Fuel Assembly Monitoring System (FAMOS) was developed to set up a NDA method for the characterization of light water reactor fuel assemblies. The applied active/passive monitoring system made total characterization of fuel assemblies possible, without any previous knowledge of fuel assembly data or reactor operating data. FAMOS III measurement system was especially developed for the determination of fuel assembly burn-up which is suitable for the control of the acceptance criteria in the so-called La Hague measurements.