Changes in Radiation Exposure Rate of Fish of the Cooling Pond of the Chornobyl NPS and Lake Azbuchyn after Water Level Lowering

Changes in the absorbed dose rate of external and internal exposure of the representatives of fish fauna of the cooling pond of the Chornobyl NPS and Lake Azbuchyn after the interruption of water supply into the cooling pond at the end of 2014 were investigated in 2014-2021. Changes in hydrological regime resulted in the decrease in water level in the cooling pond by 6.5-7.0 m, whereas in Lake Azbuchyn - by 2.5-3.0 m. In this case, 90Sr concentration activity in the water and biota increased. It has been found that in 2021 dose load from the incorporated 90Sr on fish of the cooling pond increased on the average by a factor of 4.5, whereas in Lake Azbuchyn - by a factor of 7.5 as compared to previous period (prior to a decrease in water level). The external dose rate for fish of the cooling pond remained almost unchanged, whereas in Lake Azbuchyn it increased as a result of replacing littoral and sub-littoral zones of the lake with the sections of the bottom characterized by an essentially higher level of radio-nuclide contamination.