Research reactor bottom structure and installation method

Abstract

The invention relates to the technical field of nuclear reactor structures, in particular to a reactor bottom structure for a research reactor and an installation method.The reactor bottom structure is installed in a reactor lower cell and comprises an anti-seismic supporting structure fixed to the bottom face of the reactor lower cell and a blow-off pipeline system fixed to the anti-seismic supporting structure; the ventilation cooling structure is fixed on the top surface of the under-reactor chamber; the control rod driving mechanism is inversely mounted; a stator coil in the control rod driving mechanism is arranged in a cylinder in the ventilation cooling structure, a pressure-resistant shell in the control rod driving mechanism is arranged in the anti-seismic supporting structure, and an anti-seismic plate in the anti-seismic supporting structure is fixed to the pressure-resistant shell. A drainage connecting pipe arranged at the bottom end of the control rod driving mechanism is connected with the blow-off pipeline system. The reactor bottom structure has a compact structural size, provides limiting and cooling for the CRDM, and is also provided with a blow-off pipeline system for regularly discharging radioactive wastes to reduce the irradiation dose of the under-reactor cell.

Description

Technical Field

[0001] The present invention relates to the technical field of nuclear reactor structures, and in particular to a reactor bottom structure for a research reactor and an installation method thereof. Background Art

[0002] The reactor top structure is one of the important components of the current mainstream pressurized water reactor. It is located at the top of the reactor and its main functions include: (1) providing a limit for the control rod drive mechanism (CRDM) to limit excessive deformation of the drive mechanism under earthquake conditions to maintain its normal function; (2) providing cooling for the CRDM to ensure that the CRDM temperature does not exceed the limit.

[0003] However, the core of some research reactors is located in the lower part of the pressure vessel, and a large space needs to be reserved in the upper part for operations such as installation and removal of irradiated samples and replacement of materials. In order to avoid affecting the operating space in the upper part of the core, the CRDM cannot be arranged on the top of the reactor. Therefore, unlike the mainstream pressurized water reactor, the CRDM of the above-mentioned research reactor is arranged at the bottom of the reactor. Therefore, the top structure used to protect the CRDM in the mainstream pressurized water reactor is no longer applicable to the above-mentioned research reactor. At the same time, the CRDM of the above-mentioned research reactor is arranged in layers to save space, so that the stator coils of the upper and lower layers of CRDM are staggered to achieve a close arrangement of the CRDM, but the layered arrangement will lead to inconsistent CRDM heights, and the existing structure cannot meet the needs of CRDMs arranged at two heights.

[0004] In addition, the reactor bottom space of the above research reactor is small, and the size of the transport channel is also limited, which puts strict requirements on the size of the reactor bottom structure. At the same time, the above research reactor also needs to regularly discharge the radioactive waste generated inside the reactor from the bottom of the pressure vessel, which requires a special sewage pipe system to be set up at the bottom of the reactor.

[0005] To this end, a new reactor bottom structure is needed to meet the unique layout, space requirements and sewage discharge needs of the above-mentioned research reactor CRDM. Summary of the invention

[0006] The object of the present invention is to provide a bottom structure for a research reactor and an installation method, which solves the problem that the safety requirements, installation space requirements and sewage discharge requirements under the unique research reactor CRDM arrangement are difficult to meet.

[0007] The present invention is achieved through the following technical solutions:

[0008] In a first aspect, a reactor bottom structure for a research reactor is provided, which is installed inside a reactor bottom chamber, and includes: a seismic support structure fixed to the bottom surface of the reactor bottom chamber, a sewage pipe system fixed to the seismic support structure, a ventilation cooling structure fixed to the top surface of the reactor bottom chamber, and an inverted control rod drive mechanism;

[0009] The stator coil in the control rod drive mechanism is arranged in the cylinder in the ventilation cooling structure, the pressure shell in the control rod drive mechanism is arranged inside the seismic support structure, the seismic plate in the seismic support structure is fixed on the pressure shell, and the drainage pipe arranged at the bottom end of the control rod drive mechanism is connected to the sewage pipe system.

[0010] Furthermore, the seismic support structure also includes an upper circumference, a middle circumference, a lower circumference, legs, supporting columns, supporting ring plates, limit support blocks and adjustment screws. The upper circumference, middle circumference and lower circumference are fixedly arranged on the supporting columns to form a main frame, and the legs are fixedly arranged on the lower circumference; the supporting ring plate is fixedly arranged on the upper circumference, the limit support block is fixedly arranged on the supporting ring plate, and the adjustment screw is fixedly arranged on the limit support block. The adjustment screw adjusts the gap between the limit support block and the seismic plate by rotating.

[0011] Furthermore, the upper circumferential cylinder, the middle circumferential cylinder, the lower circumferential cylinder and the supporting ring plate are all two-petal structures, and the two petals of the upper circumferential cylinder, the middle circumferential cylinder and the lower circumferential cylinder are connected by a petal connecting plate; the two petals of the supporting ring plate are connected by the limiting support block.

[0012] Furthermore, a transition plate is provided between the supporting legs and the bottom surface of the small chamber under the pile.

[0013] Furthermore, the ventilation and cooling structure also includes a flange and an exhaust pipe, wherein the exhaust pipe is arranged on one side of the flange-connected cylinder, and the exhaust pipe is connected to an external ventilation system; and there is a gap between the cylinder and the stator coil in the control rod drive mechanism.

[0014] Furthermore, the flange and the cylinder are both of a petal-type structure; a flange rib is also provided on the flange, and the diameter of the flange is larger than the diameter of the top hole of the small chamber under the pile; a cylinder rib is also provided on the outer side of the cylinder.

[0015] Furthermore, the sewage pipe system includes two layers of sewage pipes, a drainage ring pipe and a drainage outlet main pipe; each layer of sewage pipe includes a primary valve, a secondary valve and a drainage branch pipe; the water outlet of the primary valve is connected to the water inlet of the secondary valve through a drainage branch pipe, and the water outlet of the secondary valve is also connected to the water inlet of the drainage ring pipe through the drainage branch pipe, and the water outlet of the drainage ring pipe is connected to the drainage outlet main pipe; the water inlet of the primary valve is connected to the drainage pipe in the control rod drive mechanism, and the number of primary valves is the same as the number of control rod drive mechanisms.

[0016] Furthermore, the secondary valve in the upper sewage pipeline is installed on the valve fixing plate of the upper surrounding tube, and the secondary valve in the lower sewage pipeline is installed on the valve fixing plate of the middle surrounding tube.

[0017] Furthermore, the drainage ring pipe is configured as a two-section structure that matches the two-petal structure of the upper enclosure or the middle enclosure, and the drainage ring pipe is fixed on a supporting column below the secondary valve in the lower sewage pipeline.

[0018] In a second aspect, a method for installing a bottom structure for a research reactor is provided, the method comprising the following steps:

[0019] Installing the control rod drive mechanism on the bottom head of the reactor pressure vessel;

[0020] The ventilation and cooling structure is transported to the small chamber under the pile in petals, and installed on the top surface of the small chamber under the pile, and then the petals are connected to each other;

[0021] fixing the anti-seismic plate to the pressure shell of the control rod drive mechanism;

[0022] Connect the primary valve in the sewage pipe system to the drainage pipe of the control rod drive mechanism;

[0023] Transport the seismic support structure to the chamber below the pile in petals; connect the two petals of the lower shroud together, and fix the legs and the support columns on the lower shroud; fix the secondary valve on the valve fixing plates of the upper shroud and the middle shroud, and fix the middle shroud and the upper shroud on the support columns in turn; and then fix the support ring plate on the upper shroud;

[0024] Fix the drainage ring pipe in the sewage pipeline system on the supporting column below the secondary valve in the lower sewage pipeline, and connect the pipelines in the sewage pipeline system to complete the installation.

[0025] The technical solution of the present invention has at least the following advantages and beneficial effects:

[0026] The bottom structure disclosed in the present invention has a compact structural size and provides position limiting and cooling for CRDM. At the same time, the bottom structure is also provided with a sewage pipe system to regularly discharge radioactive waste to reduce the radiation dose of the small room under the pile. Among them, the seismic support structure and the ventilation and cooling structure adopt a separate design, which greatly reduces the height of the equipment and facilitates the installation and transportation of the narrow space of the small room under the pile; the sewage pipe system improves safety by setting two valves, and the integrity of the pressure boundary can still be guaranteed by the secondary valve in the event of leakage of the primary valve; and the sewage pipe system is arranged in layers, and the drainage ring pipe is used to connect and realize the clustering and extraction of multiple branches, which greatly simplifies the pipeline layout and realizes the layout and disassembly of complex pipeline systems in narrow spaces; the ventilation and cooling structure can also realize the transportation, installation and disassembly of a single petal by dividing the structure into petals, which greatly reduces the demand for space size of the ventilation and cooling structure. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1It is the layout diagram of the small chamber under the pile structure;

[0028] Figure 2 It is a schematic diagram of the two-petal separation of the seismic support structure and the sewage pipe system;

[0029] Figure 3 It is the front view of the seismic support structure;

[0030] Figure 4 is a top view of the seismic support structure;

[0031] Figure 5 It is the AA section view of the seismic support structure;

[0032] Figure 6 It is the front view of the ventilation and cooling structure;

[0033] Figure 7 It is a top view of the ventilation and cooling structure;

[0034] Figure 8 It is the cross-sectional view of the ventilation cooling structure BB;

[0035] Fig. 9 It is the main view of the sewage pipe system;

[0036] Fig.10 It is a top view of the sewage pipe system;

[0037] Fig.11 It is the CC section view of the sewage pipe system;

[0038] Fig.12 It is a schematic diagram of a single pipe of the sewage pipe system;

[0039] Fig.13 It is a flow chart of the installation method of the pile bottom structure;

[0040] Icons: 1-small chamber under the reactor, 2-drainage piping system, 3-seismic support structure, 4-ventilation and cooling structure, 5-control rod drive mechanism, 6-bottom head of reactor pressure vessel, 7-upper casing, 8-support column, 9-middle casing, 10-lower casing, 11-support leg, 12-transition plate, 13-connecting plate bolt, 14-nut, 15-valve fixing plate, 16-petal connecting plate, 17-limiting support block, 18-support block bolt, 19-support ring plate, 20-adjusting screw, 21-stack top fixing bolt, 22-seismic plate, 23-flange, 24-exhaust outlet pipe, 25-cylinder, 26-flange rib plate, 27-cylinder rib plate, 28-primary valve, 29-secondary valve, 30-drainage branch pipe, 31-drainage ring pipe, 32-drainage outlet main pipe. DETAILED DESCRIPTION

[0041] In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Generally, the components of the embodiments of the present invention described and shown in the drawings here can be arranged and designed in various different configurations.

[0042] Example 1

[0043] like Figure 1-Figure 12 As shown, a bottom structure for a research reactor is provided, which is installed inside a lower chamber 1, and comprises: a seismic support structure 3 fixed on the bottom surface of the lower chamber 1, a sewage pipe system 2 fixed on the seismic support structure 3, a ventilation cooling structure 4 fixed on the top surface of the lower chamber 1, and an inverted control rod drive mechanism 5; the stator coil in the control rod drive mechanism 5 is arranged in a cylinder 25 in the ventilation cooling structure 4, the pressure shell in the control rod drive mechanism 5 is arranged inside the seismic support structure 3, the seismic plate 22 in the seismic support structure 3 is fixed on the pressure shell, and the drainage pipe arranged at the bottom end of the control rod drive mechanism 5 is connected with the sewage pipe system 2.

[0044] In the specific implementation process, the research reactor uses a bottom structure such as Figure 1 As shown, the control rod drive mechanism 5 is inverted and installed at the bottom of the reactor. The control rod drive mechanism 5 is arranged in two layers to save space. The stator coils of the two layers of the control rod drive mechanism 5 are staggered so that the control rod drive mechanism 5 can be arranged closely. The bottom structure is installed inside the small room 1 under the reactor, wherein the anti-seismic support structure 3 is fixed to the bottom surface of the small room 1 under the reactor, the sewage pipeline system 2 is fixed on the anti-seismic support structure 3, and the ventilation cooling structure 4 is fixed to the top surface of the small room 1 under the reactor. The cylinder 25 of the ventilation cooling structure 4 surrounds the stator coil of the control rod drive mechanism 5 (the main heating part of the control rod drive mechanism 5) inside. The drainage pipe at the bottom end of the control rod drive mechanism 5 is connected to the sewage pipeline system 2, and the sewage inside the reactor is discharged through the control rod drive mechanism 5 and then discharged by the sewage pipeline system 2. The seismic support structure 3 surrounds the pressure shell of the control rod drive mechanism 5 inside, and the seismic plates 22 on the seismic support structure 3 are fixed on the pressure shell. The seismic support structure 3 limits the displacement of the control rod drive mechanism by limiting the displacement of the seismic plates 22, thereby preventing excessive displacement under earthquake conditions.

[0045] Specific as Figure 2-Figure 5As shown, the seismic support structure 3 is mainly composed of an upper circumference 7, a middle circumference 9, a lower circumference 10, legs 11 and support columns 8. Six support columns 8 connect the upper circumference 7, the middle circumference 9 and the lower circumference 10 into a whole by welding, and three legs 11 are welded to the lower circumference 10. The upper circumference 7, the middle circumference 9 and the lower circumference 10 are divided into two halves, which are connected as a whole by a split connecting plate 16, connecting plate bolts 13 and nuts 14. Therefore, the seismic support structure 3 can be divided into two halves during transportation and installation (such as Figure 2 As shown in the figure, the seismic support structure 3 is fixed to the bottom of the small room 1 under the pile by the top fixing bolts 21 through the legs 11. A transition plate 12 is arranged between the legs 11 and the bottom of the small room 1 under the pile. The thickness of the transition plate 12 can be adjusted on site to compensate for the height error of the bottom of the small room 1 under the pile.

[0046] The anti-seismic plate 22 is fixed on the pressure shell of the control rod drive mechanism 5, and one control rod drive mechanism 5 corresponds to one anti-seismic plate 22. The support ring plate 19 is welded to the upper shroud 7. The support ring plate 19 is divided into two halves, which are respectively welded to the two halves of the upper shroud 7. The limit support block 17 is fixed to the support ring plate 19 by the support block bolt 18. The limit support block 17 also connects the two halves of the support ring plate 19 as a whole. The adjustment screw 20 is fixed to the limit support block 17. The gap between the adjustment screw 20 and the anti-seismic plate 22 can be adjusted by rotating the adjustment screw 20. A certain gap should be ensured between the adjustment screw 20 and the anti-seismic plate 22 to allow the control rod drive mechanism 5 to deviate outward due to the thermal expansion of the bottom head of the pressure vessel when the reactor is hot. At the same time, the gap value needs to be limited to prevent excessive deformation of the control rod drive mechanism 5 under earthquake conditions.

[0047] Specific as Figure 6-Figure 8As shown, the ventilation cooling structure 4 is mainly composed of a flange 23, an exhaust pipe 24 and a cylinder 25, and the flange 23, the exhaust pipe 24 and the cylinder 25 are connected by welding. The flange 23 is composed of a large circular plate and a flange rib 26, that is, the large circular plate is the main structure of the flange 23. The large circular plate should be able to cover the top opening of the small chamber 1 under the pile to form a closed ventilation flow channel. At the same time, since the diameter of the top opening of the small chamber 1 under the pile is large, a long part of the large circular plate is suspended in the air, so it is necessary to set the flange rib 26 to enhance the rigidity of the flange 23. The main body of the flange 23 (i.e., the large circular plate) can be divided into four petals, and the petals are connected by bolts. The cylinder 25 surrounds the control rod drive mechanism 5 to form a ventilation flow channel. The gap between the cylinder 25 and the control rod drive mechanism 5 should be controlled to avoid the gap being too large, resulting in most of the cooling air not entering the internal control rod drive mechanism 5 but flowing out from the edge. The cylinder 25 is also divided into four petals, which are connected by bolts. Since the cylinder is easily deformed after the petals are divided, a cylindrical rib plate 27 is arranged outside the cylinder to enhance the rigidity of the cylinder 25. Two exhaust pipes 24 are arranged on the flange 23, and the exhaust pipes 24 are connected to the external ventilation system. The cooling air flows through the control rod drive mechanism 5 by exhausting air to cool it.

[0048] Specific as Figure 9-12 As shown, the inlet of the sewage pipe system 2 is a primary valve 28, which is welded to the drainage pipe on the control rod drive mechanism 5, and the number of primary valves 28 is the same as the number of control rod drive mechanisms 5; the secondary valve 29 is fixed on the valve fixing plate 15 on the upper shroud 7 and the middle shroud 9, and the primary valve 28 and the secondary valve 29 are connected through a drainage branch pipe 30, and the number of secondary valves 29 is the same as the number of control rod drive mechanisms 5. The outlet of each secondary valve 29 is connected to the drainage ring pipe 31 through the drainage branch pipe 30, and the sewage inside the reactor flows through the primary valve 28 and the secondary valve 29 through the control rod drive mechanism 5, and is collected through the drainage ring pipe 31, and finally flows to the external sewage system through the drainage outlet main pipe 32.

[0049] The sewage pipeline system 2 is arranged in two layers to adapt to the layered arrangement of the control rod drive mechanism 5. The primary valve 28 of the upper pipeline is welded to the upper control rod drive mechanism 5, and the secondary valve 29 is installed on the valve fixing plate 15 of the upper enclosure 7. The primary valve 28 of the lower pipeline is welded to the lower control rod drive mechanism 5, and the secondary valve 29 is installed on the valve fixing plate 15 of the middle enclosure 9. The drainage ring pipe 31 is set as a two-stage structure matching the two-petal structure of the upper enclosure 7 or the middle enclosure 9, and the drainage ring pipe 31 is fixed on the supporting column 8 below the secondary valve 29 in the lower sewage pipeline. It should be noted that the secondary valves 29 in the upper and lower sewage pipelines are connected to the drainage ring pipe 31 through the drainage branch pipe 30.

[0050] The bottom structure disclosed by the above embodiment has a compact structure size and provides position limiting and cooling for CRDM. At the same time, the bottom structure is also provided with a sewage pipe system 2 to discharge radioactive waste regularly to reduce the irradiation dose of the under-pile chamber 1. Among them, the seismic support structure 3 and the ventilation and cooling structure 4 adopt a separate design, which greatly reduces the height of the equipment and facilitates the installation and transportation of the narrow space of the under-pile chamber 1; the sewage pipe system 2 improves safety by setting two valves, and the integrity of the pressure boundary can still be guaranteed by the secondary valve 29 in the event of leakage of the primary valve 28; and the sewage pipe system 2 is arranged in layers, and the drainage ring pipe 31 is used to connect and realize the clustering and extraction of multiple branches, which greatly simplifies the pipeline layout and realizes the layout and disassembly of complex pipeline systems in narrow spaces; the ventilation and cooling structure 4 can also realize the transportation, installation and disassembly of a single petal by dividing the structure into petals, which greatly reduces the demand for the space size of the ventilation and cooling structure 4.

[0051] Example 2

[0052] like Fig.13 As shown, a method for installing a bottom structure of a research reactor is provided, the method comprising the following steps:

[0053] Installing the control rod drive mechanism 5 on the bottom head 6 of the reactor pressure vessel;

[0054] The ventilation cooling structure 4 is transported to the under-pile chamber 1 in petals, and installed on the top surface of the under-pile chamber 1, and then the petals are connected to each other;

[0055] Fixing the anti-vibration plate 22 on the pressure shell of the control rod drive mechanism 5;

[0056] Connect the primary valve 28 in the sewage pipe system 2 to the drainage pipe of the control rod drive mechanism 5;

[0057] The seismic support structure 3 is transported to the pile chamber 1 in petals; the two petals of the lower shroud 10 are connected together, and the legs 11 and the support columns 8 are fixed on the lower shroud 10; the secondary valve 29 is fixed on the valve fixing plates 15 of the upper shroud 7 and the middle shroud 9, and the middle shroud 9 and the upper shroud 7 are fixed on the support columns 8 in sequence; and the support ring plate 19 is fixedly set on the upper shroud 7;

[0058] The drainage ring pipe 31 in the sewage pipeline system 2 is fixed on the support column 8 below the secondary valve 29 in the lower sewage pipeline, and the pipelines in the sewage pipeline system 2 are connected to complete the installation.

[0059] When multiple reactor bottom structural members adopt a split design, the above-mentioned installation method can be used to complete the installation of the reactor bottom structure in a smaller reactor bottom chamber. Although the structure adopts a split design, it still has high strength through the arrangement of structures such as reinforcing ribs, and can ensure the safety of the reactor in the event of an earthquake.

[0060] The above are only preferred embodiments of the present invention and are not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A bottom structure for a research reactor, characterized in that: Installed inside the under-pile chamber (1), comprising: an anti-seismic support structure (3) fixed to the bottom surface of the under-pile chamber (1), a sewage pipe system (2) fixed to the anti-seismic support structure (3), a ventilation cooling structure (4) fixed to the top surface of the under-pile chamber (1), and an inverted control rod drive mechanism (5); The stator coil in the control rod drive mechanism (5) is arranged in a cylinder (25) in the ventilation cooling structure (4), the pressure shell in the control rod drive mechanism (5) is arranged inside the seismic support structure (3), the seismic plate (22) in the seismic support structure (3) is fixed on the pressure shell, and the drainage pipe arranged at the bottom end of the control rod drive mechanism (5) is connected to the sewage pipe system (2).

2. A research reactor bottom structure according to claim 1, characterized in that: The seismic support structure (3) further comprises an upper circumference tube (7), a middle circumference tube (9), a lower circumference tube (10), a support leg (11), a support column (8), a support ring plate (19), a limit support block (17) and an adjustment screw (20); the upper circumference tube (7), the middle circumference tube (9) and the lower circumference tube (10) are fixedly arranged on the support column (8) to form a main frame; the support leg (11) is fixedly arranged on the lower circumference tube (10); the support ring plate (19) is fixedly arranged on the upper circumference tube (7); the limit support block (17) is fixedly arranged on the support ring plate (19); the adjustment screw (20) is fixedly arranged on the limit support block (17); the adjustment screw (20) is rotated to adjust the gap between the limit support block (17) and the seismic plate (22).

3. A research reactor bottom structure according to claim 2, characterized in that: The upper circumferential tube (7), the middle circumferential tube (9), the lower circumferential tube (10) and the supporting ring plate (19) are all two-petal structures, and the two petals of the upper circumferential tube (7), the middle circumferential tube (9) and the lower circumferential tube (10) are connected by a petal connecting plate (16); and the two petals of the supporting ring plate (19) are connected by the limiting support block (17).

4. A research reactor bottom structure according to claim 2, characterized in that: A transition plate (12) is also provided between the supporting legs (11) and the bottom surface of the small chamber (1) below the pile.

5. A research reactor bottom structure according to claim 1, characterized in that: The ventilation cooling structure (4) further comprises a flange (23) and an exhaust pipe (24); the exhaust pipe (24) is arranged on a side of the flange (23) connected to the cylinder (25), and the exhaust pipe (24) is connected to an external ventilation system; a gap is provided between the cylinder (25) and the stator coil in the control rod drive mechanism (5).

6. A research reactor bottom structure according to claim 5, characterized in that: The flange (23) and the cylinder (25) are both of split-flange structure; a flange rib plate (26) is also provided on the flange (23), and the diameter of the flange (23) is larger than the diameter of the top opening of the small chamber (1) under the pile; a cylinder rib plate (27) is also provided on the outer side of the cylinder (25).

7. A research reactor bottom structure according to claim 1, characterized in that: The sewage pipeline system (2) comprises two layers of sewage pipelines, a drainage ring pipe (31) and a drainage outlet main pipe (32); each layer of sewage pipeline comprises a primary valve (28), a secondary valve (29) and a drainage branch pipe (30); the water outlet of the primary valve (28) is connected to the water inlet of the secondary valve (29) via the drainage branch pipe (30), the water outlet of the secondary valve (29) is also connected to the water inlet of the drainage ring pipe (31) via the drainage branch pipe (30), and the water outlet of the drainage ring pipe (31) is connected to the drainage outlet main pipe (32); the water inlet of the primary valve (28) is connected to the drainage pipe in the control rod drive mechanism (5), and the number of the primary valves (28) is the same as the number of the control rod drive mechanism (5).

8. A research reactor bottom structure according to claim 7, characterized in that: The secondary valve (29) in the upper sewage discharge pipeline is installed on the valve fixing plate (15) of the upper surrounding cylinder (7), and the secondary valve (29) in the lower sewage discharge pipeline is installed on the valve fixing plate (15) of the middle surrounding cylinder (9).

9. A research reactor bottom structure according to claim 8, characterized in that: The drainage ring pipe (31) is configured as a two-section structure that matches the two-petal structure of the upper enclosure (7) or the middle enclosure (9), and the drainage ring pipe (31) is fixed on a supporting column (8) below the secondary valve (29) in the lower sewage pipeline.

10. A method for installing a bottom structure for a research reactor, characterized in that: The method comprises the following steps: Installing a control rod driving mechanism (5) on a bottom head (6) of a reactor pressure vessel; The ventilation cooling structure (4) is transported to the under-pile chamber (1) in petals, and installed on the top surface of the under-pile chamber (1), and the petals are then connected to each other; Fixing the anti-vibration plate (22) on the pressure shell of the control rod drive mechanism (5); Connecting a primary valve (28) in the sewage pipe system (2) to a sewage pipe of the control rod drive mechanism (5); The anti-seismic support structure (3) is transported in petals to the lower chamber (1); the two petals of the lower shroud (10) are connected together, and the legs (11) and the support columns (8) are fixed to the lower shroud (10); the secondary valve (29) is fixed to the valve fixing plates (15) of the upper shroud (7) and the middle shroud (9), and the middle shroud (9) and the upper shroud (7) are fixed to the support columns (8) in sequence; and the support ring plate (19) is fixedly arranged on the upper shroud (7); The drainage ring pipe (31) in the sewage pipeline system (2) is fixed on the supporting column (8) below the secondary valve (29) in the lower sewage pipeline, and the pipelines in the sewage pipeline system (2) are connected to complete the installation.

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