Environmental Engineering Reference
In-Depth Information
nuclear power generation capacities, stimulated the LTO of VVERs too.
(This tendency might be changed by the Fukushima nuclear accident fol-
lowing the Great Tohuku earthquake in Japan March 2011.) Accumulation
of the experiences and scientifi c evidence for justifi cation for longer than
designed operation of NPPs, provides a good basis for LTO of the VVER.
Good market positions of NPPs overall in the VVER operating countries,
with high levels of public acceptance and positive public attitudes, help in
supporting the operation of NPPs in these countries.
Considerable progress has been achieved at VVER plants with respect to
the improvement of the performance and plant reliability. The load factor
of the majority of VVER plants is over 80%; in some places for example at
Paks and at Dukovany NPP it is around 90%.
The national regulation for allowing the approval of an extension
beyond designed operational lifetime is also a condition of the LTO.
According to Šváb (2007) and IAEA (2006, 2007a), there are two prin-
cipal regulatory approaches to LTO, depending on the legislation for the
operational licence. The operational licence in VVER operating countries
may be either limited or unlimited in time. In countries where the oper-
ational licence is not time limited, the basis of regulatory approval is the
periodic safety review (PSR). In those countries where the operational
licence has a limited validity in time, a formal renewal of the operational
licence is needed.
The internationally accepted rules and requirements regarding PSR are
documented in the IAEA Safety Guide NS-G-2.10 (IAEA, 2003). One of the
objectives of the PSR is to review the condition of the SSCs, and whether it
is adequate to meet their intended safety functions. This includes knowledge
of any existing or anticipated ageing and obsolescence of plant systems and
equipment. In particular, the objective of the review of PSR Safety Factor
4: 'Ageing,' is to determine whether the ageing of SSCs is being effectively
managed. This means whether or not the required safety functions are main-
tained, and whether an effective ageing management programme is in place
for future plant operation (NS-G-2.10 para 4.21 of IAEA, 2003). The design
lifetime is a technical limit for the operation, which is based on assumptions
by the designer regarding time limit of performance and functionality of
systems, structures and components due to ageing. The PSR used for jus-
tifi cation of extension of operational lifetime beyond the design lifetime
has to demonstrate that the prolonged operation is safe, despite expiration
of the design lifetime. It means the PSR has to review all the time limiting
analyses made by the designer. When reviewing the ageing of the plant, both
programmatic aspects and technical aspects of ageing management should
be evaluated. Rules for developing and establishing and attributes for ade-
quacy of ageing management programmes are given in the IAEA Safety
Guide NS-G-2.12 (IAEA, 2009).
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