Sensitivity study of a new model for assessing time-dependent risk in ageing NPP

The nuclear power plants risk reduction by application of the probabilistic safety assessment is one of the main focuses of the nuclear safety today. The goal is the reduction of the unavailability of the nuclear power plants safety systems. On the other hand, the world NPP fleet is ageing fast. Equipment ageing has gradually become a major concern in the nuclear industry since the number of safety systems components, that are approaching their wear-out stage, is rising fast. A previously developed model for assessing time-dependent unavailability of ageing safety equipment is briefly presented and discussed herein. One of the essential features of the model is that it simultaneously considers the effects of performing surveillance testing as well as preventive maintenance, corrective maintenance and overhaul. Also, the ageing-implicated adverse effects on component availability are being explicitly considered as an integral part of this time-dependent unavailability model. Subsequently, the model can be coupled to commercial software for systemand plant-level modelling. This paper is aimed towards performing sensitivity analysis of the developed model. A component level resolution is selected as the basis for performing the analysis. Investigation of the influence of different component-relevant input parameters on the calculated equipment unavailability is the goal of the analysis. The dependency of the calculated component unavailability on the corresponding surveillance test interval is of a particular interest. The results are presented and discussed.