engleski

Developing a Seismic PSA Model with RiskSpectrum

Seismic probabilistic safety analysis (PSA) is a tool for the assessment of risk to which complex technical systems such as nuclear power plants and their environment are exposed due to earthquakes. It has proven to be very useful tool for identifying weak points in plant’ s response to seismic events and quantifying the risk associated with them. Typically, modelling of accident sequences induced by an earthquake takes as a basis and starting point plant’ s PSA model for internal initiating events. RiskSpectrum® is widely used tool for PSA modelling. It was proven to be very efficient tool for building and handling of PSA models for internal events and hazards (e.g. internal fire and flooding events) of many plants. RiskSpectrum can also be very efficiently used to build a seismic PSA model. In the paper we present the bases of the approach to developing a seismic PSA model with RiskSpectrum PSA. Seismic PSA consists of three major elements: seismic hazard analysis, seismic fragility analysis and a plant's logic model of accident sequences induced by a seismic event. The first two elements are needed to provide an input for quantifying the seismic PSA model and computing seismic risk in terms of, for example, seismically induced reactor core damage frequency. The third element is a seismic PSA model to be built with RiskSpectrum. When seismic PSA model is considered in relation to a PSA model for internal initiating events, there are some differences to be pointed out. In seismic PSA a range of seismic events with various ground motion levels needs to be accounted for. Hazard frequency generally decreases for events with increasing peak ground acceleration. (As with other hazards, the events bearing larger destruction potential are expected to occur less frequently.) Conditional failure probabilities, on the other hand, generally increase with increasing ground acceleration level. Hence, seismic initiators' frequencies and seismic failure probabilities for plant’ s systems, structures and components are strongly co-related as they both depend on the ground acceleration level. This is not so in the internal initiating events PSA, where both initiators and system failures occur randomly and failure probabilities are independent from initiator frequencies (apart from certain functional dependencies which may apply). This dictates a different risk quantification procedure to be applied with the seismic PSA model, as compared to the model for internal initiating events.

PSA; Seismic events; RiskSpectrum

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