Environmental Engineering Reference
In-Depth Information
Consequences (radiation dose
limit, Zv/year)
Forbidden zone
Residual
risk
Risk of failures taken into
account in design (design
failures)
Risk of malfunction and
disruption in normal service
Probability,
1/reactor·year
1.23
The relationship between consequences of failure the probability
of its occurrence (residual risk is the risk that exists despite all
the measures taken).
- stress corrosion cracking;
- intercrystalline corrosion;
- corrosion-erosion wear;
- fretting corrosion;
- accelerated radiation metal embrittlement of the reactor vessel;
- propagation of latent defects of continuity of metal.
Tables 1.1 and 1.2 list the main types of damage (ageing) for VVER
(PWR) and BWR reactors
10,11
.
The most dangerous types of the damage not considered in the design
are associated with the appearance of cracks which may give rise to leaks
and to very large leaks at destruction. Examples of such cases are shown
in Figs. 1.24-1.26.
There are many causes of cracks and damage in service. In the
chronological order they can be divided into three groups
5,etc.
:
- design flaws;
- shortcomings of manufacture;
- shortcomings of operation.
It was shown in Ref. 12 that the greatest contribution to the total
amount of damage detected during operation comes from deficiencies of
manufacturing technology (so-called technological defects) (Fig. 1.27).
Technological defects grow during service and can lead to small leaks
(continuous stable defects) or large leaks due to destruction.
Defects associated with deficiencies in production or operation are
removed usually by repair (Fig. 1.27). Upgrading or modernisation is usually
required to address the design shortcomings.
Ageing of equipment and pipelines with defects is associated with
the kinetics of their propagation under operational loads. From a safety
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