TABLE OF CONTENTS Event trees are inductive logic methods for identifying the various accident sequences which can generate from a single initiating event. The approach is based on the discretization of the real accident evolution in few macroscopic events. The accident sequences which derive are then quantified in terms of their probability of occurrence.
The events delineating the accident sequences are usually characterized in terms of: i) the intervention (or not) of protection systems which are supposed to take action for the mitigation of the accident ( system event tree); ii) the fulfillment (or not) of safety functions ( functional event tree); iii) the occurrence or not of physical phenomena ( phenomenological event tree).
Typically, the functional event trees are an intermediate step to the construction of system event trees: following the accident-initiating event, the safety functions which need to be fulfilled are identified; these will later be substituted by the corresponding safety and protection systems.
The system event trees are used to identify the accident sequences developing within the plant and involving the protection and safety systems.
The phenomenological event trees describe the accident phenomenological evolution outside the plant (fire, contaminant dispersion, etc.).
In the following, we shall give only the basic principles of the technique. The interested reader is invited to look at the specialized literature for further details, e.g. [1], [2], [3], [4], [5], [6], [7], [8], from which most of the material herein contained has been taken.
An event tree...
