Regional Basic Professional Training Course in Korea

Regional Basic Professional Training Course (BPTC) on Nuclear Safety
figures; in such cases, the frequency of surveillance may be based on the best
estimates by the operating organization for future failure rates and other criteria;
and
The difficulty of assessing the significance of common cause failures.
Where there is only limited experience on the reliability of structures, systems or
components, the initially adopted surveillance frequency is based upon conservative
assumptions.
The reliability of SS&C may be adversely affected through the experience of an
excessive number of thermal, mechanical or other cycles. Therefore, to reduce cycling
caused by testing, the testing of components providing a given safety function may be
suspended during any period when that particular safety function is not required to be
available, provided the surveillance requirements are met before a change in operational
state is made that requires the safety function to be available.
The reliability of SS&C may be adversely affected if technological limits defined by the
designer are exceeded. The surveillance procedures take these limits into consideration.
The reliability of SS&C may be degraded by personnel‐caused faults (e.g. calibration of
redundant instruments on the same day by one individual, which may introduce similar
errors and thus increase the potential for common failure). The frequency of such faults
may be reduced, for example, by establishing detailed procedures.
Where certain redundant systems and components are kept on stand‐by, operation of these
systems and components are rotated in order to subject all components to similar
operating duties and consequently to similar surveillance procedures and frequencies.
Maintenance intervals are adjusted to ensure that these systems and components do not
wear out at the same time. Diverse methods are used where practicable during the testing
❙ 760 ❙