Phase change energy storage system applied to nuclear reactor containment passive accident mitigation

Abstract

The invention discloses a phase change energy storage system applied to nuclear reactor containment passive accident mitigation, and belongs to the technical field of nuclear reactor safety. The problems that in an existing nuclear reactor containment vessel accident relieving system, response of active equipment lags, and a traditional phase change energy storage device cannot adapt to material thermal expansion and cold contraction due to the fixed volume design, and leakage or failure is caused are solved. The phase change heat storage container is fixedly suspended near the inner wall of the containment along the containment in an array manner, and the variable volume structure is mounted at the upper end of the phase change heat storage container and is communicated with the phase change heat storage container. According to the invention, heat is efficiently stored based on the PCM passive characteristic, and the temperature and pressure peak values of the containment are weakened; the variable volume structure adapts to thermal expansion and cold contraction and balances the pressure difference; the heat exchange efficiency is enhanced; the device is compact in structure, easy to maintain and suitable for nuclear reactor transformation and new projects.

Description

Technical Field

[0001] The present invention relates to the field of nuclear reactor safety technology, and in particular to a phase change energy storage system used for mitigating passive accidents of nuclear reactor containment vessels. Background Art

[0002] During nuclear reactor operation, an accident that causes a sharp rise in temperature and pressure within the containment vessel could damage the containment's structural integrity and sealing, potentially leading to a release of radioactive material. Accident mitigation measures for the Hualong One nuclear power plant, a third-generation large pressurized water reactor, primarily rely on a passive containment cooling system and an active containment spray system or external auxiliary cooling system. However, these systems may not respond in a timely manner or may fail in extreme situations.

[0003] Phase change thermal storage media (PCM) undergo a phase change (e.g., from solid to liquid) during the heat absorption process, which is accompanied by a certain amount of heat absorption expansion, which can cause structural damage to the thermal storage system or reduce heat absorption efficiency. Existing phase change energy storage devices are typically fixed-volume structures and cannot effectively cope with the thermal expansion and contraction characteristics of PCM. This often leads to leakage or failure of the thermal storage medium during long-term operation. Therefore, developing a variable-volume heat absorption device that can adapt to the thermal expansion and contraction characteristics of PCM is of great significance for improving the safety of nuclear reactors.

[0004] After a nuclear reactor accident, the pressure within the containment vessel can fluctuate significantly. Therefore, it's important to consider the impact of this pressure change on the thermal storage system. According to the equilibrium theory of first-order phase transitions, for a given molar mass of a substance, its volume and phase transition temperature change with the pressure it is subjected to. Therefore, pressure changes within the containment vessel will induce volume changes in the PCM. This volume change, caused by changes in ambient pressure, can potentially cause structural fatigue in the thermal storage device. Therefore, the effective volume of the phase change thermal storage system should also vary with the volume change of the PCM.

[0005] Therefore, in summary, the current nuclear reactor containment accident mitigation technology has the following key defects:

[0006] Insufficient reliability of the active system: The hybrid design of passive cooling and active spray systems may lead to response delays or mechanical failures in extreme accidents (such as plant-wide power outages and multiple faults), making it impossible to promptly suppress sudden temperature and pressure increases in the containment, threatening structural integrity.

[0007] Design flaws in phase-change energy storage devices: Traditional fixed-volume phase-change heat storage devices cannot adapt to the thermal expansion during the PCM phase change (such as the volume expansion during solid-liquid phase change) and the additional volume changes caused by pressure fluctuations. Long-term operation can easily lead to container rupture, medium leakage, or structural fatigue, reducing heat storage efficiency and safety.

[0008] Lack of dynamic pressure adaptability: Pressure changes inside the containment directly affect the phase change temperature and volume of the PCM through phase equilibrium theory. Existing technologies lack a dynamic compensation mechanism for the pressure-volume coupling effect, further exacerbating the risk of device failure.

[0009] This field urgently needs to propose a technical solution to solve the above problems. Summary of the Invention

[0010] The present invention proposes a phase change energy storage system for passive accident mitigation of nuclear reactor containment. By rapidly absorbing heat within the containment after an accident and effectively absorbing the volume change characteristics of the phase change heat storage medium through a variable volume design, the heat absorption efficiency and operational stability of the heat storage device are improved. This solves the problems of delayed response of active equipment in existing nuclear reactor containment accident mitigation systems and leakage or failure caused by the inability of traditional phase change energy storage devices to adapt to thermal expansion and contraction of materials due to their fixed volume design.

[0011] A phase change energy storage system for passive accident mitigation of a nuclear reactor containment vessel comprises a containment vessel, a phase change heat storage container and a variable volume structure. The phase change heat storage container is fixedly suspended in an array-like manner near the inner wall of the containment vessel, and the variable volume structure is mounted on the phase change heat storage container and is in communication with the phase change heat storage container.

[0012] Furthermore, the phase change heat storage container is filled with a phase change heat storage medium, and a gas flow channel is provided in the phase change heat storage medium.

[0013] Furthermore, the phase change temperature of the phase change heat storage medium is not lower than the maximum temperature of the nuclear reactor containment under normal operating conditions, and the boiling point of the phase change heat storage medium is higher than the maximum temperature inside the containment under the extended design conditions of the nuclear reactor; the phase change heat storage medium is at least one of paraffin, composite salts or metal alloys, and the phase change heat storage medium remains liquid and does not vaporize during the phase change process.

[0014] Furthermore, the filling structure of the phase change heat storage medium includes a plate structure, a shell and tube structure and a packed bed structure.

[0015] Furthermore, the phase change heat storage container is also provided with an enhanced condensation heat exchange unit, which includes the wall of the phase change heat storage container, external fins and high thermal conductivity fins. The external fins and high thermal conductivity fins are respectively welded to the inner wall and outer wall of the phase change heat storage container.

[0016] Furthermore, the high thermal conductivity fins are embedded in the phase change heat storage medium and adopt foam metal or metal alloy porous medium; the surface of the outer fins is provided with micro-rib grooves for destroying the condensate film and promoting turbulence.

[0017] Furthermore, the maximum volume compensation amount of the variable volume structure satisfies the following relationship:

[0018] V≥ΔV T +ΔV P

[0019] Where, ΔV T is the volume change of the phase change heat storage medium caused by temperature change, ΔV P It is the volume change of the phase change heat storage medium caused by the pressure fluctuation in the containment, and the variable volume structure automatically balances the pressure difference inside and outside the phase change heat storage container through deformation.

[0020] Furthermore, the variable volume structure adopts a passive trigger mechanism to achieve volume compensation by reserving expansion space or integrating an elastic structure, and the integrated elastic structure is a bellows, an expansion joint, a diaphragm plate or an expansion box.

[0021] Furthermore, the response time of the system is less than 5 minutes, the heat storage capacity of a single phase change heat storage container is ≥5000MJ, and the total heat storage capacity of the system covers the heat release demand of the containment within 24 hours after the accident.

[0022] Furthermore, the system also includes a shell wall fixing bracket, and the phase change heat storage container is fixedly suspended near the inner wall of the containment vessel through the shell wall fixing bracket in an array manner.

[0023] Beneficial effects of the present invention: A phase change energy storage system for passive accident mitigation of a nuclear reactor containment vessel of the present invention, based on the passive characteristics of PCM, can efficiently absorb and store a large amount of heat in the containment vessel after a nuclear reactor accident during the phase change process, thereby reducing temperature and pressure peaks; the variable volume structure can effectively adapt to the thermal expansion and contraction characteristics of PCM, thereby avoiding damage or leakage of the device, while having a pressure regulation function, thereby ensuring stable operation of the device in extreme environments and balancing the internal and external pressure differences; the device can also automatically adjust its volume according to pressure changes in the containment vessel, thereby enhancing dynamic adaptability; in addition, its structure is compact, easy to install and maintain, and is suitable for the renovation of existing nuclear reactors and new construction projects. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 This is a schematic structural diagram of a phase change energy storage system for passive accident mitigation of a nuclear reactor containment vessel according to the present invention;

[0025] Figure 2 It is a schematic diagram of the working process of the variable volume structure;

[0026] Figure 3 is a schematic diagram of the basic structure of phase change heat storage medium. Figure 3 (a) is a phase change heat storage medium with a plate structure; Figure 3 (b) Phase change heat storage medium of shell and tube structure (filled in tube); Figure 3 (c) Phase change heat storage medium of shell and tube structure (filled outside the tube); Figure 3 (d) packed bed (spherical) phase change heat storage medium;

[0027] Figure 4 Schematic diagram of the variable volume structure before and after volume change;

[0028] Figure 5 This is a structural diagram of the enhanced condensation heat exchange unit.

[0029] Among them, 1 is the containment shell, 2 is the phase change heat storage container, 3 is the external fin, 4 is the high thermal conductivity fin, 5 is the wall of the phase change heat storage container, 6 is the variable volume structure, 11, 12, 13, and 14 are the filled phase change heat storage medium, and 21, 22, 23, and 24 are gas flow channels. DETAILED DESCRIPTION

[0030] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. All other embodiments obtained by ordinary technicians in this field based on the embodiments of the present invention without making any creative efforts shall fall within the scope of protection of the present invention.

[0031] Reference Figure 1 and Figure 2 As shown, a phase change energy storage system for passive accident mitigation of a nuclear reactor containment vessel comprises a containment vessel 1, a phase change heat storage container 2 and a variable volume structure 6. The phase change heat storage container 2 is fixedly suspended in an array along the containment vessel 1 near the inner wall of the containment vessel 1, and the variable volume structure 6 is mounted on the phase change heat storage container 2 and communicated with the phase change heat storage container 2.

[0032] Specifically, the present invention achieves efficient passive accident mitigation within the containment vessel through the coordinated design of an array layout and a variable volume structure 6. The phase-change heat storage vessels 2 are fixedly suspended in an array near the inner wall of the containment vessel 1. This layout fully utilizes the internal space of the containment vessel 1 while shortening the heat transfer path, enabling the system to rapidly respond to temperature changes under accident conditions. The array arrangement also increases the contact area between the phase-change heat storage medium and the high-temperature gas within the containment vessel 1, enhancing heat transfer efficiency and ensuring rapid absorption of large amounts of heat after an accident. The variable volume structure 6 is mounted on and connected to the upper end of the phase-change heat storage vessels 2, cleverly addressing the volumetric changes caused by thermal expansion and contraction of the phase-change heat storage medium. When the phase-change heat storage medium expands due to rising temperature, the variable volume structure 6 automatically expands to accommodate the increased volume, preventing safety hazards caused by excessive pressure within the phase-change heat storage vessel 2. Conversely, when the temperature decreases, the variable volume structure 6 contracts to maintain system stability. This passive pressure balancing mechanism requires no external energy source, ensuring system reliability and safety under accident conditions. Through this innovative design, the system can quickly and effectively absorb and store heat when a nuclear reactor accident occurs, alleviating the rise in temperature and pressure inside the containment vessel and buying valuable time for accident handling.

[0033] Furthermore, the phase-change heat storage container 2 is filled with a phase-change heat storage medium, and a gas flow channel is provided in the phase-change heat storage medium.

[0034] Specifically, the present invention achieves efficient transfer and storage of heat within the containment vessel 1 through the coordinated design of the phase change heat storage medium and the gas flow channel. The phase change heat storage medium filled in the phase change heat storage container 2 can absorb and store a large amount of heat through the phase change process after a nuclear reactor accident occurs, effectively reducing the temperature and pressure within the containment vessel 1. The gas flow channel provided in the phase change heat storage medium provides an efficient channel for heat transfer, so that the high-temperature gas in the containment vessel 1 can quickly exchange heat with the phase change heat storage medium, thereby enhancing the heat transfer process. This design not only improves the response speed of the system, ensuring that heat absorption begins within a short period of time after the accident, but also enhances the heat storage capacity of the phase change heat storage medium, enabling it to continue to function for a longer period of time. Through the guidance of the gas flow channel, the high-temperature gas can evenly contact the phase change heat storage medium, avoiding the occurrence of local overheating and ensuring the stability and reliability of the system.

[0035] Furthermore, the phase change temperature of the phase change thermal storage medium is not lower than the maximum temperature of the nuclear reactor containment under normal operating conditions, and the boiling point of the phase change thermal storage medium is higher than the maximum temperature within the containment under the nuclear reactor's designed extended operating conditions. The phase change thermal storage medium is at least one of paraffin wax, a composite salt, or a metal alloy, and the phase change thermal storage medium remains liquid and does not vaporize during the phase change process. For example, PCMs with suitable phase change temperatures can be selected from paraffin wax, polyethylene glycol, fatty acids, sugar alcohols, inorganic salts, metal alloys, composite materials, and the like.

[0036] Specifically, the present invention ensures the safe and efficient operation of the system under all operating conditions of the nuclear reactor by precisely controlling the thermal properties of the phase-change heat storage medium. The phase change temperature of the phase-change heat storage medium is not lower than the maximum temperature under normal operating conditions of the nuclear reactor containment vessel 1, so that the phase-change heat storage medium remains in a solid state during normal operation and does not participate in heat exchange, thereby avoiding interference with the normal operation of the reactor. When an accident occurs, when the temperature inside the containment vessel 1 rises to the phase change temperature of the phase-change heat storage medium, the phase-change heat storage medium rapidly undergoes a phase change, absorbs a large amount of heat, and effectively reduces the temperature and pressure inside the containment vessel 1. The boiling point of the phase-change heat storage medium is higher than the maximum temperature inside the containment vessel 1 under the extended operating conditions of the nuclear reactor design, and it remains liquid and does not vaporize during the phase change process. This characteristic ensures that the phase-change heat storage medium will not cause a sharp increase in pressure due to vaporization under extreme operating conditions, thereby avoiding the risk of overpressure accidents in the system. Phase-change heat storage media give priority to solid-liquid phase-change heat storage media with large phase change latent heat and small volume change;

[0037] Further, refer to Figure 3 As shown, the filling structure of the phase change heat storage medium includes a plate structure, a shell and tube structure and a packed bed structure.

[0038] Specifically, after an accident, the phase change heat storage medium absorbs the heat released by the nuclear reactor into the containment vessel 1, and while absorbing the heat, it undergoes a phase change itself, storing the heat inside the phase change heat storage medium; the phase change heat storage container 2 is made of high-temperature resistant, corrosion-resistant, and radiation-resistant materials, and is made of stainless steel, and is filled with phase change heat storage medium.

[0039] Further, refer to Figure 5 As shown, the phase change heat storage container 2 is also provided with an enhanced condensation heat exchange unit, which includes a phase change heat storage container wall 5, external fins 3 and high thermal conductivity fins 4. The external fins 3 and high thermal conductivity fins 4 are respectively welded to the inner wall and outer wall of the phase change heat storage container wall 5.

[0040] Specifically, the enhanced condensation heat exchange unit installed on the phase-change heat storage container 2 utilizes external fins 3 and high-thermal conductivity fins 4 to enhance the heat transfer performance inside and outside the phase-change heat storage container 2, respectively. The external fins 3 are welded to the outer wall of the phase-change heat storage container 2. The micro-rib groove design on their surface can destroy the condensate film, reduce thermal resistance, and promote turbulence formation, further enhancing convective heat transfer. The high-thermal conductivity fins 4 are embedded within the phase-change heat storage medium. They use foam metal or metal alloy porous media. The high porosity and high thermal conductivity of the medium significantly improve the heat conduction efficiency within the phase-change heat storage medium, allowing heat to be quickly transferred from the wall of the phase-change heat storage container 2 to the phase-change heat storage medium. This synergistic internal and external enhanced heat transfer design effectively shortens the system's response time and increases the heat storage rate of the phase-change heat storage medium, ensuring that after a nuclear reactor accident, the system can quickly absorb and store large amounts of heat, reducing the temperature and pressure within the containment vessel 1.

[0041] Furthermore, the high thermal conductivity fins 4 are embedded in the phase change heat storage medium and are made of foam metal or metal alloy porous medium; the surface of the outer fins 3 is provided with micro-rib grooves for destroying the condensate film and promoting turbulence.

[0042] Specifically, the present invention achieves directional enhancement of the heat transfer efficiency on both the inside and outside of the phase-change thermal storage medium through the refined design of the surface structure of the high-thermal-conductivity fins 4 and the outer fins 3. The high-thermal-conductivity fins 4 are embedded within the phase-change thermal storage medium and utilize a porous medium of foamed metal or metal alloy. Their unique three-dimensional pore structure significantly increases the contact area with the phase-change thermal storage medium. At the same time, the high thermal conductivity of the metal forms an efficient heat conduction channel, effectively compensating for the inherently low thermal conductivity of the phase-change thermal storage medium and accelerating the rate of heat transfer from the wall of the phase-change thermal storage container 2 to the interior of the phase-change thermal storage medium. The micro-rib grooves on the surface of the outer fins 3 target the condensation heat transfer characteristics of the gas side of the containment vessel 1. By disrupting the continuity of the condensate film and causing it to fall off quickly, they also induce turbulence, enhancing gas disturbances and reducing the thermal resistance at the gas-solid interface. This design not only improves the condensation heat transfer efficiency of high-temperature, humid gas on the outer wall of the phase-change thermal storage container 2, but also accelerates heat transfer to the phase-change thermal storage container 2 by enhancing convection. With the synergistic effect of the two, the system achieves full-process heat transfer enhancement of "gas-side condensation enhancement - wall heat conduction optimization - efficient material heat storage" in a passive mode without the need for external power, ensuring that the heat in the containment can be quickly absorbed and transferred after the accident.

[0043] Furthermore, the maximum volume compensation amount of the variable volume structure 6 satisfies the following relationship:

[0044] V≥ΔV T +ΔV P

[0045] Where, ΔV Tis the volume change of the phase change heat storage medium caused by temperature change, ΔV P It is the volume change of the phase change heat storage medium caused by the pressure fluctuation in the containment, and the variable volume structure 6 automatically balances the pressure difference between the inside and outside of the phase change heat storage container 2 through deformation.

[0046] Specifically, the present invention realizes the pressure self-balancing and volume adaptive control of the phase change energy storage system under extreme working conditions through the precise design of the variable volume structure 6. The maximum volume compensation amount of the variable volume structure 6 is calculated by the formula V≥ΔV T +ΔV P Carry out quantitative design to ensure that it can simultaneously accommodate the volume change ΔV of the phase change heat storage medium caused by temperature change T and the volume change ΔV caused by pressure fluctuations in the containment P This dual redundant design fundamentally avoids the risk of container rupture caused by thermal expansion and contraction or pressure shock in traditional energy storage systems. The variable volume structure 6 automatically balances the pressure difference between the inside and outside of the phase change heat storage container 2 through deformation. This passive triggering mechanism does not require external energy intervention and can achieve pressure regulation only by relying on the elastic properties of the material itself, ensuring that the system can still operate stably in the complex environment after the accident. This adaptive pressure balance mechanism not only improves the safety and reliability of the system, but also extends the service life of the equipment and reduces maintenance costs. Through this innovative design, the system can effectively respond to the volume changes and pressure fluctuations of the phase change heat storage medium when a nuclear reactor accident occurs, providing the containment vessel 1 with continuous and reliable heat absorption and storage functions, significantly improving the safety performance of the nuclear reactor.

[0047] Furthermore, the variable volume structure 6 adopts a passive trigger mechanism to achieve volume compensation by reserving expansion space or integrating an elastic structure, and the integrated elastic structure is a bellows, an expansion joint, a diaphragm plate or an expansion tank.

[0048] Specifically, the present invention achieves dynamic adaptive compensation of the volume changes of the phase-change heat storage medium by the variable volume structure 6 through the integrated design of a passive trigger mechanism and an elastic structure. The variable volume structure 6 uses a passive trigger mechanism, requiring no external energy or control signal, and relies solely on the volume change characteristics of the phase-change heat storage medium to autonomously adjust its volume, ensuring the reliability of the system under extreme operating conditions such as nuclear reactor accidents. By reserving expansion space or integrating elastic structures such as bellows, expansion joints, diaphragms, and expansion boxes, the thermal expansion and contraction behavior of the phase-change heat storage medium during the phase change process can be accurately matched. For example, the bellows and expansion joints absorb volume changes through their own elastic deformation, the diaphragms balance pressure by moving the partition cavity, and the expansion box provides compensation space through the additional cavity volume. This diversified structural design not only meets the volume compensation requirements under different operating conditions, but also avoids the potential failure risks of traditional active control systems through its passive characteristics, ensuring that the system can still operate stably when the pressure in the containment fluctuates. This design solves the problem of device damage and leakage caused by volume changes of phase-change heat storage media at the structural level. At the same time, it simplifies the system architecture through a passive mechanism, improving the safety and reliability of nuclear reactor accident mitigation. Figure 4 As shown, it is a schematic diagram of the state before and after the volume change of the variable volume structure 6. In this embodiment, the upper end of the phase change heat storage container 2 limits the variable volume structure 6 so that its displacement path is limited to a controllable range.

[0049] Furthermore, the response time of the system is less than 5 minutes, the heat storage capacity of a single phase-change heat storage container 2 is ≥5000MJ, and the total heat storage capacity of the system covers the heat release demand of the containment 1 within 24 hours after the accident.

[0050] Specifically, the present invention achieves efficient and reliable passive heat mitigation under nuclear reactor accident conditions by strictly controlling the key performance indicators of the system. The system response time is less than 5 minutes. Its design intention is that when a nuclear reactor accident occurs, the phase change heat storage container 2 can be quickly started and quickly absorb the rapidly rising heat in the containment vessel 1, effectively suppressing the growth rate of temperature and pressure in the early stage of the accident, and gaining extremely valuable time for subsequent accident handling. The heat storage capacity of a single phase change heat storage container is ≥5000MJ, ensuring that a large amount of heat can be continuously absorbed during the accident to maintain the thermal balance in the containment vessel 1. The total heat storage capacity of the system covers the heat release demand of the containment vessel 1 within 24 hours after the accident, and it also guarantees the heat control of the entire accident process from the time dimension, so that the containment vessel 1 can maintain a stable state for a long time, avoiding the risk of pressure runaway and structural damage caused by heat accumulation. This performance design from rapid response to continuous and efficient heat storage has comprehensively improved the safety and reliability of the nuclear reactor containment under accident conditions.

[0051] Furthermore, the system further includes a shell wall fixing bracket, and the phase change heat storage container 2 is fixedly suspended near the inner wall of the containment vessel 1 by the shell wall fixing bracket in an array manner.

[0052] Specifically, the present invention realizes the stable installation and efficient heat transfer of the phase change energy storage system in the containment shell through the coordinated design of the shell wall fixing bracket and the array layout. The shell wall fixing bracket suspends the phase change heat storage container in an array near the inner wall of the containment shell. This installation method not only ensures the structural stability of the system under accident conditions by utilizing the mechanical strength of the bracket, but also maximizes the contact area between the phase change heat storage container and the high-temperature gas in the containment shell through the array distribution. The array layout enables the phase change heat storage container 2 to evenly cover the heat concentration area in the containment shell 1 (such as the dome and wall of the containment shell 1), shortens the heat transfer path, strengthens the natural convection effect, and ensures that the high-temperature gas can quickly and evenly exchange heat with the surface of the phase change heat storage container 2. At the same time, the modular array structure design allows the failure of a single phase change heat storage container 2 without affecting the overall function, thereby improving the redundancy and reliability of the system.

[0053] In order to make the purpose, technical solution and advantages of the present invention clearer, the technical solution of the present invention will be described in detail below.

[0054] Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all the embodiments.

[0055] Based on the embodiments of the present invention, all other implementations obtained by persons of ordinary skill in the art without inventive effort are within the scope of protection of the present invention. To make the embodiments easier to understand, the following provides a variety of embodiments or implementation methods to illustrate the relevant devices and functions of the present invention.

[0056] The specific implementation methods of the passive phase change heat absorption system of the present invention will be described in detail below in conjunction with the purpose of the passive phase change heat absorption system of the present invention.

[0057] 1. Phase change heat storage medium

[0058] The selection requirement for phase change heat storage medium is that the phase change temperature is slightly higher than the temperature under normal operating conditions inside the containment, and it has the advantages of high latent heat and good stability (such as paraffin, composite salts or metal alloys).

[0059] 2. Phase change heat storage container 2

[0060] The structure and material of the phase change heat storage container 2 adopt a stainless steel shell structure, such as high temperature resistant austenitic stainless steel (such as 316L).

[0061] The structural strength of the phase-change heat storage container 2 is obtained by mechanical analysis and calculation based on the load that the design structure and the installation location can bear.

[0062] The main structure of the phase change heat storage container 2 is sealed by welding: the interface between the phase change heat storage container 2 and the variable volume structure 6 can be sealed by welding or flange bolting to prevent leakage of the phase change heat storage medium.

[0063] 3. Variable volume structure 6

[0064] The volume change of the phase change heat storage medium is caused by two factors: temperature change and pressure change of the phase change heat storage medium. The working process of the variable volume structure 6 is as follows: Figure 2 shown.

[0065] When the pressure is constant, the density of the phase change heat storage medium will change at different temperatures, which will cause the volume of the phase change heat storage medium to change. The volume change of the phase change heat storage medium is: ΔV T变 .

[0066] In addition, from the concept of phase equilibrium, when there is a pressure change in the containment 1, the phase change temperature of the phase change heat storage medium has a certain relationship with the pressure ΔV P变 The change in volume caused by a change in pressure.

[0067] According to the above volume change analysis, the volume compensation amount V of the phase change heat storage container 2 integrated with the variable volume structure 6 should theoretically be: V ≥ ΔV T +ΔV P .

[0068] The two volume changes of the phase-change heat storage medium 6 have an impact on the stability of the phase-change heat storage container 2. These two factors need to be considered when designing the device to prevent leakage.

[0069] The variable volume structure 6 completely adopts a passive trigger mechanism, relying on the volume change characteristics of the phase change heat storage medium for autonomous adjustment, without the need for external energy or control signals.

[0070] The phase change heat storage container 2 integrates a variable volume structure 6, and specifically adopts one of the following design methods to achieve the volume compensation function: bellows, expansion joints, diaphragm plates, expansion boxes or reserved natural expansion space, etc.

[0071] 4. Enhanced heat exchange structure

[0072] High thermal conductivity ribs 4 are welded inside the wall 5 of the phase change heat storage container to increase the contact area with the phase change heat storage medium, make up for the low heat transfer coefficient of the phase change heat storage medium, and promote heat transfer.

[0073] External fins 3 are welded to the outside of the phase change heat storage container wall 5 to enhance heat exchange on the space side of the containment vessel 1 .

[0074] The main purpose of the enhanced condensation heat exchange unit is to destroy the film condensation, thereby enhancing the heat transfer efficiency outside the wall 5 of the phase change heat storage container.

[0075] Natural convection vertical flow channels are formed between the outer fins 3, and the natural convection effect of the hot air in the containment vessel 1 after an accident is utilized to enhance the heat absorption efficiency.

[0076] 5. System layout

[0077] Multiple phase change heat storage containers 2 are evenly suspended in the dome and wall areas of the containment vessel 1 and fixed by shell wall fixing brackets, covering the heat concentration area in the containment vessel 1.

[0078] The system adopts a modular redundant layout, and the failure of a single phase change heat storage container 2 does not affect the overall function.

[0079] 6. Passive Workflow

[0080] Based on the characteristics of a phase-change heat storage medium, the passive accident mitigation phase-change energy storage system utilizes a passive triggering mechanism. During normal nuclear reactor operation, the solid-state sensible heat of the phase-change heat storage medium contributes to macro-thermal regulation within containment 1. If the temperature within containment 1 rises abnormally, the passive accident mitigation phase-change energy storage system automatically intervenes, with the phase-change latent heat and liquid sensible heat of the phase-change heat storage medium contributing to thermal management within containment 1.

[0081] The high-temperature gas in the containment vessel 1 contacts the surface of the heat storage container 2 through natural convection, and the heat is quickly transferred to the phase-change heat storage medium through the enhanced condensation heat exchange unit.

[0082] After absorbing heat, the phase change heat storage medium undergoes a solid-liquid phase change, storing the heat in the form of latent heat and sensible heat. At the same time, the phase change heat storage medium expands in volume, triggering the variable volume structure 6 to compensate for the volume change.

[0083] After absorbing heat, the phase change heat storage medium reduces the gas temperature in the containment vessel 1 and suppresses further pressure increase.

[0084] The variable volume structure 6 of the phase change heat storage container 2 balances the pressure difference between the inside and the outside through deformation, thereby preventing the passive accident mitigation phase change energy storage system itself from being damaged by the pressure difference.

[0085] 7. Key parameter design

[0086] The heat storage capacity of a single phase change heat storage container 2 is designed according to the heat load of the containment. For example, the heat storage capacity of a single phase change heat storage container is ≥5000MJ, and the total heat storage capacity of the system needs to cover the heat release demand within 24 hours after the accident.

[0087] The response time of the passive accident mitigation phase change energy storage system should be less than 5 minutes from the occurrence of the accident to the system's heat absorption startup.

[0088] 8. Long-term performance test

[0089] By regularly taking out a small amount of phase change heat storage medium for thermal testing and analysis, reliability under long-term standby conditions is ensured.

[0090] The present invention forms a highly efficient passive heat absorption and pressure balance mechanism by suspending the phase change heat storage container in an array along the inner wall of the containment and matching it with a variable volume structure connected at the upper end. The array layout expands the heat exchange area and shortens the heat transfer path, enabling the system to quickly respond to accident conditions. The variable volume structure 6 automatically compensates for the volume change of the phase change material caused by temperature and pressure changes by reserving expansion space or integrating elastic components such as bellows. T +ΔV P ), to avoid damage and leakage of the container, and at the same time, the passive trigger mechanism can balance the internal and external pressure difference without external energy; by filling the phase change heat storage container 2 with phase change materials such as paraffin whose phase change temperature is higher than the normal operating temperature of the containment, boiling point is higher than the extreme working temperature and remains in liquid state without vaporization, and setting a gas flow channel to ensure stability during normal operation and rapid phase change and heat absorption in the event of an accident, and the gas flow channel guides the high-temperature gas to evenly contact the material, thereby enhancing the heat transfer efficiency; by respectively welding high thermal conductivity fins 4 (such as foam metal porous media) and external fins 3 (with micro-rib grooves) on the inside and outside of the phase change heat storage container wall 5, the inner side compensates for the heat conduction of the phase change material Insufficient, the condensate film is destroyed on the outside, turbulence is promoted, and two-way heat transfer enhancement is achieved on the gas side and the material side; a modular redundant array is formed by fixing the bracket on the shell wall, and the failure of a single phase change heat storage container 2 does not affect the overall function, and the heat concentration area is evenly covered. Combined with the performance design of response time < 5 minutes, heat storage of a single phase change heat storage container 2 ≥ 5000MJ, and total heat storage covering the heat release demand for 24 hours after the accident, it finally achieves efficient suppression of temperature and pressure peaks in the containment 1, ensures the structural integrity and sealing of the containment 1, and at the same time has the advantages of compact structure, adaptability to transformation and new construction projects, and long-term reliable operation.

[0091] While the specific embodiments of the present invention have been described in detail above, these are intended to be exemplary only, and the present invention is not limited thereto. Any equivalent modifications or substitutions to the present invention that would be apparent to those skilled in the art are also within the scope of the present invention. Therefore, any equivalent modifications or substitutions made without departing from the spirit and scope of the present invention are intended to be encompassed within the scope of the present invention.

Claims

1. A phase change energy storage system for passive accident mitigation of nuclear reactor containment, characterized in that: The invention comprises a containment shell (1), a phase-change heat storage container (2) and a variable volume structure (6); the phase-change heat storage container (2) is fixedly suspended in an array along the containment shell (1) near the inner wall of the containment shell (1); and the variable volume structure (6) is installed on the phase-change heat storage container (2) and is in communication with the phase-change heat storage container (2).

2. The phase change energy storage system for passive accident mitigation of nuclear reactor containment according to claim 1, characterized in that: The phase-change heat storage container (2) is filled with a phase-change heat storage medium, and a gas flow channel is provided in the phase-change heat storage medium.

3. The phase change energy storage system for passive accident mitigation of nuclear reactor containment according to claim 2, characterized in that: The phase change temperature of the phase change heat storage medium is not lower than the maximum temperature of the nuclear reactor containment under normal operating conditions, and the boiling point of the phase change heat storage medium is higher than the maximum temperature inside the containment under the nuclear reactor design extended operating conditions; the phase change heat storage medium is at least one of paraffin, composite salts or metal alloys, and the phase change heat storage medium remains liquid and does not vaporize during the phase change process.

4. The phase change energy storage system for passive accident mitigation of a nuclear reactor containment vessel according to claim 3, characterized in that: The filling structures of phase change heat storage media include plate structure, shell and tube structure and packed bed structure.

5. The phase change energy storage system for passive accident mitigation of nuclear reactor containment according to claim 2, characterized in that: The phase change heat storage container (2) is also provided with an enhanced condensation heat exchange unit, which comprises a phase change heat storage container wall (5), external fins (3) and high thermal conductivity fins (4), wherein the external fins (3) and high thermal conductivity fins (4) are respectively welded to the inner wall and the outer wall of the phase change heat storage container wall (5).

6. The phase change energy storage system for passive accident mitigation of a nuclear reactor containment vessel according to claim 5, characterized in that: The high thermal conductivity fins (4) are embedded in the phase change heat storage medium and adopt foam metal or metal alloy porous medium; the surface of the outer fins (3) is provided with micro-rib grooves for destroying the condensate film and promoting turbulence.

7. The phase change energy storage system for passive accident mitigation of a nuclear reactor containment vessel according to claim 1, characterized in that: The maximum volume compensation amount of the variable volume structure (6) satisfies the following relationship: V≥ΔV T +ΔV P Where, ΔV T is the volume change of the phase change heat storage medium caused by temperature change, ΔV P The volume change of the phase change heat storage medium caused by the pressure fluctuation in the containment vessel is the volume change, and the variable volume structure (6) automatically balances the pressure difference between the inside and outside of the phase change heat storage container through deformation.

8. The phase change energy storage system for passive accident mitigation of a nuclear reactor containment vessel according to claim 7, characterized in that: The variable volume structure (6) adopts a passive trigger mechanism and realizes volume compensation by reserving expansion space or integrating an elastic structure, wherein the integrated elastic structure is a bellows, an expansion joint, a diaphragm plate or an expansion box.

9. The phase change energy storage system for passive accident mitigation of a nuclear reactor containment vessel according to claim 1, characterized in that: The response time of the system is less than 5 minutes, the heat storage capacity of a single phase-change heat storage container (2) is ≥5000 MJ, and the total heat storage capacity of the system covers the heat release demand of the containment within 24 hours after the accident.

10. The phase change energy storage system for passive accident mitigation of a nuclear reactor containment vessel according to claim 1, characterized in that: The system further comprises a shell wall fixing bracket, and the phase change heat storage container (2) is fixedly suspended near the inner wall of the containment vessel (1) via the shell wall fixing bracket in an array manner.

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