Environmental Engineering Reference
In-Depth Information
5 Trend analysis to predict degradation processes and to perform correc-
tions in time
6 Acceptance criteria to assure that the functions of the SSCs are
maintained
7 Correction measures to prevent or solve problems
8 Feedback process to ensure that preventive actions are effective and
appropriate
9 Administrative control of the processes
10 Information retrieval from operational practice to ensure that ageing
management is properly carried out.
The same attributes can be applied while reviewing the adequacy of existing
plant programmes.
8.4.4 Review and validation of the time-limited ageing
analyses
TLAAs and their role in the justifi cation of LTO
Although the wording is sometimes different, the term 'time-limited ageing
analyses' is understood by the VVER operators in a very similar way to its
defi nition in 10CFR54.3 (Requirements for Renewal of Operating Licenses
for Nuclear Power Plants). The role of the review and revalidation of the
TLAAs in the justifi cation of LTO is also the same as international practice.
Existing TLAAs should be reviewed and revalidated with an assumed
extended time of plant operation. The evaluation of each identifi ed TLAA
should justify that the safety function of the SC will remain within design
safety margins during the extended period of operation. The plants have
to demonstrate either in the context of the PSR or in the licence renewal
application that:
the analysis remains valid for the period of LTO;
the analysis has been projected to the end of the period of LTO via
removing the conservatism used in the TLAA analysis by less conserva-
tive assumptions and methods for analysis; or
the effects of ageing on the intended function(s) will be adequately man-
aged for the period of LTO.
The scope of the required analyses
The identifi ed TLAAs cover the usual areas: fatigue calculations, assessment
of embrittlement, changes of material properties, etc. However, the scope of
TLAAs for some VVERs differs from the usual one either because of the
peculiarities of the design or because of national regulation. For example, in
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