JPS6142833B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a nuclear fuel element, and more particularly to a nuclear fuel element having a mechanism for preventing migration of fuel pellets within the fuel element.

Nuclear fuel materials used as fuel for nuclear reactors are
These are formed into fuel pellets, covered with a cladding material to form fuel elements, and inserted into a nuclear reactor. FIG. 1 shows the general shape of a nuclear fuel element used in a fast breeder reactor as an example. Inside a cladding tube 1, there are a core pellet 2, which is a heating element, and blankets arranged above and below the core pellet 2. Fuel pellets constituted by top pellets 3 and 4 are inserted. Additionally, a gas plenum 5 is provided for storing the gas produced by nuclear fission, in which fuel pellets 2, 3, 4 are stored during transport, handling or use of nuclear fuel elements. A plenum spacer consisting of a combination of a sleeve 8 and a plenum spring 11 is provided to prevent the cladding tube from moving, and an upper end plug 7 and a lower end plug 6 are welded to both ends of the cladding tube 1.

This gas plenum section 5 occupies about half of the total length of the fuel element, since it is required to achieve a high burnup in the fuel element of a fast reactor, and therefore a large amount of fission product gas is generated. .

In this conventional nuclear fuel element, the number of members inserted into the gas plenum section 5 to hold the fuel pellets 2, 3, 4 increases, and the effective volume of the plenum section 5 decreases accordingly. Moreover, the nuclear fuel element becomes longer, which is not only inconvenient to handle, but also the longer the nuclear fuel element becomes, the larger the reactor becomes, resulting in an economic disadvantage.

As another conventional technique, as shown in Fig. 2,
There is a method of locking the plenum spring 11 with a compression body 12. In this case, the compressed body is a wire-like spring made of stainless steel such as Inconel, and is manufactured so that the outer diameter of the spring is larger than the inner tube of the cladding tube 1 in its natural length state, and the fuel element is assembled. In this case, use a special insertion jig to reduce the diameter of the spring, insert it into the cladding tube, remove the spring from the insertion jig at a predetermined position, and press it onto the inner surface of the cladding tube. It locks the plenum spring,
When inserting the spring into the cladding tube, the inner surface of the cladding tube may be damaged, and when the spring is crimped to the inner surface of the cladding tube, the spring and the inner surface of the cladding tube come into contact with each other in an edge-like manner, causing local damage to the cladding tube. This results in a load being applied, which poses a problem in terms of the strength of the fuel element.

In addition, in this case, the compressed body deforms during use or loses its elasticity in high-temperature environments.
There are drawbacks such as the inability to perform the original function of preventing fuel pellet movement.

Therefore, in order to shorten the length of the nuclear fuel element from the point of view of economy, it is possible to reduce the local load on the cladding tube without reducing the effective volume of the gas plenum, and to maintain its function for the entire period of use. A nuclear fuel element having a fuel pellet migration prevention mechanism is desired.

The present invention has been made to meet the above-mentioned needs, and does not reduce the effective volume of the gas plenum.
It is an object of the present invention to provide a nuclear fuel element that effectively retains fuel pellets and reduces damage to cladding tubes. That is, the present invention has a fuel pellet movement prevention mechanism that stacks and fixes a plurality of fuel pellets in the cladding tube in the axial direction via a spring member disposed in the gas plenum, and both ends of the cladding tube are sealed. In the nuclear fuel element, this fuel pellet movement prevention mechanism consists of a hollow cylindrical support member solid-phase joined to the inner surface of the cladding tube.

An embodiment of the present invention will be described below with reference to the drawings. The present invention differs from the conventional example in that a third compression body is used instead of the sleeve 8 in FIG. 1 or the compression body 12 in FIG.
As shown in the figure, a hollow cylinder 9 is used, and other parts are the same as the conventional example.

The hollow cylinder 9 has an outer diameter slightly smaller than the inner diameter of the cladding tube 1, and is made of heat-proof steel such as stainless steel.

After inserting the hollow cylinder 9 into a predetermined position within the cladding tube 1, an alternating magnetic field is applied from outside the cladding tube to generate a current in the hollow cylinder 9 and the inner surface of the cladding tube. heated,
Then, by supplying a pulsed magnetic field from the outside, a pulsed current flows between the two, and by applying pressure using the electromagnetic force instantaneously generated between the two, the outside of the hollow cylinder 9 is It is fixed within the cladding tube 1 by electromagnetic solid phase bonding, which solid phase welds the periphery and the inner periphery of the cladding tube 1 .

The inner diameter of the hollow cylinder 9 is not particularly specified, but a larger one is desirable in order to reduce the effective volume reduction rate of the gas plenum portion, but it is necessary to have a contact cross-sectional area sufficient to support the plenum spring. Further, the length of the hollow cylinder 9 is desirably as short as possible in order to reduce the effective volume reduction rate of the gas plenum portion as described above, but it is sufficient to have a length of about 1 cm for convenience of handling.

According to the present invention, the effective volume of the gas plenum portion 5 formed within the cladding tube is increased by the removal of the sleeve 8 compared to the conventional example shown in FIG.
A large amount of fission product gas can be stored without increasing the length of the nuclear fuel element.

In addition, compared to the conventional example shown in Fig. 2, when inserting a hollow cylindrical support into the cladding tube, the outer diameter of the hollow cylindrical support is slightly smaller than the inner diameter of the cladding tube. It can be easily placed in a predetermined position without damaging the inner surface of the tube 1.

Furthermore, since the hollow cylindrical support is joined to the inner surface of the cladding tube, there is no loss of the function of preventing the movement of fuel pellets due to elasticity reduction during use, which is seen in the prior art shown in FIG.

[Brief explanation of the drawing]

1 and 2 are longitudinal sectional views showing a conventional nuclear fuel element, and FIG. 3 is a longitudinal sectional view showing an embodiment of the present invention. DESCRIPTION OF SYMBOLS 1... Cladding tube, 2... Fuel pellet, 3... Fuel pellet, 4... Fuel pellet, 5... Gas plenum part,
6... End plug, 7... End plug, 8... Sleeve, 9... Hollow cylindrical support, 12... Compression body.

Claims (1)

[Claims] 1. A nuclear fuel element in which a plurality of fuel pellets are fixed in a stacked manner in the axial direction in a cladding tube via a spring disposed in a plenum, and the openings at both ends of the cladding tube are sealed with end plugs, in which the fuel in the spring is The end portion on the side not in contact with the pellet is supported by a hollow cylindrical support, and the side surface of the hollow cylindrical support is joined to the inner surface of the cladding tube by electromagnetic solid phase joining. nuclear fuel elements.