Developing a robust design basis for critical infrastructures against extreme external floods

摘要

Extreme floods represent a major threat to human civilization. Insurance losses caused by floods have a large contribution to risk from natural events. Big river floods in Europe (Germany 2002, Middle Europe 2013) have challenged the emergency preparedness of governments and caused regional critical situations including human losses. The occurrence of extreme external floods has frequently surprised the designers and operators of critical infrastructures and lifelines. After the Fukushima disaster nuclear authorities recognized that extreme floods may have significant consequences on the safety of nuclear power plants. Therefore both IAEA as well as WENRA required the development of robust methods of hazard analysis for new plants as well as for the safety review of existing plants to avoid cliff edge effects. The paper presents the application of a recently developed method of hazard assessment for extreme natural events for the case of extreme external floods. The method allows for the consideration of unexpected extreme events ("black swan" events) of natural origin delivering the basis of a robust design of safety features. The hazard assessment method is making use of some general properties of heavy tail distributions and theory of records. The new method is combined with traditional statistical hazard assessment methods in a procedure for the development of a robust design basis for extreme river flood protection for critical infrastructures. The application of the method is demonstrated on the example of developing the design basis for a nuclear power plant against extreme external floods. The hazard assessment results are compared with the results of hazard assessment using conventional probabilistic and modelling hazard analysis methods. The risk and design implications are discussed.