Bottom device and fuel assembly

Abstract

The invention discloses a bottom device and a fuel assembly, belongs to the technical field of reactor engineering, and mainly aims at changing the flow channel form when a cooling medium flows through a foreign matter prevention plate and avoiding the situation of uneven flow field distribution. According to the main technical scheme, the bottom device comprises a lower pipe base and a foreign matter prevention plate connected with the lower pipe base; the foreign matter prevention plate is provided with a first surface and a second surface which are arranged back to back along the flow path direction of the cooling medium, the first surface faces the lower reactor core plate, and the lower reactor core plate is provided with a cooling medium flow channel hole; a first convex part is arranged at the position, opposite to the cooling medium runner hole, in the first surface, and the first convex part protrudes towards the side where the lower reactor core plate is located; the first face is further provided with a second protruding part, the second protruding part is connected with the first protruding part, and the protruding direction of the second protruding part is the same as the protruding direction of the first protruding part.

Description

Technical Field

[0001] This application belongs to the field of reactor engineering technology, specifically relating to a bottom device and fuel assembly. Background Technology

[0002] Currently, foreign object shields (FOPs) mostly adopt a flat plate structure. When the cooling medium flows through the FOP and enters the reactor core, the uneven distribution of the flow field on the surface of the FOP can lead to significant differences in the flow rate of the cooling medium in different areas. This means that the cooling medium entering the reactor core cannot evenly cover all fuel rods, and some fuel rods may experience localized overheating due to insufficient cooling. This not only affects the service life of the fuel rods but also poses a potential risk to the operational safety of the nuclear reactor. Summary of the Invention

[0003] In view of this, this application provides a bottom device and a fuel assembly, the main purpose of which is to change the flow channel morphology of the cooling medium when it flows through the foreign object protection plate, so as to avoid uneven flow field distribution.

[0004] To achieve the above objectives, this application mainly provides the following technical solutions: One aspect of this application provides a bottom device, including a lower tube seat and a foreign object protection plate connected to the lower tube seat; The foreign object protection plate has a first side and a second side arranged opposite to each other along the flow path of the cooling medium. The first side faces the lower core plate, and the lower core plate is provided with cooling medium flow channel holes. A first protrusion is provided on the first surface at a position relative to the cooling medium flow channel hole, and the first protrusion protrudes toward the side where the lower core plate is located; The first surface is further provided with a second protrusion, which is connected to the first protrusion, and the protrusion direction of the second protrusion is the same as that of the first protrusion.

[0005] Optionally, the portion of the lower core plate relative to the foreign object protection plate has at least four cooling medium flow channel holes, and the at least four cooling medium flow channel holes are distributed in a rectangular array on the lower core plate; the first protrusion includes at least four first rectification units, and the at least four first rectification units correspond one-to-one with the at least four cooling medium flow channel holes and are coaxially arranged.

[0006] Optionally, the end face of the first rectifier unit facing the lower core plate is a first gradient surface, and the position where the first gradient surface intersects with the central axis of the first rectifier unit is a first position. The first position is the highest point of the first gradient surface along the convex direction of the first rectifier unit, and the height of the first gradient surface gradually decreases from the first position towards the edge of the first rectifier unit.

[0007] Optionally, the second convex portion comprises at least one second rectifying unit, the second rectifying unit is located in an area surrounded by at least four first rectifying units arranged in a rectangular array, and four sides of the second rectifying unit are respectively connected with sides of adjacent first rectifying units among the at least four first rectifying units. Optionally, an end surface of the second rectifying unit facing the lower core plate is a second gradient surface, a position intersecting with a central axis of the second rectifying unit in the second gradient surface is a second position, the second position is a highest position of the second gradient surface in a convex direction of the second rectifying unit, and a height of the second gradient surface gradually decreases from the second position to an edge direction of the second rectifying unit.

[0008] Optionally, the second convex portion further comprises at least four third rectifying units, the at least four third rectifying units are respectively arranged in areas surrounded by two adjacent first rectifying units among the at least four first rectifying units and an edge of the first surface, and each third rectifying unit is connected with the two first rectifying units.

[0009] Optionally, an end surface of the third rectifying unit facing the lower core plate is a third gradient surface, a position of a midpoint of a side of the third rectifying unit coinciding with the edge of the first surface in the third gradient surface is a third position, the third position is a highest position of the third gradient surface in a convex direction of the third rectifying unit, and a height of the third gradient surface gradually decreases from the third position to an edge direction of the third rectifying unit.

[0010] Optionally, the second convex portion further comprises at least four fourth rectifying units, the at least four fourth rectifying units are respectively arranged at four corners of the first surface, and each fourth rectifying unit is connected with an adjacent first rectifying unit.

[0011] Optionally, an end surface of the fourth rectifying unit facing the lower core plate is a fourth gradient surface, a position of a vertex of a corner of the first surface in the fourth gradient surface is a fourth position, the fourth position is a highest position of the fourth gradient surface in a convex direction of the fourth rectifying unit, and a height of the fourth gradient surface gradually decreases from the fourth position to an edge direction of the fourth rectifying unit.

[0012] Optionally, a convex height of the first convex portion relative to the first surface is greater than a convex height of the second convex portion relative to the first surface, a first filter hole is arranged on the first convex portion, a second filter hole is arranged on the second convex portion, and a hole diameter of the first filter hole is smaller than a hole diameter of the second filter hole.

[0013] In another aspect of the present application, a fuel assembly is provided, comprising the bottom device described in any one of the above.

[0014] By means of the technical scheme, the application has at least the following beneficial effects: The application provides a bottom device and a fuel assembly, wherein the first convex part is arranged corresponding to the cooling medium flow channel hole of the lower core plate, can form a block and a flow of the concentrated cooling medium, and avoids excessive gathering of the cooling medium in the area directly opposite the cooling medium flow channel hole; the second convex part connected with the first convex part can further guide the cooling medium to diffuse to the area of the anti-foreign matter plate away from the cooling medium flow channel hole, supplement the originally insufficient flow area, and realize flow balance in the whole plate range. At the same time, the first convex part and the second convex part jointly change the flow channel form of the cooling medium, can inhibit the formation of vortex and eddy flow in the gap between the anti-foreign matter plate and the lower core plate, reduce flow disturbance, further guarantee uniform entry of the cooling medium into the core, and ensure consistent cooling effect on the fuel rod. BRIEF DESCRIPTION OF DRAWINGS

[0015] Figure 1 FIG. 1 is a structural schematic view of a bottom device of an optional embodiment of the application from one perspective; Figure 2 FIG. 2 is a structural schematic view of the bottom device of the optional embodiment of the application from another perspective; Figure 3 FIG. 3 is a structural schematic view of a lower core plate of an optional embodiment of the application; Figure 4 FIG. 4 is a flow rate simulation schematic view of a traditional flat plate type anti-foreign matter plate; Figure 5 FIG. 5 is a flow rate simulation schematic view of the anti-foreign matter plate shown in FIG. 1; Figure 1 and Figure 2 FIG. 6 is a flow rate simulation schematic view of the anti-foreign matter plate shown in FIG. 2.

[0016] The reference signs are as follows: 1, lower tube support; 11, lower tube support frame; 12, leg; 2, anti-foreign matter plate; 21, first face; 22, second face; 221, first flow regulating unit; 222, second flow regulating unit; 223, third flow regulating unit; 224, fourth flow regulating unit; 3, lower core plate; 31, cooling medium flow channel hole; 4, first rate area; 5, second rate area; 6, third rate area; 7, fourth rate area; 8, fifth rate area. DETAILED DESCRIPTION

[0017] In the description of the present application, it should be understood that the terms "center", "longitudinal", "transverse", "length", "width", "thickness", "upper", "lower", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", "clockwise", "counterclockwise" and the like indicate the orientation or positional relationship shown in the drawings, which are for the purpose of facilitating the description of the present application and simplifying the description, and do not indicate or imply that the device or element referred to must have a particular orientation, be constructed and operated in a particular orientation, and therefore cannot be understood as limiting the present application.

[0018] In addition, the terms "first", "second" are only for descriptive purposes and cannot be understood as indicating or implying relative importance or implicitly indicating the number of the technical features indicated. Therefore, the features defined with "first", "second" can explicitly or implicitly include one or more of the features. In the description of the present application, the meaning of "multiple" is two or more, unless otherwise explicitly specified and limited.

[0019] In the present application, unless otherwise explicitly specified and limited, the terms "mounting", "connecting", "connecting", "fixing" and the like should be understood broadly, for example, it can be fixed connection, or detachable connection, or integrally connected; it can be mechanical connection, or electrical connection; it can be directly connected, or indirectly connected through intermediate medium, or the communication between the two elements inside. For those skilled in the art, the specific meaning of the above terms in the present application can be understood according to the specific circumstances.

[0020] The preferred embodiments of the present application are described below in conjunction with the accompanying drawings, it should be understood that the preferred embodiments described herein are only used to illustrate and explain the present application, and are not used to limit the present application.

[0021] The fuel assembly comprises a bottom device, an upper device, a plurality of guide tubes, a plurality of grids and a plurality of fuel rods. The guide tubes are longitudinally arranged and fixed at both ends in the bottom device and the upper device, respectively. The bottom device is for the cooling medium to enter the fuel assembly, and the upper device is for the cooling medium to come out of the fuel assembly. The grids are transversely arranged and fixed at intervals in the length direction of the guide tubes. The grids have a plurality of grid bars, and the fuel rods are respectively arranged in the corresponding grid bars.

[0022] The fuel assembly is vertically placed in use, and the bottom device is placed on the upper surface of the lower core plate 3 of the nuclear reactor by the support leg 12. The bottom device has a cooling medium channel formed therein, and the lower core plate 3 also has a cooling medium channel formed thereon. The cooling medium channel of the lower core plate 3 is opposite to the bottom device, so that the reactor cooling medium sequentially passes through the lower core plate 3 and the bottom device, contacts the fuel rods and cools the fuel rods, thereby forming heat exchange between the cooling medium and the fuel rods.

[0023] In some embodiments, the bottom device includes a lower tube seat 1 and a foreign object shield 2 disposed on the lower tube seat 1. A cooling medium flow channel hole 31 is formed on the lower core plate 3 to create a cooling medium channel. In practical applications, the cooling medium, after passing through the cooling medium flow channel hole 31, must first flow through the foreign object shield 2 before entering the core.

[0024] In this situation, due to the lack of a guiding structure, the cooling medium in the traditional flat-plate foreign object shield 2 will naturally flow towards the area with less resistance. This results in a concentration of flow in the area of ​​the foreign object shield 2 relative to the cooling medium flow channel holes 31, while the flow in the areas further away is insufficient. At the same time, since there is a gap between the foreign object shield 2 and the lower core plate 3, the cooling medium may form eddies or flow around within the gap, disrupting the original flow stability and further amplifying the differences in cooling medium flow in different areas. Ultimately, this leads to the cooling medium entering the core failing to uniformly cover the fuel rods.

[0025] In view of this, the first aspect of this application provides a bottom device, and the second aspect of this application provides a fuel assembly. The bottom device is applied to the fuel assembly to change the flow path morphology of the cooling medium when it flows through the foreign object protection plate 2, so as to avoid uneven flow field distribution.

[0026] In some possible implementations disclosed in this application, see [link to relevant documentation]. Figures 1 to 3 As shown, the bottom device includes a lower tube seat 1 and a foreign object prevention plate 2 connected to the lower tube seat 1; the foreign object prevention plate 2 has a first surface 21 and a second surface 22 arranged opposite to each other along the flow path of the cooling medium, the first surface 21 faces the lower core plate 3, and the lower core plate 3 has a cooling medium flow channel hole 31; a first protrusion is provided in the first surface 21 at a position relative to the cooling medium flow channel hole 31, the first protrusion protrudes towards the side where the lower core plate 3 is located; the first surface 21 also has a second protrusion, the second protrusion is connected to the first protrusion, and the protrusion direction of the second protrusion is the same as the protrusion direction of the first protrusion.

[0027] In this embodiment, the first protrusion is positioned corresponding to the cooling medium flow channel hole 31 of the lower core plate 3, which can block and divert the concentrated flow of cooling medium, preventing excessive accumulation of cooling medium in the area directly opposite the cooling medium flow channel hole 31. The second protrusion connected to the first protrusion can further guide the cooling medium to diffuse towards the area on the foreign object shield 2 away from the cooling medium flow channel hole 31, supplementing the area with insufficient flow and achieving flow balance across the entire plate. At the same time, the first and second protrusions together change the flow channel morphology of the cooling medium, which can suppress the formation of eddies and flow around the gap between the foreign object shield 2 and the lower core plate 3, reduce flow disturbance, further ensure that the cooling medium enters the core uniformly, and ensure consistent cooling effect on the fuel rods.

[0028] The lower tube support 1 comprises a lower tube support frame 11 and four supporting legs 12 arranged at the lower tube support frame 11. The lower tube support frame 11 is fixed to the outer periphery of the anti-foreign matter plate 2. The supporting legs 12 are arranged at four corners of the lower tube support frame 11. At least two opposite supporting legs 12 are provided with a pin hole for mounting and fixing.

[0029] The first surface 21 of the anti-foreign matter plate 2 is a surface first contacted by the cooling medium and faces the lower core plate 3 below. The second surface 22 is a surface second contacted by the cooling medium and faces the core inside.

[0030] Specifically, in some examples, the first surface 21 is a curved surface structure, and the second surface 22 is a planar structure. In other examples, the first surface 21 and the second surface 22 are both curved surface structures and parallel to each other. In the embodiment, the first surface 21 is a curved surface structure, and the second surface 22 is a planar structure. The end surface of the lower tube support frame 11 close to the core is flush with the second surface 22, and the end surface of the lower tube support frame 11 away from the core exceeds the first surface 21, that is, the end surface of the lower tube support frame 11 away from the core is closer to the lower core plate 3 than the first surface 21.

[0031] The first surface 21 comprises a first convex part and a second convex part. The first convex part faces the cooling medium flow channel hole 31 of the lower core plate 3 and protrudes in the direction of the cooling medium flow channel hole 31. The second convex part is the area of the first surface 21 except the first convex part. The second convex part is connected with the first convex part and protrudes in the same direction as the first convex part.

[0032] Specifically, the first convex part and the second convex part are connected with each other and can be integrally formed by additive manufacturing or the like. When the cooling medium flows out of the cooling medium flow channel hole 31 of the lower core plate 3 and impacts the anti-foreign matter plate 2, the first convex part on the first surface 21 will push the cooling medium to flow and bend to avoid local accumulation. The cooling medium after flowing through the first convex part will flow to the second convex part and spread to the edge and corner of the anti-foreign matter plate 2 under the guidance of the second convex part. Finally, the cooling medium can uniformly cover the entire first surface 21 of the anti-foreign matter plate 2 and then enter the core through the second surface 22. It should be noted that when the cooling medium impacts the first convex part and the second convex part, the convex curved surface structure of the first convex part and the second convex part can not only make the flow direction of the cooling medium bend, but also reduce the flow velocity pressure difference of the cooling medium, thereby realizing uniform distribution of flow.

[0033] In some possible implementation examples of the present application, referring to Figure 2 and Figure 3As shown, the portion of the lower core plate 3 relative to the foreign matter prevention plate 2 has at least four cooling medium flow channel holes 31, which are arranged in a rectangular array on the lower core plate 3; the first convex portion includes at least four first rectifying units 221, which correspond to the at least four cooling medium flow channel holes 31 one by one and are coaxially arranged.

[0034] In this embodiment, the portion of the lower core plate 3 relative to the foreign matter prevention plate 2 has four cooling medium flow channel holes 31, which are arranged in a rectangular array, thereby providing a relatively regular initial inflow path for the cooling medium; the first rectifying unit 221 corresponding to the cooling medium flow channel hole 31 can accurately block and distribute the cooling medium flowing out of each cooling medium flow channel hole 31, thereby avoiding the situation that the cooling medium excessively gathers in the region of the foreign matter prevention plate 2 corresponding to a single cooling medium flow channel hole 31, and accurately controlling the initial flow state of each cooling medium. At the same time, since the cooling medium flow channel holes 31 are arranged in a rectangular array, the corresponding first rectifying units 221 also form a rectangular array layout, which can make the cooling medium spread from multiple dispersed starting points on the foreign matter prevention plate 2, and then, in cooperation with the second convex portion connected to the first rectifying unit 221, the cooling medium can be more uniformly guided to each region of the foreign matter prevention plate 2, especially the edge and corner regions outside the rectangular array coverage range, which are originally prone to insufficient flow, thereby effectively compensating for the uneven flow distribution defect of the traditional flat plate type foreign matter prevention plate 2 and further ensuring the balance of the cooling medium flow in the entire plate range. In addition, the corresponding and coaxial arrangement enables the cooling medium to directly contact the first rectifying unit 221 after flowing out of the flow channel hole, thereby reducing the disordered flow space of the cooling medium in the gap between the foreign matter prevention plate 2 and the lower core plate 3, suppressing the formation of unstable flow phenomena such as vortex flow and eddy flow, laying a stable flow foundation for the uniform entry of the cooling medium into the core, and ultimately ensuring that the fuel rods in the core can obtain consistent and reliable cooling effect.

[0035] In this embodiment, the four cooling medium flow channel holes 31 can be arranged in a rectangular array of two rows and two columns. In this embodiment, the center axis of each first rectifying unit 221 coincides with the center axis of the corresponding cooling medium flow channel hole 31.

[0036] Specifically, in some examples, the projection shape of the first rectifying unit 221 on the plane perpendicular to the protruding direction thereof is a polygon; in other examples, the projection shape of the first rectifying unit 221 on the plane perpendicular to the protruding direction thereof is a circle. In this embodiment, the projection shape of the first rectifying unit 221 on the plane perpendicular to the protruding direction thereof is a polygon.

[0037] In the above embodiment, referring to Figure 2As shown, the end face of the first rectifying unit 221 towards the lower core plate 3 is a first tapered surface, the position of the first tapered surface intersecting the central axis of the first rectifying unit 221 is a first position, the first position is the highest point of the first tapered surface in the protruding direction of the first rectifying unit 221, and the height of the first tapered surface gradually decreases from the first position to the edge direction of the first rectifying unit 221. That is, the first rectifying unit 221 has a structure of high in the middle and low at the periphery.

[0038] Here, when the cooling medium flows out of the lower core plate 3 cooling medium flow hole 31 and impacts the first tapered surface, the first position of the highest point can first form an effective block to the concentrated cooling medium, and at the same time, due to the gradual decrease in height of the first tapered surface from the first position to the edge, a smooth flow guide slope is formed, which can guide the cooling medium to diffuse naturally and orderly along the slope to the edge of the first rectifying unit 221, avoiding excessive accumulation of cooling medium at the first position, and realizing uniform distribution of the cooling medium. At the same time, the smooth tapered structure avoids the flow disorder of the cooling medium caused by abrupt blocking, reduces the impact loss of the cooling medium in the flow process, reduces the probability of unstable flow phenomena such as vortex flow and eddy flow, and enables the cooling medium to diffuse to other areas of the anti-foreign matter plate 2 in a more stable flow state. In addition, this tapered distribution and flow guiding method can further cooperate with the second protrusion to ensure that the cooling medium uniformly covers the entire plate range of the anti-foreign matter plate 2, and provides a reliable guarantee for the subsequent uniform cooling medium entering the core and uniformly cooling the fuel rods, thereby improving the cooling efficiency and safety of the fuel assembly. In some possible implementation embodiments disclosed in the present application, referring to Figure 2 As shown, the second protrusion includes at least one second rectifying unit 222, the second rectifying unit 222 is located in the area surrounded by at least four first rectifying units 221 arranged in a rectangular array, and the four sides of the second rectifying unit 222 are respectively connected to the sides of the adjacent first rectifying units 221 among the at least four first rectifying units 221; wherein the end face of the second rectifying unit 222 towards the lower core plate 3 is a second tapered surface, the position of the second tapered surface intersecting the central axis of the second rectifying unit 222 is a second position, the second position is the highest point of the second tapered surface in the protruding direction of the second rectifying unit 222, and the height of the second tapered surface gradually decreases from the second position to the edge direction of the second rectifying unit 222.

[0039] In this embodiment, one second rectifying unit 222 is arranged. By arranging the second rectifying unit 222 in the area surrounded by the four first rectifying units 221 in the first surface 21, the cooling medium flowing to the center of the anti-foreign matter plate 2 from the first rectifying units 221 can be blocked and guided again. By using the second gradual surface structure with a high middle and a low periphery, the cooling medium concentrated in the central area can be further diffused to the periphery, filling the blank area formed by the four first rectifying units 221, avoiding the accumulation of cooling medium in the central area, and at the same time cooperating with the flow splitting effect of the first rectifying units 221 to promote the cooling medium to cover the entire plate range of the anti-foreign matter plate 2 more evenly, reduce the flow difference between different areas, and ensure that the cooling medium enters the core stably and evenly.

[0040] In this embodiment, the area surrounded by the four first rectifying units 221 arranged in a rectangular array is approximately diamond-shaped, and the diamond-shaped area is the second rectifying unit 222.

[0041] In this embodiment, the second rectifying unit 222 is in contact with the four first rectifying units 221, i.e., the four sides of the second rectifying unit 222 are in contact with the adjacent sides of the four first rectifying units 221. For example, the left side of the second rectifying unit 222 is in contact with the right side of the left first rectifying unit 221, and the front side is in contact with the back side of the front first rectifying unit 221, forming a seamless overall structure.

[0042] In this embodiment, the second rectifying unit 222 also has a structure with a high middle and a low periphery.

[0043] Specifically, on the second gradual surface, the point intersecting the central axis of the second rectifying unit 222 is the highest point of the entire second gradual surface in the convex direction, which is the second position. From the second position, the height of the second gradual surface gradually and smoothly decreases in the direction of the four sides of the second rectifying unit 222, eventually forming a slope structure with a high middle and a low periphery. Here, the central axis of the second rectifying unit 222 coincides with the central axis of the anti-foreign matter plate 2.

[0044] In some possible implementation embodiments disclosed in the present application, referring to Figure 2 As shown in the figure, the second convex portion further includes at least four third rectifying units 223, and the at least four third rectifying units 223 are arranged in the areas surrounded by the edges of the first surface 21 and adjacent two first rectifying units 221 among the at least four first rectifying units 221, and each third rectifying unit 223 is in contact with the two first rectifying units 221.

[0045] In this embodiment, four third rectifying units 223 are arranged. The third rectifying units 223 are arranged in the areas enclosed by the edges of the first surface 21 and the adjacent two first rectifying units 221 among the four first rectifying units 221, and each is connected to two first rectifying units 221. On one hand, the third rectifying units 223 can receive the cooling medium diverted from the adjacent two first rectifying units 221, and guide the cooling medium to the edge-enclosed area which is originally insufficient in flow due to being far away from the cooling medium flow channel hole 31, by means of the connection structure of the third rectifying units 223 and the first rectifying units 221. On the other hand, the connection of the third rectifying units 223 and the first rectifying units 221 forms a continuous flow path, avoiding the formation of vortex or eddy flow of the cooling medium in the edge-enclosed area, further optimizing the flow field distribution of the entire anti-foreign matter plate 2, ensuring that the cooling medium can uniformly cover each area of the anti-foreign matter plate 2 including the edge-enclosed area, and finally making the cooling medium enter the core in a stable and balanced flow state, providing consistent and reliable cooling for all fuel rods in the core, greatly improving the cooling safety and efficiency of the fuel assembly.

[0046] When the four first rectifying units 221 are arranged in a rectangular array, the adjacent two first rectifying units 221 will jointly enclose an independent area with the edge of the anti-foreign matter plate 2.

[0047] Specifically, the area jointly enclosed by the adjacent two first rectifying units 221 and the edge of the anti-foreign matter plate 2 is approximately triangular, and this triangular area is the third rectifying unit 223.

[0048] The projection shape of the third rectifying unit 223 on a plane perpendicular to the protruding direction of the third rectifying unit 223 is an isosceles triangle, the base of the projection of the third rectifying unit 223 is fitted to the edge of the first surface 21 of the anti-foreign matter plate 2, and the length of the base is adapted to the width of the area enclosed by the adjacent two first rectifying units 221 and the edge of the anti-foreign matter plate 2, i.e. the two ends of the base need to extend to the side ends of the adjacent two first rectifying units 221 close to the edge of the anti-foreign matter plate 2, to ensure that the isosceles triangle can completely cover the enclosed area, avoiding the existence of cooling medium coverage gaps in the edge area due to improper base size. The two waists of the projection of the third rectifying unit 223 are respectively in contact with and connected to the sides of the adjacent two first rectifying units 221, and the contact and connection surfaces are smooth. Here, the side of the third rectifying unit 223 corresponding to each waist is completely fitted to the side of the corresponding first rectifying unit 221, to ensure that the two waists can uniformly receive the cooling medium from the two first rectifying units 221.

[0049] In the above embodiment, referring to Figure 2As shown, the third rectifying unit 223 has a third gradual surface facing the end surface of the lower core plate 3. The third position of the third rectifying unit 223 is the midpoint of the side edge coinciding with the first surface 21. The third position is the highest point of the third gradual surface in the convex direction of the third rectifying unit 223. The height of the third gradual surface gradually decreases from the third position to the edge of the third rectifying unit 223.

[0050] Here, the side edge of the third rectifying unit 223 coinciding with the first surface 21 is the bottom edge of the projection of the third rectifying unit 223 in the plane perpendicular to the convex direction. The third position of the third rectifying unit 223 is the midpoint of the bottom edge of the projection. The third position is the highest point of the third gradual surface, which can effectively block the cooling medium flowing from the adjacent first rectifying unit 221, avoid excessive accumulation in the edge-enclosed area, ensure that the cooling medium can evenly cover the edge area, and ultimately provide consistent cooling effect for all fuel rods in the core, thereby improving the cooling reliability and safety of the fuel assembly.

[0051] Here, the third rectifying unit 223 can be understood as a half-derivative structure of the second rectifying unit 222.

[0052] Specifically, the third rectifying unit 223 and the second rectifying unit 222 both adopt a gradual surface with high in the middle and low on the four sides as a flow guide carrier, and the height change mode of the gradual surface is the same. The second position of the second rectifying unit 222 at the center axis is the highest point, and the height decreases uniformly in the direction of the four sides, forming a four-way diffusion slope surface covering the rectangular array-enclosed area. The third position of the third rectifying unit 223 corresponding to the midpoint of the edge of the first surface 21 is the highest point, and the height decreases in the direction of the two waist edges and the bottom edge, wherein the two waist edges are connected to the first rectifying unit 221, and the bottom edge is attached to the edge of the anti-foreign matter plate 2, thereby forming a three-way diffusion slope surface covering the triangular-enclosed area. It should be noted that the structure of the third rectifying unit 223 is derived from the second rectifying unit 222, and only the diffusion direction is adjusted due to the different shape of the installation area. Essentially, the four-way flow guide of the second rectifying unit 222 is simplified to a three-way flow guide suitable for the edge area, which is equivalent to cutting off half of the functional module of the second rectifying unit 222.

[0053] In some possible implementation embodiments of the present disclosure, referring to Figure 2 As shown, the second convex part further includes at least four fourth rectifying units 224, which are arranged at the four corners of the first surface 21 one by one, and each fourth rectifying unit 224 is connected to an adjacent first rectifying unit 221.

[0054] In this embodiment, four fourth rectifying units 224 are arranged. By arranging the fourth rectifying units 224 at the four corners of the first surface 21 one by one and connecting each fourth rectifying unit 224 with an adjacent first rectifying unit 221, the flow of the cooling medium can be supplemented and the flow field can be optimized for the dead angle area prone to poor cooling medium flow in the traditional structure of the four corners of the anti-foreign matter plate 2. On the one hand, the fourth rectifying unit 224 can effectively receive the cooling medium diverted from the adjacent first rectifying unit 221, and guide the cooling medium smoothly and orderly to the four corners of the anti-foreign matter plate 2 through the connection structure of the fourth rectifying unit 224 and the first rectifying unit 221, thereby completely filling the flow blank in the four corner areas due to the long distance from the cooling medium flow channel hole 31 and avoiding the problem of insufficient coverage of the cooling medium in the four corners of the traditional flat plate type anti-foreign matter plate 2. On the other hand, the connection of the fourth rectifying unit 224 and the first rectifying unit 221 forms a continuous and complete flow guide path, which blocks the possibility of unstable flow such as vortex and eddy flow of the cooling medium in the four corner areas, further optimizes the flow field distribution of the anti-foreign matter plate 2, and ensures that the cooling medium can uniformly cover every area of the anti-foreign matter plate 2 including the four corners. Finally, the cooling medium enters the core in a stable and balanced flow state, providing consistent and reliable cooling for all fuel rods in the core, greatly improving the comprehensiveness, safety and efficiency of fuel assembly cooling, and achieving uniform distribution of the cooling medium in the anti-foreign matter plate 2 without dead angle and full range.

[0055] The projection shape of the first rectifying unit 221 on the plane perpendicular to the protruding direction is approximately octagonal, which can form a more uniform flow dividing interface when in contact with the cooling medium. When the cooling medium impacts the first rectifying unit 221, the edges of the octagonal shape can uniformly disperse the cooling medium in eight different directions, avoiding excessive concentration of the cooling medium in a single direction, and further improving the uniformity and comprehensiveness of the flow division.

[0056] Specifically, the four first rectifying units 221 arranged in a rectangular array are smoothly connected by their sides. Each first rectifying unit 221 has eight edges, of which: four edges are smoothly connected with the sides of the adjacent second rectifying unit 222, third rectifying unit 223 or fourth rectifying unit 224; two edges are smoothly connected with the sides of the adjacent first rectifying unit 221 arranged in a rectangular array; and the remaining two edges coincide with the edges of the anti-foreign matter plate 2. Through this multi-dimensional edge connection design, the first rectifying unit 221 and other rectifying units, the edges of the anti-foreign matter plate 2 form a continuous and gapless flow guide interface, so that the cooling medium can uniformly diffuse along these connection edges during flow, further ensuring the flow balance of the anti-foreign matter plate 2 in the whole area.

[0057] The corner of the first surface 21 and the two sides of the adjacent first rectifying unit 221 together enclose an independent area.

[0058] Specifically, the corner of the first face 21 and the area surrounded by the two side edges of the adjacent first rectifying unit 221 is approximately triangular or quarter circular, and the triangular area or quarter circular area is the fourth rectifying unit 224.

[0059] In the above embodiment, referring to Figure 2 As shown in the figure, the end face of the fourth rectifying unit 224 towards the lower core plate 3 is a fourth gradient face, and the position of the corner vertex of the first face 21 on the fourth gradient face is a fourth position, the fourth position being the highest point of the fourth gradient face in the direction of the convexity of the fourth rectifying unit 224, and the height of the fourth gradient face gradually decreases in the direction of the edge of the fourth rectifying unit 224 from the fourth position.

[0060] Here, the corner vertex of the first face 21 is the intersection of the two adjacent side edges of the first face 21. On the fourth gradient face, the position of the corner vertex of the first face 21 is the fourth position, and the fourth position is the highest point of the fourth gradient face, which can effectively block the cooling medium flowing into the four-corner area of the anti-foreign matter plate 2 from the adjacent first rectifying unit 221, avoid excessive accumulation in the corner dead angle, and ensure that the cooling medium can evenly cover all areas of the first face 21 including the four corners, providing consistent and reliable cooling for all fuel rods in the core, greatly improving the comprehensiveness, safety and efficiency of fuel assembly cooling.

[0061] In some possible implementation embodiments disclosed in the present application, referring to Figure 2 As shown in the figure, the convex height of the first convex part relative to the first face 21 is greater than the convex height of the second convex part relative to the first face 21; the first convex part is provided with a first filter hole, and the second convex part is provided with a second filter hole, and the aperture of the first filter hole is smaller than the aperture of the second filter hole.

[0062] In this embodiment, the first convex part has a higher convex height than the second convex part, which can more efficiently block the cooling medium flowing out of the cooling medium flow channel hole 31, so that the first convex part can first step up the strong diversion of the cooling medium with high flow rate, avoiding its direct impact on the central area of the anti-foreign matter plate 2; and the lower second convex part can receive the diverted cooling medium and gently guide it to spread towards the edge and corner, further weakening the flow disturbance and reducing the formation of vortex or eddy current, ensuring more stable flow field distribution of the whole plate. Further, the first convex part is provided corresponding to the cooling medium flow channel hole 31, and the first filter hole thereof has a smaller aperture, which can preferentially intercept small foreign matters entering from the cooling medium flow channel hole 31, avoiding the foreign matters flowing to the core along with the cooling medium, and protecting the fuel rods from damage; the cooling medium received by the second convex part has been preliminarily filtered by the first convex part, and the second filter hole adopts a larger aperture design, which can not only intercept the remaining larger size foreign matters, but also reduce the flow resistance of the cooling medium, avoiding the flow loss caused by the blockage of the filter hole, and balancing the filtering effect and flow efficiency.

[0063] The cross-sectional shape of the first filter hole is the same as the cross-sectional shape of the second filter hole.

[0064] Specifically, in some examples, the cross-sectional shape of the first filter hole and the second filter hole are both circular; in another example, the cross-sectional shape of the first filter hole and the second filter hole are both triangular. In addition, the cross-sectional shape of the first filter hole and the second filter hole can also be rectangular, pentagonal, or other shapes.

[0065] Here, by comparing the flow rate simulation results of Figure 4 and Figure 5 , the difference in cooling medium flow rate distribution of the two foreign matter prevention plates 2 can be clearly seen. Figure 4 The conventional flat plate foreign matter prevention plate 2 has a flow rate divided into three regions: the first rate area 4 opposite the cooling medium flow channel hole 31 has a flow rate greater than 5.175 m / s, the second rate area 5 around the first rate area 4 has a flow rate of 2.724 m / s to 4.086 m / s, and the remaining area is the third rate area 6 with a flow rate of 0.272 m / s to 1.634 m / s. The flow rates of the three regions differ significantly, resulting in a large difference in cooling medium flow at different positions; while Figure 5 The foreign matter prevention plate 2 of the embodiment shown in the figure has a flow rate divided into only two regions: the fourth rate area 7 opposite the cooling medium flow channel hole 31 and the fifth rate area 8 in the remaining area both have a flow rate in the interval of 4.192 m / s to 5.030 m / s, which can effectively avoid the problems of large flow rate pressure difference and uneven flow, and further prevent uneven cooling of the fuel rod.

[0066] Those skilled in the art will readily understand that the above advantageous modes can be freely combined and superimposed without conflict.

[0067] The above is only a preferred embodiment of the present application and is not intended to limit the present application. Any modifications, equivalent replacements, and improvements made within the spirit and principles of the present application shall be included in the protection scope of the present application. The above is only a preferred embodiment of the present application, and it should be noted that for ordinary skilled in the art, without departing from the technical principles of the present application, a number of improvements and modifications can be made, which should be considered as the protection scope of the present application.

Claims

1. A bottom device, comprising a lower tube seat and a foreign object protection plate connected to the lower tube seat, characterized in that: The foreign object protection plate has a first side and a second side arranged opposite to each other along the flow path of the cooling medium. The first side faces the lower core plate, and the lower core plate is provided with cooling medium flow channel holes. A first protrusion is provided on the first surface at a position relative to the cooling medium flow channel hole, and the first protrusion protrudes toward the side where the lower core plate is located; The first surface is further provided with a second protrusion, which is connected to the first protrusion, and the protrusion direction of the second protrusion is the same as that of the first protrusion.

2. The bottom device according to claim 1, characterized in that, The lower core plate has at least four cooling medium flow channel holes on the portion relative to the foreign object protection plate, and the at least four cooling medium flow channel holes are distributed in a rectangular array on the lower core plate; the first protrusion includes at least four first rectification units, and the at least four first rectification units correspond one-to-one with the at least four cooling medium flow channel holes and are coaxially arranged.

3. The bottom device according to claim 2, characterized in that, The end face of the first rectifier unit facing the lower core plate is a first gradient surface. The position where the first gradient surface intersects with the central axis of the first rectifier unit is a first position. The first position is the highest point of the first gradient surface along the convex direction of the first rectifier unit, and the height of the first gradient surface gradually decreases from the first position toward the edge of the first rectifier unit.

4. The bottom device according to claim 2, characterized in that, The second protrusion includes at least one second rectifier unit, which is located within the area enclosed by at least four first rectifier units arranged in a rectangular array, and the four sides of the second rectifier unit are respectively connected to the sides of the adjacent first rectifier units among the at least four first rectifier units. The end face of the second rectifier unit facing the lower core plate is the second gradient surface. The position where the second gradient surface intersects with the central axis of the second rectifier unit is the second position. The second position is the highest point of the second gradient surface along the convex direction of the second rectifier unit, and the height of the second gradient surface gradually decreases from the second position towards the edge of the second rectifier unit.

5. The bottom device according to claim 4, characterized in that, The second protrusion also includes at least four third rectifier units, which are respectively disposed in the area enclosed by two adjacent first rectifier units and the edge of the first surface, and each third rectifier unit is connected to two first rectifier units.

6. The bottom device according to claim 5, characterized in that, The end face of the third rectifier unit facing the lower core plate is the third gradient surface. On the third gradient surface, the position of the midpoint of the side of the third rectifier unit that coincides with the edge of the first surface is the third position. The third position is the highest point of the third gradient surface along the convex direction of the third rectifier unit, and the height of the third gradient surface gradually decreases from the third position towards the edge of the third rectifier unit.

7. The bottom device according to claim 4, characterized in that, The second protrusion also includes at least four fourth rectifier units, which are disposed one-to-one at the four corners of the first surface, and each of the fourth rectifier units is connected to an adjacent first rectifier unit.

8. The bottom device according to claim 7, characterized in that, The end face of the fourth rectifier unit facing the lower core plate is the fourth gradient surface. On the fourth gradient surface, the position of the corner vertex relative to the first surface is the fourth position. The fourth position is the highest point of the fourth gradient surface along the convex direction of the fourth rectifier unit, and the height of the fourth gradient surface gradually decreases from the fourth position towards the edge of the fourth rectifier unit.

9. The bottom device according to claim 1, characterized in that, The first protrusion has a greater protrusion height relative to the first surface than the second protrusion has a greater protrusion height relative to the first surface; the first protrusion has a first filter hole and the second protrusion has a second filter hole, the diameter of the first filter hole is smaller than the diameter of the second filter hole.

10. A fuel assembly, characterized in that, Includes the bottom device as described in any one of claims 1-9.

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