JPH10153682A - Method for exchanging reactor core shroud - Google Patents

Abstract

PROBLEM TO BE SOLVED: To extend the life of a plant by performing cladding machining, coating machining, or laser surface heat treatment to the welded part or the total surface of partial or total equipment such as a CRD stub tube, shroud support support leg, and a shroud head in a process for exchanging a shroud. SOLUTION: In a method for exchanging a shroud, water at the bottom of a reactor is drained and plasma flame spraying machining of the outer surface of a CRD stub tube 1 and a housing 2 is performed while water is poured into an annulus part as a measure for screening radiation. A shot penning nozzle is turned by a turning mechanism 3 along the outer surface of the housing 2 and the stub tube 1 due to the drive of a CRD housing motor 8. A flame spraying gun 4 is mounted at the tip of an arm and is positioned at a part to be executed by a rack pinion mechanism 5 for driving in axial direction. An entire device is supported by an axle 7 provided inside from a ring 6 and moves. Other inspection tools are also mounted.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of replacing a core shroud of a reactor internal structure, and more particularly to a method of replacing a core shroud accompanied with inspection, preventive maintenance, and repair of equipment in the reactor.

[0002]

2. Description of the Related Art With the long-term operation of a nuclear power plant, various preventive maintenance techniques, replacement and repair techniques of each equipment have been developed for the purpose of improving the reliability and prolonging the life of furnace equipment.

For example, it is planned to install automatic equipment in a furnace during periodic inspection of a plant, access the equipment in the furnace, and implement various countermeasure methods. Above all, there is a concern that stress corrosion cracking may occur due to residual tensile stress remaining in the welded portion, and techniques for countermeasures have been developed.

[0004] Precious metal cladding or precious metal coating is to clad or coat the equipment surface in the furnace by cladding or coating with a Ni-based or Fe-based alloy containing a small amount (less than 1%) of Pd, Pt, Rh or a mixture thereof. In this technique, the potential lowering effect due to hydrogen implantation is significantly increased to suppress SCC. The Nb-stabilized Νi-based alloy is an alloy in which the carbon contained in the alloy is stabilized by Nb, the generation of a Cr-deficient phase at a crystal grain boundary or a dendrite grain boundary is prevented, and the SCC resistance is improved, and the SCC sensitivity is obtained. SCC can be suppressed by cladding and coating on the alloy material.

[0005] Laser surface heat treatment is a technique for removing SCC susceptibility by heating the surface of a material sensitized by welding or the like to a solution temperature of 1000 ° C. or higher, then quenching, and homogenizing the surface. However, in order to apply the technology to in-furnace equipment with high radiation, it is necessary to construct all technologies remotely underwater, and therefore, it is necessary to develop dedicated automatic equipment suitable for the target site. Similarly, inspection and repair techniques also require dedicated automatic equipment corresponding to each technique and target equipment, and thus require a long preparation period and development costs before construction.

Further, when each technology is applied using a remote automatic device, there is a limit on the automatic device side such as positioning accuracy. Problems can occur.

Further, if the above countermeasures are implemented at the time of the periodic inspection, the period of the regular inspection is prolonged, the operation rate of the plant is reduced, and there is a problem in terms of economy.

[0008]

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned conventional problems, and provides a technology for inspecting, preventing, and repairing the internal structure of an existing nuclear power plant at a low cost. An object of the present invention is to provide a method of exchanging a core shroud that can be performed.

[0009]

In order to achieve the above object, the present invention removes the upper part of the shroud and the internal structure of the shroud such as a reactor pressure vessel head and a steam dryer, and chemically decontaminates the inside of the furnace using a chemical. Then, in the method of exchanging the core shroud for cutting the shroud support cylinder portion, draining the reactor water and welding a new shroud, the following process is performed.

(1) In a shroud replacement step, a jet pump riser pipe and a jet pump diffuser
Jet pump riser brace arm, water level instrumentation nozzle, recirculation nozzle, water supply nozzle, CRD stub tube, incore monitor housing, shroud support support leg, shroud head, steam dryer, core spray piping, baffle plate, upper grid plate, core Cladding processing, coating processing or laser surface heat treatment is performed on the welded portion or the entire surface of any one of the devices such as the support plate or all the devices.

(2) In the shroud replacement process, the outside of the new shroud is sealed and welded, and then water is injected into a downcomer to shield radiation from a jet pump and a pressure vessel. Cladding, coating or laser surface heat treatment is performed on the welded portion or the entire surface.

(3) Cladding, coating, or laser surface heat treatment is performed on the welded portion of the shroud support and the new shroud or on the entire surface.

(4) Cladding, coating, or laser surface heat treatment is applied to the new shroud weld in advance.

Cladding is a technique in which the metal to be coated is melted and solidified together with the surface layer of the metal (base material) to be coated, and the two are joined. It is desirable that the metal material to be coated has excellent corrosion resistance. If the material to be coated (base material) is a Ni-based alloy, the material to be coated (cladding material) may also be, for example, the American Society of Mechanical Engineers (ASME) standard S
It must be a Ni-based alloy corresponding to ERNiCr-3 of FA5.14, but in order to ensure excellent corrosion resistance, the chemical composition of the cladding layer surface after cladding is determined from the weight% of each alloy component. N = 0.13 × (Νb + 2 × Ti)
The value of / C is preferably 12 or more. Coating materials suitable for cladding are described in, for example, [Yamauchi et al., Corrosion and Corrosion Prevention Association Spring Conference 1982 Preprints, A-31.
3. ]It is described in.

In the cladding by the tungsten inert gas arc welding method, a metal material to be coated is formed into a wire and supplied to a base material melted by an arc generated between the base material and a tungsten electrode. This is a method of obtaining a clad layer by melting and solidifying together with the base material.
Also, instead of supplying the metal to be coated in the form of a wire, the metal to be coated is formed into a thin plate (or foil) and pasted on the surface of the equipment to be coated in advance, and the metal is generated between the thin plate and the tungsten electrode. A method may be used in which the thin plate and the surface layer of the base material are both melted and solidified by the applied arc.
Cladding by the laser welding method is a method of irradiating a metal material covering a focused laser beam into a wire and irradiating the surface of a base material, and melting and solidifying both to obtain a clad layer. These methods have high bonding strength with the base material and are highly reliable without peeling off even when a large strain occurs in the base material due to the use conditions of the equipment. The coating process is a technique in which the metal to be coated is made into fine particles, which are sprayed onto the surface of the metal (base material) to be coated while being heated by plasma or flame.

As the metal to be coated, the cladding or the coating material is Ni containing no more than 1% of a noble metal such as Pd, Pt or Rh or a mixture of these noble metals.
Or a Fe-based alloy. These alloys are also used as cladding cladding metal materials. Plasma coating is a method of spraying metal particles to be coated in a semi-molten state (a state in which the surfaces of the metal particles are molten) with the heat of the plasma, and spraying the metal particles at a high speed on the surface of the base material to obtain a coating layer. The coating layer is obtained by accelerating the particles with the energy of the combustion gas and colliding the particles with the surface of the base material at supersonic speed. Both coating layers have lower bonding strength with the base material than the cladding layer because the metal to be coated and the metal of the base material surface layer are not completely melted, but the temperature of the base material is substantially 500 ° C or higher. Does not rise, so that the base material is not thermally degraded. Therefore, it is suitable as a method for coating a corrosion-resistant metal on austenitic stainless steel that has been subjected to high intensity neutron irradiation.

The laser surface heat treatment is a technique for improving the SCC resistance of the furnace internals by irradiating a material surface with a high-power laser beam and rapidly heating and cooling the surface layer. There are two types of laser surface heat treatment, a laser solution treatment in which the maximum heating temperature is 1000 ° C. or more and a melting point or less, and a laser melting treatment in which heating is performed at a temperature equal to or more than the melting point.

Since the core shroud is located closest to the core, the core shroud is not only exposed to high-temperature and high-pressure water, but also there is a concern about material deterioration due to neutron irradiation, and the core shroud is replaced from the viewpoint of improving the reliability and extending the life of the plant. This is known (Japanese Patent Application No. 6-331310). In the replacement work, after decontaminating the inside of the furnace using chemical agents, in the aerial environment,
Since the old shroud is cut off and the new shroud is welded, an environment in which a worker can work in the furnace for a short time is provided.

In addition, since equipment such as a steam dryer, a core spray line, a shroud head, and an upper grid plate located above the shroud are removed in advance and stored in the equipment storage pool, inspection of welds in the storage pool is performed.
Cladding, coating, laser surface melting, repair, and replacement are possible.

In the manufacturing process, it is effective to carry out cladding, coating or laser surface heat treatment on the new shroud weld or on the entire surface to increase the SCC resistance.

With respect to structures at the bottom of the furnace, such as a CRD stub tube weld, a CM housing weld, a shroud support, and a support leg, inspections such as VT inspection, ultrasonic inspection, and RT inspection are possible in an aerial environment. Further, it is also possible for an operator to perform cladding or coating as a surface modification or to install an automatic machine at the bottom of the furnace. Repair and replacement work can be performed in a short time and reliably by using an operator or an automatic machine. In particular, the automated machine has a furnace with internal structure removed, which reduces dimensional restrictions, carrying-in and installation conditions, and has more design latitude than conventional products. be able to.

When the furnace bottom work is performed, the space between the shroud and the pressure vessel is filled with water in order to keep the dose in the furnace low, so that the water level instrumentation nozzle, the recirculation nozzle, and the baffle plate The access hole cover, the baffle plate and the shroud, and the weld between the baffle plate and the pressure vessel are in an underwater environment and need to be installed underwater.
At this time, it is necessary to install a head on a remote automatic device and perform automatic construction.However, there is no obstacle such as a sensing line, and a large space above the jet pump is secured. The workability of installation and relocation has been improved. For the same reason, the inspection, repair, and replacement work of the above-mentioned parts can be performed in a shorter time and at lower cost than before by performing the work accompanying the replacement work of the core shroud.

Further, after the jet pump inlet mixer is removed, a shield lid is provided on the riser pipe upper part and the diffuser upper part so that water does not leak out of the furnace and to the furnace bottom part, so that the respective inner surfaces become an air environment,
Each can be accessed from the furnace bottom and outside the pressure vessel. Therefore, inspection, cladding, coating, and laser surface melting of welds can be performed in an aerial environment. However, installing automatic equipment inside riser pipes and diffusers reduces the exposure of workers. be able to.

Various operations inside the jet pump diffuser include an ultrasonic probe, an eddy current probe, a television camera, an upright standing on the CRD housing in the reactor pressure vessel and attached to the tip inside the reactor pressure vessel. A drive unit that positions tools such as a PT device, an EDM electrode, a grinder, a welding head, a polishing tool, a plasma spray gun, and an HVOF spray gun; a guide wheel that guides the tip along the reactor pressure vessel; Inside the furnace that performs various operations on the inner surface of the diffuser of the jet pump, which is composed of a positioning mechanism inserted into the jet pump diffuser, a guide wheel whose tip is aligned on the inner surface of the diffuser, and a drive unit that positions a tool on the inner surface of the diffuser. It is performed using a working device, also a jet pump diffuser, jet pump For various operations inside the riser tube, after removing the inlet mixer, ultrasonic probe, eddy current probe, TV camera, PT device, EDM electrode, grinder, plasma spray gun, HVOF attached to the tip from the upper opening A drive unit for positioning tools such as a spray gun and a welding head, a positioning mechanism for inserting the tip into the jet pump diffuser, a guide wheel whose tip is centered on the diffuser and riser pipe inner surfaces, and a diffuser and riser pipe The operation is performed using an in-furnace operation device that is configured with a drive unit that positions a tool on a surface and performs various operations on a diffuser of a jet pump and an inner surface of a riser pipe.

(Operation) According to the core shroud replacement method of the present invention, inspection of various furnace internal structures, cladding or coating work, and repair work are performed in conjunction with the core shroud replacement work performed in the air. Therefore, the reliability of the furnace internal structure can be further improved as compared with the conventional core shroud replacement method.

Some of them are as follows.

[Precious Metal Cladding or Coating] When the surface of the furnace equipment is coated with an alloy containing a trace amount of noble metal, the corrosion potential of the equipment can be effectively reduced with a small amount of hydrogen injected.

FIG. 1 shows a 308 stainless steel containing SUS304 stainless steel, Pt and 0.1% Pd in a ΔVOF.
The graph shows the hydrogen concentration dependence of the water potential at 285 ° C of the electrode coated on the surface of 304 steel. As can be seen from this figure, the potential of the SUS304 steel is -200 mV _SHE or more even at a hydrogen concentration of 45 ppb, but the 304 steel coated with 0.1% Pd has a potential of -300 m at a hydrogen concentration of 25 ppb like Pt.
V _SHE or less [YJKim, LWNiedrach, MEI
ndig, and PLAndresen, J.Min., Met.and Matrials.Soc.
Vol.44, p.14 (1992)].

FIG. 2 shows a constant strain rate stress corrosion cracking (CER).
T :) shows the potential of the Pd-coated test piece and the uncoated autoclave in the test. In this figure, the suffix indicates the molar ratio of hydrogen to oxygen, and the potential of the autoclave always indicates a value higher than the threshold potential of SCC generation. The following values are shown.
At this time, Table 1 shows the autoclave and P
As shown in the d-coating test piece corrosion potential, if the potential is equal to or lower than the limit potential, the generation of SCC can be suppressed.
It is clear that the coating is effective in suppressing SCC under hydrogen implantation.

[0030]

[Table 1] [Nb-stabilized Ni-base alloy] As shown in FIG. 3, the intergranular corrosion rate of the Ni-base alloy weld metal (IGA Penetration Rate)
It can be seen that, among the chemical components of the alloy, when the value of N based on the weight percent of Nb, Ti and C exceeds 12, it rapidly decreases and the corrosion resistance improves.

[Laser Surface Heat Treatment] In the laser solution heat treatment, the surface of a material having SCC sensitivity is heated to a solid solution temperature of 1000 ° C. or more by irradiating a laser beam, and the C at grain boundaries is increased.
The SCC resistance is improved by rapid cooling so that the r-deficient layer disappears and then does not resensitize. Since the laser beam has a very high energy density, the material surface can be rapidly heated and cooled in a short time.

FIG. 4 shows the cross-sectional metallographic structure of a test piece which was subjected to laser solution treatment by irradiating the surface of a heat-sensitized 304 stainless steel with a 1 kW YAG laser beam.
Obata, Takahashi: Atomic Energy Society of Japan "1994 Autumn Meeting" P4
3]. The surface layer of approx.
The Cr carbide precipitated at the crystal grain boundaries when heated to at least 00 ° C. is solid-dissolved to form a metallographic layer having excellent SCC resistance. This material was subjected to a CBB test, which is a type of SCC test, in high-temperature water. As a result, it was confirmed that the SCC resistance was improved by laser solution heat treatment. Also, it has been reported that laser surface melting treatment has an effect of similarly improving the SCC resistance of stainless steel [J. Stew
art et al .: Corrosion, Vol. 46, p. 618 (1990)].

[0033]

BEST MODE FOR CARRYING OUT THE INVENTION

(1) FIG. 5 shows the CRD stub tube 1 with the core shroud replacement method of the present invention in a state where water at the bottom of the furnace is drained and injected into the annulus as a radiation shielding measure.
1 shows the configuration of an apparatus for performing plasma spray coating on the outer surface of a housing 2.

This device comprises a swivel mechanism 3 for swiveling the shot peening nozzle along the outer surfaces of the housing 2 and the stub tube 1 by driving a CRD housing motor.
And this mechanism is fixed to the top of the housing as shown. A thermal spray gun 4 is attached to a tip of an arm extending below the turning mechanism 3, and the thermal spray gun 4 is positioned at a construction target portion by a rack and pinion mechanism 5 and is driven in an axial direction. The entire apparatus is supported by wheels 7 installed inward from the ring 6 and is movable along the outer surface of the housing.

With this apparatus, it is possible to perform coating processing on the welded portion between the lower mirror of the reactor pressure vessel and the stub tube and the welded portion between the housing and the stub tube. further,
By installing an inspection tool such as VT and UT, a repair tool such as a welding torch, and a cutting tool such as an EDM electrode in place of the spray gun, inspection, repair, and replacement of the welded portion can be easily performed.

(2) FIG. 6 shows the construction of a construction apparatus for performing plasma spraying on the outer surface of the welded portion of the shroud support cylinder 17 and the new shroud 18 in the core shroud replacement method of the present invention. This device has a plasma spray gun running guide 1 on the outer surface when a new shroud is manufactured.
9 is installed, and the traveling vehicle 20 is run along the guide to perform plasma spraying on the welded portion.
In addition, accurate positioning is possible by moving the head 32 up and down by the rack and pinion mechanism 21. Further, by attaching an inspection tool such as VT or UT instead of the plasma spray gun, it becomes possible to inspect the welded portion.

(3) FIG. 7 shows a configuration of a plasma spraying apparatus for welding the baffle plate 27 and the shroud support cylinder 17 in the core shroud replacement method of the present invention.

After the existing shroud is cut and removed, the plasma spraying apparatus can be run along the welded portion of the baffle plate 27 and the shroud support cylinder 17 by making the cut portion function as a rail to perform plasma spraying. This device comprises a traveling vehicle 31, an arm 38 having joints, and an elevating shaft 35 for moving the head up and down, and can be positioned at any position.

Also, the traveling vehicle 31 is fixed on a rail,
By the above-mentioned mechanism, the plasma spraying can be performed by approaching the welding portion of the baffle plate 27 and the jet pump diffuser 29. VT, U instead of plasma spray gun
Inspection tools such as T, repair tools such as welding torch, E
By attaching a cutting tool such as a DM electrode, inspection, repair, and replacement of the welded portion can be easily performed.

(4) FIG. 8 relates to a method of replacing the core shroud, in which the water at the bottom of the furnace is drained and, as a measure for shielding radiation, the stub tube and the mirror welded under the reactor pressure vessel are poured into the annulus. 1 shows a configuration of an apparatus for performing shot peening on a furnace bottom portion.

Using this apparatus, a work table 54 at the bottom of the furnace is used.
From above, a worker performs shot peening on the furnace bottom. The apparatus is also provided with a mechanism that is attached to the tip of an operation pole (not shown) and that facilitates management of construction conditions such as a shot projection distance and an angle.

In this apparatus, a projection nozzle 40 is provided at the end of a straight pipe 48 for supplying metal powder. Also, three points of wheels 42 supported so as to be able to move up and down linearly by a combination of a spring 43 and a linear bush 48 with respect to the construction surface, and a stopper fixed to a support member that moves directly with each wheel 42 At 51, the limit switch 44 can be turned on / off. A stopper 50 is provided on a shaft 49 which is also supported by the wheels 42 and is linearly moved by the linear bush 48. The stopper 50 is provided so as to be linearly movable by a combination of the linear guide 52 and the spring 46. Limit switch 45 connected via shaft 49
However, an ON / OFF input can be made by raising the stopper 50.

According to the apparatus shown in FIG. 8, if the projection distance in the construction conditions is long, the limit switch 4
4 are all OFF, and if too close, any signal of the limit switch 45 is OFF. Regarding the projection angle in the construction conditions, a setting is made so that any signal of the limit switch 44 is turned off when an appropriate projection angle condition is not satisfied centering on 90 degrees. Although not shown in FIG. 8, the construction speed can be managed by detecting the rotational speed or rotational position of the wheel 42.

[0044]

According to the present invention, it is possible to carry out inspection of a reactor internal structure, surface modification technology, and repair technology in a short time, at low cost, and in a short period of time. It is possible to improve the performance and extend the life.

[Brief description of the drawings]

FIG. 1 is a graph showing the dependence of corrosion potential on hydrogen concentration in high-temperature water in 304 steel coated with 308L containing Pd by 高温 VOF.

FIG. 2 is a graph showing the potential of an autoclave and a Pd-coated specimen during a CERT test.

FIG. 3 is a graph showing a relationship between an IGSCC development speed and a parameter N;

FIG. 4 is a diagram showing an enlarged cross-sectional metal structure after laser-SHT.

FIG. 5 is a perspective view showing a main part of the CRD stub tube outer surface construction apparatus.

FIG. 6 is a diagram showing a main part of a new shroud / shroud support cylinder welding portion construction apparatus.

FIG. 7 is a diagram showing the state of plasma spraying of a new shroud / shroud support cylinder simulation specimen.

FIG. 8 is a diagram schematically showing a furnace bottom construction device.

[Explanation of symbols]

1 ... stub tube, 2 ... housing, 3 ... rotating mechanism, 4 ... spray gun, 5 ... rack and pinion, 6 ...
Ring, 7 wheel, 8 motor, 9 base part
10 ... Elevating shaft, 11 ... Motor, 12 ... Tilt shaft,
13 flexible tube, 14 cable, 15 projection tube, 16 straight pipe part, 17 shroud support cylinder, 18 new shroud, 19 guide rail, 20 traveling vehicle, 21 ...... Rack pinion, 2
2 ... spray gun, 23 ... motor, 24 ... traveling vehicle, 2
5 Tube 26, Projection tube 27 Baffle plate 28 Shroud support leg 29
... Jet pump diffuser, 30 ... Reactor pressure vessel, 31 ... Vehicle, 32 ... Swirl axis, 33 ... Swirl axis, 34 ... Swift axis, 35 ... Elevating shaft, 36 ... Cable, 37 ... Cable, 38, arm, 39, cut surface, 40, projection nozzle, 41, plasma, 42
Wheels 43 springs 44 limit switches 45
... Limit switch, 46 ... Spring, 47 ... Straight pipe for projection, 48 ... Linear bush, 49 ... Shaft, 5
0 ... stopper, 51 ... stopper, 52 ... linear bush, 53 ... shaft, 54 ... work table

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Hiroshi Sakamoto 8th Shinsugita-cho, Isogo-ku, Yokohama-shi, Kanagawa Prefecture Inside the Toshiba Yokohama Office (72) Inventor Yasuhiro Yuguchi 8th Shinsugita-cho, Isogo-ku, Yokohama-shi, Kanagawa (72) Inventor Yukio Hemi, 1st office, Komukai Toshiba-cho, Sachi-ku, Kawasaki-shi, Kanagawa Inside Toshiba R & D Center

Claims (11)

[Claims] 1. The upper part of the shroud and the internal structure of the shroud such as a reactor pressure vessel top lid and a steam dryer are removed, and the inside of the furnace is chemically decontaminated using chemicals. After the shroud support cylinder is cut, the reactor water is drained. In the core shroud replacement method of welding the shroud, in the shroud replacement step, a jet pump riser pipe and a jet pump diffuser, a jet pump riser brace arm, a water level instrumentation nozzle, a recirculation nozzle, a water supply nozzle,
CRD stub tube, in-core monitor housing,
Shroud support support leg, shroud head,
Cladding, coating, or laser surface heat treatment is applied to the welded parts or all surfaces of any or all of the equipment such as steam dryers, core spray piping, baffle plates, upper lattice plates, core support plates, etc. A method of exchanging a core shroud, which is performed. 2. A shroud upper part and a shroud inner structure such as a pressure vessel upper lid and a steam dryer are removed, the inside of the furnace is chemically decontaminated with a chemical, the shroud support cylinder is cut, and the furnace water is drained. In the replacement method of the core shroud to be welded, in the shroud replacement process, the outside of the new shroud is sealed and then welded into the downcomer to shield the radiation from the jet pump and the pressure vessel, and then all the reactor water at the bottom of the furnace is drained. ,
Cladding, welding on the bottom of the furnace or the entire surface
A method of exchanging a core shroud, comprising performing coating or laser surface heat treatment. 3. The upper part of the shroud and the internal structure of the shroud such as a reactor pressure vessel top lid and a steam dryer are removed, and the inside of the furnace is chemically decontaminated using chemicals. After the shroud support cylinder is cut, the reactor water is drained. A method of exchanging a core shroud for welding a shroud, wherein cladding processing, coating processing or laser surface heat treatment is performed on a shroud support and a new shroud weld or the entire surface. 4. The upper part of the shroud and the internal structure of the shroud such as the upper cover of the reactor pressure vessel and the steam dryer are removed, and the inside of the furnace is chemically decontaminated with chemicals. After the shroud support cylinder is cut, the reactor water is drained. A method of exchanging a core shroud for welding a shroud, wherein a cladding process, a coating process, or a laser surface heat treatment is applied to a new shroud weld in advance. 5. The cladding or coating material according to claim 1, wherein the cladding or coating material is a Ni-based or Fe-based alloy containing 1% or less of a noble metal such as Pd, Pt or Rh or a mixture of these noble metals. 5. The method for exchanging a core shroud according to any one of items 4 to 4. 6. A cladding material comprising, by weight, 3% or less of Fe, 18 to 22% of Cr, and 2 to 3% of N.
b, consisting of 67% or more of Ni and other unavoidable impurities.
Claims: A Ni-based alloy, wherein the value of N in the formula N = 0.13 x (Nb + 2 x Ti) / C determined from the weight percent of each alloy component is 12 or more. The method for exchanging a core shroud according to any one of Items 1 to 4. 7. The cladding material according to claim 6, wherein the cladding material is clad by a tungsten inert gas arc welding method or a laser welding method. 2. The method for replacing a core shroud according to claim 1. 8. The method according to claim 1, wherein the coating is performed by a plasma spray method or an HVOF (High Velocity Oxygen Fuel) method. 9. The method for exchanging a core shroud according to claim 1, wherein the laser surface heat treatment is performed by a laser surface melting method or a laser surface solution heat treatment method. . 10. Various operations inside the jet pump diffuser include an ultrasonic probe, an eddy current probe, and a television set upright on the CRD housing inside the reactor pressure vessel and attached to the tip inside the reactor pressure vessel. Camera, PT device, ED
Drive for positioning tools such as M electrode, grinder, welding head, polishing tool, plasma spray gun, HVOF spray gun, guide wheel for guiding the tip along the reactor pressure vessel, and jet pump diffuser for the tip A work mechanism for performing various operations on the inner surface of the diffuser of the jet pump, which is composed of a positioning mechanism to be inserted into the inside, a guide wheel whose tip is centered on the inner surface of the diffuser, and a drive unit for positioning a tool on the inner surface of the diffuser. The method for exchanging a core shroud according to any one of claims 1 to 9, wherein the method is performed using the core shroud. 11. Various operations inside the jet pump diffuser and the jet pump riser pipe are performed by removing an inlet mixer, and then installing an ultrasonic probe, an eddy current probe, a television camera, a PT device attached to a tip from an upper opening. , EDM electrode, grinder, plasma spray gun,
A drive unit for positioning tools such as HVOF spray guns and welding heads, a positioning mechanism for inserting the tip into the jet pump diffuser, a guide wheel whose tip is centered on the inner surface of the diffuser and riser pipe, a diffuser and a riser 10. The apparatus according to claim 1, further comprising a drive unit configured to position a tool on an inner surface of the pipe, and a diffuser of a jet pump, and an in-furnace operation device for performing various operations on an inner surface of the riser pipe. The method for replacing a core shroud according to any one of the above items.