Regional Basic Professional Training Course in Korea

e indicated according to their specificities.
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9. Probabilistic Safety Analysis
Fault tree analysis is the most common method used for representing the failure logic of
plant systems. It is a deductive failure analysis, that is, an analytical technique whereby
an undesired state of a system is specified, and the system is then analysed in the context
of its environment andoperation to find all credible ways in which the undesired state
could be brought about. Techniques for fault tree construction and quantification can be
found in several references, for example [9.12].
During the fault tree construction, the following points have to be considered with
particular attention:
The boundaries of the system and the limits with other systems, for example the
boundary between a front-line system (safety injection) and its support systems
(electrical supplies, component cooling system, etc.);
The operating modes of the systems, the sub-systems or components (running or
stand
The components failure modes to be considered (active and/or passive failure,
failure to run and/or failure upon demand);
The dependencies between systems or between parts of a system (shared
equipment, shared support system.)
The possible unavailability due to testing, maintenance or human error
The modes of actuation (automatic or manual) and the corresponding signals
An analysis of the operating experience related to the system should be useful.
Other methods
As it will be explained fault tree models can be used for quantification if combined with