A natural circulation heat rejection system for a heap pit, a nuclear power plant reactor, and a heat rejection method thereof

Abstract

This application belongs to the field of nuclear power technology, and particularly relates to a pit natural circulation heat rejection system, a nuclear power plant reactor, and a heat rejection method thereof. The pit natural circulation heat rejection system includes a pit exhaust air system and a chimney for drawing air. The pit exhaust air system includes an air inlet pipe, an air outlet pipe, an air inlet fan, a first valve, a second valve, a third valve, and an exhaust air fan. The air inlet fan and the first valve are sequentially connected in series on the air inlet pipe along the air inlet direction of the air inlet pipe. The second valve is arranged on a branch pipe communicated with the air inlet pipe. The third valve and the exhaust air fan are sequentially connected in series on the air outlet pipe along the air outlet direction of the air outlet pipe. The air inlet pipe passes through the side of the reactor hall and the containment and then is connected to the pit. This application takes away the heat of the pit in a passive natural circulation manner to solve the technical problems that the current fast reactors do not consider the design and application of pit natural circulation heat rejection, and the design of the pit ventilation system is relatively complex.

Description

Technical Field

[0001] This application belongs to the field of nuclear power technology, and particularly relates to a natural circulation heat rejection system for a reactor pit, a nuclear power plant reactor, and a heat rejection method thereof. Background Art

[0002] A fast reactor using liquid metal as a coolant is a typical high-temperature system, and the reactor pit where the reactor is located is subjected to high temperatures both under normal and accident conditions. The original design is to set up a complex ventilation system to ensure that the temperature of the reactor pit is below the temperature at which concrete loses its crystal water under normal operating conditions. Under accident conditions, it is also necessary to consider whether the auxiliary facilities will fail, leading to a further expansion of the accident consequences.

[0003] When a fast reactor nuclear power plant is operating normally, the fan of the reactor ventilation system operates normally, continuously replacing the air in the reactor pit, discharging it to the atmosphere through the ventilation duct and chimney, and maintaining the reactor pit in a negative pressure state. The negative pressure design ensures that the gas flow direction is from the reactor building to the reactor pit during normal operation, preventing a very small amount of radioactive substances released by the reactor from entering the reactor hall and threatening the safety of operating personnel. Radiation monitoring continuously monitors the radioactive levels in the reactor building and the top shield of the reactor.

[0004] When a design basis accident occurs in a sodium-cooled fast reactor nuclear power plant, the primary circuit boundary can remain intact, and the radioactive substances in the reactor are contained within the primary circuit boundary. Therefore, in most cases, the reactor pit does not need to perform the function of radioactive containment; however, there is a certain amount of heat dissipation on the surface of the reactor vessel, which needs to be removed to maintain the temperature of the reactor body and the equipment in the reactor pit within a certain range. Currently, a reactor pit exhaust system is set up to drive the gas inside the reactor pit to be discharged through a fan to cool the equipment inside the reactor pit.

[0005] During a severe accident, the radioactive substances in the reactor main vessel leak into the containment through the equipment at the top of the main vessel. When the containment radiation monitoring system detects abnormal radioactivity, it triggers the operation of the containment isolation system, and the isolation valves on the coolant pipes and ventilation pipes passing through the containment device are automatically isolated. At this time, the inner containment is in a sealed state, which can effectively prevent the leakage of radioactive substances to the environment during a severe accident and affect the environment. After the containment device is sealed for a period of time, the short-lived radioactive substances with a relatively large proportion in the radioactive substances decay, and only a small amount of long-lived radioactive substances remain. At this time, the containment isolation state is released, and the reactor ventilation system is started to filter and controllably discharge the radioactive substances at an elevated height.

[0006] However, currently, fast reactors do not consider the design and application of natural circulation heat rejection in the reactor pit, and the design of the reactor pit ventilation system is relatively complex. Summary of the Invention

[0007] In view of this, the present application is committed to providing a pit natural circulation heat rejection system, a nuclear power plant reactor, and a heat rejection method thereof, which can remove the heat of the pit in a passive natural circulation manner, so as to solve the technical problems that the current fast reactors do not consider the design and application of pit natural circulation heat rejection, and the design of the pit ventilation system is relatively complex.

[0008] The first aspect of the present application provides a pit natural circulation heat rejection system, which is applied to the nuclear island part of a nuclear power plant. The nuclear island part of the nuclear power plant includes a reactor body, a pit, a containment building, and a reactor hall. The reactor body is located in the pit, and the upper parts of the reactor body and the pit are the containment building. The reactor hall surrounds the outside of the containment building. The pit natural circulation heat rejection system includes a pit exhaust air system and a chimney. The pit exhaust air system includes an inlet duct, an outlet duct, an inlet fan, a first valve, a second valve, a third valve, and an exhaust fan. The inlet fan and the first valve are sequentially connected in series along the air inlet direction of the inlet duct and are located in the area between the containment building and the reactor hall. The second valve is arranged on a branch duct communicated with the inlet duct and is located on the side of the first valve close to the containment building. Both the second valve and the branch duct are located in the area between the containment building and the reactor hall. The third valve and the exhaust fan are sequentially connected in series along the air outlet direction of the outlet duct and are located in the area between the containment building and the reactor hall. The outlet duct is connected to the pit after passing through the containment building. The chimney is connected to the air outlet of the outlet duct and is located outside the reactor hall. The inlet duct is connected to the pit after passing through the side of the reactor hall and the containment building.

[0009] In a specific embodiment of the present application, the inlet duct extends to a first linear distance from the bottom surface of the pit. The outlet duct extends to a second linear distance from the bottom surface of the pit. The second linear distance is greater than the first linear distance.

[0010] In a specific embodiment of the present application, the reactor body is a liquid metal reactor body.

[0011] In a specific embodiment of the present application, the core outlet temperature of the liquid metal reactor body is greater than 500 °C.

[0012] In a specific embodiment of the present application, the liquid metal reactor body is a sodium-cooled fast reactor body.

[0013] In a specific embodiment of the present application, the height and layout position of the chimney are obtained through the coupled calculation of the natural circulation driving force and the flow resistance.

[0014] The second aspect of the present application provides a nuclear power plant reactor, which includes the nuclear island part of the nuclear power plant and a pit natural circulation heat rejection system according to the first aspect of the present application.

[0015] The third aspect of the present application provides a heat rejection method for a nuclear power plant reactor. The heat rejection method for the nuclear power plant reactor includes: when the reactor is in a normal power operation condition, opening the first valve and the third valve of the pit natural circulation heat rejection system in the embodiment of the present application, closing the second valve, and the exhaust fan and the chimney will discharge the air in the pit into the environment after filtration; when the reactor is in a shutdown and refueling condition, closing the intake fan and the exhaust fan, and adopting a natural circulation mode to maintain the temperature and negative pressure of the pit; when the reactor is in an accident condition, the containment is automatically isolated, and then, opening the third valve and setting the second valve to a 5% valve opening degree.

[0016] The beneficial effects of the technical solution of the present application are as follows: By arranging a chimney outside the reactor hall and connecting the chimney to the pit through an air outlet pipe, and by setting the first valve, the second valve and the third valve, the opening and closing of the first valve, the second valve and the third valve are used to take away the heat of the pit in a passive natural circulation manner, which is beneficial to maintaining the structural integrity of the reactor body and the pit, and assisting in enhancing the natural circulation ability inside the reactor, improving the safety and economy of the reactor, and simplifying the operation. In addition, when the primary pressure boundary of the pit natural circulation heat rejection system is not damaged or the influence of the leakage of radioactive nuclides is not higher than the minor damage required by the national standard for the annual emission amount, the natural circulation heat of the pit can be discharged. In an accident condition, the heat can be reliably discharged through the natural circulation mode by the pit natural circulation heat rejection system, and at the same time, the filtered organized emission of the gas in the containment can be realized, and it can play an auxiliary role in discharging the residual heat of the reactor accident. Brief Description of the Drawings

[0017] Figure 1 The figure shows a schematic diagram of a nuclear power plant reactor provided by an embodiment of the present application. Detailed Embodiments

[0018] The technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present application without creative efforts shall fall within the protection scope of the present application.

[0019] At least one embodiment of the present application provides a natural circulation heat rejection system for a reactor pit, which is applied to the nuclear island part of a nuclear power plant. The nuclear island part of the nuclear power plant includes a reactor body 1, a reactor pit 2, a containment 3, and a reactor hall 10. The reactor body 1 is located in the reactor pit 2, and the upper parts of the reactor body 1 and the reactor pit 2 are the containment 3. The reactor hall 10 surrounds the outside of the containment 3. The natural circulation heat rejection system for the reactor pit includes a reactor pit exhaust system and a chimney 9 for drawing air. The reactor pit exhaust system includes an inlet duct, an outlet duct, an inlet fan 4, a first valve 5, a second valve 6, a third valve 7, and an exhaust fan 8. The inlet fan 4 and the first valve 5 are serially arranged on the inlet duct in the inlet direction of the inlet duct and are located in the area between the containment 3 and the reactor hall 10. The second valve 6 is arranged on a branch duct communicated with the inlet duct and is located on the side of the first valve 5 close to the containment 3. Both the second valve 6 and the branch duct are located in the area between the containment 3 and the reactor hall 10. The third valve 7 and the exhaust fan 8 are serially arranged on the outlet duct in the outlet direction of the outlet duct and are located in the area between the containment 3 and the reactor hall 10. The outlet duct passes through the containment 3 and then is connected to the reactor pit 2. The chimney 9 for drawing air is connected to the outlet of the outlet duct. The inlet duct passes through the side of the reactor hall 10 and the containment 3 and then is connected to the reactor pit 2.

[0020] It should be noted that the reactor body 1 refers to all components within the entire reactor vessel, including the reactor core and the primary circuit system, etc. The chimney 9 for drawing air can be located outside the reactor hall 10, or part of it can be outside the reactor hall 10 and part of it can be inside the reactor hall 10. The outlet duct can also pass through the top of the reactor hall and the containment 3 and then be connected to the reactor pit 2.

[0021] Next, in combination with Figure 1 , the working principle of the natural circulation heat rejection system for the reactor pit will be specifically described.

[0022] When the reactor is operating at normal power, the reactor body 1 is in a high-temperature state. When starting the natural circulation heat rejection system for the reactor pit, the first valve 5 and the third valve 7 are opened, the second valve 6 is closed, and the exhaust fan 8 and the chimney 9 for drawing air filter and discharge the air in the reactor pit 2 into the environment.

[0023] When the reactor is in the shutdown and refueling condition, the first valve 5 and the third valve 7 are in the open state, the second valve 6 is in the closed state, the temperature of the reactor body 1 is relatively low, and the heat load of the reactor pit is small. Then, the inlet fan 4 and the exhaust fan 8 can be turned off, and the natural circulation mode can be adopted to maintain the temperature and negative pressure of the reactor pit 2.

[0024] When the reactor is in an accident condition, the first valve 5 is in a closed state, the containment 3 is automatically isolated, and the short-lived nuclides are allowed to decay first. At this time, the temperature in the reactor pit 2 will increase, and the radioactive level will also accumulate. After that, the third valve 7 is opened, and the second valve 6 is set to a small opening (e.g., 5% valve opening) to maintain the natural circulation cooling of the reactor pit 2 and achieve the filtered organized discharge of the residual radioactivity.

[0025] The natural circulation heat removal system for the reactor pit provided by the embodiments of the present application arranges a chimney 9 outside the reactor hall 10 and connects the chimney 9 to the reactor pit 2 through an air outlet pipe. By setting the first valve 5, the second valve 6, and the third valve 7, the opening and closing of the first valve 5, the second valve 6, and the third valve 7 are used to remove the heat from the reactor pit in a passive natural circulation manner, which is beneficial to maintaining the structural integrity of the reactor body 1 and the reactor pit 2, and assisting in enhancing the natural circulation capacity inside the reactor, improving the safety and economy of the reactor, and simplifying the operation. In addition, when there is no damage to the primary pressure boundary or the influence of the leakage of radioactive nuclides is a minor damage not higher than the annual emission requirement in the national standard, the natural circulation heat removal of the reactor pit 2 can be maintained. In an accident condition, the heat can be reliably discharged through the natural circulation heat removal system of the reactor pit, and at the same time, the filtered organized discharge of the gas in the containment 3 can be realized, and it can play an auxiliary role in discharging the residual heat of the reactor accident.

[0026] In at least one embodiment of the present application, the air inlet pipe extends to a first linear distance D1 from the bottom surface of the reactor pit 2. 底 The air outlet pipe extends to a second linear distance D2 from the bottom surface of the reactor pit 2. 底 The second linear distance D2 is greater than the first linear distance D1. In this way, by reasonably designing the positions where the air inlet pipe and the air outlet pipe extend into the reactor pit 2, the efficiency of natural circulation heat removal is higher.

[0027] It should be noted that the air inlet fan 4 can be installed on the horizontal ground S1 of the reactor hall 10.

[0028] In at least one embodiment of the present application, the reactor body 1 is a reactor body of a liquid metal reactor. Further, in some embodiments, the core outlet temperature of the reactor body of the liquid metal reactor is greater than 500 °C.

[0029] It should be noted that the reactor body of the liquid metal reactor includes, but is not limited to, the reactor body of a sodium-cooled fast reactor or the reactor body of a lead-cooled fast reactor. The embodiments of the present application do not make specific limitations in this regard. For example, the core outlet temperature of the reactor body of a sodium-cooled fast reactor can be 565 °C. The core outlet temperature of the reactor body of a lead-cooled fast reactor can be 540 °C.

[0030] In at least one embodiment of the present application, the height and arrangement position of the chimney 9 are obtained through the coupled calculation of the natural circulation driving force and the flow resistance. In this way, the height and arrangement position of the chimney 9 can meet the requirements of natural circulation ventilation under normal power operation conditions and accident conditions.

[0031] It should be noted that the resistance magnitude can be determined by geometric parameters such as the pipeline length, inner diameter of the pipe, and elbows in the pipe, and the natural circulation driving force can be determined by reasonably setting the position and height of the chimney.

[0032] At least one embodiment of the present application further provides a nuclear power plant reactor, which includes the nuclear island part of the nuclear power plant and a pit natural circulation heat removal system in any one of the above embodiments of the present application. The nuclear island part of the nuclear power plant includes a reactor body 1, a pit 2, a containment 3, and a reactor hall 10. The containment 3 is placed in the pit 2, and the reactor body 1 is located inside the pit 2 and the containment 3. The reactor hall 10 surrounds the outside of the containment 3. The pit natural circulation heat removal system includes a pit exhaust system and a chimney 9. The pit exhaust system includes an intake duct, an outlet duct, an intake fan 4, a first valve 5, a second valve 6, a third valve 7, and an exhaust fan 8. The intake fan 4 and the first valve 5 are sequentially connected in series along the intake direction of the intake duct and are located in the area between the containment 3 and the reactor hall 10. The second valve 6 is arranged on a branch duct communicating with the intake duct, and is located on the side of the first valve 5 close to the containment. Both the second valve 6 and the branch duct are located in the area between the containment 3 and the reactor hall 10. The third valve 7 and the exhaust fan 8 are sequentially connected in series along the exhaust direction of the outlet duct and are located in the area between the containment 3 and the reactor hall 10. The outlet duct passes through the containment 3 and then is connected to the pit 2. The chimney 9 is connected to the outlet of the outlet duct and is located outside the reactor hall 10. The intake duct passes through the side of the reactor hall 10 and the containment 3 and then is connected to the pit 2.

[0033] It should be noted that the nuclear power plant reactor includes a pit natural circulation heat removal system in any one of the above embodiments of the present application, has corresponding technical features, and can achieve corresponding technical effects, which will not be elaborated here.

[0034] The nuclear power plant reactor provided by the embodiment of the present application simplifies the traditional pit ventilation system and the containment design, and at the same time enables the pit natural circulation heat removal system in the nuclear power plant reactor to have a partial auxiliary heat removal function. Through the design of the chimney 9 connecting the pit 2, the requirements for the ventilation system under normal power operation conditions and accident conditions are reduced, and the passive safety of the reactor is improved.

[0035] At least one embodiment of the present application further provides a heat removal method for a nuclear power plant reactor, and the heat removal method for the nuclear power plant reactor includes the following steps.

[0036] S100: When the reactor is operating at normal power, open the first valve 5 and the third valve 7 of the pit natural circulation heat removal system in the embodiment of the present application, close the second valve 6, and the exhaust fan 8 and the chimney 9 will discharge the air in the pit 2 into the environment after filtration.

[0037] S200: When the reactor is in the shutdown and refueling condition, turn off the intake fan 4 and the exhaust fan 8, and adopt the natural circulation mode to maintain the temperature and negative pressure of the pit 2.

[0038] S300: When the reactor is in an accident condition, the containment 3 is automatically isolated. After that, open the third valve 7 and set the second valve 6 to an opening of 5%.

[0039] The heat removal method of the nuclear power plant reactor can refer to the specific description of the working principle of the pit natural circulation heat removal system above, and will not be elaborated here. The heat removal method of the nuclear power plant reactor uses the pit natural circulation heat removal system in the above embodiment of the present application, includes corresponding technical features, and can achieve corresponding technical effects, which will not be elaborated here.

[0040] It should be noted that the combination manner of each technical feature in the embodiment of the present application is not limited to the combination manner recorded in the embodiment of the present application or the combination manner recorded in the specific embodiment. All the technical features recorded in the present application can be freely combined or combined in any manner, unless contradictions occur between them.

[0041] As shown in the present application and the claims, unless the context clearly indicates an exceptional situation, words such as "a" and / or "the" are not specifically singular and may also include the plural. Generally speaking, the term "comprising" only indicates the inclusion of the clearly identified steps and elements, and these steps and elements do not constitute an exclusive list. The method or device may also include other steps or elements.

[0042] The above are only the preferred embodiments of the present application and are not intended to limit the present application. Any modifications, equivalent replacements, etc. made within the spirit and principle of the present application shall be included within the protection scope of the present application.

Claims

1. A natural circulation heat removal system for a pile pit, characterized in that: The invention is applied to the nuclear island part of a nuclear power plant, wherein the nuclear island part of the nuclear power plant includes a reactor body, a reactor pit, a containment shell and a reactor hall, the reactor body is located in the reactor pit, the upper part of the reactor body and the reactor pit is the containment shell, and the reactor hall is surrounded on the outside of the containment shell, the natural circulation heat removal system of the reactor pit includes a reactor pit exhaust system and an air extraction chimney, the reactor pit exhaust system includes an air inlet duct, an air outlet duct, an air inlet fan, a first valve, a second valve, a third valve and an exhaust fan, the air inlet fan and the first valve are sequentially arranged on the air inlet duct along the air inlet direction of the air inlet duct and are located between the containment shell and the reactor hall. The second valve is arranged on a branch pipe connected to the air inlet pipe and is located on the side of the first valve close to the containment shell; the second valve and the branch pipe are both located in the area between the containment shell and the reactor hall; the third valve and the exhaust fan are sequentially arranged on the air outlet pipe along the air outlet direction of the air outlet pipe and are located in the area between the containment shell and the reactor hall; the air outlet pipe passes through the containment shell and is connected to the reactor pit, the air extraction chimney is connected to the air outlet of the air outlet pipe and is located outside the reactor hall, and the air inlet pipe passes through the side of the reactor hall and the containment shell and is connected to the reactor pit; The second valve is used to maintain an opening of 5% after the containment is automatically isolated when the reactor is in an accident condition.

2. A natural circulation heat removal system for a pile pit according to claim 1, characterized in that: The air inlet duct extends to a first linear distance from the bottom surface of the stacking pit, and the air outlet duct extends to a second linear distance from the bottom surface of the stacking pit, and the second linear distance is greater than the first linear distance.

3. The natural circulation heat removal system for a pile pit according to claim 1, characterized in that: The stack body is a liquid metal reactor stack body.

4. The natural circulation heat removal system for a pile pit according to claim 3 is characterized in that: The core outlet temperature of the liquid metal reactor body is greater than 500°C.

5. The natural circulation heat removal system for a pile pit according to claim 3 is characterized in that: The main body of the liquid metal reactor is a sodium-cooled fast reactor.

6. A natural circulation heat removal system for a pile pit according to any one of claims 1 to 5, characterized in that: The height and layout of the wind chimney are obtained through the coupling calculation of the natural circulation driving force and flow resistance.

7. A nuclear power plant reactor, characterized in that: include: The nuclear island portion of a nuclear power plant; and, A natural circulation heat removal system for a pile pit as claimed in any one of claims 1 to 6.

8. A method for removing heat from a nuclear power plant reactor, characterized in that: The heat removal method of the nuclear power plant reactor is based on the natural circulation heat removal system of the reactor pit according to claim 1, wherein the heat removal method of the nuclear power plant reactor comprises: When the reactor is in normal power operation, the first valve and the third valve of the natural circulation heat removal system of the reactor pit are opened, the second valve is closed, and the exhaust fan and the air extraction chimney filter the air in the reactor pit and discharge it into the environment; When the reactor is in a shutdown and refueling condition, the air inlet fan and the air exhaust fan of the natural circulation heat removal system of the reactor pit are turned off, and the natural circulation mode is adopted to maintain the temperature and negative pressure of the reactor pit; When the reactor is in an accident condition, the containment of the natural circulation heat removal system of the reactor pit is automatically isolated, after which the third valve is opened and the second valve is set to a 5% valve opening.

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