Regional Basic Professional Training Course in Korea

Regional Basic Professional Training Course (BPTC) on Nuclear Safety
with another one that can lead to higher consequences (this will introduce additional
conservatism into the process), or a frequency cut-off can be used as a means of
screening out less important PDSs.
9.4.4. Accident progression and containment analysis
9.4.4.1. Containment event tree
In general, in level 2 PSA, the progression of severe accidents and containment failure
modes that lead to releases of fission products beyond the containment boundary is
represented using an event tree, named Containment Event Tree (CET) or Accident
Progression Event Tree (APET). The nodes (or questions) of the CET must address all of
the relevant issues important to the progression of severe accidents, containment response
and source terms.
The CET structure must be logical, complete, consistent and at an appropriate level of
detail, as mandated by the objectives of the level 2 PSA.
For each nodal question, the conditional probabilities of the branches should be
determined by fixed values, or by a specific model, such as fault tree or logical model,
identifying different situations as a function of a previous accident progression. These
models can also provide the values of some variables in order to determine the
containment failure modes or the attributes for fission product releases.
It is generally useful to divide the event tree into time frames, delineated by the major
events in the accident progression:
In-vessel processes during the early phase of damage progression;
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