Reliability analysis of emergency core cooling system of VVER-1000 reactor with incorporation of aging effects

The nuclear power plant fleet is aging fast. More than 70 percent of NPPs all over the world have been in operation for more than 25 years. So, explicit consideration of the risk effect of aging is of great importance to NPPs safety and evaluation of the systems reliability. This paper addresses an age-dependent unavailability model in which the effects of maintenance programs and surveillance tests as well as aging of components are incorporated. As a case study, the developed unavailability model is applied on the emergency core cooling system of a VVER-1000 reactor. The results show that the presented approach will have a significant impact on the reliability evaluation of the system and subsequently on the conclusions made with probabilistic safety assessment of NPP.