Regional Basic Professional Training Course in Korea

❙ 585 ❙
9. Probabilistic Safety Analysis
1. The approach shall rely as far as possible on real experience. This experience can
be operational events and incidents, and simulator tests, as well as visits and
interviews. In case of post-accident interactions, although some transferability
studies are necessary, simulator experiments appear as the most important source of
information.
2. The approach has to take into account the specific situation of the plant under study,
by an analysis of the man-machine interface (indicators), the documentation
available for the operators (normal and emergency operating procedures (EOPs)),
the operational practices (for example workload), and the training of the operators.
3. The approach has to take into account as far as possible elements given by human
factor sciences. This aspect is difficult to describe in detail, but a first step is to
include (or at least to consult) a human factors specialist in the HRA team.
9.3.5.3. Pre-accident actions
Category A actions:
This category covers latent errors that contribute to the unavailability of equipment.
Examples of category A actions are miscalibration of sensors, misalignment of valves or
of subsystems, failure to restore power supplies, failure to remove bypasses on protection
systems, and failure to remove locks on pumps/valves. These failures are identified
during system analysis.
A well-known and appropriate approach is THERP method [9.14] that provides tables for
quantification. Moreover, a validation by plant specific experience should be desirable.
Particular attention has to be paid to the treatment of recoveries and of dependencies
between category A actions.
Category B actions:
This category covers all the human actions that could lead to initiating events.