JPH11304978A - Core shroud - Google Patents

Abstract

PROBLEM TO BE SOLVED: To sufficiently obtain the same performance as existing equipment which is applicable for exchange or new set in a plant with low operation floor, and capable of executing at relatively low operation cost. SOLUTION: The core shroud has an upper ring 3, an upper shell 4, a middle ring 5, a middle shell 7, a lower ring 8 and a lower shell 9 from the top, forms a coolant flow path in a reactor pressure vessel, and supports an upper grid plate 6 for supporting the upper end part of the fuel assemblies with the middle ring. On the other hand, a core support plate for supporting lower end part of a fuel assembly is supported with a lower ring. In this case, it is structured in two split configuration of an upper half shroud 1 constituted integrally with the upper ring, the upper shell and the middle ring, and a lower half shroud 2 constituted integrally with the middle shell, the lower ring and the lower shell, and in the constitution that the upper half should and the lower half shroud are fixed tight.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a core shroud installed as a reactor internal structure in a reactor pressure vessel of a boiling water reactor.
The present invention relates to a core shroud that can be easily replaced even in a plant having a low operation floor.

[0002]

2. Description of the Related Art A core shroud, which is a cylindrical structure provided in a reactor pressure vessel of a boiling water reactor, includes an upper ring, an upper shell, an intermediate ring, an intermediate shell,
It has a configuration including a lower ring and a lower body. Each part of the core shroud is made of a stainless steel plate, and these parts are assembled as an integral structure by welding. The intermediate ring supports an upper lattice plate for supporting the upper end of the fuel assembly, while the lower ring supports a core support plate for supporting the lower end of the fuel assembly.

[0003] In this core shroud, a fuel assembly is loaded inside to form a core, and a flow path flowing upward in the core is formed, and at the same time, an annulus space is formed between the core shroud and the furnace wall on the outer peripheral side. And, it guides the recirculating flow of the coolant flowing downward. The lower part of the core shroud is supported by a shroud support leg welded to the bottom of the reactor pressure vessel and a shroud support plate welded to the inner wall of the pressure vessel.

[0004]

Generally, in a structure using stainless steel having a high carbon content, stress corrosion cracking occurs in the heat affected zone near the weld due to aging in a high temperature environment. It has been known. Also in the above-described core shroud made of such a material and used in contact with a high-temperature reactor coolant, there is a concern about occurrence of stress corrosion cracking.

[0005] As a countermeasure against such stress corrosion cracking of the core shroud, the core shroud is replaced after a certain period of time has passed. However, in the currently established shroud replacement method, the upper half and the lower half are replaced. The core shroud, which is divided into approximately equal parts, is carried into the operation floor of the reactor building, integrated by welding on the operation floor, and then introduced into the reactor pressure vessel and installed.

However, in a plant where the height of the operation floor is low, it is impossible to assemble the core shroud divided into the upper half and the lower half on the operation floor, so that the current welding method cannot be applied. .

Therefore, the present inventors have made the upper half shroud a small height by integrating the upper ring, the upper shell and the intermediate ring of the core shroud, and integrally cut the upper half shroud into the intermediate ring portion. Has proposed a technique of forming an upper lattice plate by welding and welding in a reactor pressure vessel. If this technology is adopted, it is possible to cope with a plant where the height of the operation floor is low. However, in this case, the integrally cut upper lattice plate significantly increases the manufacturing cost, and the upper lattice plate must be thinner than before because of material procurement.
There are concerns that the fuel support conditions will change and the plant's seismic resistance will change.

The present invention has been made in view of such circumstances, and can be applied to a plant having a low operation floor as a replacement or a new one, and can be implemented at a relatively low cost. Moreover, it is an object of the present invention to provide a core shroud capable of sufficiently obtaining the same performance as existing facilities.

[0009]

In order to achieve the above object, according to the first aspect of the present invention, a cylindrical structure installed via a shroud support in a reactor pressure vessel of a boiling water reactor. The upper ring, the upper body, the middle part ring, the middle part body, the lower ring and the lower body are configured from above, and a coolant flow path is formed in the reactor pressure vessel, and the middle part is formed. In a core shroud in which a ring supports an upper lattice plate for supporting an upper end portion of a fuel assembly and a lower ring supports a core support plate for supporting a lower end portion of the fuel assembly, the upper ring, the upper body and The upper half shroud, which integrally forms the intermediate ring, and the lower half shroud, which integrally forms the intermediate body, lower ring, and lower body, have a two-part structure. Providing a core shroud, characterized in that the arrangement for fastening and fixing the shroud and lower half shroud.

According to the second aspect of the present invention, in the core shroud according to the first aspect, a plurality of counterbore portions are recessed at intervals in a circumferential direction on an upper surface of an intermediate ring projecting toward an inner surface of a lower end of the upper half shroud. In each of the counterbore portions, a bolt insertion hole that penetrates the intermediate ring downward is formed, and the bolt insertion hole is inserted into a plurality of portions corresponding to the bolt insertion hole at the upper end of the lower half shroud. A stud bolt inserted into the hole is projected upward, and an intermediate ring of the upper half shroud is fastened to the lower half shroud by a nut screwed to the stud bolt at the counterbore. A core shroud is provided.

According to a third aspect of the present invention, in the core shroud according to the second aspect, the upper surface of the middle ring of the upper half shroud is a seating surface of the upper lattice plate, and the upper end surface of the stud bolt protruding upward from the counterbore portion. Is provided so as to be disposed below the seating surface.

According to a fourth aspect of the present invention, in the core shroud according to the second or third aspect, the stud bolt is embedded in a flange portion formed at the upper end portion of the lower half shroud so as to have a larger thickness than the intermediate body. A core shroud is provided.

According to a fifth aspect of the present invention, in the core shroud according to any one of the second to fourth aspects, a plurality of aligners for centering the upper lattice plate are provided on the seating surface of the intermediate ring of the upper half shroud. A core shroud provided with a groove is provided.

According to a sixth aspect of the present invention, in the core shroud according to any one of the second to fifth aspects, an eccentric sleeve is fitted into a bolt insertion hole formed in an intermediate ring of the upper half shroud. A core shroud characterized in that the insertion position of the stud bolt can be adjusted by inserting the stud bolt into the hole of the sleeve.

According to a seventh aspect of the present invention, in the core shroud according to any of the second to sixth aspects, the upper surface of the intermediate ring of the upper half shroud is not directly used as the seating surface of the upper lattice plate, A core shroud characterized in that a block-shaped pedestal is placed and fixed on an upper surface of a partial ring, and the upper surface of the pedestal is used as a seating surface of an upper lattice plate.

According to the eighth aspect of the present invention, in the core shroud according to the seventh aspect, the pedestal for seating the upper lattice plate is welded to the upper surface of the intermediate ring of the upper half shroud, or the upper half shroud and the lower half shroud. The core shroud is characterized in that the core shroud is fixed by tightening three pieces using stud bolts used for fastening the core shroud.

[0017]

Embodiments of a core shroud according to the present invention will be described below with reference to the drawings.

First Embodiment (FIGS. 1 to 7) FIG. 1 is an overall sectional view showing a core shroud according to the present embodiment, and FIG. 2 is a sectional view taken along line AA of FIG. FIG. 3-
FIG. 7 is an enlarged partial view showing a main part.

As shown in FIGS. 1 and 2, the core shroud of the present embodiment is divided into an upper half shroud 1 and a lower half shroud 2. The upper half shroud 1 has an upper ring 3, an upper body 4, and an intermediate ring 5 integrally in that order from above, and has a relatively small vertical height.
The upper ring 3 and the intermediate ring 5 project a predetermined length toward the inner peripheral side of the upper body 4. The upper surface of the intermediate ring 5 is used as a seating surface of the upper lattice plate 6, and the upper lattice plate 6 is placed on the seating surface.

The lower half shroud 2 has an intermediate body 7, a lower ring 8 and a lower body 9 integrally arranged in this order from the top, and has a relatively large vertical height. A flange portion 10 is formed at the upper end of the lower half shroud 2 so as to have a greater wall thickness than that of the intermediate body. The core support plate 11 is placed on the lower ring 8.

The upper half shroud 1 and the lower half shroud 2 are fastened and fixed to each other by stud bolts 12 described below. Then, it is installed in a reactor pressure vessel (not shown) via a shroud support.

FIG. 3 is an enlarged sectional view showing a fastening joint between the upper half shroud 1 and the lower half shroud 2 by the stud bolt 12, and FIG. 4 is a plan view of FIG. FIG. 5 is an enlarged sectional view taken along line BB of FIG.

As shown in these figures, a plurality of counterbore portions 13 are recessed at intervals in the circumferential direction on the upper surface of the intermediate ring 5 protruding from the inner surface of the lower end of the upper half shroud 1.
Each of the counterbore portions 13 is provided with a bolt insertion hole 14 penetrating the intermediate ring 5 downward.

On the other hand, stud bolts 12 inserted into the bolt insertion holes 14 project upward at a plurality of positions corresponding to the bolt insertion holes 14 at the upper end of the lower half shroud 2. The stud bolt 12 is embedded in a flange portion 10 formed at the upper end of the lower half shroud 2 with a greater thickness than the intermediate body 7.

The upper half shroud 1 is placed on the lower half shroud 2, and the stud bolt 12 of the lower half shroud 2 is inserted into the bolt insertion hole 14 of the upper half shroud 1. The intermediate ring 5 is connected to the flange portion 1 by a nut 15 screwed to the stud bolt 12 at a counterbore portion 13.
0. Here, the upper end surface of the stud bolt 12 protruding upward from the counterbore portion 13 is set to be disposed below the seating surface of the intermediate ring 5, and the upper lattice plate is placed on the seating surface of the intermediate ring 5. The seating of No. 6 is not inhibited.

A pair of inner and outer eccentric sleeves 16 and 17 are fitted in the bolt insertion holes 14 formed in the intermediate ring 5, and the stud bolts 12 are inserted into the holes of the inner small-diameter eccentric sleeve 16. The insertion position of the stud bolt 12 can be adjusted by inserting and rotating the eccentric sleeves 16 and 17 as appropriate. These sleeves 16,1
On 7, a nut is fitted to the stud bolt 12.
With such a structure, the displacement of the stud bolt 12 and the like can be absorbed, and the core of the upper half shroud 1 and the lower half shroud 2 does not shift.

FIG. 6 is an enlarged sectional view showing a centering component of the upper lattice plate 6 provided on the upper surface of the intermediate ring 5 of the upper half shroud 1, and FIG. 7 is a plan view of FIG. .

As shown in FIGS. 6, 7 and 2, an upper surface opening type aligner groove 18 for centering the upper lattice plate 6 is provided at a plurality of positions, for example, at 90 ° intervals on the upper surface of the intermediate ring 5. It is provided in four places. This aligner groove 18
Then, a projection (not shown) provided on the peripheral portion of the upper lattice plate 6 is fitted to perform centering. Thus, the upper lattice plate 6 can be centered only by access from above. That is, the protrusions provided on the peripheral edge portion of the upper lattice plate 6 in the radial direction at intervals in the circumferential direction,
The upper lattice plate is naturally centered by fitting into the aligner grooves 18 respectively.

The upper ring 3 of the upper half shroud 1
The inner and outer diameters of the upper shell 4 and the intermediate ring 5 are the same as those of the conventional fully integrated core shroud, and the height of the upper ring 3 and the upper shell 4 (the distance from the upper surface of the upper ring 3 to the upper surface of the intermediate ring 5). ) Is equivalent to a conventional core shroud. Further, the intermediate ring 5 is thicker by a depth corresponding to the seating surface of the nut.

The inner and outer diameters of the middle shell 7, the lower ring 8, and the lower shell 9 of the lower half shroud 2 are equal to those of the conventional core shroud. Further, with respect to the height of the lower half shroud 2, the height of the intermediate body 7 including the flange portion 10 becomes lower than that of the conventional core shroud by an increase in the thickness of the intermediate ring 5 of the upper half shroud 1. ing. And
The installation positions of the upper lattice plate 6 and the core support plate 11 are the same as those of the conventional core shroud.

According to the core shroud having such a configuration, the upper half shroud 1 having a small height is mounted on the lower half shroud 2 having a large height, and assembly can be performed by fastening with the stud bolts 12. Assembly work can be easily performed in the reactor pressure vessel. Therefore, even in a plant where the height of the operation floor is low and the shroud cannot be assembled on the operation floor, it is possible to provide a furnace internal structure necessary for replacement. Further, it is applicable not only for replacement but also as a furnace internal structure for construction.

Moreover, according to the present embodiment, the counterbore 1
The upper end surface of the stud bolt 12 projecting upward from 3
It is set to be disposed below the seating surface of the intermediate ring 5, so that the seating of the upper lattice plate 6 on the seating surface of the intermediate ring 5 is not hindered. In addition, since the nut 15 is fitted on the sleeves 16 and 17, the displacement of the stud bolt 12 and the like can be absorbed, and the center shift between the upper half shroud 1 and the lower half shroud 2 does not occur. Furthermore, since the aligner groove 18 is provided in the intermediate ring 5 so that the upper lattice plate 6 can be centered, the upper lattice plate 6 can be centered only by access from above.

In addition, since the structure capable of securing the upper lattice plate installation surface can be ensured even if it can be divided, the radial dimension does not need to be increased from the conventional core shroud. In-core structures such as the core support plate can be used without any change.

Second Embodiment (FIGS. 8 to 12) FIG. 8 is a cross-sectional view corresponding to FIG. 2 of the first embodiment, and FIGS. 9 to 12 are portions corresponding to FIGS. FIG.

In the present embodiment, only the structure of the intermediate ring 5 of the upper half shroud 1 is different from that of the first embodiment.

That is, in this embodiment, the upper surface of the intermediate ring 5 of the upper half shroud 1 in the first embodiment is not directly used as the seating surface of the upper lattice plate 6, but as shown in FIGS. A block-shaped pedestal 19 is mounted and fixed on the upper surface of the intermediate ring 5 having a small thickness, and the upper surface of the pedestal 19 is used as a seating surface of the upper lattice plate 6.
The pedestal 19 for seating the upper lattice plate is fixed to the upper surface of the middle ring 5 of the upper half shroud 1 by welding.

The configuration for forming the aligner groove is also different. That is, as shown in FIGS. 11 and 12, the aligner block 20 is mounted on the intermediate ring 5 and fixed by welding or the like. The aligner block 20 is provided with an aligner groove 18. The inner diameter and the outer diameter of the upper body 4 are the same as those of the first embodiment, but the inner height is increased by the reduction of the thickness of the intermediate ring. The other configuration is the same as that of the first embodiment. Therefore, the same reference numerals as those in the first embodiment denote the corresponding positions in the drawing, and a description thereof will be omitted.

According to the present embodiment, the thickness of the intermediate ring 5 can be reduced, so that the configuration of the upper half shroud 1 can be simplified.

Third Embodiment (FIGS . 13 and 14) FIGS. 13 and 14 are views corresponding to FIGS. 9 and 10 of the second embodiment, respectively.

As shown in FIGS. 13 and 14,
In the present embodiment, the pedestal for seating the upper lattice plate is fastened to the upper surface of the middle ring 5 of the upper half shroud 1 with three stud bolts 12 used for fastening the upper half shroud 1 and the lower half shroud 2. Is fixed. That is, a block-shaped upper lattice plate receiving seat 21 is provided, and the upper lattice plate receiving seat 21 is integrally fastened between the upper half shroud 1 and the lower half shroud 2 by the stud bolt 12 and the nut.

Although not shown, the upper lattice plate receiving seat may be widened to form an aligner groove so that the aligner block can also be used.

With such a configuration, the number of welding points is reduced, so that work can be facilitated and labor can be reduced.

[0043]

As described above, according to the present invention, even in a plant where the height of the operation floor is low and the shroud cannot be assembled on the operation floor, the furnace internal structure necessary for replacement is provided. can do.

Further, the present invention is applicable not only for replacement but also as a furnace internal structure for construction.

[Brief description of the drawings]

FIG. 1 is an overall sectional view showing a core shroud according to a first embodiment of the present invention.

FIG. 2 is a sectional view taken along line AA of FIG.

FIG. 3 is a partial explanatory view in the embodiment.

FIG. 4 is a partial explanatory view in the embodiment.

FIG. 5 is a partial explanatory view in the embodiment.

FIG. 6 is a partial explanatory view in the embodiment.

FIG. 7 is a partial explanatory view in the embodiment.

FIG. 8 is an overall cross-sectional view showing a core shroud according to a second embodiment of the present invention.

FIG. 9 is a partial explanatory view in the second embodiment.

FIG. 10 is a partial explanatory view in the second embodiment.

FIG. 11 is a partial explanatory view in the second embodiment.

FIG. 12 is a partial explanatory view in the second embodiment.

FIG. 13 is a partial explanatory view showing a third embodiment of the present invention.

FIG. 14 is a partial explanatory view of the third embodiment.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Upper half shroud 2 Lower half shroud 3 Upper ring 4 Upper trunk 5 Intermediate ring 6 Upper lattice plate 7 Intermediate trunk 8 Lower ring 9 Lower trunk 10 Flange part 11 Core support plate 12 Stud bolt 13 Counterbore part 14 Bolt insertion hole 15 Nut 16, 17 Eccentric sleeve 18 Aligner groove 19 Pedestal 20 Aligner block 21 Upper lattice plate receiving seat

Claims (8)

[Claims] 1. A cylindrical structure installed through a shroud support in a reactor pressure vessel of a boiling water reactor, and includes an upper ring, an upper shell, an intermediate ring, an intermediate shell, and a lower ring from above. And each part of the lower body, while forming a coolant flow path in the reactor pressure vessel, while supporting the upper lattice plate for supporting the upper end of the fuel assembly by the intermediate ring, In a core shroud supporting a core support plate for supporting a lower end portion of the fuel assembly by a lower ring, an upper half shroud integrally forming the upper ring, an upper trunk and an intermediate ring, an intermediate trunk, a lower ring and The lower torso has a two-part structure consisting of a lower half shroud that is integrally configured, and the upper half shroud and the lower half shroud are fastened and fixed. And core shroud. 2. The core shroud according to claim 1, wherein a plurality of counterbore portions are recessed at intervals in a circumferential direction on an upper surface of an intermediate ring projecting from an inner surface of a lower end of the upper half shroud,
A bolt insertion hole penetrating the intermediate ring downward is formed in each of the counterbore portions, and a plurality of portions corresponding to the bolt insertion holes at the upper end of the lower half shroud are provided with the bolt insertion holes. A stud bolt inserted through the upper half shroud is projected upward, and an intermediate ring of the upper half shroud is fastened to the lower half shroud by a nut screwed into the stud bolt at the counterbore portion. And core shroud. 3. The core shroud according to claim 2, wherein an upper surface of an intermediate ring of the upper half shroud is a seating surface of an upper lattice plate, and an upper end surface of a stud bolt protruding upward from a counterbore portion is the seating surface. A core shroud characterized in that the core shroud is disposed below the core shroud. 4. The core shroud according to claim 2, wherein the stud bolt is embedded in a flange formed at the upper end of the lower half shroud with a greater thickness than the intermediate body. And core shroud. 5. The core shroud according to claim 2, wherein a plurality of aligner grooves for centering the upper lattice plate are formed on the seating surface of the intermediate ring of the upper half shroud. A core shroud characterized by the following. 6. The core shroud according to claim 2, wherein an eccentric sleeve is fitted into a bolt insertion hole formed in an intermediate ring of the upper half shroud, and a stud is inserted into the hole of the eccentric sleeve. A core shroud wherein the stud bolt insertion position can be adjusted by inserting a bolt. 7. The core shroud according to claim 2, wherein the upper surface of the middle ring of the upper half shroud is not directly used as the seating surface of the upper lattice plate, but is provided on the upper surface of the middle ring. A core shroud wherein a block-shaped pedestal is placed and fixed, and the upper surface of the pedestal is used as a seating surface for an upper lattice plate. 8. The core shroud according to claim 7, wherein the pedestal for seating the upper lattice plate is used for welding to the upper surface of the intermediate ring of the upper half shroud or for fastening the upper half shroud and the lower half shroud. A core shroud which is fixed by fastening three pieces using stud bolts.