JPS61247995A - Fuel aggregate - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a fuel assembly using short water rods for the purpose of improving thermal-hydraulic characteristics. This invention relates to a fuel assembly that prevents floating.

[Technical background of the invention and its problems]

As shown in FIG. 3, a conventional fuel assembly has a plurality of elongated fuel rods 3 between an upper support plate 1 and a lower support plate 2.
3a and one or more water rods 4 of the same length as the fuel rods are arranged in a square grid, and the fuel rods 3 are roughly arranged.
The fuel rods 3 and water rods 4 are supported by spacers 5 provided at multiple locations in the axial direction. The upper and lower support plates 1.2 hold both ends of the fuel rods 3 and 3a and the water rod 4 to prevent rotation.

Also, eight (sometimes four) of the fuel rods 3 are combined fuel rods 3a, and screw shafts (not shown) are provided at both ends of the fuel rods. It is screwed into a screw hole (not shown) and connected to the screw shaft at the upper end by tightening an upper nut 6.

Furthermore, springs are interposed between all the fuel rods 3, 38 and the water rods 4 and the upper support plate 1 to absorb the elongation of the fuel rods 3 and the like during use.

The water rod 4 supports the spacer #j'5 and has holes 8a formed in its upper and lower side walls.

The coolant flows out from 8b toward the fuel rods 3 to suppress the generation of voids in the coolant above the fuel assembly, and furthermore, a moderator passage is formed within the fuel assembly to improve the power distribution within the fuel assembly. It has the function of flattening the surface. In addition, the lower end of the water rod 4 is formed into a prismatic shape and has a corner formed in the lower support plate 3 in order to prevent the water rod 4 itself from rotating when handling the fuel assembly or using the reactor. Fitted into the hole. This prevents the water rod 4 from rotating and prevents the spacer 5 from falling off in the axial direction.

Incidentally, in recent years, core fuel designs have been carried out to improve nuclear and thermal-hydraulic characteristics, and as one of these efforts, attempts have been made to adopt fuel assemblies in which water rods are made thicker and shorter. The structure of the fuel assembly, as shown in FIG. 4, is basically the same as that in FIG. 3, except that the conventional fuel assembly 4a has a larger diameter and shorter length.

However, the conventional fuel assembly shown in FIG. 4 has the following problems.

That is, since the upper end of the water rod 4a is free, in the conventional fixing method by fitting a square column and a square hole, the water rod 4a floats upward in the axial direction, and its lower end comes off from the lower support plate 2. In some cases, the water rod 4a may rotate, making it difficult to maintain support by the spacer 5. For this reason, a method was adopted in which the lower end of the water rod 4a was screwed to the lower support plate 2, but
Since the screws loosened due to hydraulic vibration during use of the reactor, there was a risk that the water rod 4a would rotate.

[Purpose of the invention]

The present invention has been made in consideration of these points, and an object of the present invention is to provide a fuel assembly that can stably prevent the water rod from rotating and floating.

[Summary of the invention]

The present invention provides a fuel assembly in which fuel rods and water rods are arranged in a square lattice shape, and lower ends of the water rods are connected to a lower support plate, the fuel assembly comprising a female thread extending in the axial direction from the lower end of the water rods. In addition to screwing the hole, a through hole that intersects with the female threaded hole is bored in the lower end of the water rod, and a through hole coaxial with the through hole of the water rod is bored in the lower support plate. The male threaded shaft is provided so as to protrude upward, and a pin is inserted into the female threaded hole and the through hole of the male threaded shaft of the water rod which are screwed to each other and fixed, and the female threaded hole and the male threaded shaft are screwed together. The pin prevents the water rod from floating, and the pin prevents the water rod from rotating.

[Embodiments of the invention]

The present invention will be explained below with reference to embodiments shown in the drawings. Note that the same components as those of the conventional device described above are denoted by the same reference numerals in the drawings, and the explanation thereof will be omitted.

FIG. 1 shows a first embodiment of the present invention, in which a water rod 4 is attached to the lower end of a Zircaloy tube 9 having a shorter dimension than the fuel rod 3 shown in FIG. It is constructed by fixing the end plug 10 by welding. A female threaded hole 11 extending in the axial direction of the water rod 4 is screwed into the center of the lower end surface of the lower end plug 10. A diametrically extending through hole 12 is provided in a protruding manner. On the other hand, in a portion of the lower support plate 2 that supports the water rod 4 where the water rod 4 is assembled, there is a male threaded shaft 13 that protrudes upward and can be screwed into the female threaded hole 11. This male threaded shaft 13 is provided with a transverse through hole 14 that assumes a coaxial position with the through hole 12 of the lower end plug 10 when the male threaded shaft 13 is screwed into the female threaded hole 11. There is.

To connect the water rod 4 and the lower support plate 2, first insert the male threaded shaft 1 protruding from the lower support plate 2 into the female threaded hole 11 of the lower end plug 10 of the water rod 4.
3, and make sure that both are fully screwed together and that the male threaded shaft 1
This screwing operation is stopped when the through hole 14 of No. 3 assumes a coaxial position with the through hole 12 of the lower end plug 10. Next, a tapered pin 15 as shown in the figure was inserted into the through hole 12.14 of the lower aB end plug 1o and the male threaded shaft 13, and the relative rotation of the lower end plug 10 and the male threaded shaft 13 was restrained by this pin 15. In this state, the pin 15 is fixed to the lower end plug 10 and the male threaded shaft 13 by welding or brazing.

If the lower end plug 10 of the water rod 4 and the male threaded shaft 13 of the lower support plate 2 are connected in this way, the lower end plug 10
The water rod 4 is prevented from floating by screwing the female threaded hole 11 and the male threaded shaft 13, and the pin 15 is inserted into the lower end plug 1o and the through hole 12.14 of the male threaded shaft 13. The rotation of the water rod 4 is also restricted.

Therefore, the water rod 4 is completely prevented from floating and rotating.

FIG. 2 shows a second embodiment of the present invention, in which a hexagonal bolt 16 is provided in place of the male threaded shaft 13 of the first embodiment. That is, a vertical bolt insertion hole 17 is bored in the portion of the lower support plate 2 into which the water rod 4 is installed, and the head 18 of the hexagonal bolt 16 is fitted into the lower end of the bolt insertion hole 17. It is a hexagonal recess 19 that is prevented from rotating. Note that a through hole 20 similar to the through hole 14 of the layer screw shaft 13 is bored in the hexagonal bolt 16.

Therefore, these bolt insertion holes 17 of the lower support plate 2
When the hexagonal bolt 16 is inserted into the recess 19, the hexagonal bolt 16 is held in a non-rotating state. and a through hole 12 for a hex bolt 16.
By inserting and fixing the pin 15 in 20, it becomes possible to completely restrain the floating and rotation of the water rod 4 and to support the water rod 4, as in the previous embodiment.

Note that the shape of the bolt 16 is not limited to only a hexagonal shape.

〔Effect of the invention〕

As explained above, in the fuel assembly according to the present invention, the fuel rods and water rods are arranged in a square lattice, and the lower ends of the water rods are connected to a lower support plate. A female screw hole is screwed in the axial direction from the lower end of the rod, and a through hole that intersects with this female screw hole is bored in the lower end of the water rod, and the lower support plate has a hole coaxial with the through hole of the water rod. A male threaded shaft having a through hole bored therein is provided so as to protrude upward, and a pin is inserted into the female threaded hole of the water rod and the through hole of the male threaded shaft, which are screwed together, to secure the water rod. Therefore, it is possible to reliably prevent the water rod from rotating or floating, and the reliability of the fuel assembly itself can be further improved.

[Brief explanation of the drawing]

Figures 1 and 2 are part of the main parts of an embodiment of a fuel assembly according to the present invention, respectively! The exploded front view, FIGS. 3 and 4 are longitudinal sectional front views of conventional fuel assemblies, respectively. 2... Lower support plate, 3... Fuel rod, 4... Water rod, 10... Lower end plug, 11... Female threaded hole,
12...Through hole, 13...Male screw shaft, 14...Through hole, 15...Pin, 16...Hexagon bolt, 20...
...Through hole. Applicant's agent Kiyoshi Inomata Figure 4

Claims (1)

[Scope of Claims] 1. In a fuel assembly formed by arranging fuel rods and water rods in a square grid, and connecting the lower ends of the water rods to a lower support plate, in the axial direction from the lower ends of the water rods. A female threaded hole is screwed into the lower end of the water rod, and a through hole that intersects with this female threaded hole is formed in the lower end of the water rod, and a through hole coaxial with the through hole of the water rod is formed in the lower support plate. A fuel assembly characterized in that a male threaded shaft is provided so as to protrude upward, and a pin is inserted into the female threaded hole of the water rod and the through hole of the male threaded shaft that are screwed together to fix the fuel assembly. body. 2. The fuel assembly according to claim 1, wherein the male threaded shaft is constituted by a bolt having a polygonal head for preventing rotation.