Environmental Engineering Reference
In-Depth Information
indicate the evolution of degradation directly, for example the wall thick-
ness of piping. The water chemistry parameters can be used as indirect con-
trolling parameters of all internal surface corrosion mechanisms.
Defi nition of the method for the detection of ageing effects
Most of the postulated ageing effects can be detected during the execution
of the current programmes of the plant, as follows:
Non-destructive testing performed in the context of in-service inspec-
tion programmes
Visual inspections performed in the frame of maintenance programmes
Visual structural inspections
Walk-down inspections.
Monitoring, trending and condition evaluation
A defi nition of the methods for monitoring, trending and condition eval-
uation is the fi fth step in the development of the AMPs. For example, the
monitoring of the trend of fast neutron fl uence absorption in the critical
components of the reactor pressure vessel is one of the most important indi-
rect ageing management elements. The monitoring of load cycles defi ned
during design and of their parameters belongs to the ageing management of
fatigue degradation mechanism. The monitoring of the number and growth
of crack-indications found during material inspections and visual inspec-
tions in the frame of in-service inspection can be assigned to each local deg-
radation phenomenon. The monitoring and trending of the value of wall
thickness reduction could be taken into account in the case of degradation
forms with general material loss. In the case of heat exchangers, the moni-
toring of the number of plugged tubes can also be considered as an element
of the ageing management programme.
Acceptance criteria
The acceptance criteria are expressed as a limit value for the controlled
parameter of the ageing. The limit value corresponds to the performance or
functioning with required margin. Acceptance criteria have to be defi ned
for each component, or commodity, for each degradation mechanism in
relation to fulfi lment of the intended safety function. The acceptance crite-
ria can be derived from stress calculations in case of allowable wall thick-
ness of piping, or fatigue calculation regarding allowable load cycles. The
acceptance criteria for degradation phenomena entailing decrease of the
brittle toughness are determined by the relevant TLAA analysis results.
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