Terminology, concepts and definitions - Probabilistic Safety Assessment for Optimum Nuclear Power Plant Life Management (PLiM) - page 2

according to the criterion of resistance to partial destruction with the
formation of a leak (a continuous stable defect).
Useful life of the third kind - the useful life of EP or their elements
according to the criterion of formation of dead-end defects in metal with
the size larger than permissible size.
Useful life of the fourth kind - the useful life of EP or their elements
according to the criterion of fatigue strength, creep strength, corrsion
resistance, etc. loss of stability, shape changes.
Fitness for purpose - a set of technical characteristics of EP determining
the possibility of their exploitation.
Note. Fitness for purpose is the characteristic of only EP, while the service life
of EP depends on fitness for purpose of EP and the service conditions.
Reliability - the property of the object to maintain in time and within
the established ranges the values of all parameters characterising its ability
to perform the required functions in specified terms and conditions for use,
maintenance, storage and transportation (GOST 27.002-89).
For EP of NPP working in conditions of thermomechanical loading, the
ability to perform the required functions is the property of strength.
Note
1. The concept of reliability includes the concept of failure-free operation,
durability, maintainability, and storability.
2. Reliability of the EP of NPP can be evaluated using different criteria. The
most important criteria are:
- Criterion of resistance to complete destruction of the structure or element
( reliability of the first kind );
- Criterion of resistance to partial destruction of the structural element with
formation of leaks, loss of integrity, etc. ( reliability of the second kind );
- Criterion of the resistance of the structure or its elements of to the formation
of defects in metal ( reliability of the third kind ).
- Criterion determined by the resistance to fatigue crack initiation, creep, stress
corrosion cracking, or unacceptable shape variations ( reliability of the fourth kind ).
Safety of EP - reliability of EP or their components in respect of to
human life, health and ecology of the environment.
Note:
1. Resistance to total destruction of the elements of EP defines nuclear, radiation
and industrial safety of NPP, as well as the efficiency of their operation (in terms
of costs to eliminate accidents and to reduce load factor) is measured by indicators
of the reliability of the first kind;
2. Resistance to partial destruction of the elements of EP with the formation of a
leak determines radiation and partially nuclear and industrial safety and effectiveness
of plant operation in part of the costs for eliminating the consequences of damage
and a reduced load factor; it is measured as the reliability of the second kind;
3. Resistance to the formation in the elements of EP of discontinuity defects
identifies only the efficiency of nuclear plant operation in terms of the costs
to eliminate defects and the reduction of the load factor; it is measured by the
reliabilities of the third and fourth kind;
Endurance - the property of EP or their elements to retain strength,
service life, reliability and safety in the presence of cracks or crack-like

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