Lightning- and overvoltage protection of nuclear power plants. Verification of the sufficient safety of I and C installations even for lightning strikes with extreme parameters

Even for extreme weather incidents NPPs are forced to ensure frequencies of non-tolerable status of less than 10^-4/a. This is also valid for the effects of lightning strikes. The existing verification for lightning and overvoltage protection of an NPP in Germany is a deterministic one: for a defined event its sufficient control must be the proven. In this study the approach for a verification regarding the safety related I and C systems of NPP leading to the required frequency target value and the steps necessary are presented. The assessment is summarised with the results and estimation of the frequency value that lightning strikes to the NPP are not certainly controlled, also taking into account additional protection measures.