Multi-Objective Optimization of Testing and Maintenance in Nuclear Power Plants Considering Component Ageing

The study presented herein is aimed towards improvement of nuclear power plant safety by utilizing the probabilistic safety assessment methodology. A new time-dependent unavailability model of ageing safety equipment within the nuclear industry is proposed. Equipment ageing along with effects of corrective maintenance and preventive maintenance are modelled as an integral part of the new time-dependent unavailability model. The development and coding of the new model is seen as the first highlight of the thesis. Subsequently, a platform for multi-objective multi-dimensional optimization of the surveillance requirements of selected safety equipment is developed and coded-the second highlight. The platform accommodates options for optimization of wide range of surveillance requirements-related variables. The goal herein is optimization of the surveillance test interval for selected equipment. Moreover, the multi-objective optimization is being performed on plant level, being the third highlight of this thesis. The core damage frequency is the selected plant risk measure for the analysis herein and the first objective function. Test and maintenance costs and the associated incurred dose, modelled through the exposure time, are considered as the second and third objective functions in the process of multi-objective optimization of selected equipment surveillance test interval. The obtained results are discussed and the importance of the inclusion of safety equipment ageing in the plant longterm probabilistic safety assessment is recognized. The results of the optimization show that the risk-informed surveillance test intervals designated as optimal within this thesis are different from the deterministically-determined ones.