Migration of Technogenic Radionuclides in the Cooling Pool of the Beloyarsk NPP and the Pyshma River

Data on contents of ¹³⁷Cs, ⁹⁰Sr, and ³H in surface water and their accumulation in bottom sediments and floodplain soils of the Pyshma River at a distance of up to 50 km from the Beloyarsk Reservoir on the 2024 are presented. An assessment of the annual discharges of artificial radioisotopes in the surveyed river section, including discharges from the Beloyarsk Reservoir, was executed. Using the annual drains balance calculation method, the main source of technogenic radionuclides entering the Pyshma River was identified as the Olkhovka swamp-river system, where average annual discharge of ¹³⁷Cs and ⁹⁰Sr from the Olkhovka River is 1.6 times higher than from the Beloyarsk Reservoir. The integrated stocks of ¹³⁷Cs in the bottom sediments and floodplain soils of the Pyshma River amounted to 8.63 GBq, which is 8.4 times greater than the stocks of ⁹⁰Sr and 4.3 times higher than the annual ¹³⁷Cs discharge at the endpoint of the surveyed river section. It was shown that ¹³⁷Cs entering the Pyshma River is sorbed by components of the river ecosystem, maintaining its reserves at a stable level. The annual ⁹⁰Sr discharge through the final river cross-section of the surveyed segment of the Pyshma River is 7.1 times greater than its integral reserves in floodplain soils and bottom sediments; therefore, this radionuclide, which has a higher migration capacity, is carried away with the water flow beyond the surveyed section of the river. It was shown that the uncontrolled removal of technogenic radionuclides from the Olkhovskoye swamp into the open hydrographic network creates a potential threat of radiation safety for downstream sections of the Pyshma river, which is part of the Ob-Irtysh river system, determines the need for systematic radioecological monitoring of aquatic ecosystems affected by the Beloyarsk NPP.

⁹⁰Sr, ¹³⁷Cs, tritium, water, migration, annual runoff, bottom sediments, floodplain soils, integral stocks, Beloyarsk NPP, Olkhovka swamp-river system (OBRS), Pyshma River