An ultrasonic sensor for pressure and fission-gas release measurements in fuel rods for pressurised water reactors

A sensor for measurement of the fuel rod internal pressure and fission-gas release is developed for nuclear applications. The measurement of acoustic velocity and attenuation of the gas allows to calculate both pressure and composition of a mixture. The small acoustic impedance of gas compared to solid one induces a strong insertion loss which prevent propagation of ultrasonic waves inside pipes. We proposed a method to reduce the acoustic impedance mismatches to ensure sufficient wave propagation inside the gas. Out-of-pile test have been carried out : PZT materials have been tested under gamma irradiations. Temperature behaviour was also studied. (author)