Lifetime evaluation of Bohunice NPP components

Lifetime evaluation of selected components of the primary and secondary system have been taken into consideration for many years in Bohunice NPP. For each particular component and its parts, determination of failure mechanisms can be sorted based on theoretical analysis of operational conditions and operational feedback from the present experience. Within the scope of NPP lifetime assessment, the full calculation and failure analysis is performed for these parts and components. Operational experience shows that interaction of particular damage mechanisms occurs. Based on worldwide NPP operating experience it can be stated that the fatigue damage is the determining degradation mechanism for assessed components. Fatigue damage is affected by the following mechanism influence: -operating pressure level fluctuation (fatigue damage is affected by maximum (minimum) value of transitions, not the effect performance (pressure increase/decrease deformation effects by non-stationary thermal fields which occurs by unexpected fluid temperature changes. In addition, both of the mechanisms perform in existing residual stress; additional load dilations and dynamic effects environment. (authors)