Passive containment heat export system

Abstract

The utility model discloses a passive containment heat export system which comprises a first water tank, a liquid level control valve, a second water tank, an ascending pipeline, a containment penetration piece and an in-shell heat exchanger, the first water tank, the liquid level control valve, the second water tank and the ascending pipeline are arranged outside a containment and communicated with each other, the in-shell heat exchanger is arranged in the containment, and the ascending pipeline is communicated with the in-shell heat exchanger through the containment penetration piece; the second water tank is communicated with the in-shell heat exchanger through the descending pipeline; the second water tank can contain a cooling medium, and the cooling medium flows through the descending pipeline from the second water tank to the in-shell heat exchanger and then returns to the second water tank through the containment penetration piece and the ascending pipeline; the first water tank can contain a cooling medium which reaches the second water tank from the first water tank through the liquid level control valve. According to the passive containment heat export system disclosed by the embodiment of the utility model, factors for enhancing the natural circulation capability after flash evaporation can be fully utilized, and the requirements on the operation condition and the heat carrying capability of a PCS (Personal Computer System) after an accident are met.

Description

Technical Field

[0001] This utility model relates to the field of nuclear power technology, and in particular to a passive containment heat removal system. Background Technology

[0002] In pressurized water reactor nuclear power plants, during a Loss of Coolant Accident (LOCA) or a Steam Line Break (SLB) within the containment, a large amount of high-energy water or steam enters the containment, causing a rise in temperature and pressure within the containment. For LOCA, in addition to the short-term release of a large amount of mass and energy, the reactor's remaining power also needs to be released into the environment through the containment during the long-term phase. Therefore, a containment heat release and decompression system is required to remove the heat accumulated within the containment and control the temperature and pressure within the containment. Systems used for containment heat release include active containment spray systems and passive containment heat removal systems.

[0003] Currently, such as Figure 1 As shown, the passive containment cooling system (PCS) used in pressurized water reactor nuclear power plants includes: heat exchanger 101, external high-level water tank 102 (PCS tank), and connecting pipes, valves, and steam-water separators. Water is used as the heat transfer medium, relying on the density difference between the rising and falling sections of the system to achieve passive natural circulation cooling. The heat exchanger and external water tank are designed in multiple rows, symmetrically arranged along the containment, and the pipes in each row are kept as short as possible to reduce system circulation resistance and increase system heat transfer capacity. In the initial stage of system commissioning, when the water temperature in the PCS tank is low, the system operates in single-phase water circulation; as the PCS tank temperature rises to near saturation temperature, flash evaporation occurs in the rising section, forming a two-phase natural circulation. However, due to the need to meet the long-term heat transfer requirements after an accident, the PCS tank is relatively large. For a megawatt-class pressurized water reactor unit, a design with three PCS tanks is used, with each tank holding approximately 1000 m³ of water. 3The PCS water tank needs to be positioned high above the containment vessel due to the need for natural circulation, which places high demands on the tank and its supporting structure. The cantilevered arrangement of the PCS system's external water tank on the outer shell of the double-layer containment vessel presents significant structural design requirements and construction challenges. For reactors with a single-layer containment design, the technical solution of suspending a large-volume PCS water tank on the outer wall of a single-layer containment vessel is difficult to implement because the containment vessel requires prestressing after structural construction. Furthermore, patent CN102637464 discloses an enhanced heat exchange device for a passive heat removal system in a double-layer concrete containment vessel, including a heat exchanger assembly, riser pipes, downcomer pipes, a hot water tank, and a steam-water separator. The height of the hot water tank is higher than the height of the heat exchanger assembly. The working fluid inside the heat exchanger expands upon heating and flows upwards, entering the steam-water separator in the hot water tank outside the containment vessel. After cooling, the lower-temperature, higher-density working fluid flows downwards along the downcomer from the steam-water separator in the hot water tank outside the containment vessel into the internal heat exchanger. The entire process relies on natural circulation to complete the heat removal function. However, the aforementioned device cannot meet the requirement of discharging the reactor's surplus power in the long term. Summary of the Invention

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

[0005] Therefore, the first objective of this utility model is to propose a passive containment heat removal system that can accommodate sufficient cooling medium to meet the long-term heat carrying requirements after an accident, thereby meeting the requirements of the PCS system's operating conditions and heat carrying capacity after an accident.

[0006] To achieve the above objectives, the first aspect of this utility model provides a passive containment heat removal system, the heat removal system comprising:

[0007] The containment structure includes a first water tank, a level control valve, a second water tank, and a riser pipe, all connected to the outside of the containment building.

[0008] The containment penetration and the in-shell heat exchanger installed inside the containment are connected by the riser pipe to the in-shell heat exchanger via the containment penetration.

[0009] The second water tank is connected to the heat exchanger inside the shell via a downcomer pipe.

[0010] The second water tank can hold the cooling medium. The cooling medium flows from the second water tank through the downcomer to the heat exchanger inside the shell, and then returns to the second water tank through the containment penetration and the riser.

[0011] The first water tank can hold the cooling medium, which flows from the first water tank to the second water tank via a level control valve.

[0012] Furthermore, the bottom of the first water tank is higher than the bottom of the second water tank in the direction perpendicular to the ground.

[0013] Furthermore, the diameters of the ascending pipe and the descending pipe satisfy the condition: 1.5a ≤ b ≤ 2.5a, where a represents the diameter of the descending pipe and b represents the diameter of the ascending pipe.

[0014] Furthermore, the diameters of the containment penetration and the downcomer pipe satisfy: a≤c≤1.5a, where a represents the diameter of the downcomer pipe and c represents the diameter of the containment penetration.

[0015] Furthermore, the shell-mounted heat exchanger includes heat transfer tubes with an inner diameter of 15mm-18mm, a wall thickness of 1.2mm-1.5mm, and a length of 3m-4.5m.

[0016] Furthermore, the length of the extension section of the rising pipe that is submerged in the second water tank satisfies the following condition: 0.5m ≤ h ≤ 2m, where h represents the length of the extension section.

[0017] Furthermore, the distance between the cooling medium level in the second water tank and the outlet of the rising pipe in the direction perpendicular to the ground is 0.5m-1m.

[0018] Furthermore, the height of the liquid level in the second water tank satisfies: 1m≤k≤2.5m, where k represents the height of the liquid level in the second water tank.

[0019] Furthermore, the outlet temperature range of the heat transfer tube is 102℃~112℃.

[0020] Furthermore, the outlet temperature of the heat transfer tube is lower than the saturation temperature of the cooling medium.

[0021] Furthermore, the vapor content of the cooling medium at the outlet of the rising pipe is less than or equal to 0.023.

[0022] By applying the above-described technical solution of this utility model, at least the following technical effects are achieved:

[0023] 1. This passive containment heat removal system, while accommodating sufficient cooling medium to meet the long-term heat carrying requirements after an accident, fully utilizes the enhanced natural circulation capacity after flash evaporation, thus meeting the requirements of the PCS system's operating conditions and heat carrying capacity after an accident.

[0024] 2. The passive containment heat removal system separates the first and second water tanks, which increases the flexibility and application range of the PCS system layout.

[0025] 3. This passive containment heat removal system reduces the volume of the second water tank participating in the heat exchange cycle, ensuring that the support structure can meet the stability requirements of the second water tank, thereby guaranteeing the overall safety and reliability of the PCS system.

[0026] 4. In this passive containment heat removal system, the bottom of the first water tank is higher than the bottom of the second water tank in the direction perpendicular to the ground, so that the cooling medium in the first water tank can be passively replenished to the second water tank.

[0027] Additional aspects and advantages of this invention 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 the invention. Attached Figure Description

[0028] The accompanying drawings, which form part of this specification, are used to provide a further understanding of this utility model. The illustrative embodiments and descriptions of this utility model are used to explain this utility model and do not constitute an undue limitation thereof. In the drawings:

[0029] Figure 1 A schematic diagram of a passive containment heat removal system in the prior art is presented;

[0030] Figure 2 A schematic diagram of a passive containment heat removal system according to one embodiment is shown.

[0031] Reference numerals: 1. First water tank; 2. Liquid level control valve; 3. Second water tank; 4. Rising pipe; 5. Containment penetration; 6. Internal heat exchanger; 61. Heat transfer tube; 7. Falling pipe; 8. Connecting pipe; 9. Rising pipe isolation valve; 10. Falling pipe isolation valve; 101. Heat exchanger; 102. External high-level water tank. Detailed Implementation

[0032] It should be noted that, where there is no conflict, the embodiments and features in the embodiments of this utility model can be combined with each other. The present utility model will now be described in detail with reference to the accompanying drawings and embodiments.

[0033] The present invention will be further described in detail below with reference to specific embodiments. These embodiments should not be construed as limiting the scope of protection claimed by the present invention.

[0034] In this description, it should be noted that, unless otherwise explicitly specified and limited, the terms "installation," "connection," and "joining" 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 of two components. Those skilled in the art can understand the specific meaning of the above terms in this utility model based on the specific circumstances. Furthermore, in the description of this utility model, unless otherwise stated, "a plurality of" means two or more.

[0035] Example 1

[0036] According to a first aspect of this utility model, a passive containment cooling system (PCS) is proposed. In this embodiment, as... Figure 2 As shown, the first water tank 1 and the second water tank 3 are interconnected. Specifically, the second water tank 3 is located outside the containment vessel, corresponding to the PCS system, while the first water tank 1 can be arranged in other buildings. This allows the first water tank 1 to hold sufficient cooling medium to meet the long-term heat requirements after an accident, while reducing the volume of the second water tank 3. Consequently, the second water tank 3 can be manufactured as a single unit and can be mounted on the outer non-prestressed containment vessel of a double-layer containment vessel or on a single-layer prestressed containment vessel, ensuring that the supporting structure meets the stability requirements of the second water tank 3. Furthermore, by arranging the first water tank 1 and the second water tank 3 separately, the flexibility and application range of the PCS system layout can be increased.

[0037] In this embodiment, as Figure 2 As shown, the PCS system includes a second water tank 3 connected to the outside of the containment and an ascending pipe 4. Furthermore, the PCS system also includes a containment penetration 5 and an internal heat exchanger 6 disposed within the containment. Specifically, the ascending pipe 4 is connected to the internal heat exchanger 6 via the containment penetration 5. Additionally, the PCS system also includes a descending pipe 7. Specifically, the second water tank 3 is connected to the internal heat exchanger 6 via the descending pipe 7. It should be noted that the ascending pipe 4 is the hot section, and the descending pipe 7 is the cold section.

[0038] The second water tank 3 can hold the cooling medium, which flows from the second water tank 3 through the downcomer 7 to the shell heat exchanger 6, and then returns to the second water tank 3 via the containment penetration 5 and the riser 4, thus performing a heat exchange cycle between the second water tank 3 and the shell heat exchanger 6. Specifically, the cooling medium flows from the second water tank 3 into the downcomer 7, is heated by the shell heat exchanger 6, and then returns to the second water tank 3 via the containment penetration 5 and the riser 4, thereby dissipating heat from the containment. It should be noted that in the initial stage of the heat exchange cycle, the circulation of the cooling medium is a single-phase cycle.

[0039] In this embodiment, as Figure 2 As shown, the PCS system also includes a first water tank 1 and a level control valve 2 connected to the outside of the containment, and the first water tank 1, the level control valve 2, the second water tank 3, and the riser pipe 4 are connected. Furthermore, the first water tank 1 can contain cooling medium, which travels from the first water tank 1 to the second water tank 3 via the level control valve 2 to ensure that the liquid level in the second water tank 3 meets the heat dissipation requirements of the containment.

[0040] Specifically, as the heat exchange cycle continues, due to the smaller volume of the cooling medium in the second water tank 3, the cooling medium in the second water tank 3 will be heated to saturation, and the circulation of the cooling medium will enter a two-phase cycle. Simultaneously, the first water tank 1 and the second water tank 3 are connected by a pipe. As the cooling medium in the second water tank 3 evaporates, the liquid level in the second water tank 3 drops. Under the action of gravity, the liquid level control valve 2 automatically opens, and the cooling medium in the first water tank 1 flows into the second water tank 3 through the connecting pipe between the first water tank 1 and the second water tank 3 to replenish the cooling medium lost in the second water tank 3. It should be noted that the bottom of the first water tank 1 is higher than the bottom of the second water tank 3 in the direction perpendicular to the ground, thus allowing the cooling medium in the first water tank 1 to be passively replenished into the second water tank 3. This ensures that the cooling medium in the second water tank 3 can carry away the heat accumulated inside the containment after an accident, thereby controlling the temperature and pressure inside the containment to meet safety requirements.

[0041] It should be noted that, compared to existing PCS systems, the cooling medium in the first water tank 1 is only used to replenish the cooling medium in the second water tank 3 and does not participate in the heat exchange cycle within the PCS system. The PCS system in this embodiment mainly operates in a two-phase cycle. The cooling medium in the second water tank 3 is near saturation and, after entering the downcomer pipe 7, its subcooling gradually increases with increasing pressure under the pressure of the cooling medium. After being heated by the shell-mounted heat exchanger 6, the cooling medium, as the pressure decreases in the rising pipe 4, flashes into steam when the pressure falls below the saturation pressure of the heated cooling medium. This flashing continues as the position rises and the pressure continues to decrease until it enters the second water tank 3. There, the cooling medium flows back into the second water tank 3, while the steam is discharged from the top of the second water tank 3.

[0042] It should be understood that after the cooling medium flashes in the rising pipe, the density of the mixed fluid is significantly reduced, increasing the density difference between the falling pipe 7 and the rising pipe 4. This, in turn, increases the natural circulation drive head of the PCS system, which is beneficial for increasing the heat carrying capacity of the PCS system. For example, using water as the cooling medium, at one atmosphere, the density of saturated water vapor is less than one-thousandth that of saturated water. Therefore, even if a very small portion of water flashes into water vapor, the volume fraction of water vapor is extremely significant. This characteristic makes the two-phase volumetric flow rate of vapor and liquid in the rising pipe 4 after flashing significantly higher than the single-phase water volumetric flow rate in the falling pipe 7. In this embodiment, the cooling medium can be replenished to the second water tank 3 by the drop in the liquid level of the first water tank 1. Therefore, the cooling medium volume of the second water tank 3 is relatively small, and the cooling medium in the second water tank 3 will be quickly heated to saturation. This allows full utilization of the enhanced natural circulation capacity after flashing, reducing its adverse effects, and thus meeting the requirements of the PCS system's operating conditions and heat carrying capacity after an accident.

[0043] Furthermore, if the flash section of the rising pipe 4 and the other single-phase water pipes in the PCS system, such as the falling pipe 7, have the same dimensions, the flow velocity in the flash section will increase significantly, leading to a greater pressure drop and a decrease in the circulating flow rate of the PCS system, thus affecting the heat carrying capacity of the PCS system. Therefore, to further ensure efficient heat carrying of the PCS system, the diameters of the rising pipe 4 and the falling pipe 7 are set to satisfy: 1.5a ≤ b ≤ 2.5a. Preferably, b = 2a provides the best heat carrying effect. Here, a represents the diameter of the falling pipe, and b represents the diameter of the rising pipe. In addition, the diameters of the containment penetration 5 and the falling pipe 7 are set to satisfy: a ≤ c ≤ 1.5a. Here, a represents the diameter of the falling pipe, and c represents the diameter of the containment penetration.

[0044] Furthermore, the in-shell heat exchanger 6 includes heat transfer tubes 61. For a typical large pressurized water reactor, the design temperature requirement for the containment after an accident is 145°C, the design pressure requirement is 0.42 MPa, and the long-term pressure requirement 24 hours after the accident is less than half of the peak design pressure, i.e., 0.21 MPa, corresponding to a temperature requirement of approximately 120°C. Both the design pressure requirement and the peak design pressure are gauge pressures. When the above temperature and pressure ranges are met, the PCS system can operate stably and meet the heat carrying capacity requirements. To meet the above operating range requirements, in this embodiment, when the cooling medium at the inlet of the downcomer 7 is close to or at saturation, the outlet temperature range of the heat transfer tubes 61 is 102°C to 112°C, and the outlet temperature of the heat transfer tubes 61 is lower than the local saturation temperature of the cooling medium to avoid flashing within the heat transfer tubes 61. In addition, to ensure that the PCS system can maintain stable natural circulation, in this embodiment, the vapor content of the cooling medium at the outlet of the riser 4 is less than or equal to 0.023.

[0045] Furthermore, in order to achieve the above-mentioned requirements for outlet temperature and steam content, the diameter ratio of the rising pipe 4 and the falling pipe 7, the height of the rising pipe 4, the length, inner diameter and wall thickness of the heat transfer pipe 61, and the structure of the second water tank 3 need to be set.

[0046] In this embodiment, the diameters of the rising pipe 4 and the falling pipe 7 are set to 1.5a≤b≤2.5a, according to the aforementioned 1.5a≤b≤2.5a. Here, a represents the diameter of the falling pipe, and b represents the diameter of the rising pipe. Furthermore, the smaller the diameters of the containment penetration 5 and the falling pipe 7, the longer the required height of the rising pipe 4. In this embodiment, the height of the rising pipe 4 is 8m-15m. Additionally, in this embodiment, the inner diameter of the heat transfer tube 61 is 15mm-18mm, and the wall thickness of the heat transfer tube 61 is 1.2mm-1.5mm. Simultaneously, the length of the heat transfer tube 61 should not be too long, ideally 3m-4.5m, to prevent excessive water temperature rise within the heat transfer tube when the temperature and pressure inside the containment shell are high, which could lead to vaporization and affect the stability of the flow within the heat transfer tube. In addition, the riser pipe 4 has an extension section that submerges into the second water tank 3. The length of this extension section should not be less than 0.5m, nor should it be too long, causing the second water tank 3 to be too high. The length of this extension section satisfies the following condition: 0.5m ≤ h ≤ 2m, where h represents the length of the extension section. Simultaneously, the distance between the cooling medium level in the second water tank 3 and the outlet of the riser pipe 4 in the direction perpendicular to the ground is 0.5m-1m. Furthermore, the height of the liquid level in the second water tank 3 satisfies the following condition: 1m ≤ k ≤ 2.5m, where k represents the height of the liquid level in the second water tank 3.

[0047] It should be noted that the structural dimensions of the first water tank 1 and the second water tank 3 must meet the space requirements for the arrangement of the rising pipe 4, the containment penetration 5, the falling pipe 7, the connecting pipe 8 between the first and second water tanks, as well as the liquid level control valve 2, the rising pipe isolation valve 9, and the falling pipe isolation valve 10.

[0048] Example 2

[0049] In one specific embodiment, parameters such as the diameter of each loop pipe and the area of ​​the in-shell heat exchanger in the PCS system depend on the power output of the pressurized water reactor unit and the number of PCS systems configured. In this embodiment, for a 1,000 MW pressurized water reactor unit, three groups of nine PCS systems are configured, with each group comprising three PCS systems, and each column including one PCS system as described in Embodiment 1 above. In this embodiment, the parameters of each loop pipe and in-shell heat exchanger in the PCS system are as follows: the inner diameter of the downcomer 7 is 200 mm, and the heat transfer area of ​​the heat transfer tube 61 in the in-shell heat exchanger 6 is 100–130 m². 2 The inner diameter of the containment penetration 5 is 200 mm, and the inner diameter of the riser pipe 4 is 400 mm. Furthermore, in this embodiment, the second water tank 3 has a height of approximately 4 m and an internal cooling medium volume of approximately 6 m³. 3 .

[0050] It should be noted that the diameter and length of each loop pipe in the PCS system, as well as local structures such as elbows and valves, all affect the natural circulation resistance and circulation flow rate. Therefore, the above parameters can be further adjusted and optimized based on the actual PCS system layout design. Using the parameter design in this embodiment, when the shell temperature reaches 145℃, the heat carrying capacity of each PCS system is no less than 6MW; when the shell temperature is 120℃, the heat carrying capacity of each PCS system can reach 2MW.

[0051] By applying the technical solutions in the above embodiments of this utility model, the following technical effects are achieved:

[0052] 1. This passive containment heat removal system, while accommodating sufficient cooling medium to meet the long-term heat carrying requirements after an accident, fully utilizes the enhanced natural circulation capacity after flash evaporation, thus meeting the requirements of the PCS system's operating conditions and heat carrying capacity after an accident.

[0053] 2. The passive containment heat removal system separates the first and second water tanks, which increases the flexibility and application range of the PCS system layout.

[0054] 3. This passive containment heat removal system reduces the volume of the second water tank participating in the heat exchange cycle, ensuring that the support structure can meet the stability requirements of the second water tank, thereby guaranteeing the overall safety and reliability of the PCS system.

[0055] 4. In this passive containment heat removal system, the bottom of the first water tank is higher than the bottom of the second water tank in the direction perpendicular to the ground, so that the cooling medium in the first water tank can be passively replenished to the second water tank.

[0056] The above are merely several specific embodiments of this utility model, but the protection scope of this utility model is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the technical scope disclosed in this utility model, based on the technical solution and inventive concept of this utility model, should be included within the protection scope of this utility model.

[0057] 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.

[0058] 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 utility model. 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 passive containment heat removal system, characterized in that, The passive containment heat removal system includes: The enclosure is equipped with a first water tank (1), a level control valve (2), a second water tank (3), and a riser pipe (4) connected to the outside of the containment. The containment penetration (5) and the in-shell heat exchanger (6) disposed inside the containment, wherein the riser (4) is connected to the in-shell heat exchanger (6) via the containment penetration (5); Downcomer pipe (7), the second water tank (3) is connected to the shell heat exchanger (6) via the downcomer pipe (7); The second water tank (3) can contain cooling medium, which flows from the second water tank (3) through the downcomer (7) to the in-shell heat exchanger (6), and then returns to the second water tank (3) through the containment penetration (5) and the riser (4); The first water tank (1) can contain the cooling medium, which flows from the first water tank (1) to the second water tank (3) via the level control valve (2).

2. The passive containment heat removal system according to claim 1, characterized in that, The bottom of the first water tank (1) is higher than the bottom of the second water tank (3) in the direction perpendicular to the ground.

3. The passive containment heat removal system according to claim 1, characterized in that, The diameters of the ascending pipe (4) and the descending pipe (7) satisfy: 1.5a ≤ b ≤ 2.5a, where a represents the diameter of the descending pipe and b represents the diameter of the ascending pipe.

4. The passive containment heat removal system according to claim 1, characterized in that, The diameters of the containment penetration (5) and the descent pipe (7) satisfy: a≤c≤1.5a, where a represents the diameter of the descent pipe and c represents the diameter of the containment penetration.

5. The passive containment heat removal system according to claim 1, characterized in that, The shell heat exchanger (6) includes a heat transfer tube (61) with an inner diameter of 15mm-18mm, a wall thickness of 1.2mm-1.5mm, and a length of 3m-4.5m.

6. The passive containment heat removal system according to claim 1, characterized in that, The length of the extension section of the rising pipe (4) that is submerged in the second water tank (3) satisfies the following condition: 0.5m ≤ h ≤ 2m, where h represents the length of the extension section.

7. The passive containment heat removal system according to claim 1, characterized in that, The distance between the level of the cooling medium in the second water tank (3) and the outlet of the rising pipe (4) in the direction perpendicular to the ground is 0.5m-1m.

8. The passive containment heat removal system according to claim 6, characterized in that, The height of the liquid level in the second water tank (3) satisfies: 1m≤k≤2.5m, where k represents the height of the liquid level in the second water tank (3).

9. The passive containment heat removal system according to claim 5, characterized in that, The outlet temperature range of the heat transfer tube (61) is 102℃~112℃.

10. The passive containment heat removal system according to claim 5, characterized in that, The outlet temperature of the heat transfer tube (61) is lower than the saturation temperature of the cooling medium.

11. The passive containment heat removal system according to claim 1, characterized in that, The vapor content of the cooling medium at the outlet of the rising pipe (4) is less than or equal to 0.023.

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