The aim of the study was to conduct a radioecological assessment of the Leningrad NPP marine cooling reservoir – Koporye Bay of the Gulf of Finland. According to the international basic safety standards, accepted at the IAEA General Conference, this issue is of particular relevance due to the need to justify protection from technogenic radiation exposure both to humans and the environment. The assessment was based on the long-term radioecological monitoring data (1973–2019) within the Leningrad NPP observation area: radionuclides concentration in seawater, bottom sediments, and hydrobionts. The reference levels of radionuclides content in seawater and bottom sediments were used as indicators of the radiation state of the marine environment; their calculation procedure is defined in the Recommendations R 52.18.852-2016 and R 52.18.873-2018, issued by the Federal Service for Hydrometeorology and Environmental Monitoring (the Ministry of Natural Resources and Environment of the Russian Federation). These recommendations, developed by RPA “Typhoon” specialists, contain a methodology for assessing the radioecological state of the marine environment by the level of radionuclides activity, based on the principles, ensuring the maintenance of favorable environment, safety of marine hydrobionts, and radiation protection of humans. In the presence of various radionuclides in the marine environment, the sum of technogenic radionuclide activity ratios in seawater (bottom sediments) to the corresponding reference levels shall be below 1. According to monitoring data in the early period of NPP operation (1973–1985), a wide spectrum of technogenic radionuclides was observed in the marine ecosystem components. Along with 137Cs, significant contributors to the contamination of seawater and bottom sediments were 54Mn and 60Co. In contrast to reference levels for 137Cs, reference levels for 54Mn and 60Co in seawater are determined by an environmental criterion, not a radiation-hygienic one. The presence of technogenic radionuclides in algae was registered at distances, exceeding 10 km from the NPP. Biogenic transfer of corrosion radionuclides (54Mn, 60Co, and 65Zn) by fish into rivers, flowing into the Koporye Bay, was noted. The Chernobyl disaster led to a noticeable increase in the pollution of the Koporye Bay with technogenic radionuclides. In May – December 1986, the sum of technogenic radionuclide activity ratios in seawater to the reference levels exceeded the pre-accidental level by 100 times, and in bottom sediments – by 30 times. In 1986, 137Cs and 134Cs were the main contributors to the marine ecosystem radioactive contamination. Currently, the technogenic radioactivity of seawater and bottom sediments of the Koporye Bay is mainly determined by 137Cs; its level is relatively constant, which indicates the stability of the radioecological situation in the Leningrad NPP marine cooling reservoir.
Assessment of radiation state of marine environment in the Leningrad NPP area according to long-term monitoring data (1973–2019)
