Patent Number: 044951418
Section: summary

BACKGROUND OF THE INVENTION The present invention relates to a tagging gas releasing element for detection of a failed fuel, which element is contained in a nuclear fuel rod. As a method for detecting failed or burst fuels, there is known a so-called tagging method which comprises laballing, or tagging nuclear fuel rods by a tagging gas, sensing leakage of the tagging gas, that is, breakage of a cladding tube of the nuclear fuel rod, by a sensing device disposed in the outside of the fuel rod, and determining a nuclear fuel assembly including the failed fuel rod (see, for example, U.S. patent application Ser. No. 729,317 filed on May 15, 1968). A prior art method for introducing a tagging gas in a nuclear fuel rod is known in which the tagging gas is sealed in a capsule and, after assembling and sealing the capsule in the nuclear fuel rod, the tagging gas is released and filled in the nuclear fuel rod. For example, according to a method disclosed in French Patent Application No. 7223402, a tagging gas is filled in a capsule composed of a hardly fusible substance, the capsule is arranged within each fuel rod, and the tagging gas is released into the fuel rod through a passage of the capsule intercepted by an easily fusible seal having a melting point lower than the temperature for operating the fuel rod in a nuclear reactor. However, such a prior art tagging gas releasing element is defective in that the manufacture is very difficult because of a complicated structure of the capsule and since the capacity required of the element is large, designing of the nuclear fuel rod is remarkably limited. SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide a tagging gas releasing element having a very simple structure easy to be manufactured. It is another object of the present invention to provide a tagging gas releasing element having a diminished size which moderate limitations on designing of a nuclear fuel rod. Briefly, a tagging gas releasing element according to the present invention comprises an inorganic solid material holding a tagging gas therein. The tagging gas is composed of a rare gas, and is injected or adsorbed in the inorganic solid material. In the present invention, as the inorganic solid material, there may be employed metals such as titanium, aluminum, zirconium, nickel and stainless steel; alloys of these metals; films of these metals and alloys; and heat-resistant inorganic compound solids such as zeolite, activated carbon and boron nitride. The tagging gas comprises rare gas including isotopes thereof such as, for example, xenon, krypton, neon or helium, or mixtures containing two or more of these rare gases at a predetermined mixing ratio. Injection of the tagging gas into the inorganic solid material or adsorption of the tagging gas in the inorganic solid material may be performed according to an ion injection method, a high pressure induced diffusion method, a thermal diffusion method, a physical adsorption method or combination of these methods. These and other objects and features of the present invention will be apparent from the description of the preferred embodiments of the invention, taken in conjunction with the accompanying drawings.