Abstract
The goal of this study is to realize an ultrasonic sensor for pressure and composition of released fission gases in PWR reactor fuel rods. This work was supported by EDF which wants to increase the time of use of fuels rods and thus the burn up. A physical modeling of the sensor allowed establishing the size of the piezoelectric transducer and optimal characteristics of coupling layers to inject a maximum of acoustic power in the gas. Furthermore, a specific signal processing was designed and made it possible to perform measurement with the pellets hold-down spring. This spring disturbs highly the establishment of the stationary wave in the cavity. We studied the diffraction phenomena by a spring, by using the equivalent source method, and we carried out the possibility to perform the measurement with the spring that seemed impossible to achieve. This study allowed achieving, with the sensor at the same place, the measure of the pressure with ±1.8 bars of accuracy and with ±1% on the concentration of xenon.