Regional Basic Professional Training Course in Korea

❙ 581 ❙
9. Probabilistic Safety Analysis
basis of the time spent in each state, in accordance with the operating profile.
Other cases of division: The division of the frequency of the sub-initiating events
adopted for functional reasons can be made either on the basis of experience
feedback (for example loss of the feedwater plant), or system reliability studies
(e.g., electrical power blackout), or by using engineering judgment on the basis of
studies made in other countries (e.g. the division between large and intermediate
primary system breaks and the distribution between secondary system breaks
upstream and downstream of the isolation valves).
9.3.3. Reliability data of components
The reliability parameters that are used in the PSAs are the following:
Failure rate to run (for a component in operation);
Failure upon demand or failure to start (for a component in stand-by);
Failure rate during stand-by;
Repair rate or repair time;
Unavailability for maintenance or for testing.
As for the initiating events frequency, priority has to be given to specific operating
experience as far as possible. In order to obtain specific estimates of these parameters, it
is first necessary to organize data collection as complete as possible. This data collection
has to contain all the information relating to failures or malfunctioning of components.
Other information also needed is total running time (or the number of demands), test
intervals and test duration, unavailability for maintenance, and, repair time.