Abstract: To determine the quantity of filling and/or loading of the drum of a clarifying centrifuge loaded with radioactive fluids from nuclear power plants, and to determine the burn-off, the gamma rays from the fluids are measured spectroscopically. From the gamma spectrum for one or several nuclides present in said fluids, the gamma line is evaluated to quantitatively determine the filling and/or loading quantity. The amount of the fluid supplied is preferably determined by means of the gamma spectrum of cesium 137/134. The sedimented solid portions, are preferably determined by means of the gamma spectrum of rhodium 106. To measure the burn-off, the gamma radiation of cesium and/or cerium is spectroscopically measured during the initial filling phase of the drum, the measuring phase lying between the beginning of the filling and the beginning of sedimentation.