A passive containment vessel and a passive containment cooling system

Abstract

The application discloses a kind of passive cooling containment and passive cooling safety system, belong to nuclear power field.Passive cooling containment includes cylindrical shell, and multiple three-dimensional twisted fin arrays are arranged in the circumference of the outer wall of shell discretely.Three-dimensional twisted fin has first axis at first end and second axis at second end, and first axis and second axis form an angle between them, and fin surface extends smoothly between first axis and second axis.In the event of an accident, three-dimensional twisted fin can form disturbance to the cooling air flow on the surface of containment, promote the mixing of near-surface hot air flow and far-surface cold air flow, improve the heat dissipation capacity of containment, and improve the safety of nuclear power plant.

Description

Technical Field

[0001] This invention belongs to the field of nuclear power, specifically relating to a passively cooled containment vessel and a passively cooled safety system. Background Technology

[0002] The containment vessel of a nuclear power plant is the last line of defense against the leakage of radioactive materials. Under accident conditions, the passive containment cooling system (PCCS) used in current large pressurized water reactors (such as AP1000 and CAP1400) can ensure that the pressure and temperature inside the containment vessel are below design limits for 72 hours.

[0003] According to the design requirements of the existing passive containment cooling system, within 72 hours after an accident, the passive containment cooling system continuously removes heat from the containment in a passive manner: the outer surface of the containment is sprayed with gravity-fed hydrophobic water from the passive containment cooling water tank, and the heat inside the containment is carried away by natural convection air in the form of sensible heat and water vapor; cold air from the environment enters through the normally open air duct, rises along the outer surface of the containment, and then returns to the environment through the high-level exhaust section, thus carrying away the heat from the containment. If the containment water tank is not replenished after 72 hours to maintain the water film cooling on the outside of the containment, the limited heat-carrying capacity of the containment's natural air cooling will be insufficient to remove all the heat from the containment, causing the containment to heat up and pressurize, and potentially exceeding the containment design pressure.

[0004] To improve the heat exchange capacity of the containment vessel, existing technologies have proposed various solutions for setting fins or ribs on the containment vessel wall.

[0005] Chinese patent application CN103377733A discloses a fully passive residual heat removal system for the reactor core after an accident in a large pressurized water reactor nuclear power plant. This system has several rows of fins fixed to the inner and / or outer walls of the vertical section and / or dome of the containment, and several rows of heat exchange fans fixed to the inner walls. The internal convective heat transfer is enhanced through fan disturbance. However, the heat exchange fans rely on emergency DC power, which poses a risk of failure under prolonged power outage scenarios exceeding design baseline accidents, thus it is not a truly passive reinforcement solution.

[0006] Chinese patent CN206116027U discloses a passive containment cooling system with high heat transfer, which features fins on the inner and / or outer sidewalls of the containment. This design increases the heat transfer area and guides the liquid film through the fins, thereby improving liquid film coverage and heat transfer efficiency. However, the fins in this design are straight plates, and the airflow is guided solely by the vertical or inclined arrangement of the fins, failing to induce three-dimensional vortices within the airflow channels.

[0007] Therefore, providing a passively cooled containment with stronger heat dissipation capabilities is of positive significance for improving the safety of nuclear power plants. Summary of the Invention

[0008] The purpose of this invention is to provide a passively cooled containment structure that improves the utilization efficiency of cooling water during passive cooling in accident conditions. This invention also provides a passively cooled safety system.

[0009] According to one aspect of the present invention, a passively cooled containment vessel is provided, comprising a shell, the shell being a cylindrical structure. A plurality of three-dimensional twisted fins are discretely arranged circumferentially on the outer wall of the shell; each three-dimensional twisted fin has a first axis at a first end and a second axis at a second end, the first end of the three-dimensional twisted fin being connected to the surface of the shell, the first axis extending axially along the shell and forming an angle θ with the second axis, and the fin surface extending smoothly between the first axis and the second axis; the plurality of fins are arranged in a fin array spaced apart from each other in the circumferential and axial directions of the shell.

[0010] The heat transfer capacity of the containment is enhanced by arranging fins on its outer surface. The fin roots are positioned along the axial direction of the containment, preventing lateral obstruction of longitudinal water film flow and ensuring uniform water film coverage in the passive containment cooling system. Three-dimensional twisted fins enhance the airflow vortex effect, further improving fin heat transfer. This passively cooled containment significantly improves the passive cooling capacity of the containment under accident conditions by increasing the heat transfer area, enhancing airflow disturbance, and accommodating water film flow on the outer wall of the containment. It fully utilizes existing flow channels and the high thermal conductivity of the steel containment. This eliminates the need for external energy sources, improving containment heat dissipation efficiency and enhancing the safety and reliability of the nuclear reactor.

[0011] Furthermore, in some embodiments, 0 < θ ≤ 90°.

[0012] Furthermore, in some embodiments, the three-dimensional twisted fins have a rectangular or airfoil-shaped cross-section in the radial direction of the housing.

[0013] Furthermore, in some embodiments, the lowest point of the second axis is higher in the vertical direction than the highest point of the first axis.

[0014] Furthermore, in some embodiments, the three-dimensional twisted fins are twisted in a left-handed or right-handed direction, with left-handed and right-handed three-dimensional twisted fins alternately arranged.

[0015] Furthermore, in some embodiments, the three-dimensional twisted fins are arranged in a matrix on the shell.

[0016] Furthermore, in some embodiments, the circumferential spacing between adjacent three-dimensional twisted fins is 20cm-200cm, and the axial spacing between adjacent three-dimensional twisted fins is 5cm-200cm.

[0017] Furthermore, in some embodiments, the height of the three-dimensional twisted fin along the axial direction of the shell is 5cm-50cm, the length of each fin extending radially outward along the shell is 5cm-30cm, and the thickness of the three-dimensional twisted fin is 5mm-50mm.

[0018] Furthermore, in some embodiments, the shell surface is also provided with a plurality of straight fins, which are arranged in a mixed manner with the three-dimensional twisted fins.

[0019] According to another aspect of the present invention, a passive cooling safety system is provided, comprising a containment vessel, a shielded enclosure, a baffle plate, and a cooling water spray system. The containment vessel and the baffle plate are disposed within the shielded enclosure. The baffle plate surrounds the containment vessel and forms an airflow channel between the baffle plate and the outer wall of the containment vessel. The cooling water spray system is disposed at the top of the shielded enclosure and is capable of spraying cooling water onto the containment vessel. The containment vessel is a passive cooling containment vessel provided in any of the foregoing embodiments.

[0020] Furthermore, in some embodiments, the end of the three-dimensional twisted fin containing the second axis is configured as a free end or connected to the guide plate. Attached Figure Description

[0021] Figure 1 This is a schematic diagram of a passive cooling safety system structure in one embodiment; Figure 2 This is a top view of the containment structure in one embodiment; Figure 3 This is a schematic diagram of a three-dimensional twisted fin structure in one embodiment; Figure 4 This is a schematic diagram of a three-dimensional twisted fin structure in another embodiment; Figure 5 This is a planar schematic diagram of the three-dimensional twisted fin arrangement in one embodiment; Figure 6 This is a three-dimensional schematic diagram of the arrangement of three-dimensional twisted fins in one embodiment; Figure 7 This is a three-dimensional temperature distribution cloud map of a twisted fin in one embodiment; Figure 8 A temperature distribution cloud map of a pair of proportional straight fins; Figure 9 This is a schematic diagram of a three-dimensional twisted fin structure in another embodiment.

[0022] Meaning of the reference numerals in the attached figures: 1-Containment vessel; 2-Three-dimensional twisted fin; 21-First axis; 22-Second axis; 23-Fin surface; 24a-Fin cross section; 24b-Fin cross section; 3-Guide plate; 4-Shielded building; 41-Air inlet; 42-Exhaust outlet; 5-Cooling water spray system; 51-Passive water tank; 52-Cooling water distribution device; 6-Straight fin.

[0023] The purpose of the above-described drawings is to provide a detailed description of the present invention so that those skilled in the art can understand the technical concept of the invention, and is not intended to limit the invention. For the sake of brevity, the above-described drawings only schematically depict the structures related to the technical features of the present invention, and do not depict the complete structure and all details strictly according to actual scale. Detailed Implementation

[0024] The present invention will now be described in further detail with reference to specific embodiments and accompanying drawings.

[0025] The term "embodiment" as used herein means that a particular feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment herein. The phrase appearing in various places in the specification does not necessarily refer to the same embodiment, nor is it limited to mutually exclusive, independent, or alternative embodiments. Those skilled in the art will understand that the embodiments herein can be combined with other embodiments without causing structural conflicts.

[0026] In this description, terms such as "upper," "lower," "left," "right," "lateral," "longitudinal," "height," "length," and "width," which indicate orientation or positional relationships, are intended to accurately describe the embodiments and simplify the description, and are not intended to limit the parts or structures involved to have a specific orientation, or to be installed or operated in a specific orientation, and should not be construed as limiting the embodiments described herein. In this description, "a plurality of" means at least two.

[0027] Advanced large pressurized water reactor nuclear power plants employ passive containment cooling systems, requiring continuous cooling of the containment vessel by passive means using cooling water stored in the containment tank for 72 hours after an accident. To further improve the containment's heat dissipation efficiency, some technical solutions incorporate protruding fins on the containment surface to increase the heat dissipation area and improve heat exchange efficiency. During this period, containment cooling primarily relies on the evaporation of cooling water and convective heat transfer through the water film surface. However, after an accident, the airflow over the containment surface tends to form a relatively stable laminar flow. The airflow near the containment vessel is hotter and lacks mixing with the cooler airflow on the outside. Therefore, relying solely on the passive containment cooling system results in insufficient heat dissipation efficiency, hindering further improvements in the safety performance of the nuclear power plant.

[0028] In order to overcome the above-mentioned problems of the prior art, one embodiment of the present invention provides a passively cooled containment vessel that can further improve the heat dissipation efficiency of the containment vessel after an accident.

[0029] In one embodiment, a passive cooling safety system for nuclear power plants, such as Figure 1 As shown, the system includes a containment vessel 1, a shielded enclosure 4, a baffle plate 3, and a cooling water spray system 5. The containment vessel 1 and the baffle plate 3 are located within the shielded enclosure 4. The baffle plate 3 surrounds the containment vessel 1, forming an airflow channel between the baffle plate 3 and the outer wall of the containment vessel 1, and an air intake channel between the baffle plate 3 and the shielded enclosure 4. The cooling water spray system is located at the top of the shielded enclosure 4 and sprays cooling water onto the containment vessel 1. The cooling water spray system includes a passive water tank 51 located at the top of the shielded enclosure 4 and a cooling water distribution device 52. When the pressure inside the containment vessel 1 exceeds the water-cooling trigger pressure, the cooling water in the passive water tank 51, under the influence of gravity (as shown by arrow c), is sprayed onto the outer surface of the containment vessel 1 through the cooling water distribution device 52, forming a water film for cooling. The air inlet 41 of the shielded building 4 allows cold air from the environment to enter. As shown by arrow a, the cold air flows sequentially through the air intake channel formed by the shielded building 4 and the guide plate 3, and the airflow channel formed by the guide plate 3 and the containment vessel 1, and then, as shown by arrow b, is discharged from the exhaust port 42 at the top of the shielded building 4, achieving convective heat dissipation for the containment vessel 1. Combined with... Figure 2 The containment vessel 1 is a cylindrical structure made of steel, which has good thermal conductivity. Three-dimensional twisted fins 2 are arranged on the outer wall of the containment vessel 1 to increase the heat exchange area between the containment vessel 1 and the gas. Simultaneously, the twisted structure of the three-dimensional twisted fins 2 can disturb the gas flow, disrupt the thermal boundary layer, improve the convective heat transfer coefficient, and enhance heat transfer efficiency. The three-dimensional twisted fins 2 can be made of the same steel as the containment vessel 1, or they can be made of other high thermal conductivity metals with good microstructure compatibility. They can be fixedly connected to the outer wall of the containment vessel 1 by welding, bolting, or other fixing methods known to those skilled in the art.

[0030] In a preferred embodiment, such as Figure 3As shown, the three-dimensional twisted fin 2 has a first axis 21 and a second axis 22, wherein the first end of the first axis 21 is connected to the surface of the containment 1, and in different embodiments, the second end of the second axis 22 is configured as a free end or welded to the guide plate 3. The first axis 21 extends along the axial direction of the containment 1 and forms an angle θ with the second axis. The fin surface of the three-dimensional twisted fin 2 extends smoothly between the first axis and the second axis. In a preferred embodiment, 0 < θ ≤ 90°. Multiple three-dimensional twisted fins 2 are arranged in a fin array, spaced apart from each other in the circumferential and axial directions of the containment 1. The first end of the three-dimensional twisted fin 2 is connected to the outer wall of the containment 1 and extends along the axial direction of the containment 1, so that the extension direction of the fin surface 23 of the three-dimensional twisted fin 2 at the first end is consistent with the water film flow direction of the outer wall of the containment 1, avoiding lateral obstruction to the longitudinal water film flow and ensuring the uniformity of water film coverage of the passive cooling system. The three-dimensional twisted fin 2 can be constructed as follows: First, the shape of the fin section 24a is defined on multiple radial sections along the containment 1. In this embodiment, it is a rectangular surface. The first axis 21 and the second axis 22 are the axes of symmetry along the length of the fin section 24a at the first and second ends, respectively. Then, each section is connected between the first axis 21 and the second axis 22 along the stacking line d. Specifically, for example, the fin section 24a can be rotated while moving along the stacking line from the first axis 21 to generate the three-dimensional twisted fin 2. The rotation can be left-handed or right-handed. Through rotation, the fin surface of the three-dimensional twisted fin 2 forms a continuous helical surface.

[0031] In another embodiment, such as Figure 4 As shown, the fin section 24b of the three-dimensional twisted fin 2 is an airfoil.

[0032] Under accident conditions, the passive containment cooling system uses gravity to spray cooling water onto the outer surface of containment 1 for water film cooling. The cooling airflow rises along the outer surface of containment 1. The three-dimensional twisted fins 2 increase the heat exchange area between containment 1 and the cooling airflow. At the same time, the three-dimensional twisted fins 2 interfere with the flow of cooling airflow, disrupting the laminar flow parallel to containment 1, promoting the mixing between the hot airflow near the surface of containment 1 and the cold airflow away from the surface of containment 1, providing a convective heat transfer coefficient, thereby improving heat transfer efficiency.

[0033] Specifically, as θ increases, the disturbance effect of the three-dimensional twisted fin 2 on the airflow is enhanced, and the destruction effect of the thermal boundary layer is more significant. Figure 7 The image shows the temperature distribution cloud map of the three-dimensional twisted fin 2 when θ = 90°. Figure 8The diagram shows the temperature distribution cloud map of the straight fin 6 (θ=0°). It can be seen that the end temperature of the three-dimensional twisted fin 2 is significantly lower than that of the straight fin 6, and significant turbulence is formed above the three-dimensional twisted fin 2. Simulation calculations show that the heat dissipation efficiency of the three-dimensional twisted fin 2 is approximately 10% higher than that of the straight fin 6. Therefore, in the preferred embodiment, 45° < θ ≤ 90°, and more preferably 90°.

[0034] like Figure 5 and Figure 6 As shown, the three-dimensional twisted fins 2 are arranged in an array, spaced apart from each other in the circumferential and axial directions of the containment 1. The array of three-dimensional twisted fins 2 covers the entire vertical outer surface of the containment 1 to achieve uniform heat dissipation of the containment. The three-dimensional twisted fins 2 are arranged alternately with left-handed and right-handed fins. The vortex directions generated by the three-dimensional twisted fins 2 with different vortices are opposite as shown by arrows e and f, forming a vortex coupling effect, further enhancing the airflow turbulence and improving the heat transfer efficiency. In different embodiments, the left-handed and right-handed three-dimensional twisted fins 2 can be alternately arranged along the circumference of the containment 1, or along the axial direction of the containment 1, or alternately arranged in both the circumferential and axial directions; they can be alternated in units of a single left-handed or right-handed three-dimensional twisted fin 2, or in units of a fin group composed of multiple left-handed or right-handed three-dimensional twisted fins 2 with the same vortex direction.

[0035] In a preferred embodiment, the three-dimensional twisted fins 2 are arranged in a matrix on the containment 1. Adjacent three-dimensional twisted fins 2 in the circumferential direction of the containment 1 have the same height, and adjacent three-dimensional twisted fins 2 in the axial direction of the containment 1 are arranged vertically along the same generatrix on the outer circumferential surface of the containment 1. The uniform distribution of flow channels between adjacent three-dimensional twisted fins 2 is beneficial for uniform airflow distribution and stable flow. In other embodiments, adjacent three-dimensional twisted fins 2 can also be arranged in a staggered manner, that is, the two closest three-dimensional twisted fins 2 are neither at the same height nor on the same generatrix on the outer circumferential surface of the containment 1.

[0036] In a preferred embodiment, such as Figure 5As shown, the circumferential spacing s1 between adjacent three-dimensional twisted fins 2 is 20cm-200cm, and the axial spacing s2 between adjacent three-dimensional twisted fins 2 is 5cm-200cm. The height l1 of the three-dimensional twisted fins 2 along the axial direction of the containment 1 is 5cm-50cm, the radial extension length of each three-dimensional twisted fin 2 along the containment 1 is 5cm-30cm, and the thickness w1 of the three-dimensional twisted fins 2 is 5mm-50mm. The fin height determines the effective heat exchange area of ​​the fin, the radial extension length of the fin affects the spacing between the fin tip and the guide plate 3, and the fin thickness is related to the structural strength and thermal conductivity of the fin. In a preferred embodiment, when the circumferential spacing of the three-dimensional twisted fins 2 is 30cm, the axial spacing is 10cm, the length of the three-dimensional twisted fins 2 is 10cm, the height is 10cm, and the thickness is 2cm, the air heat exchange capacity of the containment can be increased by 40% compared to when no fins are arranged.

[0037] In some preferred embodiments, such as Figure 9 As shown, the lowest point of the second axis 22 of the three-dimensional twisted fin 2 is higher than the highest point of the first axis 21 in the vertical direction. That is, the second end (terminal end) of the three-dimensional twisted fin 2 is entirely located above the first end (root) of the three-dimensional twisted fin 2, causing the three-dimensional twisted fin 2 to extend upward from the first end to the second end. If the second end of the three-dimensional twisted fin 2 is lower than the first end, some cooling water may flow along the three-dimensional twisted fin 2 to the second end and then detach from the surface of the containment 1, falling at the second end in the form of water droplets, resulting in insufficient utilization of cooling water. Figure 9 The three-dimensional twisted fin structure shown prevents cooling water from dripping from the ends of the fins, improving the efficiency of cooling water utilization and ensuring continuous water film coverage. Simultaneously, the upward extension of the three-dimensional twisted fins 2 aligns with the upward direction of natural convection airflow, which helps guide airflow upwards and reduces airflow resistance.

[0038] In some preferred embodiments, the surface of the containment vessel 1 is also provided with some straight fins (θ=0°). In some embodiments, the straight fins can be mixed with the three-dimensional twisted fins 2 to form a fin array. In other embodiments, the straight fins or the three-dimensional twisted fins 2 can be concentrated in different areas of the surface of the containment vessel 1. Specifically, in one embodiment, combined with Figure 1As shown by arrow a, the cooling airflow flows in from the air inlet 41 and through the bottom of the guide plate 3. At this time, the overall temperature of the cooling airflow is relatively low. The lower 1 / 3 section of the containment 1 is provided with a straight fin array to reduce the resistance of the fins to the cooling airflow and promote the rapid flow of the cooling airflow to participate in heat exchange. As the cooling airflow rises, the temperature of the cooling airflow near the surface of the containment 1 increases and the heat exchange efficiency decreases. The middle 1 / 3 of the containment 1 is provided with a three-dimensional twisted fin array 2. The disturbance of the three-dimensional twisted fin 2 is used to disrupt the laminar flow in the cooling airflow, promote the mixing of the near-surface hot airflow and the far-surface cold airflow, and improve the convective heat exchange efficiency.

[0039] The passive cooling containment and the passive cooling safety system using the passive cooling containment provided in the above embodiments effectively improve the convective heat dissipation efficiency of the cooling water film surface by discretizing the three-dimensional twisted fins 2 on the outer wall of the containment, and further optimize the safety of the nuclear power plant.

[0040] The purpose of the above embodiments is to provide a further detailed description of the present invention in conjunction with the accompanying drawings, so that those skilled in the art can understand the technical concept of the present invention. Within the scope of the present invention, optimization or equivalent substitution of the technical features involved, as well as combination of implementation methods in different embodiments without causing structural and principle conflicts, all fall within the protection scope of the present invention.

Claims

1. A passively cooled containment structure, the passively cooled containment structure comprising a shell, the shell being a cylindrical structure, characterized in that, Multiple three-dimensional twisted fins are discretely arranged on the outer wall of the shell in the circumferential direction; the three-dimensional twisted fins have a first axis at a first end and a second axis at a second end, the first end of the three-dimensional twisted fins is connected to the surface of the shell, the first axis extends along the axial direction of the shell and forms an angle θ with the second axis, and the fin surface extends smoothly between the first axis and the second axis; the multiple fins are arranged in a fin array with intervals between each other in the circumferential and axial directions of the shell.

2. The passively cooled containment vessel according to claim 1, characterized in that, 0 < θ ≤ 90°.

3. The passively cooled containment vessel according to claim 1 or 2, characterized in that, The three-dimensional twisted fins have a rectangular or airfoil-shaped cross-section in the radial direction of the shell.

4. The passively cooled containment vessel according to claim 1 or 2, characterized in that, The lowest point of the second axis is higher than the highest point of the first axis in the vertical direction.

5. The passively cooled containment vessel according to claim 1 or 2, characterized in that, The three-dimensional twisted fins are twisted in either left-handed or right-handed directions, with left-handed and right-handed three-dimensional twisted fins alternating.

6. The passively cooled containment vessel according to claim 1 or 2, characterized in that, The three-dimensional twisted fins are arranged in a matrix on the shell.

7. The passively cooled containment vessel according to claim 1 or 2, characterized in that, The circumferential spacing between adjacent three-dimensional twisted fins is 20cm-200cm, and the axial spacing between adjacent three-dimensional twisted fins is 5cm-200cm.

8. The passively cooled containment vessel according to claim 1 or 2, characterized in that, The height of the three-dimensional twisted fin along the axial direction of the shell is 5cm-50cm, the length of each fin extending radially outward along the shell is 5cm-30cm, and the thickness of the three-dimensional twisted fin is 5mm-50mm.

9. The passively cooled containment vessel according to claim 1 or 2, characterized in that, The shell surface is also provided with a plurality of straight fins, which are arranged in a mixed manner with the three-dimensional twisted fins.

10. A passive cooling safety system, comprising a containment vessel, a shielded building, a baffle plate, and a cooling water spray system, wherein the containment vessel and the baffle plate are disposed within the shielded building, the baffle plate surrounds the containment vessel and forms an airflow channel between the baffle plate and the outer wall of the containment vessel, and the cooling water spray system is disposed at the top of the shielded building and is capable of spraying cooling water onto the containment vessel; characterized in that, The containment structure is a passively cooled containment structure as described in any one of claims 1 to 9.

11. The passive cooling safety system according to claim 10, characterized in that, The second end of the three-dimensional twisted fin is configured as a free end or connected to the guide plate.

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