according to claim 7 or 9. ..