Lower nozzle and fuel assembly

Abstract

To provide a lower nozzle and a fuel assembly further improved in earthquake resistance and strength rigidity.SOLUTION: The lower nozzle forms a lower part of the fuel assembly, and includes a lower nozzle main body having a plate shape extending in a horizontal direction and having a hole forming region in which a plurality of holes penetrating in a vertical direction are arranged, and a plurality of leg parts protruding downward from an outer peripheral part of the lower nozzle main body and formed in a circumferential direction, in which the lower nozzle main body has a solid part in which no hole is formed at a center of the lower nozzle main body in the hole forming region in a plan view.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present disclosure relates to a bottom nozzle and a fuel assembly. [Background technology]

[0002] A fuel assembly applied to a light water reactor includes a bottom nozzle, a fuel assembly body, and an upper nozzle (see, for example, Patent Document 1 below). The bottom nozzle has a plurality of holes (guide tube mounting holes) for inserting a plurality of guide tubes included in the fuel assembly body, and a plurality of holes (coolant flow holes) for circulating light water as a coolant. The coolant flows through the coolant flow holes in the bottom nozzle around the guide tubes, i.e., the fuel rods, cooling them, and then flows through the top nozzle and further upward into the upper plenum. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 11-109074 Summary of the Invention [Problem to be solved by the invention]

[0004] The bottom nozzle bears the load of the fuel assembly body and the top nozzle, and it has been confirmed that the load is concentrated at the center of the bottom nozzle, causing the center to deform and become convex downward. This has led to the issue of not being able to fully secure the seismic performance and strength and rigidity required of the bottom nozzle.

[0005] The bottom nozzle bears the load of the fuel assembly itself and the top nozzle. Given the expected future changes in external factors, such as an increase in the level of earthquake motion, there was a risk that the bottom nozzle would not be able to fully meet the seismic performance and strength and rigidity required if the current design remained unchanged.

[0006] The present disclosure has been made to solve the above-mentioned problems, and has an object to provide a bottom nozzle and a fuel assembly with further improved seismic resistance and strength and rigidity. [Means for solving the problem]

[0007] In order to solve the above problems, the bottom nozzle of the present disclosure is a bottom nozzle that forms the bottom of a fuel assembly, and comprises a bottom nozzle body that is shaped like a plate extending horizontally and has a hole formation region in which a plurality of holes that penetrate in the vertical direction are arranged, and a plurality of leg portions that protrude downward from the outer periphery of the bottom nozzle body and are formed in the circumferential direction, and the bottom nozzle body has a solid portion in which no holes are formed, at the center of the hole formation region in a plan view of the bottom nozzle body.

[0008] The fuel assembly according to the present disclosure includes the above-described bottom nozzle, a fuel assembly main body inserted into the hole of the bottom nozzle from above, and an upper nozzle attached to the upper end of the fuel assembly main body. [Effects of the Invention]

[0009] According to the present disclosure, it is possible to provide a bottom nozzle and a fuel assembly with further improved seismic resistance and strength and rigidity. [Brief explanation of the drawings]

[0010] [Figure 1] FIG. 1 is a perspective view illustrating a configuration of a fuel assembly according to an embodiment of the present disclosure. [Figure 2] FIG. 2 is a plan view illustrating a configuration of a bottom nozzle according to an embodiment of the present disclosure. [Figure 3] FIG. 10 is a side view illustrating a modified example of a bottom nozzle according to an embodiment of the present disclosure. DETAILED DESCRIPTION OF THE INVENTION

[0011] (Configuration of fuel assembly 1) Hereinafter, a fuel assembly 1 and a bottom nozzle 10 according to an embodiment of the present disclosure will be described with reference to FIGS. 1 and 2. FIG.

[0012] This fuel assembly 1 is used as a fuel (heat source) for a light water reactor, for example. As shown in FIG.

[0013] (Bottom nozzle 10) The bottom nozzle 10 supports the fuel assembly body 20 from below. The bottom nozzle 10 has a bottom nozzle body 11 and multiple legs 12. The bottom nozzle body 11 is plate-shaped and extends horizontally. The bottom nozzle body 11 has a square shape in plan view. Note that the planar shape of the bottom nozzle body 11 is not limited to a square, and can be changed to a rectangle, polygon, or circle as appropriate depending on the design and specifications.

[0014] The bottom nozzle body 11 has a hole formation region 41 and a solid portion 42. The hole formation region 41 is a region excluding the region (center portion) where diagonal lines connecting the corners of the bottom nozzle body 11 intersect. A plurality of holes 50 are formed in the hole formation region 41. These holes 50 include guide tube mounting holes 51 and coolant flow holes 52. Guide tubes 61 (described later) are inserted into the guide tube mounting holes 51. Light water, serving as a coolant (primary coolant), is supplied to the coolant flow holes 52 from a lower plenum located further below the bottom nozzle 10. These holes 50 penetrate the bottom nozzle body 11 in the vertical direction. The diameter of the holes 50 is constant throughout the entire region in the vertical direction. Furthermore, these holes 50 are arranged in a lattice pattern at intervals from one another in a plan view. The diameter of the guide tube mounting holes 51 is larger than the diameter of the coolant flow holes 52. Furthermore, the number of guide pipe mounting holes 51 is smaller than the number of coolant flow holes 52 .

[0015] The diameter and arrangement of the coolant flow holes 52 are set so that the pressure drop of the coolant flowing therethrough is appropriate. The number and arrangement of the guide pipe mounting holes 51 are appropriately set corresponding to the guide pipes 61 that are set to match the arrangement of the control rods, which is set taking into account the nuclear characteristics and thermal flow characteristics within the reactor core. As an example, in this embodiment, the guide pipe mounting holes 51 have a row that is arranged in a square shape with the center of the lower nozzle body 11 as the geometric center of gravity in a plan view, and another row that is arranged in a circular ring shape further outward. The coolant flow holes 52 are arranged in a lattice pattern so as to fill the spaces between these guide pipe mounting holes 51.

[0016] A solid portion 42 is provided in the center of the bottom nozzle body 11, excluding the hole formation region 41. In other words, no hole 50 is formed in this solid portion 42. Conventionally, an opening for introducing in-core instrumentation equipment has been provided in this center portion. However, as will be described later, in this embodiment, a configuration (described later) for introducing the in-core instrumentation equipment from the top nozzle 30 side is adopted, making it possible to form the solid portion 42 in the bottom nozzle body 11. The solid portion 42 has the same thickness as the remaining portion of the bottom nozzle body 11. Furthermore, the solid portion 42 and the remaining portion are integrally formed from a single material.

[0017] In plan view, the cross-sectional area of ​​the solid portion 42 is larger than the cross-sectional area of ​​the above-described guide pipe mounting hole 51. The cross-sectional area of ​​the solid portion 42 here refers to the area of ​​an inscribed circle defined by the innermost coolant flow hole 52 that surrounds the solid portion 42 from the outer periphery side.

[0018] Legs 12 are integrally provided on the underside of each of the four corners of the bottom nozzle body 11. In other words, a plurality of these leg parts 12 are provided at intervals in the circumferential direction on the outer periphery of the bottom nozzle body 11. Each leg part 12 has a columnar shape with a rectangular cross section that protrudes downward from the bottom nozzle body 11. The four leg parts 12 have the same length in the vertical direction. The lower end surfaces of these leg parts 12 abut against reactor internal structures (not shown). That is, the load of the fuel assembly 1 is supported by these leg parts 12.

[0019] (Fuel assembly body 20) The fuel assembly main body 20 includes multiple guide tubes 61, multiple fuel rods 62, and multiple support grids 63. The guide tubes 61 are cylindrical and extend vertically. Control rods and other components for controlling nuclear fission reactions are inserted into the guide tubes 61 as needed. The guide tubes 61 guide the insertion direction of the control rods. The insertion depth of the control rods is adjusted appropriately depending on the operating state of the light-water reactor. The fuel rods 62 are formed by loading, for example, pellet-shaped (cylindrical) nuclear fuel pellets stacked vertically. Although not shown in detail, the fuel rods 62 mainly include a cylindrical cladding tube, the nuclear fuel pellets contained within the cladding tube, an upper end plug closing the upper opening, a lower end plug closing the lower opening, and a spring that presses each fuel pellet downward from the inner surface of the upper end plug. The guide tubes 61 and the fuel rods 62 have the same vertical length.

[0020] The support grid 63 is a frame through which the fuel rods 62 and guide tubes 61 are inserted. The support grid 63 is provided to supplement the rigidity of these components. A plurality of support grids 63 are arranged at intervals in the vertical direction. The support grid 63 has a plurality of openings formed therein for inserting the fuel rods 62 and guide tubes 61. The arrangement of these openings is the same as that of the holes 50 of the bottom nozzle 10.

[0021] (Top nozzle 30) The top nozzle 30 has a plurality of upper coolant flow holes 31 and upper guide pipe mounting holes 32 through which guide pipes 61 are inserted. An upper plenum (not shown) is provided above the top nozzle 30 for discharging light water as coolant. The top nozzle 30 also has an opening (not shown) for introducing in-core instrumentation equipment. The in-core instrumentation equipment refers to a detector that measures the number of neutrons produced by nuclear fission in the reactor, and a cylindrical member that houses the detector.

[0022] (Action and effect) The fuel assembly 1 configured as described above is supported by reactor internal structures (not shown) to form the core of a light water reactor. When neutrons are emitted from the neutron source, a chain reaction of nuclear fission occurs inside the fuel assembly 1, generating high heat. This heat causes the light water used as the coolant (primary coolant) to become superheated. The superheated primary coolant exchanges heat with the secondary coolant flowing in a separate system. The secondary coolant, heated by the heat exchange, is supplied to a power generating turbine and drives the turbine. The rotational energy of the turbine drives the rotation of the generator, ultimately producing electricity.

[0023] Here, it has been confirmed that the bottom nozzle 10 bears the load of the fuel assembly main body 20 and the top nozzle 30, and therefore the central part of the bottom nozzle 10 is deformed so as to be convex downward. This has caused a problem that the earthquake resistance and strength rigidity required for the bottom nozzle 10 cannot be sufficiently ensured. To solve this problem, the above-mentioned configurations are adopted in this embodiment.

[0024] According to the above-described configuration, a solid portion 42 without a hole 50 is provided at the center of the bottom nozzle body 11. This increases the rigidity of the bottom nozzle body 11 compared to, for example, a conventional configuration in which an opening for inserting in-core instrumentation equipment is provided at the center. More specifically, even when a load is applied from the fuel assembly body 20 installed above the bottom nozzle body 11, the solid portion 42 can stably withstand the load. This further improves the seismic resistance of the bottom nozzle 10. In other words, conventional configurations, which have openings for inserting in-core instrumentation equipment, tend to generate stress by expanding the openings when a load is applied, resulting in the bottom nozzle body 11 becoming convex downward as described above. However, according to the above-described configuration, the bottom nozzle body 11 does not have such an opening, significantly reducing the possibility of deformation.

[0025] According to the above-mentioned configuration, the coolant flow holes 52 and the guide pipe mounting holes 51 can be provided while providing the solid portion 42 in the center of the bottom nozzle body 11. That is, it becomes possible to apply the conventional core design as it is. Therefore, it is possible to improve the strength and rigidity of the bottom nozzle 10 while minimizing the degradation of core performance.

[0026] According to the above configuration, it is possible to provide a fuel assembly 1 with improved strength, rigidity, and earthquake resistance.

[0027] (Other embodiments) The above describes in detail the embodiments of the present disclosure with reference to the drawings, but the specific configuration is not limited to this embodiment, and design changes and the like are also included within the scope that does not deviate from the gist of the present disclosure.

[0028] For example, a modified version of the bottom nozzle 10 may have the configuration shown in FIG. 3. In the example shown in the figure, an auxiliary leg 13 is provided on the underside of the solid portion 42 of the bottom nozzle body 11. The auxiliary leg 13 is columnar and protrudes downward from the underside of the solid portion 42. The lower end of the auxiliary leg 13 is at the same height as the lower ends of the other legs 12. In other words, the auxiliary leg 13, together with the other four legs 12, supports the load applied to the bottom nozzle body 11 from below. The cross-sectional shape of the auxiliary leg 13 may be rectangular, circular, or polygonal. It is desirable to set the cross-sectional area appropriately according to the design and specifications.

[0029] According to the above configuration, the auxiliary legs 13 are provided on the lower surface of the solid portion 42 located at the center of the bottom nozzle 10. As a result, even when a load is applied from the fuel assembly main body 20 installed above the bottom nozzle main body 11, the solid portion 42 and the auxiliary legs 13 can stably withstand the load. This further improves the seismic resistance of the bottom nozzle 10. In particular, the central portion of the bottom nozzle 10 tends to be deformed downwardly due to the load of the fuel assembly main body 20. However, according to the above configuration, the auxiliary legs 13 in the central portion can stably resist such deformation. Even if a slight downward convex deformation occurs, the possibility that the deformation will affect the bottom nozzle main body 11 can be minimized as long as the auxiliary legs 13 do not buckle. Therefore, the stability of the fuel assembly 1 can be further improved, and seismic resistance can be significantly improved.

[0030] In addition, the number of guide tubes 61 and fuel rods 62 and the number of coolant flow holes 52 described in the above embodiment are merely examples, and can be changed as appropriate depending on the size and design of the reactor, etc.

[0031] <Additional Notes> The bottom nozzle 10 and the fuel assembly 1 described in each embodiment can be understood, for example, as follows.

[0032] (1) The bottom nozzle 10 according to the first aspect is a bottom nozzle 10 that forms the bottom of a fuel assembly 1, and comprises a bottom nozzle body 11 that is plate-shaped and extends horizontally, and has a hole formation region 41 in which a plurality of holes 50 that penetrate in the vertical direction are arranged, and leg portions 12 that protrude downward from the outer periphery of the bottom nozzle body 11 and are formed in a circumferential direction, and the bottom nozzle body 11 has a solid portion 42 in which no holes 50 are formed, at the center of the bottom nozzle body 11 in a plan view within the hole formation region 41.

[0033] According to the above configuration, the rigidity of the lower nozzle body 11 can be increased.

[0034] (2) The bottom nozzle 10 according to a second aspect is the bottom nozzle 10 of (1), in which the plurality of holes 50 include a coolant flow hole 52 and a plurality of guide pipe mounting holes 51.

[0035] According to the above configuration, the strength and rigidity of the bottom nozzle 10 can be improved while minimizing the deterioration of core performance.

[0036] (3) The bottom nozzle (10) according to a third aspect is the bottom nozzle (10) of (1) or (2), further comprising an auxiliary leg portion (13) extending downward from the lower surface of the solid portion (42).

[0037] According to the above configuration, even when the load of the fuel assembly main body 20 installed on the upper part of the lower nozzle main body 11 is applied, the load can be stably received by the solid portion 42 and the auxiliary leg portion 13.

[0038] (4) A fuel assembly 1 according to a fourth aspect includes a bottom nozzle 10 according to any one of the aspects (1) to (3), a fuel assembly body 20 inserted from above into the hole 50 of the bottom nozzle 10, and an top nozzle 30 attached to the upper end of the fuel assembly body 20.

[0039] According to the above configuration, it is possible to provide a fuel assembly 1 with improved strength, rigidity, and earthquake resistance. [Explanation of symbols]

[0040] 1... fuel assembly 10... lower nozzle 11... lower nozzle body 12... leg 13... auxiliary leg 20... fuel assembly body 30... upper nozzle 31... upper coolant flow hole 32... upper guide tube mounting hole 41... hole forming region 42... solid portion 50... hole 51... guide tube mounting hole 52... coolant flow hole 61... guide tube 62... fuel rod 63... support grid

Claims

1. A bottom nozzle forming a bottom portion of a fuel assembly, a lower nozzle body having a plate-like shape extending horizontally and having a hole forming region in which a plurality of holes extending vertically therethrough are arranged; a plurality of legs formed in a circumferential direction and projecting downward from an outer periphery of the lower nozzle body; Equipped with The lower nozzle body is The bottom nozzle has a solid portion in which the holes are not formed, at the center of the bottom nozzle body in a plan view within the hole formation region.

2. The bottom nozzle according to claim 1 , wherein the plurality of holes includes a coolant flow hole and a plurality of guide tube attachment holes.

3. The bottom nozzle according to claim 1 or 2, further comprising an auxiliary leg portion extending downward from a lower surface of the solid portion.

4. A lower nozzle according to claim 1 or 2; a fuel assembly main body inserted into the hole of the bottom nozzle from above; an upper nozzle attached to an upper end of the fuel assembly body; A fuel assembly comprising:

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