JPS6252271B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to nuclear fuel elements, and more particularly to nuclear fuel elements containing tag gas for nuclear fuel element failure detection.

Nuclear fuel elements loaded into nuclear reactors generally have a structure in which multiple nuclear fuel pellets are loaded into a long fuel cladding tube, and an end plug is welded to the end to seal it. Fission product gases accumulate within the fuel element. At this time, if the fuel element is damaged for some reason, the fission product gas is released into the coolant, causing radioactive contamination. In such a case, the reactor must be shut down and the damaged nuclear fuel element replaced, but since a reactor core is generally made up of tens of thousands of nuclear fuel elements or more, Locating a damaged nuclear fuel element is not easy.

In order to eliminate such difficulties, a method called the tag gas method has been devised. This is a method in which a tag gas whose composition is known in advance is sealed inside a fuel element, and when a failure occurs, the composition of the tag gas released together with the fission product gas is detected to determine which fuel element has failed. It is. One possible method for sealing tag gas into fuel elements using the tag gas method is to mix tag gas into the atmospheric gas when welding end plugs, but the composition of each nuclear fuel element manufactured on a mass production line is different. It is difficult to enclose predetermined amounts of different tag gases, and it requires many steps, so it cannot be said to be a preferable method. Therefore, a method has been devised in which a capsule filled with a predetermined tag gas is manufactured in advance, loaded into a fuel element together with nuclear fuel pellets, an end plug is welded, and then the capsule is opened. To open the capsule, a window is provided in a part of the capsule, and this window is sealed with a low-melting point metal. After welding the end plug, the nuclear fuel element is heated to melt the low-melting point metal, and the tag gas is released into the fuel element. There are known methods of releasing In this method, the capsule has a simple structure, is easy to manufacture, and can be opened reliably, but the molten metal may adhere to the inner surface of the cladding tube.
This may cause corrosion of the cladding. In particular, in the case of austenitic stainless steel, which is often used as cladding in fast reactors, Cd, Al, Ga, Sn, Si, Bi, Pb
Since low melting point metals such as metals are highly corrosive, it is undesirable for these metals to adhere to them.

The present invention has been made to eliminate the above-mentioned drawbacks, and provides a nuclear fuel element containing tag gas that has a simple structure and does not cause corrosion of the cladding tube.

That is, in the present invention, a tag gas capsule having an ultra-thin diaphragm and a piercing part for breaking through the diaphragm is sealed in a nuclear fuel element, and the tag gas capsule is loaded into a nuclear reactor or heated. This is a nuclear fuel element containing a tag gas, characterized in that the internal pressure is increased and the diaphragm is expanded so that the piercing portion pierces the diaphragm and the tag gas is released into the nuclear fuel element.

Hereinafter, one embodiment of a nuclear fuel element according to the present invention will be described with reference to FIGS. 1 to 3.

In FIG. 1, reference numeral 1 denotes a cylindrical tag gas capsule body, which is sealed with an extremely thin diaphragm 2. 3
This is a puncture tool provided with a sharp tip pierced portion 4 and a tag gas discharge hole 5 in order to break through the diaphragm 2. In addition,
Reference numeral 6 denotes an introduction pipe for introducing tag gas into the capsule, which is crushed and sealed after filling the tag gas. When the tag gas capsule configured in this way is sealed into a nuclear fuel rod and heated, the pressure inside the tag gas capsule increases, the diaphragm 2 expands outward, and the second
As shown in the figure, it is broken through by the piercing part 4,
Tag gas is released from the tag gas release hole 5 into the nuclear fuel element. Generally, when assembling a nuclear fuel element, gases such as Ar and He are contained within the nuclear fuel element at 1 atm or more.
Since it is sealed at a pressure of about 2 atmospheres, when sealing the tag gas into the capsule, it is necessary to mix the tag gas with a gas such as Ar or He and seal it at a pressure higher than the pressure inside the nuclear fuel element. Further, since heating for opening the capsule can be performed by loading the capsule into a nuclear reactor, there is no need to provide a special heating device.

As described above, when the nuclear fuel element containing tag gas according to the present invention is used, it is possible to exhibit a predetermined performance as a nuclear fuel element containing tag gas without corroding the inner surface of the cladding tube. In the embodiment, a case is shown in which a tag gas discharge hole is provided, but for example, a through hole 7 may be provided in the piercing portion as shown in FIG. 3. In other words, the external shape of the tag gas capsule and the shape of the punctures are arbitrary, as long as the diaphragm is expanded outward by the pressure increase inside the tag gas capsule due to heating, and the tag gas is released by breaking through the punctures. be.

[Brief explanation of the drawing]

FIG. 1 is a vertical cross-sectional view showing the tag gas capsule according to the present invention before opening, FIG. 2 is a vertical cross-sectional view showing the tag gas capsule after opening, and FIG. 3 is a vertical cross-sectional view showing the tag gas capsule according to the present invention. FIG. 3 is a longitudinal cross-sectional view showing an example. 1...Tag gas capsule body, 2...Diaphragm, 3
...Piercing tool, 4...Piercing portion, 5...Tag gas release hole, 6...Introduction pipe, 7...Through hole.

Claims (1)

[Claims] 1. A nuclear fuel element that is placed in a nuclear reactor that is filled with filler gas and sealed, and that is loaded with a capsule containing nuclear fuel material and tag gas,
A diaphragm in which the pressure of the tag gas sealed in the capsule is higher than the pressure of the filling gas, and the capsule expands and deforms due to an increase in pressure difference between the inside and outside of the capsule due to a rise in temperature, and a piercing portion that breaks through the diaphragm during the expansion and deformation. A tag gas-filled nuclear fuel element characterized by comprising: