Several recent astonishing events at nuclear plants are recalled in this paper. These events are of the type of ‘possible but not credible’ events. The Fukushima tsunami (2011) is the most recent and catastrophic one. A discussion is made on the present (very conservative) safety philosophy and on the reasons why, notwithstanding it, catastrophe (uncontained core melts) may happen at nuclear plants. The importance of ‘chance’ besides ‘probability’ is described. Possible future events of this kind are briefly discussed. Very exceptional preventive plant provisions for existing installations are described as examples of extreme remedial actions. A need for a change of ‘mindset’ in the nuclear industry is illustrated. An example of a possible economic solution to the problem of cost is also mentioned.
Keywords: black swan, chance, Davis Besse vessel, defence in depth, Fukushima, Kashiwazaki-Kariva earthquake, nuclear safety, probabilistic approach, September 2001, sixth level of defence in depth, stuxnet