A molten material retention and cooling system within a pressure vessel

Abstract

The utility model provides a kind of pressure vessel inside molten material retention cooling system, it is applied to nuclear power plant, pressure vessel inside molten material retention cooling system includes: containment, the bottom of containment has heap pit;Spent fuel pool, spent fuel pool installs heat exchanger device, the cold source of heat exchanger device is located outside containment;Pressure vessel, pressure vessel is located in heap pit;Water inlet pipe, the first end of water inlet pipe is communicated with spent fuel pool, the second end of water inlet pipe is communicated with heap pit, and switch piece is set on water inlet pipe;Exhaust pipe, the first end of exhaust pipe is communicated with heap pit, the second end of exhaust pipe is communicated with spent fuel pool, the above cooling system can combine active and passive working mode and effectively discharge residual heat of reactor core from containment, to reliably retain molten material in pressure vessel, while also simplifying the arrangement of cooling system, and safety and economy are considered.

Description

Technical Field

[0001] This utility model relates to the field of nuclear power technology, and in particular to a cooling system for retaining molten material inside a pressure vessel. Background Technology

[0002] In the safety design of nuclear power plants, sump water injection is typically used to remove residual core heat during severe accidents, thereby trapping molten material within the pressure vessel and preventing it from melting through and leaking into the containment. However, in compact small pressurized water reactors (SWPs), the design of systems for sump water injection, steam venting, and containment condensate collection faces significant challenges due to limited space. If residual core heat cannot be effectively removed in time after a severe accident through water injection, the pressure vessel may melt down, resulting in the release of large amounts of radioactive material into the environment.

[0003] In existing technologies, taking a certain third-generation reactor type as an example, external cooling technology for the pressure vessel is used to retain molten material. This scheme submerges the reactor pit with water from the internal refueling tank, completely immersing the lower half of the pressure vessel in cooling water. Water cooling continuously removes heat from the outer surface of the pressure vessel, effectively preventing molten core material from penetrating the lower end cap and migrating towards the containment. The system also has four steam venting channels. After an accident, cooling water enters from the bottom of the pit, generates steam upon contact with the high-temperature walls, rises through the venting channels to the containment, condenses, and then flows back into the pit, thus establishing a natural circulation. However, this molten material retention scheme still has the following drawbacks:

[0004] 1) The heat has not been removed from the containment and a containment heat removal system is still needed to remove the heat.

[0005] 2) The water level in the refill water tank must be maintained, and a condensate return tank must be installed at a high level, which places high demands on the layout.

[0006] 3) When heat is removed, the water level needs to be high to ensure that the heat is successfully removed from the pile pit, and the required water volume is also high.

[0007] Therefore, there is an urgent need to develop a more reliable molten material retention and cooling system that can ensure the core molten material is always contained within the pressure vessel, while taking into account both the safety and economy of nuclear power plants. Utility Model Content

[0008] The purpose of this invention is to provide a pressure vessel molten material retention and cooling system that offers higher reliability, better safety, and better economy.

[0009] To achieve the above objectives, this utility model provides a molten material retention and cooling system for pressure vessels, applicable to nuclear power plants. The molten material retention and cooling system for pressure vessels includes:

[0010] A containment vessel, the bottom of which has a stacking pit;

[0011] A spent fuel water tank, wherein a heat exchanger device is installed in the spent fuel water tank, and the cold source of the heat exchanger device is located outside the containment.

[0012] A pressure vessel located within the crater;

[0013] A water inlet pipe, the first end of which is connected to the spent fuel water pool, and the second end of which is connected to the stack pit, and a switch is provided on the water inlet pipe;

[0014] An exhaust pipe, the first end of which is connected to the pile pit, and the second end of which is connected to the spent fuel water pool.

[0015] In one embodiment of the present invention, the water inlet pipe is configured to allow cooling water in the spent fuel water pool to flow by gravity into the reactor pit.

[0016] Furthermore, in one embodiment of the present invention, the second end of the water inlet pipe is disposed near the bottom of the pile pit.

[0017] Furthermore, in one embodiment of the present invention, the first end of the exhaust pipe is disposed near the top of the pile pit.

[0018] In one embodiment of the present invention, the cooling system further includes an elevated water tank, which is connected to the spent fuel water pool, and the elevated water tank is configured such that the cooling water therein can flow by gravity into the spent fuel water pool.

[0019] In one embodiment of the present invention, the elevated water tank is located above the spent fuel water pool and is connected to the spent fuel water pool via a water supply pipe, and an isolation valve is provided on the water supply pipe.

[0020] In one embodiment of this utility model, the elevated water tank is located outside the containment structure.

[0021] In one embodiment of the present invention, the spent fuel water pool is located inside the containment. The heat exchanger device includes a heat exchanger, a cold water inlet pipe, and a return water pipe. The heat exchanger is installed inside the spent fuel water pool. One end of the cold water inlet pipe is connected to the inlet of the heat exchanger, and the other end extends outside the containment and is connected to the cold water source. One end of the return water pipe is connected to the outlet of the heat exchanger, and the other end is connected to the cold water source.

[0022] In one embodiment of the present invention, the spent fuel water pool is located outside the containment vessel and adjacent to it.

[0023] In one embodiment of this utility model, the switching element is a bursting membrane.

[0024] Compared with the prior art, the present invention has at least the following beneficial effects:

[0025] The spent fuel pool, crater, inlet pipe, and exhaust pipe equipped with heat exchangers form a passive circulation system that utilizes the gravity of water and the density difference between different forms of water to create a natural circulation system, combined with an active heat exchange system. This system not only removes residual core heat from the crater but also further discharges heat outside the containment vessel. This reliably ensures that the molten core material remains contained within the pressure vessel, preventing it from melting through the pressure vessel and entering the containment vessel, thus avoiding a serious accident that would release large amounts of radioactive material into the environment and improving the safety of the nuclear power plant.

[0026] Since the spent fuel pool heat exchanger is designed to remove decay heat from both the spent fuel pool and the entire reactor core, there is no need to increase the capacity of the heat exchanger due to the retention cooling system, thus avoiding increased costs. Furthermore, there is no need to install a high-level condensate return tank on the containment, which has stringent layout requirements. Because it forms a closed loop with the spent fuel pool containing the heat exchanger, it is not necessary to maintain an extremely high crater flooding level to ensure effective establishment and maintenance of the circulation, reducing the overall requirements for cooling water volume and taking into account economic efficiency.

[0027] Furthermore, even in the event of a power outage and when the heat exchanger cannot function properly, the aforementioned retention cooling system can still maintain a passive operating mode to cool the residual heat in the reactor core, preventing the molten core material from melting through the pressure vessel and entering the containment, thus further improving the reliability and safety of the retention cooling system. Attached Figure Description

[0028] The accompanying drawings, which are incorporated in and form part of this specification, illustrate embodiments consistent with this application and, together with the description, serve to explain the principles of this application. It is obvious that the drawings described below are merely some embodiments of this application, and those skilled in the art can obtain other drawings based on these drawings without any inventive effort.

[0029] In the attached diagram:

[0030] Figure 1 A schematic diagram of a molten material retention and cooling system in a pressure vessel according to an embodiment of the present invention;

[0031] The attached figures are labeled as follows:

[0032] 100. Reactor pit; 200. Spent fuel pool; 300. Heat exchanger unit; 310. Heat exchanger; 320. Cold water inlet pipe; 330. Return water pipe; 340. Pump; 400. Pressure vessel; 500. Inlet pipe; 510. Bursting membrane; 600. Exhaust pipe; 700. High-level water tank; 800. Make-up water pipe; 810. Isolation valve; 900. Reactor core. Detailed Implementation

[0033] The following specific examples illustrate the implementation of this utility model. Those skilled in the art can easily understand other advantages and effects of this utility model from the content disclosed in this specification. This utility model can also be implemented or applied through other different specific embodiments. Various details in this specification can also be modified or changed based on different viewpoints and applications without departing from the spirit of this utility model. In the absence of conflict, the following embodiments and features in the embodiments can be combined with each other.

[0034] It should be noted that the illustrations provided in the following embodiments are only schematic representations of the basic concept of the present invention. The drawings only show the components related to the present invention and are not drawn according to the actual number, shape and size of the components. In actual implementation, the form, quantity and proportion of each component can be arbitrarily changed, and the layout of the components may also be more complex.

[0035] In nuclear power plants, molten material retention cooling systems are effective emergency measures for severe accidents involving core meltdown. They prevent molten material from melting through the pressure vessel and leaking into the containment, thus preventing the release of large amounts of radioactive material into the environment. Existing technologies typically utilize refueling tanks, sump pits, steam venting channels, and elevated condensate return tanks within the containment to create a natural circulation between liquid water and steam to remove residual core heat. However, in compact small pressurized water reactors (SWPs), the design of systems for sump water injection, steam venting, and condensate collection within the containment faces significant challenges due to limited space. More importantly, these systems often fail to remove heat from the containment. This invention provides a more reliable molten material retention cooling system that balances economy and safety. Its principle involves establishing a passive-active heat removal path between the spent fuel pool (equipped with a heat exchanger) and the sump pit. The specific implementation method is as follows:

[0036] Please see Figure 1This utility model provides a molten material retention and cooling system for a pressure vessel 400, applicable to nuclear power plants. It includes: a containment vessel with a crater 100 at its bottom; a spent fuel pool 200 equipped with a heat exchanger 300, the cold source of which is located outside the containment vessel. In specific embodiments, the spent fuel pool 200 can be located inside or outside the containment vessel, and the cold source can be seawater, etc.; and a pressure vessel 400. 00 is located within the crater 100; a water inlet pipe 500, the first end of which is connected to the spent fuel water pool 200, and the second end of which is connected to the crater 100; a switch is provided on the water inlet pipe 500, which in a specific embodiment can be an isolation valve 810 or a rupture membrane 510; an exhaust pipe 600, the first end of which is connected to the crater 100, and the second end of which is connected to the spent fuel water pool 200.

[0037] When a core 900 meltdown accident occurs, the switch on the inlet pipe 500 switches to the open state. Cooling water in the spent fuel pool 200 enters the crater 100 through the inlet pipe 500 under the action of gravity, cooling the molten core 900 inside the lower head of the pressure vessel 400 to prevent it from melting through the pressure vessel 400 and entering the containment. The water in the crater 100 absorbs the heat from the molten core 900 and vaporizes into water vapor. The water vapor enters the spent fuel pool 200 through the exhaust pipe 600 and is condensed into liquid water by the pool water and the heat exchanger device 300. The heat exchanger device 300 also cools the water in the spent fuel pool 200. The above process is continuously cyclical, which can continuously and stably remove the heat from the molten core 900.

[0038] The above process combines a passive method of natural circulation using the gravity of water and the density difference of water in different forms with an active method of heat exchange using the heat exchanger 310 device. This not only removes the residual heat of the reactor core 900 from the crater 100, but also further discharges the heat outside the containment vessel. This reliably ensures that the molten material of the reactor core 900 is contained within the pressure vessel 400, preventing it from melting through the pressure vessel 400 and entering the containment vessel, thus preventing a serious accident that would release a large amount of radioactive material into the environment and improving the safety of the nuclear power plant.

[0039] Since the heat exchanger unit 300 of the spent fuel pool 200 is designed to remove the decay heat from the spent fuel pool and the decay heat from the entire reactor core 900, there is no need to increase the capacity of the heat exchanger unit 300 due to the retention cooling system, which means that the cost of the heat exchanger unit 300 will not increase. In addition, there is no need to set up a high-level condensate return tank on the containment with high layout requirements. Since it forms a closed loop with the spent fuel pool 200 containing the heat exchanger unit 300, it is not necessary to maintain an extremely high flood level in the reactor pit 100 to ensure the effective establishment and maintenance of the circulation, which reduces the overall requirements for the cooling water volume and takes into account economic efficiency.

[0040] Furthermore, even in the event of a power outage and when the heat exchanger unit 300 cannot function properly, the aforementioned retention cooling system can still maintain a passive operating mode to cool the residual heat of the reactor core 900, preventing the molten material from the reactor core 900 from melting through the pressure vessel 400 and entering the containment, thus further improving the reliability and safety of the retention cooling system.

[0041] Please see Figure 1 In one embodiment of this utility model, the water inlet pipe 500 is configured to allow the cooling water in the spent fuel water pool 200 to flow by gravity into the sump 100. The above structural design allows the cooling water in the spent fuel water pool 200 to enter the sump 100 without relying on power devices such as the pump 340 that require electricity. Even in the face of severe conditions such as a complete power outage, the system can still operate and has a faster response speed, so that sufficient flooding height can be quickly established before the lower end cap of the pressure vessel 400 is melted through. In a specific embodiment, in order to make it easier for the cooling water in the spent fuel water pool 200 to flow by gravity into the sump 100 and reduce the requirement for the water level height of the spent fuel water pool 200, the bottom of the spent fuel water pool 200 can be set higher than the bottom of the sump 100.

[0042] Please see Figure 1In one embodiment of this utility model, the second end of the water inlet pipe 500 is located near the bottom of the pile pit 100. If the second end of the water inlet pipe 500 is located in the middle or top of the pile pit 100, due to the high density of cold water, it will sink directly to the bottom, while the water at the bottom, heated by the high-temperature pressure vessel 400, will rise naturally. This will cause thermal stratification of the water in the pile pit 100: a high-temperature water layer at the bottom and a low-temperature water layer at the top. This thermal stratification will ensure that the lower end of the pressure vessel 400 is always surrounded by high-temperature fluid, which is extremely dangerous. Severely deteriorating the cooling conditions could lead to insufficient local cooling capacity and melt-through. However, by placing the cooling water inlet at the bottom of the crater 100, the low-temperature cooling water injected from the bottom will directly impact and scour the outer surface of the lower head of the pressure vessel 400. This upward jet will disrupt the tendency of thermal stratification, promote the mixing of water in the crater 100, and make the water temperature in the entire crater 100 more uniform. This ensures that the lower half of the pressure vessel 400, especially the weakest area of ​​the lower head, is always in contact with the low-temperature cooling water, thereby obtaining the most effective cooling.

[0043] Please see Figure 1 In one embodiment of the present invention, the first end of the exhaust pipe 600 is located near the top of the pile pit 100. The steam generated by heating in the pile pit 100 will naturally rise and accumulate at the top of the pile pit 100 due to the density difference. Therefore, by setting the inlet of the exhaust pipe 600 at the top of the pile pit 100, the generated steam can be captured and discharged in the most direct, smoothest and least resistant way, thereby ensuring the efficient operation of the natural circulation loop.

[0044] Please see Figure 1 In one embodiment of the present invention, the cooling system further includes an elevated water tank 700, which is connected to the spent fuel water pool 200. The elevated water tank 700 is configured such that the cooling water therein can flow by gravity into the spent fuel water pool 200. When the water in the spent fuel water pool 200 is insufficient, water can be replenished to the spent fuel water pool 200 through the elevated water tank 700 to maintain the water level and heat trap function of the spent fuel water pool 200 for a long time, thereby ensuring that the entire molten material retention cooling system can operate stably for a long time.

[0045] Please see Figure 1 In one embodiment of this utility model, the elevated water tank 700 is located above the spent fuel water pool 200 and is connected to the spent fuel water pool 200 through a water supply pipe 800. The position of the elevated water tank 700 provides a clear gravity head, ensuring that water supply can be achieved by gravity. An isolation valve 810 is provided on the water supply pipe 800. The isolation valve 810 is normally closed under normal operating conditions. When the water level of the spent fuel water pool 200 is detected to be below a set value, the isolation valve 810 is opened. In a specific embodiment, the isolation valve 810 can be a manual valve or an electric valve.

[0046] In one embodiment of the present invention, the elevated water tank 700 is located outside the containment vessel. This not only saves space inside the containment vessel, but more importantly, it allows operators to more easily add water to the elevated water tank 700 and open the isolation valve 810 more conveniently.

[0047] In one embodiment of this utility model, the spent fuel water pool 200 is located inside the containment vessel. The heat exchanger device 300 includes a heat exchanger 310, a cold water inlet pipe 500, and a return water pipe 330. The heat exchanger 310 is installed inside the spent fuel water pool 200. One end of the cold water inlet pipe 500 is connected to the inlet of the heat exchanger 310, and the other end extends outside the containment vessel and is connected to the cold water source. In a specific embodiment, in order to ensure that cooling water enters the heat exchanger 310 at high speed and reliably, a power pump 340 can be installed on the cold water inlet pipe 500. One end of the return water pipe 330 is connected to the outlet of the heat exchanger 310, and the other end is connected to the cold water source.

[0048] The above structural design constitutes a complete, closed, and efficient thermal management system that can ultimately exhaust heat outside the containment, enabling the cooling system to not only start efficiently in the early stages of an accident, but also to provide long-term, controllable cooling protection.

[0049] In one embodiment of this utility model, the spent fuel water tank 200 is located outside and adjacent to the containment. Placing the spent fuel water tank 200 outside the containment can further save space in the containment. At the same time, the spent fuel tank located outside the containment is easier for personnel to access during normal operation and after an accident, so as to carry out monitoring and maintenance work. In addition, since the spent fuel water tank 200 itself is located outside the containment, the connection between the cold water inlet pipe 500 and the return pipe 330 and the cold water source is more direct and convenient, without having to pass through the containment. The spent fuel water tank 200 is located adjacent to the containment to make the inlet pipe 500 and the exhaust pipe 600 as short as possible, reduce flow resistance, and facilitate the establishment of natural circulation.

[0050] In one embodiment of this utility model, the switching component is a rupture membrane 510. Given that a core meltdown at 900 MW is an extremely severe accident, the molten material retention cooling system only needs to perform its safety function once to achieve its design purpose. Compared to the reusable but complex isolation valve 810, which requires significant installation space, the rupture membrane 510, as a disposable component, has significant advantages such as simple structure, high reliability, and convenient installation. Therefore, the rupture membrane 510 is more suitable for the operating characteristics and safety requirements of this cooling system.

[0051] The above embodiments are merely illustrative of the principles and effects of this utility model and are not intended to limit the scope of this utility model. Any person skilled in the art can modify or alter the above embodiments without departing from the spirit and scope of this utility model. Therefore, all equivalent modifications or alterations made by those skilled in the art without departing from the spirit and technical concept disclosed in this utility model should still be covered by the claims of this utility model.

Claims

1. A molten material retention and cooling system for pressure vessels, applied in nuclear power plants, characterized in that, include: A containment vessel, the bottom of which has a stacking pit; A spent fuel water tank, wherein a heat exchanger device is installed in the spent fuel water tank, and the cold source of the heat exchanger device is located outside the containment. A pressure vessel located within the crater; A water inlet pipe, the first end of which is connected to the spent fuel water pool, and the second end of which is connected to the stack pit, and a switch is provided on the water inlet pipe; An exhaust pipe, the first end of which is connected to the pile pit, and the second end of which is connected to the spent fuel water pool.

2. The molten material retention and cooling system in a pressure vessel according to claim 1, characterized in that, The inlet pipe is configured to allow cooling water in the spent fuel pool to flow by gravity into the reactor pit.

3. The molten material retention and cooling system in a pressure vessel according to claim 2, characterized in that, The second end of the water inlet pipe is located near the bottom of the pile pit.

4. The molten material retention and cooling system in a pressure vessel according to claim 2, characterized in that, The first end of the exhaust pipe is positioned near the top of the crater.

5. The molten material retention and cooling system in a pressure vessel according to claim 1, characterized in that, It also includes an elevated water tank connected to the spent fuel pool, wherein the elevated water tank is configured such that cooling water therein can flow by gravity into the spent fuel pool.

6. The molten material retention and cooling system in a pressure vessel according to claim 5, characterized in that, The elevated water tank is located above the spent fuel water pool and is connected to the spent fuel water pool via a water supply pipe, which is equipped with an isolation valve.

7. The pressure vessel molten material retention and cooling system according to claim 5, characterized in that, The elevated water tank is located outside the containment structure.

8. The molten material retention and cooling system in a pressure vessel according to claim 1, characterized in that, The spent fuel water pool is located inside the containment. The heat exchanger device includes a heat exchanger, a cold water inlet pipe, and a return water pipe. The heat exchanger is installed inside the spent fuel water pool. One end of the cold water inlet pipe is connected to the inlet of the heat exchanger, and the other end extends outside the containment and is connected to a cold water source. One end of the return water pipe is connected to the outlet of the heat exchanger, and the other end is connected to the cold water source.

9. The molten material retention and cooling system in a pressure vessel according to claim 1, characterized in that, The spent fuel water pool is located outside and adjacent to the containment.

10. The molten material retention and cooling system in a pressure vessel according to claim 1, characterized in that, The switching element is a rupture membrane.

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