Physico–statistical approach taking defects into account and using binomial distribution - Probabilistic Safety Assessment for Optimum Nuclear Power Plant Life Management (PLiM) - page 101

The composite unit - part of equipment or pipeline (e.g., body, primary
coolant header, heat exchanger pipes, seal assembly of the primary and
secondary circuits, tube units, etc). The composite unit is divided into
elements.
Element - a component part into which the composite unit is divided
to analyze growth of defects. The element is divided into cells.
Cell - part of the metal volume into which the element for the analysis
of defect nucleation is divided.
Determining the reliability of equipment and pipelines includes the
following procedures:
- decomposition of the considered composite unit into elements for the
analysis of propagation of defects;
- dividing the elements into cells for the analysis of defect nucleation;
- formation of the data for the element in question;
- formation of the data for the cell in question;
- uncertainty analysis of initial data;
- determination of the probability of nucleation of defects by the fatigue-
mechanical and corrosion mechanisms in the investigated cell;
- adjustment of the size distribution of defects for the given elements
as a result of metal inspection and analysis of nucleation of new defects,
analysis of growth of defects;
- adjustment of the distribution of the number of defects for these
elements based on metal inspection, analysis of nucleation of new defects;
analysis of the nucleation of new defects based on the cumulation of fatigue,
mechanical and corrosion damage;
- analysis of propagation of corrosion fatigue defects;
- distribution of defects on the basis of the mechanisms of their critical
growth depending on the conditions in which the given element works;
- analysis of the critical growth of defects using the brittle fracture
criterion;
- analysis of the critical growth of defects using the ductile fracture
criterion;
- analysis of the critical growth of defects using the elastic plastic
fracture criterion;
- determination of equivalent size D 0 on the basis of the size of
continuous defects;
- determination of the probability of leaks by equivalent D 0 in this
element with the uncertainties of input data taken into account;
- determination of the probability of large-scale destruction of the
element in question, taking into account the uncertainty of initial data;
- determination of the probability of leaks by equivalent D 0 for the
considered composite unit of equipment or piping;
- determination of the probability of large-scale destruction for the
considered composite unit of equipment or piping;
- determination of the failure intensity of the composite unit element;

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