[en] At present various radiotracer techniques are widely used in many branches of industry and environmental protection. The data obtained during radiotracer experiment allow to determine dynamic characteristic of a facility under investigation as well as to create models of a process occurring inside the apparatus (identification). Radiotracers techniques were successfully used for observation, examination of two cases of facilities: case 1 - the sedimentation basin, case 2 - the flue gas irradiation reactor for NOx and SO2 removal . Case 1 Removal of suspended matter from sewage is one of the stages of sewage purification especially in biological treatment. The process is usually realized in two steps, preliminary sedimentation with biological sludge recirculation and secondary step where the sewage is finally clarified in a big settling basin. For prolongation of its exploitation time the sludge transport and sedimentation mechanism have to be known in detail. Using the tracer method the principal characteristic of a big sedimentation basin, 36000 m3 capacity, were determined. As a tracer for sediment, the La-140 radioisotope firmly adsorbed on the sludge grains, was used. The labeled sediment spatial distribution and bathymetry measurements were measured by mean of specially equipped boat. The residence time distribution of the sewage was also measured using fluorescence as a tracer. The cross section of tank most convenient for location of any sludge removing system was determined. Case 2 Technology for flue gas desulfurization and denitrification with electron beam is in implementation stage. Experimental and theoretical studies have proved that mixing conditions and multistage irradiation is essential for high NOx removal efficiency. Gas flow structure for electron accelerators switched on and switched off was determined. Radiotracer test have been performed on the pilot plant installation (20000 Nm3/h) using Br-82, in form of methyl bromide, as a gas tracer. Paralelly to radiotracer experiments study using computational flow dynamics were performed. Comparison of the results obtained during both methods application is discussed