JPH0626878Y2 - Fuel assembly - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Industrial field of application) The present invention relates to a fuel assembly, and in particular, a spacer is held in a predetermined axial position by a water rod or a spacer holding fuel element. Regarding fuel assemblies.

(Prior Art) In general, a fuel assembly has a structure in which a large number of fuel elements are passed through square or polygonal spacer cells and held at equal intervals, and the upper and lower sides thereof are inserted into and supported by holes in a tie plate. Has been adopted.

That is, FIG. 3 is a longitudinal sectional view of the fuel assembly, in which the fuel assembly includes a large number of fuel elements 1 and one water rod 2, and an upper tie plate 3 and a lower tie plate 4.
In addition to supporting the fuel element 1 with spacers 5 at a plurality of positions in the longitudinal direction of the fuel element 1, each fuel element 1 is supported at an appropriate position, and the fuel element 1 is internally housed in a long tubular fuel channel 6.

As shown in FIG. 4, each spacer 5 is provided in a substantially square tubular outer frame 7 with a plurality of dividers and bars intersecting each other to form a large number of substantially square fuel rod insertion cells 8. It was formed.

By the way, the spacers 5 arranged at a plurality of positions along the entire length of the fuel assembly for holding the fuel elements 1 at predetermined intervals are
It is necessary to prevent axial movement due to vibration during use in the nuclear reactor.

Therefore, as shown in FIGS. 4 and 5, a stopper piece that engages with the upper and lower edges of the bar 8a of the spacer 5 is provided on one of the water rod 2 or one of the fuel elements arranged at the center of the fuel assembly. 10 is provided, and the water rod 2
Alternatively, an end plug 11 having a square shank portion is attached to the lower end of the fuel element as shown in FIG. 6 (b). On the other hand, the lower tie plate 4 is provided at its predetermined position with a square hole into which the shank portion having a square cross section of the water rod or the fuel element is inserted.

Then, when assembling the fuel assembly, the water rod 2 or the spacer-holding fuel element is inserted into the predetermined cell 8 of the spacer 5, and the water rod or the spacer-holding fuel element is rotated by about 45 ° around the axis to stop the stopper. Piece 1
0 is engaged with the upper and lower edges of the bar 8a of the spacer 5,
The spacer is prevented from moving, and the shank portion having a square cross section such as the water rod 2 is inserted into the square hole of the lower tie plate to prevent the rotation of the water rod 2 or the like around the axis.

(Problems to be solved by the invention) However, in such a case, a stopper piece is provided on the water rod or the spacer holding fuel element, and the shank portion of the lower end plug is processed to have a square cross section, and further, to the lower tie plate. It is necessary to make a square hole, and in the square processing of the shank portion of the end plug, special equipment and equipment are required and a lot of man-hours are required. In addition, there is a problem that the square hole processing of the lower tie plate requires special equipment and jigs, is technically difficult, and requires a lot of man-hours.

The present invention has been made in view of the above circumstances, and an object thereof is to obtain a fuel assembly for manufacturing a water rod or a fuel element for supporting a spacer and a lower tie plate at low cost.

[Constitution of device]

The present invention relates to a fuel assembly in which a large number of fuel elements or fuel elements and water rods are bundled at a predetermined interval by spacers and joined by an upper and lower tie plates, and the water rods or spacer holding fuel elements are attached to the upper and lower end edges of the spacers. In addition to projecting a stopper piece that engages, an eccentric shaft portion is formed at the tip of the lower end plug shank portion, and the lower end plate that inserts and engages the lower end plug shank portion has the shape of the shank portion. It is characterized in that a corresponding eccentric stepped hole is provided.

(Operation) After inserting the water rod or fuel element for supporting the spacer into a predetermined cell of the spacer, pivoting about the axis,
The stopper pieces are engaged with the upper and lower edges of the spacer, and the eccentric shaft portion of the lower end plug is inserted into the eccentric stepped hole of the lower tie plate. Then, the engagement of the eccentric shaft portion and the eccentric stepped hole prevents the rotation of the water rod and the like around the axis, and the spacer is reliably held by the stopper piece.

(Embodiment) An embodiment of the present invention will be described below with reference to FIGS. 1 and 2.

In FIG. 1, reference numeral 2 is a water rod for supporting a spacer, and a stopper piece (not shown) engaging with the upper and lower end edges of the spacer is provided at a predetermined position on the water rod 2 as in the conventional case. It is projected.

The lower end plug 11 welded to the lower end of the water rod 2 is formed with a cylindrical large-diameter shank portion 11a having the same axis as the water rod 2, and at the tip of the large-diameter shank portion 11a, A cylindrical small-diameter shank portion 11b, which is eccentric to the large-diameter shank portion 11a, is integrally formed.

On the other hand, in the lower tie plate 4, at the mounting position of the water rod 2 for supporting the spacer, large eccentric parts corresponding to the large diameter shank portion 11a and the small diameter shank portion 11b of the lower end plug 11 of the water rod 2 are attached. Diameter hole 12a
And an eccentric stepped hole 12 formed of a small diameter hole 12b. Then, when the stopper piece of the water rod 2 is rotated to a position where it engages with both upper and lower edges of the spacer, the lower end plug 11 thereof is inserted and fixed in the eccentric stepped hole 12 of the lower tie plate 4. There is.

Then, when assembling the fuel assembly, the water rod 2 for supporting the spacer is inserted into a predetermined cell of the spacer as in the conventional case, and the water rod 2 is rotated by a predetermined angle to move the stopper pieces to the upper and lower end edges of the spacer. Then, the lower end plug 11 of the water rod 2 is inserted into the eccentric stepped hole 12 of the lower tie plate 4. That is, as shown in FIG. 2, the large diameter shank portion 11a is fitted into the large diameter hole 12a of the lower tie plate 4, and the small diameter shank portion 11b is fitted into the small diameter hole 12b.

Therefore, due to the engagement of the shank portion and the hole of the lower tie plate, the rotation of the water rod 2 around the shaft plug is prevented, and the engagement between the stopper piece of the water rod 2 and the spacer is released. Is reliably prevented.
Although the water rod has been described in the above embodiment, it is needless to say that it can be applied to a fuel element for supporting a spacer.

[Effect of device]

As described above, in the present invention, the water rod for supporting the spacer or the lower end plug of the fuel element is provided with the large-diameter shank portion and the small-diameter shank portion eccentric to the large shank portion, and the shank portion is used as the lower tie plate. Since the eccentric stepped hole is provided so as to be inserted and engaged, the engagement prevents rotation of the water rod or the fuel element around the axis, and the stopper piece and the spacer are inadvertently disengaged. There is nothing to do. Moreover, since the eccentric shaft portion is formed on the lower end plug and the stepped holes which are eccentric to each other are formed on the lower tie plate, the machining is extremely easy and special equipment and the like are required. Nothing.

[Brief description of drawings]

1 (a) is a side view of a fuel element in a fuel assembly of the present invention, FIG. 1 (b) is an upper end view of the same, and FIG. 2 is a view showing a state in which the fuel element is attached to a lower tie plate, FIG. 3 is a vertical cross-sectional view of the fuel assembly, FIG. 4 is a plan view of the spacer, FIG. 5 is an explanatory view showing a state where the water rod is inserted into the cells of the spacer, and FIG. FIG. 6B is a side view of the water rod of FIG. 1 ... Fuel element, 2 ... Water rod, 4 ... Lower tie plate, 5 ... Spacer, 8 ... Cell, 10 ... Stopper piece, 11 ... Lower end plug, 11a ... Large diameter shank part, 11b ... small diameter shank part, 12a ... large diameter hole, 2
b ... small diameter hole.

Claims (1)

[Scope of utility model registration request] 1. A fuel assembly in which a plurality of fuel elements or fuel elements and water rods are bundled at a predetermined interval by spacers and are joined by an upper and lower tie plates, and upper and lower end edges of the spacers are attached to water rods or spacer holding fuel elements. A stopper piece that engages with
Form an eccentric shaft at the tip of the lower end plug shank,
A fuel assembly in which an eccentric stepped hole corresponding to the shape of the shank portion is provided in the lower tie plate into which the lower end plug shank portion is inserted and engaged.