Abstract: Nuclear reactor fuel rod leakage is determined by measurement of vibrational characteristics of a resilient, flexible means sealed within the upper end caps of the fuel elements. The flexible means, which is preferably a metallic diaphragm, is set into motion and the vibration measurements are made by a special tool which fits over the end cap of the fuel element to be tested.

Abstract: A system for the measurement of the length of the plenum chamber in a nuclear fuel rod, both before and after service in the nuclear reactor. The system basically comprises inserting the fuel rod into a casing having an eddy current sensing coil therein and advancing it until the coil output provides a signal indicative of the end of the plenum spring being centrally located within the coil. At an end of the casing is provided a plenum chamber length transducer of the displacement type, such as a linear variable differential transformer, which contacts the adjacent end cap of the fuel rod and when the coil provides an appropriate readout corresponding to proper location of the plenum spring end produces an output signal which is indicative of the length of the plenum chamber.