**Author details**

great importance and has to take into account the specific boundary conditions of the site and facility under consideration. The evaluation and (re)modification of planning and technical criteria will potentially influence the scope and placement of future projects, in particular adjustments in construction techniques and systems employed to better reflect the demands

Therefore, a reliable and meaningful assessment of hazards and combination of hazards is important, based on comprehensive, traceable qualitative and quantitative screening analyses

The extensions and enhancements of the methods for systematically considering natural external hazards in risk assessment have been successfully validated as far as applicable for a selected German nuclear power plant site. In this context, the potential for further iterative improvements has been recognized. Moreover, advances in the methodological approach for those hazards, for which according to the site characteristics of the reference plant the methods could not been applied, seem to be necessary. The methodology will be completed in the near future in order to address the entity of hazards of the different hazard classes identified in [2] and the corresponding hazard combinations and to provide a procedure for

In order to limit the analytical efforts and to prevent mistakes as much as possible in the screening of the huge amount of hazards and hazard combinations, the development of an analytical tool for supporting the screening of hazards has already been started. By means of a scroll down menu based on qualitative arguments formulated as questions to be answered by yes or no, such as "Is the site a tidal site?", various hazards can be directly screened out qualitatively. The menu offers to provide inputs on a generic or plant design-specific basis. The tool will offer, in a second step, to also semi-automatically perform the quantitative screening by selecting from a predefined menu of quantitative criteria, such as an occurrence frequency threshold value and apply these to those hazards or hazard combinations not qualitatively screened out. The tool will be as far as possible independent of database software products to enable any possible user to apply it without software restrictions. In addition, the output will

For the detailed analyses in the frame of hazard risk assessment it is intended to advance the topological modeling methods provided by GRS in the analytical tool pyRiskRobot [5] for an as far as practicable automated integration of event combinations within particular natural

The authors would like to thank the German Federal Ministry for the Environment, Nature Conservation and Nuclear Safety (BMU) and the German Federal Ministry for Economic Affairs and Energy (BMWi) for funding and supporting the work presented in this chapter.

of potentially more variable and extreme climatic conditions.

as a prerequisite of detailed (probabilistic) safety assessments.

be documented in simple, written text form as well as graphically.

hazards in the probabilistic plant models.

**Acknowledgements**

assessing their risk.

142 Probabilistic Modeling in System Engineering

Berg Heinz-Peter<sup>1</sup> \* and Roewekamp Marina2

