**Abstract**

The safety of nuclear power plants with respect of natural hazards can be ensured by adequate characterization of hazards and proven design solutions to cope with natural hazard effects. Design and severe accident management require characterization of very rare event. The events identified for the design basis and for the safety analysis are with annual probability 10<sup>−</sup><sup>4</sup> –10<sup>−</sup><sup>5</sup> and 10<sup>−</sup><sup>7</sup> , respectively. In this chapter, a brief insight into the actual issues of natural hazard safety of nuclear power plants and related scientific challenges is provided. The state of the art of ensuring safety of nuclear power plants with respect to natural hazard is briefly presented with focus on the preparedness to the accident sequences caused by rare natural phenomena. The safety relevance of different hazards and vulnerability of NPPs to different hazards are discussed. Specific attention is made to the non-predictable phenomena with sudden devastating effects like earthquakes and fault ruptures. Post-event conditions that affect the on-site and off-site accident management activities are also considered. The "specific-to-nuclear" aspects of the characterization of hazards are discussed. This is a great challenge for the sciences dealing with hazard characterization. The possibility for ensuring nuclear safety is demonstrated presenting cases when the nuclear power plants survived severe natural phenomena.

**Keywords:** nuclear power plant, safety, design, design basis, severe accident, operational experience
