Heat removal system for containment vessel

Abstract

Disclosed in the present invention is a heat removal system for a containment vessel, comprising a heat exchanger provided in the containment vessel, a cooling liquid tank, and a steam collecting devi

Description

The disclosure relates to the field of nuclear reactor safety, and in particular to a containment heat removal system. Background A containment serves as a last physical safety barrier of a pressurized water reactor nuclear power plant. In order to guarantee the safety of the nuclear power plant, it is of significant importance to maintain the integrity of the containment, so as to avoid leaking massive radioactive substances under an accident. When major accidents such as a large break accident of a primary loop or a main steam pipeline fracture of a secondary loop occur in the nuclear power plant, a large quantity of high-temperature and high-pressure steam is released to the containment, resulting in rapid increase of a temperature and a pressure in the containment. Consequently, the containment faces the risk of overpressure damage and large-scale uncontrolled release of the radioactive substances, thus posing a serious threat to the surrounding environment and personnel safety. In order to guarantee the integrity of the containment, after the research on a passive containment heat removal technology, various countries have attempted to remove huge decay heat in the containment under accident conditions only through natural forces such as gravity and a fluid density difference. For a concrete containment, the main research solution involves a closed system and an opened system. In the closed system, a closed natural circulation loop is typically composed of an internal heat exchanger, an external heat exchanger, a cooling water tank, a connection pipeline, a valve, etc. Such solutions have not been applied to engineering because of more heat transfer links, a more complex structure, a lower heat discharge capacity, etc. In the opened system, an opened natural circulation loop is typically composed of an internal heat exchanger, a cooling water tank, a connection pipeline, a valve, etc. Such solutions feature fewer heat transfer links, a less complex structure, and a higher heat discharge capacity, etc. These opened system solutions are in face of the risks of steam hammer vibration, two-phase flow excitation, flow stagnation, etc., and thus it is rather difficult to apply these opened system solutions to engineering applications. In the patent No. 201410126253.3, several outlets with valves are arranged at a portion of a system riser, which is positioned at a water tank. A measurement and control system is responsible for opening and closing the valves, so as to eliminate the adverse effect of the water level in the water tank. However, the solution is not feasible in a wet engineering environment having severe water level fluctuation, and especially the measurement and control system fails in the case of a plant-wide power outage. Accordingly, the valves cannot be opened or closed normally. To deal with such accident scenarios is the basic starting point to configure a new-generation nuclear power system with a passive containment heat removal system. Relying on the designs in patents No. 202110361911.7 and 201580075448.2, steam hammer vibration has been overcome. However, the problems that a water level static pressure in a water tank significantly reduces a natural system circulation capacity, and concentration and aggregation of non-condensable gas outside a heat transfer pipe of an internal heat exchanger dramatically increases heat transfer resistance are still to be addressed. Under the constraint of these shortcomings, a heat discharge capacity of a system can only satisfy the demand of beyond design basis accidents. Detailed structures of significant apparatuses in the system have not been disclosed in the patents. In view of the above technical problems, the disclosure is provided. Summary A primary object of the disclosure is to provide a containment heat removal system. Therefore, the risks of steam hammer vibration, two-phase flow excitation, flow stagnation, etc. are eliminated, and the adverse effect of a liquid level of a coolant tank is eliminated; an aggregation degree of non-condensable gas outside heat transfer pipes of a heat exchanger is effectively reduced, and a working medium flow rate between the heat transfer pipes is obviously improved; and accordingly, a heat discharge capacity of the system is remarkably improved, and the containment heat removal system is capable of coping with the design basis accidents. In order to realize the above objectives, the disclosure provides a containment heat removal system. The containment heat removal system includes a heat exchanger arranged inside a containment, a coolant tank and a steam collection device arranged in the coolant tank, where the heat exchanger is in communication with a medium in the coolant tank; and a medium in the heat exchanger absorbs heat of the containment and is discharged into the coolant tank through the steam collection device, and the medium in the coolant tank is returned to the heat exchanger. The steam collection device includes steam discharge valve assemblies corresponding to different liquid level heights of the coolant tank, where each of the steam discharge valve assemblies configured such that when a liquid level height is lowered, each of the steam discharge valve assemblies is automatically opened under self-force, and at least part of the medium entering the steam collection device enters the coolant tank through the steam discharge valve assemblies, so that a static pressure difference between an inner side and an outer side of the steam collection device is balanced, and a system circulation driving force under a low liquid level height is increased. Further, the steam collection device includes a steam collection pipe and sleeves at a plurality of stages sleeving the steam collection pipe, where the sleeves at a plurality of stages are distributed in a direction of the liquid level height, a sleeve at a first stage of the sleeves at a plurality of stages is positioned at a lowest portion, and a stage number is increased in sequence along with an increase in the liquid level height; and each of the sleeves at a plurality of stages is movable in an axial direction of the steam collection pipe along with a change in the liquid level height, and the sleeves at a plurality of stages are configured to move downwards in sequence from a higher stage to a lower stage when the liquid level height is decreased. Further, the steam collection pipe is provided with steam discharge ports at a plurality of stages in a height direction, where the steam discharge ports at a plurality of stages are arranged corresponding to the sleeves at a plurality of stages, and the steam discharge port and the sleeve are combined to form the steam discharge valve assemblies; and the sleeves at a plurality of stages move downwards in sequence from a higher stage to a lower stage, so that the steam discharge ports at a plurality of stages are opened in sequence from high to low. Further, a plurality of limiters sleeve an outer wall of the steam collection pipe, the limiters are distributed in the axial direction of the steam collection pipe to divide the steam collection pipe into a plurality of independent regions in the axial direction, and the sleeves at a plurality of stages are arranged in the independent regions respectively. Further, the sleeves at a plurality of stages are independent of one another and correspond to different liquid level heights. Further, a hollow cavity is delimited by each of the sleeves at a plurality of stages, and a buoyancy applied to the hollow cavity in the coolant tank is greater than a gravity applied to the sleeve. Further, an inner diameter of a sleeve at a previous stage of the sleeves at a plurality of stages is greater than an outer diameter of a sleeve at a next stage, adjacent sleeves are arranged together in a nested manner, and the sleeve at the previous stage is movable along an outer wall of the sleeve at the next stage. Further, the containment heat removal system includes a first locating portion, where the first locating portion is sleeved on an outside of the steam collection pipe, and the first locating portion defines a highest position of the sleeves at a plurality of stages and prevents the sleeves at a plurality of stages from being separated from the steam collection pipe from an upper portion of the steam collection pipe. Further, a steam discharge region is defined above the first locating portion in the axial direction of the steam collection pipe, and a reinforcement ring is arranged on a portion, corresponding to the steam discharge region, of an outer wall of the steam collection pipe, so as to enhance stability of the steam collection pipe. Further, a maximum length of the sleeves at a plurality of stages in the axial direction of the steam collection pipe is not shorter than a length of the steam discharge region in the axial direction of the steam collection pipe, so that the sleeves at a plurality of stages completely cover all the steam discharge ports within a length range of the steam collection pipe. Further, the containment heat removal system further includes a fourth locating portion, where the fourth locating portion is sleeved on an outside of the steam collection pipe, and the fourth locating portion defines a lowest position of the sleeves at a plurality of stages and prevents the sleeves at a plurality of stages from being separated from the steam collection pipe from a lower portion of the steam collection pipe. Further, a top of each of the sleeves at a plurality of stages is provided with a second locating portion, and second locating portions of adjacent sleeves make contact with each other to prevent a sleeve at a previous stage from being separated from a bottom of a sleeve at a next stage. Further, a bottom of each of the sleeves at a plurality of stages is provided with a third locating portion, and the third locating portion of the sleeve at a previous stage makes contact with the second locating portion of the sleeve at a next stage to prevent the sleeve at the previous stage from being separated from the sleeve at the next stage when the sleeve at a previous stage moves upwards. Further, an inner diameter of the second locating portion equals an outer diameter of the steam collection pipe, and an outer diameter of the second locating portion equals an inner diameter of the sleeve at a previous stage. Further, an inner diameter of the third locating portion equals an outer diameter of the sleeve at a next stage. Further, an outer diameter of the first locating portion equals an inner diameter of the sleeve at the first stage. Further, the containment heat removal system further includes a flow guide hood, where the flow guide hood is sleeved on an outside of the sleeves at a plurality of stages. Further, a liquid discharge port is provided at a bottom of the flow guide hood, and a cooling medium in the flow guide hood is discharged through the liquid discharge port, so as to reduce disturbance to a liquid level. Further, a steam-water separation hood is arranged at a top of the steam collection pipe, and the steam-water separation hood performs steam-water separation on a steam-water mixture flowing out of an outlet of the steam collection pipe. Further, the containment heat removal system further includes a support column, where the support column supports the steam-water separation hood, so as to maintain a predetermined distance between the steam-water separation hood and the flow guide hood. Further, the heat exchanger includes a first heat transfer pipe bundle and a second heat transfer pipe bundle, where the first heat transfer pipe bundle and the second heat transfer pipe bundle are symmetrically distributed in a mirror image. Further, the heat exchanger further includes a distribution header and a confluence header, where the first heat transfer pipe bundle is in communication with the distribution header and the confluence header, and the second heat transfer pipe bundle is in communication with the distribution header and the confluence header; and the medium enters the first heat transfer pipe bundle and / or the second heat transfer pipe bundle through the distribution header and flows out of the heat exchanger through the confluence header. Further, the second heat transfer pipe bundle and the first heat transfer pipe bundle are symmetrically arranged on two axial sides of the distribution header and / or two axial sides of the confluence header, and a hollow region is delimited by the second heat transfer pipe bundle, the first heat transfer pipe bundle, the distribution header, and the confluence header, and the medium accelerates in the hollow region. Further, the distribution header and the confluence header are horizontally arranged, and openings of the distribution header and the confluence header are provided on the same side. Further, the first heat transfer pipe bundle and / or the second heat transfer pipe bundle includes a plurality of heat transfer pipe rows, where the plurality of heat transfer pipe rows are arranged in parallel, and a pressure difference is formed between a heat transfer pipe row closer to the hollow region and a heat transfer pipe row farther away from the hollow region to accelerate medium flow. Further, the heat transfer pipe row includes a plurality of heat transfer pipes, where the plurality of heat transfer pipes are arranged in an axial direction of the distribution header and / or an axial direction of the confluence header. Further, the heat transfer pipe includes a first pipe section, a second pipe section, and an intermediate pipe section connecting the first pipe section and the second pipe section, where the first pipe section is in communication with the confluence header, and the second pipe section is in communication with the distribution header. Further, the first pipe section has a smaller length than the second pipe section. Further, an included angle between the second pipe section and the intermediate pipe section is 60°-80°. Further, a distance between adjacent heat transfer pipes is 2-3 times a diameter of the heat transfer pipe. Further, the heat exchanger includes support partitions, where the support partitions are arranged between the heat transfer pipes and perpendicular to the intermediate pipe sections of the heat transfer pipes. Further, the containment heat removal system further includes a riser section and a downcomer section, where the riser section connects the confluence header and the coolant tank, and the downcomer section connects the coolant tank and the distribution header. The containment heat removal system provided by the disclosure has the technical effects as follows: 1. The steam collection device employed in the containment heat removal system of the disclosure can automatically balance the static pressure difference between the inner side and the outer side of the steam collection pipe in a passive manner while completely eliminating the risks of steam hammer vibration, two-phase flow excitation, and flow stagnation in a steam-liquid two-phase flow phase. Accordingly, the adverse effect of the liquid level of the coolant tank on the natural circulation flow of the passive containment heat removal system can be eliminated. 2. The heat exchanger employed in the containment heat removal system of the disclosure significantly reduces the flow resistance and has a compact structure without increasing a manufacturing difficulty of the heat exchanger. Accordingly, the heat transfer on the inner side and the outer side of the heat transfer pipe is remarkably enhanced, and the heat exchanger becomes an efficient heat exchanger having the small flow resistance and the high heat exchange capacity. 3. In the disclosure, by optimizing the configuration of the containment heat removal system, the flow stability and the natural circulation capacity of the system are significantly enhanced, a heat discharge power level of the passive containment heat removal system is remarkably increased, and thus the system is capable of coping with the design basis accidents. 4. The containment heat removal system of the disclosure is simple in composition, the steam collection device is convenient to assemble and disassemble, and the system is high in stability. Brief Description of the Drawings The accompanying drawings of the description are used for providing further understanding of the disclosure, as a constitute part of the disclosure. Illustrative embodiments of the disclosure and their description serve to explain the disclosure, instead of limiting the disclosure improperly. In the accompanying drawings: Fig. 1 shows a schematic structural diagram of a containment heat removal system according to the disclosure; Fig. 2 shows a schematic structural diagram of a steam collection device according to Embodiment 1 of the disclosure; Fig. 3 shows a front view of an entire structure of a heat exchanger according to an embodiment of the disclosure; Fig. 4 shows a side view of a heat exchanger according to an embodiment of the disclosure; Fig. 5 shows a schematic structural diagram of an arrangement of heat exchange pipes according to an embodiment of the disclosure; Fig. 6 is a schematic structural diagram of a single heat exchange pipe according to an embodiment of the disclosure; Fig. 7 shows a variation trend of a heat discharge power of a heat exchanger along with a containment pressure according to an embodiment of the disclosure; Fig. 8 shows a trend diagram of a pressure in a containment with time under a hypothetical reactor accident according to an embodiment of the disclosure; Fig. 9 shows a schematic structural diagram of a steam collection device according to Embodiment 2 of the disclosure; Fig. 10 shows a schematic structural diagram of sleeves at a plurality of stages in a steam collection device according to Embodiment 2 of the disclosure; Fig. 11 shows a top view of a steam collection device according to Embodiment 2 of the disclosure; Fig. 12 shows a schematic diagram of a locating structure in a steam collection device according to Embodiment 2 of the disclosure; and Fig. 13 shows a schematic diagram of locating structures positioned on an upper portion and a lower portion of a sleeve in a steam collection device according to Embodiment 2 of the disclosure. The above accompanying drawings include the reference numerals as follows: 20:heat exchanger; 30: coolant tank; 40: steam collection device; 480: steam discharge valve assemblies; 410: steam collection pipe; 415: limiter; 420: sleeve; 460: steam discharge port; 416: first locating portion; 411: reinforcement ring; 418: fourth locating portion; 422: second locating portion; 424: third locating portion; 430: flow guide hood; 431: liquid discharge port; 440: steamwater separation hood; 450: support column; 230: first heat transfer pipe bundle; 240: second heat transfer pipe bundle; 210: distribution header; 220: confluence header; 234: heat transfer pipe row; 2342: heat transfer pipe; 2344: first pipe section; 2346: second pipe section; 2348: intermediate pipe section; 260: support partition; 50: riser section; and 60: downcomer section. Detailed Description of the Embodiments It should be noted that embodiments of the disclosure and features in the embodiments can be mutually combined without conflicts. The disclosure will be described in detail below in conjunction with the accompanying drawings and the embodiments. The disclosure will be further described in detail below with reference to specific embodiments, which should not be interpreted as limiting the scope of protection claimed by the disclosure. The terms “comprise” and “include” indicates the presence of a feature but does not exclude the presence or addition of one or more other features when in use. The orientation or position relations indicated by the terms “transverse”, “up”, “down”, “front”, “rear”, “left”, “right”, “top”, “bottom”, “inside”, “outside”, etc. are based on the orientation or position relations shown in the accompanying drawings, are merely for facilitating the description, rather than indicating or implying that the device or element referred to must have a particular orientation or be constructed and operated in a particular orientation, and therefore cannot be interpreted as limiting the disclosure. In addition, the terms “first” and “second” are merely descriptive and cannot be interpreted as indicating or implying the relative importance. In the description, it should be noted that unless otherwise explicitly specified and defined, the terms “mounting”, “connecting”, and “connection” should be understood in a broad sense, for embodiment, they can denote a fixed connection, a detachable connection, an integrated connection, a direct connection, an indirect connection via an intermediate medium, or communication inside two elements. For those of ordinary skill in the art, the specific meanings of the above terms in the disclosure can be understood according to specific circumstances. In addition, in the description of the disclosure, “a plurality of” indicates two or more unless otherwise specified. Embodiment 1: The disclosure provides a containment heat removal system. As shown in Fig. 1, the containment heat removal system includes a heat exchanger 20 arranged inside a containment, a coolant tank 30and a steam collection device 40 arranged in the coolant tank 30, where the heat exchanger 20 is in communication with a medium in the coolant tank 30. A medium in the heat exchanger 20 absorbs heat of the containment and is discharged into the coolant tank 30 through the steam collection device 40, and the medium in the coolant tank 30 is returned to the heat exchanger 20, so as to form a circulation loop. With the heat in the containment removed constantly, the medium in the coolant tank 30 is evaporated continuously. Consequently, a liquid level is lowered, a system circulation driving force is reduced, and a heat discharge capacity is reduced. In order to avoid such a situation, the disclosure provides a steam collection device to eliminate the adverse effect of liquid level lowering. As shown in Fig. 2, the steam collection device 40 includes steam discharge valve assemblies 480 corresponding to different liquid level heights of the coolant tank 30, where each of the steam discharge valve assemblies 480 is configured such that when a liquid level height is lowered, each of the steam discharge valve assemblies 480 is automatically opened under self-force; and at least part of the medium entering the steam collection device 40 enters the coolant tank 30 through the steam discharge valve assemblies 480, so that a static pressure difference between an inner side and an outer side of the steam collection device 40 is balanced, and a system circulation driving force under a low liquid level height is increased. In the disclosure, the self-force applied to the steam discharge valve assemblies 480 includes buoyancy applied to the steam discharge valve assemblies in a cooling medium and self-gravity of the steam discharge valve assemblies. In the disclosure, the cooling medium includes, but is not limited to an aqueous medium. Specifically, the steam collection device 40 is of a cylinder structure and includes a steam collection pipe 410 and sleeves 420 at a plurality of stages sleeving the steam collection pipe 410, where the sleeves 420 at a plurality of stages are distributed in a direction of the liquid level height, a sleeve at a first stage of the sleeves at a plurality of stages is positioned at a lowest portion, and a stage number is increased in sequence along with an increase in the liquid level height; and each of the sleeves 420 at a plurality of stages is movable in an axial direction of the steam collection pipe 410 along with a change in the liquid level height, and the sleeves at a plurality of stages are configured to move downwards in sequence from a higher stage to a lower stage when the liquid level height is lowered. The steam collection pipe 410 is provided with steam discharge ports at a plurality of stages in a height direction, the steam discharge ports at a plurality of stages are arranged corresponding to the sleeves at a plurality of stages, and the steam discharge ports 460 and the sleeves 420 are combined to form the steam discharge valve assemblies480; and the sleeves 420 at a plurality of stages move downwards in sequence from a higher stage to a lower stage, so that the steam discharge ports 460 at a plurality of stages are opened in sequence from high to low. When the liquid level of the coolant tank is higher than a predetermined value, since the buoyancy of the cooling medium applied to the sleeves is greater than self-gravity of the sleeves, the sleeves completely cover the steam discharge ports, and a steam-water mixture entering the steam collection pipe is discharged from the top. When the liquid level of the coolant tank is lower than the predetermined value and during lowering process, since the liquid level of the coolant tank is lowered, the buoyancy applied to the sleeves is reduced, and the gravity of the sleeves is greater than the buoyancy applied to the sleeves. Accordingly, at least one sleeve moves downwards in the axial direction of the steam collection pipe, so that at least one steam discharge port is opened, and at least part of the steam-water mixture entering the steam collection pipe is discharged through the steam discharge port. According to the steam collection device provided by the disclosure, the buoyancy of sleeve varies with the liquid level, so that the sleeve moves in the axial direction of the steam collection pipe. Therefore, the steam discharge port is controlled to be automatically opened or closed, a heat discharge capacity of the system under the low liquid level is guaranteed, and the natural system circulation is promoted. In an embodiment of the disclosure, a plurality of limiters 415 sleeve an outer wall of the steam collection pipe 410, and the limiters 415 are distributed in the axial direction of the steam collection pipe 410 to divide the steam collection pipe 410 into a plurality of independent regions in the axial direction; and the sleeves 420 at a plurality of stages are independent of one another and are arranged in the independent regions respectively to correspond to different liquid level heights, so as to respond to the change in the liquid level height of the cooling medium. The limiters 415 define maximum displacement of up-and-down movement of the sleeves and prevent the sleeves from being separated from the steam collection pipe. The limiters 415 in the disclosure include, but are not limited to baffle structures. When a coolant in the coolant tank 30 is at a full liquid level, all the sleeves are positioned at upper limiters under the action of buoyancy. Therefore, the steam discharge ports are in a closed state, so that direct contact between steam at an upper outlet of the steam collection device and the cooling medium in the coolant tank 30 is avoided. When a large quantity of cooling medium in the coolant tank 30 is evaporated because the heat is discharged from the passive containment heat removal system, the liquid level of the cooling medium in the coolant tank is lowered. Accordingly, a sleeve in the steam discharge valve assemblies 480 at an uppermost stage gradually moves downwards firstly owing to buoyancy lowering until it reaches a lower limiter. In such a process, the corresponding steam discharge port is opened, so that the pressure between the inner side and the outer side of the steam collection pipe 410 is maintained substantially in equilibrium. As the liquid level of the cooling medium continues being further lowered, remaining sleeves repeat the action of the sleeve at the uppermost stage in sequence, so that the opened state and the closed state of the steam discharge ports are automatically adjusted in a passive manner. In a first aspect, the occurrence of steam hammer vibration and two-phase flow excitation with destructive risks can be avoided while the adverse effect of the liquid level in the coolant tank 30 on the natural system circulation can be eliminated, natural circulation flow stagnation can be prevented, and the natural circulation flow and the flow stability of the system can be remarkably improved. In order to guarantee that the sleeves move in the axial direction of the steam collection pipe along with a change in buoyancy, a hollow cavity is delimited by each of the sleeves 420 at a plurality of stages, and buoyancy applied to the hollow cavity in the coolant tank 30 is greater than the gravity applied to the sleeves. Also, as shown in Fig. 2, the steam collection device further includes a flow guide hood 430, where the flow guide hood 430 is sleeved on an outside of the sleeves 420 at a plurality of stages. The flow guide hood 430 is concentrically arranged with the steam collection pipe 410 to avoid the impact of the change in the liquid level in the coolant tank on the coolant tank. A liquid discharge port 431 is provided at a bottom of the flow guide hood 430, and a steam-water mixture enters the flow guide hood 430 to increase the liquid level, so that a cooling medium in the flow guide hood 430 is discharged through the liquid discharge port 431. Accordingly, disturbance from the steam-water mixture to the liquid level of the coolant tank is reduced, and the driving stability of natural system circulation is ensured. In addition, a steam-water separation hood 440 is arranged at a top of the steam collection pipe 410, and the steam-water separation hood 440 performs steam-water separation on a steam-water mixture flowing out of an outlet of the steam collection pipe 410. A liquid phase separated enters the flow guide hood 430, so that an excessive impact load from a high-speed fluid at the upper outlet of the steam collection pipe on the coolant tank is avoided, and the entrainment loss of steam flow to the liquid phase is reduced. The steam-water separation hood 440 in the disclosure is of a cambered structure. In order to maintain a predetermined distance between the steam-water separation hood 440 and the flow guide hood 430 and improve a steam-water separation effect, the steam collection device further includes a support column 450, and the support column 450 supports the steam-water separation hood 440. In order to increase a heat transfer coefficient of the system and improve a heat transfer effect, a structure of the heat exchanger is innovatively designed in the disclosure, and thus a plurality of enhanced heat transfer effects are coupled to one another. Specifically, as shown in Fig. 3, the heat exchanger 20 includes a first heat transfer pipe bundle 230 and a second heat transfer pipe bundle 240, and the first heat transfer pipe bundle 230 and the second heat transfer pipe bundle 240 are symmetrically distributed in a mirror image. The heat exchanger 20 further includes a distribution header 210 and a confluence header 220, where the first heat transfer pipe bundle 230 is in communication with the distribution header 210 and the confluence header 220, and the second heat transfer pipe bundle 240 is in communication with the distribution header 210 and the confluence header 220; and the medium enters the first heat transfer pipe bundle 230 and / or the second heat transfer pipe bundle 240 through the distribution header 210 and flows out of the heat exchanger 20 through the confluence header 220. The second heat transfer pipe bundle 240 and the first heat transfer pipe bundle 230 are symmetrically arranged on two axial sides of the distribution header 210 and / or two axial sides of the confluence header 220, a hollow region is delimited by the second heat transfer pipe bundle 240, the first heat transfer pipe bundle 230, the distribution header 210, and the confluence header 220, and the medium accelerates in the hollow region. Non-condensable gas entering an upper portion of the heat transfer pipe bundle flows vertically downwards under the action of gravity, so as to form a fluid acceleration region having a high density in a hollow barrel-shaped region of the heat exchanger. Accordingly, the steam-air mixture can finally scour across a lower pipe section of the heat transfer pipe bundle at a high flow rate, so that the condensation heat transfer outside the pipes of the heat exchanger can be further enhanced. Further, as shown in Fig. 4, the distribution header 210 and the confluence header 220 are horizontally arranged in the heat exchanger. Therefore, steam containing a large amount of non-condensable gas outside the heat exchanger can smoothly enter a heat transfer pipe bundle region to generate the condensation heat exchange. Moreover, openings of the distribution header 210 and the confluence header 220 are arranged on the same side. Therefore, the connection between the heat exchanger and other members can be facilitated while the vortex loss at an inlet / outlet of the heat exchanger can be reduced to a maximum extent, and the heat exchange capacity can be improved. Preferably, the distribution header 210 and the confluence header 220 in the disclosure employ a pipe structure having a sealing head at one end and an inlet / outlet at the other end. In this way, a flow path of the medium in the heat exchanger is in a “II” shape. Therefore, the uniformity of flow distribution between the heat transfer pipes is improved, the flow resistance of the heat exchanger is reduced, and the heat exchange capacity is improved. Further, as shown in Figs. 5 and 3, the first heat transfer pipe bundle 230 and / or the second heat transfer pipe bundle 240 in the disclosure includes a plurality of heat transfer pipe rows 234, where the plurality of heat transfer pipe rows 234 are arranged in parallel. Preferably, 3-5 pipes rows are provided in the embodiment in total. As the steam is condensed continuously, a pressure difference is formed between a heat transfer pipe row 234 closer to the hollow region and a heat transfer pipe row 234 farther away from the hollow region. The pressure difference accelerates the steam flow, so that the heat transfer is effectively enhanced. Also, the heat transfer pipe row 234 includes a plurality of heat transfer pipes 2342, where the plurality of heat transfer pipes 2342 are arranged in an axial direction of the distribution header 210 and / or an axial direction of the confluence header 220. In this way, as shown in Fig. 5, pitches a and b are formed between adjacent heat transfer pipes. In the embodiment, the pitches a and b may be the same or not. The pitch of heat transfer pipes is preferably 2-3 times the diameter of the heat transfer pipes, where a is preferably 2 times the diameter of the heat transfer pipes, and b is preferably 3 times the diameter of the heat transfer pipes. In order to further improve a heat exchange efficiency, the heat exchanger of the disclosure is composed of scalene C-shaped heat transfer pipes. Specifically, as shown in Fig. 6, the heat transfer pipe 2342 includes a first pipe section 2344, a second pipe section 2346, and an intermediate pipe section 2348 connecting the first pipe section 2344 and the second pipe section 2346, where the first pipe section 2344 is in communication with the confluence header 220, and the second pipe section 2346 is in communication with the distribution header 210. Preferably, the first pipe section 2344 has a smaller length than the second pipe section 2346. An included angle between the second pipe section 2346 and the intermediate pipe section 2348 is 60°-80°. In this way, the heat exchanger has an end surface in a trapezoidal structure and is in a polygonal hollow structure in the axial direction. The non-condensable gas entering the first pipe section 2344 and the intermediate pipe section 2348 flows vertically downwards under the action of gravity, so as to form a fluid acceleration region having a high density in the hollow region of the heat exchanger. Therefore, the steam-air mixture can finally scour across the second pipe section 2346 positioned at a lower portion at a high flow rate, so that the condensation heat transfer of the heat exchanger is further enhanced. In addition, as shown in Fig. 3, the heat exchanger 20 in the disclosure further includes support partitions 260, where the support partitions 260 are arranged between the heat transfer pipes 2342 and perpendicular to the intermediate pipe sections 2348 of the heat transfer pipes 2342. In one aspect, the support partition 260 plays a role of supporting the heat transfer pipe bundle to protect the heat transfer pipe against flow excitation. Moreover, the support partition 260 plays a role of guiding and diverting condensed liquid outside the pipe and the non-condensable gas aggregated near a pipe wall. Therefore, a condensed liquid film and a non-condensable gas film are thinned, so that the heat transfer resistance is reduced, and the heat transfer effect is enhanced. Preferably, the heat exchanger in the disclosure includes a plurality of support partitions 260. The support partitions 260 are in an elongated strip shape, and a distance between adjacent support partitions is preferably greater than 0.5 m. In another aspect, as shown in Fig. 1, the containment heat removal system further includes a riser section 50 and a downcomer section 60, where the riser section 50 connects the confluence header 220 and the coolant tank 30, and the downcomer section 60 connects the coolant tank 30 and the distribution header 210. The downcomer section 60, the riser section 50, and the heat exchanger 20 serve as primary flow resistance members of the containment heat removal system. During design, the proportion of the flow resistance of each member should be rationally distributed to avoid an excessive resistance proportion of one or two members. Preferably, the riser section 50 should have a greater diameter than the downcomer section 60. Therefore, the situation that owing to the excessive flow resistance, the loop has an insufficient natural circulation capacity, and thus the heat discharge capacity of the system is reduced can be avoided. In addition, the containment heat removal system further includes isolation valves positioned on the riser section 50 and the downcomer section 60 respectively. Under normal conditions, these valves remain a normally-opened state. When a pipeline or apparatus positioned on an inner side of the containment in the containment heat removal system leaks, the isolation valves are closed to maintain the integrity of a pressure bearing boundary of the containment and prevent radioactive substances in the containment from leaking to an external environment. The composition of the containment heat removal system is described in detail below. The heat exchanger 20 is mounted on a portion, above an operation platform, of an inner wall surface of the containment, and the coolant tank 30 is arranged at a position, higher than the heat exchanger 20, of an outer side of the containment, so as to maintain a sufficient height difference between the heat exchanger 20 and the coolant tank 30. An upper end of the downcomer section 60 is connected with an outlet of the coolant tank 30, and a lower end of the downcomer section 60 is connected with the inlet of the heat exchanger 20. Accordingly, an upper end of the riser section 50 is connected with an inlet of the coolant tank 30, and a lower end of the riser section 50 is connected with the outlet of the heat exchanger 20. The steam collection device 40 is mounted inside the coolant tank 30, and the coolant tank 30 is connected with an outlet of the riser section 50 through a flange positioned at a bottom of the coolant tank 30. The isolation valves on the downcomer section 60 and the riser section 50 are positioned on the outer side of the containment When the containment heat removal system is put into operation, the coolant in the coolant tank 30 flows into a pipe side of the heat exchanger 20 through the downcomer section 60. The steam in the containment is condensed on an outer surface of the heat transfer pipe of the heat exchanger 20. The released latent vaporization heat is transferred to the coolant in the heat transfer pipe, so that the temperature of the coolant is increased continuously in a flow process. A heated cooling medium enters the riser section 50 until it flows back to the coolant tank 30. The flow of the medium fluid in the system only depends on a driving force provided through a density difference between the medium fluid in the downcomer section 60 and the medium fluid in the riser section 50 without an external power input, and thus the medium fluid is in a natural circulation flow state. When a temperature of the cooling medium in the coolant tank is low, the system is in a single-phase natural circulation state and transfers the decay heat in the containment to the coolant tank 30. When a temperature of the cooling medium in the coolant tank 30 is increased to a saturation temperature at a local pressure, the system enters a two-phase natural circulation state, and the steam-water mixture generated is discharged into atmosphere through steam discharge holes on the coolant tank 30, thereby removing passive heat. Based on the results of single experiments completed and a calculation and analysis program verified through experiments, after comparative calculation and analysis are performed on the containment heat removal system under the preferred solution of the disclosure and the prior art, the variation condition of a heat discharge power of a single heat exchanger along with the pressure in the containment is obtained, as shown in Fig. 7, and the variation condition of the pressure in the containment with time under a most egregious hypothetical reactor accident is obtained, as shown in Fig. 8. It can be seen that the heat exchange power of the single heat exchanger of the disclosure is multiplied compared with the heat exchange power of the single heat exchanger in the prior art. According to the system of the disclosure, it is guaranteed that the pressure in the containment after the accident can be reduced to be 1 / 2 of the design pressure (0.52 MPa absolute pressure) or below within 24 hours, and maintains stable for a long time, so that the requirement for coping with design basis accidents is satisfied. However, a system in the prior art can only control a pressure in the containment to fluctuate around 0.35 MPa, thereby only satisfying the demand for coping with beyond design basis accidents. In conclusion, the containment heat removal system according to the embodiment has the technical effects as follows: 1. The steam collection device employed in the containment heat removal system of the disclosure can automatically balance the static pressure difference between the inner side and the outer side of the steam collection pipe in a passive manner while completely eliminating the risks of steam hammer vibration, two-phase flow excitation, and flow stagnation in a steam-liquid two-phase flow phase. Accordingly, the adverse effect of the liquid level of the coolant tank on the natural circulation flow of the passive containment heat removal system can be eliminated. 2. The heat exchanger employed in the containment heat removal system of the disclosure significantly reduces the flow resistance and has a compact structure without increasing a manufacturing difficulty of the heat exchanger. Accordingly, the heat transfer on the inner side and the outer side of the heat transfer pipe is remarkably enhanced, and the heat exchanger becomes an efficient heat exchanger having the small flow resistance and the high heat exchange capacity. 3. In the disclosure, by optimizing the configuration of the containment heat removal system, the flow stability and the natural circulation capacity of the system are significantly enhanced, a heat discharge power level of the passive containment heat removal system is remarkably increased, and thus the system is capable of coping with the design basis accidents. 4. The containment heat removal system of the disclosure is simple in composition, the steam collection device is convenient to assemble and disassemble, and the system is high in stability. Embodiment 2 A containment heat removal system in the embodiment is basically the same as that in Embodiment 1. That is, as shown in Fig. 9, a steam discharge valve assembly 480 is composed of a sleeve 420 and a steam discharge port 460 positioned on an outer wall of a steam collection pipe 410. The difference from Embodiment 1 lies in that as shown in Figs. 10 and 11, an inner diameter of a sleeve at a previous stage of sleeves 420 at a plurality of stages in the embodiment is greater than an outer diameter of a sleeve at a next stage, adjacent sleeves 420 are arranged together in a nested manner, and the sleeve at the previous stage is movable along an outer wall of the sleeve at the next stage. In order to prevent the sleeves 420 at a plurality of stages from being separated from the steam collection pipe 410, the disclosure provides a limiting structure for a steam collection device. Specifically, as shown in Fig. 12, the steam collection device includes a first locating portion 416, where the first locating portion 416 is sleeved on an outside of the steam collection pipe 410, and the first locating portion 416 defines a highest position of the sleeves at a plurality of stages and prevents the sleeves at a plurality of stages from being separated from the steam collection pipe 410 from an upper portion of the steam collection pipe 410. In the disclosure, the first locating portion 416 is positioned at a lower region of the steam collection pipe. Preferably, the first locating portion 416 is welded to an outer side of the steam collection pipe 410, and the first locating portion 416 is of an annular structure. An outer diameter of the first locating portion 416 equals an inner diameter of a sleeve at a first stage. A steam discharge region is defined above the first locating portion 416 in an axial direction of the steam collection pipe 410, and as shown in Fig. 10, a reinforcement ring 411 is arranged on a portion, corresponding to the steam discharge region, of the outer wall of the steam collection pipe 410, so as to enhance stability of the steam collection pipe 410. Also, as shown in Fig. 10, the steam collection device further includes a fourth locating portion 418, where the fourth locating portion 418 is sleeved on an outside of the steam collection pipe 410, and the fourth locating portion 418 defines a lowest position of the sleeves 420 at a plurality of stages and prevents the sleeves 420 at a plurality of stages from being separated from the steam collection pipe 410 from a lower portion of the steam collection pipe 410. In the disclosure, the fourth locating portion 418 is a limiting flange, and the fourth locating portion 418 is positioned at a position, close to an inlet, of a bottom of the steam collection pipe 10 and lower than the first locating portion 416. As shown in Figs. 10 and 12, the first locating portion 416 and the fourth locating portion 418 define a non-steam discharge region in the axial direction of the steam collection pipe 410, and a steam discharge region is defined above the first locating portion 416 in the axial direction of the steam collection pipe 410. Steam discharge ports are provided at a portion, corresponding to the steam discharge region, of the outer wall of the steam collection pipe, instead of a portion, corresponding to the non-steam discharge region, of the outer wall of the steam collection pipe. As shown in Fig. 10, a maximum length of the sleeves 420 at a plurality of stages in the axial direction of the steam collection pipe 410 is not less than a length of the steam discharge region in the axial direction of the steam collection pipe 410. When the coolant tank is in full liquid level, a height of the hollow sleeves at a plurality of stages is not less than that of the steam collection pipe 410. The hollow sleeves at a plurality of stages can completely block all the steam discharge ports 460 in the steam discharge region, so as to expose the non-steam discharge region. Also, a height of the sleeve at the first stage is greater than a length of the non-steam discharge region in the axial direction of the steam collection pipe. When there is no liquid level in the coolant tank, the sleeve at the first stage can completely cover the non-steam discharge region. In addition, in order to prevent the sleeves at a plurality of stages from being separated from one another, in the disclosure, locating portions are arranged on the sleeves at a plurality of stages. Specifically, as shown in Fig. 13, a top of each of the sleeves at a plurality of stages is provided with a second locating portion 422, and second locating portions 422 of adjacent sleeves make contact with each other to prevent the sleeve at a previous stage from being separated from a bottom of the sleeve at a next stage. Preferably, in the disclosure, the second locating portion 422 is of an annual structure, an inner diameter of the second locating portion 422 equals an outer diameter of the steam collection pipe 410, and an outer diameter of the second locating portion 422 equals an inner diameter of the sleeve at a previous stage. Also, a bottom of each of the sleeves at a plurality of stages is provided with a third locating portion 424, and the third locating portion 424 of the sleeve at a previous stage makes contact with a second locating portion 422 of the sleeve at a next stage to prevent the sleeve at a previous stage from being separated from the sleeve at a next stage when the sleeve at a previous stage moves upwards. Preferably, in the disclosure, the third locating portion 424 is of an annual structure, an inner diameter of the third locating portion 424 equals an outer diameter of the sleeve at a next stage, and an outer diameter of the third locating portion 424 equals an outer diameter of a sleeve at a present stage. In the disclosure, the second locating portions 422 and the third locating portions 424 are detachably connected with the sleeves 420 at a plurality of stages. Preferably, the second locating portions 422 and the third locating portions 424 are fixed to the sleeves 420 through rivets, so as to facilitate assembly and disassembly. When buoyancy of the sleeve at a previous stage is greater than self-gravity of the sleeve at the previous stage, the sleeve at the previous stage moves upwards and tries to be separated from the sleeve at a next stage. In this case, the second locating portion of the sleeve at the next stage abuts against the third locating portion of the sleeve at the previous stage, so as to prevent the sleeve at the previous stage from being separated from the sleeve at the next stage from the top of the sleeve at the next stage. A third locating portion of a sleeve at a lowest stage abuts against the first locating portion, so as to prevent the situation that the sleeves at a plurality of stages are separated from the steam collection pipe under the action of buoyancy. When buoyancy of the sleeve at the previous stage is greater than self-gravity of the sleeve at the previous stage, the sleeve at the previous stage moves downwards and tries to be separated from the sleeve at a next stage. In this case, the second locating portion of the sleeve at the next stage abuts against the second locating portion of the sleeve at the previous stage, so as to prevent the sleeve at the previous stage from being separated from the sleeve at the next stage from the bottom of the sleeve at the next stage. The sleeves at a plurality of stages move downwards in sequence from high to low and finally fall above the fourth locating portion. In conclusion, the steam collection device according to the embodiment has the technical effects as follows: 1. The sleeves move in the axial direction of the steam collection pipe along with the change in the liquid level under the action of the buoyancy applied to the cooling medium and the self-gravity of the cooling medium, so as to open or close the steam discharge ports and guarantee the heat discharge capacity of the system under the low liquid level. 2. The sleeves at a plurality of stages are arranged in a nested manner, and a plurality of locating plates are arranged, so that the sleeves at a plurality of stages are prevented from being separated from one another, and the structural stability is guaranteed. 3. The steam collection device of the containment heat removal system according to the disclosure is simple in structure and convenient to assemble, disassemble, and maintain. 4. By structurally optimizing the sleeves at a plurality of stages, the sleeves at a plurality of stages block an entire steam discharge region, so that a height of an ascending section is increased. Accordingly, a length of a two-phase natural circulation section is increased, the driving force of the system is increased, and the heat removal capacity of the system is improved. What are described above are merely the preferred embodiments of the disclosure, but are not intended to limit the disclosure. Those skilled in the art can make various modifications and variations to the disclosure. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the disclosure should fall within the scope of protection of the disclosure.

Claims

1. A containment heat removal system, comprising a heat exchanger (20) arranged inside a containment, a coolant tank (30) arranged outside the containment and a steam collection device (40) arranged in the coolant tank (30), wherein the heat exchanger (20) is in communication with a medium in the coolant tank (30); a medium in the heat exchanger (20) absorbs heat of the containment and is discharged into the coolant tank (30) through the steam collection device (40), and the medium in the coolant tank (30) is returned to the heat exchanger (20);the steam collection device (40) comprises steam discharge valve assemblies (480) corresponding to different liquid level heights of the coolant tank (30), wherein each of the steam discharge valve assemblies (480) is configured such that when a liquid level height is lowered, each of the steam discharge valve assemblies (480) is automatically opened under self-force; and at least part of the medium entering the steam collection device (40) enters the coolant tank (30) through the steam discharge valve assemblies (480), so that a static pressure difference between an inner side and an outer side of the steam collection device (40) is balanced, and a system circulation driving force under a low liquid level height is increased.

2. The containment heat removal system according to claim 1, wherein the steam collection device (40) comprises a steam collection pipe (410) and sleeves at a plurality of stages sleeving the steam collection pipe (410), the sleeves at a plurality of stages are distributed in a direction of the liquid level height, a sleeve at a first stage of the sleeves at a plurality of stages is positioned at a lowest portion, and a stage number is increased in sequence along with an increase in the liquid level height; and each of the sleeves at a plurality of stages is movable in an axial direction of the steam collection pipe (410) along with a change in the liquid level height, and the sleeves at a plurality of stages are configured to move downwards in sequence from a higher stage to a lower stage when the liquid level height is decreased.

3. The containment heat removal system according to claim 2, wherein the steam collection pipe (410) is provided with steam discharge ports (460) at a plurality of stages in a height direction, the steam discharge ports (460) at a plurality of stages are arranged corresponding to the sleeves (420) at a plurality of stages, and the steam discharge ports (460) and the sleeves (420) are combined to form the steam discharge valve assemblies (480); and the sleeves (420) at a plurality of stages move downwards in sequence from a higher stage to a lower stage, so that the steam discharge ports(460) at a plurality of stages are opened in sequence from high to low.

4. The containment heat removal system according to claim 3, wherein a plurality of limiters (415) sleeve an outer wall of the steam collection pipe (410), the limiters (415) are distributed in the axial direction of the steam collection pipe (410) to divide the steam collection pipe (410) into a plurality of independent regions in the axial direction, and the sleeves (420) at a plurality of stages are arranged in the independent regions respectively.

5. The containment heat removal system according to claim 4, wherein the sleeves (420) at a plurality of stages are independent of one another and correspond to different liquid level heights.

6. The containment heat removal system according to claim 2 or 3, wherein a hollow cavity is delimited by each sleeve (420) of the sleeves (420) at a plurality of stages, and a buoyancy applied to the hollow cavity in the coolant tank (30) is greater than a gravity applied to the sleeve (420).

7. The containment heat removal system according to claim 3, wherein an inner diameter of a sleeve at a previous stage of the sleeves (420) at a plurality of stages is greater than an outer diameter of a sleeve at a next stage, adjacent sleeves are arranged together in a nested manner, and the sleeve at the previous stage is movable along an outer wall of the sleeve at the next stage.

8. The containment heat removal system according to claim 2 or 3, comprising a first locating portion (416), wherein the first locating portion (416) is sleeved on an outside of the steam collection pipe (410), and the first locating portion (416) defines a highest position of the sleeves at a plurality of stages and prevents the sleeves at a plurality of stages from being separated from the steam collection pipe (410) from an upper portion of the steam collection pipe (410).

9. The containment heat removal system according to claim 8, wherein a steam discharge region is defined above the first locating portion (416) in the axial direction of the steam collection pipe (410), and a reinforcement ring (411) is arranged on a portion, corresponding to the steam discharge region,of an outer wall of the steam collection pipe (410), so as to enhance stability of the steam collection pipe (410).

10. The containment heat removal system according to claim 9, wherein a maximum length of the sleeves (420) at a plurality of stages in the axial direction of the steam collection pipe (410) is not shorter than a length of the steam discharge region in the axial direction of the steam collection pipe (410), so that the sleeves (420) at a plurality of stages completely cover all the steam discharge ports (460) within a length range of the steam collection pipe (410).

11. The containment heat removal system according to claim 2 or 3, further comprising a fourth locating portion (418), wherein the fourth locating portion (418) is sleeved on an outside of the steam collection pipe (410), and the fourth locating portion (418) defines a lowest position of the sleeves (420) at a plurality of stages and prevents the sleeves (420) at a plurality of stages from being separated from the steam collection pipe (410) from a lower portion of the steam collection pipe (410).

12. The containment heat removal system according to claim 2 or 3, wherein a top of each of the sleeves at a plurality of stages is provided with a second locating portion (422), and second locating portions (422) of adjacent sleeves make contact with each other to prevent a sleeve at a previous stage from being separated from a bottom of a sleeve at a next stage.

13. The containment heat removal system according to claim 12, wherein a bottom of each of the sleeves at a plurality of stages is provided with a third locating portion (424), and the third locating portion (424) of the sleeve at a previous stage makes contact with the second locating portion (422) of the sleeve at a next stage to prevent the sleeve at the previous stage from being separated from the sleeve at the next stage when the sleeve at a previous stage moves upwards.

14. The containment heat removal system according to claim 12, wherein an inner diameter of the second locating portion (422) equals an outer diameter of the steam collection pipe (410), and an outer diameter of the second locating portion (422) equals an inner diameter of the sleeve at aprevious stage.

15. The containment heat removal system according to claim 13, wherein an inner diameter of the third locating portion (424) equals an outer diameter of the sleeve at a next stage, and an outer diameter of the third locating portion (424) equals an outer diameter of a sleeve at a present stage.

16. The containment heat removal system according to claim 9, wherein an outer diameter of the first locating portion (416) equals an inner diameter of the sleeve at the first stage.

17. The containment heat removal system according to claim 2 or 3, further comprising a flow guide hood (430), wherein the flow guide hood (430) is sleeved on an outside of the sleeves (420) at a plurality of stages.

18. The containment heat removal system according to claim 17, wherein a liquid discharge port (431) is provided at a bottom of the flow guide hood (430), and a cooling medium in the flow guide hood (430) is discharged through the liquid discharge port (431), so as to reduce disturbance to a liquid level.

19. The containment heat removal system according to claim 18, wherein a steam-water separation hood (440) is arranged at a top of the steam collection pipe (410), and the steam-water separation hood (440) performs steam-water separation on a steam-water mixture flowing out of an outlet of the steam collection pipe (410).

20. The containment heat removal system according to claim 19, further comprising a support column (450), wherein the support column (450) supports the steam-water separation hood (440), so as to maintain a predetermined distance between the steam-water separation hood (440) and the flow guide hood (430).

21. The containment heat removal system according to claim 1, wherein the heat exchanger (20) comprises a first heat transfer pipe bundle (230) and a second heat transfer pipe bundle (240), and the first heat transfer pipe bundle (230) and the second heat transfer pipe bundle (240) are symmetrically distributed in a mirror image.

22. The containment heat removal system according to claim 21, wherein the heat exchanger (20) further comprises a distribution header (210) and a confluence header (220), wherein the first heat transfer pipe bundle (230) is in communication with the distribution header (210) and the confluence header (220), and the second heat transfer pipe bundle (240) is in communication with the distribution header (210) and the confluence header (220); and the medium enters the first heat transfer pipe bundle (230) and / or the second heat transfer pipe bundle (240) through the distribution header (210) and flows out of the heat exchanger (20) through the confluence header (220).

23. The containment heat removal system according to claim 22, wherein the second heat transfer pipe bundle (240) and the first heat transfer pipe bundle (230) are symmetrically arranged on two axial sides of the distribution header (210) and / or two axial sides of the confluence header (220), a hollow region is delimited by the second heat transfer pipe bundle (240), the first heat transfer pipe bundle (230), the distribution header (210), and the confluence header (220), and the medium accelerates in the hollow region.

24. The containment heat removal system according to claim 23, wherein the distribution header (210) and the confluence header (220) are horizontally arranged, and openings of the distribution header (210) and the confluence header (220) are provided on the same side.

25. The containment heat removal system according to claim 23 or 24, wherein the first heat transfer pipe bundle (230) and / or the second heat transfer pipe bundle (240) comprises a plurality of heat transfer pipe rows (234), the plurality of heat transfer pipe rows (234) are arranged in parallel, and a pressure difference is formed between a heat transfer pipe row (234) closer to the hollow region and a heat transfer pipe row (234) farther away from the hollow region to accelerate medium flow.

26. The containment heat removal system according to claim 24, wherein the heat transfer pipe row (234) comprises a plurality of heat transfer pipes (2342), and the plurality of heat transfer pipes (2342) are arranged in an axial direction of the distribution header (210) and / or an axial direction of the confluence header (220).

27. The containment heat removal system according to claim 26, wherein the heat transfer pipe (2342) comprises a first pipe section (2344), a second pipe section (2346), and an intermediate pipe section (2348) connecting the first pipe section (2344) and the second pipe section (2346), the first pipe section (2344) is in communication with the confluence header (220), and the second pipe section (2346) is in communication with the distribution header (210).

28. The containment heat removal system according to claim 27, wherein the first pipe section (2344) has a smaller length than the second pipe section (2346).

29. The containment heat removal system according to claim 28, wherein an included angle between the second pipe section (2344) and the intermediate pipe section (2348) is 60°-80°.

30. The containment heat removal system according to any one of claims 26-28, wherein a distance between adjacent heat transfer pipes (2342) is 2-3 times a diameter of the heat transfer pipe (2342).

31. The containment heat removal system according to claim 26 or 27, wherein the heat exchanger (20) comprises support partitions (260), the support partitions (260) are arranged between the heat transfer pipes (2342) and perpendicular to the intermediate pipe sections (2348) of the heat transfer pipes (2342).

32. The containment heat removal system according to any one of claims 22-24, further comprising a riser section (50) and a downcomer section (60), wherein the riser section (50) connects the confluence header (220) and the coolant tank (30), and the downcomer section (60) connects the coolant tank (30) and the distribution header (210).INTERNATIONAL SEARCH REPORT International application No. PCT / CN2023 / 081974A. CLASSIFICATION OF SUBJECT MATTER G21C15 / 18(2006.0l)i; G21C15 / 02(2006.01)i According to International Patent Classification (IPC) or to both national classification and IPC B. FIELDS SEARCHED Minimum documentation searched (classification system followed by classification symbols) IPC G21C Documentation searched other than minimum documentation to the extent that such documents are included in the fields searched Electronic data base consulted during the international search (name of data base and, where practicable, search terms used) CNABS; CNTXT; CNKI; VEN; USTXT; EPTXT; WOTXT: ,5(2¾ 'iO, HA 1 M SR, Sf Hi, SR, Rflt, Containment, Nuclear, safety shell, buoyant, gravit+, float+, heat, cool+, vapor+ C. DOCUMENTS CONSIDERED TO BE RELEVANT Category* Citation of document, with indication, where appropriate, of the relevant passages Relevant to claim No. A CN 107210071 A (JOINT-STOCK COMPANY SCIENTIFIC RESEARCH AND DESIGN INSTITUTE FOR ENERGY TECHNOLOGIES ATOMPROEKT) 26 September 2017 (2017-09-26) abstract, description, paragraphs [0007]-[0047], and figure 1 1-32 A A CN 105489258 A (SHANGHAI NUCLEAR ENGINEERING RESEARCH &DESIGN INSTITUTE) 13 April 2016 (2016-04-13) entire document CN 113140335 A (CHINA NUCLEAR POWER ENGINEERING CO., LTD.) 20 July 2021 (2021-07-20) entire document 1-32 1-32 A CN 113593733 A (CHINA NUCLEAR POWER ENGINEERING CO., LTD.) 02 November 2021 (2021-11-02) entire document 1-32 A US 4950448 A (GENERAL ELECTRIC COMPANY) 21 August 1990 (1990-08-21) entire document 1-32 | | Further documents are listed in the continuation of Box C. | J | See patent family annex. * Special categories of cited documents: “T” later document published after the international filing date or priority “A” document defining the general state of the art which is not considered date and not in conflict with the application but cited to understand the to be of particular- relevance principle or theory underlying the invention “D” document cited by the applicant in the international application -‘X” document of particular relevance; the claimed invention cannot be “E" earlier application or patent but published on or after the international considered novel or cannot be considered to involve an inventive step filing date when the document is taken alone “L" document which may throw doubts on priority claim(s) or which is “Y” document of particular relevance; the claimed invention cannot be cited to establish the publication date of another citation or other considered to involve an inventive step when the document is special reason (as specified) combined with one or more other such documents, such combination “O” document referring to an oral disclosure, use, exhibition or other being obvious to a person skilled in the ait means document member of the same patent family “P” document published prior to the international filing date but later than the priority date claimed Date of the actual completion of the international search 10 September 2023 Date of mailing of the international search report 22 September 2023 Name and mailing address of the ISA / CN China National Intellectual Property Administration (ISA / CN) China No. 6, Xitucheng Road, Jimenqiao, Haidian District, Beijing 100088 Authorized officer Telephone No.INTERNATIONAL SEARCH REPORT Information on patent family members International application No. PCT / CN2023 / 081974Patent document cited in search report Publication date (day / month / year) Patent family member) s) Publication date (day / month / year) CN 107210071 A 26 September 2017 None CN 105489258 A 13 April 2016 None CN 113140335 A 20 July 2021 None CN 113593733 A 02 November 2021 None US 4950448 A 21 August 1990 None

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