Quantitative and Qualitative Reliability Assessment of Reparable Electrical Power Supply Systems using Fault Tree Method and Importance Factors

Abstract

For safety purpose, the electrical power supply system of a Nuclear Power Plants NPP must be reliable in all operation modes. The 1E safety class of NPP’s load can be supplied from various independent electrical sources namely: main power system (electrical grid), generator (house load operation), auxiliary power system and emergency power system (e.g. Diesel generator). In this paper, the quantitative and qualitative reliability assessment of electrical power supply system model of an NPP are performed using fault tree analysis (FTA) method and importance factors. The quantitative reliability assessment is based on the calculation of the failure probability obtained by the fault tree. Furthermore, the following importance factors: Fussel-Vesely (FV), Risk Reduction Worth (RRW) and Risk Achievement Worth (RAW) are used to identify the most important components in the system. In addition, the Minimal Cut Set (MCS) method is used as a tool for qualitative reliability assessment. The obtained results provide an insight on the reliability level of the power supply system as well as its important components. In practice, the electrical systems reliability can be improved using the appropriate techniques such as redundancy, diversity, inspection time optimization and so on.