JPH0298697A - Method for repairing neutron flux monitor housing - Google Patents

Abstract

PURPOSE:To prevent the degradation in corrosion resistance by cutting an existing neutron monitor housing from the part lower than the welded padding seat thereof, subjecting the weld zone to an annealing heat treatment and welding a housing for exchange to a transition piece. CONSTITUTION:The end of the cut ICM housing 3 is formed by finishing the inside surface thereof smooth so that an instrumentation tube moving therein can smoothly move into and out of the housing. The transition piece 3B is inserted into the expanded through-hole 1A at the bottom end 1D of an RPV and the weld zone 4E of the transition piece is welded by a remote controlled automatic welding machine. The ICM housing 3 consisting of an SUS 304 material having the possibility of degrading the corrosion resistance is averted from the heat treating position by cutting and the transition piece 3B is interposed between this housing and the ICM housing 3A for exchange at the point to be directly inserted to the inside surface of the through-hole 1A, by which the weld zone can be exposed at the time of the heat treatment, therefore, the heat treatment (annealing) after the local welding with the high workability and high reliability is possible.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention is directed to the use of a neutron flux monitor housing (hereinafter referred to as ICM housing) in a nuclear reactor pressure vessel (hereinafter referred to as RPV) during the service life of a nuclear power plant. The present invention relates to a repair method, and particularly to a relatively easy repair method for an ICM housing.

[Conventional technology]

The ICM housing of the RPV of the boiling water reactor has a structure as shown in FIG. That is, a through hole IA is provided in the RPV lower mirror ID which is overlay welded using Inconel material or the like, and the weld overlay seat 2 is attached so as to communicate with the through hole IA. R on this weld overlay seat 2
An ICM housing 3 is welded through a welded portion 4 through the ID wall of the PV lower mirror.

Conventional boiling water reactor ICM housing 3 is 5US
304 series steel pipes are used, and assuming that a through crack 4A occurs at or near the welded part 4 of the ICM housing 3 and there is a possibility that reactor cooling water may leak, the IC
It is necessary to establish a repair method for the M housing 3 in advance.

As a countermeasure against the above possibility, Utility Model No. 56-82696
According to the publication, in order to prevent leakage as shown in Figure 6, the upper end is connected to the lower head plate ID of the reactor pressure vessel, and the lower end is connected to I.
There is a method of attaching the cylindrical adapter 6 by forming a lower mirror welding part 4B and an adapter welding part 4C on the CM housing 3, respectively.

[Problem to be solved by the invention]

However, with the above-mentioned conventional measures, post-weld annealing heat treatment is required for the lower mirror weld 4B, which is the weld to the reactor pressure vessel, which is the most important equipment, and in order to satisfy this requirement, the lower mirror weld 4B When heat treatment is applied to the IJ, the heat is transferred toward the ICM housing.) There is a possibility that the quality of the IJ and ICM housing 3 deteriorates to a state where the corrosion resistance is poor due to the heat treatment of the lower mirror weld portion 4B.

SUMMARY OF THE INVENTION An object of the present invention is to provide a method for repairing an ICM housing in which the ICM housing can be repaired while minimizing deterioration in quality.

[Means to solve the problem]

The present invention achieves the above object by penetrating the wall of the reactor pressure vessel and inserted into the inner side of a cylindrical weld overlay seat attached to the inner surface of the reactor pressure vessel.

A method for repairing an existing cylindrical neutron flux monitor housing that is connected to the weld overlay seat at a welded portion.

The existing neutron flux monitor housing is cut from a portion below the weld overlay seat, and the inner diameter of the through hole of the neutron flux monitor housing is cut from the outer surface of the lower mirror of the reactor pressure vessel. Extend cutting to a depth just before the end, insert a transition piece with a larger outer diameter than the existing neutron flux monitor housing into the enlarged diameter through-hole from the bottom of the reactor pressure vessel, and weld the welded part. This is a method for repairing a neutron flux monitor housing, characterized by applying an annealing heat treatment to the transition piece, and then welding and assembling a replacement housing to the transition piece.

[Effect]

The effect of the invention of the present application is that when a transition piece is welded to the reactor pressure vessel at the in-plane penetration position and annealing heat treatment is applied to the welded portion, a replacement housing is welded and attached to the transition piece after the heat treatment. Therefore, the heat of the heat treatment is not transferred to the replacement housing, and the corrosion resistance of the replacement housing is not deteriorated.

〔Example〕

An embodiment of the present invention will be described below with reference to FIGS. 1 to 5.

Figure 4 shows RPVl showing the RI) V of a boiling water reactor.
is R1) V fuselage 1. C, RPV lower mirror ID and RPV
It consists of an upper lid (not shown). The RPVI is fixed by a skirt 5 on a pedestal (not shown) of the reactor containment vessel. The ICM/N housing 3 is fixed to the RPV lower mirror ID.

FIG. 3 shows a cross-sectional view of the ICM housing 3 fixedly attached to the RPV lower mirror ID. An overlay part IB of Inconel is formed on the inner surface of the RPV lower 1 [D, and a weld overlay seat 2 is overlay welded onto this overlay part IB. Said IC
The M housing 3 passes through the RPV lower mirror ID and is fixed to the weld overlay seat 2 by a weld portion 4. When a through crack 4A occurs in the ICM housing 3 at or near the welded portion 4, a path 12 through which the coolant leaks is assumed.

According to the embodiment shown in FIG. 1, the ICM housing 3 is cut at a portion below the cylindrical weld overlay seat 2 attached to the inner surface of the reactor pressure vessel 1, and the through hole IA of the ICM housing 3 is cut. Expand by cutting. The depth of the enlarging process shall be up to the position in front of the cut CM housing end. The cutting process performed here is performed by a sealing device 11 shown in FIG. 5 to treat drainage around the ICU housing, and by a remote-controlled processing machine 9 from below the RPVL. The cut end of the ICM housing 3 is
As shown in Figure 1, the inner surface is smoothed so that the instrumentation tube that moves inside can be carried in and out smoothly. Next, RPV
Insert the transition bead 3B into the enlarged through hole IA of the lower mirror ID.

The transition piece welding portion 4E is welded using a remote-controlled automatic welding machine, and here, the welding portion is locally subjected to post-weld heat treatment (annealing). This heat treatment is necessary to relieve stress in the welded part, and the ICM housing 3, which is made of 5US304 material that may cause a decrease in corrosion resistance due to heat treatment, is avoided from the heat treatment by cutting, and the inner surface of the through hole IA is directly cut. By intervening the transition piece 3B between the replacement ICM housing 3A where welding is to be performed, the welded area can be exposed during heat treatment, allowing for localized post-weld heat treatment (annealing) with high workability and reliability. It has become.

Unlike S tJ S 304, the characteristic of Inconel used for transition piece 3B is that it is less susceptible to deterioration of corrosion resistance due to heat treatment. It is possible to attach the replacement ICM housing 3A without causing any thermal effects.

After that, finish the surface of the welded part smoothly, and after R, attach the replacement ICM housing 3A to the 1-transition bead 3.
Weld to B and complete the repair work.

The above-mentioned cutting and finishing will be performed using a remote-controlled processing machine, and welding will also be performed using a remote-controlled welding machine.

Although FIG. 1 shows an example in which Inconel is used for the transition piece 3B, FIG. 2 shows an example in which carbon steel is used for the transition piece 3B.

The working method is the same as the example shown in Fig. 1, but when low-alloy steel is used for the transition piece 3B, Inconel overlay 8 is applied to the lower side of the transition piece 3B, and the replacement ICM is
A welding groove is formed to connect with the housing 3A. By using this Inconel overlay 8, it becomes possible to perform repair work on the ICM housing 3 in which the replacement ICM housing 3A is made of highly corrosion-resistant stainless steel such as 5US316L material.

According to the present invention, local post-weld heat treatment accompanying repair welding, 1 (
The ICM housing below the RP V bottom roughness can be easily replaced with a new product with high corrosion resistance, increasing the reliability of the product after repair.
Since the ICM housing can be repaired by remote control, it is possible to obtain a relatively easy and effective repair method that can minimize radiation exposure to workers.

〔Effect of the invention〕

As described above, according to the present invention, the reliability of the neutron flux monitor housing is maintained high even after repair, and the safety of the nuclear reactor is high.

[Brief explanation of the drawing]

FIG. 1 is a sectional view of the ICM housing after repair, which is an embodiment of the present invention. FIG. 2 is a sectional view of the ICM housing after repair, which is an embodiment using an alternative to that shown in FIG. Figure 4 is a cross-sectional view of the ICM housing for explaining the outline of the repair method, Figure 4 is a cross-sectional view of the RPV lower structure, Figure 5 is a diagram explaining the remote operation method used for repair work, Figure 6 is the ICM for explaining the conventional repair method. FIG. 3 is a sectional view of the housing. ■...Reactor pressure vessel, IA...through hole, IB...
・Meat filling. IC...RPV fuselage, ID...R, PV lower mirror, 2
...Weld overlay seat, 3...ICM housing, 3A...
・Replacement ICM housing, 3B...Transition piece, 4...Welded part, 4A...Through crack, 4B...
...Lower mirror welding part. 4C...Adapter welding part, 4D...Replacement ICM housing welding part, 4E...Transition piece welding part, 5...Skirt, 6...Adapter, 7...
Stub tube, 8... Inconel overlay, 9... Remote controlled processing machine, 10... Remote controlled welding machine, 11.
...Water seal device, 12...Leakage route, 13...Core support plate.

Claims (1)

[Claims] 1. A cylindrical weld pad that is inserted into the inner side of the cylindrical weld pad installed on the inner surface of the reactor pressure vessel through the wall of the reactor pressure vessel, and is connected to the weld pad at a welded portion. A method for repairing an existing neutron flux monitor housing, wherein the existing neutron flux monitor housing is cut from a portion below the weld overlay seat, and the inner diameter of the through hole of the neutron flux monitor housing is adjusted to the inner diameter of the through hole of the reactor pressure vessel. Extend cutting to a depth in front of the end of the neutron flux monitor housing cut from the outer surface of the lower mirror, and insert a transition piece with an outer diameter larger than the existing neutron flux monitor housing into the enlarged diameter through hole into the reactor pressure vessel. A method for repairing a neutron flux monitor housing, the method comprising: inserting and welding a neutron flux monitor housing from below, subjecting the welded portion to annealing heat treatment, and then welding and assembling a replacement housing to the transition piece.