Regional Basic Professional Training Course in Korea

Regional Basic Professional Training Course (BPTC) on Nuclear Safety
If the specific experience feedback is not sufficient (too small number of failures), other
information sources can be used, for example international data banks or data used in
other PSAs. However, the applicability of such data to the plant under consideration has
to be analysed. Specific data can be aggregated with generic data using Bayesian method.
The data collection gives raw data, which have to be analysed and processed in order to
obtain the reliability parameters. During raw data processing, particular problems are
encountered, for example:
The failures reported are only partial failures and the failure criticality has to be
assessed (was the component still able to run in an emergency situation?).
If an important modification of a component has been carried out, is the modified
component to be considered as a new component? Is it possible to anticipate the
effects of a modification?
In case of a new plant, what are the most appropriate data before any experience
feedback?
The PSA position when examining these problems has to be as realistic as possible,
but must keep a conservative position when the evidence is not sufficient.
9.3.4. Common cause failure (CCF)
Common cause failures are failures which are due to the same cause and which can affect
simultaneously, or within a short period of time, a number of redundant components. The
common points identified (for example the common support systems) are explicitly
introduced in the systems models and are not considered as CCFs. The CCFs can result,
for instance, from errors in design, fabrication or installation, or from the effects of the
environment (normal or accident condition). A typical example would be the failure of
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