JPS6033436Y2 - fuel assembly - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a fuel assembly, and more particularly to a fuel assembly with improved finger springs for adjusting leakage flow rate and a lower tie plate.

When a conventional fuel assembly is used in a nuclear reactor, a coolant creates a pressure difference between the inside and outside of a rectangular cylindrical fuel channel, and this pressure difference of several atmospheres causes the channel to expand.

In addition, since the fuel channel is exposed to high neutron flux in a nuclear reactor, it is thought that creep distortion occurs in the fuel channel, and the center of each side of the fuel channel swells due to the creep phenomenon.

Therefore, in a fuel assembly that has been used for several years, the gap between the fuel channel and the lower tie plate increases, resulting in an increase in leakage flow rate.

Conventionally, a finger spring is interposed between the lower tie plate and the fuel channel to prevent the flow rate leakage.

However, in a fuel assembly that has been used for many years, the amount of creep deformation of the fuel channel is likely to increase, and as a result, the finger spring cannot follow the amount of deformation, resulting in a large gap between the finger spring and the fuel channel.

As the flow rate of coolant leaking from the inside of the fuel channel to the outside increases through this gap, the flow rate of coolant inside the fuel channel decreases, causing the inside of the fuel bundle to overheat.
There is a risk of fuel damage.

In addition, due to the insertion of the fuel channel during fuel assembly assembly and the vibration of the fuel assembly during reactor operation, the finger springs at some corners may become unintentionally distorted, creating a gap between them and the lower tie plate. There are cases where it is possible.

This, together with the above-mentioned creep deformation of the fuel channel, increases the flow rate of coolant leaking from the inside of the fuel channel to the outside, leading to fuel damage, and furthermore, it can cause deterioration of the thermal hydraulic characteristics inside the reactor. Connect.

The present invention was developed to eliminate the above-mentioned drawbacks, and uses finger springs with a shape that can follow the creep deformation of the fuel channel to prevent unnecessary leakage of coolant from the fuel channel fitting part. At the same time,
By preventing the finger springs from being inadvertently distorted during fuel channel assembly, the thermal conditions within the fuel assembly are maintained during reactor operation, preventing fuel damage, thereby creating a fuel with excellent thermal-hydraulic properties. The goal is to provide a collective.

That is, the present invention has a water rod 4 and a fuel rod 3.3'.
, a lattice-shaped spacer 5 that aligns and supports the fuel rods and the water rods in an axially spaced manner, a cylindrical fuel channel 6 that surrounds the fuel rods and the water rods, and a cylindrical fuel channel 6 that surrounds the fuel rods and the water rods; an upper tie plate 1 fitted to the upper part of the rod; a lower tie plate 2 fitted to the lower part of the water rod and fuel rod and having a finger pocket 18 on the side; and a lower tie plate 1 fitted to the lower part of the fuel rod of the lower tie plate. A finger portion 16a is pressed by the end plug hole 12 and the fuel rod lower end plug 11 and fixed to the side of the upper surface of the lower tie plate, and has a cut in the sagging portion of the side of the lower tie plate.

16b and a finger spring 16 with a part of the finger housed in the finger pocket, the lower tie plate is located above the hole 12 for inserting the lower end plug 11 of the fuel rod at the four corners. The end surface and the upper surface 17a of the corner 17 of the lower tie plate are integrally formed at the same height, and the ridge 1 of the finger pocket
8a is a fuel assembly characterized in that it is always located inside the ridge 20 of the lower tie plate.

Further, the finger spring is a fuel assembly that is bent so that the central finger portion 16b of the finger spring contacts itself only once at the apex portion 19 at the tip thereof.

Hereinafter, one embodiment of the fuel assembly of the present invention will be described in detail with reference to the drawings.

The fuel assembly of the present invention is shown in FIG. 1 (a schematic diagram partially shown in cross section).

), it mainly consists of an upper tie plate 1, a lower tie plate 2, a plurality of fuel rods 3, one or more water rods 4, a spacer 5, and a fuel channel 6 that accommodates these.

The upper and lower tie plates 1 and 2 support both ends of the fuel rods 3 and water rods 4, and a plurality of spacers 5 are provided in the axial direction within the fuel channel to support the fuel rods 3 and water rods 4 in alignment. ing.

The upper tie plate 1 passes through the fuel rod upper end plug 8 while compressing the outer spring 7, and connects the fuel rod 3' (usually 8
It is fixed to the fuel rod 3' by a nut 9 in the upper part.

The coupling fuel rod 3' is screwed to the lower tie plate 2.

Fuel rods 3 and water rods 4 other than the coupling fuel rod 3'
The upper end of the fuel rod is inserted into the upper tie plate 1 through an external spring, and the lower end is inserted into the lower tie plate 2.
The fuel rod is inserted into the fuel rod through the lower end plug 11.

The fuel channel 6 is inserted from above the upper tie plate 1.

The upper end of the fuel channel 6 is fixed by a post 1a and a henna nut 1b provided in the upper tie plate 1 for fixing the fuel channel 6.

Further, the lower end of the fuel channel 6 is simply inserted into the side surface of the lower tie plate 2 via a finger spring (not shown) and is a free end.

FIG. 2 is a perspective view showing a part of the upper corner of the lower tie plate 2 of the present invention.

In the figure, the finger spring is not shown, and only one of the fuel rod lower end plugs 11 is shown.

The upper surface of the lower tie plate 2 is provided with a hole 12 into which a fuel rod lower end plug 11 is inserted and a hole 13 which is a flow path for a coolant.

The upper surface of the holes 12 at the four corners of the lower tie plate 2 is the upper surface 1 of the corner 17 at the upper corner of the side surface of the lower tie plate 2.
It is formed at the same height as 7a.

The corner portion 17 is continuous with and integrally formed with a ridge portion 20 on the side surface of the upper tie plate 2.

The height of the ridge 17b, which is the contact point between the corner 17 and the ridge 20, that is, the upper surface 17a of the corner 17 that bends in the horizontal direction from the upper end surface of the ridge 20 is clearly shown in FIG. 4, which will be described later. The finger spring 16 is located above the bendable corner 18a of the finger pocket 18.

FIG. 3 partially shows the state in which the fuel rod lower end plug 11 of the fuel rod 3 is inserted into the upper tie plate 2, the finger spring 16 is attached, and the fuel rod is surrounded by the fuel channel 6 (shown in cross section). It is.

The upper surface of the finger spring 16 is the lower tie plate 2.
The fuel rod is fixed to the lower tie plate 2 by being pressed by the upper surface 12a of the hole 12 and the fuel rod lower end plug 11.

(See also FIG. 4) The side surface of the finger spring 16 is notched to form a leaf, and is housed in the finger pocket 1B of the lower tie plate 2.

FIG. 4a is a longitudinal sectional view showing a state in which the fuel channel 6 is not inserted into the lower tie plate 2, and shows the lower end plug 1 of the fuel rod.
1 is a three-dimensional display.

FIG. 4 shows a state in which the fuel channel 6 is inserted into the lower tie plate 2 and the finger spring 16 is pressed and bent by the fuel channel 6.

The shape of the finger spring 16 will be explained in detail.

The finger spring 16 has two types of finger parts 16.
It has a, 16b structure.

One shape is located at the left and right end portions of the finger spring 16 at an upper fixed position of the lower tie plate 2 (the finger spring 16 is sandwiched between the fuel rod lower end plug 11 and the upper surface 12a of the hole 12).

) hangs down from the side surface of the lower tie plate 2 like a skirt, and has a finger portion 16a that is inserted into the finger pocket 18 in an inverted S-shape.

The shape of the other finger portion is located at the horizontal center of the finger spring 16, and has a finger portion 16b bent inward at the lower end of the finger pocket 18 and wavy at the tip.

As shown in FIG. 4, after the finger portions 16b of the central portion of the wavy-shaped finger spring 16 are fitted with the fuel channel 6, the wavy apex portions 19 come into contact with each other, and the elastic force is applied. is maintained at multiple locations.

Next, the process of inserting the fuel channel 6 into the lower tie plate 2 from above will be explained.

When inserted, since the corner 17 is located at the upper end of the corner of the lower tie plate 2, the four corners of the lower end of the fuel channel 6 are guided by the corner 17, so that the finger spring 16 above the ridge 18a of the finger pocket 18 is inserted.
The skirt is inserted without contacting the upper skirt 16c.

Next, the operation of the present invention will be explained.

Corners 17 provided at the four corners of the lower tie plate 2 protect the lower end of the fuel channel 6 from coming into contact with the upper skirt 16c of the finger spring 16 when the fuel channel 6 is inserted.
Do not deform.

That is, the skirt upper part 16 of the finger spring 16
c does not come into contact with the lower end of the fuel channel 6 and cause plastic deformation of the finger spring 16.

On the other hand, the central finger portion 16b is more bent in its initial shape than the end finger portion 16a, as shown in FIG. 4a.

This has the effect of increasing the restoring force when the finger spring 16b is forcibly pressed after the fuel channel 6 is inserted (FIG. 4b).

As a result, when a creep phenomenon occurs in the fuel channel 6, the amount of strain in the central portion increases, so that the finger portion 16b can sufficiently follow the strain.

Furthermore, the wavy apex portions 19 of the finger portions 16b are in contact with each other and elastic energy is stored at each location, so that no plastic deformation occurs in the finger springs 16.

Therefore, when the fuel channel 6 is inserted, the fin niger spring 16 is not inadvertently deformed by being guided by the four corners 17 of the lower tie plate 2.
Further, even when the fuel channel 6 undergoes creep deformation, it can be sufficiently followed by the elastic deformation of the finger spring 16 of the present invention.

As described above, according to the present invention, even if the fuel channel 6 undergoes creep deformation, the finger spring 1 can be reliably
6 can follow suit and prevent unnecessary coolant leakage.

Furthermore, even when the fuel channel 6 is inserted during fuel assembly, the finger springs can be protected by the four corners of the upper surface of the lower tie plate, making it possible to prevent inadvertent leakage of coolant.

Therefore, by supplying sufficient coolant into the fuel assembly, fuel damage can be prevented and safe operation of the nuclear reactor can be ensured.

Furthermore, by improving the characteristics of individual fuel assemblies, stable operation of the entire core becomes possible.

[Brief explanation of drawings]

FIG. 1 is a longitudinal section showing an embodiment of a fuel assembly according to the present invention, FIG. 2 is a perspective view showing a part of the lower tie plate in FIG. 1, and FIG. 3 is a lower type of the fuel assembly in FIG. 2. Side view showing the corners of the rate and the main parts of the finger spring,
FIG. 4 shows the finger spring in FIG. 3, in which a is a side view showing the finger spring before the fuel channel is attached, and b is a side view showing the finger spring after the fuel channel is inserted. 1... Upper tie plate, 2... Lower tie plate, 3... Fuel rod, 5...
Spacer, 6...Fuel channel, 11...
... Fuel rod lower end plug, 12 ... hole, 13 ...
...hole, 16...finger spring,
16a... Part of the finger at the end, 16b...
...Part of the fingers in the center, 16c...Upper part of the skirt, 17...Corner, 17a...
・Top surface of corner, 18...finger pocket,
18a... Edge of finger pocket.

Claims (2)

[Scope of utility model registration request] (1) A water rod 4, a fuel rod 3, 3', a lattice-shaped spacer 5 that aligns and supports the fuel rod and the water rod at a distance in the axial direction, and a spacer that surrounds the fuel rod and the water rod. a cylindrical fuel channel 6;
an upper tie plate 1 fitted onto the upper portions of the water rods and fuel rods; a lower tie plate 2 fitted onto the lower portions of the water rods and fuel rods and having finger pockets 18 on the sides; A finger is pressed by the fuel rod lower end plug hole 12 and the fuel rod lower end plug 11 and fixed to the side of the upper surface of the lower tie plate, and has a cut in the hanging part of the side of the lower tie plate. A finger spring 1 having portions 16a and 16b and having a portion of the fingers accommodated in the finger pocket.
6, the lower tie plate is such that the upper end surface of the hole 12 for insertion of the fuel rod lower end plug 11 at the four corners is at the same height as the upper surface 17a of the corner portion 17 of the lower tie plate. The ridge 18a of the finger pocket is formed integrally with the ridge 20 of the lower tie plate.
A fuel assembly characterized by being always located on the inside. (2) The above-mentioned finger spring is registered as a utility model, characterized in that the central finger portion 16b of the finger spring is bent so as to contact itself only once at the apex portion 19 at the tip thereof. A fuel assembly according to claim 1.