Development of 3+ level probabilistic safety assessment method for severe accidents in nuclear power plants and application for akkuyu nuclear power plant

The aim of this thesis was to develop 3+ Level Probabilistic Safety Analysis (PSA) Method for nuclear power plants and apply the developed method to Akkuyu Nuclear Power Plant (NPP) which will be established in Mersin, Turkey. First of all, a literature survey was performed to understand the basic principles of nuclear safety, emergency management approaches, international standards of urgent and early protective actions and mass evacuation practices. In order to provide a comprehensive understanding for PSA, 2nd and 3rd Level PSA applications were performed for Akkuyu NPP. For Level 2 PSA application, a simplified containment event tree was prepared and modeled with SAPHIRE code. For Level 3 PSA application, atmospheric distribution calculations were performed using PAVAN and dose distributions that may reach to the public in case of a severe accident, were estimated using RASCAL. In addition, dose distributions for normal operational conditions were estimated with NRCDOSE as an exercise. The data obtained were used to verify the data presented in Akkuyu NPP Environmental Impact Assessment Report. Finally, Level 3+ PSA Methodology was developed. It is based on a probabilistic approach to delaying evacuation due to disruptions in off-site emergency management processes. According to related regulations in Turkey, in the case of severe accidents in NPP, people in the Urgent and Early Protective Action Planning Zone (UPZ) will be evacuated. In this study, an evacuation model for UPZ was developed and analyzed using the fault tree method. Moreover, uncertainty analyzes were performed to determine the confidence intervals of the results. A risk matrix was developed by evaluating different combinations of disruptions that may occur independently of each other and their possible consequences. Lastly, developed Level 3+ PSA Methodology was applied for Akkuyu NPP. As a result, it is concluded that the developed method is a method that can be used to base plans on numerical data and analysis, to make the necessary arrangements in the plans by anticipating possible problems and to develop morerealistic emergency management approaches in this way.