JP5015213B2 - Lower tie plate of fuel assembly and fuel assembly - Google Patents

Description

  The present invention relates to a lower tie plate of a nuclear fuel assembly, and more particularly, to a lower tie plate that achieves a low pressure loss in a lower region, and a fuel assembly including the lower tie plate.

  In general, a large number of fuel assemblies are loaded in the core of a boiling water reactor. FIG. 13 is a diagram showing an example of a fuel assembly 10 employed in a boiling water reactor. The fuel assembly 10 has an upper tie plate 11 and a lower tie plate 12, and both ends of these tie plates have both ends. A plurality of fuel rods 13, a water rod 14, a fuel spacer 15 that bundles these fuel rods, and a channel box 16 that surrounds the fuel rod bundle bundled by the fuel spacer 15 and is attached to the upper tie plate 11. I have. As the fuel rod, a partial length fuel rod 17 whose height does not reach the upper tie plate 11 may be employed. A fuel assembly having the above-described structure is loaded in a lattice shape in the core of the nuclear reactor, a control rod is disposed at the center of the four fuel assemblies 10, and a plurality of local parts are used to detect the neutron flux. An output area monitor is arranged.

  The fuel assembly 10 is supported by a core support plate and an upper lattice plate (not shown), and is surrounded by a cylindrical shroud. Accordingly, the coolant flows into the channel box 16 from below through the orifices of the fuel support fittings and the lower tie plates 12 of the fuel assemblies 10, and is heated by the fuel assemblies. ) To form a gas-liquid two-phase flow. The effective fuel assembly length of a commercial BWR that is currently operating is about 3.7 m.

  The fuel assemblies in the boiling water reactor as described above have been 7 × 7 type, 8 × 8 type, improved 8 × 8 type, and high burnup 8 × 8 since commercial power generation was performed in Japan. A type and a high burnup 9 × 9 type have been adopted. These improvements will increase the capacity of fissile material per fuel assembly, and by optimizing the distribution of enrichment within the fuel assembly and optimal placement of combustible poisons, higher burnup and longer operating cycles will be realized. The economic efficiency of the core has been improved. From high burn-up 8 × 8 fuel to 9 × 9 fuel, there are two deteriorations in stability due to transient characteristics and nuclear factors due to increase in the absolute value of void reactivity coefficient accompanying high burn-up / long-term operation cycle. The large diameter water rod 14 is used. In addition, the deterioration of stability based on the thermo-hydraulic factor due to the increase in the two-phase flow pressure loss accompanying the increase in the fuel assembly lattice is due to the reduction of the spacer pressure loss coefficient, the eight partial length fuel rods, and the high pressure loss type lower type It is prevented by the rate.

  Also, in recent fuel assemblies with higher performance, a filter function is provided in the web portion of the lower tie plate that supports the lower ends of the fuel rods and water rods in order to prevent foreign matter from entering the fuel assemblies. As a result, the soundness of the fuel is improved. The above-mentioned lower tie plate of 9 × 9 fuel employs a design that increases the resistance to flow (ie, high pressure loss) by opening a large number of holes with a small diameter of about 5 mm. Although improvements have been made, this also serves as a foreign matter filter.

  Foreign materials that are expected to enter the fuel assembly include gold dust slightly left in the reactor primary system at the time of plant construction, broken metal brushes during equipment cleaning, and fragments when equipment is damaged. Assumed. The shape is expected to vary widely, such as a plate shape, a helical spring shape (spiral shape), and a wire shape (linear shape).

  Recently, a lower tie plate that further develops the foreign matter filter function has been proposed and is being applied to a BWR operation plant. FIG. 14 is a cross-sectional view showing a schematic configuration of the lower tie plate with a foreign matter filter for the 9 × 9 fuel, and the flow rate of the lower tie plate 12 gradually increases from the coolant inlet opening 20 toward the downstream side. A nozzle portion 21, a web portion 23 that supports the lower ends of the fuel rod 13 and the water rod 14 and has a plurality of outlet openings 22 through which a coolant can be passed in a predetermined flow direction, the nozzle portion 21 and the web A coolant receiving chamber 25 is formed between the nozzle portion 21 and the web portion 23. The coolant receiving chamber 25 is surrounded by the peripheral side wall 24. A foreign matter filter 27 provided with several hundreds of small-diameter holes 26 of several mm is attached to the lower surface of the web portion 23. Here, the lower end plug of the fuel rod cladding tube and the lower end plug of the water rod penetrate the foreign matter filter 27.

  That is, the lower tie plate 12 of the fuel assembly is configured to be fitted into the opening 31 of the fuel support fitting 30 shown in FIG. 15, and the lower tie plate 12 is designed to prevent the coolant from leaking from the fitted portion. The inner surface of the opening 31 of the fuel support fitting 30 that forms the joint surface with the rate 12 is machined into a reverse headed conical shape, while the lower end of the lower tie plate 12 has the reverse headed conical opening. The outer surface thereof is formed in a reverse cone shape so as to correspond to 31. Therefore, a nozzle portion 21 is formed at the lower end portion of the lower tie plate 12 so that the flow path gradually expands upward from the coolant inlet opening 20.

  Thus, the coolant flowing into the coolant receiving chamber 25 from the coolant inlet opening 20 removes the foreign matter filter 27 except for the flow from the leak hole 28 opened in the nozzle portion 21 of the lower tie plate 12 to the bypass portion. Always pass. Therefore, most foreign matters are captured by the foreign matter filter 27 before entering the fuel assembly surrounded by the channel box 16.

JP-A-7-306284 JP 2002-62392 A

  In the conventionally proposed foreign matter filter, from the viewpoint of improving the property of trapping foreign matter in the filter section, it is promising to refine the mesh size or to install a plurality of stages. However, in such a foreign matter filter, there is a problem that the pressure loss is remarkably increased by reducing the mesh size, installing a plurality of stages, and the like, and the pressure loss of the entire lower tie plate is increased. The increase in the pressure loss of the lower tie plate may cause a decrease in the core flow rate, an imbalance in the flow distribution of the fuel assembly, a decrease in the thermal margin, and the like.

  In view of these points, the present invention provides a lower tie plate having a low-pressure loss structure in a portion other than the filter portion, and the low-pressure loss structure so that a high-pressure loss type foreign matter filter with improved foreign matter inflow prevention performance can be installed. The object is to obtain a fuel assembly with a lower tie plate.

  1st invention supports the nozzle part which a flow path expands toward a downstream side from a coolant inlet opening, the lower end of a fuel rod and a water rod, and can let a coolant pass in a predetermined flow direction. A coolant receiving chamber is formed which includes a web portion having a plurality of outlet openings and a peripheral side wall connecting the nozzle portion and the web portion, and is surrounded by the peripheral side wall between the nozzle portion and the web portion. In the lower tie plate of the nuclear reactor fuel assembly, a coolant inlet pipe for introducing a coolant is provided in the nozzle part, and a tip part of the coolant inlet pipe is formed between the nozzle part and the web part. It protrudes into the coolant receiving chamber.

  According to the measurement of the pressure loss of the lower tie plate, although it depends on the type of the lower tie plate, it was found that the pressure loss at the nozzle part and the web part was almost the same, and both were comparable. Therefore, it can be seen that if the pressure loss of the nozzle portion can be significantly reduced, the pressure loss of the lower tie plate can be halved. However, the nozzle part of the lower tie plate has a reverse cone shape as described above from the viewpoint of improving the bonding property with the fuel support fitting as described above. Is a structure that expands rapidly. For this reason, a secondary flow (vortex) region is generated other than the high-speed region of the fluid, and acts as a flow resistance.

  However, in the first invention, since the structure described above suppresses the expansion of the coolant flow path at the nozzle portion, it is possible to prevent the generation of the secondary flow due to the expansion flow (deceleration), and to generate the secondary flow. The flow resistance due to can be reduced. Therefore, the pressure loss at the nozzle portion is reduced, and the pressure loss of the lower tie plate can be halved.

  The second aspect of the invention supports the nozzle portion in which the flow path gradually expands from the coolant inlet opening toward the downstream side, the lower ends of the fuel rod and the water rod, and allows the coolant to pass in a predetermined flow direction. A coolant receiving chamber is formed which includes a web portion having a plurality of outlet openings and a peripheral side wall connecting the nozzle portion and the web portion, and is surrounded by the peripheral side wall between the nozzle portion and the web portion. In the lower tie plate of the nuclear reactor fuel assembly, the inner wall surface of the nozzle part and a part of the inner wall surface of the surrounding side wall that follows are formed in a convex curved surface in the longitudinal section so that the flow passage area gradually increases. By configuring the inner wall surface of the nozzle part and a part of the inner wall surface of the surrounding side wall as described above as described above, rapid expansion of the coolant channel is suppressed. Is done. Therefore, the generation of the secondary flow due to the expansion flow (deceleration) is prevented, the flow resistance due to the secondary flow generation is reduced, and the pressure loss at the nozzle portion can be reduced.

  The third invention supports the nozzle part in which the flow path gradually expands from the coolant inlet opening toward the downstream side, the lower ends of the fuel rod and the water rod, and allows the coolant to pass in a predetermined flow direction. A coolant receiving chamber is formed which includes a web portion having a plurality of outlet openings and a peripheral side wall connecting the nozzle portion and the web portion, and is surrounded by the peripheral side wall between the nozzle portion and the web portion. In the lower tie plate of the nuclear reactor fuel assembly, the coolant receiving chamber is disposed in parallel with the coolant inlet opening interposed therebetween, and is fixed to the inner wall surface of the peripheral side wall and the inner surface of the nozzle portion. The two flow straightening plates are provided, and the flow straightening area on the downstream side of the coolant inlet opening is suppressed by the two flow straightening plates. To reduce the pressure loss at That.

  According to a fourth aspect of the present invention, it is possible to support the nozzle portion where the flow path gradually expands from the coolant inlet opening toward the downstream side, the lower end of the fuel rod and the water rod, and allow the coolant to pass in a predetermined flow direction. A coolant receiving chamber is formed which includes a web portion having a plurality of outlet openings and a peripheral side wall connecting the nozzle portion and the web portion, and is surrounded by the peripheral side wall between the nozzle portion and the web portion. Further, in the lower tie plate of the nuclear reactor fuel assembly, a drift plate that is inclined obliquely upward from one side of the coolant inlet opening toward the upper side of the coolant inlet opening is provided. Thus, the drift plate suppresses the expansion of the flow path area on the downstream side of the coolant inlet opening, and the pressure loss at the nozzle portion can be reduced.

  5th invention supports the nozzle part which a flow path expands gradually toward a downstream from a coolant inlet opening, a fuel rod, and the lower end of a water rod, and can let a coolant pass in a predetermined | prescribed flow direction. A coolant receiving chamber is formed which includes a web portion having a plurality of outlet openings and a peripheral side wall connecting the nozzle portion and the web portion, and is surrounded by the peripheral side wall between the nozzle portion and the web portion. In the lower tie plate of the nuclear reactor fuel assembly, the axial distance between the web portion and the coolant inlet opening is 1/1 to 1/4 times the equivalent diameter of the flow path of the coolant inlet opening. It is characterized by being reduced to a range of. That is, the present invention stipulates the condition that the coolant flowing out from the coolant inlet opening flows out without decelerating from the virtual circular tube of the coolant inlet opening, and the coolant is not decelerated by this configuration. Generation of a secondary flow or the like can be prevented and pressure loss can be reduced.

  6th invention can support the nozzle part which a flow path expands toward a downstream side from a coolant inlet opening, the lower end of a fuel rod and a water rod, and can let a coolant pass in a predetermined flow direction. A coolant receiving chamber is formed which includes a web portion having a plurality of outlet openings and a peripheral side wall connecting the nozzle portion and the web portion, and is surrounded by the peripheral side wall between the nozzle portion and the web portion. In the lower tie plate of the fuel assembly for a nuclear reactor, the length of the lower end plug of the fuel rod and the water rod penetrating the web portion is set to the lower end of the fuel rod or the water rod in the peripheral portion in the coolant receiving chamber. The lower end plug of the fuel rod or water rod at the center is formed to be longer than the plug, and the axial distance between the lower end position of the lower end plug of the fuel rod or water rod and the coolant inlet opening is reduced. Also characterized by It is.

  Since the present invention is configured as described above, it is possible to prevent the secondary flow that has occurred in the lower tie plate, particularly in the nozzle portion, and to reduce the pressure loss in the nozzle portion. Furthermore, by allocating the reduced pressure loss to the filter unit, it is possible to install a filter with improved foreign matter capturing ability.

The figure which shows the example of 1st Example of the lower tie plate of this invention. The figure which shows 2nd Embodiment of the lower tie plate of this invention. The figure which shows 3rd Embodiment of the lower tie plate of this invention. The figure which shows 4th Embodiment of the lower tie plate of this invention. The figure which shows 5th Embodiment of the lower tie plate of this invention. The figure which shows 6th Embodiment of the lower tie plate of this invention. The figure which shows 7th Embodiment of the lower tie plate of this invention. The figure which shows 8th Embodiment of the lower tie plate of this invention. (A) is a longitudinal cross-sectional view which shows 9th Embodiment of the lower tie plate of this invention, (b) is sectional drawing which follows the BB line of (a). The figure which shows 10th Embodiment of the lower tie plate of this invention. The figure which shows 11th Embodiment of the lower tie plate of this invention. The figure which shows 12th Embodiment of the lower tie plate of this invention. (A) is the whole standing sectional view of the conventional fuel assembly, (b) is an enlarged sectional view along the AA line of (a). The expanded sectional view near the lower tie plate of the conventional fuel assembly. The bird's-eye view of the fuel support metal fitting to which a part tie plate is attached.

  Embodiments of the present invention will be described below with reference to the accompanying drawings.

  FIG. 1 is a diagram showing a first embodiment of a lower tie plate of a fuel assembly according to the present invention. The lower tie plate 12 is directed upward, that is, toward the downstream side of the coolant as described in the conventional example. A nozzle portion 21 whose flow path gradually expands, a web portion 23 that supports the lower ends of the fuel rod 13 and the water rod 14 and has a plurality of outlet openings 22 capable of passing a coolant in a predetermined flow direction, A coolant receiving chamber 25 is formed between the nozzle portion 21 and the web portion 23. The coolant receiving chamber 25 is formed between the nozzle portion 21 and the web portion 23.

  A circular coolant inlet pipe 35 is inserted into and fixed to the lower end of the nozzle part 21. The lower end portion of the coolant inlet pipe 35 protrudes downward from the lower surface of the nozzle portion 21 to form a coolant inlet opening 35 a, and the distal end portion of the coolant inlet pipe 35 is between the nozzle portion 21 and the web portion 23. It is inserted and protruded into the coolant receiving chamber 25 formed in the above.

  Thus, the coolant supplied to the lower tie plate 12 flows into the coolant inlet pipe 35 from the coolant inlet opening 35a at the lower end of the coolant inlet pipe 35, and flows through the coolant inlet pipe 35 to be cooled. It flows into the material receiving chamber 25. Therefore, the expansion of the flow path on the downstream side of the coolant inlet opening 35a can be significantly reduced, so that the secondary flow is prevented from occurring and the pressure loss at the nozzle portion 21 can be reduced. Further, since the space 36 between the coolant inlet pipe 35 and the inner wall surface of the nozzle portion 21 is a dead water region, metal debris such as a wire having a large specific gravity is deposited and held in the space 36.

  By the way, in the first embodiment, one coolant inlet pipe 35 is inserted and fixed to the lower end portion of the nozzle portion 21 and its tip portion is protruded into the coolant receiving chamber 25. By fixing the lower end portion of the coolant inlet pipe 35 to the coolant inlet opening 20 formed in the nozzle portion 21, the tip end portion of the coolant inlet pipe is inserted and protruded into the coolant receiving chamber 25. You can also.

  FIG. 2 is a diagram showing the second embodiment. In this embodiment, the coolant inlet pipe 35 is inserted and fixed from the lower end of the nozzle portion 21 as in the first embodiment. An expanded pipe portion 35b whose flow area gradually increases in the downstream direction is formed at the tip of the coolant inlet pipe 35 that has entered the coolant receiving chamber 25, and the tip of the coolant inlet pipe 35 is The cross-sectional area coincides with the entire area of the outlet opening 22 in the web portion 23 or is slightly larger than that.

  Thus, in this embodiment, as in the first embodiment, since the expansion of the flow path on the downstream side of the coolant inlet opening 35a can be greatly reduced, secondary flow generation can be prevented, Pressure loss at the nozzle portion 21 can be reduced. Furthermore, since the flow passage cross-sectional area of the coolant inlet pipe 35 and the entire area of the outlet opening 22 of the web portion 23 match, the occurrence of an enlarged flow from the coolant inlet pipe 35 is suppressed, and the nozzle portion 21, Thus, the pressure loss in the entire lower tie plate can be reduced.

  FIG. 3 is a diagram showing the third embodiment. Like the first embodiment, FIG. 3 shows an example in which the coolant inlet pipe 35 is inserted and fixed from the lower end of the nozzle portion 21. The axial dimension between the web part 23 and the web part 23 is defined, and the axial distance A between the tip position of the coolant inlet pipe 35 and the lower end position of the web part 23 is 1/1 of the equivalent diameter of the coolant inlet pipe 35. It is made into the range of -1/4 times.

  This condition is defined by the condition that the coolant flowing out from the coolant inlet pipe 35 flows out without decelerating from the side surface of the virtual circular pipe portion in front of the coolant inlet pipe 35. Accordingly, the flow rate of the coolant flowing out from the tip of the coolant inlet pipe 35 is not reduced, and the generation of a secondary flow or the like can be prevented, and the pressure loss at the tip of the coolant inlet pipe 35 can be further reduced.

  FIG. 4 is a diagram showing a fourth embodiment of the present invention. In the lower tie plate 12 shown in FIG. 1, a foreign matter filter 37 having a fine mesh diameter is provided on the lower surface of the web 23.

  Thus, in the present embodiment, the pressure loss in the nozzle portion 21 can be reduced by the installation of the coolant inlet pipe 35, and therefore the pressure loss in the entire lower tie plate is increased by installing the foreign matter filter 37 having a fine mesh diameter. Can be prevented. Further, although depending on the type of the lower tie plate, it is noted that the pressure loss of the nozzle portion 21 and the web portion 23 is about the same in the conventional lower tie plate. The pressure loss of the part can be up to about twice that of the prior art. Therefore, the mesh diameter of the web portion can be reduced to about half of the conventional size, and the debris capturing characteristics can be greatly improved.

  FIG. 5 is a view showing a fifth embodiment. In the structure shown in FIG. 4, a plurality of stages of foreign matter filters 38 are further provided in the coolant receiving chamber 25. Thus, in the present embodiment, as in the first embodiment, the pressure loss at the nozzle portion 21 can be reduced by the installation of the coolant inlet pipe 35. Therefore, the lower type by installing the foreign matter filter 38 in multiple stages. An increase in pressure loss across the rate can be prevented. Further, although depending on the type of the lower tie plate, it is noted that the pressure loss of the nozzle portion 21 and the web portion 23 is about the same in the conventional lower tie plate. The pressure loss of the portion 23 can be up to about twice that of the prior art. Therefore, the number of stages of the foreign matter filter 38 can be increased to about twice that of the prior art, and the debris capturing characteristics can be greatly improved.

  FIG. 6 is a diagram showing a sixth embodiment of the present invention, in which an inner wall surface of a nozzle portion 21 and a part of an inner wall surface of a peripheral side wall 24 adjacent to the nozzle portion 21 are moved inward. is there. In other words, the inner wall surface of the nozzle portion 21 and a part of the inner wall surface of the peripheral side wall 24 that follows the nozzle wall 21 are formed on the convex curved surface 39 in the longitudinal section so that the flow passage area gradually increases.

  Thus, in this embodiment as well, as in the first embodiment, the enlargement of the flow path on the downstream area side of the coolant inlet opening 20 can be greatly reduced, so that the secondary flow can be prevented and the nozzle can be prevented. The pressure loss at the portion 21 can be reduced.

  FIG. 7 is a diagram showing a seventh embodiment. In the present embodiment, a part of the inner wall surface of the nozzle portion 21 and the subsequent inner wall surface of the peripheral side wall 24 is formed into a convex curved surface 39 in the longitudinal section thereof, the thickness is increased, and the hollow portion 40 is further formed inside. It is formed. In this embodiment, as in the sixth embodiment, since the expansion of the flow path on the downstream area side of the coolant inlet opening 20 can be reduced, the generation of the secondary flow can be suppressed and the pressure loss at the nozzle portion 21 can be suppressed. Can be reduced. Furthermore, since the thickened wall of the nozzle portion 21 and the wall of the peripheral side wall 24 are made hollow, the lower tie plate 12 is reduced in weight, which is advantageous for transportation.

  FIG. 8 is a diagram showing an eighth embodiment, in which a large number of suction pipes 41 are provided on the peripheral side wall 24 of the flow path enlarged portion, and a discharge port of the suction pipe 41 is provided on the outer surface of the lower tie plate 12. It is a thing.

  By providing a large number of suction pipes 41 on the peripheral side wall 24 of the flow passage enlarged portion, separation of the flow from the wall surface can be prevented and generation of secondary flow can be suppressed, so that pressure loss at the nozzle portion 21 can be further reduced. . Furthermore, the bypass hole can be eliminated and all can be changed to a suction pipe. In that case, since the suction flow rate can be increased, separation of the flow from the wall surface can be further suppressed, and the pressure loss can be further reduced.

  FIGS. 9A and 9B are views showing a ninth embodiment of the present invention, in which two rectifying plates 42 are disposed in the coolant receiving chamber 25 with the coolant inlet opening 20 in between. They are arranged in parallel to each other, and are fixed to the inner wall surfaces of the peripheral side wall 24 facing each other and the inner surface of the nozzle portion 21. Accordingly, a flow path formed by the two rectifying plates 42, the inner wall surfaces of the peripheral side walls 24 facing each other and the inner surface of the nozzle portion 21 is communicated with the coolant inlet opening 20.

  Therefore, also in this embodiment, since the expansion of the flow path on the downstream region side of the coolant inlet opening 20 can be reduced, the generation of the secondary flow can be suppressed and the pressure loss at the nozzle portion can be reduced. Furthermore, since the rectifying plate 42 is fixed to the inner wall surface of the nozzle portion 21 and the inner surface of the peripheral side wall 24, the vibration strength to the structural material by the fluid is increased, and the reliability can be increased. Further, since the space 43 between the rectifying plate 42 and the nozzle portion 21 is a dead water region, the metal debris such as the wire has a large specific gravity as in the first embodiment, so that the effect of being able to settle and hold in the space 43 is also obtained. is there.

  FIG. 10 is a diagram showing a tenth embodiment, in which a drift plate 44 that is inclined obliquely upward from one side of the coolant inlet opening 20 toward the upper side of the coolant inlet opening 20 is provided. Both ends of the drift plate 44 are fixed to the inner surfaces of the nozzle portion 21 and the peripheral side wall 24, and a flow path formed by the drift plate 44, the nozzle portion 21 and the inner wall surface of the peripheral side wall 24 is communicated with the coolant inlet opening 20. ing.

  Thus, since the expansion of the flow path on the downstream region side of the coolant inlet opening 20 can be reduced as in the above-described embodiment, the generation of the secondary flow can be suppressed, and the pressure loss at the nozzle portion 21 can be reduced. Furthermore, by fixing the drift plate 44 to the inner wall of the nozzle portion 21 and the peripheral side wall 24, the vibration strength of the fluid to the structural material is increased, and the reliability can be increased. Moreover, since the space 45 between the drift plate 44 and the inner wall of the nozzle portion 21 becomes a dead water region and the space volume is large, the precipitation effect can be increased by this space 45 as in the first embodiment.

  FIG. 11 is a diagram showing an eleventh embodiment, wherein the axial distance L between the web portion 23 and the coolant inlet opening 20 is set to 1/1 to 1 of the equivalent diameter of the coolant inlet opening 20. The structure is reduced to a range of / 4 times. Accordingly, the axial length of the coolant receiving chamber 25 in which the flow path of the lower tie plate 12 is enlarged is defined, and the coolant flowing out from the coolant inlet opening 20 is cooled as in the embodiment shown in FIG. The flow rate of the coolant in front of the coolant receiving chamber 25 is not decelerated because it is defined by the condition of flowing out without decelerating from the side surface of the virtual circular tube portion in front of the material inlet opening 20. Since generation | occurrence | production of a flow etc. can be prevented, the pressure loss of a coolant inlet opening can be reduced.

  FIG. 12 is a view showing a twelfth embodiment. In this embodiment, the lower end plug 13a of the fuel rod 13 and the lower end plug 14a of the water rod 14 that penetrate the web portion 23 are coolants. It protrudes greatly into the receiving chamber 25, and the axial distance between the lower end position thereof and the coolant inlet opening 20 is reduced. That is, the lengths of the lower end plugs 13a, 14a of the fuel rod 13 and the water rod 14 penetrating the web portion 23 are set to the lengths of the lower end plugs of the fuel rod 13 or the water rod 14 in the peripheral portion in the coolant receiving chamber 25. The lower end plugs of the fuel rods or water rods at the center are formed longer than the lower end plugs 13a, 14a of the fuel rods 13 or water rods 14 and the coolant inlet openings. The axial distance from 20 is reduced.

  Accordingly, the lower end plugs 14a and 13a projecting into the coolant receiving chamber 25 shorten the axial distance in the coolant main flow portion, and the coolant flow velocity in the coolant receiving chamber 25 is reduced. And the generation of secondary flow is reduced. Therefore, the pressure loss of the coolant inlet opening can be reduced also by the above configuration.

DESCRIPTION OF SYMBOLS 10 Fuel assembly 12 Lower tie plate 13 Fuel rod 14 Water rod 20 Coolant inlet opening 21 Nozzle part 22 Outlet opening 23 Web part 24 Peripheral side wall 25 Coolant receiving chamber 27 Foreign material filter 28 Leakage hole 30 Fuel support bracket 35 Coolant inlet Tubes 37 and 38 Foreign matter filter 39 Projecting curved surface 40 Hollow portion 41 Suction tube 42 Current plate 44 Current plate

Claims (5)

The lower end portion below the coolant inlet opening has a cylindrical structure inserted and fitted into the upper surface opening of the fuel support fitting, and the outer peripheral surface of the upper portion of the coolant inlet opening gradually expands toward the coolant downstream side. A nozzle part having a shape, a web part having a plurality of outlet openings that support the lower ends of the fuel rod and the water rod and capable of passing a coolant in a predetermined flow direction, and the nozzle part and the web part are connected. A lower tie plate of a fuel assembly for a reactor in which a coolant receiving chamber surrounded by the peripheral side wall is formed between the nozzle portion and the web portion.
A flow path is formed so that the outer peripheral surface of the nozzle portion gradually expands toward the coolant downstream side and at least a part of the inner surface of the peripheral side wall bulges inward to prevent the secondary flow of the coolant. A lower tie plate for a fuel assembly for a nuclear reactor, wherein the lower tie plate has a convex curved surface whose area increases toward the downstream side of the coolant .   The space between the portion of the nozzle portion that gradually expands toward the downstream side of the coolant, the outer peripheral surface of the peripheral side wall, and the inner surface formed on the convex curved surface is hollow. Lower tie plate for nuclear fuel assemblies.   A plurality of suction pipes are provided on a wall body between a portion of the nozzle portion that gradually expands toward the coolant downstream side, an outer peripheral surface of the peripheral side wall, and an inner surface formed on the convex curved surface, and the suction pipe The lower tie plate for a fuel assembly for a nuclear reactor according to claim 1 or 2, wherein the discharge port is provided on a side surface of the peripheral side wall of the upper portion of the lower tie plate.   The lower tie plate for a nuclear fuel assembly according to any one of claims 1 to 3, wherein a foreign matter filter having at least one fine mesh aperture is provided in the coolant receiving chamber.   A fuel assembly comprising the lower tie plate according to any one of claims 1 to 4.

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