[en] In accordance with international practice, probabilistic safety analysis (PSA) is an established tool for studying the main risk aspects of the design and operation, to explore the importance of plant modifications and evaluation of events plant experience. Different PSA applications are very useful and flexible tool in addition to deterministic analysis. PSA can be used to optimize the different plant configurations, for justification or basis for modification of limiting conditions for operation (LCO), for planning of maintenance activities, to provide engineering evaluations in decisions making process as well as to control and monitoring the safety. This paper presents the main results and conclusions from the last update of PSA level 1 for 5 and 6 units of ''Kozloduy'' NPP. This study shows the measures of ''modernization program'' 5 and 6 units of ''Kozloduy'' NPP, realized in the period 2001-2007. PSA level 1 is performed by the team of Risk Engineering. This paper shows the main contributors to the risk. The results for internal initiating events, earthquakes, internal flooding and internal fires are given.(author).