JP7426335B2 - Lower end plug and fuel rod - Google Patents

Description

The present disclosure relates to lower end plugs and fuel rods.

For example, Patent Document 1 shows a configuration in which a plurality of fuel rods are arranged between an upper nozzle and a lower nozzle and are held by a grid as a fuel assembly constituting a reactor core. The upper nozzle and the lower nozzle are located at opposite ends of the fuel assembly and are configured to flow coolant. The lower nozzle is positioned and placed on a lower core support plate provided within the reactor vessel. The upper nozzle is positioned under an upper core support plate provided in the reactor vessel, and is configured to have a presser spring that abuts the upper core plate to press the fuel assembly against the lower core plate. .

Further, for example, Patent Document 2 discloses that, as a fuel assembly, a plurality of fuel rods are supported as a bundle in a square lattice arrangement at intervals from each other by spacer grids arranged at a plurality of locations between the upper and lower sides. Both upper and lower ends are supported by an upper tie plate and a lower tie plate, and the structure is shown as being housed in a rectangular cylindrical channel box. Then, the lower end plug provided at the lower end of the fuel rod is inserted into the insertion hole of the lower tie plate. In the lower tie plate, a plug-like member is integrally provided in a coolant passage hole formed around the insertion hole. The plug-like member includes a partition member having a spoke-shaped cross section and located within the coolant flow hole, and a plug-like member located outside with a distance from the inlet or outlet of the coolant flow hole and having a diameter larger than or equal to the diameter of the coolant flow hole. and a head having an outer diameter.

Japanese Patent Application Publication No. 10-123274 Japanese Patent Application Publication No. 2001-133574

In recent years, it has been desired to downsize the reactor core, and in doing so, it is necessary to ensure a flow path for coolant to the fuel rods.

The present disclosure solves the above-mentioned problems, and aims to provide a lower end plug and a fuel rod that can secure a coolant flow path.

To achieve the above object, the lower end plug according to one aspect of the present disclosure is fixed to the lower end of the fuel rod, and a communication portion extending from the bottom surface to the side surface is formed.

In order to achieve the above object, a fuel rod according to one aspect of the present disclosure has the lower end plug fixed to the lower end, and is directly placed and supported on the upper surface of the lower core support plate in which the through hole is formed. Ru.

The present disclosure can ensure a coolant flow path.

FIG. 1 is a schematic diagram of a nuclear reactor according to an embodiment. FIG. 2 is a schematic diagram of the inside of the furnace according to the embodiment. FIG. 3 is a partially enlarged schematic cross-sectional view of the core according to the embodiment. FIG. 4 is a partially enlarged schematic cross-sectional view of the core according to the embodiment. FIG. 5 is a schematic cross-sectional view of the core according to the embodiment. FIG. 6 is a partially cutaway schematic diagram of a control member in the core according to the embodiment. FIG. 7 is an enlarged schematic diagram of the core according to the embodiment. FIG. 8 is an enlarged bottom view of the fuel rods in the reactor core according to the embodiment. FIG. 9 is an enlarged bottom view of the fuel rods in the core according to the embodiment. FIG. 10 is an enlarged bottom view of the fuel rods in the reactor core according to the embodiment. FIG. 11 is a schematic cross-sectional view of another example of the core according to the embodiment.

Embodiments according to the present disclosure will be described in detail below based on the drawings. Note that the present invention is not limited to this embodiment. Furthermore, the constituent elements in the embodiments described below include those that can be easily replaced by those skilled in the art, or those that are substantially the same.

FIG. 1 is a schematic diagram of a nuclear reactor according to an embodiment.

The nuclear reactor 1 of the embodiment includes a reactor vessel 2, a core support structure 3, a control member drive mechanism 4, a steam generator 5, and a primary coolant pump 6.

The reactor vessel 2 includes a core support structure 3, a control member drive mechanism 4, a steam generator 5, and a primary coolant pump 6. The reactor vessel 2 is a pressure vessel, and includes a vessel body 2A that is open at the top, and a vessel lid 2B that closes the opening at the top of the vessel body 2A. The container lid 2B is removably attached to the container body 2A. The container body 2A is formed into a cylindrical shape with a closed bottom. The inside of this reactor vessel 2 is filled with primary coolant. The primary coolant consists of light water, for example.

In order to support the core 7, the core support structure 3 includes a core tank 3A, an upper core support plate 3B, and a lower core support plate 3C. The core barrel 3A is formed into a cylindrical shape extending in the vertical direction. The upper core support plate 3B is provided at the lower part of the core tank 3A, and is arranged above where the reactor core 7 is formed. The lower core support plate 3C is provided at the lower end of the core tank 3A, and is arranged below where the core 7 is formed. Note that an upper core plate may be used instead of the upper core support plate 3B. Further, a lower core plate may be used instead of the lower core support plate 3C. This core support structure 3 is arranged at the center of the reactor vessel 2 .

The control member drive mechanism 4 inserts and extracts a control member 10, which will be described later, into the reactor core 7. The control member 10 of this embodiment is inserted into multiple positions in the reactor core 7 from above. For this reason, the control member drive mechanism 4 corresponds to each control member 10 and is disposed above the reactor core 7 and at the top inside the reactor vessel 2 . The control member drive mechanism 4 is provided with a biasing device that biases the control member 10 in the direction of insertion into the reactor core 7, and is automatically activated when the drive with the control member 10 is cut off by a clutch mechanism or the like. It is inserted into the reactor core 7. Therefore, for example, in an emergency when the core temperature of the reactor core 7 exceeds a set temperature, the control member 10 is automatically inserted into the reactor core 7 to lower the reactivity of the fuel rods 8 in the reactor core 7.

The steam generator 5 is arranged inside the reactor vessel 2, and has, for example, a helical heat exchanger tube so as to surround the core tank 3A. In the steam generator 5, a secondary coolant is supplied to the inside of the heat transfer tube from outside the reactor vessel 2. The steam generator 5 exchanges heat with the primary coolant, evaporates the secondary cooling water, and generates steam. The secondary coolant is made of pure water, for example. Although not clearly shown in the figure, this steam generator 5 communicates with the outside of the reactor vessel 2 via a nozzle stub. There are two types of nozzles: one that sends the steam generated by the steam generator 5 to the outside of the reactor vessel 2, and the other that supplies secondary coolant to the steam generator 5 from the outside of the reactor vessel 2. A nozzle that sends steam to the outside of the reactor vessel 2 is connected to a steam turbine. The steam turbine is driven by steam generated by the steam generator 5, and generates electricity by a generator. The steam turbine also includes a condenser, which cools and condenses the secondary cooling water used for driving, and returns it to a low-pressure saturated liquid. This condenser is connected to a nozzle that supplies secondary coolant to the steam generator 5.

The primary coolant pump 6 guides the primary coolant from the core tank 3A to the steam generator 5. As shown in FIG. 1, the primary coolant pump 6 sends the primary coolant from the inside of the core tank 3A to the outside in the upper part of the core tank 3A, and sends the primary coolant in the lower part of the core tank 3A. It is circulated from below to above via the core support plate 3C and the upper core support plate 3B. The primary coolant is heated in the process of passing through the core bath 3A from below to above, exchanges heat with the secondary coolant of the steam generator 5 outside the core bath 3A, and then passes through the core bath 3A again from below to above. pass. A through hole 3Aa is formed in the upper part of the core tank 3A in order to send the primary coolant to the outside (see FIG. 2).

FIG. 2 is a schematic diagram showing the inside of the furnace according to the embodiment. FIG. 3 is a partially enlarged schematic cross-sectional view of the core according to the embodiment. FIG. 4 is a partially enlarged schematic cross-sectional view of the core according to the embodiment. FIG. 5 is a schematic cross-sectional view of the core according to the embodiment. FIG. 6 is a partially cutaway schematic diagram of a control member in the core according to the embodiment.

The reactor core 7 applied to the above-described nuclear reactor 1 includes, as shown in FIG. 2, fuel rods 8, a grid 9, a control member 10, a control member guide tube 11, and a neutron reflector 12.

Although the details will be described later, the fuel rod 8 is configured in a rod shape that extends in the vertical direction. As shown in FIG. 2, a plurality of fuel rods 8 are provided inside the core barrel 3A in a form extending in the vertical direction between the upper core support plate 3B and the lower core support plate 3C, and constitute the core 7. . Further, as shown in FIG. 3, the fuel rods 8 are each independent, and are arranged in a triangular lattice shape when viewed from above. The triangular lattice shape is a 60 degree lattice in plan view, and the fuel rods 8 are located at the intersections of the triangular lattice shape. The fuel rods 8 are provided inside the core barrel 3A, and all of the fuel rods composing the reactor core 7 are individually and independently arranged in a triangular lattice shape. In addition, although the fuel rods 8 of the embodiment are provided inside the core barrel 3A and all of them constituting the reactor core 7 are individually and independently arranged in a triangular lattice shape, the fuel rods 8 are provided inside the core barrel 3A. It is not excluded that all components of the core 7 are individually and independently arranged in a grid pattern.

As shown in FIG. 2, the grids 9 are provided at multiple locations in the vertical direction (in the embodiment, two locations in the vertical direction). As shown in FIG. 4, the grid 9 has cells 9A into which individual fuel rods 8 can be inserted from above. The cell 9A provides a gap 9Aa between each of the inserted fuel rods 8, and allows the primary coolant passing through the core barrel 3A from below to above to pass through the gap 9Aa. The grid 9 does not have a configuration for holding the fuel rods 8 in the cells 9A, and only allows the fuel rods 8 to be freely inserted into the cells 9A. The cells 9A are formed in a hexagonal shape when viewed from above, and the entire grid 9 has a honeycomb structure by combining a plurality of hexagonal cells 9A adjacent to each other. Therefore, the grid 9 can provide gaps 9Aa between the individual fuel rods 8 arranged in a triangular lattice shape.

The control member 10 is provided inside the core barrel 3A so that it can be inserted or withdrawn vertically along the fuel rods 8. The control member 10 is inserted along the fuel rod 8 and is arranged between the upper core support plate 3B and the lower core support plate 3C in accordance with the length of the fuel rod 8. As shown in FIGS. 2 to 5, fuel rods 8 are not placed in the core 7 where the control member 10 is placed. The control member 10 is inserted into and extracted from the reactor core 7 by the control member drive mechanism 4 described above. The control member 10 is formed of a neutron absorber. For example, boron carbide (boron carbide: B ₄ C) can be used as the neutron absorber. The control member 10 made of a neutron absorber can control the reactivity of the fuel rods 8 constituting the reactor core 7 by approaching the fuel rods 8 by inserting them and separating them from the fuel rods 8 by withdrawing them. The core temperature of the reactor can be controlled.

The control member 10 is formed as a plate 10A that follows the triangular lattice shape of the fuel rods 8, as shown in FIGS. 3 and 5. The control member 10 is formed into a triisotropically arranged plate shape in which the plate bodies 10A are combined in plan view from the insertion direction. That is, the control member 10 is formed into a triangular plate shape in which three plates 10A are combined at 120° intervals in plan view, and each plate 10A is arranged along the triangular lattice shape of the fuel rods 8. Ru. The control member 10 formed in the shape of a triisotropically arranged plate is arranged between predetermined fuel rods 8 . The control members 10 can control the reactivity of each fuel rod 8 to a constant level by arranging a plurality of control members 10 at equal intervals as shown in FIG. 5 in the core 7 composed of the fuel rods 8. Although not clearly shown in the drawings, for example, when the fuel rods 8 are arranged in a lattice shape, the control member 10 is formed as a plate body 10A that follows the lattice shape of the fuel rods 8. The plate body 10A is combined to form a cross shape. Further, the control member 10 is not limited to the triisotropically arranged plate shape or the cross shape, but is formed in the shape of a single character only by the configuration of the plate body 10A, and is provided so as to be inserted or withdrawn in the vertical direction along the fuel rod 8. It's okay.

In the control member 10, as shown in FIGS. 3 and 6, the plate body 10A includes a control material 10Aa and a covering material 10Ab that covers the control material 10Aa. The control material 10Aa is formed of a neutron absorber. The control material 10Aa is formed by dividing into a plurality of rectangular blocks, and the control material 10Aa is composed of a plurality of blocks, each of which is arranged side by side so as to form the shape of a plate 10A using a lattice 10Ac. This makes manufacturing easier. The covering material 10Ab collectively covers each control material 10Aa together with the grid 10Ac. That is, the covering material 10Ab forms the outer shell of the plate body 10A (control member 10). The covering material 10Ab is made of pure iron or stainless steel, for example.

The control member guide tube 11 guides the movement of the control member 10 into and out of the reactor core 7 . As shown in FIGS. 2 and 3, the control member guide tube 11 is formed into a cylindrical shape to match the outer shape of the control member 10 in a plan view. The control member guide tube 11 is arranged between the upper core support plate 3B and the lower core support plate 3C. As shown in FIG. 4, the control member guide tube 11 is joined to the grid 9 by welding or the like. This control member guide tube 11 is doped with burnable poisons such as erbium oxide (Er ₂ O ₃ ), gadolinium oxide (Gd ₂ O ₃ ), and boron carbide (B ₄ C).

The neutron reflector 12 is arranged around the outer periphery of the reactor core 7 and is provided in a cylindrical shape so as to surround each fuel rod 8 . The neutron reflector 12 includes a reflective material 12A and a reinforcing material 12B. The reflective material 12A is configured as an inner cylinder arranged inside the cylindrical shape of the neutron reflector 12. The reflective material 12A is made of beryllium oxide (BeO), a compound containing beryllium (Be), aluminum oxide (Al ₂ O ₃ ), a compound containing aluminum, or aluminum oxide, a compound containing magnesium (Mg). Contains magnesium (MgO). The reinforcing material 12B is provided on the outer periphery of the reflecting material 12A, and is configured as an outer cylinder arranged outside the cylindrical shape of the neutron reflector 12. Note that the neutron reflector 12 may have a configuration including only the reflecting material 12A.

FIG. 7 is an enlarged schematic diagram of the core according to the embodiment. FIG. 8 is an enlarged bottom view of the fuel rods in the reactor core according to the embodiment. FIG. 9 is an enlarged bottom view of the fuel rods in the core according to the embodiment. FIG. 10 is an enlarged bottom view of the fuel rods in the reactor core according to the embodiment.

Details of the fuel rod 8 will be explained with reference to FIGS. 7 to 10.

As described above, the fuel rod 8 is configured in a rod shape that extends in the vertical direction. As shown in FIG. 7, the fuel rod 8 includes a nuclear fuel 8A, a cylindrical member 8B, an upper end plug 8C, a lower end plug 8D, and an elastic member 8E.

Nuclear fuel 8A contains uranium, which is a nuclear fuel material. The nuclear fuel 8A is in the form of cylindrical pellets, and a plurality of nuclear fuels are provided in one fuel rod 8.

The cylindrical member 8B is formed into a cylindrical shape so as to accommodate a plurality of nuclear fuels 8A in the form of a plurality of pellets along the vertical direction.

The upper end stopper 8C is formed into a substantially cylindrical shape and is fixed to the upper end of the cylindrical member 8B to close the opening at the cylindrical upper end of the cylindrical member 8B. Therefore, the upper end plug 8C constitutes the upper end of the fuel rod 8.

The lower end stopper 8D is formed into a substantially cylindrical shape and is fixed to the lower end of the cylindrical member 8B to close the opening at the cylindrical lower end of the cylindrical member 8B. Therefore, the lower end plug 8D constitutes the lower end of the fuel rod 8.

The elastic member 8E is provided inside the cylinder member 8B between the uppermost nuclear fuel 8A and the upper end plug 8C, and uses elastic force to direct the nuclear fuel 8A toward the lower end plug 8D, which is the lower end side of the cylinder member 8B. energize. Therefore, the plurality of nuclear fuels 8A housed inside the cylinder member 8B are pressed toward the lower end plug 8D by the elastic member 8E and are supported while being restricted from moving in the vertical direction.

This fuel rod 8 has a lower core support plate 3C attached to the lower end of the core barrel 3A, and a grid 9, a control member guide tube 11, and a neutron reflector 12 are arranged inside the core barrel 3A. It is inserted into cell 9A from above. The fuel rods 8 are supported in such a manner that a lower end plug 8D constituting the lower end is placed directly on a flat portion of the upper surface 3Cb of the lower core support plate 3C. Although the lower core support plate 3C is formed with a through hole 3Ca that penetrates in the vertical direction, the fuel rods 8 are directly inserted into the flat part of the upper surface 3Cb of the lower core support plate 3C without passing through the through hole 3Ca. placed. The fuel rod 8 does not pass through the through hole 3Ca because at least the outer diameter of the lower end plug 8D is formed larger than the inside diameter of the through hole 3Ca. Alternatively, the fuel rod 8 is inserted into the cell 9A of the grid 9 and its movement in the horizontal direction is suppressed, thereby avoiding the position of the through hole 3Ca and not passing through the through hole 3Ca. An upper core support plate 3B is arranged above the fuel rods 8. Although the upper core support plate 3B is formed with a through hole 3Ba that penetrates in the vertical direction, the fuel rods 8 are inserted between the upper core support plate 3B and the lower core support plate 3C without passing through the through hole 3Ba. placed between. A space is formed between the upper end plug 8C forming the upper end of the fuel rod 8 and the upper core support plate 3B. The fuel rod 8 does not pass through the through hole 3Ba because the outer diameter of at least the upper end plug 8C is larger than the inside diameter of the through hole 3Ba. Alternatively, the fuel rod 8 is inserted into the cell 9A of the grid 9 and its movement in the horizontal direction is suppressed, thereby avoiding the position of the through hole 3Ba and not passing through the through hole 3Ba. The through holes 3Ba of the upper core support plate 3B and the through holes 3Ca of the lower core support plate 3C allow the primary coolant to pass through the inside of the core 7 in which the fuel rods 8 are arranged, as shown by arrows in FIG. In this way, the reactor core 7 is configured. Further, as shown in FIG. 2, a control member drive mechanism 4 is installed. The control member drive mechanism 4 is supported by a support member 20 at a position above the core barrel 3A.

Here, since the lower end plug 8D constituting the lower end of the fuel rod 8 is formed in a cylindrical shape, the bottom surface 8Da is flat and the side surface 8Db is formed in an annular shape. As shown in FIGS. 7 to 10, a notch 8Dc is formed as a communication portion. The notch 8Dc is formed from the bottom surface 8Da of the lower end plug 8D to the side surface 8Db. The cutout 8Dc does not communicate with the inside of the cylindrical member 8B. The notch 8Dc is formed in a tapered shape so as to widen outward from the bottom surface 8Da of the lower end plug 8D toward the side surface 8Db. The notch 8Dc allows the bottom surface 8Da of the lower end plug 8D to communicate with the side surface 8Db into the through hole 3Ca of the lower core support plate 3C in a configuration in which the fuel rod 8 is placed directly on the lower core support plate 3C. Therefore, as shown by the arrow in FIG. 7, the primary coolant passes through the lower core support plate 3C from the lower side of the lower core support plate 3C through the through holes 3Ca, and passes through the notches 8Dc to the adjacent fuel rods. 8 to the gap 9Aa. The primary coolant guided into the gaps 9Aa of the fuel rods 8 passes through the upper core support plate 3B via the through holes 3Ba of the upper core support plate 3B, and is sent above the core 7.

In the embodiment, the notches 8Dc are arranged at multiple locations in the circumferential direction of the lower end plug 8D. The notches 8Dc of the lower end plug 8D shown in FIGS. 7 and 8 are formed at four locations in the circumferential direction of the lower end plug 8D, and the flat part of the bottom surface 8Da of the lower end plug 8D is formed in a cross shape when viewed from the bottom. There is. Therefore, in the lower end plug 8D shown in FIGS. 7 and 8, when the through holes 3Ca of the lower core support plate 3C are arranged in a grid pattern in a plan view, and the fuel rods 8 are arranged in a grid pattern in a plan view, The bottom surface 8Da is placed in contact with the flat portion of the upper surface 3Cb of the lower core support plate 3C, and the notch 8Dc can be configured to communicate with the four through holes 3Ca in the vertical direction. Moreover, the notches 8Dc of the lower end plug 8D shown in FIG. 9 are formed at two locations in the circumferential direction of the lower end plug 8D, and the flat part of the bottom surface 8Da of the lower end plug 8D is formed into a single character shape when viewed from the bottom. . Therefore, in the lower end plug 8D shown in FIG. 9, when the through holes 3Ca of the lower core support plate 3C are arranged in a grid pattern in a plan view, and the fuel rods 8 are arranged in a grid pattern in a plan view, the bottom surface 8Da is It is placed in contact with the flat part of the upper surface 3Cb of the lower core support plate 3C, and can be configured such that the notches 8Dc communicate with the four through holes 3Ca in the vertical direction. Moreover, the notches 8Dc of the lower end plug 8D shown in FIG. 10 are formed at three locations in the circumferential direction of the lower end plug 8D, and the flat part of the bottom surface 8Da of the lower end plug 8D has a triisotropic plate shape when viewed from the bottom. It is formed. Therefore, the lower end plug 8D shown in FIG. 8Da is placed in contact with the flat part of the upper surface 3Cb of the lower core support plate 3C, and the notch 8Dc can be configured to communicate vertically with the three through holes 3Ca. In addition to the above-mentioned notch 8Dc, the communication portion may be a through hole formed from the bottom surface 8Da of the lower end plug 8D to the side surface 8Db, although it is not clearly shown in the drawings.

FIG. 11 is a schematic cross-sectional view of another example of the core according to the embodiment.

In the core 7 shown in FIG. 5, the control member 10 is formed in the shape of a triisotropically arranged plate in plan view, but in the core 7 shown in FIG. 11, the control member 10' is formed in a circular shape in plan view. . The control member 10' is formed in a cylindrical shape extending in the vertical direction, and although not clearly shown in the figure, a control member divided into cylindrical shapes is collectively covered with a covering material. The control member 10' is arranged between predetermined fuel rods 8. The control members 10' can control the reactivity of each fuel rod 8 to a constant level by arranging a plurality of control members 10' at equal intervals as shown in FIG. 11 in the core 7 made up of the fuel rods 8. Although not shown in the drawings, the control member 10' is configured to be inserted into or extracted from a cylindrical control member guide tube extending in the vertical direction. The control member guide tube is provided in a portion where the fuel rods 8, which are arranged in a triangular lattice shape or a lattice shape in plan view, are not arranged, and is joined to the grid 9 by welding or the like. Although the control member 10' shown in FIG. 11 is configured to be thicker than one fuel rod 8, it may have a thickness equivalent to one fuel rod 8.

As described above, in the core structure of the embodiment, all the fuel rods 8 of the core 7 are independently arranged in a triangular lattice shape.

Therefore, according to the core structure of the embodiment, by arranging the fuel rods 8 in a triangular lattice shape, the fuel rods 8 are arranged densely compared to the case where fuel assemblies are used. Therefore, compared to a core using fuel assemblies, the extra gap between the cylindrical core and the core tank 3A can be reduced, the amount of fuel loaded can be increased, and the amount of neutrons leaking from the core can be reduced. As a result, according to the core structure of the embodiment, it is possible to improve the nuclear fuel filling rate and maximize the amount of fuel loaded, which in turn makes it possible to downsize the reactor core 7 and extend the life of the reactor core 7. .

Here, by densely arranging the fuel rods 8, it is possible to downsize the core and extend the life of the core, but if the fuel rods 8 are placed too close together, the void reactivity becomes positive. The fuel rods 8 are arranged at a distance that makes the reactivity negative. Void reactivity refers to the reactivity that occurs inside the reactor core through the generation of voids (bubbles) or changes in the amount of voids due to boiling of the primary coolant or other causes.

Further, the core structure of the embodiment includes a control member guide tube 11 disposed between predetermined fuel rods 8 and a control member 10 inserted into the control member guide tube 11, and the control member 10 The control member guide tube 11 is formed as a plate body 10A that follows the triangular lattice arrangement of the fuel rods 8, and the control member guide tube 11 is provided along the triangular lattice arrangement of the fuel rods 8 so that the control member 10 formed as the plate body 10A can be inserted therein. ing.

Therefore, according to the core structure of the embodiment, coexistence of the control member 10 and the control member guide tube 11 with the fuel rods 8 arranged in a triangular lattice pattern can be achieved. Specifically, the exclusion area of the fuel rods 8 can be minimized for the fuel rods 8 arranged in a triangular lattice pattern, contributing to an increase in the amount of fuel loaded. As a result, according to the core structure of the embodiment, compatibility with the triangular lattice arrangement of the fuel rods 8 can be improved, and the strength of the fuel structure can be increased. For example, as shown in FIG. 11, the cylindrical control member 10' cannot minimize the exclusion area of the fuel rods 8 with respect to the triangular lattice arrangement of the fuel rods 8; has low affinity. Further, by forming the control member 10 as a plate body 10A, a large surface area of the control member 10 can be ensured, the neutron absorption capacity is increased, and the value of the control member 10 is increased. For example, as a configuration to ensure a large surface area, a cylindrical control member 10' as shown in FIG. 11 can be considered, but the interior of the cylindrical shape becomes difficult to absorb neutrons due to the self-shielding effect. On the other hand, if the control member 10 is made of a plate body 10A, the surface area can be increased while reducing the thickness from the surface to the inside, and the neutron absorption ability can be ensured. As a result, according to the reactor core structure of the embodiment, it is possible to ensure reactor shutdown ability and achieve structural feasibility in which the number of control member drive mechanisms 4 can be reduced without increasing the number of control members 10. In the core structure of the embodiment, the reactor shutdown ability achieves a predetermined degree of subcriticality by inserting all the control members 10 at low temperature and zero output. In order to secure the reactor shutdown capability, it is necessary to increase the number of control members 10, which leads to an increase in the size of the reactor core 7. However, according to the core structure of the embodiment, the reactor shutdown capability is secured and the number of control members 10 is increased. The number of control member drive mechanisms 4 can be reduced without increasing the number, contributing to miniaturization of the reactor core 7.

Further, in the core structure of the embodiment, the control member 10 is formed into a triisotropically arranged plate shape, which is a combination of the plate bodies 10A when viewed from the insertion direction.

According to the core structure of the embodiment, the triangularly arranged plate-shaped control member 10 can further improve compatibility with the triangular lattice arrangement of the fuel rods 8, and further increase the fuel structure strength.

Furthermore, in the core structure of the embodiment, the control member 10 includes a control material 10Aa divided into a plurality of parts, and a covering material 10Ab that collectively covers each control material 10Aa.

According to the core structure of the embodiment, by covering the control member 10Aa with the covering material 10Ab, changes in the dimensions of the control member 10 due to irradiation of the control member 10Aa with neutrons can be suppressed, and leakage of gas generated from the control member 10Aa can be suppressed. can be suppressed.

Further, in the core structure of the embodiment, a burnable poison is added to the control member guide tube 11.

According to the reactor core structure of the embodiment, there is surplus reactivity at the beginning of nuclear fuel combustion, and neutrons are absorbed by burnable poison, so that the surplus reactivity at the beginning of operation can be reduced. Generally, the number of control members 10 is increased in order to reduce surplus reactivity at the initial stage of operation, but according to the core structure of the embodiment, the number of required control members 10 can be reduced. Furthermore, after absorbing neutrons, burnable poisons convert into nuclides that do not absorb neutrons, so there is no reduction in reactivity after the initial stage of operation.

In addition, the core structure of the embodiment includes a neutron reflector 12 that is arranged on the outer periphery of the core 7 and surrounds each fuel rod 8, and the neutron reflector 12 is made of one of beryllium oxide, aluminum oxide, and magnesium oxide. It consists of a reflector 12A including one.

Beryllium, aluminum, and magnesium have a smaller neutron absorption cross section than stainless steel, and have a larger neutron scattering cross section than the neutron absorption cross section, so they have high neutron reflection ability. Furthermore, as a result, according to the core structure of the embodiment, the thickness of the neutron reflector 12 can be formed thinner than that of stainless steel. In addition to its neutron-reflecting function, beryllium consumes one neutron and releases two neutrons through a neutron reaction, and splits into two alpha particles. This beryllium neutron reaction releases more neutrons than it consumes, increasing the number of neutrons in the system. As a result, according to the reactor core structure of the embodiment, the neutron reflection efficiency is high, and in order to bring fissile material below the critical mass into a critical state or increase the fission reaction at the critical mass, nuclear characteristics (criticality) This will improve core life and extend the life of the reactor core.

Moreover, in the core structure of the embodiment, the neutron reflector 12 further includes a stainless steel reinforcing material 12B around the outer periphery of the reflector 12A.

In the case of the neutron reflector 12 including only the reflector 12A, the structural strength and shielding performance are insufficient, and the strength and shielding properties tend to deteriorate. Therefore, according to the core structure of the embodiment, by reinforcing and shielding with the stainless steel reinforcing material 12B, it is possible to compensate for the deficiency caused by the reflector 12A.

Further, the core structure of the embodiment includes a grid 9 having cells 9A through which each fuel rod 8 is inserted, and the grid 9 has a honeycomb structure in which the cells 9A are formed in a hexagonal shape.

By inserting each fuel rod 8 into the cell 9A, the plurality of fuel rods 8 can be independently arranged in a triangular lattice shape. Cell 9A does not fix each fuel rod 8 by insertion, and does not support each fuel rod 8 individually. Further, the cell 9A provides a gap 9Aa between each fuel rod 8 through which the primary coolant passes. Generally, when supporting the fuel rods 8, an elastic member for supporting the fuel rods 8 is provided on the grid 9, but in this case, it is difficult to increase the density of the fuel rods 8 due to the provision of the elastic member. Therefore, according to the core structure of the embodiment, only the fuel rods 8 are inserted into the cells 9A, and a dense structure is realized with a triangular lattice arrangement without any special supporting structure. In addition, according to the core structure of the embodiment, the fuel rods 8 are inserted into the cells 9A without any special supporting structure, thereby realizing a dense structure and providing primary cooling between each fuel rod 8. A gap 9Aa through which the material passes can be created.

Further, in the core structure of the embodiment, the plurality of fuel rods 8 are arranged between the upper core support plate 3B and the lower core support plate 3C, and the lower ends are directly placed and supported on the lower core support plate 3C. There is.

In a core structure using fuel assemblies, an upper nozzle is arranged at the upper end of the fuel assembly, a lower nozzle is arranged at the lower end, and a spring is further provided to support the fuel assembly between the upper core support plate and the lower core support plate. Parts such as mechanisms are provided. In contrast, in the core structure of the embodiment, the fuel rods 8 are arranged between the upper core support plate 3B and the lower core support plate 3C, and the lower ends of the fuel rods 8 are placed directly on the lower core support plate 3C. I support it. As a result, according to the core structure of the embodiment, by not using parts such as the upper nozzle and the lower nozzle and the spring mechanism, it is possible to reduce the height of the core 7 and achieve miniaturization.

The lower end plug 8D of the embodiment is fixed to the lower end of the fuel rod 8, and has a communication portion (notch 8Dc) communicating from the bottom surface 8Da to the side surface 8Db.

In the embodiment, the fuel rods 8 are directly placed and supported on the upper surface 3Cb of the lower core support plate 3C in which the through holes 3Ca are formed. In contrast to this structure, the lower end plug 8D of the fuel rod 8 allows the bottom surface 8Da to the side surface 8Db to communicate with the through hole 3Ca of the lower core support plate 3C through a notch 8Dc. Therefore, the primary coolant passes through the lower core support plate 3C from the lower side of the lower core support plate 3C via the through hole 3Ca, and is sent around the adjacent fuel rods 8 via the notch 8Dc. As a result, according to the lower end plug 8D of the embodiment, the primary coolant can be passed from the bottom surface 8Da to the side surface 8Db at the lower end of the fuel rod 8, and a flow path for the primary coolant to the fuel rod 8 is secured. be able to.

In the lower end plug 8D of the embodiment, the communication portion (notch 8Dc) is formed to expand outward from the bottom surface 8Da toward the side surface 8Db.

According to the lower end plug 8D of the embodiment, the primary coolant can be guided along the periphery of the fuel rod 8.

Further, in the lower end plug 8D of the embodiment, a plurality of communicating portions (notches 8Dc) are arranged in the circumferential direction.

According to the lower end plug 8D of the embodiment, the primary coolant can be sent around the fuel rod 8 at multiple locations.

Further, in the lower end plug 8D of the embodiment, the bottom surface 8Da is formed flat.

According to the lower end plug 8D of the embodiment, the fuel rod 8 can be stably mounted.

Further, in the lower end plug 8D of the embodiment, the notches 8Dc are formed at four locations in the circumferential direction, and the bottom surface 8Da is formed in a cross shape when viewed from the bottom.

According to the lower end plug 8D of the embodiment, the primary coolant can be sent around the fuel rod 8 at a plurality of locations, and the fuel rod 8 can be stably mounted.

Further, the fuel rod 8 of the embodiment has the above-described lower end plug 8D fixed to the lower end, and is directly placed and supported on the upper surface 3Cb of the lower core support plate 3C in which the through hole 3Ca is formed.

According to the fuel rod 8 of the embodiment, the height of the reactor core 7 can be reduced and the size can be reduced by not using parts such as an upper nozzle, a lower nozzle, and a spring mechanism compared to when a fuel assembly is used. I can do it.

In addition, the nuclear reactor 1 of the embodiment includes a reactor vessel 2, a reactor core 7 having the above-mentioned core structure and disposed inside the reactor vessel 2, and a reactor core 7 disposed inside the reactor vessel 2. a steam generator 5 to which a secondary coolant is supplied from the outside of the reactor vessel 2 while the steam of the secondary coolant is discharged to the outside of the reactor vessel 2; a primary coolant pump 6 that circulates primary coolant that exchanges heat with the reactor core 7 and the steam generator 5; and a control member drive mechanism 4 that is disposed inside the reactor vessel 2 and that inserts and removes the control member 10 into the reactor core 7. , is provided.

According to the nuclear reactor 1 of the embodiment, the reactor core 7 is downsized and equipped with a small reactor core 7, and the steam generator 5, the primary coolant pump 6, the control member drive mechanism 4, and the reactor vessel 2 are It can be configured as an integrated type placed inside.

1 Nuclear reactor 2 Reactor vessel 2A Vessel body 2B Vessel lid 3 Core support structure 3A Core tank 3Aa Through hole 3B Upper core support plate 3Ba Through hole 3C Lower core support plate 3Ca Through hole 3Cb Upper surface 4 Control member drive mechanism 5 Steam generation Container 6 Primary coolant pump 7 Core 8 Fuel rod 8A Nuclear fuel 8B Cylindrical member 8C Upper end plug 8D Lower end plug 8Da Bottom surface 8Db Side surface 8Dc Notch (communication part)
8E Elastic member 9 Grid 9A Cell 9Aa Gap 10 Control member 10A Plate 10Aa Control member 10Ab Covering material 10Ac Grid 11 Control member guide tube 12 Neutron reflector 12A Reflector 12B Reinforcement material 20 Support member

Claims (4)

It is disposed between a lower core support plate in which a through hole is formed and an upper core support plate, a lower end is placed directly on the upper surface of the lower core support plate, and a gap is formed between the upper end and the upper core support plate. a lower end plug fixed to the lower end of each fuel rod;
A notch is formed from a cylindrical flat bottom surface to a side surface, and the notch communicates with the through hole in the vertical direction while the bottom surface is in contact with the top surface of the lower core support plate. , lower end plug. The lower end plug according to claim 1 , wherein a plurality of said notches are arranged in a circumferential direction. The lower end plug according to claim 1 , wherein the notches are formed at four locations in the circumferential direction , and the bottom surface is formed in a cross shape when viewed from the bottom. A fuel rod, wherein the lower end plug according to any one of claims 1 to 3 is fixed to the lower end, and is directly placed and supported on the upper surface of a lower core support plate in which a through hole is formed.

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