A safety system for a nuclear power plant containment built-in spent fuel pool

Abstract

The utility model relates to a nuclear power plant safety technical field especially relates to a kind of safety system of nuclear power plant containment built-in spent fuel pool, including closed containment, the spent fuel pool being placed in containment, spent fuel pool, stack cavity, pressure vessel, reactor core and the spent fuel water storage pool of being located outside containment;Spent fuel pool and spent fuel water storage pool are communicated with the spent fuel pool water replenishment pipe of water replenishment to spent fuel pool, and the water level of spent fuel water storage pool is higher than the spent fuel height in spent fuel pool;Spent fuel pool and stack cavity are communicated with at least two water injection pipes of water injection to spent fuel pool, and first safety valve is set on each water injection pipe;Containment inner wall lower part is equipped with water guide groove, for collecting containment inner wall condensate and backflow to spent fuel pool by gravity;The system provided by the utility model can realize long-term collaborative cooling and safety of pressure vessel, spent fuel pool built-in containment and containment body.

Description

Technical Field

[0001] This utility model relates to the field of nuclear power plant safety technology, and in particular to a safety system for a spent fuel pool built into the containment vessel of a nuclear power plant. Background Technology

[0002] Nuclear power plants are crucial energy facilities for achieving "dual carbon" goals, with small nuclear power plants attracting particular attention due to their compact layout and lower costs. These plants typically place the spent fuel pool (SFP) inside the containment vessel to optimize space utilization. However, this layout faces unique challenges in severe accidents: maintaining the integrity of the pressure vessel is essential to prevent molten material from breaching the containment vessel during a core meltdown; loss of cooling in the spent fuel pool could lead to fuel exposure and melting; and increased temperature and pressure within the containment vessel could exceed its capacity limits, potentially causing radioactive leaks. Utility Model Content

[0003] This invention provides a safety system for a spent fuel pool built into the containment vessel of a nuclear power plant. This system can achieve long-term coordinated cooling and safety of the pressure vessel, the spent fuel pool built into the containment vessel, and the containment body through passive principles.

[0004] This utility model provides a safety system for a spent fuel pool built into the containment vessel of a nuclear power plant, comprising:

[0005] The enclosure includes a spent fuel water pool and reactor cavity within the enclosure, a pressure vessel within the reactor cavity, a reactor core within the pressure vessel, and a refueling water storage pool outside the enclosure.

[0006] The spent fuel water tank and the refueling water storage tank are connected by a water supply pipe that supplies water to the spent fuel water tank by gravity. The water level in the refueling water storage tank is higher than the height of the spent fuel in the spent fuel water tank.

[0007] The spent fuel pool is connected to the reactor core by at least two water injection pipes that inject water into the spent fuel pool by gravity. Each water injection pipe is equipped with a first safety valve, which is configured to be remotely controlled by human or to open automatically when the reactor core temperature reaches a threshold.

[0008] The lower part of the inner wall of the containment is provided with a water inlet trough for collecting condensate water from the inner wall of the containment and allowing it to flow back to the spent fuel water pool by gravity.

[0009] In one embodiment of this utility model, at least two water supply pipes are provided, and each water supply pipe is provided with a second safety valve. The second safety valve is configured to be able to open automatically when manually controlled or when the core temperature reaches a threshold.

[0010] In one embodiment of the present invention, the bottom height of the refueling water storage tank is higher than the bottom height of the spent fuel water tank, and the bottom height of the spent fuel water tank is higher than the height of the reactor cavity.

[0011] In one embodiment of the present invention, the water inlet trough is annular in shape surrounding the inner wall of the containment vessel, and the outlet of the water inlet trough is suspended above the liquid surface of the spent fuel water pool.

[0012] In one embodiment of the present invention, the height of the water intake trough near the spent fuel pool is lower than or equal to the height away from the spent fuel pool.

[0013] In one embodiment of the present invention, the bottom of the stack cavity is a closed structure, and the upper part of the stack cavity is connected to the cavity inside the containment wall.

[0014] In one embodiment of this utility model, the containment shell is made of a metallic material.

[0015] In one embodiment of this utility model, the water supply pipe is provided with a one-way valve that leads to the spent fuel water tank.

[0016] In one embodiment of this utility model, the entire length of the water supply pipe exhibits a monotonically descending trend.

[0017] In one embodiment of this utility model, the top of the safety shell is arc-shaped or spherical.

[0018] The beneficial effects of this utility model are as follows: The safety system for a spent fuel pool built into the containment of a nuclear power plant proposed in this utility model can ensure the integrity of the pressure vessel, spent fuel pool, and containment under severe accidents. The system is based on passive operation and does not require external power or energy, thus ensuring high reliability. The system contains fewer devices and has a simple structure. It does not require additional water tanks or subsystems, so the cost is low and it does not add any burden to the layout inside the containment. The refueling water storage pool of this system is located outside the containment, so it can be flexibly filled with water to ensure long-term replenishment of the spent fuel pool. Attached Figure Description

[0019] 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.

[0020] In the attached diagram: Figure 1 This is a schematic diagram of the safety system structure of the spent fuel pool inside the containment vessel of a nuclear power plant, provided as an embodiment of the present invention.

[0021] The attached diagram is labeled as follows: 1. Containment vessel; 2. Spent fuel pool; 3. Reactor cavity; 4. Pressure vessel; 5. Reactor core; 6. Refueling water storage pool; 7. Make-up water pipe; 71. Second safety valve; 8. Injection pipe; 81. First safety valve; 9. Water inlet; 10. Spent fuel. Detailed Implementation

[0022] 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.

[0023] 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.

[0024] In the following description, numerous details are explored to provide a more thorough explanation of embodiments of the present invention. However, it will be apparent to those skilled in the art that embodiments of the present invention may be practiced without these specific details. In other embodiments, well-known structures and devices are shown in block diagram form rather than in detail to avoid obscuring embodiments of the present invention.

[0025] To ensure the safe development of nuclear power, it is essential to ensure that even in the event of a core 5 meltdown (a severe accident), the safety system of the spent fuel pool within the containment vessel can prevent the large-scale release of radioactive materials into the environment. Furthermore, based on the experience of the Fukushima nuclear accident, in addition to ensuring the safety of core 5, it is also crucial to ensure the safety of spent fuel 10. Core 5 is located within pressure vessel 4. In the event of a severe accident, if the molten core 5 remains within pressure vessel 4, it will not come into contact with and melt through the bottom of containment vessel 1, thus preventing the release of radioactive materials. Moreover, the decay heat of core 5 will continuously transfer to the atmospheric space within containment vessel 1, causing atmospheric temperature and pressure increases. If this exceeds the containment vessel 1's capacity, it will fail, resulting in a large-scale direct release of radioactive materials into the environment. Therefore, continuous cooling of containment vessel 1 is necessary to prevent its failure. During normal operation, the water level in spent fuel pool 2 will submerge spent fuel 10, while its own circulating cooling system will maintain the water temperature. However, in the event of a severe accident, spent fuel pool 2 typically loses its cooling capacity. The decay heat of spent fuel 10 causes the water temperature to gradually rise until it boils and evaporates. Once spent fuel 10 is exposed to air, its temperature rises rapidly, eventually causing the fuel to melt. Therefore, it is necessary to continuously replenish water to spent fuel pool 2 to ensure that spent fuel 10 remains submerged.

[0026] Existing safety systems are mostly designed for traditional large-scale nuclear power plants, and their shortcomings are mainly reflected in two aspects:

[0027] Functional limitations: Most solutions do not cover the cooling requirements of the spent fuel water pool 2 inside the containment 1, and only focus on the single-target protection of the pressure vessel 4 or containment 1;

[0028] Reliability risks: Systems that rely on active equipment (such as pumps) may be paralyzed when the power supply fails, while solutions that combine active and passive equipment increase the difficulty and cost of deployment due to the complexity of the equipment.

[0029] For compact layout and ease of fuel loading and unloading, some small nuclear power plants place the spent fuel pool 2 inside the containment vessel 1. For such small nuclear power plants, this invention designs a system that simultaneously ensures long-term cooling of the pressure vessel 4, spent fuel pool 2, and containment vessel 1 under accident conditions. This system is based on a passive safety concept and has high reliability.

[0030] It should be understood that although this case is based on the passive concept, active solutions can also be combined with the solution in this case. That is, it is also possible to add active cooling solutions for containment 1, spent fuel 10, spent fuel pool 2, core 5, and reactor cavity 3 to the solution in this case. Therefore, the solution combining active and passive solutions is also within the scope of protection of this case.

[0031] This utility model provides a safety system for a spent fuel pool inside a nuclear power plant containment structure, including a closed containment structure 1, a spent fuel pool 2 and a reactor cavity 3 placed inside the containment structure 1, a pressure vessel 4 located in the reactor cavity 3, a reactor core 5 located in the pressure vessel 4, and a refueling water storage pool 6 located outside the containment structure 1.

[0032] The spent fuel water tank 2 and the refueling water storage tank 6 are connected by a water supply pipe 7 that supplies water to the spent fuel water tank 2 by gravity. The water level in the refueling water storage tank 6 is higher than the height of the spent fuel 10 in the spent fuel water tank 2.

[0033] At least two water injection pipes 8 are connected between the spent fuel water pool 2 and the reactor cavity 3, which inject water into the spent fuel water pool 2 by gravity. Each water injection pipe 8 is equipped with a first safety valve 81, which is configured to be remotely controlled by human or to open automatically when the core 5 temperature reaches a threshold.

[0034] The lower part of the inner wall of the containment vessel 1 is provided with a water inlet trough 9, which is used to collect condensate water from the inner wall of the containment vessel 1 and return it to the spent fuel water pool 2 by gravity.

[0035] It should be noted that the enclosed containment vessel 1 serves as the core protective barrier, and its sealing effectively prevents the leakage of radioactive materials. Its material can be reinforced concrete or steel, or other materials with high strength and radiation resistance, selected according to the design parameters and safety level of the nuclear power plant. The spent fuel pool 2 and reactor cavity 3, located within containment vessel 1, are key functional areas. They can be arranged adjacently to shorten the connection path, or spaced apart to accommodate the internal spatial layout of containment vessel 1. The spent fuel pool 2 stores spent fuel 10 assemblies, while reactor cavity 3 provides installation and operating space for pressure vessel 4. Pressure vessel 4, located in reactor cavity 3, houses reactor core 5 and maintains its operating environment. Pressure vessel 4 is made of high-temperature resistant and corrosion-resistant alloy materials. Reactor core 5, located in pressure vessel 4, is the core area where the nuclear reaction occurs. The refueling water storage pool 6, located outside containment vessel 1, serves as a water source reserve. It can be located on the ground next to containment vessel 1, or underground depending on site conditions, to save ground space and enhance the protective effect.

[0036] The makeup water pipe 7 between the spent fuel water tank 2 and the refueling water storage tank 6 is the key path for makeup water to the spent fuel water tank 2. It relies on gravity for makeup water and does not require additional power equipment. The direction of the makeup water pipe 7 can be set as a straight line according to the spatial layout inside and outside the containment 1, or it can avoid other equipment through a deflection structure. Its material can be stainless steel or corrosion-resistant alloy to cope with long-term contact with water and possible radiation environment. The water level in the refueling water storage tank 6 is higher than the height of the spent fuel 10 in the spent fuel water tank 2. This design ensures that the water flow can naturally cover the spent fuel 10 components during makeup water process, avoiding the exposure of the spent fuel 10 due to insufficient water level. A filter device can also be installed on the makeup water pipe 7 as needed to prevent impurities in the water from entering the spent fuel water tank 2 and affecting the storage safety of the spent fuel 10.

[0037] At least two water injection pipes 8 between the spent fuel pool 2 and the reactor cavity 3 form a redundant water replenishment channel. The setting of multiple water injection pipes 8 can avoid the complete loss of water replenishment function when a single pipe fails, thus improving system reliability. The water injection pipes 8 can be arranged in parallel or connected to the spent fuel pool 2 and the reactor cavity 3 along different paths. Their material is similar to that of the water replenishment pipe 7, and they have good mechanical properties and corrosion resistance. The first safety valve 81 on each water injection pipe 8 is a key component for controlling water flow. It can be remotely controlled by the operator and is suitable for scenarios where the operator actively intervenes according to the accident situation. It can also be automatically opened when the core 5 temperature reaches a threshold. The threshold here can be obtained by temperature monitoring elements such as thermocouples installed in the core 5. For example, it can be triggered when the core 5 temperature reaches a preset value such as 700°C or 800°C. The valve type can be a temperature fuse valve or a mechanical trigger valve, which can operate without external power, to ensure normal operation even when the power fails.

[0038] The water inlet trough 9 at the lower part of the inner wall of containment 1 is used to collect condensate inside containment 1. The water inlet trough 9 can be set as a ring structure along the inner wall of containment 1 to ensure comprehensive collection of condensate, or it can be set as a segmented trough according to the distribution of condensate on the inner wall. Its material is compatible with the inner wall of containment 1, such as stainless steel to avoid corrosion. The condensate flows back to spent fuel pool 2 through the water inlet trough 9 by gravity. This process does not require additional power and makes full use of natural phenomena to achieve water resource recycling. The water inlet trough 9 can also be set with a certain slope to accelerate the flow of condensate to spent fuel pool 2, or connected to a diversion pipe to further guide the water flow and ensure efficient return of condensate.

[0039] The principle behind this safety system's solution to technical problems lies in its approach to addressing the multiple challenges faced by the spent fuel pool 2 within the containment vessel 1 of a small nuclear power plant under severe accident conditions. Instead of relying on active equipment, it integrates multiple passive structures to achieve comprehensive protection. By setting up a gravity water supply pipe 7 between the refueling water storage pool 6 and the spent fuel water pool 2, water is naturally supplied to the spent fuel water pool 2 using the water level difference, preventing the spent fuel 10 from being exposed due to loss of cooling. With the help of the gravity water injection pipe 8 and controllable valve between the spent fuel water pool 2 and the reactor cavity 3, water is injected into the spent fuel water pool 2 during an accident. At the same time, the water in the reactor cavity 3 can also indirectly assist in cooling the pressure vessel 4, preventing the molten material from melting through. The water inlet trough 9 on the inner wall of the containment vessel 1 collects condensate and returns it to the spent fuel water pool 2, which not only replenishes the water volume but also reduces the water vapor content in the containment vessel 1, helping to alleviate the temperature and pressure rise trend in the containment vessel 1. The coordinated action of multiple structures simultaneously covers the safety requirements of the pressure vessel 4, the spent fuel water pool 2, and the containment vessel 1, and all functions are achieved through passive methods such as gravity and natural condensation, avoiding the risk of paralysis of active equipment in the event of power failure.

[0040] The system achieves significant technical benefits. On the one hand, it effectively addresses the limitations of existing safety systems by providing simultaneous protection for pressure vessel 4, spent fuel pool 2, and containment 1 through a single system, eliminating the need for separate protection systems for different targets and improving system integration. On the other hand, its completely passive design eliminates reliance on active equipment such as pumps, reducing layout complexity and costs, while avoiding reliability risks associated with power failures. This makes it particularly suitable for scenarios with limited internal space in containment 1 of small nuclear power plants. Furthermore, the redundant design of at least two water injection pipes 8 and the recycling of condensate in the water inlet trough 9 further enhance the system's reliability and economy, ensuring the long-term safety of critical facilities under severe accidents and providing reliable safety assurance for nuclear power plants.

[0041] As an optional embodiment of this case, at least two water supply pipes 7 are provided, and each water supply pipe 7 is provided with a second safety valve 71. The second safety valve 71 is configured to be able to be opened automatically when the core 5 temperature reaches a threshold or when it is manually controlled.

[0042] It should be noted that at least two makeup water pipes 7 are installed. This multi-pipe design is to improve system reliability through redundancy and prevent the spent fuel pool 2 from losing its makeup water source in the event of a single pipe failure due to blockage, rupture, or other unexpected situations. These makeup water pipes 7 can be laid in parallel or connected to the refueling water storage pool 6 and the spent fuel pool 2 along different paths to reduce mutual interference and the impact of failures. The second safety valve 71 on each makeup water pipe 7 is a key component for controlling the opening and closing of the makeup water path. It can be manually controlled, either by operators in the control room via a remote control system or by on-site personnel. At the same time, when the core 5 temperature reaches a preset threshold, the second safety valve 71 can automatically open. This temperature threshold can be transmitted in real time by the temperature monitoring device inside the core 5. The automatic triggering mechanism of the valve can adopt a mechanical structure driven by a temperature-sensitive element or an automatic control method combined with electronic sensors to ensure a rapid response in the event of an accident.

[0043] As an optional embodiment of this case, the bottom height of the refueling water storage tank 6 is higher than the bottom height of the spent fuel water tank 2, and the bottom height of the spent fuel water tank 2 is higher than the height of the reactor cavity 3.

[0044] It should be noted that the bottom height of the refueling water storage tank 6 is higher than that of the spent fuel water tank 2, while the bottom height of the spent fuel water tank 2 is higher than that of the reactor cavity 3. This stepped height arrangement is to fully utilize gravity, allowing water to flow naturally from the refueling water storage tank 6 to the spent fuel water tank 2, and from the spent fuel water tank 2 to the reactor cavity 3 when needed, without relying on pumps or other active equipment, thus reducing the demand for external power. The height difference between the refueling water storage tank 6 and the spent fuel water tank 2 can be achieved by setting concrete foundations of different heights during foundation construction, or by utilizing the natural slope of the site. The height difference between the spent fuel water tank 2 and the reactor cavity 3 can be achieved by adjusting the installation depth of the reactor cavity 3 or raising the bottom of the spent fuel water tank 2. In addition, to optimize the water flow path, guide slopes or curved transition structures can be set at the connection points of various facilities to reduce water flow resistance.

[0045] Meanwhile, gravity-driven water flow is more stable and reliable, unaffected by mechanical failures, and can continue to function in long-term accidents, effectively preventing the risk of spent fuel 10 being exposed and the core 5 melt piercing the pressure vessel 4. In addition, this design simplifies the overall structure of the system, reduces the complexity of pipeline connections, lowers the difficulty of layout, and further improves the integration and reliability of the safety system.

[0046] As an optional embodiment of this case, the water inlet trough 9 is annular in shape surrounding the inner wall of the containment vessel 1, and the outlet of the water inlet trough 9 is suspended above the liquid surface of the spent fuel water tank 2.

[0047] It should be noted that the water inlet trough 9 adopts a ring shape surrounding the inner wall of the containment vessel 1. This structural design can form a complete collection ring along the inner wall of the containment vessel 1, ensuring that condensate can be effectively collected regardless of where it forms, avoiding water loss due to local leakage. The annular water inlet trough 9 can be a continuous, uninterrupted integral structure, or it can be spliced ​​from multiple arc-shaped trough sections. The joints are connected by seals to prevent leakage. Its material can be stainless steel or corrosion-resistant alloy compatible with the inner wall of the containment vessel 1, ensuring both structural strength and resistance to rust during long-term use. The outlet of the water inlet trough 9 is suspended above the liquid surface of the spent fuel water tank 2, that is, the outlet is kept at a certain distance from the water surface in the spent fuel water tank 2 and is not directly inserted into the water. This setting can prevent the outlet from being blocked by impurities in the water, and at the same time, it allows the water to come into contact with air during the fall, which can enhance the cooling effect to a certain extent. The outlet can be a straight pipe, or a guide plate can be installed at the end to disperse the water flow and avoid excessive local impact.

[0048] The annular water intake channel 9, by fully covering the inner wall of containment 1, maximizes the collection range of condensate, solving the problem of incomplete collection in localized water intake channels 9. The suspended outlet design utilizes gravity to allow condensate to drip naturally into the spent fuel pool 2, eliminating the need for additional diversion pipes, reducing the risk of blockage, and maintaining unobstructed water flow. This further enhances the system's cooling capacity for the spent fuel pool 2, making it particularly suitable for small nuclear power plants with high requirements for space utilization and reliability.

[0049] As an optional embodiment of this case, the height of the water inlet trough 9 near the spent fuel water tank 2 is lower than or equal to the height away from the spent fuel water tank 2.

[0050] It should be noted that the height of the water intake trough 9 near the spent fuel water tank 2 is lower than or equal to the height away from the spent fuel water tank 2. This height setting is to create a natural slope, guiding the condensate to flow towards the outlet and preventing water accumulation in the water intake trough 9. When the height near the spent fuel water tank 2 is lower than that away, a sloping slope can be formed. The slope can be set according to the length and material characteristics of the water intake trough 9, for example, by adjusting the installation angle of the trough. When the two heights are equal, the water flow can be guided to converge at the outlet through the micro-arc design at the bottom of the trough or the internal guide ribs. This design can be achieved by adjusting the height of the support when installing the water intake trough 9, or by directly molding the trough into a sloping structure during manufacturing. In terms of material, a smooth inner lining material can be used to reduce water flow resistance, effectively promote the flow of condensate in the water intake trough 9, avoid water accumulation, improve the condensate recovery efficiency, and ensure that the collected condensate can be replenished to the spent fuel water tank 2 in a timely manner. This reduces the risk of corrosion and blockage of the water intake trough 9 due to water accumulation, extends the service life of the equipment, and reduces maintenance costs.

[0051] As an optional embodiment of this case, the bottom of the stack cavity 3 is a closed structure, and the upper part of the stack cavity 3 is connected to the inner wall cavity of the containment 1.

[0052] It should be noted that the bottom of the reactor cavity 3 is a closed structure. This design effectively prevents the molten core 5 from leaking downwards, avoiding erosion of the bottom of the containment vessel 1. The closed structure can be a monolithically cast reinforced concrete base slab, fixed to the sidewall of the reactor cavity 3 by embedded parts; alternatively, a metal alloy plate of suitable thickness can be used, formed by welding or bolting to create a seal. The upper part of the reactor cavity 3 communicates with the inner cavity of the containment vessel 1. That is, the top of the reactor cavity 3 is not completely sealed, but is connected to the internal space of the containment vessel 1 through openings, grids, or ventilation channels. Protective nets or filter layers can be installed at the connection points to prevent large particles from entering the reactor cavity 3, while ensuring the flow of gas and steam. The bottom closed structure forms the first barrier, preventing molten material from penetrating the reactor cavity 3 and endangering the overall structure of containment 1. The upper part is connected to the cavity of containment 1, which utilizes the space inside containment 1 to achieve steam circulation. The high-temperature steam generated in the reactor cavity 3 can diffuse to containment 1 through the connection, reducing the risk of overheating and overpressure inside the reactor cavity 3. The temperature is reduced by the passive cooling mechanism of containment 1 (such as condensation on the inner wall), while balancing the pressure inside the reactor cavity 3 and containment 1 to avoid excessive local pressure, further improving safety under severe accident conditions.

[0053] As an optional embodiment of this case, the containment vessel 1 is made of a metallic material.

[0054] It should be noted that containment vessel 1 is made of metallic materials, which possess high strength, excellent sealing properties, and impact resistance, effectively resisting internal pressure increases and external impacts. Suitable metallic materials include low-carbon steel, welded to form a monolithic shell, with a surface coating for enhanced durability; nickel-based alloys can also be used, leveraging their high-temperature resistance and corrosion resistance to adapt to harsh environments. Metallic containment vessel 1 can be designed as a single-layer structure or employ a double-layer structure to improve structural strength. The high strength and sealing performance of metallic containment vessel 1 enhances leak resistance and reduces the risk of radioactive material leakage; its good thermal conductivity enhances the natural cooling effect of containment vessel 1, helping to control internal temperature and pressure; its compact structural design saves internal space, highly adaptable to the layout requirements of small nuclear power plants, while reducing construction complexity and manufacturing costs.

[0055] As an optional embodiment of this case, the water supply pipe 7 is provided with a one-way valve that leads to the spent fuel water tank 2.

[0056] It should be noted that the one-way valve installed on the water supply pipe 7 only allows water to flow from the refueling water storage tank 6 to the spent fuel water tank 2, preventing water in the spent fuel water tank 2 from flowing back into the refueling water storage tank 6, thus avoiding water source pollution or affecting the refueling water reserve. The one-way valve can be a spring-loaded structure, relying on spring force to close the valve and opening when the water pressure overcomes the spring force; alternatively, a gravity-type one-way valve can be used, achieving one-way sealing through the weight of the valve disc. The material of the one-way valve must be compatible with the water supply pipe 7, with corrosion-resistant stainless steel or ceramic valve cores being preferred to ensure long-term reliable operation.

[0057] As an optional embodiment of this case, the entire route of the water supply pipe 7 exhibits a monotonically descending trend.

[0058] It should be noted that the entire route of the water supply pipe 7 follows a monotonically descending trend, meaning that the entire pipeline path from the refueling water storage tank 6 to the spent fuel water tank 2 continuously decreases in elevation, with no ascending or horizontal sections. This ensures that the water flows naturally under gravity, requiring no additional power. This monotonically descending trend can be achieved by arranging the pipeline along a straight, inclined path, with the inclination angle adjusted according to the height difference between the two locations and the pipeline length; alternatively, a stepped descent can be used, connected by multiple inclined sections, each maintaining a descending trend, with smooth bends at the connections to reduce resistance. This monotonically descending path design improves water supply efficiency, ensuring that water from the refueling water storage tank 6 flows quickly and continuously into the spent fuel water tank 2; it avoids water stagnation within the pipeline, reducing blockages and corrosion caused by sedimentation, extending pipeline lifespan, and lowering maintenance costs; further enhancing the reliability and stability of the system.

[0059] As an optional embodiment of this case, the top of the containment shell 1 is arc-shaped or spherical.

[0060] It should be noted that the top of containment vessel 1 adopts an arc-shaped or spherical shell design. The arc-shaped top can be a single-curvature arc structure, for example, forming a continuous arc surface laterally or longitudinally along the top of containment vessel 1. The radius of curvature of the surface can be set according to the diameter and load-bearing requirements of containment vessel 1, and it connects smoothly to the sidewalls of containment vessel 1. The spherical shell top can use a partial sphere or a part of a complete sphere, forming a uniform curved surface with the center of the sphere as a reference. The connection between the spherical shell and the sidewalls can be achieved through tangential transitions or arc transitions, ensuring the integrity of the structure. Both types of tops can be made of the same metal material as the main body of containment vessel 1, manufactured through welding or integral molding processes to ensure a sealed connection with the sidewalls and avoid structural weak points. The curved or spherical top significantly enhances the structural strength and pressure resistance of containment 1, improves safety under extreme conditions, and reduces the risk of radioactive material leakage. The curved design promotes smooth flow of condensate and, in conjunction with the water inlet trough 9, improves the efficiency of water resource recycling. In addition, this top structure has a higher space utilization rate and is more suitable for the compact layout of small nuclear power plants compared to a flat top design. It also simplifies the connection process between the top and the sidewalls, reduces the risk of seal failure, and further improves the reliability of the system.

[0061] In this case, the reactor cavity 3 is a semi-enclosed space, with its upper part connected to the large space of the containment vessel 1 and its lower part closed; the spent fuel pool 2 is used to store spent fuel 10, which is submerged in water; the refueling water storage pool 6 contains a large amount of water during normal operation of the nuclear power plant to supply water for refueling the reactor core 5; the containment vessel 1 is the last barrier of the nuclear power plant and can exchange heat with the external atmospheric environment; after the water vapor inside the containment vessel 1 condenses on the steel containment vessel 1, it will flow downward along its wall. The return water device is a water inlet trough 9 arranged in a ring along the lower inner wall of the containment vessel 1, which relies on gravity to lead the return water back to the spent fuel pool 2 to achieve water circulation; the makeup water pipe 7 relies on gravity to use water from the refueling water storage pool 6 to make up for the spent fuel pool 2; the water injection pipe 8 relies on gravity to use water from the spent fuel pool 2 to inject water into the reactor cavity 3.

[0062] When the reactor core 5 melts in an accident, it is necessary to ensure that the molten core 5 remains inside the pressure vessel 4 to prevent it from contacting and melting through the bottom concrete of the containment vessel 1. This design uses a submerged reactor cavity 3 method, immersing the pressure vessel 4 in water to achieve continuous cooling. The water source for submerging the reactor cavity 3 comes from the spent fuel pool 2, with the outlet located at the bottom of the pool. Water from the pool enters the reactor cavity 3 from the bottom via gravity through the injection pipe 8. At this point, the spent fuel pool 2 and the reactor cavity 3 form a communicating vessel. After water evaporates from the containment vessel 1 and water from the pressure vessel 4 is sprayed onto the containment vessel 1, a large amount of water vapor will exist inside the containment vessel 1. The steel containment vessel 1 acts as a heat transfer medium, transferring heat from within the containment vessel 1 to the external atmosphere. The water vapor inside the containment vessel 1 condenses on the inner wall of the steel containment vessel 1 and then enters the spent fuel pool 2 through a return water system. When the water level in the spent fuel pool 2 drops due to the injection of water into the reactor cavity 3, it is necessary to replenish the spent fuel pool 2. The makeup water source is the refueling water storage pool 6 outside the containment 1. The water in the storage pool flows out from the bottom by gravity and enters the spent fuel water pool 2 from the bottom along the makeup water pipe 7 of the spent fuel pool 10. Since the spent fuel water pool 2 and the reactor cavity 3 form a communicating vessel, the water level in the reactor cavity 3 will continue to rise while the spent fuel water pool 2 is being makeup watered.

[0063] This invention pertains to a small nuclear power plant where the spent fuel pool 2 is integrated within the containment vessel 1. The invention achieves the following effects: 1) This system ensures the integrity of the pressure vessel 4, spent fuel pool 2, and containment vessel 1 under severe accident conditions. Based on passive system operation, it requires no external power source and is highly reliable; 2) This system contains fewer components and has a simple structure. It does not require additional tanks or subsystems, resulting in lower costs and no added burden on the containment vessel 1; 3) The refueling water storage pool 6 is located outside the containment vessel 1, allowing for flexible water injection to ensure long-term replenishment of the spent fuel pool 2.

[0064] 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 safety system for a spent fuel pool built into the containment vessel of a nuclear power plant, characterized in that... include: The enclosure includes a spent fuel water pool and reactor cavity within the enclosure, a pressure vessel within the reactor cavity, a reactor core within the pressure vessel, and a refueling water storage pool outside the enclosure. The spent fuel water tank and the refueling water storage tank are connected by a water supply pipe that supplies water to the spent fuel water tank by gravity. The water level in the refueling water storage tank is higher than the height of the spent fuel in the spent fuel water tank. The spent fuel pool is connected to the reactor core by at least two water injection pipes that inject water into the spent fuel pool by gravity. Each water injection pipe is equipped with a first safety valve, which is configured to be remotely controlled by human or to open automatically when the reactor core temperature reaches a threshold. The lower part of the inner wall of the containment is provided with a water inlet trough for collecting condensate water from the inner wall of the containment and allowing it to flow back to the spent fuel water pool by gravity.

2. The safety system for a spent fuel pool inside a nuclear power plant containment vessel according to claim 1, characterized in that, At least two water supply pipes are provided, and each water supply pipe is equipped with a second safety valve. The second safety valve is configured to be manually controlled or to open automatically when the core temperature reaches a threshold.

3. The safety system for a spent fuel pool inside a nuclear power plant containment vessel according to claim 1, characterized in that, The bottom height of the refueling water storage tank is higher than the bottom height of the spent fuel water tank, and the bottom height of the spent fuel water tank is higher than the height of the reactor cavity.

4. A safety system for a spent fuel pool inside a nuclear power plant containment vessel according to claim 1, characterized in that, The water intake channel is annular in shape, encircling the inner wall of the containment vessel, and the outlet of the water intake channel is suspended above the liquid surface of the spent fuel water pool.

5. The safety system for the spent fuel pool inside the containment vessel of a nuclear power plant according to claim 4, characterized in that, The height of the water intake channel near the spent fuel pool is lower than or equal to the height away from the spent fuel pool.

6. A safety system for a spent fuel pool inside a nuclear power plant containment vessel according to claim 1, characterized in that, The bottom of the reactor cavity is a closed structure, and the upper part of the reactor cavity is connected to the cavity inside the containment wall.

7. A safety system for a spent fuel pool inside a nuclear power plant containment vessel according to claim 1, characterized in that, The containment vessel is made of metallic material.

8. A safety system for a spent fuel pool inside a nuclear power plant containment vessel according to claim 1, characterized in that, The water supply pipe is equipped with a one-way valve that leads to the spent fuel water tank.

9. A safety system for a spent fuel pool inside a nuclear power plant containment vessel according to claim 1, characterized in that, The entire length of the water supply pipe exhibits a monotonically descending trend.

10. A safety system for a spent fuel pool inside a nuclear power plant containment vessel according to claim 1, characterized in that, The top of the containment structure is either arc-shaped or spherical.

Images