JPH0749395A - Steel structure of lower dry well and installation thereof - Google Patents

Abstract

PURPOSE:To shorten the work schedule while enhancing the work efficiency in the installation of steel structure of lower dry well Within a reactor container. CONSTITUTION:A main beam 2 for upper floor, a main beam 3 for lower floor having an outer diameter smaller than the inner peripheral diameter of a ring 6 for reinforcing the foundation of reactor body, steel structural members including columns 4 and small beams 5, a heat-exchanger 11, and pipings 12, 13 for control rod and instrumentation are assembled integrally on the outside of the foundation 1 for reactor body. The assembly is then suspended in the foundation 1 having inner peripheral surface secured with the reinforcing ring 6. The main beam 2 for upper floor is temporarily set on the reinforcing ring 6 and then the main beam 2 is shifted horizontally thus setting the installing position of the main beam 3 for lower floor coupled with the main beam 2 for upper floor through columns. Thereafter, the steel structural members are set and the machines are installed along with the pipings thereof.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a lower drywell steel structure in a reactor containment vessel and a method of installing the same.

[0002]

2. Description of the Related Art A conventional technique for installing a lower drywell steel frame structure will be described with reference to FIGS.
FIG. 3 is a schematic vertical sectional view of the entire conventional reactor containment vessel, and FIG.
5 is a schematic longitudinal sectional view of a conventional control rod housing supporting rest beam and its vicinity, FIG. 5 (a) is an explanatory view of a conventional steel structure installation procedure, and FIG. 5 (b) is FIG.
It is a BB arrow line view of (a) of FIG.

As shown in FIG. 3, an upper dry well 20, a lower dry well 21, and a suppression chamber 22 are formed in the reactor containment vessel 17, and the reactor pressure vessel 19 and the reactor pressure vessel 19 are connected to each other. The reactor shield wall 23 that shields the emitted radiation, the reactor body foundation 1 that supports them, and the like are stored.

An internal pump 25 is attached to the lower portion of the reactor pressure vessel 19, and the lower dry well 21 serves as a maintenance space for the internal pump 25.

The lower dry well 21 is located inside the reactor body foundation 1 and below the reactor pressure vessel 19, and an access tunnel 24 for accessing the lower dry well 21 from the outside of the reactor containment vessel 17 is provided. It is installed so as to penetrate the reactor building 18 and the suppression chamber 22 and is used for carrying in various equipment such as the internal pump 25, and the pipes described later.

As shown in FIG. 4, the lower dry well 21 is provided with a heat exchanger 11 for cooling the internal pump 25, a control rod pipe 12 and an instrumentation pipe to be described later. Main beam 2 for upper floor and main beam 3 for lower floor, which are steel frames of the steel structure of the well 21.
Has been installed.

Further, the lower dry well 21 includes an upper floor support member 27 for supporting the upper floor main beam 2, a lower floor support member for supporting a lower floor main beam, which will be described later, and a small beam, which will be described later. It is installed in an equal arrangement.

A control rod housing supporting rest beam 26 is installed on the inner circumference of the lower floor main beam 3, and the control rod housing 16 is connected to the control rod housing supporting rest beam 26 by a connecting bolt. It is supported. Further, the main beam 2 for the upper floor and the main beam 3 for the lower floor are grating-like steel plate-like floors, and the grating 2
8 are laid.

Next, the procedure for installing the steel frame structure of the lower dry well 21 will be described. In FIG. 5A, first, the reinforcing ring 6 for the reactor body foundation is installed on the inner surface of the reactor body foundation 1 as a strength member of the reactor body foundation 1.

Next, the lower floor main beam 3 is loaded into the lower dry well 21 from above by a crane (not shown), and the lower floor support plate 8 and the reactor body foundation 1,
By welding each of the lower floor support member 29 and the reactor body foundation 1, the lower floor support plate 8 and the lower floor main beam 3, and the lower floor support member 29 and the lower floor main beam 3,
The main beam 3 for the lower floor is installed in the lower part of the reactor body foundation 1.

Further, after the upper floor main beam 2 is placed on the reactor body foundation reinforcing ring 6, the upper floor main beam 2 and the reactor body foundation reinforcing ring 6 and the upper floor support plate 7 are placed.
And the upper floor support member 27 are welded to each other to complete the installation of the upper floor main beam 2.

The plurality of upper floor main beams 2 and the plurality of lower floor main beams 3 are both internal pumps 2.
The vertical route for maintenance of 5 is avoided, the inner circumference of the reactor body foundation 1 is equiangularly divided, and the reactor body foundations 1 are installed at equal intervals in the circumferential direction.

After these basic steel structures are completed, the heat exchanger 11 and the control rod pipe 12, the below-mentioned instrumentation pipe, the grating 28, and the lower floor are used from the upper part using the crane or the access tunnel 24. A stair handrail (not shown) that goes up, and a beam (which will be welded to the main beam 2 for the upper floor and the main beam 3 for the lower floor as a receiving member of the grating 28) to be described later are carried in, and the beam and heat exchange are performed. The equipment 11, the control rod pipe 12, the instrumentation pipe, the grating 28, and the handrail are installed in this order.

Further, as shown in FIG. 5 (a), a transverse beam-shaped reinforcing plate 30 is provided between the inner cylindrical steel plate and the outer cylindrical steel plate which are constituent members of the reactor body foundation 1. Further, as shown in FIG. 5B, the internal pump 25 and the vent pipe 10 are positioned substantially on the same radial line, and the upper floor main beam 2 and the lower floor main beam 3 are As described above, it is arranged in the middle of the rib 9 for the foundation of the reactor body, avoiding the ascending / descending route for maintenance of the internal pump 25.

[0015]

However, the conventional method for installing the steel structure of the lower dry well has the following problems to be solved.

(1) Since the main beam for the upper floor and the main beam for the lower floor are arranged in the middle of the ribs for the foundation of the reactor body, avoiding the ascending / descending route for maintenance of the internal pump, Both the beam and the main beam for the lower floor,
It is not possible to arrange them so that they are on the same radial line as the ribs for the reactor body foundation.

That is, the main beam for the upper floor and the main beam for the lower floor are supported only by the portion of the inner cylindrical steel plate of the reactor body foundation located between the ribs for the reactor body foundation. The load of the control rod housing and other equipment is applied to both main beams in this condition. Therefore, it is necessary to provide a transverse beam-shaped reinforcing plate between the inner cylindrical steel plate and the outer cylindrical steel plate.

(2) When installing the steel structure of the lower drywell, the overlay error between the centerline of the steel structure of the lower drywell and the centerline of the reactor pressure vessel is ±
High accuracy is required within 1.5 mm.

That is, the installation of the lower drywell steel frame structure is carried out under such severe conditions.
In this case, conventionally, the main beam for the upper floor and the main beam for the lower floor, which are the steel frame of the steel structure, are first installed.

Then, a restorent beam for supporting the control rod housing is installed on the inner circumference of the main beam for the lower floor. The rest beam for supporting the control rod housing has a function of restraining horizontal shake at the lower floor level of the control rod housing whose upper portion is connected to the inside of the reactor pressure vessel. Therefore, the installation accuracy of the lower floor main beam greatly affects the installation accuracy of the lower drywell steel structure.

When such a lower floor main beam is installed, a lower floor support plate for supporting the lower floor main beam is provided so that the installation accuracy of the restraint beam for supporting the control rod housing can be maintained within an allowable value. , And adjusting the installation position of the floor support member that holds the lower floor main beam from above and below.

However, in this way, it is a very difficult work to carry out welding and welding while adjusting the installation positions of these steel frame structural members to complete the installation with high precision, which causes an increase in man-hours and process delays. Becomes

(3) After the main beam for the lower floor is installed as described above, the main beam for the upper floor is subsequently installed to complete the steel frame, and thereafter, using the crane, from the top, Or from access tunnel, beam, heat exchanger,
Bring in control rod piping, instrumentation piping, grating and handrails, and attach them to the steel frame.

However, when these are carried in, it is difficult to carry them in because the steel frames such as the main beams for the upper floor and the main beams for the lower floor have already been installed and the carry-in route is narrow. The work efficiency at the time of installation does not rise and a large construction period is required.

(4) The upper floor support member and the lower floor support member hinder the passage and workability of the lower floor and the work area located below the lower floor.

Further, since the control rod pipes and instrumentation pipes are radially installed in the area between the upper floor and the lower floor, it is necessary to support the control rod pipes and the instrumentation pipes.

In this case, the upper floor support member may be used as a support member for the control rod pipe and the instrumentation pipe, but since the upper floor support member is also used as a support member for the upper floor main beam. , The support points are offset to the base side of the reactor body. That is, a suitable position for supporting the control rod pipe and the instrumentation pipe is an intermediate point between the reactor pressure vessel and the reactor body foundation, but it is impossible to support it at this point.

In the above case, if the upper floor supporting member is arranged vertically and connected to the upper floor main beam and the lower floor main beam so as to withstand the load of the above pipes, the above pipe It becomes possible to support the kind. However, in all cases, including this case, the installation will be on-site work.

That is, the welding and joining work at the site is carried out in order of the reactor body foundation and the lower floor support plate, the lower floor support plate and the lower floor main beam, the lower floor main beam and the vertical column, and the vertical column. And the joint between the main beam for the upper floor and the reinforcement ring for the reactor body foundation that has been installed in advance on the reactor body foundation.

In this case, an error is likely to occur in the installation, and it is difficult to adjust the gap between the vertical column and the main beam for the upper floor which is caused by this error, which causes a process delay.

An object of the present invention is to provide a drastic improvement measure in the method of suspending and installing a steel frame structure in a lower dry well to eliminate the above-mentioned problems and to shorten the process and improve work efficiency.

[0032]

The above object can be achieved as follows.

(1) A rib for a reactor body foundation that is located inside the reactor containment vessel and is provided between the inner cylinder steel plate and the outer cylinder steel plate and between the inner cylinder steel plate and the outer cylinder steel plate is used. Inside a certain reactor main body foundation, an internal pump for sending circulating water to the reactor pressure vessel is installed, and in the steel structure of the lower dry well, the main beam for floor construction with its outer end branched into multiple parts. A plurality of radial arrangements, and the outer ends are joined to a support member fixed to the inner peripheral surface of the inner cylindrical steel plate.

(2) In (1), the fixing portion of the support member to the inner peripheral surface of the inner cylindrical steel plate is located at a position close to the fixing portion of the inner cylindrical steel plate and the reactor body foundation rib.

(3) An interface for sending circulating water to the reactor pressure vessel is placed inside the reactor main body, which is located inside the reactor containment vessel and has a reinforcing ring for the reactor main body fixedly provided on the inner peripheral surface thereof. Null pumps, heat exchangers for internal pumps, control rod piping and instrumentation piping equipment and pipes, and steel structural members consisting of multiple upper floor main beams, lower floor main beams, vertical columns and beam girders. In the method of installing the steel structure of the lower drywell, the outer diameter of the main beam for the lower floor is made smaller than the inner diameter of the reinforcing ring for the reactor body foundation, By inserting the main beam for the lower floor from above, the main beam for the lower floor is located below the reinforcement ring for the foundation of the reactor body, and the main beams for the upper floor are connected to the reinforcement ring for the foundation of the reactor body. Set up Among the main beams for the upper floor and the main beams for the lower floor, the main beams for the upper floor and the main beams for the lower floor, which are located at the same vertical position, are connected through vertical columns to form a multi-tiered floor structure. To let.

(4) In (3), an upper-floor main beam, a lower-floor main beam, vertical columns, and girder steel frame structural members,
In addition, the heat exchanger of the internal pump, the control rod piping, and the instrumentation piping are integrated and integrated outside the reactor body foundation, and then suspended inside the reactor body foundation, and the main beam for the upper floor is installed. Temporarily place it on the reinforcement ring for the foundation of the reactor body and adjust the position of the main beam for the lower floor.

[0037]

According to the present invention, the inner peripheral surface of the inner cylindrical steel plate in the supporting member is divided into a plurality of Y-shaped outer end portions of the upper floor main beam and the lower floor main beam, and is joined to these outer end portions. The fixed portion to the inner tubular steel plate and the rib for the reactor body foundation is set close to the fixed portion. Therefore, it is possible to transmit the load received by these both main beams to the entire reactor body foundation, and it is possible to reduce the local stress generated in the inner tubular steel sheet.

Further, since the main beam for the upper floor, the main beam for the lower floor, the vertical column, the beam, the heat exchanger, the pipe for the control rod, and the pipe for the instrumentation are integrated and suspended in the reactor body foundation, It is possible to eliminate the work of adjusting the gap between the floor main beam and the vertical column.

Further, since the outer diameter of the lower floor main beam is smaller than the outer diameter of the upper floor main beam, it interferes with the reinforcement ring for the reactor body foundation which is fixed to the reactor body foundation. The main beam portion for the lower floor can be carried into the lower dry well without any trouble.

As a result, the main beam for the upper floor, which is carried into the lower dry well, can be temporarily placed on the reinforcing ring for the reactor body foundation, which is fixed to the reactor body foundation in advance. Horizontal position adjustment of the upper floor main beam becomes extremely easy.

That is, when the main beam for the upper floor is moved in the horizontal direction, the main beam for the lower floor, which is connected to the main beam for the upper floor via the vertical pillar, is also moved in the horizontal direction accordingly. The position adjustment work of the main beam for the lower floor, which is the steel frame for fixing the restraint beam for supporting the control rod housing, becomes easy.

Further, the outer diameter of the main beam for the lower floor carried into the lower dry well is smaller than the inner diameter of the main beam for the upper floor temporarily placed on the reinforcement ring for the foundation of the reactor body, Since there is a sufficient space space with the inner wall of the foundation, welding work between the reactor body foundation and the lower floor support plate becomes easy.

[0043]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to FIGS. FIG. 1 is a bird's-eye view of an essential part of one embodiment of the present invention, FIG. 2 (a) is an explanatory view of the installation procedure of a steel frame structure, and FIG. 2 (b) is A- of FIG. 2 (a). FIG.

In this embodiment, a steel frame structural member including an upper floor main beam 2, a lower floor main beam 3, a vertical column 4 and a beam 5 in FIG. 1, a heat exchanger 11, a control rod pipe 12 and This is a case where the equipment and piping of the instrumentation piping 13 are incorporated and integrated on an outdoor surface plate of a factory or a local site, and this is suspended and installed in the reactor body foundation 1, and FIG. Shows the state of.

At the time of performing this installation, the vent pipe 1
0 and the internal pump 25 (see FIG. 5) are substantially existing on the same radius line, and the vent pipe 10 and the reactor main body foundation rib 9 have different arrangement angles, and they are already installed. In such a state, the upper floor main beam 2 and the lower floor main beam 3 are radially arranged at positions where the inner circumference of the reactor body foundation 1 is divided into equal angles so as to vertically move the internal pump 25. Install it in a position that avoids interference with.

The reactor main body foundation rib 9 and the vent pipe 1 described above.
This embodiment is the same as the conventional one with respect to the arrangement positions of 0 and the internal pump 25, and the installation positions of the upper floor main beam 2 and the lower floor main beam 3.

However, conventionally, the outer ends of the plurality of main beams 2 for the upper floor and the main beam 3 for the lower floor are joined to the inner core steel plate of the reactor main body foundation 1 at the two locations of the main ribs 9 of the reactor body. Is joined to the support member that is fixed to the middle part of the.

On the other hand, in the present embodiment, in the support member in which the outer end portions of the upper floor main beam 2 and the lower floor main beam 3 are branched into a plurality of Y-shapes and joined to these outer end portions. The fixed portion of the reactor main body foundation 1 to the inner peripheral surface of the inner cylindrical steel plate is set at a position close to the fixed portion of the inner cylindrical steel plate and the rib 9 for the reactor main body foundation.

Since such a fixing method is adopted,
The load bearing strength of the upper floor main beam 2 and the lower floor main beam 3 is improved, and it is safe even if the load of the control rod housing 16 and other equipment is applied to the upper floor main beam 2 and the lower floor main beam 3. It is possible to secure the sex. The branched portion is also used for supporting grating (see FIG. 3).

That is, conventionally, the main beam 2 for the upper floor is used.
Also, in order to improve the load bearing strength of the main beam 3 for the lower floor, the reinforcing plate 30 (see FIG. 5) was provided between the inner cylindrical steel plate and the outer inner cylindrical steel plate of the reactor body foundation 1. However, in this embodiment, the reinforcing plate 30 is omitted because it is not necessary.

When assembling the steel structure of the lower dry well outdoors, a temporary scaffold is constructed so that the installation of each device satisfies the required accuracy. Assembling the main beam 2 for the upper floor and the main beam 3 for the lower floor, and the temporary combination of the restraint beam 26 for supporting the control rod housing and the main beam 3 for the lower floor, which require high accuracy,
All are performed on a surface plate so that high reliability can be obtained with high accuracy.

The outer diameter of the main beam 3 for the lower floor is made smaller than the inner diameter of the reinforcing ring 6 for the foundation of the reactor body, and the steel frame structure of the lower dry well integrated outdoors is used for the lower floor. The main beam 3 can be suspended in the reactor body foundation 1 without interfering with the reinforcement ring 6 for the reactor body foundation. At the time of hoisting, a hoisting metal fitting 14 is welded to the upper part of the main beam 2 for the upper floor that is radially installed, and a large crane (not shown) is connected via a wire 15.
Is being hung up.

The outer diameter of the upper floor main beam 2 is made larger than the inner diameter of the reactor body foundation reinforcing ring 6 fixed to the inner surface of the reactor body foundation 1. And
The outer end of the main beam 2 for the upper floor is temporarily placed on the reinforcement ring 6 for the foundation of the reactor body, and the main beam 2 for the upper floor is slid on the reinforcement ring 6 for the foundation of the reactor body in a horizontal plane. By this, the horizontal position adjustment of the lower floor main beam 3, which is connected to the upper floor main beam 2 via the vertical column 4, is performed.

As a result, the installation accuracy of the lower floor main beam 3 is improved, so that the installation accuracy of the dry well steel frame structure can be reliably maintained within the required accuracy. Next, the procedure for installing the steel structure of the lower dry well of this embodiment will be described with reference to FIG.

First, the wire 15 is hung on the hanging metal fitting 14 welded to the upper floor main beam 2 and the integrated steel structure of the lower dry well is lifted by a crane (not shown) to atomize the inner peripheral surface. The reinforcing ring 6 for the reactor body foundation is suspended in the reactor body foundation 1 in which the reinforcement ring 6 is fixedly installed.

In this case, the reinforcement ring 6 for the reactor body foundation
Suspending until the lower surface of the upper floor main beam 2 is in contact with the upper surface of the upper floor, and placing the upper floor main beam 2 on the reinforcement ring 6 for the foundation of the reactor body, the steel structure of the lower dry well is temporarily placed. To do.

Next, the temporarily placed lower dry well steel structure is horizontally moved, and the reactor pressure vessel 19 and the control rod housing 1 penetrating the lower portion of the reactor pressure vessel 19 are moved.
The centering with the lower floor main beam 3 that greatly affects the position setting of 6 is performed. That is, this centering is performed by sliding the upper floor main beam 2 on the reinforcement ring 6 for the reactor body foundation.

The adjustment allowance at the time of centering is the gap between the outer end of the upper floor main beam 2 and the inner peripheral surface of the reactor body foundation 1, which have been manufactured to have a small diameter in advance. The reinforcement ring 6 for the reactor body foundation is originally fixed to the reactor body foundation 1 to secure the rigidity of the reactor body foundation 1. However, in the present embodiment, since it is attached horizontally, , The upper beam main beam 2 is placed on the reinforcement ring 6 for the foundation of the reactor body, the steel frame structure of the lower drywell is temporarily placed, and is used for the position adjustment of the lower beam main beam 3. .

In this embodiment, when the position of the main beam 3 for the lower floor is adjusted, only the reinforcement ring 6 for the foundation of the reactor body is in contact with the steel frame structure of the lower dry well, so that the steel frame structure of the lower dry well is contacted. The object is similar to a steel frame structure that requires high accuracy, but this installation method enables reliable installation within the required accuracy.
That is, after setting the position as described above, the installation is performed by welding.

Thereafter, the upper floor main beam 2 and the reactor main body foundation reinforcing ring 6, the upper floor main beam 2 and the upper floor support plate 7, and the lower floor main beam 3 and the lower floor support plate 8 are attached. The welding of the steel structures of the lower dry well in the reactor body foundation 1 is completed.

As described above, since the steel frame structure of the lower dry well is integrally assembled outdoors, it becomes possible to use the control rod pipe having a long dimension, and the man-hours for welding the control rod pipe are reduced. Can be made.

[0062]

According to the present invention, the following effects can be obtained.

(1) The main beam for the upper floor and the main beam for the lower floor are divided into a plurality of outer end portions, and the ribs for the foundation of the reactor body are not obstructed without hindering the elevation route for maintenance of the internal pump. Since the load can be transmitted to the main beams for the upper floor and the main beams for the lower floor, the load bearing strength is improved, and it is not necessary to provide a reinforcing plate in the reactor body foundation. Further, the branched portion is also used for supporting the grating.

(2) Since the lower drywell steel frame structure is assembled inside the factory or outdoors at the site, welding and assembling work are facilitated and work efficiency is greatly improved.

(3) Since the main beam for the lower floor of the steel frame structure of the lower drywell which is integrally suspended is carried in below the reinforcing ring for the foundation of the reactor body, the main beam for the upper floor is vertically Since it is not necessary to adjust the clearance between the pillar and the pillar, the process can be shortened.

(4) The main beam for the upper floor of the steel frame structure of the lower drywell, which is integrally suspended, is temporarily placed on the reinforcing ring for the foundation of the reactor body and can move freely in the horizontal direction. The main beam for the floor can be installed with high accuracy. Further, the horizontal alignment work of the restraint beam for supporting the control rod housing becomes easy, and the installation work efficiency is significantly improved.

(5) Since the vertical columns connecting the main beams for the upper floor and the main beams for the lower floor are arranged vertically and in a well-fitted manner, the support members for the control rod pipes and the integrated lower dry beams are arranged. It is useful as a reinforcing member for a steel structure of a well. In addition, the space areas of the upper floor and the lower floor can be made sufficiently wide.

(6) Since the integrated structure of the lower drywell steel frame structure is performed outdoors, it becomes possible to use control rod pipes having a long dimension, and it is possible to reduce the welding man-hours of the control rod pipes. it can.

[Brief description of drawings]

FIG. 1 is a bird's-eye view of essential parts of an embodiment of the present invention.

FIG. 2 is an explanatory diagram of a steel frame structure installation procedure.

FIG. 3 is a schematic vertical sectional view of an entire conventional reactor containment vessel.

FIG. 4 is a schematic vertical cross-sectional view of a conventional control rod housing supporting rest beam and its vicinity.

FIG. 5 is an explanatory view of a conventional procedure for installing a steel frame structure.

[Explanation of symbols]

1 ... Reactor body foundation, 2 ... Upper floor main beam, 3 ... Lower floor main beam, 4 ... Vertical column, 5 ... Beam, 6 ... Reactor body foundation reinforcing ring, 7 ... Upper floor support plate , 8 ... Lower floor support plate, 9 ... Reactor body foundation rib, 10 ... Vent pipe, 11 ... Heat exchanger, 12 ... Control rod pipe, 13 ... Instrumentation pipe, 14 ... Suspension fitting, 15 ... Wire , 16 ... Control rod housing, 17 ... Reactor containment vessel, 18 ... Reactor building, 19 ... Reactor pressure vessel, 20 ... Upper drywell,
21 ... Lower dry well, 22 ... Suppression chamber, 23 ... Reactor shield wall, 24 ... Access tunnel, 2
5 ... Internal pump, 26 ... Restorent beam for supporting control rod housing, 27 ... Support member for upper floor,
28 ... Grating, 29 ... Lower floor support member, 3
0 ... Reinforcing plate.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Hideyasu Furukawa 3-1-1, Saiwaicho, Hitachi-shi, Ibaraki Hitachi Ltd. Hitachi factory

Claims (4)

[Claims] 1. A reactor main body foundation rib which is located in a reactor containment vessel and is provided between an inner cylinder steel plate and an outer cylinder steel plate and between the inner cylinder steel plate and the outer cylinder steel plate. The main structure for the floor structure, in which the outer end is branched into multiple parts in the steel structure of the lower drywell, where an internal pump for sending circulating water to the reactor pressure vessel is installed inside the foundation of the reactor main body. A lower drywell steel structure, wherein a plurality of beams are radially arranged and the outer end portions are joined to a support member fixed to the inner peripheral surface of the inner cylindrical steel plate. 2. The fixing portion of the supporting member to the inner peripheral surface of the inner cylindrical steel plate is located at a position close to the fixing portion of the inner cylindrical steel plate and the nuclear reactor main body foundation rib. Lower drywell steel structure. 3. An interface for feeding circulating water to a reactor pressure vessel inside a reactor main body foundation, which is located in the reactor containment vessel and has the reinforcing ring for the reactor main body foundation fixed to the inner peripheral surface thereof. Null pump, heat exchanger of the internal pump, equipment and piping for control rod piping and instrumentation piping, and a plurality of upper floor main beams, lower floor main beams, vertical columns and beam beams In a method for installing a steel structure of a lower drywell for installing a member, an outer diameter of the main beam for the lower floor is made smaller than an inner peripheral diameter of the reinforcing ring for the reactor body foundation to reinforce the reactor body foundation. By inserting the lower floor main beam from above in the hole of the ring, the lower floor main beam is positioned below the reactor body foundation reinforcing ring, and a plurality of upper floor main beams are provided. The atom The main beam for the upper floor and the main beam for the lower floor, which are mounted on the reinforcing ring for the foundation of the furnace body and are located at the same vertical position among the plurality of main beams for the upper floor and the main beam for the lower floor, respectively. A method for installing a steel frame structure of a lower dry well, in which a plurality of steps of floor structures are formed by connecting the above-mentioned vertical columns. 4. A main beam for the upper floor, a main beam for the lower floor, a steel structural member of the vertical columns and the girders, a heat exchanger of the internal pump, a control rod pipe and an instrumentation pipe. After being integrated and integrated outside the reactor main body foundation, it is suspended inside the reactor main body foundation, and the upper floor main beam is temporarily placed on the reactor main body reinforcement ring, and the lower part The method for installing a steel structure for a lower drywell according to claim 3, wherein the position of the main beam for the floor is adjusted.