Triangular inclined plane type high heat load first wall structure

Abstract

The invention discloses a triangular slope type high-heat-load first wall structure which comprises a first wall body, a reinforcing structure and a protective structure. The first wall body is in a U shape, a heat exchange structure is arranged on the outer wall of the first wall body, the heat exchange structure comprises a plurality of triangular slope heat exchange units which are arranged in parallel at intervals in the transverse direction, and each triangular slope heat exchange unit and the outer wall of the first wall body define a cooling flow channel. The reinforcing structure is a rib plate arranged on the inner wall of the first wall body; the protection structure is an armor which is arranged on the outer side of the heat exchange structure and faces the plasma area. The triangular slope heat exchange units, the armors and the rib plates are designed on the first wall body, so that the heat carrying performance and the pressure bearing performance of the first wall can be effectively improved, the high-heat-load heat carrying requirement of 0.5-1 MW / m < 2 > of the first wall of the fusion reactor can be met, meanwhile, the material consumption of the first wall is reduced, and therefore the neutron penetrability of the first wall is improved, and the heat transfer efficiency of the first wall is improved. And the core performance of the cladding is improved.

Description

Technical Field

[0001] The invention relates to the technical field of nuclear fusion reactors, and in particular to a triangular inclined surface high heat load first wall structure for a fusion reactor. Background Art

[0002] In nuclear fusion reactions, deuterium-tritium fuel is heated and confined to reach the Lawson criterion, forming a high-temperature plasma of hundreds of millions of degrees. In this process, the first wall, as a key component of the fusion reactor blanket, plays a vital role. It not only directly faces the high-temperature plasma, covering more than 80% of the high-temperature plasma area, but also bears the extremely high heat load from the high-temperature plasma. Therefore, the design of the first wall structure is directly related to the stability and safety of the nuclear fusion reaction, and is one of the core components of the nuclear fusion reactor.

[0003] With the continuous advancement of fusion energy technology, the performance requirements for the first wall structure are also increasing. In the fusion reaction, the first wall needs to withstand an average heat load of up to 0.5MW / m2, and in some local areas, this value is even higher. In addition, the first wall is also a container for the functional materials coated in the cladding, and is the first pressure-bearing boundary when the internal pipe of the cladding ruptures. Therefore, ensuring the structural integrity of the first wall in the event of a coolant breach is crucial to the safe operation of the fusion reactor.

[0004] Currently, low activated ferrite martensitic stainless steel (RAFMs) is a mature choice for the first wall structural material. However, the allowable temperature of this material is only 550°C, which limits the performance of the first wall to a certain extent. Although there are other advanced structural materials such as vanadium alloys, oxide dispersoid stainless steel (ODS) and silicon carbide composites (SiC / SiC f ) etc., but these materials are still immature and difficult to be widely used in the first wall structure.

[0005] In order to cope with the high heat load of the first wall, the existing technical means mainly rely on setting a rectangular flow channel inside the first wall and using high-pressure water or helium as a coolant to remove heat, such as the patent CN114420314A. This design has been widely used in the design of tritium-producing blankets such as the Chinese Solid Ceramic Tritium Breeder Test Blanket (HCCB TBM). However, due to the limited structural heat exchange area, this design still faces great challenges when facing a heat load demand of more than 0.5MW / m2. If the convective heat transfer performance is enhanced by increasing the coolant flow rate, although the heat carrying capacity can be improved to a certain extent, it will also cause a large pressure drop in the coolant, thereby reducing the economy of the fusion reactor.

[0006] In order to further improve the heat carrying capacity of the first wall, some researchers have proposed a method of enhancing convective heat transfer, that is, adding flow channel plugs inside the flow channel to improve the convective heat transfer efficiency of the flow channel wall. Although this method improves the heat carrying capacity of the first wall to a certain extent, it also brings new problems. Due to the addition of plugs inside the flow channel, the structure of the first wall becomes extremely complex and the process difficulty is greatly increased. At the same time, the increase in flow channel resistance also leads to an increase in coolant pressure drop and energy consumption. In addition, enhanced convective heat transfer may also cause vibration and noise problems, which will have an adverse effect on the stability of the reactor.

[0007] In terms of the pressure-bearing performance of the first wall box body facing the breach of the coolant in the proliferation zone, the existing structure mainly improves the pressure-bearing performance by increasing the wall thickness or adding partitions. However, both methods have obvious disadvantages. Although increasing the wall thickness can improve the pressure-bearing capacity, it will also lead to poor neutron penetration, thus affecting the nuclear performance of the blanket. Although adding partitions can improve the pressure-bearing performance to a certain extent, the nuclear heat generated in the partitions requires additional flow channels to be designed to be discharged, which increases the complexity of the internal structure of the blanket. At the same time, the partitions will also absorb neutrons, resulting in a decrease in the nuclear performance of the blanket.

[0008] In summary, the first wall structure design scheme in the prior art still has certain deficiencies in dealing with high heat load and pressure bearing performance. Therefore, a new first wall design scheme is urgently needed to significantly improve the heat carrying capacity, neutron penetration and pressure bearing performance of the first wall. Summary of the invention

[0009] The purpose of the present invention is to provide a triangular inclined surface high heat load first wall structure in view of the fact that the first wall structure design scheme in the prior art still has certain deficiencies in coping with high heat load and pressure bearing performance. The first wall structure adopts a triangular inclined surface to change the heat load incident angle, reduce the surface heat load, and increase the heat exchange area, so that the heat carrying performance of the first wall is greatly improved, and can withstand 0.5-1MW / m 2 The high heat load from the fusion reactor plasma; at the same time, by adding ribs on the inner side of the first wall, the wall thickness of the first wall can be effectively reduced, the penetration of fusion neutrons can be improved, and the pressure bearing performance and nuclear performance of the first wall can be increased.

[0010] The present invention is achieved through the following technical solutions:

[0011] The present invention provides a triangular inclined surface high heat load first wall structure, comprising a first wall body, a reinforcement structure and a protective structure; the first wall body is U-shaped, a heat exchange structure is arranged on the outer wall of the first wall body, and a cooling flow channel is formed in the heat exchange structure; the reinforcement structure is a rib plate arranged on the inner wall of the first wall body; the protective structure is armor arranged on the outer side of the heat exchange structure facing the plasma area.

[0012] As a preferred solution of the present invention, the heat exchange structure includes a plurality of triangular slope heat exchange units arranged in parallel with each other and spaced apart in the transverse direction, and each triangular slope heat exchange unit and the outer wall of the first wall body form a cooling channel.

[0013] As a preferred solution of the present invention, the spacing between adjacent triangular slope heat exchange units is 4 mm to 6 mm.

[0014] As a preferred solution of the present invention, the inclination angles of the slopes on both sides of the triangular slope heat exchange unit are 30° to 60°, and the thickness is 2mm to 3mm.

[0015] As a preferred solution of the present invention, a rounded corner is provided between the tops of the two side slopes of the triangular slope heat exchange unit, and a rounded corner is provided between the bottoms of the two side slopes of the triangular slope heat exchange unit and the first wall body.

[0016] As a preferred solution of the present invention, the armor is made of tungsten material or beryllium material.

[0017] As a preferred solution of the present invention, the armor is connected to the heat exchange structure by hot isostatic pressing welding or coating.

[0018] As a preferred solution of the present invention, the armor is divided into multiple blocks along the cooling channel direction, and gaps are provided between adjacent blocks.

[0019] As a preferred embodiment of the present invention, the armor is attached to a plurality of triangular inclined heat exchange units on the outer wall of the first wall body, and the armor is provided with a rounded corner at the front end portion close to the plasma, and the rounded corner size is smaller than the inner rounded corner.

[0020] As a preferred solution of the present invention, the first wall body includes a front portion and two side portions connected to its two ends, the front portion is provided with ribs in both horizontal and vertical directions, and the side portions are provided with ribs in one horizontal or vertical direction.

[0021] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0022] The present invention arranges a plurality of triangular inclined heat exchange units on the outer wall of the first wall body as a heat exchange structure, arranges armor as a protective structure in the area outside the heat exchange structure facing the plasma, and arranges a rib plate on the inner wall of the first wall body as a reinforcement structure, which can not only effectively improve the heat carrying performance and pressure bearing performance of the first wall, but also meet the requirements of 0.5-1MW / m 2 The high heat load heat carrying demand is met, while reducing the material usage of the first wall, thereby improving the neutron penetration of the first wall and increasing the nuclear performance of the blanket. The first wall design structure has important value in fusion reactors and also has important potential for use in other similar fields facing high heat loads. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] In order to more clearly illustrate the technical solutions of the exemplary embodiments of the present invention, the following briefly introduces the drawings required for use in the embodiments. It should be understood that the following drawings only illustrate certain embodiments of the present invention and should not be regarded as limiting the scope. For those of ordinary skill in the art, other relevant drawings can be obtained based on these drawings without creative work. In the drawings:

[0024] Figure 1 This is a schematic diagram of the triangular slope type high heat load first wall structure in the present invention;

[0025] Figure 2 It is a schematic cross-sectional view of the front portion AA of the first wall in the present invention;

[0026] Figure 3 This is an axonometric view of the triangular slope type high heat load first wall structure in the present invention;

[0027] Figure 4 It is a partial enlarged view of the first wall corner (B) in the present invention;

[0028] Figure 5 It is a partial enlarged view of the side portion (C) of the first wall in the present invention;

[0029] Figure 6 It is a partial enlarged view of another corner (D) of the first wall in the present invention.

[0030] Marks and corresponding parts names in the attached drawings:

[0031] 1-first wall body, 2-triangular slope heat exchange unit, 3-rib plate, 4-armor. DETAILED DESCRIPTION

[0032] In order to make the objectives, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with embodiments and drawings. The exemplary embodiments of the present invention and their description are only used to explain the present invention and are not intended to limit the present invention.

[0033] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by technicians in the technical field to which this application belongs; the terms used herein are only for the purpose of describing specific embodiments and are not intended to limit this application; the terms "including" and "having" in the specification and claims of this application and the above-mentioned figure descriptions and any variations thereof are intended to cover non-exclusive inclusions.

[0034] In the description of the embodiments of the present application, technical terms such as "first" and "second" are only used to distinguish different objects and cannot be understood as indicating or implying relative importance or implicitly indicating the number, specific order or primary and secondary relationship of the indicated technical features.

[0035] Reference to "embodiments" herein means that a particular feature, structure, or characteristic described in conjunction with the embodiments may be included in at least one embodiment of the present application. The appearance of the phrase in various locations in the specification does not necessarily refer to the same embodiment, nor is it an independent or alternative embodiment that is mutually exclusive with other embodiments. It is explicitly and implicitly understood by those skilled in the art that the embodiments described herein may be combined with other embodiments.

[0036] In the description of the embodiments of the present application, the term "and / or" is only a description of the association relationship of associated objects, indicating that three relationships may exist. For example, A and / or B can represent: A exists, A and B exist at the same time, and B exists. In addition, the character " / " in this article generally indicates that the associated objects before and after are in an "or" relationship.

[0037] In the embodiments of the present application, the same reference numerals represent the same components, and for the sake of brevity, detailed descriptions of the same components are omitted in different embodiments. It should be understood that the thickness, length, width and other dimensions of various components in the embodiments of the present application shown in the drawings, as well as the overall thickness, length, width and other dimensions of the integrated device are only exemplary descriptions and should not constitute any limitation to the present application.

[0038] In the description of the embodiments of the present application, the term "multiple" refers to more than two (including two). Similarly, "multiple groups" refers to more than two groups (including two groups), and "multiple pieces" refers to more than two pieces (including two pieces), unless otherwise clearly and specifically defined.

[0039] In the description of the embodiments of the present application, the technical terms "center", "longitudinal", "lateral", "length", "width", "thickness", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", "clockwise", "counterclockwise", "axial", "radial", "circumferential", etc. indicate orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings, which are only for the convenience of describing the embodiments of the present application and simplifying the description, and do not indicate or imply that the referred device or element must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be understood as a limitation on the embodiments of the present application.

[0040] In the description of the embodiments of the present application, unless otherwise clearly specified and limited, technical terms such as "installed", "connected", "connected", "fixed" and the like should be understood in a broad sense. For example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection or an indirect connection through an intermediate medium, and it can be the internal connection of two elements or the interaction relationship between two elements. For those of ordinary skill in the art, the specific meanings of the above terms in the embodiments of the present application can be understood according to the specific circumstances.

[0041] The conventional first wall structure is a plate-type design with a rectangular flow channel inside. The first wall heating surface of this structure is perpendicular to the heat load. When facing high heat load (especially when the heat load of a fusion reactor exceeds 0.5MW / m 2 ), it is difficult to achieve the purpose of heat transfer; adding a plug-in structure in a rectangular flow channel is difficult to achieve in processing, and the fluid resistance is also very large. On the other hand, conventional designs have not considered using the characteristics of ribs to increase the pressure-bearing performance of the structure and reduce the material consumption of the structure.

[0042] In view of this, in order to further improve the heat carrying capacity of the first wall and at the same time make the first wall have good neutron penetrability and high pressure bearing performance, the applicant has invented a new first wall structural design scheme after in-depth research. This scheme is expected to greatly improve the heat carrying capacity of the first wall and at the same time have the characteristics of good neutron penetrability and high pressure bearing performance.

[0043] Please refer to Figures 1 to 6 A triangular inclined high heat load first wall structure provided in an embodiment of the present application includes a first wall body 1, a reinforcement structure and a protective structure; the first wall body 1 is U-shaped, and a heat exchange structure is arranged on the outer wall of the first wall body 1, and a cooling flow channel is formed in the heat exchange structure; the reinforcement structure is a rib plate 3 arranged on the inner wall of the first wall body 1; the protective structure is an armor 4 arranged on the outer side of the heat exchange structure facing the plasma area.

[0044] It should be noted that the first wall body 1 in this embodiment includes a front portion and two side portions connected to the two ends of the front portion, the front portion and the two side portions form a U-shaped structure, and the two side portions are connected to the ends of the front portion by a rounded transition, and the rounded transition area forms the corner of the first wall.

[0045] By arranging a heat exchange structure on the outer wall of the first wall body 1, and arranging an armor 4 as a protective structure in the area outside the heat exchange structure facing the plasma, and arranging a rib plate 3 as a reinforcement structure on the inner wall of the first wall body 1, not only can the heat carrying performance and pressure bearing performance of the first wall be effectively improved, but also can meet the requirements of the first wall of the fusion reactor of 0.5-1MW / m 2 The high heat load heat carrying demand is met, and at the same time the thickness of the first wall body 1 is reduced, thereby improving the neutron penetration of the first wall and increasing the nuclear performance of the blanket. The first wall structure is expected to greatly improve the heat carrying capacity of the first wall, and at the same time has the characteristics of good neutron penetration and high pressure bearing performance. It has important value in fusion reactors and also has important use potential in other similar fields facing high heat loads.

[0046] According to some embodiments of the present application, the heat exchange structure includes a plurality of triangular slope heat exchange units 2 arranged in parallel with each other in a transverse direction, and each triangular slope heat exchange unit 2 forms a cooling channel with the outer wall of the first wall body 1. The triangular slope heat exchange unit 2 is arranged on the plasma side of the first wall body 1, and has two inclined slopes, the two side slopes form a tip at one end away from the first wall body 1, and the two bottoms at the other end are connected to the first wall body 1.

[0047] The heat exchange structure adopts a plurality of triangular slope heat exchange units 2, each of which has a cooling channel inside. Since the triangular slope changes the incident angle of the heat load, the surface heat load is reduced, and the heat exchange area is increased, so that the heat carrying performance of the first wall is greatly improved, and it can withstand 0.5-1MW / m 2 High heat loads from fusion reactor plasma.

[0048] It should be noted that the coolant introduced into the cooling channel can be helium, pressurized water, supercritical carbon dioxide or liquid lithium, etc. The coolant flows in from one side and flows out from the other side. At the same time, the heat exchange efficiency can be further improved by increasing the roughness of the cooling channel of the triangular slope heat exchange unit 2.

[0049] According to some embodiments of the present application, the spacing between adjacent triangular slope heat exchange units 2 is 4 mm, that is, the triangular slope heat exchange units 2 are arranged in sequence with a spacing of 4 mm on the first wall body 1. Of course, the spacing between the triangular slope heat exchange units 2 can be designed to have different spacing sizes according to heat exchange needs.

[0050] According to some embodiments of the present application, the inclination angle of the inclined surfaces on both sides of the triangular inclined surface heat exchange unit 2 is 60°, the side length of the inclined surfaces on both sides is 10 mm, and the wall thickness of the inclined surfaces on both sides is 2 mm. The inclined surfaces on both sides of the triangular inclined surface heat exchange unit 2 are arranged symmetrically, that is, the cross section of the cooling channel formed inside it is an equilateral triangle. Through this special structure, the contact inclination angle between the heat load and the first wall can be changed, thereby increasing the heat-bearing area of ​​the heat load and reducing the heat load per unit area. For example, by adopting an inclination angle of 60°, the heat load of the first wall can be effectively reduced to 1 / 2 of the original.

[0051] It should be noted that the triangular slope heat exchange unit 2 has certain differences in processing difficulty and improvement of heat exchange performance when using different inclination angles. The triangular slope heat exchange unit 2 can be designed with different spacings and different inclination angles according to the distribution characteristics of heat exchange.

[0052] According to some embodiments of the present application, the chamfers of the top tips of the two side slopes of the triangular slope heat exchange unit 2 are R2.5mm to ensure that the wall thickness at the corners is consistent with the wall thickness at other positions. The chamfers between the bottom of the two side slopes of the triangular slope heat exchange unit 2 and the first wall body 1 are R0.5mm to reduce the stress concentration caused by the sharp corners.

[0053] According to some embodiments of the present application, the armor 4 is made of a tungsten material with a high atomic number and low sputtering, or a beryllium material with a relatively high sputtering atomic number and low sputtering. By arranging the armor 4 outside the triangular slope heat exchange unit 2, the first wall is protected to prevent the sputtering effect between the plasma and the wall from affecting the plasma.

[0054] According to some embodiments of the present application, the armor 4 is connected to the triangular slope heat exchange unit 2 by hot isostatic pressing welding or coating. The armor 4 is mainly used to protect the interaction between the plasma and the first wall. For a high heat load environment that does not require the armor 4, the armor 4 can be ignored in the design. Since there is no plasma bombardment on the side, the armor 4 is not arranged, and the corner area between the front and the side is arranged with the armor 4.

[0055] According to some embodiments of the present application, the armor 4 is divided into multiple pieces along the cooling channel direction, and gaps are provided between adjacent pieces. The armor 4 has gaps along the channel direction, which can reduce its thermal stress. Specifically, each tungsten armor 4 has a length of 50 mm along the channel direction, and its cross-sectional shape is also triangular, and the gap between the tungsten armor 4 is 0.5 mm.

[0056] According to some embodiments of the present application, the armor 4 is arranged to fit a plurality of triangular inclined heat exchange units 2 on the outer wall of the first wall body 1, and the armor 4 is provided with a rounded corner at the front end portion close to the plasma, and the rounded corner size is smaller than the inner rounded corner. Due to the interaction between the plasma and the armor 4, as the operation time of the fusion reactor increases, the armor 4 is gradually consumed and thinned, so a smaller chamfer can be used at the front end close to the plasma to increase the thickness of the armor 4 at this location and improve the service life of the armor 4.

[0057] The wall thickness of the tungsten armor 4 is 2 mm, and the chamfer near the tip of the triangular bevel is consistent with the chamfer of the triangular bevel, which is R2.5 mm, to ensure that the armor 4 and the triangular bevel can be well welded into a whole. Since the outer side of the armor 4 is most strongly affected by the plasma drifting particles, its chamfer is set to R2 mm to make it thicker.

[0058] According to some embodiments of the present application, the first wall body 1 includes a front portion and two side portions connected to the two ends thereof, the front portion is provided with ribs 3 in both horizontal and vertical directions, and the side portions are provided with ribs 3 in one horizontal or vertical direction. Since the front portion of the first wall has the worst pressure bearing performance, ribs 3 in both horizontal and vertical directions are provided on the inner wall of the front portion of the first wall to improve its pressure bearing performance. Ribs 3 in only one direction are provided on the side portion, which may be horizontal or vertical ribs 3, to reduce the number of ribs 3 and reduce the influence of the structure on neutron penetration.

[0059] Specifically, the size of the grid can be adjusted according to the actual size of the first wall, and the typical grid size on the front is a square grid rib plate 3 of 80 mm×80 mm. The thickness of the rib plate 3 is about 5 mm, and the height is about 20 mm. Of course, the horizontal and vertical heights of the grid rib plate 3 can also be adjusted to be unequal according to the calculation results.

[0060] By adopting the first wall structure solution in this embodiment, the front thickness of the first wall body 1 is reduced from 30 mm to 18 mm, and the front wall thickness is reduced by 40%, which greatly improves the neutron penetration rate. By simply increasing the thickness of the side, the pressure bearing capacity of the side of the first wall body 1 is improved, and the complexity of the first wall box body is reduced.

[0061] This solution can effectively improve the heat carrying capacity and pressure bearing capacity of the first wall. For the commonly used 8MPa helium coolant, it can withstand 0.5-1MW / m 2 The high heat load is twice that of the first wall of the ordinary rectangular flow channel. The helium pressure drop does not increase significantly compared with the first wall of the conventional rectangular flow channel. On the other hand, the rib plate 3 inside the first wall reduces the material consumption of the first wall, thereby improving the neutron penetration of the first wall and increasing the nuclear performance of the blanket.

[0062] The specific implementation methods described above further illustrate the objectives, technical solutions and beneficial effects of the present invention in detail. It should be understood that the above description is only a specific implementation method of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A triangular slope type high heat load first wall structure, characterized in that: It includes a first wall body, a reinforcement structure and a protective structure; the first wall body is U-shaped, a heat exchange structure is arranged on the outer wall of the first wall body, and a cooling flow channel is formed in the heat exchange structure; the reinforcement structure is a rib plate arranged on the inner wall of the first wall body; the protective structure is armor arranged on the outer side of the heat exchange structure facing the plasma area.

2. The triangular slope type high heat load first wall structure according to claim 1, characterized in that: The heat exchange structure comprises a plurality of triangular slope heat exchange units which are arranged in parallel with each other and spaced apart in the transverse direction, and each triangular slope heat exchange unit and the outer wall of the first wall body form a cooling channel.

3. The triangular slope type high heat load first wall structure according to claim 2, characterized in that: The spacing between adjacent triangular slope heat exchange units is 4 mm to 6 mm.

4. The triangular slope type high heat load first wall structure according to claim 2, characterized in that: The inclination angles of the inclined surfaces on both sides of the triangular inclined surface heat exchange unit are 30° to 60°, and the thickness is 2mm to 3mm.

5. The triangular slope type high heat load first wall structure according to claim 2, characterized in that: A rounded corner is arranged between the tops of the two side slopes of the triangular slope heat exchange unit, and a rounded corner is arranged between the bottoms of the two side slopes of the triangular slope heat exchange unit and the first wall body.

6. The triangular slope type high heat load first wall structure according to any one of claims 1 to 5, characterized in that: The armor is made of tungsten material or beryllium material.

7. The triangular slope type high heat load first wall structure according to claim 6, characterized in that: The armor is connected to the heat exchange structure by hot isostatic pressing welding or coating.

8. The triangular slope type high heat load first wall structure according to any one of claims 1 to 5, characterized in that: The armor is divided into multiple blocks along the cooling channel direction, and gaps are provided between adjacent blocks.

9. The triangular slope type high heat load first wall structure according to any one of claims 2 to 5, characterized in that: The armor is attached to a plurality of triangular inclined heat exchange units on the outer wall of the first wall body. The armor is provided with a rounded corner at the front end portion close to the plasma, and the size of the rounded corner is smaller than the inner rounded corner.

10. The triangular slope type high heat load first wall structure according to any one of claims 1 to 5, characterized in that: The first wall body includes a front portion and two side portions connected to both ends thereof, the front portion is provided with ribs in both horizontal and vertical directions, and the side portions are provided with ribs in one direction, horizontal or vertical.

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