The current level of β-radioactivity in the Zaporizhzhya storage lake

The condition control of the Ukrainian rivers is an integral part of the population safety level. The change of such state can occur for several reasons. The first is the increase of pollution level from the working enterprises. The second – the efficiency reduction of protective constructions which store the radioactive wastes of (tailings dam). And the third – movement changes of water masses which are capable to lift the radio nuclides received earlier from the river bed (for example, the accident on the Chernobil atomic station). Therefore, the aim of the work was the modern level evaluation of b-nuclide pollution (90Sr and 137Cs) in water of Zaporizhzhya storage lake on the largest density points of the industrial enterprises on the Dnieper river in the sequence Kamenskoe – Dnipro – Zaporizhzhya at different seasons of the three years. Within 2014–2016 we carried out investigations of Zaporizhzhya storage lake b-radiation level for different seasons. The sampling was made at depth from 1,0 m to 1,5 m on six points. These points corresponded to the coast ones of Zaporizhzhya storage lake which are bound up with the industrial enterprises wastes of Kamenskoe and Dnipro or the small rivers fall points into the Dnieper River. The sampling points were: a coastal area 200 m below the Dneprodzerzhinsky dam, the river port, Starie Kodaki, the mouth of the river Mokra Sura, village Vojskove and Fyodorivka. The water mass of 5 kg was taken from these points and poured into the glass bottles. For radioactive pollution level determination in river's points we used two samples by 60 dm3 volume or caesium (137Cs) and strontium (90Sr) definition. 90Sr activity in water was determined radiochemically by oxalates sedimentation method with the subsequent measurement on the UMF-1500 installation. The isotope 137Cs was besieged by potassium ferrocyanide from a muriatic solution with the subsequent measurement on a small background installation The general β-radioactivity (Bq/l) was determined in the samples on the radiometer-«Beta» with the help of the SBT-13 counter by direct measurement method of samples. We showed that the levels of general β-activity water or at the investigated selection points of Zaporizhzhya storage lake fluctuated on average from 0,14 to 0,24 Bq/l, the content of 90Sr radionuclides in water is from 0,029 to 0,055 Bq/l, for 137Cs – is 0,042 Bq/l. In autumn β-activity level in Zaporozhzhya storage lake water decreased in comparison with spring – summer seasons. It is typical for storage lakes with a superficial filling which is followed by a relative increase of radioactive materials in water from deeply lying breeds bottom. For 90Sr, the effect of fluctuations in its concentration is observed, depending on the presence of industrial centers on the way of water movement along the Zaporizhzhya Reservoir. This effect not marked for 137Cs. An assessment of the level of water pollution has shown that in our time the indicators of the studied isotopes do not exceed the permissible levels of radioactivity stipulated by the norms of radiation safety of Ukraine from 1997.