It is well known that in the Hungarian PWR-type nuclear power plant Paks the radioactive waste waters are collected in common tanks. These water streams contain radioactive isotopes in ultra-low concentration and inactive compounds as major components (borate 1.7 g/dm3, sodium-nitrate 0.4 g/dm3, sodium-hydroxide 0.16 g/dm3, and oxalate 0.25 g/dm3). These low salinity solutions were evaporated by adding sodium-hydroxide, untill 400 g/dm3 salt content is reached. There is about 6000 m3 concentrated evaporator bottom residues in the tanks of the PWR. We have developed a complex technology for the selective separation of the long live radionuclides and for the partial recycle of boric acid from this evaporator bottom residue. A wastewater treatment system has been developed by using a cesium selective inorganic ion exchanger. The selective separation of cesium (137Cs, 134Cs) from high salt concentration and strongly alkaline evaporator bottom residue in Paks Nuclear Power Plant has a volume reduction factor about 1800–3500 at the value of the decontamination factor DF≫100, for the samples of four tanks of the Hungarian PWR Paks.