JPS6335955B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a spacer for a nuclear fuel assembly, which allows a large number of fuel elements to be held at a constant distance from each other and supported by a constant force. .

As shown in FIGS. 4 to 6, the spacer is constructed by partitioning the inside of the outer circumferential wall plate 1 by intersecting vertical and horizontal partition plates 2, 2..., 3, 3... It is divided into the required number of cells 4, 4... of the same size surrounded by the four sides of the board, and clips 5, 5... are attached to the four sides of each cell 4, 4... by sandwiching the wall board, respectively. A clip-on version is known.

In the above conventional example, as clearly shown in Figs. 1 and 2, clips 5, 5... are held in the partition plates 2, 2..., 3, 3... on both sides of the plates. Elastic pieces a, a' are protruded by bending, and the fuel elements A, A' inserted into the cells 4, 4...
... is configured to be held between the elastic pieces a', a' of both clips 5, 5, and serves as a spacer.

However, in the case of recent boiling reactor BWR,
As is known, the thermal neutron flux distribution decreases within a nuclear fuel assembly, so efforts have been made to equalize the power distribution by changing the enrichment of fuel elements within the assembly, but this has not produced satisfactory results. It's not on.

Therefore, a water pipe is installed in the center of the assembly in alignment with the fuel element, thereby increasing the thermal neutron flux within the assembly. In order to improve the effectiveness, we not only increased the number of water pipes, but also
We are trying to make the diameter of the tube as thick as possible.

Therefore, as shown in FIG.
Elastic pieces a, a that should elastically hold the fuel elements A, A of 5
can have a sufficiently protruding shape, but
The elastic pieces a', a' that should hold the water tube B have almost no protruding length, and the clips 5, 5 are
By being pushed by A, a slight gap S is created between the pieces a, a' and the partition plates 2, 2.

As a result, the pressing force of the clips 5, 5 against the water pipe B becomes extremely small compared to the holding force against the fuel elements A, A, and the water pipe B is subjected to hydraulic vibration due to the cooling water flowing through the pipe B. As a result, the water pipe B will continue to be in intermittent contact with the spacer and other structural members, causing fretting corrosion in that part, and in extreme cases, even causing damage to the nuclear fuel assembly. be.

Next, in the conventional example shown in FIG. and a non-elastic piece C with a protruding fixing protrusion b.
The fuel element A is clamped and held by the elastic piece a' and the inelastic piece C, but when trying to clamp the water pipe B with this kind of conventional clips 5, 5, Become like Ro.

In other words, the elastic pieces a, a in the left and right clips
When the fuel rod is pressed by the fuel elements A and A, as shown in C of the figure, the elastic piece a tends to expand from the state shown by the broken line before the fuel rod is inserted, as shown by the solid line after the fuel rod is inserted. The elastic pieces a' and a' on the side of the water pipe B that are connected to this are strongly pressed against the partition plates 2 and 2, and as shown in the figure, the water pipe B and the elastic pieces are connected to each other.
A slight gap S' is formed between a' and a', and the water pipe B becomes loose and becomes unable to stop its fretting.

In view of the above points, the present invention eliminates the concept of relying on the elasticity of the clip as in the prior art and adopts an inelastic clip in order to maintain the water pipe satisfactorily. Instead of being fixedly attached to the bulkhead plate, the clip is attached so that it can be moved laterally, and is also attached to the fuel element inserted into the adjacent cell located outside the water pipe. In this method, by providing a structure in which a clip with elasticity directed toward the water pipe is pressed against the water pipe, it is possible to elastically hold the water pipe at a predetermined position with a predetermined holding force, and to completely prevent the occurrence of fretting. This is the object of the present invention.

The present invention will be described in detail with reference to the illustrated embodiments. As described above, the outer peripheral side wall plate 1, the partition wall plates 2, 2..., 3,
3..., cells 4, 4..., clips 5, 5..., and the cells 4, 4... are provided with fuel elements A,
A... and water tube B are inserted and held by clips provided on the four sides of cell 4, but in the present invention, water tube B is inserted as shown in Fig. 3. Inelastic clips 5', 5' are attached to all four sides of the water pipe cell 4'.

That is, as shown in the same figure, the inelastic clips 5', 5' are connected to a water pipe abutting piece 6 that protrudes into the water pipe cell 4', and to adjacent cells adjacent to the four sides of the water pipe cell 4'. 4, 4... consists of a fuel element abutting piece 7 protruding from inside, and in the illustrated example, a water pipe abutting piece 6.
has a flat plate shape, whereas the fuel element abutting piece 7 has two fixing protrusions 8, 8' protruding in a wave shape.

As in the conventional example, the inelastic clips 5', 5' are attached by clamping the contact pieces 6, 7 to the partition plate 2 with the upper and lower ends fixed. In the present invention, this attachment state is not fixed as in the conventional example, but the clips 5', 5'... and the partition walls 2, 2... on each side are fixed.
. . , 3, 3, . . . , a transition gap g is formed between them.

Furthermore, in the present invention, in the four adjacent cells 4, 4... described above, fuel elements inserted into the cells 4, 4... are provided on each side opposite to the four sides of the water pipe cell 4'. An elastic piece 9 of the clip 5 is provided to direct and press the water pipes A, A, . . .

Therefore, in the above configuration, the elastic piece 9 pushes the fuel element A toward the water pipe B with a force F as shown in the figure, and this pushing force is applied to the inelastic clip 5'.
However, since the clip 5' has no elasticity and has the shifting gap g as described above, it is not deformed by the holding force of the elastic piece 9 of the fuel element A. The pushing force on the water pipe B by the movable clip 5' is therefore equal to the holding force of the fuel element in question, so that the water pipe is held with a sufficient predetermined holding force. be held.

Here, FIG. 4 to FIG. 6 show what kind of clips 5, 5, etc. should be arranged according to various embodiments of the spacer according to the present invention, but in FIG. 8 rows 8 used in BWR
Two water pipes B are installed in the center, and here a clip made of only elastic pieces marked with black triangles is used on the outer wall plate 1. The one shown in the figure (B) can be used.

Furthermore, in order to hold the fuel element A, there is a clip with elastic pieces and fixing protrusions on both sides, shown as black semicircular triangle marks, and a clip with fixing protrusions on both sides, shown as black semicircular marks. are used, and specific examples of these clips are shown in FIGS. 8 and 9, respectively.

Therefore, in FIG. 4, it is sufficient to prepare four types of clips: three types of clips 5 and an inelastic clip 5', which is for water pipes and is shown as a white semicircle mark. In the embodiment of the non-elastic clip shown in FIG. 10, the fixing protrusions 8, 8' of the non-elastic clip 5' are protruded in a trapezoidal shape, unlike in FIG. 3.

Next, in the embodiment shown in Fig. 5, a clip with a fixing protrusion on only one side is used, which is shown as a black semicircle mark compared to the one in the previous figure, and therefore there are five types, and the former is more In comparison, less time is spent on quality control during mass production.

6 shows a case in which the fuel elements are arranged in 9 rows and 9 columns, and there is only one water tube B, and the basic configuration is the same as that in FIG. 4, using four types of clips.

To give a specific example here, the outer peripheral wall plate and bulkhead plate are made of 0.65 mm thick Zircaloy plate material, which is difficult to absorb neutrons in a nuclear reactor, while the material of the clip maintains its strength even in high temperatures and corrosive atmospheres. Nickel-based alloys such as Inconel X-750 and Inconel 718 are suitable, but here we used Inconel .

The total length of the clip was 35 mm, and in the case of an inelastic clip for a water pipe, the gap was set to 0.67 mm, which was larger than the wall thickness of the partition plate to form a displacement gap.

For the spacer configured as above,
When we investigated its characteristics, it was confirmed that both the fuel element and the water pipe were held with a force of approximately 1 kg, and no fretting occurred at all.

The present invention, as embodied by the above embodiments,
In this type of clip-forming spacer,
The fuel elements A, A, . . . inserted into the adjacent cells are placed on each side of the adjacent cells 4, 4, which are opposite to the four sides of the water tube cell 4' into which the water tube B is inserted. Elastic pieces 9 of the clip 5 are arranged to press the clip 5 toward the water pipe cell 4', and water pipe contact pieces 6 are provided on the four sides of the water pipe cell 4' to project into the cell, and water pipe contact pieces 6 project into the adjacent cells 4, 4... The inelastic clip 5' consisting of the fuel element abutting piece 7 is held in place, and at this time, the partition plate 2,
2..., 3, 3... and the inelastic clip 5', the clip 5' is connected to each fuel element A, A,... by the elasticity of the elastic piece 9 of the clip 5.
By being pushed through the clip, a displacement gap g sufficient to elastically hold the water tube B is formed, so the displacement of the inelastic clip by the gap increases the holding force of the fuel element. The same force is sufficient to hold the clip, which eliminates the problem of flattening, and because the clip utilizes the displacement of an inelastic body rather than the elasticity of the clip itself, the water pipe abutting piece The protruding length only needs to be very small, so that a sufficiently thick water tube can be inserted into the water tube cell, and the purpose of equalizing the power distribution of the nuclear fuel assembly can be effectively achieved.

[Brief explanation of the drawing]

A in Figure 1 is a longitudinal front explanatory view showing the holding state of the fuel element in a conventional spacer, B is a longitudinal front explanatory view showing the holding state of the water pipe, and Fig. 2 is the same as Fig. 1. Different conventional examples are shown in which A and B are vertical cross-sectional front explanatory views showing the holding state of the fuel element and water tube, respectively, C is a modified explanatory view of the clip in the same figure, and FIG. 3 is a nuclear fuel assembly according to the present invention. A vertical cross-sectional front view showing the main parts of the body spacer,
4, 5, and 6 are explanatory plan views showing different types of spacers according to the present invention, and A in FIGS. 7, 8, 9, and 10 is the previous figure. A symbolic diagram showing the form of the illustrated clip, and (b) in the same figure is a front view showing a longitudinal section of a partition plate that is a specific example thereof. 1...Outer peripheral side wall plate, 2...Vertical partition plate, 3...
Horizontal bulkhead plate, 4...Cell, 4'...Cell for water pipes,
5...Clip, 5'...Inelastic clip, 6...
... Water pipe contact piece, 7 ... Fuel element contact piece, 9 ... Elastic piece of clip, A ... Fuel element, B ... Water pipe,
g...Gap for transition.

Claims (1)

[Claims] 1. Divide the inside of the outer peripheral wall board into a required number of cells of the same size surrounded by four sides by intersecting vertical and horizontal partition walls, and attach the wall board to each of the four sides of each cell. In the spacer which elastically holds the fuel element and water pipe inserted into the same cell by the clips inserted, each side of the adjacent cell opposite to the four sides of the water pipe cell into which the water pipe has been inserted is Elastic pieces of the clip are arranged to direct and press the fuel element inserted into the adjacent cell toward the water pipe, and the four sides of the water pipe cell are provided with water pipe abutting pieces that protrude into the cell and the adjacent cell. An inelastic clip consisting of a fuel element abutting piece protruding inward is clamped between the bulkhead plate on each side and the clip, and the inelastic clip is held in place by the elasticity of the elastic piece of the clip. . A spacer for a nuclear fuel assembly, characterized in that a spacer for a nuclear fuel assembly is formed by being pushed through each fuel element to form a displacement gap sufficient to elastically support the water tube.