JPH0311756Y2 - - Google Patents

Description

[Detailed Description of the Invention] (Field of Industrial Application) This invention relates to an improvement of a lower tie plate in a fuel assembly, mainly for a boiling water reactor.

(Prior art) As shown in Fig. 3, a fuel assembly for a boiling water reactor is constructed from an upper tie plate 1 having an inverted U-shaped handle 1a and four corner posts 1b, and an opening 2a at the lower end. A lower tie plate 2 in the shape of a square honeycomb platform into which coolant flows, a predetermined number of fuel rods 3 erected between both tie plates 1 and 2, and between the upper and lower tie plates 1 and 2. A rectangular cylindrical channel box 5 is fitted on the outside of a fuel bundle consisting of several stages of lattice-like spacers 4 that hold each fuel rod 3 at a constant interval, and the fuel bundle is loaded into a nuclear reactor. It is done like this.

The channel box 5 has the role of ensuring a flow path for the coolant flowing inside and a passage for the control rods between adjacent assemblies, as well as increasing the rigidity of the fuel bundle.
A triangular piece 5a is attached to one diagonal corner of the upper end, and is supported by opposing corner posts 1b of the upper tie plate 1, and one of the triangular pieces 5a is connected to a spring assembly 5b for maintaining spacing in the furnace. They are screwed together to the fuel bundle.

On the other hand, on the upper surface of the honeycomb-shaped lower tie plate 2, as shown in FIG. The control members 6 are provided in a square arrangement, and on the side periphery are control members 6 made of comb-like leaf springs for controlling the amount of leakage of the coolant flowing inside the channel box 5. The ring body at the upper end is fitted into the boss 2b at the outermost periphery and is installed vertically.

During periodic reactor inspections, the channel boxes 5 are removed in the fuel storage pool to inspect the fuel rods 3. After the inspection, those with little deformation are left as they are, and those with significant deformation are replaced with new ones. Fitted into the bundle.

(Problem to be solved by the invention) By the way, the work of attaching and detaching the channel box is done by setting the fuel assembly to be inspected in the attaching and detaching device installed along the side wall of the pool. Although it is not very difficult, the channel box is hoisted by a crane and then lowered approximately 6 months below the water surface by remote control.
The work of fitting the fuel bundle into the fuel bundle at a distance of about It is slightly smaller than the rate and spacer part, and a control member made of a leaf spring is installed vertically around the side, making it difficult to fit together, and the fuel bundle may be bent or twisted, or even slightly difficult to handle. The lower end of the channel box may sit on the flat surface of the lower tie plate at the four corners where the ring of the control member is not present, or may hit the control member, preventing smooth fitting and damaging it.

Therefore, this invention provides a lower tie plate of a fuel assembly in which a channel box can be easily and smoothly fitted without the lower end of the channel box climbing onto the upper surface or damaging the leaf spring member. It is something to do.

(Means for solving the problem) This invention for the above purpose has a rectangular honeycomb platform shape, has an opening for coolant inflow at the lower end, and fits the lower end plug of the fuel rod on the upper surface. A lower tie plate of the fuel assembly is provided with a predetermined number of bosses in a square arrangement, and a control member for controlling the amount of coolant leakage is arranged on the side periphery of at least four corners around the upper surface. A further feature is that a rising guide wall whose outer surface is a conical surface that tapers upward from the side circumferential surface in a predetermined range is formed.

(Embodiment) Fig. 1 shows an embodiment of this invention, in which the inside of the lower tie plate 12 in the shape of a square honeycomb platform is hollow, and the lower end is fitted with a core grid. cross-shaped opening 12a for
The lower end plug 13a of the fuel rod 113 is provided on the upper surface so that the coolant flows in from the lower side.
A predetermined number of bosses 12b to be fitted are provided in a square arrangement, and around the periphery, a narrow flat surface 12c and an outwardly downward slope 12d are formed except for the four corners. A ring body 16 at the upper end is provided with a control member 16 made of a comb-like leaf spring for controlling the amount of leakage of the coolant flowing inside the channel box 15 from the lower end.
a is fitted into the outermost boss 12b and is vertically installed, and at the four corners of the upper surface of the lower tie plate 12, the outer surface tapers upward from the side circumferential surface of the tie plate 12. A rising guide wall 17 having a substantially quarter-arc shape and having an inclined conical surface 17a is formed to surround the boss 12b at the corner.

Therefore, when the channel box 15 is inserted into the fuel bundle in the storage pool after a periodic fuel inspection, if the channel box 15 approaches the lower tie plate 12 and the alignment with the lower tie plate 12 is somewhat poor, the channel Box 15
The lower end of the corner comes into contact with the conical surface 17a of the rising guide wall 17 at one of the four corners of the lower tie plate 12, and the channel box 15 is guided by this and its attitude with respect to the lower tie plate 12 is corrected, and both As a result, the fitting operation can be carried out smoothly.

In FIG. 2, a recess 20 of a required width is formed on the side circumferential surface, and a control member 16 made of a plate or the like curved vertically in the recess 20 is connected to upper and lower horizontally elongated clasps 21a. , 21b to control the amount of coolant leaking from the lower end of the channel box 15 (Japanese Patent Publication No. 57-21078 or Japanese Patent Publication No. 55-14397). In this case, a rising guide wall 17 whose outer surface forms a conical surface 17a that tapers inward is formed over the entire upper surface periphery of the lower tie plate 12.

If this is done, the alignment of the channel box 15 will be better, and it will be easier to fit into the channel box 15.

(Effect of the invention) As described above, in this invention, as a lower tie plate of a fuel assembly for a boiling water reactor, at least four corners of the upper surface periphery are provided so that the outer surface extends upwardly inwards from the side peripheral surface. Since the rising guide wall, which has a tapered conical surface, is formed in the required range, when installing the channel box, there is a possibility that the fuel bundle may be bent or twisted, or the channel box may not come into contact with the lower tie plate due to handling. Even if the alignment is poor, the bottom end of the channel box will come into contact with one of the rising guide walls before reaching the top surface of the lower tie plate, and its posture will be corrected and it will automatically connect to the lower tie plate. This allows for easy and smooth mating work to the lower tie plate, and prevents the lower end of the channel box from climbing onto the top surface of the tie plate, making the mating work difficult. There is no chance of damage to the component.

[Brief explanation of the drawing]

FIG. 1 is a perspective view of one embodiment of this invention. FIG. 2 is a perspective view of another embodiment. FIG. 3 is a partially cutaway perspective view of the fuel assembly. FIG. 4A is a partially cutaway front view of a conventional lower tie plate. Figure B is an enlarged view of the circular part. In the figure, 12...lower tie plate, 12a...
Opening, 12b...Boss, 13...Fuel rod, 15
... Channel box, 16 ... Control member, 1
7... Rising guide wall, 17a... Conical surface.

Claims (1)

[Scope of utility model registration request] It has a rectangular honeycomb platform shape, has an opening 12a at the lower end for coolant inflow, and has a predetermined number of bosses 12b in a square arrangement on the upper surface into which the lower end plugs of the fuel rods 13 are fitted, and on the side periphery. In the lower tie plate in which the control member 16 for controlling the amount of coolant leakage is disposed, at least four corners of the upper surface periphery,
A lower tie plate in a fuel assembly formed by forming a rising guide wall 17 in a required range, the outer surface of which is a conical surface 17a that tapers upward from the side peripheral surface.