JPS6120829B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Nuclear fuel elements are typically used as primary sealed containers for radioactive materials. For this purpose, a gas plenum is provided within the nuclear fuel element to accommodate gaseous radioactive substances generated by fission of fuel pellets, which are nuclear fuel materials. Traditionally, this gas plenum has been provided on top of the nuclear fuel element.
However, in recent years the demand for extending the life of fuel has increased.
As the requirements become more and more severe, consideration is being given to installing the same plenum below the fuel element.
In this case, in order to hold the fuel pellet at a predetermined position within the nuclear fuel element, an intermediate end plug must be provided in the middle of the nuclear fuel element (at the lower end of the fuel pellet). In this case, one end of the intermediate support is usually welded and fixed by TIG welding or the like to the cladding of the fuel element that accommodates the fuel pellets, and the other end of the intermediate support is fixed to the cladding of the nuclear fuel element that forms the gas plenum. It is necessary to fix the nuclear fuel element by welding, and the welding process is significantly increased compared to the manufacturing of the nuclear fuel element when a gas plenum is formed on the top of the nuclear fuel element.In addition, the inspection process to confirm the soundness of the welded part is required. The number of man-hours also increases significantly, making the manufacturing cost of the nuclear fuel element expensive, and the large number of welded parts increases the risk that the integrity of the welded parts will be impaired when the nuclear fuel element is used.

The present invention has been made in view of the above circumstances.
The object is to provide a nuclear fuel element with a fuel pellet support that reduces the welding process for providing the intermediate support and in which the integrity of the nuclear fuel element is not compromised by the weld.

An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 is a longitudinal sectional view showing the entire nuclear fuel element of the present invention.

As can be seen from FIG. 1, the nuclear fuel element includes a cladding tube 5 whose both ends are sealed by an upper end plug 1 and a lower end plug 2, an intermediate support section 3 provided in the middle of the cladding tube 5, and an intermediate support section 3 provided in the middle of the cladding tube 5. The fuel pellets 4 are supported by the fuel pellets 4 and stacked in the cladding tube 5 between the support portion and the upper end plug 1, and the cladding tube 5 is formed between the support portion 3 and the lower end plug 1. It consists of a hollow gas plenum 6. The cladding tube 5, the upper and lower end plugs, and the intermediate support are made of stainless steel or other stainless steel.

FIG. 2 is an enlarged sectional view of the vicinity of the intermediate support portion. As can be seen from FIG. 2, the intermediate support portion 3, which is made of the same material as the cladding tube 5, such as stainless steel, has an outer diameter slightly smaller than the inner diameter of the cladding tube 5, and has a fuel pellet storage portion of the fuel element. It has a ventilation hole 7 for communicating between the gas plenum and the gas plenum.

The intermediate support part 3 generates a current in the outer peripheral part of the intermediate support part 3 and the inner surface of the cladding tube by a high-frequency alternating magnetic field supplied from the outside of the cladding tube. Both surfaces are heated by this current, and then a pulsed magnetic field is applied. By supplying it from the outside, a pulsed current flows between them, and by applying pressure using electromagnetic force that is instantaneously generated between them, both the intermediate support part 3 and the inner surface of the cladding tube are solid-state bonded. It is joined to the inner surface of the cladding tube by electromagnetic solid state joining.

The ventilation hole 7 provided in the intermediate support part 3 may be composed of several pores, as shown in FIG. 3, to prevent the ventilation hole from being blocked by fragments of pellets, for example. . Furthermore, as shown in Fig. 4, even if a fine mesh filter made of stainless steel or the like is inserted into the ventilation hole of the intermediate end stopper on the fuel pellet storage side, the air permeability between the fuel pellet part and the gas plenum part will be reduced. is guaranteed.

In a nuclear fuel element configured in this way, it is necessary to divide the cladding tube into two and weld the intermediate end plug to the cladding tube using TIG etc. in order to form an intermediate partition section in which a gas plenum section is installed at the bottom. There is no risk that the integrity of the nuclear fuel element will be compromised due to an increase in the number of welded parts because the plenum part is provided at the bottom because the welding points are the same as those for the nuclear fuel element when the gas plenum part is provided at the top. Further, by using the same method, the cladding tube is not divided into two to provide an intermediate support portion, so that the manufacturing cost of the nuclear fuel element does not increase. In addition, since the cladding tube and the intermediate support part are joined by electromagnetic solid phase welding, there is no need to melt the material of the joint part during joining, unlike conventional TIG welding, and the material is not melted in the solid phase below the melting point. Since it can be bonded and heated instantaneously and uniformly, the heat affected zone is small and residual stress can be made extremely small, improving the performance of nuclear fuel elements.

[Brief explanation of the drawing]

FIG. 1 is a longitudinal sectional view showing one embodiment of the present invention, FIG. 2 is a longitudinal sectional view showing essential parts of the invention, and FIGS. 3 and 4 show essential parts of other embodiments of the invention. FIG. DESCRIPTION OF SYMBOLS 1... Upper end plug, 2... Lower end plug, 3... Intermediate support part, 4... Fuel pellet, 5... Cladding tube, 6
...Gas plenum section, 7...Vent hole, 8...Mesh filter.

Claims (1)

[Claims] 1. A cladding tube whose ends are sealed by an upper end plug and a lower end plug, an intermediate support portion having a ventilation hole provided in the middle portion of the cladding tube, and the intermediate support portion and the upper end. In a nuclear fuel element formed from fuel pellets stacked between plugs and a gas plenum formed between an intermediate support part and a lower end plug, the intermediate support part is electromagnetically solid-phase joined to the inner surface of the cladding tube. A nuclear fuel element characterized by: 2. The nuclear fuel element according to claim 1, characterized in that a mesh filter is filled in the vent hole of the intermediate support portion on the side facing the fuel pellets.