Terminology, concepts and definitions - Probabilistic Safety Assessment for Optimum Nuclear Power Plant Life Management (PLiM) - page 48

Reconstruction

Repair

Repair

Operating time

1.27 The defects detected during operation: 1) flaws inherent
in the manufacturing stage and missed in inspection; repair is
required; 2) increase in the number of defects associated with
deficiencies of design, require reconstruction; 3) increase of the
number of defects due to deficiencies of operation; require repair;
4) the total number of defects.

and allowable stresses. Procedures and methods of solutions used in these
studies somewhat differed from those used than in the traditional tasks
of ensuring the strength, namely, they were based on probability theory
and mathematical statistics. Here we must bear in mind that most of
the calculated values with which we have to operate in the calculations
of structural elements are not strictly defined and may have different
random deviations from their mean values. Therefore, each calculated value
should be expressed not by the number but by a distribution function that
characterises the probability of occurrence of all possible numerical values
of this quantity. It is also assumed that the given calculation situation will
be repeated many times and that the law of large numbers can be used here
to judge the frequency of occurrence of certain events on the basis of the
theoretically calculated probability of their appearance.
Another circumstance that requires estimates of the probability of
destruction of equipment and pipelines is the need to optimise the costs
of operating equipment and pipelines which, to ensure their safety, are
subjected to periodic non-destructive testing, hydraulic testing, technical
inspection, maintenance and repair work, upgrades. Obviously, in the case
of excessive optimistic estimates of strength reliability (failure probability
is zero) the above work seemed superfluous, and if exaggerated pessimistic
estimates are obtained (the probability of failure is 1), these measures
are insufficient. Obviously, the optimum organisation of operational
technologies of non-destructive testing, maintenance and repairs is only
possible on the basis of revised estimates of reliability and lifetime of
equipment and pipelines. As shown below, only the quantitative safety

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