Patent Number: 039403130
Section: summary

BACKGROUND OF THE INVENTION 1. Field of the Invention The invention relates to a nuclear fuel rod for a water-cooled nuclear reactor and to means for detecting leaks in the fuel rod. More particularly, the invention relates to such a fuel rod equipped with a detection device disposed inside the rod for detecting a leak. 2. Description of the Prior Art Previously, it has been only possible to examine fuel cells for leaks as a whole. Since the fuel cells are constructed with plurality of individual fuel rods, it is relatively difficult to find the individual defective fuel rod or rods in the fuel cell that have been ascertained as faulty. It is known to provide a ferromagnetic body inside the nuclear reactor fuel rod. The ferromagnetic body includes a mounting mechanism which is destroyed by cooling water entering in the event of damage, so that the ferromagnetic body can drop from its original position to the end of the nuclear fuel column situated in the fuel rod. This change of location can then be detected by magnetic measuring techniques without removing the fuel rod from the fuel cell assembly. In this connection, reference may be had to U.S. Pat. application, Ser. No. 885,407 filed on Dec. 16, 1969. This solution, however, is relatively complicated and the reliability of operation cannot be considered as 100 percent. The need therefore existed for other means to detect defective fuel cells. SUMMARY OF THE INVENTION It is an object of the invention to provide a detection device for detecting leaks in nuclear fuel rods. It is another more specific object of the invention to provide a moisture sensor that can be positioned in the fuel rod for detecting moisture that penetrates into the rod in event of a leak therein. According to the invention, a moisture sensor is provided for a nuclear fuel rod of a water-cooled nuclear reactor. The fuel rod has an end cap and a charge of nuclear fuel. The moisture sensor is disposed between the end cap and charge and has a capsule-like housing having an inner space. Inlet means in the form of openings are provided in the housing through which moisture can pass in the event of a leak in the fuel rod. A ferromagnetic material is disposed in the inner space of the housing together with moisture detection means responsive to moisture for altering the disposition of the ferromagnetic material in this inner space. In a preferred embodiment of the invention, the moisture detection means is a pressed body made of the ferromagnetic material and an other material that decomposes and expands in volume when subjected to moisture. In addition, the housing is made of water-resistant material. According to an alternate embodiment of the invention, the ferromagnetic material is in the form of particles and the moisture detection means is a cup-like container made of non-magnetic, water resistant material. The container is filled with the particles and is freely movable in the inner space of the housing. The detection means includes a lid covering the container, the lid being made of a pressed material different from the ferromagnetic material. The material of the lid is such that the lid decomposes and expands in volume in response to moisture so as to lock the container with the particles contained therein in position in the housing. The decomposable material consists of powdered aluminum and water-soluble organic or inorganic mercury compounds such as mercury nitrate, mercury iodide or aluminum amalgam. The mercury compounds act here essentially as catalysts for the decomposition of the aluminum powder, which is accompanied by a corresponding increase in volume, especially since the original pressed bodies disintegrate because of these phenomena. Although the invention is illustrated and described herein as a device for detecting defective nuclear reactor fuel rods, it is nevertheless not intended to be limited to the details shown, since various modifications may be made therein within the scope and the range of the claims. The invention, however, together with additional objects and advantages will be best understood from the following description and in connection with the accompanying drawing.