FACTORS LIMITING LIFE TIME OF NUCLEAR POWER PLANTS WITH PRESSURIZED-WATER REACTORS

The aim of the thesis is to analyze the state of preparedness of nuclear power plants (NPP) for long term operation (LTO) based on the IAEA SALTO (Safety Aspects of Long Term Operation) peer review service, analysis of the most significant failures, accidents and operational experience with type reactors PWR/VVER focusing on cases caused by equipment ageing and identification of major structures and components limiting life time of PWR/VVER-type nuclear power plants, and possible measures to ensure their required service life. Based on the results of the IAEA SALTO peer review service, an analysis of the main deficiencies and measures of NPPs in preparation for a safe LTO was performed, focusing on topics whose deeper knowledge is important for the future more precise determination of technical factors limiting the lifetime of NPPs. The main deficiencies and measures in the preparatory phase for LTO and the most important technical measures are summarized in chapter 4.5. The main deficiencies and the most important technical corrective measures in the area of ageing management of structures and components are discussed separately. The history of major failures and operational experience of nuclear power plants with PWR/VVER reactors from the point of view of ageing of structures and components is analyzed in chapter 6.2. The result is a statistic analysis of ageing-related events, an overview of the most significant PWR/VVER reactor failures with an impact on their service life, a statistical overview and discussion of the most important degradation mechanisms, and other important findings from the history of major failures and operational experience. Chapter 6.3 analyzes factors limiting the operation of nuclear power plants with PWR/VVER reactors with focus on structures and components potentially limiting the life of PWR/VVER reactors and possible measures to ensure their required life. In conclusion, the main reasons of permanent shut down of NPPs (actual and potential) for 40, 60 and 80 years of operation and the measures to ensure their required life are summarized