[en] An instrument for measuring strain of cladding for nuclear fuels has been developed for use during in-core characterization tests of candidate materials. Employing a microwave sensor of coaxial geometry, a strain of several microinches can be detected. At the opposite extreme, the large dynamic range of the instrument permits measuring strain equal to ten percent of the original specimen dimension. In all configurations tested, the sensor comprises a hollow metal cylinder enclosing a test specimen positioned coaxially within the cylinder. Microwave energy is absorbed by the specimen/sensor unit at particular frequencies related to size of the specimen. Consequently, determination of specimen size results from measurement of the resonant absorption frequencies of the sensor