Gromov G. Risk-Informed Method for Operational Safety Assessment of Nuclear Power Plants.

The dissertation is intended to resolve, using the risk-informed method, the issue of scientificly justified safety analyses of nuclear installations. The risk-informed method combines the advantages of deterministic and probabilistic safety assessment tools. The method permits to enhance safety of nuclear installations through the concentration of resources on aspects with high risk impacts and increases the effectiveness of nuclear installations owing to decrease in regulatory burden on the licensee and optimal use of material and financial resources. The method proposed for use of information on risks in safety-relevant decision-making integrates probabilistic and deterministic aspects of NPP safety assessments. The method for risk management and optimization in NPP operation has been improved and further developed. The principles for making risk-informed decisions are specified and formalized. An algorithm on using risk assessments for safety analyses of nuclear installations and decision-making criteria are proposed. The algorithm includes elements and stages sufficient to make well-grounded decisions. It is shown how to implement each stage. Probabilistic acceptance criteria are formulated to assess upgrades at NPPs in terms of risk and recommendations on their application are provided. Key definitions and requirements for the scope of risk assessments to be compared with safety criteria are proposed and scientifically grounded. The dissertation results have been implemented at Rivne NPP units 1 and 2 and South Ukraine NPP unit 1 in support of safety justification of upgrading measures. Keywords: nuclear power plant, probabilistic safety analysis, risk-informed decision-making, core damage frequency.