To prevent fuel handling errors in sodium cooled fast reactors, identifying fuel subassemblies by ultrasound is a method that is being studied. It is based on the reading of a code (aligned notches) engraved on the subassembly head by an emitting/receiving ultrasonic sensor. This reading is performed in sodium with high temperature transducers. The resulting one-dimensional C-scan can be likened to a binary code expressing the subassembly type and number. A first experiment in liquid sodium at 200°C demonstrates the feasibility of this method. This reading method is sensitive to misalignment and misorientation between the ultrasonic beam and the subassembly head. Furthermore, the reading quality and robustness depends on various parameters (ultrasonic frequency, focal distance, code dimensions and geometry, subassembly head diameter, etc.). To avoid heaviness of numerous tests, a numerical model, validated thanks to a water experiment, is developed using CIVA software.