Passive residual heat removal system and method for nuclear reactor

Abstract

The present invention provides a passive residual heat removal system and method for a nuclear reactor. The system comprises: a reactor system, comprising a hot end and a cold end, wherein the hot end outputs a fluid outwards, and the cold end inputs a fluid inwards; and a residual heat removal system, comprising a multi-stage heat exchanger, wherein every two adjacent stages of heat exchangers are respectively connected by means of an intermediate header. The hot end is connected to an inlet of a first-stage heat exchanger by means of an inlet pipeline; the intermediate header is provided with a side outlet, and the side outlet and an outlet of a last-stage heat exchanger are respectively connected to the cold end by means of outlet pipelines to form a multi-stage heat exchange loop; and the inlet pipeline and each outlet pipeline are respectively provided with an isolating valve. According to the present invention, different requirements for the heat removal capacity of a residual heat removal system under different accidents can be met, the design of the multi-stage heat exchanger avoids an excessively large or small heat removal amount, and adverse effects on a nuclear reactor system due to a false start of a passive residual heat removal system are reduced.

Description

[0003] IInder normal operating conditions, heat from the reactor core of the nuclear reactor is transferred to the steam turbine through a main heat exchanger such as a steam generator to generate power, or is transferred to the heat / steam supply system to generate heat energy or steam. If an accident occurs in a nuclear reactor, the main heat exchanger such as the steam generator is unavailable, and a residual heat removal system must be arranged to remove the residual heat from the reactor core in time to prevent the accident from further deteriorating into a severe accident and causing the harm of a large amoun t of radioacti ve release.

[0004] Traditional second-generation nuclear power plants generally use an active residual heat removal system to remove the residual heat from the reactor core. However, the active system relies on external power and needs to be equipped with support systems such as a component cooling water system. Once the external power or support system is lost, the active residual heat removal system will be unable to perform its functions, resulting in failure to remove the reactor core heat, thereby threatening the safety of the nuclear reactor.

[0005] Passive residual heat removal systems are used in some third-generation nuclear powder plants. The function execution of the passive residual heat removal system does not rely on external power, nor does it require support systems such as the component cooling water system, and instead, it relies on natural physical law's (density difference, natural circulation, heat conduction, etc.) to remove the reactor core heat, which makes the failure probability of the passive residual heat removal system much lower than that of the active residual heat removal system, thereby improving the safety of the nuclear reactor.

[0006] The inventors have found that different accidents (such as loss of coolant accidents (LOCA accidents) and non-LOCA accidents may have different requirements on the heat removal capacity of the passive residual heat removal system. The existing passi ve residual heat removal system cannot reasonably address different accidents. If the heat removing capacity of the residual heat removal system is too small, excessive heat would accumulate in the reactor core, which may cause reactor core melting; and if the heat-removing capacity of the residual heat removal system is too large, the main system of the nuclear reactor would be overcooled and thermal shock may occur, which leads to fatigue of key components and threatening the integrity of the pressure-bearing structure, and may lead to more severe accident consequences if the passive residual heat removal system is mistakenly started. SUMMARY

[0007] In view of the problems existing in the prior art, the present invention provides a passive residual heat removal system and method for a nuclear reactor, which can meet the different requirements for the heat-removing capacity of the residual heat removal system under different accidents while avoiding the heat-removing capacity being too small or too large, and which can reduce the adverse effect on the nuclear reactor system caused by the mistake start-up of the passive residual heat removal system.

[0008] A first aspect of the present invention provides a passive residual heat removal system for a nuclear reactor, including:

[0009] a reactor system comprising a hot end and a cold end, wherein the hot end is configured to output a fluid outwards and the cold end is configured to input a fluid inwards; and

[0010] a residual heat removal system comprising multiple stages of heat exchangers, wherein every two adjacent stages of heat exchangers are connected by means of an intermediate header,

[0011] wherein the hot end is connected to an inlet of a first-stage heat exchanger by means of an inlet pipeline, the intermediate header is provided with a side outlet, and the side outlet and an outlet of a last-stage heat exchanger are respectively connected to the cold end by means of outlet pipelines to form a multi-stage heat exchanger loop; and isolating valves are provided on the inlet pipeline and each outlet pipeline respectively.

[0012] In some embodiments of the present invention, the heat exchanger includes multiple groups of basic heat exchange modules, and the basic heat exchange module is composed of a heat exchange tube bundle and end tube plates arranged at both ends of the heat exchange tube bundle, the heat exchange tube bundle includes a plurality of heat exchange tubes arranged in a predetermined sequence, and the end tube plates have through holes corresponding to the heat exchange tubes.

[0013] In some embodiments of the present invention, the multiple groups of basic heat exchange modules of the heat exchanger are connected in parallel and / or in series.

[0014] In some embodiments of the present invention, the inlet pipeline is connected to the heat exchanger by means of an inlet header, and the inlet header is provided with a plurality of outlet tubes which are respectively connected to the multiple groups of basic heat exchange modules connected in parallel of the heat exchangers.

[0015] In some embodiments of the present invention, the outlet pipeline is connected to the heat exchanger by means of an outlet header, and the outlet header is provided with a plurality of inlet tubes which are respectively connected to the multiple groups of basic heat exchange modules connected in parallel of the heat exchangers.

[0016] In some embodiments of the present invention, the heat exchange tubes of the heat exchange tube bundle are straight tubes or bent tubes.

[0017] In some embodiments of the present invention, the residual heat removal system further includes a heat sink water tank in which the multiple stages of heat exchangers are arranged stage by stage from top to bottom.

[0018] In some embodiments of the present invention, the heat sink water tank is a water tank with a certain amount of water or a natural cooling water source, and a height of a water surface of the heat sink water tank is higher than that of the first-stage heat exchanger.

[0019] In some embodiments of the present invention, the reactor system and the residual heat removal system are arranged in a containment, a backflow collection tank is provided above the heat sink water tank, and the backflow collection tank is connected to the containment and connected to the heat sink water tank through a backflow7 pipeline.

[0020] A second aspect of the present invention provides a passive residual heat removal method for a nuclear reactor, including steps of:

[0021] disposing multiple stages of heat exchangers, wherein every two adjacent stages of heat exchangers are connected by means of an intermediate header, and the intermediate header is provided with a side outlet;

[0022] connecting a hot end of a reactor system to an inlet of a first-stage heat exchanger by means of an inlet pipeline;

[0023] connecting the side outlet and an outlet of a last-stage heat exchanger to a cold end of the reactor system by means of outlet pipelines respectively to form a multi-stage heat exchange loop;

[0024] disposing isolating valves on the inlet pipeline and each outlet pipeline respectively;

[0025] when the reactor system is operating normally, enabling the isolating valve on the inlet pipeline to be in an opened state, and enabling the isolating valve on each outlet pipeline to be in a closed state; and

[0026] when an accident occurs, opening the isolating valve on each outlet pipeline to form a connected fluid circulation loop, wherein heat generated by the reactor system is carried by a fluid flowing through the inlet pipeline from the hot end for heat exchange by the multiple stages of heat exchangers, and the fluid that has transferred the heat returns to the cold end of the reactor system through the outlet pipeline, thereby forming circulation.

[0027] The technical solutions of the present invention has the following beneficial effects:

[0028] The pass!ve residual heat removal system for a nuclear reactor of the present invention adopts a passive safety design concept, does not rely on external power (such as a power supply, a steam source, etc.), and does not require support systems (such as the component cooling water system, a power supply, etc.); and the failure probability of the system is extremely low, which improves the safety of the nuclear reactor. The system relies on natural physical laws (density differences, natural circulation, etc.), so that a fluid is driven to form a natural circulation in the reactor system and a passive residual heat removal system, thereby removing the residual heat from the reactor core.

[0029] The passive residual heat removal system for a nuclear reactor of the present invention can meet the different requirements for the heat-removing capacity of the residual heat removal system under different accidents. By designing the multiple stages of heat exchangers, the heat-removing capacity is prevented from being too large or too small, and the adverse effect on the nuclear reactor system caused by the mistake start-up of the passive residual heat removal system is reduced.

[0030] In the present invention, the heat exchanger of the passive residual heat removal system can be expanded according to the requirements of nuclear reactors with different power levels, can be designed in a modular manner, and can be installed in a flexible manner. The system can address the requirements for reactor core residual heat removal in different accidents, and has characteristics of strong scalability, flexible installation, and suitability for nuclear reactors with different power levels.

[0031] It should be understood that the above general description and the following detailed description are exemplary only and do not limit the present application. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] In order to illustrate the technical solutions of the embodiments of the present application more clearly, the accompanying drawings to be used in the embodiments of the present application will be briefly introduced below. Apparently, the accompanying drawings described below are only the specific embodiments of the present application, and those skilled in the art can obtain other embodiments according to the following accompanying drawings without making creative efforts.

[0033] FIG. 1 is a schematic structural diagram of a passive residual heat removal system for a reactor according to a specific embodiment of the present invention;

[0034] FIG. 2 is a schematic diagram of a basic heat exchange module according to a specific embodiment of the present invention;

[0035] FIG. 3 is a schematic diagram of a basic heat exchange module according to another specific embodiment of the present invention;

[0036] FIG. 4 is a schematic arrangement diagram of a heat exchange tube bundle according to a specific embodiment of the present invention,

[0037] FIG. 5 is a schematic arrangement diagram of a heat exchange tube bundle according to another specific embodiment of the present invention;

[0038] FIG. 6 is a schematic diagram of an end tube plate according to a specific embodiment of the present invention;

[0039] FIG. 7 is a schematic diagram of an end tube plate according to another specific embodiment of the present invention;

[0040] FIG. 8 is a schematic diagram of basic heat exchange modules connected in series according to a specific embodiment of the present invention;

[0041] FIG. 9 is a schematic diagram of basic heat exchange modules connected in parallel according to a specific embodiment of the present invention;

[0042] FIG. 10 is a schematic diagram of a basic heat exchange module and a bent pipe type basic heat exchange module that are connected in series according to a specific embodiment of the present invention;

[0043] FIG. II is a schematic diagram of a parallel connection of series connections of basic heat exchange modules and bent pipe type basic heat exchange modules according to a specific embodiment of the present, invention;

[0044] FIG. 12 is a schematic diagram of the parallel arrangement of end tube plates of multiple groups of basic heat exchange modules according to a specific embodiment of the present invention;

[0045] FIG. 13 is a schematic structural diagram of an inlet header of a heat exchanger according to a specific embodiment of the present invention;

[0046] FIG. 14 is a schematic diagram of an intermediate header of a heat exchanger according to a specific embodiment of the present invention; and

[0047] FIG. 15 is a schematic structural diagram of a passive residual heat removal system for a reactor according to another specific embodiment of the present invention.

[0048] Reference numbers: 10-Reactor system; 1001-Hot end; 1002-Cold end; 70-Residual heat removal system; 1 -Inlet isolating valve; 2-First outlet isolating valve; 3-Second outlet isolating valve; 11 -Inlet pipeline; 12-Inlet header; 121-Inlet ellipsoid head; 123-Outlet ellipsoid head; 122-Cylindrical barrel; 125-Inlet; 124-Outlet tube, 21-First outlet pipeline; 22-First outlet header; 23-Intermediate header; 140-Main connecting tube; 150-Side outlet; 111-Tube flange; 31-Second outlet pipeline; 32~Second outlet header, 33-Second intermediate header, 20-First-stage heat exchanger; 100-Basic heat exchange module; 110-End tube plate; 101-Metal round tube; 102-Flange bolt hole; 104-Hexagonal flange, 105-Round flange; 120-Heat exchange straight tube bundle; 200- Bent tube type basic heat exchange module; 130-Heat exchange bent tube bundle, 30-Second-stage heat exchanger; 40-Third-stage heat exchanger; 42-Third outlet header; 50-Heat sink water tank; 51-Backflow collection tank; 52-Backflow pipeline; 60-Containment.

[0049] The accompanying drawings, which are incorporated in and constitute a part of Description, illustrate embodiments consistent with the present application and together with Description serve to explain the principles of the present application. DETAILED DESCRIPTION

[0050] In order to better understand the technical solutions of the present application, the embodiments of the present application will be described in detail below in conjunction with the accompanying drawings.

[0051] It should be understood that the described embodiments are only some of the embodiments of the present application, rather than all of them. Based on the embodiments in this application, all other embodiments obtained by those skilled in the art without creative efforts fall within the protection scope of this application.

[0052] The existing passive residual heat removal system cannot reasonably address different accidents. If the heat-removing capacity of the residual heat removal system is too small, excessive heat would accumulate in the reactor core, which may cause the reactor core to melt; and if the heat-removing capacity of the residual heat removal system is too large, the main system of the nuclear reactor would be overcooled and thermal shock may occur, which leads to the fatigue of key components and threatens the integrity of the pressure-bearing structure, and which may further bring more severe accident consequences when the passive residual heat removal system is mistakenly started.

[0053] In order to meet the different requirements for the heat-removing capacity of the residual heat removal system under different accidents, avoid the heat-removing capacity being too large or too small, and reduce the adverse effect on the nuclear reactor system caused by the mistake start-up of the passive residual heat removal system, the present invention provides a passive residual heat removal system for a nuclear reactor.

[0054] FIG. lisa schematic structural diagram of a passive residual heat removal system for a reactor according to a specific embodiment of the present invention.

[0055] As shown in FIG. 1, the passive residual heat removal system for a nuclear reactor of the present invention includes a reactor system 10 and a residual heat removal system 70, both of which are installed in a containment 60. The reactor system 10 may be a primary side system or a secondary side system of the nuclear reactor, such as a steam generator. When an accident occurs, the main heat exchangers such as the steam generator are unavailable, and the heat in the reactor core cannot be transferred outwards through the main heat exchangers such as the steam generator. In order to prevent the accident from further deteriorating into a severe accident, a trigger signal (representing situations such as high temperature at the outlet of the reactor core, low water level in the steam generator, low pressure in the pressurizer, etc.) for the residual heat removal system 70 may be used to start the residual heat removal system 70 to bring out the heat in the reactor system 10.

[0056] The reactor system 10 includes a hot end 1001 and a cold end 1002. The hot end 1001 outputs a fluid outwards, and the cold end 1002 inputs a fluid inwards. In the present invention, the fluid flows out from the hot end 1001 to the residual heat removal system 70, and the heat-exchanged fluid flows back into the reactor system 10 from the cold end 1002. The hot end 1001 may be a primary side hot tube section or a secondary side outlet of the nuclear reactor; and the cold end 1002 may be a primary side cold tube section or a secondary side inlet of the nuclear reactor.

[0057] The residual heat removal system 70 includes multiple stages of heat exchangers, and every two adjacent stages of heat exchangers are connected through an intermediate header 23. The embodiment shown in FIG. 1 is described in detail by taking two stages of heat exchangers (a first-stage heat exchanger 20 and a second-stage heat exchanger 30) as an example. Of course, the present invention is not limited to two stages of heat exchangers, and the number of heat exchangers may be set according to actual usage requirements.

[0058] The hot end 1001 is connected to an inlet of the first-stage heat exchanger 20 through an inlet pipeline 11, the intermediate header 23 is provided with a side outlet 150 (see FIG. 14), and the side outlet 150 and an outlet of a last-stage heat exchanger are respectively connected to the cold end 1002 through the outlet pipeline to form a multi-stage heat exchange loop. The laststage heat exchanger in FIG. 1 is the second-stage heat exchanger 30. The side outlet 150 of the intermediate header 23 is connected to the cold end 1002 through a first outlet pipeline 21, and the outlet of the second-stage heat exchanger 30 is connected to the cold end 1002 through a second outlet pipeline 31.

[0059] Isolating valves are provided on the inlet pipeline 11 and each outlet pipeline respectively. In FIG. 1, an inlet isolating valve 1 is provided on the inlet pipeline 11, a first outlet isolating valve 2 is provided on the first outlet pipeline 21, and a second outlet isolating valve 2 is provided on the second outlet pipeline 31.

[0060] During normal operation of the nuclear reactor, the inlet isolating valve 1 on the inlet pipeline 11 is in an open state, and the first outlet isolating valve 2 and the second outlet isolating valve 3 are in a closed state. The inlet isolating valve 1 is opened so that before it is put into operation, the fluid temperature in the inlet pipeline 11 is already higher than fluid temperatures in the first outlet pipeline 21 and the second outlet pipeline 31, which is conducive to strengthening the initial natural circulation when the passive residual heat removal system 70 is put into operation. The inlet isolating valve 1 is opened, while the first outlet isolating valve 2 and the second outlet isolating valve 3 are closed, so that when the passive residual heat removal system 70 is put into operation, the operation only needs ensuring that the first outlet isolating valve 2 and the second outlet isolating valve 3 can be opened, instead of opening all isolating valves, thereby eliminating the risk of operational failure of the passive residual heat removal system 70 caused by the failure of the inlet isolating valve 1. When the inlet isolating valve 1 is opened, while the first outlet isolating valve 2 and the second outlet isolating valve 3 are closed, the fluid from the inlet isolating valve 1 is blocked in the mainstream direction, and no large-scale fluid will flow in. However, if the inlet isolating valve 1, the first outlet isolating valve 2 and the second outlet isolating valve 3 are all closed, the fluid in the heat exchange tube bundles of the first-stage heat exchanger 20 and the second-stage heat exchanger 30 of the passive residual heat removal system 70 will be in a water body sealing state. Due to the existence of heat conduction and heat leakage, after the fluid in the heat exchange tube bundles of the first-stage heat exchanger 20 and the second-stage heat exchanger 30 of the passive residual heat removal system 70 are heated and expanded in the water body sealing state, the heat conduction and heat leakage may threaten the structural boundary formed by the isolating valves and the heat exchange tube bundles of the first-stage heat exchanger 20 and the second-stage heat exchanger 30, which may lead to, for example, the leakage of the isolating valves. Therefore, even if the inlet isolating valve 1 is in an open state, since the first outlet isolating valve 2 and the second outlet isolating valve 3 are in a closed state, the fluid from the inlet isolating valve 1 is blocked in the mainstream direction, no large-scale fluid will flow in, and the heat leakage of a small amount of fluid entering the heat exchange tube bundles of the first-stage heat exchanger 20 and the second-stage heat exchanger 30 through convection or secondary flow are acceptable.

[0061] On the other hand, during normal operation of the nuclear reactor, when the inlet isolating valve 1 of the passive residual heat removal system 70 is mistakenly opened due to operating errors or system abnormalities, it will also cause the fluid of the reactor system 10 to enter the first-stage heat exchanger 20 to remove the heat energy from the reactor system 10, which in turn causes unexpected temperature and pressure drops of the reactor system 10; however, since the heat exchange capacity of the first-stage heat exchanger 20 is relatively small, the adverse effect on the reactor system 10 is relatively small.

[0062] When an accident occurs, the main heat exchanger such as the steam generator is unavailable, and the heat in the reactor core cannot be transferred outwards through the main heat exchanger such as the steam generator. In order to prevent the accident from further deteriorating into a severe accident, trigger signals (representing high temperature at the outlet of the reactor core, low water level in the steam generator, low pressure in the pressurizer, etc.) for the passive residual heat removal system 70 may be used to start the passive residual heat removal system 70 to open the first outlet isolating valve 2 and the second outlet isolating valve 3 in the middle of the passive residual heat removal system 70, so that a connected fluid circulation loop is formed between the reactor system 10 and each stage of heat exchanger.

[0063] The heat generated in the reactor system 10 is carried by the fluid, the fluid sequentially enters respective stages of heat exchangers (the first-stage heat exchanger 20 and the second-stage heat exchanger 30) through the inlet pipeline 11, the heat of the fluid is transferred to the outside by the heat exchangers, and the fluid then passes through the first outlet pipeline 21 and the second outlet pipeline 31, and returns to the reactor system 10. During the entire process, the fluid forms a natural circulation loop under the drive of the density difference between the fluid in the reactor system 10 and the fluid in each stage of heat exchangers.

[0064] FIG 2 is a schematic diagram of a basic heat exchange module according to a specific embodiment of the present invention.

[0065] As shown in FIG. 2, in some embodiments of the present invention, the heat exchangers (the first-stage heat exchanger 20 and the second-stage heat exchanger 30) include multiple groups of basic heat exchange modules 100. The basic heat exchange module 100 is composed of a heat exchange tube bundle and end tube plates 110 arranged at both ends of the heat exchange tube bundle.

[0066] FIG. 3 is a schematic diagram of a basic heat exchange module according to another specific embodiment of the present invention.

[0067] In some specific embodiments, the heat exchange tubes of the heat exchange tube bundle are straight tubes or bent tubes. The heat exchange tube bundle of the basic heat exchange module 100 in FIG. 2 is the heat exchange straight tube bundle 120, and its heat exchange tubes are straight tubes; and the heat exchange tube bundle of the of bent pipe type basic heat exchange module 200 shown in FIG. 3 is the heat exchange tube bundle of bent tubes, and its heat exchange tubes are bent tubes. The first-stage heat exchanger 20 and the second-stage heat exchanger 30 may include multiple groups of basic heat exchange modules 100, or may include multiple groups of bent pipe type basic heat exchange modules 200, or may include a combination of the basic heat exchange module 100 and the bent pipe type basic heat exchange module 200.

[0068] The heat exchange tubes of both the heat exchange straight tube bundle 120 and the heat exchange bent tube bundle 130 are metal round tubes 101 with a certain thickness (see FIG. 4 and FIG. 5) arranged in parallel. The inner diameter of the round tubes is between 5 mm and 25 mm, and the thickness of the tube wall is between 0.5 mm and 5 mm, or the specifications complying with national standards are adopted; the length of the metal round tube 101 may be customized according to needs, and the material of the metal round tube 101 may be stainless steel, titanium alloy, aluminum alloy, etc. The form of the metal round tube 101 is a straight tube for the basic heat exchange module 100, and is a round tube with a 90-degree bending part in the middle of the tube for the bent pipe type basic heat exchange module 200. Each type of basic heat exchange module only uses one form of round tubes, that is, round tubes that are all straight tubes or round tubes that all include the 90-degree bending part. The number of metal round tubes 101 constituting the heat exchange straight tube bundle 120 and the heat exchange bent tube bundle 130 may be customized as required.

[0069] FIG. 4 is a schematic arrangement diagram of the heat exchange tube bundle according to a specific embodiment of the present invention; FIG. 5 is a schematic arrangement diagram of the heat exchange tube bundle according to another specific embodiment of the present invention; FIG. 6 is a schematic diagram of the end tube plate according to a specific embodiment of the present invention; and FIG. 7 is a schematic diagram of the end tube plate according to another specific embodiment of the present invention.

[0070] As shown in FIGS. 4 to 7, the heat exchange straight tube bundle 120 and the heat exchange bent tube bundle 130 include a plurality of heat exchange tubes arranged in a predetermined sequence, and the end tube plate 110 is provided with through holes corresponding to the heat exchange tubes.

[0071] The metal round tubes 101 of the heat exchange straight tube bundle 120 and the heat exchange bent tube bundle 130 may be arranged in crossed rows or in straight rows. FIG. 4 shows a schematic diagram of the heat exchange tube bundle arranged in straight rows, which means that the center points of respective metal round tubes 101 form straight lines in both the X-axis direction and the Y-axis direction. FIG. 5 shows a schematic diagram of the heat exchange tube bundle arranged in crossed rows, which means that the metal round tubes 101 are arranged in a straight line in the X-axis direction, and are staggered in the Y-axis direction.

[0072] The center distance between adjacent metal round tubes 101 is 1.1 to 2 times the outer diameter of the metal round tubes 101; and the center distance between adjacent metal round tubes 101 remains unchanged in the length direction.

[0073] The two end tube plates 110 of the basic heat exchange module 100 are respectively connected to the two ends of the heat exchange straight tube bundle 120 by welding. The two end tube plates 110 of the bent pipe type basic heat exchange module 200 are respectively connected to the two ends of the heat exchange bent tube bundle 130 by welding.

[0074] As shown in FIGS. 6 and 7, each end tube plate 110 has openings 103 with the number and size corresponding to those of the metal round tubes 101. The two ends of each metal round tube 101 are connected respectively to the openings of the two end tube plates 110, and each end tube plate 110 is also provided with flange bolt holes 102 for connecting the two end tube plates 110 through bolts.

[0075] The end tube plate 110 shown in FIG. 6 may be provided with a round flange 105, which follows national standard specifications to reduce manufacturing costs. FIG. 6 exemplarily shows the arrangement manner of the metal round tubes 101 in straight rows. Of course, when the round flange 105 is provided, the arrangement manner of the metal round tubes 101 may also be in crossed rows, which is not limited specifically. The end tube plate 110 shown in FIG. 7 may otherwise be provided with a hexagonal flange 104. FIG. 7 exemplarily shows the arrangement manner of the metal round tube 101 in crossed rows. Of course, when the hexagonal flange 104 is provided, the arrangement manner of the metal round tube 101 may be in straight rows, which is not limited specifically.

[0076] FIG. 8 is a schematic diagram of basic heat exchange modules connected in series according to a specific embodiment of the present invention; FIG. 9 is a schematic diagram of basic heat exchange modules connected in parallel according to a specific embodiment of the present invention; FIG. 10 is a schematic diagram of a basic heat exchange module and a bent pipe type basic heat exchange module connected in series according to a specific embodiment of the present invention; and FIG. 11 is a schematic diagram of a parallel connection of series connections of basic heat exchange modules and bent pipe type basic heat exchange modules according to a specific embodiment of the present invention.

[0077] As shown in FIGS. 8 to 11, in some embodiments of the present invention, multiple groups of basic heat exchange modules of the heat exchanger are connected in parallel and / or in series.

[0078] According to the requirements of installation / maintenance convenience, the first-stage heat exchanger 20 and the second-stage heat exchanger 30 may be configured in different combination of basic heat exchange modules, including but not limited to the series connection of multiple groups of straight tube type basic heat exchange modules 100, the parallel connection of multiple groups of straight tube type basic heat exchange modules 100, the series connection of the straight tube type basic heat exchange module 100 and the bent pipe type basic heat exchange module 200, and the parallel connection of multiple groups of series connections of the straight tube type basic heat exchange modules 100 and the bent pipe type basic heat exchange modules 200, etc.

[0079] The series connection manner of the basic heat exchange modules in FIG. 8 is to connect the two basic heat exchange modules 100 into one body, so that the fluid flows in from the inlet of the first basic heat exchange module 100, enters the second basic heat exchange module 100, and flows out from the outlet of the second basic heat exchange module 100 (the direction indicated by the arrow in FIG. 8).

[0080] The parallel connection manner of the basic heat exchange modules in FIG. 9 is to place two basic heat exchange modules 100 side by side, and divide the inlet pipeline into two pipelines to be connected with the two basic heat exchange modules 100 respectively, so that the fluids enter the two basic heat exchange modules 100 respectively, flow out from respective outlets of the two basic heat exchange modules 100 and then merge into one outlet pipeline (the direction indicated by the arrow in FIG. 9).

[0081] In FIG. 10, the basic heat exchange module 100 and the bent pipe type basic heat exchange module 200 are connected in series into one body, so that the fluid flows in from the inlet of the bent pipe type basic heat exchange module 200, enters the basic heat exchange module 100, and flows out from the outlet of the basic heat exchange module 100 (the direction indicated by the arrow in FIG. 10). Of course, depending on the arrangement manner of the pipelines, the fluid may flow in from the inlet of the basic heat exchange module 100, enter the bent pipe type basic heat exchange module 200, and flow out from the outlet of the bent pipe type basic heat exchange module 200.

[0082] FIG. 11 shows that two groups of a basic heat exchange module 100 and a bent pipe type basic heat exchange module 200, which are connected in series into one body as shown in FIG. 10, are connected in parallel. The fluids enter the two groups of the basic heat exchange module 100 and the bent pipe type basic heat exchange module 200 which are connected in series, then flow out from the respective outlets, and then merge into one outlet pipeline (the direction indicated by the arrow in FIG. 11).

[0083] FIG. 12 is a schematic diagram of the parallel arrangement of end tube plates of multiple groups of basic heat exchange modules according to a specific embodiment of the present invention.

[0084] As shown in FIG. 12, after multiple groups of basic heat exchange modules 100 or bent pipe type basic heat exchange modules 200 are connected in parallel, multiple groups of end tube plates 110 are arranged in parallel. FIG. 12 shows seven hexagonal flanges 104, one of which is located at the center, and the other six hexagonal flanges 104 are respectively close to six sides of the hexagonal flange 104 at the center. Such parallel arrangement may make the heat exchange straight tube bundle 120 or the heat exchange bent tube bundle 130 form a closer arrangement, thereby fully reducing the space required for installation. The basic heat exchange module 100 and the bent pipe type basic heat exchange module 200 may be modularly prefabricated in a manufacturing factory and then transported to the nuclear reactor site for assembly, which facilitates construction and installation.

[0085] FIG. 13 is a schematic structural diagram of the inlet header of the heat exchanger according to a specific embodiment of the present invention.

[0086] Please refer to FIGS. 1 and 13, in some embodiments of the present invention, the inlet pipeline 11 is connected to the heat exchanger through the inlet header 12, the inlet header 12 is provided with a plurality of outlet tubes 124, and the plurality of outlet tubes 124 are respectively connected to multiple groups of basic heat exchange modules 100 connected in parallel of the heat exchanger.

[0087] Please continue to refer to FIG. 13, the inlet header 12 is composed of an inlet ellipsoid head 121, an outlet ellipsoid head 123, a cylindrical barrel 122, an inlet 125 and an outlet tube 124. The diameter of the cylindrical barrel 122 is not smaller than the diameter of the inlet pipeline 11. The inlet ellipsoid head 121 is connected to the inlet pipeline 11 through the inlet 125, and the outlet ellipsoid head 123 is connected to the inlet of the first-stage heat exchanger 20 through the outlet tube 124. When the first-stage heat exchanger 20 is composed of multiple groups of basic heat exchange modules 100 connected in parallel, the outlet ellipsoid head 123 may be connected with a plurality of outlet tubes 124 that are symmetrical along the center axis of outlet ellipsoid head 123, and the outlet tubes 124 correspond to the parallel-connected basic heat exchange modules 100 one to one.

[0088] In some embodiments of the present invention, the second outlet pipeline 31 and the second-stage heat exchanger 30 are connected through the second outlet header 32. The second outlet header 32 is provided with a plurality of inlet tubes, and the plurality of inlet tubes are respectively connected to multiple groups of basic heat exchange modules 100 connected in parallel of the second-stage heat exchanger 30.

[0089] The first outlet pipeline 21 and the intermediate header 23 are connected through the first outlet header 22, and the inlet tube of the first outlet header 22 is connected to the side outlet 150 of the intermediate header 23.

[0090] In some embodiments, the inlet header 12, the first outlet header 22, and the second outlet header 32 have the same structure, and the diameter of the cylindrical barrel 122 is not smaller than that of the inlet pipeline 11, the first outlet pipeline 21, or the second outlet pipeline 31. The inlet tubes of the first outlet header 22 and the second outlet header 32 are the outlet tubes 124 of the inlet header 12.

[0091] FIG. 14 is a schematic diagram of the intermediate header of the heat exchanger according to a specific embodiment of the present invention.

[0092] As shown in FIG. 14, the intermediate header 23 includes a main connecting tube 140 and a side outlet 150. The side outlet 150 is provided on the side of the main connecting tube 140, and the top and bottom of the main connecting tube 140 are provided with end tube plates 110, which match the end tube plate 110 of the basic heat exchange modules 100 of the first-stage heat exchanger 20 and the second-stage heat exchanger 30 and are connected and fixed with the latter by bolts through the flange bolt holes 102. A tube flange 111 is installed on the side outlet 150. The main connecting tube 140 is in the form of a straight round tube, and its inner diameter is not less than the diameter of the largest circumscribed circle of the tube bundle hole region of the end tube plates 110 to ensure that all the fluids in the tube bundle connected to the end tube plate 110 can enter the main connecting tube 140; the length of the main connecting tube 140 is no longer than the length of one group of basic heat exchange modules 100; and two ends of the main connecting tube 140 are connected to two end tube plates 110 respectively. The side outlet 150 is in the form of a round tube, and the inner diameter thereof is no larger than that of the main connecting tube 140; the side outlet 150 may be composed of multiple bent sections and straight pipe sections, and its length and extending direction are determined based on installation needs, so that the intermediate header 23 can be connected to the inlet of the first outlet header 22; and one end of the side outlet 150 is connected to the side of the middle of the main connecting tube 140, and the other end thereof is connected to the tube flange 111.

[0093] Please continue to refer to FIG. 1, in some embodiments of the present invention, the residual heat removal system 70 further includes a heat sink water tank 50. Respective heat exchangers are arranged in the heat sink water tank 50 stage by stage from top to bottom. For example, in the embodiment in FIG. 1, the first-stage heat exchanger 20 is located above the second-stage heat exchanger 30.

[0094] In some embodiments of the present invention, the hot sink water tank 50 is a water tank with a certain amount of water, or may be a natural cooling water source such as rivers, lakes, seas, etc., and the height of the water surface of the hot sink water tank 50 is higher than that of the first-stage heat exchanger 20 and that of the second-stage heat exchanger 30.

[0095] In some embodiments of the present invention, the reactor system 10 and the residual heat removal system 70 are arranged in a containment 60. A backflow collection tank 51 is provided above the heat sink water tank 50, connected to the containment 60, and connected to the hot sink water tank 50 through a backflow pipeline 52. The hot sink water tank 50 is used together with the containment 60, the backflow collection tank 51, and the backflow pipeline 52. One end of the backflow pipeline 52 is connected to the bottom of the backflow collection tank 51, and the other end thereof is located above the hot sink water tank 50.

[0096] The first-stage heat exchanger 20, the intermediate header 23, and the second-stage heat exchanger 30 are fixedly installed in the hot sink water tank 50, and both the central elevations of the first-stage heat exchanger 20 and the second-stage heat exchanger 30 are higher than the central elevation of the hot end 1001 of the reactor system 10. According to different application scenarios, when the reactor system 10 is the primary side system of the nuclear reactor, the hot end 1001 of the reactor system 10 is the reactor core; and when the reactor system 10 is the secondary side system of the nuclear reactor, the hot end 1001 of the reactor system 10 is the heat exchange tube bundles of the heat exchangers of the primary and secondary sides.

[0097] The heat generated in the reactor system 10 is carried by a fluid, and the fluid sequentially enters respective stages of heat exchangers (the first-stage heat exchanger 20 and the second-stage heat exchanger 30) through the inlet pipeline 11, and heat is transferred by the heat exchangers to the hot sink water tank 50. The fluid returns to the reactor system 10 after flowing through the first outlet pipeline 21 and the second outlet pipeline 31. During the entire process, the fluid forms natural circulation under the drive of the density difference between the fluid in the reactor system 10 and the fluids in respective stages of heat exchangers.

[0098] The water in the hot sink water tank 50 is continuously heated until it is saturated and evaporated. The generated steam is cooled by the inner wall surface of the containment 60 and condensed into water; and the water is collected by the backflow collection tank 51 and returned to the hot sink water tank 50 through the backflow pipeline 52, thereby achieving long term circulation. The heat on the inner wall surface of the containment 60 is brought to the outer wall surface through heat conduction, and is finally discharged into the atmospheric environment through convection heat transfer or other manners. During an accident, with the continuous heat removal of the system and the decrease of the decay heat of the reactor core, the system's heat removal capacity finally matches the decay heat of the reactor core, and more severe accident conditions are no longer possible in the power plant.

[0099] Under certain accident conditions (such as LOCA accident) or at different stages of the accident, if more residual heat removal capacity is needed, the number of outlet isolating valves to be opened may be increased according to a trigger signal (representing low pressure of the pressurizer, for example). In this way, the fluid flowing from the reactor system 10 enters the multiple stages of heat exchangers to transfer heat to the heat sink water tank 50, which results in a lower enthalpy of the fluid returning to the reactor system 10. In this entire process, the fluid also forms natural circulation under the drive of density differences.

[0100] FIG. 15 is a schematic structural diagram of a passive residual heat removal system for a reactor according to another specific embodiment of the present invention.

[0101] According to different accidents to be dealt with by different nuclear reactors, more stages of heat exchangers may be added on the basis of the first-stage heat exchanger 20 and the second-stage heat exchanger 30. As shown in FIG. 7, a third-stage heat exchanger 40 may be provided, and a second intermediate header 33 is provided between the second-stage heat exchanger 30 and the third-stage heat exchanger 40. Specifically, the outlet of the second-stage heat exchanger 30 is connected to the inlet of the second intermediate header 33; the outlet of the second intermediate header 33 is connected to the inlet of the third-stage heat exchanger 40; the outlet of the second intermediate header 33 is connected to the inlet of the second outlet header 32; and the outlet of the third-stage heat exchanger 40 is connected to the inlet of the third outlet header 42, so as to more flexibly respond to the requirements for residual heat removal in various accidents. Of course, the present invention is not limited to providing two stages or three stages of heat exchangers, and different numbers of heat exchangers may be provided according to actual needs.

[0102] According to the above-mentioned passive residual heat removal system for a nuclear reactor, the present invention further provides a passive residual heat removal method for a nuclear reactor, which includes the following steps.

[0103] In step SI, multiple stages of heat exchangers are disposed, wherein every two adjacent stages of heat exchangers are connected by means of an intermediate header, and the intermediate header is provided with a side outlet.

[0104] In step S2, the hot end of the reactor system is connected to the inlet of the first-stage heat exchanger by means of the inlet pipeline.

[0105] In step S3, the side outlet and the outlet of the last-stage heat exchanger are connected respectively to the cold end of the reactor system by means of outlet pipelines respectively to form a multi-stage heat exchange loop.

[0106] In step S4, isolating valves are disposed on the inlet pipeline and each outlet pipeline respectively.

[0107] In step S5, when the reactor system is operating normally, the isolating valve on the inlet pipeline is enabled to be in an opened state, and the isolating valve on each outlet pipeline is enabled to be in a closed state.

[0108] In step S6, when an accident occurs, the isolating valve on each outlet pipeline is opened to form a connected fluid circulation loop, wherein heat generated by the reactor system is carried by a fluid flowing through the inlet pipeline from the hot end for heat exchange by the multiple stages of heat exchangers, and the fluid that has transferred the heat returns to the cold end of the reactor system through the outlet pipeline, thereby forming circulation.

[0109] Further, the number of stages of the heat exchangers used is selected according to different accidents or different stages of the accident.

[0110] The above are only preferred embodiments of the present application, and are not intended to limit the present application. For those skilled in the art, the present application may have various modifications and changes. Any modifications, equivalent replacements, improvements, etc. made within the ideas and principles of this application shall be included in the protection scope of this application.

Claims

What is claimed is:

1. A passive residual heat removal system for a nuclear reactor, comprising:a reactor system comprising a hot end and a cold end, wherein the hot end is configured to output a fluid outwards and the cold end is configured to input a fluid inwards; anda residual heat removal system comprising multiple stages of heat exchangers, wherein every two adjacent stages of heat exchangers are connected by means of an intermediate header,wherein the hot end is connected to an inlet of a first-stage heat exchanger by means of an inlet pipeline; the intermediate header is provided with a side outlet, and the side outlet and an outlet of a last-stage heat exchanger are respectively connected to the cold end by means of outlet pipelines to form a multi-stage heat exchanger loop; and isolating valves are provided on the inlet pipeline and each outlet pipeline respectively.

2. The passive residual heat removal system for the nuclear reactor according to claim 1, wherein the heat exchangers comprise multiple groups of basic heat exchange modules composed of a heat exchange tube bundle and end tube plates arranged at both ends of the heat exchange tube bundle, wherein the heat exchange tube bundle comprises a plurality of heat exchange tubes arranged in a predetermined sequence, and the end tube plates have through holes corresponding to the heat exchange tubes.

3. The passive residual heat removal system for the nuclear reactor according to claim 2, wherein the multiple groups of basic heat exchange modules of the heat exchangers are connected in parallel and / or in series.

4. The passive residual heat removal system for the nuclear reactor according to claim 3, wherein the inlet pipeline is connected to the heat exchangers by means of an inlet header, and the inlet header is provided with a plurality of outlet tubes which are respectively connected to the multiple groups of basic heat exchange modules connected in parallel of the heat exchangers.

5. The passive residual heat removal system for the nuclear reactor according to claim 3, wherein the outlet pipeline is connected to the heat exchangers by means of an outlet header, and the outlet header is provided with a plurality of inlet tubes which are respectively connected to the multiple groups of basic heat exchange modules connected in parallel of the heat exchangers.

6. The passive residual heat removal system for the nuclear reactor according to claim 2, wherein the heat exchange tubes of the heat exchange tube bundle are straight tubes or bent tubes.

7. The passive residual heat removal system for the nuclear reactor according to claim 1, wherein the residual heat removal system further comprises a heat sink water tank in which the multiple stages of heat exchangers are arranged stage by stage from top to bottom.

8. The passive residual heat removal system for the nuclear reactor according to claim 7, wherein the heat sink water tank is a water tank with a certain amount of water or a natural cooling water source, and a height of a water surface of the heat sink water tank is higher than that of a first-stage heat exchanger.

9. The passive residual heat removal system for the nuclear reactor according to claim 8, wherein the reactor system and the residual heat removal system are arranged in a containment, a backflow collection tank is provided above the heat sink water tank, and the backflow collection tank is connected to the containment and connected to the heat sink water tank through a backflow pipeline.

10. A passive residual heat removal method for a nuclear reactor, comprising steps of:disposing multiple stages of heat exchangers, wherein every two adjacent stages of heat exchangers are connected by means of an intermediate header, and the intermediate header is provided with a side outlet;connecting a hot end of a reactor system to an inlet of a first-stage heat exchanger by means of an inlet pipeline;connecting the side outlet and an outlet of a last-stage heat exchanger to a cold end of the reactor system by means of outlet pipelines respectively to form a multi-stage heat exchange loop;disposing isolating valves on the inlet pipeline and each outlet pipeline respectively;when the reactor system is operating normally, enabling an isolating valve on the inlet pipeline to be in an opened state, and enabling an isolating valve on each outlet pipeline to be a closed state; andwhen an accident occurs, opening the isolating valve on each outlet pipeline to form a connected fluid circulation loop, wherein heat generated by the reactor system is carried by a fluid flowing through the inlet pipeline from the hot end for heat exchange by the multiple stagesof heat exchangers, and the fluid that has transferred the heat returns to the cold end of the reactor system through the outlet pipeline, thereby forming circulation.

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