Patent Number: 046631127
Section: summary

BACKGROUND OF THE INVENTION 1. Field of the Invention The invention relates to a method for determining the contents of a fuel rod within a test range extending along the length of the fuel rod. The objective in particular is to distinguish fuel pellets of pure uranium dioxide from those which are doped with oxides of rare earths, for instance, with gadolinium oxide, Gd.sub.2 O.sub.3. 2. Description of the Prior Art Heretofore, for this purpose, the closed fuel rod has been irradiated with a neutron source and subsequently, the secondary radiation of the fuel rod was recorded over its length. This secondary radiation of differently doped fuel pellets can be distinguished from the radiation of pure UO.sub.2 in the fuel rod. However, this so-called "rod scanning" requires considerable equipment in the form of a large number of measuring devices and radiation protection measures which represent a substantial investment. SUMMARY OF THE INVENTION An object of the invention is to provide a method for distinguishing doped fuel pellets from those of pure UO.sub.2 in fuel rods with materially less investment cost than the method heretofore used, and in particular without the requirement for the radiation protection measures previously needed. With the foregoing and other objects in view, there is provided in accordance with the invention a method for determining the contents of a fuel rod containing fuel pellets of pure uranium dioxide and doped fuel pellets within a test range extending along the length of the fuel rod which comprises concentrically surrounding the fuel rod with a test coil and moving the test coil from the beginning to the end of the test range, measuring the impedance of the test core as a function of its position during movement, and feeding the test coil an a-c voltage with a frequency sufficiently low to produce a measurement value in the region of a fuel pellet of pure uranium dioxide which clearly distinguishes from a measurement value in the region of a doped fuel pellet. Other features which are considered as characteristic for the invention are set forth in the appended claims. Although the invention is illustrated and described herein as embodied in a method for determining the contents of a fuel rod, it is nevertheless not intended to be limited to the details shown, since various modifications may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.