A lead-cooled fast reactor in-vessel containment

Abstract

The utility model discloses a lead -cooling fast reactor in -core containment structure for placing in reactor vessel, including inner enclosure cylinder, and the coaxial setting of inner enclosure cylinder and reactor vessel, the both ends fixed with first baffle and second baffle of inner enclosure cylinder respectively, first baffle and second baffle respectively extend to the inner wall of reactor vessel along the outer circumferential radial of both ends of inner enclosure cylinder outward, and with the fixed connection of reactor vessel inner wall, heat exchanger contains the position between first baffle and the outer wall of inner enclosure cylinder and is provided with bubble protection baffle, and the both sides of heat exchanger contains the position are provided with bubble protection baffle respectively, and the one end of bubble protection baffle along reactor vessel axial extension is fixedly connected with first baffle, and the other end of bubble protection baffle along reactor vessel axial extension has the fluid flow channel between second baffle, the utility model solves the prior art, if the heat exchanger break accident occurs, and the technical problem of the bubble produced easily enters the core and leads to the lead -cooling fast reactor system safety risk intensification.

Description

Technical Field

[0001] This utility model relates to the field of nuclear power engineering technology, specifically to an internal enclosure structure for a lead-cooled fast reactor that can provide both support and bubble protection in the event of a heat exchanger rupture accident. Background Technology

[0002] Lead-cooled fast reactors, as one of the fourth-generation advanced nuclear energy systems, have significant advantages in safety and economy. However, they still face the safety risk threat of heat exchanger rupture accidents. A heat exchanger rupture accident allows the working fluid from the secondary loop to enter the reactor vessel. Under the entrainment effect of the working fluid in the primary loop, bubbles enter the reactor core, leading to a sharp deterioration in core heat transfer and, in severe cases, core failure. To prevent bubbles from entering the reactor core and causing serious consequences, the reactor internals, in addition to providing support for the reactor equipment, must also possess bubble protection capabilities.

[0003] In related technologies, the protection of in-core containment structures against changes in the flow characteristics of in-core gases and coolants after an accident has clear deficiencies: Previous designs for in-core components only considered the safety and reliability of the mechanical structure, neglecting the potential risks to core thermal-hydraulic safety posed by changes in coolant flow and post-accident bubbles, thus exacerbating core fuel safety risks. Furthermore, the in-core components lack specific safety flow protection measures, relying solely on reducing overall system flow rates to mitigate post-accident risks. These problems directly lead to high requirements for system safety response design after a heat exchanger rupture accident, harboring inherent safety risks.

[0004] In related technologies, how to ensure the flow within the reactor and the thermal safety of the reactor core after a heat exchanger rupture accident is a technical problem that urgently needs to be solved by those skilled in the art. Utility Model Content

[0005] The purpose of this invention is to provide an internal containment structure for a lead-cooled fast reactor to address the technical problem in the prior art where, in the event of a heat exchanger rupture accident, the generated air bubbles can easily enter the reactor core, exacerbating the safety risks of the lead-cooled fast reactor system. The internal containment structure provided by this invention can protect the reactor core in the event of a heat exchanger rupture accident, thus helping to reduce the safety risks to the reactor's primary circuit after such an accident.

[0006] To solve the above-mentioned technical problems, the present invention adopts the following technical solution:

[0007] A lead-cooled fast reactor in-reactor enclosure structure, for placement within the reactor vessel, comprising:

[0008] An inner shroud is coaxially arranged with the reactor vessel; a first baffle and a second baffle are fixed at both ends of the inner shroud; the inner shroud can provide protection for the core structure and support for the structure inside the reactor vessel.

[0009] The first and second partitions extend radially outward along the outer periphery of both ends of the inner circumference cylinder to the inner wall of the reactor vessel and are fixedly connected to the inner wall of the reactor vessel.

[0010] A heat exchanger receiving position is provided between the first baffle and the outer wall of the inner cylinder, and bubble protection baffles are respectively provided on both sides of the heat exchanger receiving position; the second baffle is used to guide the flow of coolant in the reactor and to provide a position for the heat exchanger positioning guide hole;

[0011] One end of the bubble protection baffle extending axially along the reactor vessel is fixedly connected to the first baffle.

[0012] The bubble protection baffle extends axially along the reactor vessel at one end and has a fluid flow channel between it and the second baffle. The bubble protection baffle can reduce the probability of heat exchanger bubbles entering the reactor core in the event of a heat exchanger rupture accident, thereby improving safety during a reactor accident.

[0013] This solution prevents air bubbles from entering the core with the coolant after a heat exchanger rupture accident in a lead-cooled fast reactor, thus avoiding localized heat transfer deterioration and potential serious accidents such as core overheating. The bubble protection measures reduce the proportion of millimeter-sized bubbles entering the core from 30% to 5%, significantly improving reactor safety.

[0014] Furthermore, the first partition has two symmetrically arranged heat exchanger receiving positions between it and the outer wall of the inner cylinder, and the second partition is arranged corresponding to one of the heat exchanger receiving positions.

[0015] The inner circumferential cylinder is fixed with a second partition plate at one end and a third partition plate is also fixed thereon. The third partition plate extends radially outward along the outer periphery of the corresponding end of the inner circumferential cylinder to the inner wall of the reactor vessel and is fixedly connected to the inner wall of the reactor vessel. The third partition plate is set in a position corresponding to another heat exchanger accommodating position.

[0016] Each heat exchanger housing is provided with bubble protection baffles on both sides. One end of each bubble protection baffle extending along the axial direction of the reactor vessel is fixedly connected to the first baffle. The other end of any bubble protection baffle extending along the axial direction of the reactor vessel has a fluid flow channel between it and the second or third baffle. The fluid flow channel is used to guide the coolant through the fluid flow channel and flow from the heat exchanger into the main circulation pump.

[0017] The second and third baffles are used to guide the flow of coolant in the reactor and provide the arrangement position for the symmetrically arranged heat exchanger positioning guide holes.

[0018] Furthermore, a hot and cold pool partition is provided between the two adjacent ends of the second partition and the third partition. The hot and cold pool partition has an upper guide positioning hole for the main circulation pump, and correspondingly, a lower guide positioning hole for the main circulation pump is provided at a corresponding position on the first partition. This partition is used to install both ends of the main circulation pump and to guide and position the main circulation pump. The hot and cold pool partition separates the reactor hot pool and the cold pool.

[0019] Furthermore, the hot and cold pool partition includes a first bent plate, a parallel plate, and a second bent plate. The parallel plate is spaced apart from the second and third partitions. The first and second bent plates extend axially along the reactor vessel toward the second and third partitions, respectively. One end of the first bent plate is fixedly connected to the second partition, and one end of the second bent plate is fixedly connected to the third partition. This arrangement effectively adapts to the structure of the main circulation pump, isolating the upper part of the main circulation pump from the reactor hot pool section.

[0020] Furthermore, the second partition and the third partition are respectively provided with heat exchanger guide positioning holes for installing the heat exchanger and guiding and positioning the heat exchanger.

[0021] Furthermore, reinforcing ribs are provided at the fixed connection between the bubble protection partition and the first partition. This makes the structure of the bubble protection partition more stable and its position more stable, and it is less likely to deform due to the erosion of the coolant.

[0022] Furthermore, the extension length of the reinforcing rib away from the bubble protection partition is 1 / 5 to 1 / 6 of the width of the bubble protection partition.

[0023] Furthermore, the bubble protection baffle extends axially along the reactor vessel for 1 / 2 to 3 / 5 of the length of the line connecting the center of the upper and lower positioning guide holes of the main circulation pump. Within this distance range, it can effectively block bubbles generated by heat exchanger rupture accidents, reducing the proportion of millimeter-sized bubbles entering the reactor core from 30% to 5%, greatly improving reactor safety.

[0024] Furthermore, the thickness of the bubble protection baffle is 1.1 to 1.2 times the thickness of the first baffle; the length:width:thickness of the bubble protection baffle is 50:80:1 to 50:80:2. This configuration meets the structural performance requirements of the in-core components while reducing the flow resistance to the coolant.

[0025] Furthermore, the bubble protection baffle is a rectangular baffle. This design satisfies structural performance requirements while improving the efficiency of the reactor containment structure in guiding the coolant.

[0026] The technical solution of this utility model has the following beneficial effects: The lead-cooled fast reactor internal containment structure disclosed in this utility model can effectively protect the reactor core. In the event of a heat exchanger rupture accident in a lead-cooled fast reactor, it prevents bubbles from migrating into the reactor core with the coolant, thus avoiding localized heat transfer deterioration in the core and subsequent serious accidents such as core overheating. The bubble protection measures can reduce the proportion of millimeter-sized bubbles entering the reactor core from 30% to 5%, greatly improving reactor safety. Attached Figure Description

[0027] To make the purpose, technical solution, and advantages of this utility model clearer, the present utility model will be further described in detail below with reference to the accompanying drawings, wherein:

[0028] Figure 1 This is a schematic diagram of the internal arrangement of the internal containment structure of this utility model.

[0029] Figure 2 This is a schematic diagram of the specific structure of the in-pile enclosure structure of this utility model.

[0030] Figure 3 This is a schematic diagram of the specific structure of the hot and cold pool partition of the in-core containment structure of this utility model.

[0031] Explanation of reference numerals in the attached drawings: 1-In-reactor containment structure, 101-Positioning guide hole on the main circulation pump, 102-Second baffle, 103-Bubble protection baffle, 104-Reinforcing rib, 105-First baffle, 106-Third baffle, 107-Hot / cold pool baffle, 1071-First bent plate, 1072-Parallel plate, 1073-Second bent plate, 108-Positioning guide hole for heat exchanger, 109-Fluid flow channel, 110-Inner shroud, 111-Positioning guide hole below the main circulation pump, 2-Main circulation pump, 3-Heat exchanger, 4-Reactor vessel. Detailed Implementation

[0032] The technical solutions of some embodiments of this utility model will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments disclosed in this utility model, and not all of them. Based on the embodiments provided in this utility model, all other embodiments obtained by those skilled in the art are within the protection scope of this utility model. It should be noted that the same reference numerals and letters in the drawings represent similar parts. Once a part is defined in one drawing, it will not be defined and explained again in subsequent drawings.

[0033] This invention can be applied to pool-type liquid metal reactor containers, solving the technical problem in the prior art where, if a heat exchanger rupture accident occurs, the generated bubbles can easily enter the reactor core, leading to an increased safety risk in the lead-cooled fast reactor system. It effectively avoids the situation where bubbles can easily enter the reactor core after a rupture accident in the pipeline of the pool-type reactor heat exchanger, causing the reactor core to overheat.

[0034] Overall, a solution was adopted to add baffles to guide the flow direction of the coolant. By guiding the coolant flow, the direction of the drag force of the coolant on the bubbles was changed. Combined with the effect of buoyancy, the bubbles were made to escape from the surface of the coolant instead of entering the reactor core. This reduced the probability of bubbles entering the reactor core and deteriorating heat transfer, and greatly improved the accident safety of the reactor.

[0035] To further illustrate the features of the in-pile enclosure structure 1 provided by this utility model, the following embodiments are disclosed.

[0036] In some embodiments, please refer to Figure 1 and Figure 2 A lead-cooled fast reactor in-reactor enclosure 1, for placement within the reactor vessel 4, includes:

[0037] The inner circumferential tube 110 is coaxially arranged with the reactor vessel 4; a first partition 105 and a second partition 102 are respectively fixed at both ends of the inner circumferential tube 110; the inner circumferential tube 110 can provide protection for the core structure and support for the structure inside the reactor vessel 4.

[0038] The first baffle 105 and the second baffle 102 extend radially outward along the outer periphery of both ends of the inner circumference of the inner circumference cylinder 110 to the inner wall of the reactor vessel 4 and are fixedly connected to the inner wall of the reactor vessel 4; the second baffle 102 is used to guide the flow of coolant in the reactor.

[0039] A heat exchanger receiving position is provided between the first partition 105 and the outer wall of the inner cylinder, and bubble protection partitions 103 are respectively provided on both sides of the heat exchanger receiving position.

[0040] One end of the bubble protection baffle 103 extending axially along the reactor vessel 4 is fixedly connected to the first baffle 105.

[0041] The bubble protection baffle 103 extends axially along the reactor vessel 4, and has a fluid flow channel 109 between its other end and the second baffle 102. The bubble protection baffle 103 can reduce the probability of heat exchanger bubbles entering the reactor core in the event of a heat exchanger rupture accident, thereby improving safety in the event of a reactor accident.

[0042] This solution can prevent air bubbles from entering the reactor core via the coolant after a heat exchanger rupture accident in a lead-cooled fast reactor, thus avoiding localized heat transfer deterioration and potentially serious accidents such as core overheating. The bubble protection measures can reduce the proportion of millimeter-sized bubbles entering the reactor core from 30% to 5%, significantly improving reactor safety.

[0043] Specifically, when the heat exchanger 3 is located in the heat exchanger receiving position, a gap is provided between the bottom of the heat exchanger 3 and the first partition 105.

[0044] Specifically, in this embodiment, please refer to Figure 1 and Figure 2 The flow of coolant within the reactor follows the direction from heat exchanger 3, through the main circulation pump 2, into the reactor core. After a heat exchanger rupture accident occurs in a single heat exchanger 2, bubbles are carried by the coolant and flow. After flowing out of the heat exchanger 3, the bubbles flow upward through the bubble protection baffle 103. After flowing through the fluid channel 109, most of the bubbles flow towards the hot and cold pool baffle 107, while a small number of bubbles flow towards the inlet of the main circulation pump 2 and enter the reactor core from the positioning guide hole 111 under the main circulation pump, thus reducing the safety risks of the reactor.

[0045] In some embodiments, please refer to Figure 1 and Figure 2 The first partition 105 has two symmetrically arranged heat exchanger receiving positions between it and the outer wall of the inner cylinder, and the second partition 102 is arranged corresponding to one of the heat exchanger receiving positions.

[0046] The inner circumferential cylinder 110 is fixed with a second partition 102 at one end and a third partition 106 is also fixed thereto. The third partition 106 extends radially outward along the outer periphery of the corresponding end of the inner circumferential cylinder 110 to the inner wall of the reactor vessel 4 and is fixedly connected to the inner wall of the reactor vessel 4. The third partition 106 is set in a position corresponding to another heat exchanger accommodating position.

[0047] Each heat exchanger housing is provided with a bubble protection baffle 103 on both sides. One end of each bubble protection baffle 103 extending axially along the reactor vessel 4 is fixedly connected to the first baffle 105. The other end of any bubble protection baffle 103 extending axially along the reactor vessel 4 has a fluid flow channel 109 between it and the second baffle 102 or the third baffle 106. The fluid flow channel 109 is used to guide the coolant through the fluid flow channel 109 and flow from the heat exchanger 3 into the main circulation pump 2.

[0048] The second baffle 102 and the third baffle 106 are used to guide the flow of coolant in the reactor. This arrangement enables each heat exchanger positioning guide hole 108 to have a protective structure on both sides, further preventing bubbles from entering the reactor core and further improving the safety of the system.

[0049] In some embodiments, please refer to Figure 1 and Figure 2 A hot and cold pool partition 107 is also provided between the two adjacent ends of the second partition 102 and the third partition 106. The hot and cold pool partition 107 has an upper guide positioning hole 101 for the main circulation pump. Correspondingly, a lower guide positioning hole 111 for the main circulation pump is provided at a corresponding position on the first partition 105. This partition is used to install both ends of the main circulation pump 2 and to guide and position the main circulation pump 2. The hot and cold pool partition is used to separate the reactor hot pool and the cold pool.

[0050] In some embodiments, please refer to Figure 1 and Figure 2 The second partition 102 and the third partition 106 are respectively provided with heat exchanger guide positioning holes 108 for installing heat exchangers and guiding and positioning heat exchangers 3.

[0051] In some embodiments, please refer to Figure 1 and Figure 2 The bubble protection baffle 103 extends axially along the reactor vessel 4 for 1 / 2 to 3 / 5 of the length of the line connecting the center of the upper positioning guide hole 101 and the lower positioning guide hole 111 of the main circulation pump. Within this distance range, it can effectively block bubbles generated by heat exchanger rupture accidents, reducing the proportion of millimeter-sized bubbles entering the reactor core from 30% to 5%, greatly improving reactor safety.

[0052] In some embodiments, the thickness of the bubble protection baffle 103 is 1.1 to 1.2 times the thickness of the first baffle 105; the length:width:thickness of the bubble protection baffle is 50:80:1 to 50:80:2. This configuration meets the structural performance requirements of the in-core components while reducing the impact on the flow resistance of the coolant.

[0053] In some embodiments, please refer to Figure 1 and Figure 2 The bubble protection baffle 103 is a rectangular baffle. This design satisfies structural performance requirements while improving the efficiency of the in-core containment structure 1 in guiding the coolant.

[0054] In some embodiments, please refer to Figure 3The hot and cold pool partition includes a first bent plate 1071, a parallel plate 1072, and a second bent plate 1073. The parallel plate 1072 is spaced apart from the second partition 102 and the third partition 106. The first bent plate 1071 and the second bent plate 1073 extend along the axial direction of the reactor vessel 4 toward the second partition 102 and the third partition 106, respectively. The first bent plate 1071 is fixedly connected to one end of the second partition 102, and the second bent plate 1073 is fixedly connected to one end of the third partition 106. This arrangement can well adapt to the structure on the main circulation pump 2, isolating the upper part of the main circulation pump from the reactor hot pool section.

[0055] In some embodiments, please refer to Figure 2 The bubble protection partition 103 is provided with reinforcing ribs 104 at the fixed connection between it and the first partition 105. This makes the structure of the bubble protection partition 103 more stable and its position more stable, and it is less likely to deform due to the scouring of fluid.

[0056] In some embodiments, the extension length of the reinforcing rib 104 away from the bubble protection partition 103 is 1 / 5 to 1 / 6 of the width of the bubble protection partition 103.

[0057] In some of the above embodiments, the installation process of the provided lead-cooled fast reactor in-core containment structure 1 is as follows: the in-core containment structure 1 is installed inside the reactor vessel 4, and the outer wall of the in-core containment structure 1 is fixedly connected to the inside of the reactor vessel 4. Next, the heat exchanger 3 and the main circulating pump 2 are vertically placed into the reactor one by one by hoisting. Positioning and calibration are performed through the heat exchanger positioning guide hole 108, the upper positioning guide hole 101 of the main circulating pump, and the lower positioning guide hole 111 of the main circulating pump. The heat exchanger positioning guide hole 108 allows for quick-release maintenance of the heat exchanger 3. The cylinder wall of the heat exchanger 3 is fixed to the heat exchanger positioning guide hole 108 through a quick-release connector. During disassembly and assembly, the connector sleeve is loosened, and the heat exchanger 3 can be lifted out using an off-core crane. The lower positioning guide hole 111 of the main circulation pump allows for quick disassembly and maintenance of the main circulation pump 2. The cylinder wall of the main circulation pump 2 is fixed to the lower positioning guide hole 111 of the main circulation pump through a quick-release connector. When disassembling and assembling, the connector sleeve is loosened, and the main circulation pump 2 can be lifted out by an off-site crane. The upper positioning guide hole 101 of the main circulation pump can provide stable support for the main circulation pump 2.

[0058] This utility model is described through several embodiments. In the description of this utility model, it should be understood that the terms "center," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," and "outer," etc., indicating orientation or positional relationships, are based on the orientation or positional relationships shown in the accompanying drawings and are only for the convenience of describing this utility model and simplifying the description, and do not indicate or imply that the device or element referred to has a specific orientation, or is constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on the disclosure of this utility model. Unless the context requires otherwise, throughout the specification and claims, the term "comprising" is interpreted as open and inclusive, that is, "including, but not limited to." The terms "first" and "second" are only used to distinguish different descriptive objects and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. In the description of the embodiments disclosed in this utility model, unless otherwise stated, "a plurality of" means two or more.

[0059] In the accompanying drawings, the thickness of layers and regions has been enlarged for clarity. Therefore, variations in shape relative to the drawings are contemplated due to factors such as manufacturing techniques and / or tolerances. Consequently, exemplary embodiments should not be construed as limited to the shapes of the regions shown herein, but rather include shape deviations caused, for example, by manufacturing processes. For instance, etched areas shown as rectangular would typically have curved features. Therefore, the regions shown in the drawings are schematic in nature, and their shapes are not intended to show the actual shapes of areas of the device, nor are they intended to limit the scope of the exemplary embodiments.

[0060] The above description is merely a specific embodiment disclosed in this utility model, but the scope of protection disclosed in this utility model is not limited thereto. Any changes or substitutions conceived by those skilled in the art within the technical scope disclosed in this utility model should be included within the scope of protection disclosed in this utility model. Therefore, the scope of protection disclosed in this utility model should be determined by the scope of the claims.

Claims

1. A lead-cooled fast reactor in-reactor enclosure structure for placement within the reactor vessel, characterized in that, It includes an inner circumferential cylinder, which is coaxially arranged with the reactor vessel; a first partition and a second partition are respectively fixed at both ends of the inner circumferential cylinder. The first and second partitions extend radially outward along the outer periphery of both ends of the inner circumference cylinder to the inner wall of the reactor vessel and are fixedly connected to the inner wall of the reactor vessel. A heat exchanger receiving position is provided between the first partition and the outer wall of the inner cylinder, and bubble protection partitions are respectively provided on both sides of the heat exchanger receiving position; One end of the bubble protection baffle extending axially along the reactor vessel is fixedly connected to the first baffle. The bubble protection baffle extends axially along the reactor vessel at one end and has a fluid flow channel between it and the second baffle.

2. The lead-cooled fast reactor internal containment structure according to claim 1, characterized in that, The first partition has two symmetrically arranged heat exchanger receiving positions between it and the outer wall of the inner cylinder, and the second partition is arranged corresponding to one of the heat exchanger receiving positions. The inner circumferential cylinder is fixed with a second partition plate at one end and a third partition plate is also fixed at the other end. The third partition plate extends radially outward along the outer periphery of the corresponding end of the inner circumferential cylinder to the inner wall of the reactor vessel and is fixedly connected to the inner wall of the reactor vessel. The third partition plate is set in a position corresponding to another heat exchanger accommodating position. Each heat exchanger housing is provided with bubble protection baffles on both sides. One end of each bubble protection baffle extending along the axial direction of the reactor vessel is fixedly connected to the first baffle. The other end of any bubble protection baffle extending along the axial direction of the reactor vessel has a fluid flow channel between it and the second or third baffle.

3. The lead-cooled fast reactor internal containment structure according to claim 2, characterized in that, A hot and cold pool partition is also provided between the two adjacent ends of the second partition and the third partition. The hot and cold pool partition is provided with a guide positioning hole for the main circulation pump. Correspondingly, a guide positioning hole for the main circulation pump is provided at the corresponding position on the first partition. This is used to install the two ends of the main circulation pump and guide and position the main circulation pump.

4. The lead-cooled fast reactor internal containment structure according to claim 3, characterized in that, The hot and cold pool partition includes a first bent plate, a parallel plate, and a second bent plate. The parallel plate is spaced apart from the second partition and the third partition. The first bent plate and the second bent plate extend along the axial direction of the reactor vessel toward the second partition and the third partition, respectively. The first bent plate is fixedly connected to one end of the second partition, and the second bent plate is fixedly connected to one end of the third partition.

5. The lead-cooled fast reactor internal containment structure according to claim 2, characterized in that, The second partition and the third partition are respectively provided with heat exchanger guide positioning holes for installing heat exchangers and guiding and positioning them.

6. The lead-cooled fast reactor internal containment structure according to claim 1, characterized in that, The bubble protection partition is provided with reinforcing ribs at the fixed connection between the bubble protection partition and the first partition.

7. The lead-cooled fast reactor internal containment structure according to claim 6, characterized in that, The extension length of the reinforcing rib away from the bubble protection partition is 1 / 5 to 1 / 6 of the width of the bubble protection partition.

8. The lead-cooled fast reactor in-charge containment structure according to any one of claims 1 to 7, characterized in that, The length of the bubble protection baffle along the axial direction of the reactor vessel is 1 / 2 to 3 / 5 of the length of the line connecting the center of the upper positioning guide hole and the lower positioning guide hole of the main circulation pump.

9. The lead-cooled fast reactor in-charge containment structure according to any one of claims 1 to 7, characterized in that, The thickness of the bubble protection partition is 1.1 to 1.2 times the thickness of the first partition; the length:width:thickness of the bubble protection partition is 50:80:1 to 50:80:

2.

10. The lead-cooled fast reactor in-charge containment structure according to any one of claims 1 to 7, characterized in that, The bubble protection partition is a rectangular partition.

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