A high temperature gas cooled reactor primary circuit system

Abstract

The application belongs to the technical field of nuclear energy, and particularly relates to a high-temperature gas cooled reactor primary loop system, which comprises a reactor pressure vessel, an in-core component, a high-temperature gas cooled reactor core, a molten salt heat exchanger and a hot gas conduit. The in-core component is installed in the reactor pressure vessel, and the internal cavity of the in-core component is filled with the high-temperature gas cooled reactor core. The top of the in-core component is provided with a low-temperature helium gas inlet. The hot gas conduit is of a sleeve type structure, one end of the hot gas conduit is connected with the high-temperature gas cooled reactor core, the other end of the hot gas conduit is connected with the molten salt heat exchanger, and a circulating loop is formed. The application realizes helium-molten salt heat exchange by adopting the molten salt heat exchanger, so as to solve the problems that the steam generator helium side and the water side are both in high-temperature and high-pressure working conditions at present, a complex auxiliary system needs to be equipped, the system is huge, the equipment cost is high, and the steam generator secondary loop water side heat exchange pipe rupture easily leads to the reactor core water ingress accident.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of nuclear energy, and particularly relates to a high-temperature gas cooled reactor primary loop system. BACKGROUND

[0002] The high-temperature gas cooled reactor is a representative reactor type of the fourth generation nuclear power technology, and becomes a key technology of global energy transformation due to its inherent safety, high efficiency and multi-scenario application. The high-temperature gas cooled reactor primary loop system takes helium as a coolant, and realizes energy exchange between helium and water through a steam generator, so as to realize efficient transmission and circulation of nuclear fission heat. At present, the steam generator helium side and the water side are both in high-temperature and high-pressure working conditions, and a complex auxiliary system needs to be equipped, the system is large, and the equipment cost is high. In addition, the steam generator secondary loop water side is under high pressure, and once the heat transfer tube is broken, the secondary loop water may enter the primary loop, resulting in a reactor core flooding accident. SUMMARY

[0003] Therefore, the application provides a high-temperature gas cooled reactor primary loop system, which realizes helium-molten salt heat exchange by adopting a molten salt heat exchanger, so as to solve the problems that the steam generator helium side and the water side are both in high-temperature and high-pressure working conditions at present, a complex auxiliary system needs to be equipped, the system is large, the equipment cost is high, and the heat transfer tube of the steam generator secondary loop water side is easy to break and cause a reactor core flooding accident.

[0004] The application provides a high-temperature gas cooled reactor primary loop system, which comprises a reactor pressure vessel, an in-core component, a high-temperature gas cooled reactor core, a molten salt heat exchanger and a hot gas guide pipe. The in-core component is installed inside the reactor pressure vessel, and the in-core component is filled with the high-temperature gas cooled reactor core in the internal cavity. The top of the in-core component is provided with a low-temperature helium inlet. The hot gas guide pipe is a sleeve type structure, one end of the hot gas guide pipe is connected with the high-temperature gas cooled reactor core, the other end of the hot gas guide pipe is connected with the molten salt heat exchanger, and the hot gas guide pipe forms a circulation loop, which is used for conveying the high-temperature helium flowing out of the high-temperature gas cooled reactor core to the molten salt heat exchanger, and also used for conveying the low-temperature helium after heat exchange to the high-temperature gas cooled reactor core. The molten salt heat exchanger is used for communicating with a high-temperature gas cooled reactor secondary loop system, and conveying the high-temperature molten salt after heat exchange to the high-temperature gas cooled reactor secondary loop system.

[0005] In one specific embodiment of the application, the hot gas guide pipe comprises a low-temperature helium passage and a high-temperature helium passage. The reactor pressure vessel communicates with the molten salt heat exchanger through the low-temperature helium passage and the high-temperature helium passage.

[0006] In one specific embodiment of this application, the molten salt heat exchanger includes a shell-side enclosure and a lower header, heat exchange tubes, and an upper header located within the shell-side enclosure. The lower header is connected to the bottom end of the heat exchange tubes and is connected to a high-temperature helium gas channel. The upper header is connected to the top end of the heat exchange tubes and is connected to a low-temperature helium gas channel. The shell-side enclosure has a molten salt inlet and a molten salt outlet. The molten salt outlet is used to connect to the secondary loop system of the high-temperature gas-cooled reactor.

[0007] In one specific embodiment of this application, the secondary side of the shell-side enclosure is designed with a slight positive pressure. The slight positive pressure ranges from no more than 1 MPa and is higher than the external atmospheric pressure.

[0008] In one specific embodiment of this application, the molten salt heat exchanger further includes a baffle plate. The baffle plate is installed on the left side of the cryogenic helium gas channel to separate the heat exchange tubes from the cryogenic helium gas channel on the right side.

[0009] In one specific embodiment of this application, a lower junction box inspection port is provided on the outside of the lower junction box, and an upper junction box inspection port is provided on the outside of the upper junction box. Both the lower junction box inspection port and the upper junction box inspection port are used for in-service inspection of the primary loop system boundary.

[0010] In one specific embodiment of this application, the molten salt heat exchanger further includes two rows of safety relief devices and corresponding liquid level measuring devices. The two rows of safety relief devices and corresponding liquid level measuring devices are installed at the top of the shell-side enclosure. The normal operation sequence of the safety relief devices is used for the recovery of helium micro-leakage, and the accident operation sequence of the safety relief devices is used for helium recovery in the event of a primary loop rupture accident.

[0011] In one specific embodiment of this application, the molten salt heat exchanger further includes an insulation structure that covers the surface of the shell-side containment body.

[0012] In one specific embodiment of this application, the molten salt heat exchanger further includes an insulating sleeve. The insulating sleeve is installed at the connection between the high-temperature helium gas channel and the lower header.

[0013] In one specific embodiment of this application, the cryogenic helium channel is connected to an expansion joint, which is used to eliminate thermal stress damage to the cryogenic helium channel.

[0014] In one specific embodiment of this application, the molten salt heat exchanger is a vertical, shell-and-tube heat exchanger, arranged side by side with the reactor pressure vessel. The tube-side fluid is helium, and the shell-side fluid is molten salt, with countercurrent heat exchange between the tube-side and shell-side fluids.

[0015] The beneficial effects of this technical solution are as follows: High-temperature gas-cooled reactor (HTGR) core outputs high-temperature helium to the molten salt heat exchanger via hot gas ducts. After heat exchange in the molten salt heat exchanger, the high-temperature helium forms low-temperature helium. This low-temperature helium then re-enters the HTGR core through the hot gas ducts and is reheated. The high-temperature molten salt in the molten salt heat exchanger then enters the HTGR secondary loop system. By repeating the above process, heat exchange between the HTGR and molten salt can be effectively achieved, thereby expanding the market for comprehensive utilization of HTGR nuclear energy. Furthermore, this technical solution uses a molten salt heat exchanger to achieve helium-molten salt heat exchange. On one hand, the molten salt medium in the molten salt heat exchanger has a high heat storage density and heat transfer coefficient, and the molten salt heat exchanger is small in size, which is beneficial for the miniaturization of the HTGR primary loop system. Moreover, compared to the helium-water loop, the equipment cost is lower. On the other hand, the molten salt side of the secondary loop is under low pressure. In the event of an accident, the primary loop helium is released into the secondary loop containment body, where it is collected, purified, and reused through the release channels, effectively preventing core flooding accidents. In addition, the molten salt heat exchanger design takes into account the heat transfer and heat storage properties of molten salt, which can buffer the fluctuations in the heating network and is more suitable for nuclear energy heat utilization scenarios. Attached Figure Description

[0016] Figure 1 The diagram shown is a structural schematic of a high-temperature gas-cooled reactor primary loop system provided in an embodiment of this application.

[0017] Figure 2 As shown Figure 1 The diagram shows a partially enlarged view of the area near the lower header in a primary loop system of a high-temperature gas-cooled reactor.

[0018] Figure 3 As shown Figure 1 This is another enlarged schematic diagram of a location near the lower header in a primary loop system of a high-temperature gas-cooled reactor.

[0019] Figure 4 As shown Figure 1 The diagram shows a partially enlarged view of the area near the upper header in a primary loop system of a high-temperature gas-cooled reactor.

[0020] In the diagram, 1. Reactor pressure vessel; 2. Carbon reactor internals; 3. Graphite reactor internals; 4. High-temperature gas-cooled reactor core; 5. Cryogenic helium inlet; 6. Cryogenic helium passage; 7. High-temperature helium passage; 8. Molten salt heat exchanger; 9. Lower header; 10. Heat exchange tube; 11. Upper header; 12. Expansion joint; 13. Molten salt inlet; 14. Molten salt outlet; 15. Divider; 16. Safety relief device; 17. Insulating sleeve; 18. Graphite inner sleeve; 19. Metal outer sleeve; 20. Lower header inspection port; 21. Upper header inspection port. Detailed Implementation

[0021] With reference to the drawings of the embodiments of the present application, the technical solutions in the embodiments of the present application will be described clearly and completely. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all the embodiments of the present application. Based on the embodiments of the present application, all other embodiments obtained by those of ordinary skill in the art without creative effort belong to the scope of protection of the present application.

[0022] At least one embodiment of the present application provides a high-temperature gas cooled reactor primary loop system, which refers to Figure 1 The high-temperature gas cooled reactor primary loop system comprises a reactor pressure vessel 1, an in-core structure, a high-temperature gas cooled reactor core 4, a molten salt heat exchanger 8 and a hot gas guide pipe. The in-core structure is installed inside the reactor pressure vessel 1, and the in-core structure is filled with the high-temperature gas cooled reactor core 4 in the internal cavity. The top of the in-core structure is provided with a low-temperature helium inlet 5. The hot gas guide pipe is a double-pipe structure, one end of the hot gas guide pipe is connected to the high-temperature gas cooled reactor core 4, and the other end is connected to the molten salt heat exchanger 8, forming a circulating loop, which is used for conveying the high-temperature helium gas flowing out of the high-temperature gas cooled reactor core 4 to the molten salt heat exchanger 8, and also used for conveying the low-temperature helium gas after heat exchange to the high-temperature gas cooled reactor core 4. The molten salt heat exchanger 8 is used to communicate with the high-temperature gas cooled reactor secondary loop system, and convey the high-temperature molten salt after heat exchange to the high-temperature gas cooled reactor secondary loop system.

[0023] It should be noted that the reactor pressure vessel 1 is a component that supports and contains the entire core, the in-core structure and bears a huge load. The high-temperature gas cooled reactor core 4 can be a spherical fuel element. The heat generated by the nuclear fission reaction of the high-temperature gas cooled reactor core 4 heats the low-temperature helium gas flowing in the high-temperature gas cooled reactor core 4 into high-temperature helium gas.

[0024] For example, the in-core structure comprises a carbon in-core structure 2 and a graphite in-core structure 3. The internal cavity of the graphite in-core structure 3 is filled with the high-temperature gas cooled reactor core 4. The carbon in-core structure 2 is used to support the graphite in-core structure 3 and the pebble bed core, and the graphite in-core structure 3 forms a core cavity, constitutes a fuel ball flow channel and constitutes a helium heat-carrying gas flow channel.

[0025] According to the technical scheme provided in the embodiments of the present application, the high-temperature gas cooled reactor core 4 outputs high-temperature helium gas to the molten salt heat exchanger 8 through the hot gas guide pipe, the high-temperature helium gas forms low-temperature helium gas after heat exchange in the molten salt heat exchanger 8, the low-temperature helium gas enters the high-temperature gas cooled reactor core 4 through the hot gas guide pipe to be heated again, and the high-temperature molten salt after heat exchange in the molten salt heat exchanger 8 enters the high-temperature gas cooled reactor secondary loop system. Through repeated operation of the above process, the high-temperature gas cooled reactor and the molten salt heat exchange can be effectively realized, and the market of nuclear energy comprehensive utilization of the high-temperature gas cooled reactor is further expanded. In addition, the molten salt heat exchanger 8 is adopted in the embodiments of the present application to realize helium-molten salt heat exchange. On the one hand, the molten salt medium in the molten salt heat exchanger 8 has a high heat storage density and a high heat transfer coefficient, and the molten salt heat exchanger 8 has a small volume, which is beneficial to the miniaturization of the high-temperature gas cooled reactor primary loop system, and the equipment cost is lower than that of the helium-water loop. On the other hand, the secondary loop molten salt side is low in pressure, and in the event of an accident, the primary loop helium gas is discharged into the secondary loop containment body, collected and purified through the discharge channel on the containment body for repeated use, which can effectively avoid the occurrence of the reactor core water ingress accident. In addition, the molten salt heat exchanger 8 is designed to take into account the heat transfer and heat storage properties of the molten salt, which can form a buffer for the fluctuation of the heat network and is more suitable for nuclear energy heat utilization scenarios.

[0026] In at least one embodiment of the present application, the hot gas guide pipe includes a low-temperature helium gas passage 6 and a high-temperature helium gas passage 7. The reactor pressure vessel 1 is communicated with the molten salt heat exchanger 8 through the low-temperature helium gas passage 6 and the high-temperature helium gas passage 7. In this way, the low-temperature helium gas enters the helium gas flow channel in the reactor pressure vessel 1 through the low-temperature helium gas passage 6, the low-temperature helium gas flows upward through the low-temperature helium gas inlet 5 at the top of the in-core component into the high-temperature gas cooled reactor core 4, and the low-temperature helium gas is heated again by the nuclear fission reaction of the high-temperature gas cooled reactor core 4, and then the above operation process is repeated to realize the heat exchange between the helium gas and the molten salt in the molten salt heat exchanger 8.

[0027] It should be noted that the low-temperature helium gas passage 6 and the high-temperature helium gas passage 7 combine to form the hot gas guide pipe.

[0028] For example, referring to Figure 2 , the low-temperature helium gas passage 6 can be enclosed by a metal outer sleeve 19. The high-temperature helium gas passage 7 can be enclosed by a graphite inner sleeve 18. In this way, the low-temperature helium gas passage 6 and the high-temperature helium gas passage 7 form isolation between the cold and hot helium gases.

[0029] In at least one embodiment of the present application, the molten salt heat exchanger 8 comprises a shell side containment body, a lower header 9, heat exchange tubes 10 and an upper header 11 located in the shell side containment body. The lower header 9 is connected to the bottom end of the heat exchange tubes 10 and is connected to the high temperature helium gas passage 7. The upper header 11 is connected to the top end of the heat exchange tubes 10 and is connected to the low temperature helium gas passage 6. The shell side containment body is provided with a molten salt inlet 13 and a molten salt outlet 14. The molten salt outlet 14 is used to communicate with the high temperature gas cooled reactor secondary loop system. In this way, the high temperature helium gas heated by the nuclear fission reaction in the high temperature gas cooled reactor core 4 enters the high temperature helium gas passage 7, and the high temperature helium gas enters the lower header 9 of the molten salt heat exchanger 8 from the high temperature helium gas passage 7. The helium gas after heat exchange in the heat exchange tubes 10 flows upward and converges into the upper header 11, and the low temperature helium gas after heat exchange flows downward through the upper header 11 into the low temperature helium gas passage 6. The low temperature molten salt enters the shell side of the molten salt heat exchanger 8 through the molten salt inlet 13 and flows downward to exchange heat with the high temperature helium gas in the heat exchange tubes 10. The high temperature molten salt heated to the target temperature flows out of the shell side of the molten salt heat exchanger 8 through the molten salt outlet 14, realizing heat conversion between helium gas and molten salt, and the heat carrying molten salt enters the secondary loop system.

[0030] It should be noted that the lower header 9 and the heat exchange tubes 10 can be connected by inner hole welding. The heat exchange tubes 10 can be integrated heat exchange tubes arranged in an equidistant square arrangement.

[0031] In some embodiments, the lower header 9 and the upper header 11 are both provided with uniformly distributed tube holes. The tube holes are in communication with the heat exchange tubes 10. In this way, the high temperature helium gas flows upward into the heat exchange tubes 10 through the uniformly distributed tube holes provided on the wall surface of the lower header 9, and the high temperature helium gas enters the heat exchange tubes 10 to exchange heat with the low temperature molten salt in the shell side of the molten salt heat exchanger 8. The high temperature helium gas is cooled to low temperature helium gas in the tube side, and the low temperature molten salt is heated to high temperature molten salt in the shell side. The helium gas after heat exchange in the heat exchange tubes 10 enters the upper header 11.

[0032] In at least one embodiment of the present application, the secondary side of the shell side containment body is designed to be slightly positive pressure. The range of the slightly positive pressure is not more than 1 MPa, and the slightly positive pressure is higher than the external atmospheric pressure. In this way, it can be ensured that the pressure generated after the helium gas diffuses into the gas cavity above the molten salt heat exchanger 8 under accident conditions is lower than the design pressure, and the containment body has good containment under any condition. In addition, the volume of the molten salt heat exchanger 8 in the embodiment of the present application is small, more compact, the secondary side is slightly positive pressure, and the equipment cost is lower compared with the helium-water loop.

[0033] In at least one embodiment of the present application, the molten salt heat exchanger 8 further comprises a partition plate 15. The partition plate 15 is installed on the left side of the low temperature helium gas passage 6 and is used to separate the heat exchange tubes 10 from the low temperature helium gas passage 6 on the right side.

[0034] In at least one embodiment of the present application, reference is made to Figure 3 and Figure 4The lower header 9 is provided with a lower header inspection opening 20, and the upper header 11 is provided with an upper header inspection opening 21, and the lower header inspection opening 20 and the upper header inspection opening 21 are used for in-service inspection of the one-loop system boundary.

[0035] In at least one embodiment of the present application, the molten salt heat exchanger 8 further comprises two rows of safety relief devices 16 and corresponding liquid level measuring devices. The two rows of safety relief devices 16 and the corresponding liquid level measuring devices are installed at the top of the shell side containment. The normal working sequence of the safety relief devices 16 is used for the recovery of helium micro-leakage, and the accident working sequence of the safety relief devices 16 is used for the recovery of helium in the one-loop pipe rupture accident. In this way, the molten salt side of the two-loop is low pressure, and the helium in the one-loop is discharged into the two-loop containment in the accident working condition, collected and purified through the discharge channel of the safety relief device 16 for reuse, which can effectively avoid the occurrence of the high temperature gas cooled reactor core 4 water ingress accident.

[0036] In at least one embodiment of the present application, the molten salt heat exchanger 8 further comprises a heat preservation structure, which covers the surface of the shell side containment. In this way, the heat preservation structure can reduce heat transfer loss.

[0037] In at least one embodiment of the present application, the molten salt heat exchanger 8 further comprises an insulating sleeve 17. The insulating sleeve 17 is installed at the connection between the high temperature helium passage 7 and the lower header 9. In this way, the insulating sleeve 17 can effectively reduce heat loss.

[0038] In at least one embodiment of the present application, the low temperature helium passage 6 is connected with an expansion joint 12, which is used to eliminate the damage of thermal stress to the low temperature helium passage 6.

[0039] In at least one embodiment of the present application, the molten salt heat exchanger 8 is a vertical, tube-shell heat exchanger arranged side by side with the reactor pressure vessel 1, the tube side fluid is helium, the shell side fluid is molten salt, and the tube side and the shell side fluids counter-currently exchange heat.

[0040] In the above embodiment, the high temperature helium passage 7 of the hot gas guide pipe outputs high temperature helium from the high temperature gas cooled reactor core 4, the high temperature helium in the high temperature helium passage 7 enters the heat exchange tube 10 through the lower header 9 of the molten salt heat exchanger 8, and the high temperature helium flows upward in the heat exchange tube 10 and counter-currently exchanges heat with the low temperature molten salt in the shell side of the molten salt heat exchanger 8; the low temperature helium after heat exchange enters the upper header 11 and then enters the high temperature gas cooled reactor core 4 through the low temperature helium passage 6 of the hot gas guide pipe to be heated again; and the high temperature molten salt after heat exchange enters the high temperature gas cooled reactor two-loop system; by repeatedly running the above process, the high temperature gas cooled reactor and the molten salt heat exchange can be effectively realized, and the market of nuclear energy comprehensive utilization of the high temperature gas cooled reactor can be expanded.

[0041] It should be noted that the combination modes of the technical features in the embodiments of the present application are not limited to the combination modes described in the embodiments of the present application or the combination modes described in the specific embodiments, and all the technical features described in the present application can be freely combined or integrated in any mode, unless contradictory.

[0042] As shown in the present application and claims, unless the context clearly indicates otherwise, the words "one", "a", and / or "the" do not mean to specify a single number, but also can include a plurality. Generally, the term "comprising" only indicates including the steps and elements explicitly identified, and these steps and elements do not constitute an exclusive list, and the method or device can also include other steps or elements.

[0043] The above only describes the preferred embodiments of the present application and is not intended to limit the present application, and any modification, equivalent replacement, etc. made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A high temperature gas cooled reactor primary circuit system, characterized in that, The reactor pressure vessel, the in-core component, the high-temperature gas cooled reactor core, the molten salt heat exchanger and the hot gas conduit, The reactor pressure vessel is internally provided with the in-core component, the in-core component is internally filled with the high-temperature gas cooled reactor core, the top of the in-core component is provided with a low-temperature helium gas inlet; the hot gas conduit is a sleeve type structure, one end of the hot gas conduit is connected to the high-temperature gas cooled reactor core, the other end of the hot gas conduit is connected to the molten salt heat exchanger, forming a circulating loop, for conveying the high-temperature helium gas flowing out of the high-temperature gas cooled reactor core to the molten salt heat exchanger, and for conveying the low-temperature helium gas after heat exchange to the high-temperature gas cooled reactor core; the molten salt heat exchanger is used for communicating with the high-temperature gas cooled reactor secondary loop system, and conveying the high-temperature molten salt after heat exchange to the high-temperature gas cooled reactor secondary loop system.

2. A high temperature gas cooled reactor primary circuit system according to claim 1, characterised in that, The hot gas conduit comprises a low-temperature helium gas passage and a high-temperature helium gas passage, and the reactor pressure vessel communicates with the molten salt heat exchanger through the low-temperature helium gas passage and the high-temperature helium gas passage.

3. A high temperature gas cooled reactor primary circuit system according to claim 2, characterised in that, The molten salt heat exchanger comprises a shell side containment body, a lower header, heat exchange pipes and an upper header in the shell side containment body; the lower header is connected to the bottom end of the heat exchange pipes and connected to the high-temperature helium gas passage; the upper header is connected to the top end of the heat exchange pipes and connected to the low-temperature helium gas passage; the shell side containment body is provided with a molten salt inlet and a molten salt outlet, and the molten salt outlet is used for communicating with the high-temperature gas cooled reactor secondary loop system.

4. A high temperature gas cooled reactor primary circuit system according to claim 3, characterised in that, The molten salt heat exchanger further comprises a partition plate, the partition plate is installed on the left side of the low-temperature helium gas passage, and the partition plate is used for separating the heat exchange pipes from the low-temperature helium gas passage on the right side.

5. A high temperature gas cooled reactor primary circuit system according to claim 3, characterised in that, The secondary side of the shell side containment body is designed to be micro-positive pressure, and the micro-positive pressure is not more than 1MPa, and the micro-positive pressure is higher than the external atmospheric pressure.

6. A high temperature gas cooled reactor primary circuit system according to claim 3, characterised in that, The lower header is provided with a lower header inspection opening on the outside, and the upper header is provided with an upper header inspection opening on the outside; the lower header inspection opening and the upper header inspection opening are used for in-service inspection of the one-loop system boundary.

7. A high temperature gas cooled reactor primary circuit system according to claim 3, characterised in that, The upper header and the lower header are both provided with uniformly distributed tube holes, and the heat exchange pipes are integrated heat exchange pipes, and the heat exchange pipes are connected to the upper header and the lower header by hole welding.

8. A high temperature gas cooled reactor primary circuit system according to claim 3, characterised in that, The molten salt heat exchanger further comprises two rows of safety relief devices and corresponding liquid level measuring devices, the two rows of safety relief devices and the corresponding liquid level measuring devices are installed on the top of the shell side containment body, the normal working sequence of the safety relief devices is used for recovery of helium micro-leakage, and the accident working sequence of the safety relief devices is used for helium recovery under one-loop pipe rupture accident.

9. A high temperature gas cooled reactor primary circuit system according to claim 3, characterised in that, The molten salt heat exchanger further comprises a heat preservation structure, and the heat preservation structure covers the surface of the shell side containment body.

10. A high temperature gas cooled reactor primary circuit system according to claim 3, characterised in that, The molten salt heat exchanger further comprises an adiabatic sleeve, and the adiabatic sleeve is installed at the connection between the high-temperature helium gas passage and the lower header.

11. A high temperature gas-cooled reactor primary circuit system according to any one of claims 2 to 10, characterized in that, The low-temperature helium gas passage is connected with an expansion joint, and the expansion joint is used for eliminating damage of thermal stress to the low-temperature helium gas passage.

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