Investigation of ultrasonic backward energy from various edges as a function of their 2D/3D geometry and of the incidence angle, for application to ultrasonic thermometry at the outlet of a tube

Innovative ultrasonic instrumentation to be used for future Generation IV sodium-cooled fast reactors is currently being investigated. One potential option under study here is the monitoring of the sodium temperature at the outlet of the core by using ultrasound. The main advantage of ultrasonic setups is that they can be used far from the intended subassemblies. The idea is to send an ultrasonic beam at grazing incidence towards the (cylindrical) subassembly head, and to measure the ultrasonic time of flight between the two diametrically opposite edges, in order to estimate the mean temperature across the subassembly outlet diameter. Moreover, the grazing incidence could allow considering the simultaneous temperature monitoring of several aligned subassemblies. One of the main points to be considered is the interaction between the ultrasonic beam and the immersed target, which involves specular reflection and/or diffraction, both phenomena depending on the incidence angle and the target geometry. The present paper investigates this interaction, mainly from an experimental point of view. Different geometries of “2D” (plate) and “3D” (tube) edges are tested and compared under various incidence angles. The final aim is to identify an optimal ultrasonic configuration to perform thermometry at the outlet of an immersed tube.