Terminology, concepts and definitions - Probabilistic Safety Assessment for Optimum Nuclear Power Plant Life Management (PLiM) - page 4

of the operating live or to repair does not lead to destruction of the structure.
Note:
In the manufacture of products the permissible dimensions of discontinuities
are established based on the achieved level of technology and the possibilities of
non-destructive testing. Typically, the size of discontinuities that are allowed at the
manufacturing stage and during operation differs significantly.
Destruction - The process taking place in the material resulting in the
loss of its strength.With single loading, destruction can occur by brittle,
ductile or quasi-brittle mechanism.
Fatigue - Accumulation of material damage under cyclic loading,
leading eventually to the formation of a fatigue macrocrack, its propagation
and destruction of the structure.
Creep - Plastic deformation under long-term mechanical stress and
temperature, causing thermally activated processes leading ultimately to
destruction of the structure. The property of the structure (material) to resist
destruction by creep is the rupture strength.
Object - the technical product for a specific purpose, considered during
design, manufacture, testing and service.
Objects can be different systems and their elements.
Element - the simplest part of the product, fo the purpose of reliability
may consist of many parts.
System - a set of co-operating elements, designed for independent
fulfillment of prescribed functions.
The concepts element and system are transformed, depending on the task
at hand.For example, a machine tool, in establishing its own reliability, is
considered as a system consisting of individual elements - mechanisms,
components, etc., and to study the reliability of a production line - as an
element.
Reliability of the object has the following basic conditions and events :
Good state the state of the object at which it meets all the requirements
established by regulatory and technical documentation (RTD).
Up state - the state of the object in which it is able to perform specified
functions, while maintaining the basic values of the parameters specified
by RTD.
The main parameters characterise the operation of the object in carrying
out the assigned tasks.
The concept of the good state is broader than the concept of the
up state . The object capable of operation must meet only those RTD
requirements which ensure that the normal use of the object according to
its purpose. Thus, if the object is not capable of operation, this indicates a
malfunction. On the other hand, if the object is defective, it does not mean
that it cannot be used in service.
Limiting state is the state of the object in which its intended use is
unacceptable or inappropriate.
Application (use) of the object is terminated in the following cases:
• unavoidable breach of safety;

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