JPH0638114B2 - Replacement riser brace structure - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a jet pump riser brace for fixing a riser pipe of a jet pump of a boiling water reactor (hereinafter referred to as BWR) to a reactor pressure vessel, and particularly for replacement. Regarding riser brace construction.

[Technical Background of the Invention] A conventional example will be described below with reference to FIGS. 4 to 12.
FIG. 4 is a vertical cross-sectional view showing a schematic configuration of the BWR, and reference numeral 1 in the drawing indicates a reactor pressure vessel. In the reactor pressure vessel 1, a coolant 2 and a reactor core 3 are contained. The core 3 is composed of a plurality of fuel assemblies, control rods, and the like (not shown), and is housed in the shroud 10.
The coolant 2 flows upward in the core 3 and, at that time, is heated by the nuclear reaction heat of the core 3 and becomes a two-phase flow state of water and steam. The coolant 2 in the two-phase flow state flows into the steam-water separator 4 installed above the core 3 and is separated into water and steam therein. This inner steam is introduced into a steam dryer 5 installed above the steam separator 4 and dried to become dry steam. This dry steam is used in the reactor pressure vessel 1
It is transferred to a steam turbine (not shown) via the main steam pipe 6 connected to and is used for power generation. On the other hand, the separated water flows down below the reactor core 3 through the downcomer section 7 between the reactor core 3 and the reactor pressure vessel 1.

A control rod guide tube 8 is installed below the core 3, and the control rod is inserted into and pulled out from the core 3 via the control rod guide tube 8. A control rod drive mechanism 9 is installed below the control rod guide tube 8, and the control rod drive mechanism 9 controls insertion / extraction of the control rod into / from the reactor core 3.

In the downcomer unit 7, jet pumps 11 are installed at equal intervals in the circumferential direction. On the other hand, a recirculation pump (not shown) is installed outside the reactor pressure vessel 1, and the recirculation pump, the jet pump 11 and recirculation pipes arranged between them constitute a recirculation system. ing. That is, driving water is supplied to the jet pump 11 by the recirculation pump, and the coolant 2 is forcedly circulated in the core 3 by the action of the jet pump 11.

The jet pump 11 has a structure as shown in FIG. Reference numeral 12 in the drawing denotes a riser pipe, which is connected to a recirculation inlet nozzle 13 fixed to the reactor pressure vessel 1 and is supplied from a recirculation pump to introduce the coolant 2 into the inside. . A pair of elbows 15A and 15B is connected to the upper portion of the riser pipe 12 via a transition piece 14. The pair of elbows 15A and 15B include a pair of mixing nozzles 16
A pair of inlet throats 1 through A and 16B
7A and 17B are connected. A pair of diffusers 18A and 18B are connected to the pair of inlet throats 17A and 17B. That is, the coolant 2 is jetted by the mixing nozzles 16A and 16B, and at that time, the reactor water is taken in from the surroundings. The injected coolant 2 and the reactor water that has been taken up are the inlet throat 17A.
And mixed in 17B. Then diffuser 1
Hydrostatic head recovery occurs at 8A and 18B.

In the above structure, fluid vibration is generated by the coolant flow sent from the recirculation pump. Therefore, as described above, the riser pipe 12 has its lower end at the recirculation inlet nozzle 1
3 is welded to the upper end of the riser brace 20
It is fixed to the reactor pressure vessel 1 via. The inlet throats 17A and 17B have their upper ends mechanically connected to the transition piece 14 via the mixing nozzles 16A and 16B and the bends 15A and 15B as described above, and their lower ends to the diffusers 18A and 18B. It is inserted at the top. Thus, the riser pipe 12 and the inlet throats 17A, 17A
Both B have a configuration that can sufficiently cope with the occurrence of the fluid vibration. The transition piece 1 is shown in FIG.
4 and the vicinity of the nozzle 15B are shown enlarged.

Next, referring to FIGS. 7 to 9, the nozzle 15A (15
The configuration above B) will be described in detail. A pair of ears 21 are formed on both sides of the transition piece 14, and the ears 21 project upward and a groove 22 is formed inside the upper end thereof. In this groove 22, a pair of two jet pump beams 23 having a rectangular cross section that increases toward the central portion in the longitudinal direction are fixed by fitting both ends of the jet pump beam 23 into the groove 22. In the center of the jet pump beam 23, a screw hole (not shown) is formed in the vertical direction, and the head bolt 25 is formed in this screw hole.
Are screwed together. A hexagon head 26 is formed at the upper end of the head bolt 25, and a semi-round head 27 is formed at the lower end as shown in FIG. Meanwhile, the elbow 15
In A (15B), a pedestal portion 28 whose upper end upper surface is horizontal is formed, and in this pedestal portion 28, a counterbore hole 29 is formed. The semi-round head 27 of the head bolt 25 is fitted into the counterbore hole 29 through a spherical washer 30.
In addition, reference numeral 31 in the drawing denotes a retainer, and the retainer 31 has a U-shape formed by bending both ends of a flat plate at a right angle. Further, as shown in FIG. 9, the retainer 31 is formed with a cut 31A from one end side to the center in the longitudinal direction, and the semi-rounded head 27 of the head bolt 25 is formed in the cut 31A.
Clamp the upper position of. The lower surface of the retainer 31 is brought into contact with the upper surface of the pedestal portion 28 and is fixed to the pedestal portion 28 with a hexagon bolt 32. The hexagonal bolt 32 is welded to the retainer 31 in order to prevent loosening after fastening, and reference numeral 32A in the drawing indicates the welded portion.

Since the inlet throats 17A and 17B are not fixed to the reactor pressure vessel 1, the inflow water pressure of the drive water supplied through the riser pipe 12 acts on the upper end portion and the elbows 15A and 15B. Elbow 15A above
A reaction force such as a jet pressure of driving water jetted toward the inside of the diffuser 18A (18B) from a nozzle (not shown) connected to the other end of (15B) acts upward. A large load acts due to the action of these driving water pressures. The head bolt 25 is screwed onto the jet pump beam 23 in order to face this load. Since the ear portion 21 is fixed at a fixed position, when the head bolt 25 is screwed,
The jet pump beam 23 is moved upward and both ends thereof are in contact with the upper wall surface of the groove 22. This sends an upward load. On the contrary, elbow 15A (15B)
A downward load acts on the upper end of the through the head bolt 25. The magnitude of the downward load is determined in relation to the upward load due to the reaction force of the driving water.

A keeper 33 is detachably fitted to the hexagonal head 26 of the head bolt 25. This keeper 33 has a support plate 34.
It is fixed by spot welding on top. The support plate 34 has a square shape and is fixed to the upper surface of the jet pump beam 23 by two bolts 35.

The inlet throats 17A and 17B are attached to a riser blanket 36 fixed to the riser pipe 13 as shown in FIG. The diffusers 18A and 18B are fixed to the shroud support 37 welded to the reactor pressure vessel 1.

The jet pump 11 is used in a severer condition than other devices for circulating the coolant. Therefore, a large load acts on each member, and severe stress acts on the riser brace 20 which supports the riser pipe 13 in the middle thereof.

The riser brace 20 has a structure as shown in FIGS. 10 to 12. That is, a pad 39 is formed on the inner wall of the reactor pressure vessel 1.
The four thin plates 40 are welded to each other. The thickness of these four thin plates 40 is about 10 mm. 4 above
The tips of the thin plates 40 are integrated via a block 41. The riser pipe 11 is welded to the inside of the block 41 (on the side of the reactor pressure vessel 1). Further, the riser brace 20 suppresses fluid vibration generated in the riser pipe 12 during the operation of the reactor, and also the reactor pressure vessel 1 made of carbon steel and the riser pipe 1 made of austenitic steres steel.
It absorbs the difference in thermal expansion between the two. Therefore, during operation of the nuclear reactor, it is in a deformed state while absorbing the difference in thermal expansion.

[Problems of Background Art] In the above-mentioned configuration, for example, when an excessive load is applied due to the breakage of the external pipe or the riser brace 20 is damaged, the riser brace 20 is stress-corrosion cracked (hereinafter referred to as SCC). Is called) and is likely to be damaged. If the riser brace 20 is damaged in this way, it must be replaced. That is, when the riser brace 20 is damaged, the holding function of the riser pipe 12 is lost, and thus the primary vibration frequency of the jet pump 11 is 20.
It will drop to Hz. Such a decrease in the frequency means an increase in the amplitude and may adversely affect other structures.

However, the replacement work of the riser brace 20 is extremely difficult. This will be described below. As shown in FIG. 11 and FIG. 12, the riser brace 20 is in an annular space 51 between the reactor pressure vessel 1 and the shroud 10. The space 51 is an extremely narrow place and the riser pipe 12 And the inlet throat 18A (18B) and the like are in a forested state. The gap between the block 41 and the shroud 10 is particularly narrow, which is about 1 / 2.5 of the gap on the reactor pressure vessel 1 side. For example, it is about 85 mm in a plant of 1.1 million kW class. Therefore, it is impossible or impossible to install a new riser phrase in place of the damaged riser brace 20, and improvement thereof has been demanded. Further, upon replacement, it is desirable that the rigidity of the riser brace before replacement and the rigidity of the riser brace after replacement are equal. The riser brace 20 is an important member that determines the vibration characteristics of the entire jet pump, and therefore the soundness of the device is confirmed using a strain gauge or the like in the initial stage. Therefore, when the rigidity changes, it is necessary to repeat the above confirmation work.

[Object of the Invention] The present invention has been made based on the above points, and an object of the present invention is to provide a replacement riser brace structure capable of performing a replacement work of a riser brace by a simple work. It is in.

[Outline of the Invention] That is, the replacement riser brace structure according to the present invention has a block for supporting a riser pipe of a jet pump located between a riser pipe and a reactor pressure vessel, and the shroud side of the block and the riser pipe. It is characterized in that it is welded to the reactor pressure vessel side.

That is, when the riser brace is exchanged, the place where the riser brace is installed is extremely narrow, and especially between the riser brace and the shroud is remarkable. Therefore, the block of the riser brace is positioned between the riser pipe and the reactor pressure vessel, and the shroud side of the block and the reactor pressure vessel side of the riser pipe are welded and joined, thereby enabling the replacement work. .

[Embodiment of the Invention] An embodiment of the present invention will be described below with reference to FIGS. 1 and 2. It should be noted that the same parts as those of the related art are denoted by the same reference numerals and the description thereof will be omitted. FIG. 1 is a perspective view showing the structure of a replacement riser brace 120 according to the present embodiment. In the figure, reference numeral 140 is four thin plates whose one end is welded to a bat 139, and these four thin plates 140 are blocks. 141
Are integrated through. Unlike the conventional block, the block 141 is formed in an arc shape. That is, while the riser pipe 12 is welded to the inside of the conventional block (on the side of the reactor pressure vessel 1), in the case of this embodiment, the block 141 is formed into an arc shape and the riser is placed on the outside (on the side of the shroud 10). The pipe 12 is welded. As a result, the welding work is moved from the shroud 10 side to the reactor pressure vessel 1 side, and the welding work space is expanded, which can be sufficiently performed.

Next, the replacement work of the riser brace 120 having the above configuration will be described. It should be noted that the replacement method will be described by taking the case where the worker directly performs the replacement, but the present invention is not limited to this, and it goes without saying that the same work can be performed remotely. First, in order to prevent the worker from being exposed to radiation, a living body shielding wall is installed in the reactor pressure vessel 1. Next, the load acting on the head bolt 25 is released, this is rotated, and the welding between the keeper 33 and the support plate 34 is released. After the welding is released, the head bolt 25 is rotated to loosen the screw. The beam 23 is disengaged from the groove 22 of the ear 21 by loosening the head bolt 25. Then, the beam 23 is rotated by 90 degrees and the elbow 15A is rotated.
Make it parallel to (15B). In this state, a hook is attached to the tip of the hoist of the fuel exchanger (not shown), and the hook is attached to the hook 15a (15) of the elbow 15A (15B).
engage b). After the engagement, the hoist is driven and pulled up, and the inlet throws 17A and 17B are taken out of the furnace. After the removal, the welded portion between the riser brace 20 and the riser pipe 12 is cut by, for example, electric discharge machining or the like, and this is taken out of the furnace. The cut portion is a hatched portion in FIG. After taking out, the replacement riser brace 120 is carried into the furnace, and the thin plate 140 and the pad 139, the block 141, and the riser pipe 12 are welded to each other. The welded portion is a hatched portion in FIG. 3 (B). And the inlet throats 17A and 17B first taken out of the furnace
Are loaded into the furnace and fixed. This is the riser brace 12
The replacement work of 0 ends.

As described above, according to this embodiment, the following effects can be obtained. That is, if the replacement riser brace 120 according to the present embodiment is used, the riser brace can be reliably replaced by a simple operation, and the damaged riser brace 20 can be replaced early to ensure the retention of the jet pump 11. In addition to the jet pump 11, the soundness of the entire plant can be reliably maintained.
Further, the replacement riser brace 120 of the present embodiment has the same rigidity as that of the riser brace 20 before the replacement, and therefore the device soundness data first confirmed after the replacement can be used as it is. There is no need to check the vibration characteristics etc. again.

[Effects of the Invention] As described above in detail, according to the replacement riser brace structure of the present invention, a new riser brace can be attached by a simple operation, and the soundness of the plant as well as the jet pump can be reliably maintained. It is possible to improve the safety significantly.

[Brief description of drawings]

1 to 3 are views showing an embodiment of the present invention.
FIG. 3 is a perspective view of a replacement riser brace, FIG. 2 is a perspective view showing a state in which a replacement riser brace is attached, FIG. 3 (A) is a view showing a cut portion of the replacement riser brace, and FIG. B) is a view showing a welding part of a new replacement riser brace, FIGS. 4 to 12 are views used for explaining a conventional example, and FIG. 4 is a vertical cross-sectional view showing a configuration of a boiling water reactor. FIG. 5 is a perspective view showing the vicinity of the jet pump, FIG. 6 is a view showing the vicinity of the transition piece and the elbow, FIG. 7 is a perspective view of the vicinity of the transition piece and the connecting portion with the elbow, and FIG. 8 is the transition piece. And FIG. 9 is a view showing the vicinity of the connection portion with the elbow, FIG. 9 is IX in FIG.
-IX cross-sectional view, FIG. 10 is an enlarged perspective view showing the relationship between the riser brace and the riser pipe, FIG. 11 is a view of the riser brace attached state as seen from above, and FIG. 12 is the X of FIG.
It is a II-XII sectional view. 1 ... Reactor pressure vessel, 10 ... Shroud, 11 ...
Jet pump, 12 ... Riser tube, 120 ... Riser brace, 139 ... Pat, 140 ... Thin plate, 141
……block.

Claims (1)

[Claims] 1. A plurality of plate members having one end fixed to the reactor pressure vessel side, and a jet pump provided at the other end of the plurality of plate members and located between the reactor pressure vessel and the shroud. In a riser brace comprising a block supporting a riser pipe, the block is located between the riser pipe and the reactor pressure vessel, and the shroud side of the block and the reactor pressure vessel side of the riser pipe are Replacement riser brace structure characterized by welding.