Materials management strategies for VVER reactors - Materials' Ageing and Degradation in Light Water Reactors - page 278

defi ciencies have been addressed by plant modifi cations and an acceptable
safety level has thus been achieved.
There are several advanced VVER-1000 plants presently under con-
struction, more than 20 new projects of advanced VVER design are under
preparation or consideration and several are in the bidding phase. The most
advanced versions of VVER design, showing features of Generation III
reactors, are being considered for future bids for large generating capacity
reactors.

8.3 Ageing of the VVERs - plant operational

experience

Operational experience provides the basis for preparing the strategy of age-
ing management. The experiences of the plants regarding degradation of
the lifetime-limiting structures and components have primary importance.
These are the non-replaceable long-lived structures and components. In
the VVER-440 plant design, lifetime-limiting structures and components
are the containment building, reactor pressure vessel and the steam gen-
erator (Katona et al ., 2005, 2009b; Katona and Rátkai, 2008). Unlike the
VVER-1000 and PWRs, the steam generators are practically irreplaceable
in the VVER-440/213 design. In the case of the VVER-1000, the most impor-
tant lifetime-limiting structures and components are the containment and
the reactor pressure vessel. The proven design solutions of the VVER-440
were incorporate in the VVER-1000 design: the horizontal steam generator
and also materials selection.
Alongside this, ageing the mechanical commodities, structures other than
containment and electrical equipment, are also important for the develop-
ment of an ageing management strategy. With this in mind, the operational
experience of the plants varies because of the design variation of these com-
ponents and structures at different plants.

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8.3.1 Method for the evaluation of actual plant condition

Evaluation of actual/aged condition in safety-critical SCs is the basic
method for identifying the ageing mechanisms and their effects on the
intended functions. Plant condition has to be reviewed for the feasibility
study of LTO. Review and evaluation of plant condition is an obligatory
part of both the periodic safety review (Safety Factor 2 in the PSR, see
IAEA, 2003) and the justifi cation of safe operation in the licence renewal
process.
The scope of review and evaluation of actual plant condition covers the
safety- and seismic-classifi ed SSCs and non-safety SSCs, failure of which