Radiation risk and level 3 probability safety assessment of nuclear facilities

The paper considers the current state in the field of level 3 probabilistic safety assessment (PSA Level 3) of nuclear facilities. The issues on rationing individual and social risks in various indus-tries and practice of legislative control in some countries are examined. Some attention is paid to the identification of acceptable risk level and features of radiation risk perception. The paper ad-dresses possibilities of use of PSA Level 3 methodology for radiation risk assessment. We pro-pose a practical approach to quantify specific features that may affect individual, collective and social radiation-associated cancer risks at the initial stage of severe radiation accidents at nuclear power plants. PSA Level 3 capacities are demonstrated on the example of individual and social radiation risks assessment at the initial stage of a severe accident at a model nuclear power plant. When performing numerical simulations of the consequences of the accident of such type with the program developed at the Nuclear Safety Institute of the Russian Academy of Sciences, the nuclide composition of the emission is similar to one of the emissions during the Fukushima accident, and the distribution of population density and weather conditions correspond to real values in Fukushima Prefecture. We evaluated the effectiveness of various options for protective countermeasures based on the results of risk assessments. We have shown that the PSA Level 3 methodology allows us to obtain information about the risks associated with accidents at nuclear facilities in the form of standard risk-informative safety management methods. This will strength-en scientific and technical support for the processes of interaction with experts, decision-makers, the media and the public in making a wide range of decisions in the event of a threat, occurrence and elimination of the consequences of an emergency with a radiation factor.