The largest nuclear accident in the history of the nuclear fleet. Reconstruction of events and analysis of the accident consequences to assess the risks and hazards of small nuclear power facilities

The article presents the results of studies related to the reconstruction and assessment of the radiation conse-quences of the largest nuclear accident in the history of the USSR/Russia and the world's nuclear fleets, cor-responding to the fifth (5th) hazard level according to the International INES scale, which occurred on a nuclear submarine in 1985 in Chazhma Bay. The event recovery methodology includes the collection, generalization, analysis of disparate data, modeling and retrospective forecasting using modern methods in order to restore the events and assess the consequences at the normative and background levels. The refined data of the release of dose-forming radionuclides from the submarine reactor into the surface layer of the atmosphere are given, the trajectory of the radioactive cloud transfer, the trace formation and the fallout of radioactive substances up to 400 km from the accident site are determined. The authors have estimated the time of contact with the moving cloud, the density of the fallout of radionuclides; the equivalent dose rate, the dose load from the cloud and the dose during long-term residence of the population in the contaminated area. External and internal exposure they determined by individual and cumulative exposure to 131-135I, 137Cs, 90Sr and 60Co. They considered the terri-tories of the shipyard where the accident occurred and the adjacent areas - the Dunai Peninsula, Ussuri Bay, Primorskii Krai and the border province of Heilongjiang (China). It was extremely important to analyze the damaging factors initiated by an uncontrolled self-sustaining chain reaction at the early and subsequent stages of the nuclear accident on the power installation, carrier, support infrastructure, settlements and the environment for a more complete understanding of the existing risks and dangers of using new nuclear power facilities - mobile small nuclear power stations.