Abstract:

The nuclear catastrophe, on top of the apocalyptic event in Japan, simultaneously affected six "old", scarcely back-fitted boiling water reactors to different degrees, triggered by an unprecedented earthquake and tsunami both exceeding design limits of the plants. After tackling key mechanisms and processes during the early phase of the disastrous event chain(s) first answers will be given in the presentation to the following questions:

• Have the basic safety principle ("defense-in-depth") and basic safety concept (deterministically selected design basis accidents and probabilistically treated beyond design basis accidents, combined with internal and external accident management measures) been put in question or even failed?

• Have the (residual) risk and related uncertainties been inadequately estimated or clearly underestimated? Do probabilistically calculated numbers (e.g., core damage frequencies) contradict experience?

• What are the lessons-learned with regard to risk awareness and emergency preparedness, decision making under extreme conditions and other organizational and socio-political matters? Do international agreements need to be revisited? Finally, overarching issues such as the relevance of "Fukushima" for the safety assessment of nuclear reactors and the tolerability of use of nuclear energy in general, the singularity of nuclear risks and the overruling power of concerns/perception in case of an accident will be addressed.

The talk can be attended without previous notice.