Time-dependent unavailability of equipment in an ageing NPP: Sensitivity study of a developed model

•Calculation of time-dependent unavailability of an ageing NPP equipment.•Sensitivity study of a previously developed model.•Influence of the aggregation limiter on component unavailability calculation.

A previously developed model for assessing time-dependent unavailability of ageing safety equipment is briefly presented at the beginning of this paper. One of the essential features of this model is that it simultaneously considers the effects of ageing, testing, preventive and corrective maintenance and overhaul.The main focus of 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 focus is being given to one of the specifics of the developed model – the aggregation approach, i.e. the aggregation limiter that copes with the breach of computational memory.The results show that a relatively low value of the aggregation limiter implicates discrepancies in the shape of the component unavailability as a function of the surveillance test interval in some cases. These discrepancies are being substantially reduced with the increase of the value of the limiter. Consequently, longer computational time and higher memory requirements are directed.