JP5437920B2 - Reactor pressure vessel safe-end thermal sleeve repair method - Google Patents

Description

  The present invention relates to a BWR reactor pressure vessel, and in particular, to prevent replacement of a safe end and a thermal sleeve or prevent stress corrosion cracking at the time of occurrence of stress corrosion cracking in a weld joint of a nozzle and a safe end of the reactor pressure vessel. The present invention relates to a method for replacing a safe end with improved material and a thermal sleeve.

  FIG. 7 is a vertical cross-sectional view of the reactor pressure vessel with its top cover opened. As shown in the figure, some nozzles 1 provided on the peripheral wall of the reactor pressure vessel 10 have an inner tube called a thermal sleeve 5 for flowing a fluid inside the reactor. Since this thermal sleeve 5 needs to be adjusted with the in-furnace piping 11, it is attached to the inside of the safe end 2 by welding from the inside of the furnace in consideration of workability at the time of plant construction. Reference numeral 19 in the figure is a core shroud, and 20 is a jet pump.

In addition, the safe end described in the present specification indicates a short pipe for connecting the nozzle and the outside piping.
Typical examples of the nozzle 1 include a recirculation water inlet nozzle which is a loop path for circulating the reactor water in the reactor, a water supply nozzle for supplying water into the reactor, and a core spray nozzle for injecting water into the reactor core in an emergency. is there.

  In old reactor pressure vessels, the welded portion between the nozzle 1 and the safe end 2 and the welded portion between the safe end 2 and the thermal sleeve 5 may be made of a material susceptible to stress corrosion cracking. Due to the tensile residual stress, stress corrosion cracking (SCC) may occur inside during long-term operation. In this case, it is necessary to remove the safe end 2 and the thermal sleeve 5 and replace them with the safe end 2 and the thermal sleeve 5 made of a material having excellent SCC resistance.

  However, since the furnace pipe 11 is connected to the tip of the thermal sleeve 5 and the inside of the furnace is a space where radiation is strong, access to the nozzle 1 is from outside the furnace. There is the following reason why the replacement is not possible without inserting 5.

  The welded portion of the nozzle 1 and the safe end 2 is inspected by finishing the inner and outer surfaces after welding in order to ensure high quality. In order to finish and inspect the inner surface, the thermal sleeve 5 cannot be used without it.

  Further, the welded portion between the thermal sleeve 5 and the safe end 2 needs to be subjected to butt welding with complete penetration in order to prevent formation of clevis (defect), and the safe end 2 has a groove formed on the inner surface, So that the welded portion of the safe end 2 and the nozzle 1 can be inspected from the inner surface side with respect to the position of the butt welding. The structure is such that

  Incomplete penetration welding, such as socket welding, to prevent crevice corrosion at the clevis (defect) part and increase the possibility of stress corrosion cracking, and to prevent fatigue due to vibration Further, the above-described structure is adopted.

  Therefore, the safe end 2 is formed with a groove on the inner surface so that it can be butt welded to the thermal sleeve 5, and the butt welding position at the time of plant construction is set up and welded between the safe end 2 and the nozzle 1. Is determined to be on the pipe side (outside) from the welding position of the safe end 2 and the nozzle 1 so that inspection can be performed from the inner surface side.

  For this reason, conventionally, in order to finish and inspect the inner surface after mounting the safe end 2 and to inspect the thermal sleeve 5, the only way to do this is during a large construction for replacing the furnace equipment such as shroud replacement. There wasn't.

  For example, the following patent literature can be cited as a safe end replacement method in a nuclear pressure vessel.

JP 59-199295 A

  By the way, as a recent countermeasure against stress corrosion cracking, improvement of residual stress is regarded as important. This is because, for example, a material such as SUS316 that hardly causes sensitization causes stress corrosion cracking, and it is considered that not only material improvement but also stress improvement is necessary.

  Examples of methods for improving this residual stress include polishing and peening. In order to apply polishing or peening as a method for improving the residual stress on the inner surface of the welded part between the nozzle and the safe end, it must be accessible after welding.

  That is, from the above, it is necessary to replace the safe end with the thermal sleeve after attaching the safe end first, finishing and inspecting the inner surface of the welded part, performing residual stress improvement work, etc. There was no way to access and replace only from outside the furnace.

  In order to solve such problems, the object of the present invention is an atom that can be accessed from outside the furnace, can replace the safe end and the thermal sleeve, and can improve the residual stress on the inner surface of the welded portion of the nozzle and the safe end. The object is to provide a method for repairing a safe-end thermal sleeve of a furnace pressure vessel.

In order to achieve the above object, the first means of the present invention comprises:
A nozzle is provided at a predetermined position on the peripheral wall of the reactor pressure vessel, and a piping outside the reactor is connected to the nozzle via a safe end, and a thermal sleeve is disposed inside the safe end, and one end of the thermal sleeve is provided. The present invention is directed to a method for repairing a safe-end thermal sleeve of a reactor pressure vessel whose portion is welded to the inner peripheral portion of the safe-end.

And a step of preparing a new safe end in which a thermal sleeve mounting weld groove having an inner diameter larger than the outer diameter of the weld groove of the thermal sleeve protrudes from the inner peripheral portion;
A safe end detachment step in which an existing safe end is disconnected from the nozzle, the outside pipe and the thermal sleeve, and
A nozzle and a new safe end butt welding step for forming a butt welding groove in each joint portion of the nozzle and the new safe end, and performing a butt welding of the nozzle and the new safe end;
Inserting a thermal sleeve from outside the reactor pressure vessel into the new safe end and butt-welding the new safe end thermal sleeve mounting weld groove and the thermal sleeve weld groove And an end thermal sleeve butt welding process.

According to a second means of the present invention, in the first means,
The thermal sleeve that is inserted inside the new safe end and is butt welded to the safe end is also a new thermal sleeve.

A third means of the present invention is the first or second means,
The thermal sleeve and the safe end weld are on the outer side of the reactor pressure vessel than the nozzle and the safe end weld,
Between the nozzle and new safe end butt welding process, and the new safe end thermal sleeve butt welding process,
A residual stress improving process for performing a residual stress improving process is added to the inner surface of the butt weld between the nozzle and the new safe end.

A fourth means of the present invention is the first or second means,
The thermal sleeve and the safe end weld are on the outer side of the reactor pressure vessel than the nozzle and the safe end weld,
Between the nozzle and new safe end butt welding process, and the new safe end thermal sleeve butt welding process,
A corrosion-resistant build-up welding process for performing corrosion-resistant build-up welding is added to the inner surface of the butt weld portion between the nozzle and the new safe end.

According to a fifth means of the present invention, in the third means,
Between the corrosion-resistant overlay welding process and the new safe end thermal sleeve butt welding process,
A residual stress improving process for performing a residual stress improving process is added to the inner surface of the corrosion-resistant overlay weld.

The sixth means of the present invention includes
Preparing a new thermal sleeve having a weld groove in one opening;
A thermal end detachment process in which an existing thermal sleeve is disconnected from the thermal end and detached,
Protruding a thermal sleeve mounting weld groove having an inner diameter larger than the outer diameter of the weld groove of the new thermal sleeve by overlay welding with a temper bead on the inner peripheral portion of the existing safe end;
Inserting the new thermal sleeve from the outside of the reactor pressure vessel to the inside of the existing safe end, and attaching the existing safe end thermal sleeve and a welding groove of the new thermal sleeve; Including a safe end butt welding process and a novel thermal sleeve butt welding process.

  The present invention is configured as described above, and it is possible to replace the safe end and the thermal sleeve only by accessing from the outside of the furnace without replacing the in-furnace equipment (core shroud, etc.), and the welded portion between the nozzle and the safe end. It is possible to provide a method for repairing a safe-end thermal sleeve that can improve the residual stress on the inner surface.

It is sectional drawing of the nozzle, the safe end, and thermal sleeve vicinity which concern on Example 1 of this invention. It is an expanded sectional view showing a state with time until a thermal sleeve is welded to a safe end. It is a partial perspective view of the insert ring used in the Example of this invention. In Example 1 of this invention, it is process drawing which shows the process until it attaches a novel thermal sleeve. It is sectional drawing of the nozzle which concerns on Example 2 of this invention, a safe end, and thermal sleeve vicinity. It is sectional drawing of the nozzle which concerns on Example 3 of this invention, and the safe end vicinity. It is sectional drawing in the state which open | released the upper cover of the reactor pressure vessel which is the object apparatus of this invention.

In the present invention, as described above, a nozzle is provided at a predetermined position on the peripheral wall of the reactor pressure vessel, and an external piping is connected to the nozzle through a safe end, and a thermal sleeve is disposed inside the safe end. In the method for repairing the safe-end thermal sleeve of the reactor pressure vessel in which one end of the thermal sleeve is welded to the inner periphery of the safe-end,
Preparing a new safe end in which a thermal sleeve mounting welding groove having an inner diameter larger than the outer diameter of the welding groove of the thermal sleeve is provided on the inner peripheral portion; and
A safe end detachment step in which an existing safe end is disconnected from the nozzle, the outside pipe and the thermal sleeve, and
A nozzle and a new safe end butt welding step for forming a butt welding groove in each joint portion of the nozzle and the new safe end, and performing a butt welding of the nozzle and the new safe end;
Inserting a thermal sleeve from outside the reactor pressure vessel into the new safe end and butt-welding the new safe end thermal sleeve mounting weld groove and the thermal sleeve weld groove And an end thermal sleeve butt welding process.

Thus, even without the shroud replacement work, the inner surface of the safe end welded portion can be maintained after the safe end is attached, the stress can be improved, and the thermal sleeve can be butt welded to the safe end.
Next, each embodiment of the present invention will be described with reference to the drawings.

  FIG. 1 is a cross-sectional view of the vicinity of a nozzle, a safe end, and a thermal sleeve according to a first embodiment of the present invention.

  As shown in FIG. 1, a nozzle 1 is attached to a predetermined position of the peripheral wall of the pressure vessel 1, and one groove of the safe end 2 is butt welded to the groove of the nozzle 1. In addition, a thermal sleeve base 4 protrudes from a predetermined position on the inner peripheral portion of the safe end 2, and one groove 5 a of the thermal sleeve 5 is butt welded to the thermal sleeve base 4. Further, an in-furnace pipe 11 is welded to the other groove 5 b of the thermal sleeve 5.

  In the figure, reference numeral 3 is a welded portion between the nozzle 1 and the safe end 2, 6 is a welded portion between the safe end 2 and the thermal sleeve 5, 14 is a groove formed on the inner surface of the safe end 2, and 15 is a thermal sleeve 5 and a furnace. This is a welded portion of the inner pipe 11.

  As shown in the drawing, the welded portion 3 between the nozzle 1 and the safe end 2 is outside the welded portion 3 between the nozzle 1 and the safe end 2 so that the residual stress improvement process such as peening and polishing can be performed from the inner surface. The thermal sleeve base 4 is provided in a protruding manner. Further, the welding of the safe end 2 and the thermal sleeve 5 is a butt welding that can be completely dissolved.

FIGS. 2A, 2 </ b> B, and 2 </ b> C are enlarged cross-sectional views showing a state over time until the thermal sleeve 5 is welded to the safe end 2.
As shown in FIG. 2 (a), a thermal sleeve base portion 4 is provided at a predetermined position on the inner peripheral portion of the safe end 2 so as to protrude slightly inward, and the inner periphery of the base portion 4 is provided. The part is a groove 4a.

  In this embodiment, an example is shown in which the thermal sleeve 5 is also replaced with a new one as the new safe end 2 is replaced. The new thermal sleeve 5 passes from the outside of the furnace through the safe end 2 in the direction of the arrow. In order to insert, the inner peripheral surface of the groove 4a extends straight along the axial direction of the safe end 2 so that the insertion is not hindered.

  On the other hand, the groove 5a provided at the rear end portion in the insertion direction of the thermal sleeve 5 is deformed so as to slightly protrude outward in the radial direction of the thermal sleeve 5, as shown in FIG. The inner diameter ds of the inner peripheral surface of the groove 4a of the safe end 2 is designed to be slightly larger than the outer diameter dt of the groove 5a of the thermal sleeve 5 (ds>) so that the thermal sleeve 5 can be inserted through the safe end 2. dt). Further, since the base portion 4 is provided so as to be inclined slightly toward the inside, the thermal sleeve 5 is smoothly inserted by the guide of the base portion 4.

  When the thermal sleeve 5 is inserted to a predetermined position of the safe end 2 as will be described later, the inner peripheral surface of the groove 4a of the safe end 2 and the groove 5a of the thermal sleeve 5 are placed as shown in FIG. An annular groove-shaped welding space 16 having a trapezoidal (or triangular) cross-section surrounded by both grooves 4a and 5a is formed so that the end faces are substantially orthogonal.

  After inserting the thermal sleeve 5, an insert ring 17 is inserted and installed on the back side of the welding space 16. As shown in FIG. 3, the insert ring 17 has a trapezoidal shape (this embodiment) or an annular shape having a triangular shape. When the insert ring 17 is installed on the back side of the welding space 16, one peripheral surface of the insert ring 17 is a safe end. 2 is in close contact with the inner peripheral surface of the groove 4a, and the other peripheral surface of the insert ring 17 is in close contact with the rear end surface of the groove 5a of the thermal sleeve 5, thereby closing the opening (gap) on the back side of the welding space 16. (See FIG. 2B).

  After installation of the insert ring 17, the groove 4a of the safe end 2 and the groove 5a of the thermal sleeve 5 are butt welded. Since the insert ring 17 is made of the same material as the welding material, the insert ring 17 is heated and melted during welding to form an initial layer and a back wave, and finally, as shown in FIG. The cross-sectional shape becomes a part of a trapezoidal (this embodiment) or triangular annular welded portion 6, and the safe end 2 and the thermal sleeve 5 can be reliably welded.

FIG. 4 is a process diagram showing a process until a new thermal sleeve 5 is attached.
As shown in the figure, first, in step (hereinafter abbreviated as S) 1, the existing outside pipe 7 (see FIG. 5) is cut and detached (removed), and in S 2, the existing safe end 2 is connected to the nozzle 1. Then, the existing thermal sleeve 5 is cut and separated at S3.

  Next, in S4, the nozzle 1 and the new safe end 2 are butt-welded, and in S5, the inner surface of the welded portion 3 of the nozzle 1 and the new safe end 2 is mechanically finished with a grinder or the like, and the welded portion 3 is peened. Apply residual stress improvement treatment such as polishing and polishing.

  Next, as shown in FIG. 2A, a new thermal sleeve 5 in which the outer diameter (dt) of the groove 5 a is smaller than the inner diameter (ds) of the root portion 4 of the safe end 2 is inserted in the direction of the arrow from the inner side of the safe end 2. The base 4 of the safe end 2 and the groove 5a of the thermal sleeve 5 are butt-welded to complete the attachment of the new thermal sleeve 5.

  FIG. 5 is an enlarged cross-sectional view of the main part in the vicinity of the nozzle, the safe end, and the thermal sleeve according to the second embodiment of the present invention.

  In the present embodiment, the safe end 2 is made of a material that is difficult to cause sensitization, such as SUS316 stainless steel, and the groove 14 (gap) between the safe end 2 and the thermal sleeve 5 is relatively narrow. .

  As shown in the figure, after the butt-welded new safe end 2 that has been replaced is welded to the nozzle 1, the old welded portion buttering 9 is subjected to a corrosion-resistant buildup 12 made of a material such as 82 alloy, and the corrosion-resistant buildup 12 Improve residual stress such as peening and polishing. Thereafter, the thermal sleeve 5 is inserted from the outside of the furnace in the same manner as in the first embodiment, and the groove 5a of the thermal sleeve 5 and the root portion 4 of the safe end 2 are butt welded. The cross-sectional shape of the welded portion 6 between the safe end 2 and the thermal sleeve 5 is trapezoidal or triangular like the first embodiment, and extends in a ring shape in the circumferential direction.

  Reference numeral 7 in the drawing is an out-furnace pipe, which is attached to the safe end 2 via a pipe weld 8. Reference numeral 18 denotes a corrosion-resistant build-up part formed on the inner surface of the nozzle 1 in order to shut off the old welded part buttering 9 having SCC sensitivity from the reactor water.

  The process until the new thermal sleeve 5 is attached is substantially the same as the process described in the first embodiment (see FIG. 4).

  FIG. 6 is an enlarged cross-sectional view of the main part in the vicinity of the nozzle and the safe end according to the third embodiment of the present invention. In this embodiment, the safe end 2 is made of ferritic steel and only the thermal sleeve 5 is replaced.

  The existing safe end 2 is left as it is, and the existing thermal sleeve 5 is cut off from the safe end 2 and separated.

  Thereafter, as shown in the figure, a temper-bead overlay welded portion 13 is provided by temper-bead welding on the inner peripheral portion of the existing safe end 2 to form a root portion 4 protruding inside the safe end 2. The temper bead overlay weld 13 (base 4) is processed into a butt weld groove 4a having a predetermined shape. The inner diameter ds of the groove 4a is designed to be slightly larger than the outer diameter dt of the groove 5a of the thermal sleeve 5 (not shown) as in the first embodiment (ds> dt).

  A new thermal sleeve 5 (not shown) that is exchanged through the inside of the temper bead build-up weld 13 is inserted and butt welded to the temper bead build-up weld 13 on the safe end 2 side. The thermal sleeve 5 is attached to the safe end 2.

  In the second and third embodiments, the insert ring 17 is used for welding the safe end 2 and the thermal sleeve 5 as in the first embodiment.

1 ... Nozzle,
2 ... Safe end,
3 ... Nozzle and safe end welds,
4 ... The root,
4a: groove at the base,
5 ... Thermal sleeve,
5a, 5b ... groove of the thermal sleeve,
6 ... welded part of safe end and thermal sleeve,
7 ... external piping,
8: Pipe welded part,
9 ... Existing buttering,
10 ... Reactor pressure vessel,
11 ... Furnace piping,
12 ... Corrosion-resistant buildup,
13: Temper bead overlay weld,
14 ... groove,
15 ... The welded portion of the thermal sleeve and furnace piping,
16 ... welding space,
17 ... Insert ring,
18: Corrosion-resistant overlay,
19: Core shroud,
20: Jet pump,
ds ... the inner diameter of the groove inner peripheral surface of the base portion of the safe end,
dt: The outer diameter of the groove of the thermal sleeve.

Claims (6)

A nozzle is provided at a predetermined position on the peripheral wall of the reactor pressure vessel, and a piping outside the reactor is connected to the nozzle via a safe end, and a thermal sleeve is disposed inside the safe end, and one end of the thermal sleeve is provided. In the repair method of the safe end thermal sleeve of the reactor pressure vessel in which the part is welded to the inner periphery of the safe end,
Preparing a new safe end in which a thermal sleeve mounting welding groove having an inner diameter larger than the outer diameter of the welding groove of the thermal sleeve is provided on the inner peripheral portion; and
A safe end detachment step in which an existing safe end is disconnected from the nozzle, the outside pipe and the thermal sleeve, and
A nozzle and a new safe end butt welding step for forming a butt welding groove in each joint portion of the nozzle and the new safe end, and performing a butt welding of the nozzle and the new safe end;
Inserting a thermal sleeve from outside the reactor pressure vessel into the new safe end and butt-welding the new safe end thermal sleeve mounting weld groove and the thermal sleeve weld groove A repair method for a safe-end thermal sleeve of a reactor pressure vessel, comprising: an end-thermal sleeve butt welding process. In the repair method of the safe end thermal sleeve of the reactor pressure vessel according to claim 1,
A method of repairing a safe-end thermal sleeve of a reactor pressure vessel, wherein a thermal sleeve inserted into the new safe end and butt welded to the safe end is also a new thermal sleeve. In the repair method of the safe end thermal sleeve of the reactor pressure vessel according to claim 1 or 2,
The thermal sleeve and the safe end weld are on the outer side of the reactor pressure vessel than the nozzle and the safe end weld,
Between the nozzle and new safe end butt welding process, and the new safe end thermal sleeve butt welding process,
A method for repairing a safe-end thermal sleeve of a reactor pressure vessel, comprising the step of adding a residual-stress improving process for performing a residual-stress improving process on the inner surface of a butt weld of the nozzle and a new safe-end. In the repair method of the safe end thermal sleeve of the reactor pressure vessel according to claim 1 or 2,
The thermal sleeve and the safe end weld are on the outer side of the reactor pressure vessel than the nozzle and the safe end weld,
Between the nozzle and new safe end butt welding process, and the new safe end thermal sleeve butt welding process,
A method of repairing a safe-end thermal sleeve of a reactor pressure vessel, characterized by adding a corrosion-resistant overlay welding process for performing corrosion-resistant overlay welding on the inner surface of a butt weld between the nozzle and a new safe end. In the repair method of the safe end thermal sleeve of the reactor pressure vessel according to claim 3,
Between the corrosion-resistant overlay welding process and the new safe end thermal sleeve butt welding process,
A method of repairing a safe-end thermal sleeve of a reactor pressure vessel, wherein a residual stress improvement treatment step of performing a residual stress improvement treatment is added to an inner surface of the corrosion-resistant overlay weld. A nozzle is provided at a predetermined position on the peripheral wall of the reactor pressure vessel, and a piping outside the reactor is connected to the nozzle via a safe end, and a thermal sleeve is disposed inside the safe end, and one end of the thermal sleeve is provided. In the repair method of the safe end thermal sleeve of the reactor pressure vessel in which the part is welded to the inner periphery of the safe end,
Preparing a new thermal sleeve having a weld groove in one opening;
A thermal end detachment process in which an existing thermal sleeve is disconnected from the thermal end and detached,
Protruding a thermal sleeve mounting weld groove having an inner diameter larger than the outer diameter of the weld groove of the new thermal sleeve by overlay welding with a temper bead on the inner peripheral portion of the existing safe end;
Inserting the new thermal sleeve from the outside of the reactor pressure vessel to the inside of the existing safe end, and attaching the existing safe end thermal sleeve and a welding groove of the new thermal sleeve; A safe-end / new thermal sleeve butt welding process for butt-welding a reactor.

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