JP2530010B2 - How to repair a long housing - Google Patents

Description

The present invention relates to a method for repairing a long housing such as a neutron flux monitor housing fixedly supported by a reactor pressure vessel.

(Prior art) Since the output of a nuclear reactor such as a boiling water reactor is proportional to the neutron flux, the neutron flux of the reactor is measured by a neutron flux detector (neutron flux) for the purpose of displaying the output of the reactor and evaluating burnup. It is measured and monitored by a bundle monitor).

The neutron flux detector 1 is installed in a boiling water reactor as schematically shown in FIG. 5, and a reactor core 3 is housed in a reactor pressure vessel 2 as shown by a broken line. A neutron flux monitor body 4 accommodating the neutron flux detector 1 is installed in this core 3. The illustrated example shows an example in which one neutron flux monitor main body 4 is installed for simplification.

The neutron flux monitor main body 4 is formed in a long and slender shape, the upper end thereof is elastically supported by the lower surface support hole 5a of the upper lattice plate 5, and the lower part thereof is a neutron flux monitor guide tube 6 and a neutron flux monitor housing (in-core monitor). The housing 7) projects downward, the lower end of which is supported by abutting against a neutron flux monitor flange (in-core flange) 8 and fixed by a tightening nut 9 for installation.

An upper portion of the neutron flux monitor housing 7 is fixed to the lower mirror of the reactor pressure vessel 2 by welding and is provided in a suspended state.
Since the neutron flux monitor housing 7 uses an austenitic stainless steel tube such as SUS304, if the three conditions of stress, corrosion environment, and material (generation of chromium deficient layer) are satisfied, the welded part with the reactor pressure vessel 2 Stress corrosion cracking (hereinafter referred to as SCC) may occur in the vicinity. Since SCC will not occur if any one of the three conditions is missing, various measures have been taken to prevent this stress corrosion cracking.

(Problems to be Solved by the Invention) Intergranular stress corrosion cracking (IGSCC) or welding defects due to fusion failure during welding may occur in the vicinity of the welded portion of the reactor pressure vessel 2 that fixedly supports the neutron flux monitor housing 7, Or, if the neutron flux monitor housing itself has a defect, a crack is generated in the vicinity of the welded portion or in the neutron flux monitor housing, and if the crack gradually grows and a leak path is formed, a reactor water leak may develop.

On the other hand, the neutron flux detector that measures and monitors the neutron flux in the core is different from the control rod drive mechanism that controls the reactor power output or shuts down the reactor, because it does not belong to the safety system of the reactor.
The seal support structure of the neutron flux monitor housing is not premised on the reactor safety system, and if a defect occurs in the neutron flux monitor housing itself or in the vicinity of the weld with the reactor pressure vessel, this A permanent repair method for removing defective parts is not well established.

The present invention has been made in consideration of the above-described circumstances, and identifies a defective portion near a long housing such as a neutron flux monitor housing or a welded portion and completely removes this defective portion or a potential defect occurrence site. However, it is an object of the present invention to provide a method for repairing a long housing that can reliably prevent a reactor water leak by restoring the relevant portion to a structure having the same strength as the initial support structure.

[Structure of Invention]

(Means for Solving the Problems) A method of repairing a long housing according to the present invention is a method of fixing a long housing such as a neutron flux monitor housing fixedly supported on a lower mirror welded portion of a reactor vessel to the upper and lower sides of the welded portion. After removing each of the long upper housing and the long under housing by cutting with, the defective parts including the base material part of the reactor vessel or potential defect occurrence parts are removed, and then the base material to be the strength member. The removed part is overlay welded and restored to its original state, and then a nozzle is formed by welding on the lower side of the lower mirror through hole of the reactor vessel, and rust prevention measures are taken inside the lower mirror through hole. In this method, the long under housing is inserted into the through hole of the lower mirror from below and fixed to the nozzle by welding, and the insertion tip of the long under housing is fixed to the long upper housing by welding.

(Operation) This repair method for a long housing may cause a defect in the long housing itself such as a neutron flux monitor housing or a welded portion with the reactor vessel during the operation of the reactor, and may possibly cause a defect. In the case of a large size, the relevant part is removed together with the base metal part of the reactor vessel, and then the base material removal part that becomes the strength member is overlay welded and restored to the original, while the lower side of the lower mirror through-hole part of the reactor vessel The stub is formed by welding and rust prevention measures are taken in the through hole, then the long under housing is inserted into the through hole and fixed to the stub by welding, and the insertion end of the long under housing is inserted. Is fixed to the long upper housing to effectively and surely prevent the occurrence of reactor water leaks as a support structure having the same strength as the initial fixed support structure of the long housing.

Embodiment An embodiment of the present invention will be described below with reference to the accompanying drawings.

The boiling water reactor is equipped with a reactor pressure vessel 10 as a reactor vessel as shown in FIG.
Is supported on its support pedestal 11 via a support skirt 12. A number of control rod drive mechanisms (CRD) 13 for vertically moving control rods (not shown) in and out of the reactor core are vertically installed under the reactor pressure vessel 10 (lower mirror). The CRD housing 14 of the control rod drive mechanism 13 is the reactor pressure vessel 10
It is fixed to the lower mirror by welding. The CRD housing (long housing) 14 is made of stainless steel such as SUS304 and SUS304L.

Further, the neutron flux generated in the core of the reactor is measured and monitored by the neutron flux detector 15 in order to display the output of the reactor and evaluate the burnup. The neutron flux detector 15 is disposed in an appropriate space between the CRDs 13 and has an elongated neutron flux monitor main body 16 as shown in FIG.

The neutron flux monitor main body 16 has an elongated tubular shape, and the lower side of the neutron flux monitor guide tube 17 is a long housing and the neutron flux monitor housing (in-core monitor housing).
It extends downward through 18 and its lower end is abutted against and supported by the inner peripheral shoulder of the neutron flux monitor flange 19. The neutron flux monitor flange 19 is fixed to the lower end outer peripheral flange 18a of the neutron flux monitor housing 18 with a tightening bolt 20. The neutron flux monitor body 16 supported by the neutron flux monitor flange 19 is fixed by an in-core nut (which may be an installation tightening nut) 21.

On the other hand, the neutron flux monitor housing 18 in which the neutron flux monitor main body 16 is inserted is made of stainless steel such as SUS304, SUS304L, SUS316L.
As shown in FIG. 4, the upper portion of the reactor is passed through the through hole 23 of the reactor pressure vessel 10 using carbon steel as a base material to
It is fixed by welding from the inside.

Specifically, a stainless steel build-up portion 24 is formed by welding on the inside of the reactor pressure vessel 10 and is mirror-finished. A groove is formed on the inclined side of the through hole 23 and welded with Inconel 182 or the like to form a nozzle 25. A groove is formed on the top of this nozzle 25, and this groove is welded with Inconel 82 or Inconel 182 containing Nb (niobium), and the neutron flux monitor housing (long housing ) 18 to 25
It is fixed to and sealed. The inside of the reactor pressure vessel 10 is partitioned from the pressure boundary 27 below by the welded portion 26 of the nozzle 25.

On the other hand, since the neutron flux monitor housing 18 and the CRD housing 14 which are long housings are made of stainless steel (SUS steel), when the three conditions of stress corrosion cracking (SCC) are satisfied, Stress corrosion cracking may occur at the welded part. This stress corrosion cracking occurs, or a crack occurs due to a defect in the housing itself or a welding defect associated with poor fusion during welding, and when this crack grows and becomes large, the reactor water in the reactor pressure vessel 10 leaks outside the pressure vessel. May occur.

This reactor water leak is constantly monitored and detected by various detectors, and is detected during periodic inspections. When a reactor water leak is detected or it is predicted that a reactor water leak will occur, the following repair method will completely remove the defective part of the neutron flux monitor housing and the potential defective place,
Measures to prevent reactor water leaks are taken.

1 (A) to 1 (F) show an example of a method of repairing the neutron flux monitor housing.

This repair method is an effective means when a defect is found in the vicinity of the base metal part or the welded part of the reactor pressure vessel 10, and when carrying out the above repair method, the neutron flux monitor housing 18 or the neutron flux While removing the neutron flux monitor main body 16 from the monitor guide tube 17 by removing it, insert a faucet 28 such as a bore plug at a position corresponding to the welded portion 26 that fixedly supports the neutron flux monitor housing 18, and use this faucet 28 to remove the reactor water. Prevent the outflow of.

Subsequently, as shown in FIG. 1 (A), the neutron flux monitor housing 18 is cut above the welded portion 26 by an outside cutting electric discharge machine or the like, and the upper portion of the neutron flux monitor housing 18 (hereinafter, long upper housing 18a is removed, and the neutron flux monitor housing 18 is similarly cut below the welded portion 26 by an internal cutting electric discharge machine or the like, and an under portion of the neutron flux monitor housing 18 (hereinafter referred to as a long under housing) is cut. 18b is pulled downward from the lower mirror through hole 23 of the reactor pressure vessel 10.

Then, the ultrasonic internal flaw detector (UT device), the penetration flaw detector (PT device), the visual detector (VT device), etc. are remotely operated to specify the defect portion A. In addition to identifying this defective portion A, the lower part of the through hole 23 is provided with a faucet such as a bore plug.
Seal with 29.

Then, if necessary, the boat sump 30a, 30
In order to collect b, as shown in FIG. 1 (B), the welded portion 26 is removed together with the remaining neutron flux monitor housing 18c by a welded portion removing (general-purpose electrode) electric discharge machine or the like. After this removal, the boat samples 30a and 30b of the required portions are collected as test pieces by a cylindrical boat sample electric discharge machine or the like. It is not necessary to collect the boat samples 30a and 30b.

After collecting the boat samples 30a, 30b or when the boat samples are not needed, after removing the long upper and the under housings 18a, 18b by cutting, the reactor pressure vessel 10 by the electric discharge machine for defect removal of the full-scale electrode, etc. The defect portion A including the base material portion is completely removed. After removing the defective portion A, the removed base material surface is smoothly formed into a groove state,
This groove surface B is inspected with a penetrant inspection tester (PT device) or a visual tester (VT device).

After inspecting the base material groove surface B of the reactor pressure vessel 10, the reactor water in the reactor pressure vessel 10 is removed. After removing the reactor water, the guide pipe 32 is inserted into the through hole 23 of the reactor pressure vessel 10, and the base material groove surface B is inserted in the guide pipe inserted state.
3D build-up welding of low alloy steel, which is a sound material with SCC countermeasures, is performed by the Temper Bead method using a 3D build-up welding machine to form the build-up welded portion 33. At this time,
The heater 34 is energized for local heating, and hydrogen remaining in the base material portion is released from the groove surface B.

After the overlay welding on the groove surface B of the base metal portion by the three-dimensional overlay welding machine, the guide pipe 32 is removed, and the surface of the overlay welding portion 33 is surface-processed by the electric discharge machine of the full-scale electrode or the like. Surface finishing of the overlay welding portion 33 of the low alloy steel is performed as shown in FIG. 1 (C). The build-up welded portion 33 restores and maintains the mechanical strength of the base metal portion of the reactor pressure vessel 10 to the original state. At that time, the surface of the weld overlay 33 is remotely inspected in the reactor pressure vessel 10 by the UT device or the PT device.

Then, as shown in FIG. 1 (D), the reactor pressure vessel
The outer surface of the reactor pressure vessel on the lower side of the through hole was ground with 10 outer surface grinding machines, and Inconel 82, Inconel 182, etc. were overlay welded to the ground outer surface using a two-dimensional external surface overlay welding machine. To form a weld overlay 35. The guide pipe 32 may be removed after this overlay welding.

Further, as shown in FIG. 1 (E), the reactor pressure vessel 10
After finishing the inner surface of the through-hole by using the electric discharge machine for hole-machining in the through-hole 23, the Inconel 82 and Nb-containing Inconel 182 by the Temper Bead method using the through-hole overlay welding machine etc. And the like to form the weld overlay 36. After the above overlay welding, the overlay surface of the through hole 23 is formed by using an electric discharge machine for forming, etc., and rustproofing is applied to the inner surface of the through hole.

On the other hand, a nozzle 37 is formed by forming the surface of the overlay welding portion 35 obtained by overlay welding on the lower outer surface of the reactor pressure vessel 10 by using an electric discharge machine for overlay forming of the overlay seat. . This stub
The center of the tip of 37 is J-groove machined by a standard electric discharge machine. Each machined surface is inspected by UT equipment and PT equipment.

Next, a new elongated under housing 38 is inserted from below through the through hole 23 of the reactor pressure vessel 10, and
Long upper housing 39 (This long upper housing 39
Is the long upper housing 18 cut and removed in FIG. 1 (A).
It may be a or a neutron flux monitor guide tube 17. ), The groove is machined by using a groove electric discharge machine or the like. The long upper housing 39 is inserted until the insertion tip of the long under housing 38 comes into contact with and fits.

After this insertion, the long under housing 38 is welded and fixed to the nozzle 37 via the weld 40. By fixing the long under housing 38 via the welded portion 40, the interior of the reactor pressure vessel 10 is partitioned from the lower pressure boundary. After that, the long under housing 38 is butted against the long upper housing 39 and welded. Each weld is inspected by the UT device or the PT device, and the repair work of the neutron flux monitor housing 18 is completed.

After this repair work, the neutron flux monitor housing 18
The neutron flux monitor main body 16 is inserted therein and is fixedly supported.

In the embodiment of the present invention, the method of repairing the neutron flux monitor housing has been described, but the same can be applied to the case of the CRD housing.

〔The invention's effect〕

As described above, in the method for repairing a long housing such as the neutron flux monitor housing according to the present invention, a defect may occur in the welding portion of the long housing itself or the reactor vessel, and there is a possibility that a defect may occur. In the case of a large size, the relevant part is removed together with the base material, and the base material removal part that is the strength member is overlay welded to maintain the strength, while the nozzle stub is fixed by welding to the lower mirror side of the reactor vessel. Since the long housing was fixed via the welded part of this nozzle, defects and potential defect-causing parts were completely removed, and it had the same mechanical strength as the initial support structure of the long housing. The support structure can be restored, reactor water leaks can be effectively and reliably prevented, and permanent leak prevention measures can be taken.

[Brief description of drawings]

1 (A) to 1 (F) are operation step diagrams showing an embodiment of a method for repairing a long housing according to the present invention, FIG. 2 is a diagram showing a lower structure of a boiling water reactor, and FIG. Is a diagram showing a neutron flux detector fixedly supported by the reactor pressure vessel of FIG. 2, and FIG. 4 is a diagram showing a mounting structure for fixing and supporting a neutron flux monitor housing of the neutron flux detector to the reactor pressure vessel. FIG. 5 is a diagram schematically showing an installation example of a neutron flux detector attached to a conventional boiling water reactor. 3 ... Reactor core, 5 ... Upper lattice plate, 10 ... Reactor pressure vessel, 13 ... Control rod drive mechanism, 14 ... CRD housing, 15
…… Neutron flux detector, 16 …… Neutron flux monitor main body, 17…
… Neutron flux monitor guide tube, 18 …… Neutron flux monitor housing, 18a …… Long under housing, 18b …… Long upper housing, 23 …… Through hole, 25 …… Stubstock (welded part),
26 …… Welded area, 28,29 …… Water faucet, A, A ₁ … Defective area, 30…
… Mounting seat, 32 …… Guide pipe, 33,35,36 …… Overlay weld, 34 …… Heater, 37 …… Stubstock, 38 …… Long under housing, 39 …… Long aper housing, 40 ……welded part.

 ─────────────────────────────────────────────────── ─── Continued Front Page (72) Inventor Masahiro Kobayashi 1-1-1, Shibaura, Minato-ku, Tokyo Inside Toshiba Headquarters office (72) Inventor Masaru Takahashi 1-1-1, Shibaura, Minato-ku, Tokyo Stock company Toshiba Head Office

Claims (1)

(57) [Claims] 1. A long housing, such as a neutron flux monitor housing, which is fixedly supported on a lower mirror welded portion of a reactor vessel, is cut above and below the welded portion to remove the long upper housing and the long under housing. After that, the defective part including the base metal part of the reactor vessel or the part where potential defects could occur is removed, and then the base material removal part that is the strength member is welded to the original to restore it. A nozzle is formed by welding on the lower side of the lower mirror through hole of the furnace vessel and rust prevention measures are taken in the lower mirror through hole, and then a long under housing is inserted from below into the lower mirror through hole. A method for repairing a long housing, characterized in that the long under housing is fixed to the nozzle by welding and the insertion tip of the long under housing is fixed to the long upper housing by welding.