Tunc Aldemir

Abstract:

Introduced in the 70s, the traditional approach to probabilistic risk assessment (PRA) of a nuclear reactor operation is the event-tree/fault-tree approach (ET/FT). The ET/FT approach only qualitatively accounts for the timing of events through their ordering. A new generation of methodologies is starting to receive attention for the nuclear reactor PRA. Often referred to as dynamic PRA (DPRA) methodologies¹, these methodologies explicitly account for the time element in the probabilistic system evolution and heavily incorporate plant analysis tools (e.g., RELAP², MELCOR³, MAAP5⁴) to model possible dependencies among failure events that may arise from hardware/software/firmware/process/ human interactions. DPRA methodologies are also capable of quantifying the effects of phenomenological variability and model uncertainties on the consequences of upset conditions. They can be particularly useful for the PRA modeling of passive safety systems, including representation of aging effects. An overview of the DPRA methodologies is presented, including system level applicable computational tools.

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