The ultrasonic level measurement channel forms part of the NIMSYS product line. It is used during the nuclear power plant outage to monitor the real level of water in the reactor via the primary pipe. The main application is to avoid the vortex cavitation of the pump, and to optimize duration time for maintenance of the steam generator for example. Its design makes it easy to install and limit the installation time in the reactor building. Its design is based on the round-trip time of an ultrasonic wave which is refl ected from the surface of the liquid. It can be easily and quickly installed without any modifi cation of the plant. The high performance of the ultrasonic measurement channel is ensured by the measurement stability and immunity to disturbances of the liquid surface.