JP7795447B2 - Support structure for reactor pressure vessel and nuclear power plant - Google Patents

Description

The present invention relates to a support structure for a reactor pressure vessel and a nuclear power plant equipped with this support structure.

Conventionally, inside a nuclear power plant building, there is a reactor pressure vessel, a reactor pressure vessel pedestal (hereinafter referred to as "pedestal") that supports the reactor pressure vessel, and a reactor containment vessel that houses the pressure vessel and pedestal. Furthermore, in nuclear power plants, the pedestal and reactor containment vessel are connected to each other by support structures to improve earthquake resistance.

A shear lug structure has been used for this support structure as a load transfer mechanism that suppresses only circumferential displacement without restraining radial or vertical displacement due to thermal expansion of the reactor containment vessel. The shear lug structure consists of a convex male shear lug attached to the support structure and a concave female shear lug attached to the reactor containment vessel, consisting of two protrusions that sandwich the male shear lug on either side. Typically, the female shear lug and male shear lug come into contact around the circumference of the reactor containment vessel, suppressing horizontal displacement.

An example of a conventional support structure is described in Patent Document 1. Patent Document 1 describes technology that includes a first shear lug member attached to the side of the top slab facing the opening, and a second shear lug member that is attached to the upper end of the reactor shielding wall, extends upward, and has its side facing the tip of the first shear lug member.

Another conventional support structure is described, for example, in Patent Document 2. Patent Document 2 describes the use of multiple shear lug mechanisms spaced apart in the circumferential direction, which allow relative movement in the vertical and radial directions while restricting relative movement in the circumferential direction. Furthermore, the technology described in Patent Document 2 allows relative movement in the vertical direction within the range of the vertical spacing between the convex member and the hole in the concave member, and restricts relative movement in the circumferential direction of the cylindrical body through contact between the guide plate of the concave member and the convex member.

JP 2013-205126 A Japanese Utility Model Application Publication No. 63-129900

However, the technology described in Patent Document 1 only restrains circumferential deformation of the reactor containment vessel, not radial or vertical deformation, limiting support function during an earthquake to the horizontal direction only. Furthermore, while the technology described in Patent Document 2 can restrain vertical displacement, it requires inserting a convex member into a hole in a concave member installed in advance on the wall surface of the reactor containment vessel, making it difficult to precisely adjust the gap between the shear lug members.

In consideration of the above problems, the objective of this study is to provide a support structure for a reactor pressure vessel and a nuclear power plant that can restrain vertical displacement and easily adjust the gap between shear lug members.

To solve the above problems and achieve the object, a support structure for a reactor pressure vessel is disposed between the reactor pressure vessel and a cylindrical reactor containment vessel. The support structure is installed on the wall surface of the reactor containment vessel and includes at least a female shear lug divided into two members in the vertical direction of the reactor containment vessel, and a male shear lug supported by the female shear lug.
The female shear lug is arranged with a gap between it and the wall surface of the containment vessel in the radial direction of the containment vessel. The female shear lug has a first member and a second member arranged vertically below the first member with the male shear lug sandwiched therebetween. The first member and the second member are arranged with a gap between them in the vertical direction.

The nuclear power plant also includes a reactor pressure vessel, a cylindrical reactor containment vessel that houses the reactor pressure vessel, and multiple support structures arranged between the reactor pressure vessel and the reactor containment vessel. The support structures are the same as those described above.

The reactor pressure vessel support structure and nuclear power plant configured as described above can restrain vertical displacement and easily adjust the gap between the shear lug members.

1 is a cross-sectional view showing an entire reactor building in a nuclear power plant according to a first embodiment. 2 is an enlarged view showing an end portion of a support structure of the nuclear power plant according to the first embodiment; FIG. 3 is a cross-sectional view taken along the line CC shown in FIG. 2. FIG. 4 is a cross-sectional view showing a support structure of a nuclear power plant according to a second embodiment. FIG. 10 is a cross-sectional view showing a support structure of a nuclear power plant according to a third embodiment. FIG. 10 is a cross-sectional view showing a support structure of a nuclear power plant according to a fourth embodiment. FIG. 10 is a schematic configuration diagram showing a support structure of a nuclear power plant according to a fifth embodiment. 8 is a cross-sectional view taken along line CC of FIG. 7, showing a normal state. 8 is a cross-sectional view taken along line CC in FIG. 7, showing the state when an earthquake occurs. 10 is a graph showing the vertical load-displacement characteristics of the support structure under normal conditions. 1 is a graph showing the vertical load-displacement characteristics of a support structure when an earthquake occurs.

The following describes a reactor pressure vessel support structure and a nuclear power plant according to an embodiment of the present invention, with reference to Figures 1 to 11. Note that common components in each figure are designated by the same reference numerals.

1. First Embodiment 1-1. Example of the Configuration of a Nuclear Power Plant First, the configuration of a nuclear power plant according to a first embodiment (hereinafter referred to as "this example") will be described with reference to FIG.
FIG. 1 is a cross-sectional view showing the reactor building of this example.

As shown in Figure 1, a nuclear power plant comprises a cylindrical reactor containment vessel 1 installed inside a reactor building, a reactor pressure vessel 2, a reactor pressure vessel pedestal (hereinafter referred to as "pedestal") 6, and multiple support structures 3, 4, and 5.

The reactor containment vessel 1 is cylindrical and airtight. The reactor containment vessel 1 contains a reactor pressure vessel 2, a pedestal 6, and multiple support structures 3, 4, and 5.

The reactor pressure vessel 2 is cylindrical. It is supported by a pedestal 6 within the reactor containment vessel 1. As shown in FIG. 1, the pedestal 6 extends upward from the floor formed at the bottom of the reactor containment vessel 1. The upper end of the pedestal 6 supports the reactor pressure vessel 2 via a second support structure 4.

The first support structure 3 is disposed between the reactor containment vessel 1 and the reactor pressure vessel 2 and supports the reactor pressure vessel 2. The second support structure 4 is disposed at the upper end of the pedestal 6 between the reactor containment vessel 1 and the reactor pressure vessel 2. The third support structure 5 is disposed between the pedestal 6 and the reactor containment vessel 1. The ends of the first support structure 3, second support structure 4, and third support structure 5 facing the reactor containment vessel 1 each have a shear lug structure. Since the first support structure 3, second support structure 4, and third support structure 5 all have the same configuration, the following explanation will focus on the first support structure 3. Hereinafter, the first support structure 3 will be simply referred to as the support structure 3.

1-2. Example of the Structure of the End of the Support Structure Next, the structure of the end of the support structure 3 will be described with reference to FIGS.
Fig. 2 is an enlarged view of the end portion of the support structure 3, and is an enlarged view of the area A shown in Fig. 1. Fig. 3 is a cross-sectional view taken along the line CC shown in Fig. 2.

As shown in Figures 2 and 3, the support structure 3 has a male shear lug 102 and a female shear lug 101 that supports the male shear lug 102. The male shear lug 102 is formed at the end of the support structure 3 that faces the wall surface of the containment vessel 1. As shown in Figure 3, the male shear lug 102 has a cross-shaped cross section cut in the vertical direction 111B of the containment vessel 1. That is, the male shear lug 102 has a first support piece 102A, a second support piece 102B, a third support piece 102C, and a fourth support piece 102D.

The first support piece 102A protrudes upward in the vertical direction 111B, and the second support piece 102B protrudes downward in the vertical direction 111B. The third support piece 102C and the fourth support piece 102D protrude from the boundary between the first support piece 102A and the second support piece 102B in the circumferential direction 111A of the containment vessel 1, which is perpendicular to the vertical direction 111B. The third support piece 102C protrudes toward one side in the circumferential direction 111A, and the fourth support piece 102D protrudes toward the other side in the circumferential direction 111A.

The male shear lug 102 is inserted into the female shear lug 101, which will be described later. A gap 12 is formed between the male shear lug 102 and the wall surface of the containment vessel 1 in the radial direction 11 of the containment vessel 1. This allows for displacement when the support structure 3, containment vessel 1, and reactor pressure vessel 2 thermally expand.

The female shear lug 101 has a first member 101A, a second member 101B, a third member 101C, and a fourth member 101D. Therefore, the female shear lug 101 is divided into four members 101A, 101B, 101C, and 101D. The female shear lug 101 is then fixed to the wall surface of the containment vessel 1.

The first member 101A and the third member 101C are positioned above the third support piece 102C and the fourth support piece 102D of the female shear lug 102 in the vertical direction 111B. The second member 101B and the fourth member 101D are positioned below the third support piece 102C and the fourth support piece 102D of the female shear lug 102, the first member 101A, and the third member 101C in the vertical direction 111B. In other words, the female shear lug 101 is divided in the vertical direction 111B with the female shear lug 102 sandwiched between them.

Furthermore, the first member 101A and the second member 101B are arranged on one side of the first support piece 102A and the second support piece 102B of the male shear lug 102 in the circumferential direction 111A. The third member 101C and the fourth member 101D are arranged on the other side of the first support piece 102A and the second support piece 102B of the male shear lug 102 in the circumferential direction 111A.

Furthermore, the first support piece 102A of the male shear lug 102 is sandwiched between the first member 101A and the third member 101C of the female shear lug 101 in the circumferential direction 111A. The second support piece 102B of the male shear lug 102 is sandwiched between the second member 101B and the fourth member 101D of the female shear lug 101 in the circumferential direction 111A. As a result, displacement of the support structure 3 in the circumferential direction 111A is suppressed by the support structure of the female shear lug 101 and the male shear lug 102.

Furthermore, a gap 112 is provided in the vertical direction 111B between the third support piece 102C of the male shear lug 102 and the first member 101A and second member 101B of the female shear lug 101. Similarly, a gap 112 is provided in the vertical direction 111B between the fourth support piece 102D of the male shear lug 102 and the third member 101C and fourth member 101D of the female shear lug 101. In this way, providing the gap 112 allows for thermal expansion in the vertical direction 111B.

In the event of a large displacement in the vertical direction 111B, the third support piece 102C and fourth support piece 102D of the male shear lug 102 come into contact with the female shear lug 101. As a result, the support structure 3 of this example can respond to shaking not only in the circumferential direction 111A but also in the vertical direction 111B during an earthquake. As a result, the support structure 3 can improve earthquake resistance.

Furthermore, according to the support structure 3 of this example, the female shear lug 101 has a divided structure consisting of four members 101A, 101B, 101C, and 101D. Therefore, the female shear lug 101 can be installed after the male shear lug 102 has been positioned. When installing the female shear lug 101, the first members 101A, 101B, 101C, and 101D of the female shear lug 101 can be positioned separately depending on the installation position of the male shear lug 102. This makes it easy to position the female shear lug 101 and the male shear lug 102, thereby improving the accuracy of the gap 112 adjustment work.

In this example, the female shear lug 101 is divided into four members 101A, 101B, 101C, and 101D, but this is not limited to this. The female shear lug 101 may also be divided into two roughly U-shaped members, one above the other.

2. Second Embodiment Next, a support structure according to a second embodiment will be described with reference to FIG.
5 is a cross-sectional view showing a support structure according to the second embodiment. Portions common to the support structure 3 according to the first embodiment are given the same reference numerals and redundant explanations will be omitted.

As shown in Figure 5, the support structure according to the second embodiment has a male shear lug 202 and a female shear lug 201 that supports the male shear lug 202. As shown in Figure 5, the male shear lug 202 is formed in a solid rectangular convex shape. The female shear lug 201 is arranged so as to surround the male shear lug 202.

The female shear lug 201 is formed in a hollow rectangular concave shape. The female shear lug 201 also has a first member 201A and a second member 201B. In other words, the female shear lug 201 is divided into two members 201A and 201B in the vertical direction 111B.

The first member 201A and the second member 201B are each formed in a roughly U-shape. The first member 201A is positioned at the top in the vertical direction 111B, with its opening facing downward in the vertical direction 111B. In contrast, the second member 201B is positioned at the bottom in the vertical direction 111B, with its opening facing upward in the vertical direction. A mail shear lug 202 is positioned between the first member 201A and the second member 201B.

A gap 112 is formed between the first member 201A and the upper end of the male shear lug 202 in the vertical direction 111B, and similarly, a gap 112 is formed between the second member 201B and the lower end of the male shear lug 202 in the vertical direction 111B. Therefore, the gap 112 allows for deformation during thermal expansion. Furthermore, in the event of a large displacement in the vertical direction 111B, the male shear lug 202 abuts against the female shear lug 201. This makes it possible to respond to displacement in the vertical direction 111B during an earthquake.

Furthermore, the first member 201A and the second member 201B abut against both ends of the female shear lug 202 in the circumferential direction 111A. As a result, displacement of the support structure in the circumferential direction 111A is suppressed by the support structure of the female shear lug 201 and the male shear lug 202.

As with the support structure 3 according to the first embodiment, a gap 12 is formed between the male shear lug 202 and the wall surface of the containment vessel 1 in the radial direction 11 of the containment vessel 1.

Other configurations are the same as those of the support structure 3 according to the first embodiment, so a description of those configurations will be omitted. A support structure having such a configuration can also achieve the same effects as those of the support structure 3 according to the first embodiment described above.

Furthermore, with the support structure according to this second embodiment, the mail shear lug 202 has a solid structure, which makes it possible to increase rigidity compared to the support structure 3 according to the first embodiment.

In the second embodiment, the support structure is divided into two parts, the first member 201A and the second member 201B, but it may also be divided into four parts, similar to the female shear lug 101 in the first embodiment.

3. Third Embodiment Next, a support structure according to a third embodiment will be described with reference to FIG.
6 is a cross-sectional view showing a support structure according to a third embodiment. Portions common to the support structure 3 according to the first embodiment are given the same reference numerals and redundant explanations will be omitted.

As shown in Figure 6, the support structure of the third embodiment includes a male shear lug 302 and a female shear lug 301 that supports the male shear lug 302. The female shear lug 301 has two members 301A and 301B, and its configuration is similar to that of the female shear lug 201 of the second embodiment, so its description will be omitted.

As shown in FIG. 6, the male shear lug 302 is formed in a convex shape of a solid cylinder. The female shear lug 301 is arranged so as to surround the male shear lug 302. A gap 112 is formed between the first member 301A and the upper end of the male shear lug 302 in the vertical direction 111B. Similarly, a gap 112 is formed between the second member 301B and the lower end of the male shear lug 302 in the vertical direction 111B. The first member 301A and the second member 301B abut against both ends of the male shear lug 302 in the circumferential direction 111A.

As with the support structure 3 according to the first embodiment, a gap 12 is formed between the male shear lug 302 and the wall surface of the containment vessel 1 in the radial direction 11 of the containment vessel 1.

Other configurations are similar to those of the support structure 3 according to the first embodiment and the support structure according to the second embodiment, so a description of those configurations will be omitted. A support structure having such a configuration can also achieve the same effects as the support structure 3 according to the first embodiment and the structure according to the second embodiment described above.

4. Fourth Embodiment Next, a support structure according to a fourth embodiment will be described with reference to FIG.
6 is a cross-sectional view showing a support structure according to a fourth embodiment. Portions common to the support structure 3 according to the first embodiment are given the same reference numerals and redundant explanations will be omitted.

As shown in Figure 6, the support structure of the fourth embodiment has a male shear lug 402 and a female shear lug 401 that supports the male shear lug 402. The male shear lug 402 is formed in a convex solid cylindrical shape, and its configuration is similar to that of the female shear lug 301 of the third embodiment, so a description thereof will be omitted. The female shear lug 401 is then positioned so as to surround the male shear lug 402.

The female shear lug 401 is formed in a hollow, oval, concave shape. The female shear lug 401 also has a first member 401A and a second member 401B. In other words, the female shear lug 401 is divided into two members 401A and 401B in the vertical direction 111B.

The first member 401A and the second member 401B are each formed in a roughly C-shape, which is a roughly arc-like shape. The first member 401A is positioned at the top in the vertical direction 111B, with its opening facing downward in the vertical direction 111B. In contrast, the second member 401B is positioned at the bottom in the vertical direction 111B, with its opening facing upward in the vertical direction. A male shear lug 202 is positioned between the first member 401A and the second member 401B. The inner diameters of the first member 401A and the second member 401B are formed to be equal to the outer diameter of the male shear lug 402.

A gap 112 is formed between the first member 401A and the upper end of the male shear lug 402 in the vertical direction 111B, and similarly, a gap 112 is formed between the second member 401B and the lower end of the male shear lug 402 in the vertical direction 111B. The first member 401A and the second member 401B abut against both ends of the male shear lug 402 in the circumferential direction 111A.

As with the support structure 3 according to the first embodiment, a gap 12 is formed between the male shear lug 402 and the wall surface of the containment vessel 1 in the radial direction 11 of the containment vessel 1.

Other configurations are similar to those of the support structure 3 according to the first embodiment and the support structures according to the second and third embodiments, so a description of those configurations will be omitted. A support structure having such a configuration can also achieve the same effects as those of the support structure 3 according to the first embodiment and the structures according to the second and third embodiments described above.

5. Fifth Embodiment Next, a support structure according to a fifth embodiment will be described with reference to FIGS.
Fig. 7 is an enlarged view showing the end of the support structure according to the fifth embodiment. Fig. 8 and Fig. 9 are cross-sectional views taken along line CC shown in Fig. 7, with Fig. 8 showing the normal state and Fig. 9 showing the state when an earthquake occurs. Parts common to the support structure 3 according to the first embodiment are given the same reference numerals and redundant explanations will be omitted.

As shown in Figures 7 and 8, the end of the support structure 503 has a male shear lug 502 and a female shear lug 501 that supports the male shear lug 502. Note that the configuration of the male shear lug 502 is similar to that of the male shear lug 102 in the first embodiment, so a description thereof will be omitted.

Furthermore, like the female shear lug 101 according to the first embodiment, the female shear lug 501 is divided into four members: a first member 501A, a second member 501B, a third member 501C, and a fourth member 501D. The first member 501A, the second member 501B, the third member 501C, and the fourth member 501D are arranged on the wall surface of the containment vessel 1 via guide rails 113. The first member 501A, the second member 501B, the third member 501C, and the fourth member 501D are supported by the guide rails 113 so as to be movable in the vertical direction 111B. The first member 501A, the second member 501B, the third member 501C, and the fourth member 501D are provided with drive units (not shown).

The drive unit is connected to the control device 114. The control device 114 has an earthquake detection unit 115A and a control unit 115B. The earthquake detection unit 115A detects shaking (earthquakes) of the reactor building. Information detected by the earthquake detection unit 115A is then output to the control unit 115B. Based on the information detected by the earthquake detection unit 115A, the control unit 115B controls the drive of the drive unit that moves the first member 501A, second member 501B, third member 501C, and fourth member 501D of the female shear lug 501.

As shown in Figure 8, under normal circumstances, a gap 112 is formed in the vertical direction 111B between the support pieces of the female shear lug 501 and the male shear lug 502. At this time, the four members 501A, 501B, 501C, and 501D of the female shear lug 501 are locked on the guide rails 113 by the control device 114, restricting movement in the vertical direction 111B.

When the earthquake detection unit 115A detects the occurrence of an earthquake, the control unit 115B of the control device 114 outputs a control signal to a drive unit (not shown) to unlock the female shear lug 501. Next, as shown in FIG. 9, the first member 501A, second member 501B, third member 501C, and fourth member 501D move along the guide rail 113 in a direction that abuts the male shear lug 502. As a result, in the event of an earthquake, the gap between the female shear lug 501 and the support piece of the male shear lug 502 is completely eliminated. The control device 114 then locks the four members 501A, 501B, 501C, and 501D of the female shear lug 501.

Figure 10 is a graph showing the vertical load-displacement characteristics of the support structure under normal conditions. Figure 11 is a graph showing the vertical load-displacement characteristics of the support structure during an earthquake. The vertical axis represents the load F, and the horizontal axis represents the displacement X.
As shown in FIG. 10, when there is a gap 112 under normal conditions, the stiffness of the shear lug structure is K, the gap amount is δ, and the maximum displacement amount is δ _max . When considered as a linear system, the equivalent stiffness K _eq is expressed by the following equation 1.
[Equation 1]

The equivalent stiffness K _eq shown by the dashed line in Figure 10 decreases relative to the stiffness K of the shear lug structure as the gap amount δ increases. In contrast, during an earthquake, as shown in Figure 9, the first member 501A, the second member 501B, the third member 501C, and the fourth member 501D are moved to abut against the mail shear lug 502. As a result, the gap amount δ becomes zero, and as shown in Figure 11, the equivalent stiffness K _eq matches the stiffness K of the shear lug structure, and no stiffness reduction occurs due to the gap. As a result, the earthquake resistance of the support structure 503 in the vertical direction 111B can be improved compared to the support structure 3 of the first embodiment.

Other configurations are the same as those of the support structure 3 according to the first embodiment, so a description of those configurations will be omitted. The support structure 503 having such a configuration can also achieve the same effects as those of the support structure 3 according to the first embodiment described above.

The present invention is not limited to the embodiments described above and shown in the drawings, and various modifications are possible without departing from the spirit of the invention as set forth in the claims.

Note that although words such as "parallel" and "orthogonal" are used in this specification, these do not mean only the strict terms "parallel" and "orthogonal," but also include "parallel" and "orthogonal," and may also refer to states such as "approximately parallel" and "approximately orthogonal," as long as these functions can be fulfilled.

1... Reactor pressure vessel, 2... Reactor pressure vessel, 3, 4, 5, 503... Support structure, 6... Reactor pressure vessel pedestal, 11... Radial direction, 12... Gap, 101, 201, 301, 401, 501... Female shear lug, 101A, 201A, 301A, 401A, 501A... First member, 101B, 201B, 301B, 401B, 501B... Second member, 101C, 501C... Third member, 101D, 501D... Fourth member, 102, 202, 302, 402, 502... Male shear lug, 102A... First support piece, 102B... Second support piece, 102C... Third support piece, 102D... Fourth support piece, 111A... Circumferential direction, 111B... Vertical direction, 112... Gap, 113... Guide rail, 114... Control device, 115A... Earthquake detection unit, 115B... Control unit

Claims (8)

A support structure disposed between a reactor pressure vessel and a cylindrical reactor containment vessel,
a female shear lug installed on a wall surface of the reactor containment vessel and divided into at least two members in the vertical direction of the reactor containment vessel;
a male shear lug supported by the female shear lug;
the male shear lug is disposed with a gap in the radial direction of the containment vessel relative to the wall surface of the containment vessel,
The female sheath is
A first member;
a second member disposed below the first member in the up-down direction with the mail shear lug interposed therebetween,
the first member and the second member are arranged with a gap between them and the male shear lug in the vertical direction. 2. The support structure for a reactor pressure vessel according to claim 1, wherein the first member and the second member are disposed in contact with the male shear lug in the circumferential direction of the reactor containment vessel. The cross section of the mail shear lug cut in the vertical direction is formed in a cross shape,
a first support piece that protrudes upward in the up-down direction;
a second support piece that protrudes downward in the up-down direction;
a third support piece protruding from a boundary between the first support piece and the second support piece toward one side in the circumferential direction;
a fourth support piece that protrudes from a boundary between the first support piece and the second support piece toward the other side in the radial direction,
the first member of the female shear lug is in contact with the first support piece in the circumferential direction and is disposed with a gap between it and the third support piece or the fourth support piece in the up-down direction,
3. The support structure for a reactor pressure vessel according to claim 2, wherein the second member of the female shear lug abuts against the second support piece in the circumferential direction and is disposed with a gap from the third support piece or the fourth support piece in the vertical direction. the first member and the second member are supported by guide rails provided on a wall surface of the reactor containment vessel so as to be movable in the up and down direction,
In a normal state, the first member and the second member are disposed with a gap between them and the mail shear lug in the up-down direction,
2. The support structure for a reactor pressure vessel according to claim 1, wherein, in the event of an earthquake, the first member and the second member abut against the mail shear lug, eliminating the vertical gap. The mail shear lug is formed in a rectangular convex shape,
3. The support structure for a reactor pressure vessel according to claim 2, wherein the female shear lug is surrounded by the first member and the second member, and is formed in a hollow rectangular concave shape. The male shear lug is formed in a cylindrical convex shape,
3. The support structure for a reactor pressure vessel according to claim 2, wherein the female shear lug is surrounded by the first member and the second member, and is formed in a hollow rectangular concave shape. The male shear lug is formed in a cylindrical convex shape,
3. The support structure for a reactor pressure vessel according to claim 2, wherein the female shear lug is surrounded by the first member and the second member, and is formed in a hollow, oval, concave shape. a reactor pressure vessel;
a cylindrical reactor containment vessel that contains the reactor pressure vessel;
a plurality of support structures disposed between the reactor pressure vessel and the containment vessel;
The support structure includes:
a female shear lug installed on a wall surface of the reactor containment vessel and divided into at least two members in the vertical direction of the reactor containment vessel;
a male shear lug supported by the female shear lug;
the male shear lug is disposed with a gap in the radial direction of the containment vessel relative to the wall surface of the containment vessel,
The female sheath is
A first member;
a second member disposed below the first member in the up-down direction with the mail shear lug interposed therebetween,
the first member and the second member are arranged with a gap between them and the mail shear lug in the vertical direction.