Environmental Engineering Reference
In-Depth Information
3
Physico-statistical approach:
Procedures using the defect-free model of
structural material
During operation, damage cumulates in the metal of structural components
of nuclear power plants, i.e. ageing takes place.
The basic mechanisms of ageing for various components of nuclear
power plants with PWR and BWR were given earlier in Tables 1.1 and 1.2.
It should be noted that for the limiting state of the damaged structural
element for any ageing mechanism specified in Tables 1 and 2 is determined
by the strength criteria.
For example, when erosive-corrosive wear of steam pipes takes place
failure occurs when the stresses in the wall of the pipe reach the value
equal to the fracture stress.
In radiation embrittlement, the limiting state (for example, of the reactor
casing) is determined by the brittle fracture resistance criteria.
In pitting corrosion, stresses concentrate in pits and cause the nucleation
and propagation of corrosion fatigue cracks or stress corrosion cracking.
Kinetics of development of such cracks is described in the section of the
science of strength - fracture mechanics.
Thus, one could argue that to determine the probability of failure of
components and of equipment and pipelines of nuclear power plant it is
imperative to use the strength models of failure. The physical mechanisms
of radiation embrittlement, corrosion, corrosion-erosion wear can be used,
if necessary, as auxiliary mechanisms.
The first probabilistic model of fracture developed in the context of
the science of strength was the model proposed by A.R. Rzhanitsyn
53,54,etc
.
3.1 Probability of failure under random static
loading. The method proposed by Rzhanitsyn
The modern science of strength is based on the concept of the acceptable
stress-strain state.In accordance with this concept, the strength condition is
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