Regional Basic Professional Training Course in Korea

Regional Basic Professional Training Course (BPTC) on Nuclear Safety
in the frequency of high magnitude seismic events.
Accident delineation
The identification of accident leading to core damage is undertaken by the use of event
trees that are developed for each initiating event. The questions asked at the top of an
event tree usually concern the success or failure of front line systems that may be used to
prevent core damage. The accident initiation and the system success/failure questions are
diagrammed sequentially in the order that they affect the course of the accident. The tree
branches at points where the systems either succeed on in their functions.
The failure of the system is determined from a logical model called a fault tree, which
express the system’s failure probability as a function of the failure probabilities of its
components and supporting systems. For a particular event called the top event(usually a
failure of a system to perform some extended function), a fault tree is used to identify the
combination of base events (usually component failures or operator errors) that could
lead to the top event. Due to the fact that the safety systems are usually redundant, it is
important to take into account common mode failures that are simultaneous failures of
multiple components due to some underlying common cause such as design errors or
environmental factors.
Human factor analyses are incorporatedinto current state of the art PSA studies:
unavailability of components due to maintenance errors; and failure of operators to
follow written procedures under normal operating and accident conditions.
9.1.5. PSA level 2 [9.5-6]
9.1.5.1. PSA level 2 objectives
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