JPH0622237Y2 - Fuel assembly spacer - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial field of application) The present invention relates to improvement of a spacer in a fuel assembly for a boiling water reactor.

(Prior Art) In a fuel assembly loaded in a boiling water reactor, a required number of fuel rods n and centrally arranged fuel rods 1 and 2 are arranged as shown in FIG.
The water pipes W (Fig. 6A) are arranged in a square shape, and the upper and lower ends thereof are attached to the upper and lower tie plates t ₁ and t ₂ through end plugs, and grid spacers are provided between them. S is arranged in several stages in the axial direction and is held at a constant interval, and a rectangular tube-shaped channel box C is fitted on the outside to form a fuel assembly. Standing on the socket F ₁ , during operation of the reactor, the coolant is sent so as to flow upward between the fuel rods n through the nose piece of the lower tie plate t ₂ , and this is boiled to release heat to the outside. At the same time as taking it out, the heat of the assembly is removed.

As a spacer for holding the fuel rods n at regular intervals, as shown in FIG. 5, a vertical direction in which a plurality of S-shaped vent portions 2a 'are provided in the middle of an outer plate 1'of four sides forming a square frame, A large number of cell cells 4'are formed by a required number of dividing plates 2'in a horizontal direction and by dividing bars 3'arranged alternately in the vertical direction and the horizontal direction, and at the intersections of the vertical and horizontal divide bars 3'made of Inconel. A lantern type spring 5'is provided so that the fuel rod n and the water pipe W are held by the spring 5'and the S-shaped vent portion 2a ', and four side plates as shown in FIGS. A large number of cell cells 4 are formed by partitioning the inside of the cell 1 by a predetermined number of grid plates 2 in the vertical and horizontal directions, and a clip-shaped spring 5 made of Inconel strip plate material is formed in the center of the four sides of each cell cell 4.
(See Fig. 3B) Fold it in half and attach it to each grid cell 4
The one in which the fuel rod n and the water pipe W are held by the chevron-shaped elastic pieces of the spring 5 on the two sides and the fixing protrusions of the spring on the other two sides are widely used.

(Problems to be solved by the invention) By the way, in the fuel assembly for boiling water reactor,
Along with the higher burnup of the fuel (longer exchange cycle), the liquid film existing on the inner surface of the channel box is peeled off for the purpose of improving the water / uranium ratio of the fuel to increase the reactivity and cooling capacity. In order to deflect this toward the fuel rod side, a plurality of inwardly inclined flow tabs (6 'or 6) are provided on the upper edge of the outer plate of the spacer.

However, when installing or removing the channel box during assembly, or when removing the channel box for periodic inspection and inserting the assembly into or out of the storage rack in the storage pool, the flow tabs, especially the flow tabs located at the four corners, are used. May get caught in the channel box or storage rack, and the spacer may be displaced, or the flow tab or spacer itself may be deformed or damaged.

Therefore, an object of the present invention is to provide a spacer in which the channel box can be easily attached and detached and inserted into a storage rack, and the position is prevented from being displaced or deformed.

(Means for Solving the Problems) Based on the above-mentioned object, the present invention has a structure in which a predetermined number of fuel rods or cell cells for inserting water tubes are arranged side by side inside and surrounded by outer plates on four sides. , The upper edge of the outer plate is provided with a required number of inwardly inclined flow tabs as a spacer for the fuel assembly,
On both sides of the outer plates of the four sides, inwardly inclined tabs are provided at lower edge positions symmetrical to the upper edge flow tabs, and the upper edge flow tabs and the lower edge tabs are formed from the base portion to the front portion. The feature is that each has a launching protrusion that makes a business trip to the outside.

(Embodiment) FIGS. 1 to 3 show an example of a spacer S according to the present invention. The spacer S is formed into a rectangular frame shape by four outer plates 1 and the inner side thereof has a predetermined number of vertical and horizontal grids. It is divided into a large number of cell rods 4 for inserting fuel rods by the plate 2, and in the center of the four sides surrounding each cell cell 4, a thin strip plate material of Inconel is folded in two as shown in FIG. 5 are attached so as to wrap the vertical and horizontal lattice plates 2 or the outer plate 1 from below, and among those springs 5, those attached to the vertical and horizontal lattice plates 2 have a mountain-shaped elastic piece 5a on one side. , The other side is provided with one or a plurality of fixed protrusions 5b having a square shape or an arc shape, but the spring 5 attached to the outer plate 1 does not have the fixed protrusion 5b on the other side, and each cell cell 4 Then, the chevron elastic piece 5a of the spring 5 on the two sides and the other two sides In the spring 5, the fixed protrusions 5b of the spring 5 face each other, and the upper ends 5c are joined by welding or the like. Is designed to hold,
In addition, a flow tab 6 that is inclined inward is provided at the upper edges of the four outer plates 1 in accordance with the arrangement positions of the vertical and horizontal grid plates 2 so as to obtain a stirring effect of the coolant on the inner surface of the channel box. Has been done.

However, such a structure is the same as that shown in FIGS. By the way, in this invention, in each side part of the four outer plates 1 forming the four corners of the spacer S,
Not only the upper edge but also the lower edge are provided with inwardly inclined tabs 6a at positions symmetrical to the upper edge flow tab 6, and the upper edge flow tab 6 and the lower edge tab 6a are as shown in FIG. The projecting projections 7 are formed so as to be rounded and project outward from the base portion to the front portion. Further, the coupling upper end portions 5c of the clip-shaped springs 5 attached to the outer plates 1 on four sides are formed.
Are also tilted inward in accordance with the flow tab 6.

Therefore, when the channel box C is inserted into the fuel bundle at the time of assembling the fuel assembly, or when the channel box C is removed at the time of regular inspection and the fuel bundle is inserted into the storage rack in the storage pool, Even when the upper and lower flow tabs 6 and tabs 6a located at the four corners of the spacer S come into contact with the channel box C and the storage rack, the punching projections 7 provided on them respectively serve as reinforcement and also serve as a centering guide. Unlike the conventional flow tab, it does not get caught, and the work of attaching / detaching the channel and inserting it into the storage rack can be performed smoothly.

On the other hand, when the coolant is fed into the fuel assembly from the lower side to the upper side in the operation of the furnace, the inward upper edge 5c of each clip-shaped spring 5 together with the flow tab 6 is provided around the fuel bundle. Since the coolant flowing near the inner surface of the channel box C is positively deflected to the fuel rod side, the reactivity of the fuel can be improved and the limit output of the assembly can be increased.

In the above example, the spacer using the clip type spring was described, but the present invention is not limited to this, and the spacer using the lantern type spring or the cell cell for inserting the fuel rod is formed of a circular tube element and the surrounding four sides are formed. It can also be applied to a spacer surrounded by an outer plate.

(Effect of the Invention) As described above, in the present invention, the spacers of the four outer plates are used as the spacers of the fuel assembly for the boiling water reactor in which the required number of inwardly inclined flow tabs are provided on the upper edges of the outer plates. On both sides, the upper edge of the flow tab is combined with the inwardly inclined tab at the symmetrical lower edge position, and each of them is provided with a projecting protrusion that travels outward from the base to the tip. When inserting the channel box into the fuel bundle or removing the channel box and inserting the fuel bundle into the storage rack, the flow tabs and tabs at the four corners of the spacer do not catch on the channel or rack as before, and the insertion work or The removal work is done smoothly, the position of the spacer does not shift, and the flow tabs at the four corners and the tabs are reinforced by the ejection protrusions, so they do not deform or There is no risk of damage.

[Brief description of drawings]

FIG. 1 is a plan view of an embodiment of the invention. FIG. 2 is a side view thereof. FIG. 3A is a sectional view taken along line XX of FIG. The same figure (b) is a perspective view of the outer plate one side portion. FIG. 4 is a perspective view with a part of the fuel assembly cut away. FIG. 5 is a plan view of a half portion of a conventional spacer using a lantern type spring. FIG. 6A is a plan view of a half portion of a conventional spacer using a clip spring. The same figure is a side view. In the figure, 1 ... Outer side plate, 2 ... Lattice plate 4 ... Cell cell, 5 ... Clip spring 6 ... Flow tab, 6a ... Tab 7 ... Embossing projection C ... Channel box n ... Fuel rod, S ... Spacer

Claims (1)

[Scope of utility model registration request] 1. A predetermined number of fuel rods or cell cells for inserting water tubes are arranged side by side inside, surrounded by outer plates on all four sides, and a required number of inward slopes are provided on the upper edge of the outer plate. In the spacer provided with the flow tabs, the inwardly inclined tabs are respectively provided at the lower edge positions symmetrical to the upper side flow tabs on both sides of the four outer plates, and the upper edge flow tabs and the lower edge tabs are provided. Is a spacer for the fuel assembly, each of which is provided with a projecting protrusion that travels outward from the base to the front.