2. New conditions for using this measurement technique

The aim is to be able to use this measurement technique directly on fuel assemblies stored in deactivation pools, and to determine the pressure and composition of the gaseous mixture on new or lightly irradiated rods.

The sensors and associated signal processing developed up to 2013 did not allow measurements on helium-xenon mixtures with a xenon content of less than 5% for coupling with water and with the presence of the retaining spring.

In order to optimize the acoustic measurement method, we focused on sensor response under low fission gas conditions (even for pure helium) and at low internal pressure levels.

Three types of optimization are proposed: signal processing, intrinsic sensor performance (sensitivity) and manufacturing (especially sensor-sheath contact).