**3.2. Hazard combinations screening**

For a comprehensive Hazards probabilistic risk assessment according to the state-of-the-art, hazard combinations have to be included in the analyses. Since the number of hazards in *Lgen* and the resulting combinations is much too high to consider all combinations from the beginning in a generic manner, the screening of the hazard combinations starts from those hazards (*L***total**,**individual**) which cannot be qualitatively excluded at the nuclear power plant site being analyzed, and this in turn significantly reduces the hazards' screening effort.

The longer duration external flooding hazards B3 and B4 resulting from snow melt or extreme precipitation can induce internal flooding hazards I2. All those external hydrological hazards with flooding potential not screened out individually besides B6a can in principle

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• External flooding hazards from various origins and with differing duration B2, B3, and B4 can occur as correlated events from the same root cause or together with the meteorological hazard C1 (precipitation) correlated, for example, by extreme weather conditions. In addition, flash flood B2 and heavy rainwater flooding B4 can occur correlated to F1 (subaerial

**Figure 2.** Result of the qualitative screening for combinations of those hydrological hazards not screened out at the site

result in biological flotsam at the reference site.

slope instability).

being investigated with other hazards.

In order to limit the analytical effort, at least for related hazards in a first step only first order combinations are qualitatively as well as quantitatively screened. For those combinations not screened out, potential second order combinations are identified and screened out. If there are still combinations remaining after screening, this process is repeated for the next order of combinations as long as there are combinations not yet screened out.
