**5. Conclusions and outlook**

After identification of the potential hazard induced initiating events, these have also to be screened with respect to their significance for the facility. In this context, it is important to analyze within that screening step if and how far the identified initiating events from hazards do occur quasi simultaneously and need to be modeled as common cause initiat-

• In a further step, the potential unavailability of structure, systems, and components depending on the impact by hazards needs further extension of the risk analysis model of the facility requiring for each hazard and hazard combination not screened out to identify those items which may functionally failing (so-called hazard equipment lists *HEL* as defined in [3]) and the corresponding failure dependencies (so-called hazards dependency list *HDL*, details see [3]). Again, for limiting the analytical effort, a reduction of these lists according to their risk significance by qualitative arguments and quantitative criteria is

As provided in more detail in [1, 3], the hazard equipment list for a single hazard *Hk*

EL = {SSC<sup>1</sup>

In order to quantify the failure probabilities of the remaining structures, systems, and compo-

nical reliability of systems and components and other factors affecting the hazard-induced scenarios like human reliability in case of actions (e.g., for the remaining hydrological hazards B2, B3, and B4 and their combinations, temporary flood protection measures) have to be taken

In a further analytical step, the dependencies among the failure characteristics of the vulnerable structures, systems, and components need to be investigated. Each dependency in this

ard dependency lists need to be generated based on the corresponding parameters to be estimated and are used for the qualitative plant model extension. For adequately modeling the dependencies between the structures, systems, and components and/or the hazards impact, the fault trees of the analytical risk analysis model need to be modified and multiplied for the different hazards to be considered. In addition, new elements of the fault trees have to be specified (see also [5]) within the database representing a probabilistic model of a plant

A schematic overview of the approach for the plant model extension by hazards is given in

*}Hk* is characterized by a triple *Dk = {Ak*

the set of dependent structures, systems, and components *Sk*

, …,SSCm}Hk

.

*,Sk ,ck*

for the dependency strength. The hazard equipment lists and haz-

(e.g., water level as cause for a flooding hazard-induced dependency) *Ak*

information from the facility being analyzed such as tech-

the entire number *j* of structures, systems, and components *SSCj*

and for which their failure contributes to the risk induced by *Hk*

covers

,

identified to be vulnerable to

*}* of parameters, which include

, the common characteristics of

*:*

ing events.

140 Probabilistic Modeling in System Engineering

important.

H<sup>k</sup>

nents vulnerable to the hazard *Hk*,

*,…, Dn*

in a predefined period to prevent damage.

*Hk*

list *Hk*

system.

**Figure 4**.

*DL = {D1*

the elements of *Sk*

and a correlation factor *ck*

The systematic assessment of natural hazards including their contribution to risk and their consequences such as physical and operational impacts on critical infrastructures is still of 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 of potentially more variable and extreme climatic conditions.

**Author details**

Berg Heinz-Peter<sup>1</sup>

**References**

2018 (in German)

Köln, Germany; June 2017 (in German)

\* and Roewekamp Marina2

American Nuclear Society, LaGrange Park, IL, USA; 2017

1 Bundesamt für kerntechnische Entsorgungssicherheit (BfE), Salzgitter, Germany 2 Gesellschaft für Anlagen-und Reaktorsicherheit (GRS) gGmbH, Köln, Germany

[1] Roewekamp M, Sperbeck S, Gaenssmantel G. Screening approach for systematically considering hazards and hazards combinations in PRA for a nuclear power plant site. In: Proceedings of ANS PSA 2017 International Topical Meeting on Probabilistic Safety Assessment and Analysis, September 24-28, 2017; Pittsburgh, PA, USA: On CD-ROM,

Natural Hazards: Systematic Assessment of Their Contribution to Risk and Their Consequences

http://dx.doi.org/10.5772/intechopen.76503

143

[2] Sperbeck S, et al. Analysehilfsmittel zur Bereitstellung von Informationen und Daten zur systematischen Durchführung von PSA für übergreifende Einwirkungen, GRS-A-3914, Gesellschaft für Anlagen- und Reaktorsicherheit (GRS) gGmbH, Köln, Germany; April

[3] Roewekamp M, et al. Methoden zur Bestimmung des standort- und anlagen-spezifischen Risikos eines Kernkraftwerks durch übergreifende Einwirkungen (Estimation of the Site and Plant Specific Risk of a Nuclear Power Plant from Hazards), Technical Report, GRS-A-3888, Gesellschaft für Anlagen- und Reaktorsicherheit (GRS) gGmbH,

[4] Facharbeitskreis (FAK) Probabilistische Sicherheitsanalyse für Kernkraftwerke. Methoden zur probabilistischen Sicherheitsanalyse für Kernkraftwerke, Stand: August 2005, BfS-SCHR-37/05, Bundesamt für Strahlenschutz (BfS), Salzgitter, Germany; October

2005 (in German). http://doris.bfs.de/jspui/handle/urn:nbn:de:0221-201011243824

Köln, Germany; March 2017 (in German). http://www.grs.de/publikation/grs-454

[5] Berner N, Herb J. Weiterentwicklung der Methodik zur automatisierten Integration übergreifender Einwirkungen in PSA-Modelle der Stufe 1, Technischer Fachbericht, GRS-454, ISBN 978-3-946607-36-6, Gesellschaft für Anlagen- und Reaktorsicherheit (GRS) gGmbH,

\*Address all correspondence to: bergheinzpeter@gmail.com

Therefore, a reliable and meaningful assessment of hazards and combination of hazards is important, based on comprehensive, traceable qualitative and quantitative screening analyses as a prerequisite of detailed (probabilistic) safety assessments.

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 assessing their risk.

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

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 hazards in the probabilistic plant models.
