Outlet device for a floating natural circulation system and floating natural circulation system

Abstract

The application discloses an outlet device of a floating natural circulation system and the floating natural circulation system. The floating natural circulation system comprises a box body, the box body contains liquid, and the liquid level in the box body changes with the circulation system. The outlet device comprises a floating part, the floating part is at least partially immersed in the liquid; a guide part, the guide part is arranged at the bottom of the box body, and the floating part slides along the guide part with the change of the liquid level; and an outlet part, the outlet part and the floating part slide along the guide part together with the change of the liquid level, and the outlet part is below the liquid level. The outlet device of the floating natural circulation system and the floating natural circulation system can efficiently, accurately and quickly realize automatic adjustment of the outlet position in the outlet device, so that the outlet position is always slightly lower than the liquid level surface, thereby guaranteeing the stability of the pressure difference between the liquid level and the outlet position, and maximizing the working efficiency of the floating natural circulation system.

Description

Technical Field

[0001] This application relates to the field of nuclear power technology, and in particular to an outlet device and a floating natural circulation system. Background Technology

[0002] With the continuous development of society, the demand for electrical energy is increasing. Currently, in the construction of nuclear power plants, especially third-generation nuclear power plants, passive natural circulation systems are widely used to ensure the safety of the plant. Natural circulation systems utilize the density difference of fluids to generate driving force during operation. Because natural circulation systems do not require mechanical power, they reduce the need for support systems and have high reliability. For example... Figure 1 As shown, the existing passive containment heat removal system includes an internal heat exchanger, an external high-level water tank (PCS tank), and connecting pipes, valves, and steam-water separators. Its descending section pipe inlet connects to the bottom of the tank. The PCS relies on the density difference between the rising and descending sections of the system to achieve passive natural circulation cooling. Initially, the outlet of the rising section pipe extends a distance into the tank, submerged and a considerable distance from the water surface. During the initial operation, when the water temperature in the PCS tank is low, the system operates on a single-phase water circulation, with the PCS carrying heat from the containment to heat the water within the entire PCS tank. As the system circulates, when the PCS tank temperature rises to near atmospheric pressure (saturation), flash evaporation may occur in the rising section, forming a two-phase natural circulation. Simultaneously, as the tank level decreases, the system back pressure decreases, the flash point shifts downward, flash evaporation occurs in the rising section, forming two-phase flow, and the system circulation flow rate increases.

[0003] However, as Figure 2 As shown, as the liquid level continues to drop, when the water tank level is lower than the pipe outlet height, the natural circulation drive head gradually decreases, resulting in a reduction in circulation flow and a decrease in system circulation efficiency. Patent CN102637464 discloses a method and apparatus for enhancing heat exchange in a passive heat removal system within a double-layer concrete containment, including a heat exchanger assembly, a riser pipe, a downcomer pipe, a hot water tank, and a steam-water separator. However, as the water level in the tank drops, the outlet position of the riser pipe will be higher than the water level in the tank, leading to a reduction in the system drive head and consequently affecting the operating circulation flow. Patent CN102522127 discloses a passive containment heat removal system including an expansion tank. Although this expansion tank can compensate for water volume changes caused by temperature variations during system operation, the liquid level in the expansion tank continuously decreases with system circulation, making it impossible to guarantee the stability of the operating pressure in the system. Summary of the Invention

[0004] The purpose of this application is to solve the aforementioned technical problems.

[0005] Therefore, the first objective of this application is to propose an outlet device for a floating natural circulation system that can efficiently, accurately, and quickly achieve automatic adjustment of the outlet position, so that the outlet position is always kept slightly below the liquid level surface, thereby ensuring the stability of the pressure difference between the liquid level and the outlet position, maximizing the working efficiency of the floating natural circulation system, and significantly increasing the passivity and reliability of the floating natural circulation system.

[0006] The second objective of this application is to propose a floating natural circulation system.

[0007] To achieve the above objectives, the first aspect of this application proposes an outlet device for a floating natural circulation system. The circulation system includes a tank containing liquid, the liquid level in the tank changing with the circulation system. The outlet device includes: a floating part, at least partially submerged in the liquid; a guide part disposed at the bottom of the tank, the floating part sliding along the guide part as the liquid level changes; and an outlet part, the outlet part and the floating part sliding together along the guide part as the liquid level changes, and the outlet part being below the liquid level.

[0008] Furthermore, the floating part has a centerline parallel to the liquid level, and the floating part is a ring-shaped body symmetrical about the centerline or the floating part includes multiple spheres symmetrical about the centerline.

[0009] Furthermore, the floating part has a hollow structure.

[0010] Furthermore, at least one guide rail is provided on the outer surface of the outlet section, and a guide groove is provided on the inner surface of the guide section to match the guide rail.

[0011] Furthermore, the guide section is provided with at least one drain outlet within the sliding range of the outlet section.

[0012] Furthermore, the outlet device also includes a connecting part that connects the floating part and the outlet part.

[0013] Furthermore, the floating part has a first inner boundary with a first diameter D1, the outlet part has an outer boundary with a second diameter D2, and the relationship between the first diameter and the second diameter is π(D1 / 2). 2 -π(D² / 2) 2 = n*π(D² / 2) 2 , where 3≤n≤5.

[0014] Furthermore, the vertical distance h1 from the bottom of the floating part to the liquid level is h1≥1 / 2D2.

[0015] Furthermore, the vertical distance h2 between the outlet and the liquid level is 1 / 4D2≤h2<1 / 2D2, so that the outlet is below the liquid level.

[0016] Furthermore, the guide part has a second inner boundary, and the second inner boundary has a third diameter D3. The third diameter D3 is larger than the second diameter D2, and the difference Δd between the third diameter D3 and the second diameter D2 is Δd = max{D2*1 / 100m, 0.001m}.

[0017] Furthermore, the floating section and the outlet section are welded together as one unit through a connecting section.

[0018] Furthermore, the surface roughness of the contact surface between the guide section and the outlet section is between 50 and 200 micrometers.

[0019] By applying the above-described technical solution of this application, at least the following technical effects are achieved:

[0020] 1. Based on the changes in the liquid level in the floating natural circulation system, this outlet device can automatically adjust the outlet position in an efficient, accurate, and rapid manner without human operation or external driving force. This ensures that the outlet position is always kept slightly below the liquid level surface, thereby guaranteeing the stability of the pressure difference between the liquid level and the outlet position. This maximizes the working efficiency of the floating natural circulation system and significantly increases its passivity and reliability.

[0021] 2. This outlet device avoids condensation caused by steam directly entering the liquid in the tank by setting a relatively independent space between the floating part and the outlet part, thereby effectively avoiding steam hammer and improving the reliability of the floating natural circulation system.

[0022] 3. By setting guide rails and guide grooves, the stability of the outlet device's operation can be further guaranteed.

[0023] 4. The outlet device, by incorporating a drain outlet, makes its operation more convenient.

[0024] To achieve the above objectives, a second aspect of this application proposes a floating natural circulation system, comprising a tank, an inlet pipe, a heat exchanger, and an outlet pipe. Liquid in the tank flows out from the inlet pipe, passes sequentially through the inlet pipe and the heat exchanger, and then flows back into the tank through the outlet pipe, discharging the heat acquired by the heat exchanger into the tank through the liquid. The floating natural circulation system also includes a valve located between the inlet pipe and the outlet pipe for controlling the flow of the liquid. The system is characterized by including an outlet device, where liquid flows into the outlet device after passing through the outlet pipe, and then flows out into the tank from the outlet device. The outlet device slides in a direction that changes with the liquid level, and the outlet portion of the outlet device is always located below the liquid level, creating a pressure difference between the liquid surface and the outlet portion.

[0025] By applying the above-mentioned technical solution of this application, compared with the existing passive containment heat removal system, the floating natural circulation system can form a stable pressure difference between the liquid surface and the liquid outlet, thereby maximizing the height difference of the natural circulation drive, effectively improving the heat carrying capacity and performance of the floating natural circulation system, and effectively avoiding the steam hammer phenomenon that occurs in the floating natural circulation system during the two-phase circulation of vapor and liquid.

[0026] Additional aspects and advantages of this application will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of this application. Attached Figure Description

[0027] The accompanying drawings, which form part of this application, are used to provide a further understanding of this application. The illustrative embodiments and descriptions of this application are used to explain this application and do not constitute an undue limitation of this application. In the drawings:

[0028] Figure 1 A structural diagram of a prior art passive containment heat removal system at a high water tank level is presented;

[0029] Figure 2 A structural diagram of a passive containment heat removal system in the prior art when the water tank is at a low liquid level is presented;

[0030] Figure 3 A structural diagram of the outlet device of a floating natural circulation system according to an embodiment is shown when the tank is at a high liquid level.

[0031] Figure 4 A structural diagram of the outlet device of a floating natural circulation system according to an embodiment is shown when the liquid level in the tank is low.

[0032] Figure 5 A top view of the detailed structure of the outlet device in one embodiment is shown;

[0033] Figure 6 A front view of the outlet device in a specific embodiment is shown;

[0034] Figure 7 A top view of the outlet device in one embodiment is shown;

[0035] Figure 8 A front view of the outlet device in one embodiment is shown;

[0036] Figure 9 A perspective view of an outlet device according to a preferred embodiment is presented;

[0037] Figure 10 A structural diagram of the floating natural circulation system in Example 2 at a high liquid level in the tank is shown;

[0038] Figure 11 A structural diagram of the floating natural circulation system in Example 2 when the liquid level in the tank is low is shown.

[0039] Reference numerals: 1. Box body; 2. Outlet device; 21. Floating part; 22. Guide part; 23. Outlet part; 231. Guide rail; 24. Connecting part; 3. Inlet pipe; 4. Heat exchanger; 5. Outlet pipe; 6. Valve. Detailed Implementation

[0040] It should be noted that, unless otherwise specified, the embodiments and features described in this application can be combined with each other. This application will now be described in detail with reference to the accompanying drawings and embodiments.

[0041] The present application will be further described in detail below with reference to specific embodiments, which should not be construed as limiting the scope of protection claimed in the present application.

[0042] In this description, it should be noted that, unless otherwise explicitly specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection between two components. Those skilled in the art can understand the specific meaning of the above terms in this application based on the specific circumstances. Furthermore, in the description of this application, unless otherwise stated, "a plurality of" means two or more.

[0043] Example 1:

[0044] According to the first aspect of this application, an outlet device for a floating natural circulation system is proposed.

[0045] like Figure 3 As shown, the natural circulation system includes a housing 1. Specifically, the housing 1 contains liquid, and the liquid level within the housing 1 changes as the circulation system progresses.

[0046] In this embodiment, as Figure 3 As shown, the outlet device 2 may include a floating part 21, a guide part 22, and an outlet part 23. The floating part 21 is at least partially submerged in the liquid, and the guide part 22 is located at the bottom of the housing 1. Figure 4As shown, the floating part 21 slides along the guide part 22 as the liquid level changes. Simultaneously, the outlet part 23 and the floating part 21 slide together along the guide part 22 as the liquid level changes, with the outlet part 23 positioned below the liquid level. Therefore, this outlet device can automatically, quickly, and accurately adjust the height of the outlet part according to changes in the liquid level caused by changes in system operating status or conditions, utilizing the cooperation of the floating part and the outlet part. It exhibits typical passive characteristics and high reliability, ensuring that the outlet part is always kept slightly below the liquid level surface, guaranteeing the stability of the pressure difference within the tank during system operation, thereby increasing the system's circulation flow rate and significantly improving the system's circulation efficiency.

[0047] Furthermore, in this embodiment, as Figure 5 As shown, the floating part 21 has a first inner boundary with a first diameter D1, and the outlet part 23 has an outer boundary with a second diameter D2. The relationship between the first diameter and the second diameter is πD1 / 2. 2 -πD2 / 2 2 =n*πD² / 2 2 Where 3 ≤ n ≤ 5. In a preferred embodiment, n is 4. This allows for the formation of a relatively independent space between the floating section 21 and the outlet section 23. Therefore, after the liquid flows out of the outlet section 23, it will first pass through this independent space before flowing into the housing 1. Although the overall temperature of the housing 1 is still in a supercooled state, the liquid temperature in this independent space is basically the same as the liquid temperature flowing out of the outlet section 23. Therefore, when a vapor-liquid two-phase mixture flows out of the outlet section 23, i.e., when steam appears, this vapor-liquid two-phase mixture will first contact the relatively independent space between the floating section 21 and the outlet section 23 before entering the housing 1, effectively preventing steam hammer caused by condensation due to steam directly entering the housing 1 from the outlet section 23.

[0048] In one specific embodiment, such as Figure 6 As shown, the vertical distance h1 from the bottom of the floating part 21 to the liquid level is h1≥1 / 2D2. In addition, the vertical distance h2 between the outlet part 23 and the liquid level is 1 / 4D2≤h2<1 / 2D2, so that the outlet part 23 is always below the liquid level.

[0049] Furthermore, in this embodiment, as Figure 7 As shown, the floating part 21 has a centerline parallel to the liquid level (e.g., Figure 7 (As shown by the dashed line). For example, the floating part 21 can be a ring-shaped body symmetrical about the center line, or the floating part 21 can include multiple spheres symmetrical about the center line, thereby enabling the floating part 21 to have sufficient and balanced buoyancy. In a preferred embodiment, the floating part 21 can be a hollow structure, which can significantly reduce the volume of the floating part 21 compared to a solid structure, while obtaining the same sufficient buoyancy, thereby making the structure of the outlet device 2 lighter and more compact.

[0050] Furthermore, in this embodiment, as Figure 7 and Figure 8 As shown, the outlet device 2 also includes a connecting portion 24, which connects the floating portion 21 and the outlet portion 23. In one specific embodiment, the floating portion 21 and the outlet portion 23 are welded together via the connecting portion 24, thereby making the connection between the floating portion 21 and the outlet portion 23 more stable. In a preferred embodiment, the connecting portion may be a spoke-shaped structure to further secure the outlet portion 23 to the floating portion 21, making the fit between the outlet portion 23 and the floating portion 21 more reliable.

[0051] Furthermore, in this embodiment, as Figure 5 As shown, the guide section 22 has a second inner boundary, and the second inner boundary has a third diameter D3. Specifically, the third diameter D3 is larger than the second diameter D2, and the difference Δd between the third diameter D3 and the second diameter D2 is Δd = max{D2*1 / 100m, 0.001m}. For example, for the case where the third diameter D3 is between 0.01m and 1m, the difference Δd between the third diameter D3 and the second diameter D2 can be selected as the maximum value between 1mm and D3*1 / 100. Here, 1mm is the minimum value of Δd obtained based on past data and manual experience, to avoid jamming between the guide section 22 and the outlet section 23 due to Δd being too small. Because temperature changes occur during the operation of the natural circulation system, the guide section 22 and the outlet section 23 will change in size due to thermal expansion. Therefore, a sufficient gap needs to be set between the inner boundary of the guide section 22 and the outer boundary of the outlet section 23 to ensure that the outlet section 23 can slide freely in the guide section 22 along the direction of liquid level change, thereby ensuring the stability of the natural circulation system and reducing the friction between the guide section 22 and the outlet section 23.

[0052] Furthermore, the bending deformation of the guide section 22 and the outlet section 23 within the straightness deviation range must also be considered to prevent the outlet section 23 from getting stuck during sliding due to the pressure of the guide section 22. Therefore, when the straightness of the guide section 22 and the outlet section 23 is poor, the difference Δd between the third diameter D3 and the second diameter D2 needs to be greater than the product of the length of the outlet section 23 and the straightness.

[0053] It is worth noting that, in order for the floating part 21 to use its own buoyancy to suspend the outlet part 23 in the box 1, the buoyancy F generated by the submersion of the floating part 21 is... 浮动部 Should be related to the self-weight G of the export section 23 出口部 The weight G of the floating part 21 浮动部 And the frictional resistance f between the guide section 22 and the outlet section 23 is balanced, i.e., F 浮动部 =G 浮动部 +G 出口部+f. The frictional resistance f varies depending on the structure, materials, etc., and is related to factors such as the roughness of the contact surface between the guide portion 22 and the outlet portion 23, as well as the contact pressure. To minimize friction and ensure free sliding of the outlet portion 23 within the guide portion 22, in addition to setting the difference Δd between the third diameter D3 and the second diameter D2, the range of the contact surface roughness can also be limited. Specifically, the contact surface should have sufficient roughness to increase surface hydrophobicity and reduce the adsorption force generated after liquid wets adjacent surfaces. Furthermore, a larger roughness also helps avoid the welding effect after long-term contact of smooth surfaces, and the resulting adhesion of the outlet portion 23 to the guide portion 22. At the same time, excessive roughness should also be avoided to prevent potential surface seizing. Therefore, in this embodiment, the roughness of the contact surface between the guide portion 22 and the outlet portion 23 is set between 50 and 200 micrometers, so that the contact surface between the guide portion 22 and the outlet portion 23 has both good hydrophobicity and can effectively avoid welding effects and seizing.

[0054] Furthermore, in a preferred embodiment, such as Figure 9 As shown, at least one guide rail 231 is provided on the outer surface of the outlet 23 along the sliding direction, and a guide groove is provided on the inner surface of the guide part 22 to cooperate with the guide rail 231. In a specific embodiment, the floating part 21 is annular, the guide rail 231 is provided on the outer surface of the outlet 23 along the sliding direction, and the distance between adjacent guide rails 231 is equal. A guide groove is provided on the inner surface of the guide part 22 at the position corresponding to the guide rail 231, thereby ensuring that the outlet 23 moves under the drive of the floating part 21 without rotating, and reducing the tilt of the outlet 23, thereby ensuring the stability of the outlet device operation.

[0055] Furthermore, in another embodiment, the guide portion 22 is provided with at least one drain outlet within the sliding range of the outlet portion 23.

[0056] In one specific embodiment, if a guide rail 231 is provided on the outer surface of the outlet 23 along the sliding direction, and a guide groove is provided on the inner surface of the guide 22 in conjunction with the guide rail 231, then a drain outlet is provided on the guide 22 at intervals of the guide groove, so that the liquid can be directly discharged through the drain outlet on the guide 22 after flowing out of the outlet 23, which is more convenient.

[0057] By applying the technical solutions in the above embodiments of this application, the following technical effects are achieved:

[0058] 1. Based on the changes in the liquid level in the floating natural circulation system, this outlet device can automatically adjust the outlet position in an efficient, accurate, and rapid manner without human operation or external driving force. This ensures that the outlet position is always kept slightly below the liquid level surface, thereby guaranteeing the stability of the pressure difference between the liquid level and the outlet position. This maximizes the working efficiency of the floating natural circulation system and significantly increases its passivity and reliability.

[0059] 2. This outlet device avoids condensation caused by steam directly entering the liquid in the tank by setting a relatively independent space between the floating part and the outlet part, thereby effectively avoiding steam hammer and improving the reliability of the floating natural circulation system.

[0060] 3. By setting guide rails and guide grooves, the stability of the outlet device's operation can be further guaranteed.

[0061] 4. The outlet device is designed with a drain outlet, which makes its operation more convenient.

[0062] Example 2:

[0063] According to a second aspect of this application, a floating natural circulation system is proposed, such as... Figure 10 As shown, the system includes a housing 1, an inlet pipe 3, a heat exchanger 4, and an outlet pipe 5. Liquid in the housing 1 flows out through the inlet pipe 3, passes through the inlet pipe 3 and the heat exchanger 4, and then flows back into the housing 1 through the outlet pipe 5, discharging the heat acquired by the heat exchanger 4 into the housing 1. Furthermore, the floating natural circulation system includes a valve 6, located between the inlet pipe 3 and the outlet pipe 5, used to control the flow of the liquid. The floating natural circulation system also includes an outlet device 2. Liquid flows into the outlet device 2 after passing through the outlet pipe 5, and then flows out of the outlet device 2 back into the housing 1. The outlet device 2 slides according to the liquid level, ensuring that the outlet portion 23 in the outlet device 2 is always below the liquid level, creating a stable pressure difference between the liquid surface and the outlet portion 23.

[0064] Applying the above-described technical solution of this application, compared to existing passive containment heat removal systems, the floating natural circulation system of this embodiment, when the liquid level in the tank drops, such as Figure 11 As shown, the outlet part 23 in the outlet device 2 is always located below the liquid level, forming a stable pressure difference between the liquid surface and the outlet part 23. This can maximize the natural circulation drive height difference, effectively improve the heat carrying capacity and performance of the floating natural circulation system, and effectively avoid the steam hammer phenomenon that occurs in the floating natural circulation system during the vapor-liquid two-phase circulation.

[0065] The above are merely several specific embodiments of this application, but the scope of protection of this application is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in this application, based on the technical solution and application concept of this application, should be included within the scope of protection of this application.

[0066] It should be noted that, in this document, relational terms such as "first" and "second" are used merely to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitations, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes the element.

[0067] It should be noted that, in the description of this specification, the references to terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of this application. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

Claims

1. A floating natural circulation system, comprising a tank (1), an inlet pipe (3), a heat exchanger (4), and an outlet pipe (5), wherein liquid in the tank (1) flows out from the inlet pipe (3), flows sequentially through the inlet pipe (3) and the heat exchanger (4), and then flows back into the tank (1) through the outlet pipe (5), discharging the heat acquired by the heat exchanger (4) into the tank (1) through the liquid; the floating natural circulation system further comprises a valve (6), the valve (6) being located between the inlet pipe (3) and the outlet pipe (5), for controlling the flow of the liquid, characterized in that, The floating natural circulation system includes an outlet device (2). The liquid flows into the outlet device (2) after passing through the water outlet pipe (5), and then flows out from the outlet device (2) into the tank (1). The outlet device (2) slides in a different direction as the liquid level changes. The outlet part (23) in the outlet device (2) is always located below the liquid level, forming a pressure difference between the liquid surface and the outlet part (23). The liquid level in the tank (1) changes with the circulation system. The outlet device (2) includes: a floating part (21) that is at least partially submerged in the liquid; a guide part (22) that is disposed at the bottom of the tank (1) and the floating part (21) slides along the guide part (22) as the liquid level changes; and an outlet part (23) that slides together with the floating part (21) along the guide part (22) as the liquid level changes, and the outlet part (23) is below the liquid level.

2. The natural circulation system according to claim 1, characterized in that, The floating part (21) has a center line parallel to the liquid level, and the floating part (21) is a ring-shaped body symmetrical about the center line or the floating part (21) includes a plurality of spheres symmetrical about the center line.

3. The natural circulation system according to claim 2, characterized in that, The floating part (21) is a hollow structure.

4. The natural circulation system according to claim 1, characterized in that, At least one guide rail (231) is provided on the outer surface of the outlet part (23), and a guide groove is provided on the inner surface of the guide part (22) in cooperation with the guide rail (231).

5. The natural circulation system according to claim 1, characterized in that, The guide section (22) is provided with at least one drain outlet within the sliding range of the outlet section (23).

6. The natural circulation system according to claim 1, characterized in that, The outlet device (2) further includes a connecting part (24) that connects the floating part (21) and the outlet part (23).

7. The natural circulation system according to claim 1, characterized in that, The floating part (21) has a first inner boundary with a first diameter D1, and the outlet part (23) has an outer boundary with a second diameter D2. The relationship between the first diameter and the second diameter is π(D1 / 2). 2 -π(D² / 2) 2 =n π (D² / 2) 2 , where 3≤n≤5.

8. The natural circulation system according to claim 7, characterized in that, The vertical distance h1 from the bottom of the floating part (21) to the liquid level is h1≥1 / 2D2.

9. The natural circulation system according to claim 8, characterized in that, The vertical distance h2 between the outlet (23) and the liquid level is 1 / 4D2≤h2<1 / 2D2, such that the outlet (23) is below the liquid level.

10. The natural circulation system according to claim 7, characterized in that, The guide portion (22) has a second inner boundary, the second inner boundary has a third diameter D3, the third diameter D3 is larger than the second diameter D2, and the difference Δd between the third diameter D3 and the second diameter D2 is Δd = max{D2} 1 / 100m, 0.001m}.

11. The natural circulation system according to claim 6, characterized in that, The floating part (21) and the outlet part (23) are welded together by the connecting part (24).

12. The natural circulation system according to claim 1, characterized in that, The roughness of the contact surface between the guide part (22) and the outlet part (23) is between 50 and 200 micrometers.

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