An apparatus and method for eliminating thermal stratification in pool reactors based on compressed gas

Abstract

This invention discloses a device and method for eliminating thermal stratification in a pooled reactor based on compressed gas. The device includes an independent heat exchanger, a steam generator, a reactor core, a core shielding layer, a main pump, and a temperature sensor array, all housed within the pooled reactor vessel. In this invention, through a linkage mechanism between temperature monitoring and the compressed gas-driven main pump, the weak natural circulation is converted into forced convection circulation during a complete power outage and when thermal stratification occurs. This significantly enhances the disturbance and mixing of hot and cold liquid metals within the pool, effectively eliminating temperature gradients that lead to equipment thermal fatigue and improving the safety of the reactor structure under accident conditions. Unlike simple energy storage and release, by incorporating a preheater, the residual heat from the reactor core is used to reheat and pressurize the compressed gas. This not only recovers some waste heat but also enhances the work capacity of the gas-driven turbine, achieving energy recovery and ensuring the power redundancy required to drive the main pump.

Description

Technical Field

[0001] This invention belongs to the field of passive residual heat removal technology for liquid metal nuclear reactors, and particularly relates to a device and method for eliminating thermal stratification in pool-type reactors based on compressed gas. Background Technology

[0002] Nuclear energy is a stable, low-carbon base load energy source. Liquid metal pool nuclear reactors are considered the preferred reactor type for fourth-generation nuclear energy systems due to their inherent safety. The passive residual heat removal system is the core of reactor safety. In the event of a complete power outage, this system does not rely on external energy sources and relies solely on natural physical laws (such as gravity and natural convection) to remove residual heat from the reactor core.

[0003] Existing passive waste heat removal systems suffer from the following technical defects: Weak natural circulation driving force; under SBO conditions, the coolant relies entirely on natural circulation. Due to the small driving head and low flow velocity, there is insufficient momentum to fully mix the hot and cold fluids in the heat pool, resulting in severe thermal stratification. Under gravity, low-temperature coolant accumulates at the bottom, while high-temperature coolant accumulates at the top, leading to extremely uneven temperature distribution in the vertical direction. This thermal stratification not only weakens the natural circulation strength and reduces heat removal power but also causes low-frequency temperature oscillations, leading to decreased stability of the neutron and thermal-hydraulic systems, increased risk of equipment thermal fatigue, and significant temperature gradients at the thermal stratification interface, generating enormous thermal stress on in-pile equipment such as heat exchangers, which can cause structural deformation or even damage over long-term.

[0004] Chinese patent CN115312219B discloses a passive residual heat removal system for marine liquid metal reactors, and Chinese patent CN110010255B discloses a residual heat removal system and method for lead-cooled fast reactors. These systems mainly focus on establishing external loops for the reactor or using residual heat to drive external water replenishment. They fail to directly solve the problem of thermal stratification of the coolant inside the pool reactor and also ignore the impact of fluid rheology inside the reactor on the thermal load of the equipment, leaving room for improvement. Summary of the Invention

[0005] The purpose of this invention is to propose a device and method for eliminating thermal stratification in pool reactors based on compressed gas in order to eliminate thermal stratification of coolant in liquid metal pool reactors, establish and maintain effective natural circulation of coolant in reactors, ensure effective removal of residual heat from the reactor core, and improve the safety and stability of pool reactor structures.

[0006] To achieve the above objectives, the present invention adopts the following technical solution: A device for eliminating thermal stratification in a pool-type reactor based on compressed gas includes: Independent heat exchangers, steam generators, reactor cores, core shielding layers, main pumps, and temperature sensor arrays are installed within the pool-type reactor vessel. Compressed gas storage tanks, compressed gas preheating storage tanks, preheaters, pneumatic valve assemblies, turbine assemblies, circulating pumps, coolers, and air-cooled towers are installed outside the pool-type stack container. The shell side of the independent heat exchanger is connected to the reactor core to form a first loop, and the tube side of the independent heat exchanger is sequentially connected to the circulating pump, the tube side of the preheater and the cooler to form a second loop; The pneumatic valve assembly includes a first pneumatic valve and a second pneumatic valve connected between the compressed gas storage tank and the compressed gas preheating storage tank, and a third pneumatic valve connected to the outlet end of the compressed gas preheating storage tank. The turbine assembly includes a first turbine and a second turbine, wherein the first turbine is drivenly connected to the circulating pump and the second turbine is drivenly connected to the main pump; The outlet of the third pneumatic valve is connected to the inlet of the first turbine and the second turbine. The controller is electrically connected to the temperature sensor array and each pneumatic valve. The controller is configured to control the pneumatic valve assembly to open when the temperature gradient detected by the temperature sensor array exceeds a preset threshold, so as to use compressed gas to drive the turbine assembly to do work and drive the main pump and the circulating pump to run.

[0007] As a further description of the above technical solution: The temperature sensor array is arranged at different depths within the pool reactor, with a sensor spacing of 1cm to 30cm, and is used to measure the vertical temperature distribution of the coolant in real time.

[0008] As a further description of the above technical solution: The independent heat exchanger is a shell-and-tube heat exchanger. The fluid on the shell side is liquid metal from the reactor, flowing from top to bottom, while the fluid on the tube side is the heat exchange medium, flowing from bottom to top. The preheater is installed inside the compressed gas preheating tank. The heat exchange medium of the second loop flows through its pipe side, and the compressed gas is in contact with its fin side. It is used to heat the compressed gas using the residual heat of the reactor core.

[0009] As a further description of the above technical solution: The heat exchange medium filled in the second loop is selected from one of water, supercritical carbon dioxide, lead, bismuth, lead-bismuth alloy or sodium.

[0010] As a further description of the above technical solution: The gas in the compressed gas storage tank is selected from air, carbon dioxide, or nitrogen.

[0011] As a further description of the above technical solution: The pressure range of the compressed gas storage tank is 5~20MPa; the working pressure range of the compressed gas preheating storage tank is 7~25MPa.

[0012] As a further description of the above technical solution: The cooler is installed inside the air-cooled tower and uses natural atmospheric convection to cool the heat exchange medium in the second loop.

[0013] As a further description of the above technical solution: A method for thermal stratification in a pool-type reactor based on compressed gas elimination specifically includes the following steps: S1. Under the condition of a complete power outage, the temperature gradient inside the pool reactor is monitored in real time through a temperature sensor array. S2. When the temperature gradient is detected to be greater than 2K / cm, it is determined that thermal stratification has occurred. The controller opens the first pneumatic valve and the second pneumatic valve to allow the gas in the compressed gas storage tank to enter the compressed gas preheating storage tank. S3. The compressed gas absorbs residual heat from the reactor core and expands and increases in pressure in the preheating tank through the preheater. When the pressure rises to 1.5 times the initial pressure, the controller opens the third pneumatic valve. S4. High-temperature and high-pressure gas enters the first and second turbines and expands to do work, driving the circulation pump and the main pump respectively. The main pump converts the natural circulation in the pool into forced convection circulation to eliminate thermal stratification. The circulation pump increases the flow rate of the second loop to match the heat dissipation demand. S5. When the temperature gradient recovers to less than 2K / cm, the controller controls the third pneumatic valve to slowly close at a rate of 1% / min of the total opening, so that the system smoothly transitions from forced circulation back to natural circulation.

[0014] In summary, due to the adoption of the above technical solution, the beneficial effects of the present invention are: 1. In this invention, through the linkage mechanism of temperature monitoring and compressed gas driving the main pump, when the entire field is powered off and thermal stratification occurs, the weak natural circulation is converted into forced convection circulation, which greatly enhances the disturbance and mixing of hot and cold liquid metals in the pool, effectively eliminates the temperature gradient that leads to thermal fatigue of the equipment, and improves the safety of the reactor structure under accident conditions.

[0015] 2. In this invention, by utilizing waste heat and energy gain, unlike simple energy storage and release, a preheater is set up to use the waste heat exported from the reactor core to reheat and pressurize the compressed gas. This not only recovers some waste heat but also enhances the work capacity of the gas-driven turbine, realizing energy recovery and utilization and ensuring the power redundancy required to drive the main pump.

[0016] 3. In this invention, the dynamic adjustment method based on temperature gradient, after the thermal stratification is eliminated, avoids violent fluctuations in fluid flow by controlling the extremely low rate of closure of the third pneumatic valve, ensuring an orderly and smooth transition of the system from forced circulation to natural circulation, and maintaining the continuity of passive waste heat discharge.

[0017] 4. In this invention, through an independent dual-loop drive design, a first turbine-driven circulating pump and a second turbine-driven main pump are adopted. This design ensures forced mixing in the first loop within the reactor and enhances the circulation flow rate of the second loop to match the increased heat dissipation power demand due to enhanced mixing, thereby preventing local overheating. Attached Figure Description

[0018] Figure 1 This is a schematic diagram of a device for eliminating thermal stratification in a pool-type reactor based on compressed gas, as proposed in this invention. Figure 2 This is a flowchart of a method for eliminating thermal stratification in a pool reactor based on compressed gas, as proposed in this invention.

[0019] Legend: 1. Compressed gas storage tank; 2. First pneumatic valve; 3. Second pneumatic valve; 4. Third pneumatic valve; 5. First turbine; 6. Second turbine; 7. Controller; 8. Circulating pump; 9. Preheater; 10. Compressed gas preheating storage tank; 11. Cooler; 12. Air-cooled tower; 13. Pool-type reactor vessel; 14. Temperature sensor array; 15. Main pump; 16. Independent heat exchanger; 17. Core shielding layer; 18. Steam generator; 19. Reactor core. Detailed Implementation

[0020] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0021] Please see Figures 1-2 The present invention provides a technical solution: a device for eliminating thermal stratification in a pool reactor based on compressed gas, comprising: an independent heat exchanger 16, a steam generator 18, a reactor core 19, a core shielding layer 17, a main pump 15, and a temperature sensor array 14 disposed in a pool reactor vessel 13. Compressed gas storage tank 1, compressed gas preheating storage tank 10, preheater 9, pneumatic valve assembly, turbine assembly, circulating pump 8, tube side of preheater 9, cooler 11 and air-cooled tower 12 are installed outside the pool-type stack container 13. The shell side of the independent heat exchanger 16 is connected to the reactor core 19 to form a first loop, and the tube side of the independent heat exchanger 16 is sequentially connected to the circulating pump 8 and the cooler 11 to form a second loop. The pneumatic valve assembly includes a first pneumatic valve 2 and a second pneumatic valve 3 connected between the compressed gas storage tank 1 and the compressed gas preheating storage tank 10, and a third pneumatic valve 4 connected to the outlet end of the compressed gas preheating storage tank 10. The turbine assembly includes a first turbine 5 and a second turbine 6, wherein the first turbine 5 is drivenly connected to the circulating pump 8, and the second turbine 6 is drivenly connected to the main pump 15. The outlet of the third pneumatic valve 4 is connected to the inlet of the first turbine 5 and the second turbine 6. The controller 7 is electrically connected to the temperature sensor array 14 and each pneumatic valve. The controller 7 is configured to control the pneumatic valve assembly to open when the temperature gradient detected by the temperature sensor array 14 exceeds a preset threshold, so as to use compressed gas to drive the turbine assembly to do work and drive the main pump 15 and the circulating pump 8 to run.

[0022] Specifically: In the event of a complete power outage, the liquid metal flow path within the pool reactor is the core, independent heat exchanger 16, core shielding layer 17, and the core, forming a first natural circulation loop. The heat exchange medium flow path is the independent heat exchanger 16, circulating pump 8, cooler 11, and independent heat exchanger 16, forming a second natural circulation loop. The air in the cooling tower forms a third natural circulation loop. The residual heat from the core is transferred to the atmosphere through the first, second, and third circulation loops. The temperature sensor array 14 transmits temperature data to the controller 7 in real time. When the temperature gradient is greater than 2K / cm, that is, when thermal stratification occurs in the liquid metal in the pool reactor, the controller 7 opens the first pneumatic valve 2 and the second pneumatic valve 3. After the pressure in the compressed gas preheating tank 10 and the compressed gas tank 1 is balanced, the controller 7 closes the first pneumatic valve 2 and the second pneumatic valve 3.

[0023] The compressed gas in the preheating tank absorbs part of the core waste heat through the preheater 9 and expands and increases in pressure. When the pressure increases by 1.5 times, the controller 7 opens the third pneumatic valve 4, and the compressed gas then enters the first turbine 5 and the second turbine 6 to expand and do work. The main pump 15 converts the first natural circulation in the pool reactor into the first forced convection circulation, which enhances the mixing of hot and cold liquid metals and eliminates thermal stratification in the pool reactor. The circulation pump 8 converts the second natural circulation into the second forced circulation, thereby matching the increase in waste heat discharge power caused by the conversion of the first natural circulation into the first forced circulation.

[0024] Furthermore, the temperature sensor array 14 is arranged at different depths within the pool reactor, with a sensor spacing of 1cm to 30cm, for real-time measurement of the vertical temperature distribution of the coolant.

[0025] Furthermore, the independent heat exchanger 16 is a shell-and-tube heat exchanger, with the shell-side fluid being liquid metal from inside the reactor, flowing from top to bottom, and the tube-side fluid being the heat exchange working fluid, flowing from bottom to top. The preheater 9 is installed inside the compressed gas preheating tank 10. The heat exchange medium of the second loop flows through its pipe side, and the compressed gas is in contact with its fin side. It is used to heat the compressed gas using the residual heat of the reactor core.

[0026] Furthermore, the heat exchange medium filled in the second loop is selected from one of water, supercritical carbon dioxide, lead, bismuth, lead-bismuth alloy, or sodium.

[0027] Furthermore, the gas in the compressed gas storage tank 1 is selected from air, carbon dioxide, or nitrogen.

[0028] Furthermore, the pressure range of the compressed gas storage tank 1 is 5~20MPa; the working pressure range of the compressed gas preheating storage tank 10 is 7~25MPa.

[0029] Furthermore, the cooler 11 is installed inside the air-cooled tower 12 to cool the heat exchange medium of the second loop using natural atmospheric convection.

[0030] In another embodiment, a method for eliminating thermal stratification in a pool-type reactor based on compressed gas specifically includes the following steps: S1. Under the condition of a complete power outage, the temperature gradient inside the pool reactor is monitored in real time through the temperature sensor array 14. S2. When the temperature gradient is detected to be greater than 2K / cm, it is determined that thermal stratification has occurred. The controller 7 opens the first pneumatic valve 2 and the second pneumatic valve 3, so that the gas in the compressed gas storage tank 1 enters the compressed gas preheating storage tank 10. S3. The compressed gas absorbs the residual heat of the reactor core and expands and increases in pressure in the preheating tank through the preheater 9. When the pressure rises to 1.5 times the initial pressure, the controller 7 opens the third pneumatic valve 4. S4. High-temperature and high-pressure gas enters the first turbine 5 and the second turbine 6 and expands to do work, driving the circulation pump 8 and the main pump 15 respectively. The main pump 15 converts the natural circulation in the pool into forced convection circulation to eliminate thermal stratification. The circulation pump 8 increases the flow rate of the second loop to match the heat dissipation demand. S5. When the temperature gradient recovers to less than 2K / cm, the controller 7 controls the third pneumatic valve 4 to slowly close at a rate of 1% / min of the total opening, so that the system smoothly transitions from forced circulation back to natural circulation.

[0031] In summary, compared to traditional passive residual heat removal systems, by monitoring the temperature of the coolant in a pool-type liquid metal nuclear reactor during an emergency shutdown, and promptly injecting compressed gas to drive the main pump 15 when thermal stratification occurs in the pool-type coolant, the disturbance and mixing of the coolant in the pool-type reactor are enhanced, the temperature gradient of thermal stratification is reduced, thereby reducing the thermal fatigue of the equipment and maintaining the intensity of passive residual heat removal, thus improving the structural safety of the reactor.

[0032] In this invention, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance; the term "multiple" refers to two or more unless otherwise explicitly defined. The terms "installation," "connection," "linking," and "fixing," etc., should be interpreted broadly. For example, "connection" can be a fixed connection, a detachable connection, or an integral connection; "linking" can be a direct connection or an indirect connection through an intermediate medium. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0033] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A device for eliminating thermal stratification in a pool-type reactor based on compressed gas, characterized in that, include: The independent heat exchanger (16), steam generator (18), reactor core (19), core shielding layer (17), main pump (15) and temperature sensor array (14) are installed in the pool-type reactor vessel (13). Compressed gas storage tank (1), compressed gas preheating storage tank (10), preheater (9), pneumatic valve assembly, turbine assembly, circulating pump (8), cooler (11) and air-cooled tower (12) are located outside the pool-type stack container (13). The shell side of the independent heat exchanger (16) is connected to the reactor core (19) to form a first loop, and the tube side of the independent heat exchanger (16) is sequentially connected to the tube side of the circulating pump (8), the preheater (9) and the cooler (11) to form a second loop. The pneumatic valve assembly includes a first pneumatic valve (2) and a second pneumatic valve (3) connected between the compressed gas storage tank (1) and the compressed gas preheating storage tank (10), and a third pneumatic valve (4) connected to the outlet end of the compressed gas preheating storage tank (10). The turbine assembly includes a first turbine (5) and a second turbine (6), the first turbine (5) being drivenly connected to the circulating pump (8), and the second turbine (6) being drivenly connected to the main pump (15). The outlet of the third pneumatic valve (4) is connected to the inlet of the first turbine (5) and the second turbine (6); The controller (7) is electrically connected to the temperature sensor array (14) and each pneumatic valve. The controller (7) is configured to control the pneumatic valve assembly to open when the temperature gradient detected by the temperature sensor array (14) exceeds a preset threshold, so as to use compressed gas to drive the turbine assembly to do work and drive the main pump (15) and the circulating pump (8) to run.

2. The device for eliminating thermal stratification in a pool-type reactor based on compressed gas according to claim 1, characterized in that, The temperature sensor array (14) is arranged at different depths within the pool reactor, with a sensor spacing of 1cm to 30cm, and is used to measure the vertical temperature distribution of the coolant in real time.

3. The device for eliminating thermal stratification in a pool-type reactor based on compressed gas according to claim 1, characterized in that, The independent heat exchanger (16) is a shell-and-tube heat exchanger. The fluid on the shell side is liquid metal inside the reactor, flowing from top to bottom, and the fluid on the tube side is the heat exchange medium, flowing from bottom to top. The preheater (9) is installed inside the compressed gas preheating tank (10). The heat exchange medium of the second loop flows through its pipe side, and the compressed gas is in contact with its fin side. It is used to heat the compressed gas using the residual heat of the reactor core.

4. The device for eliminating thermal stratification in a pool-type reactor based on compressed gas according to claim 1, characterized in that, The heat exchange medium filled in the second loop is selected from one of water, supercritical carbon dioxide, lead, bismuth, lead-bismuth alloy or sodium.

5. The device for eliminating thermal stratification in a pool-type reactor based on compressed gas according to claim 1, characterized in that, The gas in the compressed gas storage tank (1) is selected from air, carbon dioxide or nitrogen.

6. The device for eliminating thermal stratification in a pool-type reactor based on compressed gas according to claim 5, characterized in that, The pressure range of the compressed gas storage tank (1) is 5~20MPa; the working pressure range of the compressed gas preheating storage tank (10) is 7~25MPa.

7. The device for eliminating thermal stratification in a pool-type reactor based on compressed gas according to claim 1, characterized in that, The cooler (11) is installed inside the air-cooled tower (12) and uses natural atmospheric convection to cool the heat exchange medium of the second loop.

8. A method for thermal stratification in a reactor based on compressed gas elimination pools, applied to the apparatus for thermal stratification in a reactor based on compressed gas elimination pools as described in any one of claims 1-7, characterized in that, Specifically, the following steps are included: S1. Under the condition of a complete power outage, the temperature gradient inside the pool reactor is monitored in real time by the temperature sensor array (14). S2. When the temperature gradient is detected to be greater than 2K / cm, it is determined that thermal stratification has occurred. The controller (7) opens the first pneumatic valve (2) and the second pneumatic valve (3) to allow the gas in the compressed gas storage tank (1) to enter the compressed gas preheating storage tank (10). S3. The compressed gas absorbs the residual heat of the core and expands and increases in pressure in the preheating tank (10) through the preheater (9). When the pressure rises to 1.5 times the initial pressure, the controller (7) opens the third pneumatic valve (4). S4. High-temperature and high-pressure gas enters the first turbine (5) and the second turbine (6) to expand and do work, driving the circulation pump (8) and the main pump (15) respectively; the main pump (15) converts the natural circulation in the pool into forced convection circulation to eliminate thermal stratification; the circulation pump (8) increases the flow rate of the second loop to match the heat dissipation demand; S5. When the temperature gradient recovers to less than 2K / cm, the controller (7) controls the third pneumatic valve (4) to slowly close at a rate of 1% / min of the total opening, so that the system can smoothly transition from forced circulation back to natural circulation.

Images