the paper concerns the creation of the analysis of the unplanned shutdowns and estimation of reliability. This analysis is based on the document of all unplanned shutdowns for both units in the Czech nuclear power plant Temelin. This investigation is mainly focused on failures of some components, which have significant impact of the decrease of electrical power during operation of the power plant. Thanks to this analysis, we are able to perform the estimation of reliability of the power plant. The estimation is created in Dymola software and gives us certain information of the failures of key components, which must be solved in the future. The determination of the key components is very important step for the modeling of reliability of this power plant.