Probabilistic risk analysis of external events impact on the safety important systems of Ignalina nuclear power plant (NPP) is performed. At first, the methodology was established for screening out external events, which impact on Ignalina NPP safety is not significant. In order to estimate probabilities of external events occurrences the statistical data were collected, mathematical models were constructed and probabilities of these events occurrences were determined. For risk estimation, the following external events were studied: forest fires, external floods, aircraft crash, seismic events, extreme winds, fall of frequency in electricity network and loss of an external electricity supply. The aircraft crash event was modeled and analyzed in more detail. The crash probability estimation model is improved considering uncertain data. The aircraft crash probability on the territory of the Ignalina NPP with the radius r is expressed by the derived analytical formula. This formula is used to calculate the aircraft crash probability applying the most recent statistical data. The aircraft crash dependencies upon the amount of flights and crashes in the different radius territories were analyzed. Relationship of non-flying zone around Ignalina NPP and aircraft crash frequency was investigated. As a part of the initial conditions and parameters of aircraft crash model are not well-known or have different values for various types of aircrafts, the sensitivity analysis was performed for the model. This analysis determines the parameters that have the greatest influence on the model results. Conclusions about the importance of the parameters and sensitivity of the results are obtained using a sensitivity measures of the model under analysis.

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