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On the occasion of these operations, certain elbows of
the primary system piping can also be replaced. These
operations are needed in order to anticipate the effects of
thermal ageing which affect themechanical properties of
this equipment. The replacement of the steamgenerators of
Paluel NPP reactor 2 should also involve the replacement
of 15 elbows on the main primary system.
Incorporation of international operating
experience
In 2012, a leak from the primary system to the secondary
systemoccurred on an SGat the SanOnofreNPP (United
States). Premature wear linked to direct contact between
tubes led to this leak. ASNensured that EDFhad analysed
the phenomena underlying this deterioration and had
provideddata toprove that the SGs of theFrenchNPPswere
not significantly concernedby thismode of deterioration.
Particularmonitoring has nonetheless been implemented
on the tubes potentially concerned.
2.4.6 Monitoring the other reactor pressure
equipment
ASNisalsoresponsibleformonitoringEDF’simplementation
of the regulations applicable to non-nuclear pressure
equipment utilised in the NPPs. In this respect, ASN in
particular carries out audits and surveillance visits on the
site inspectiondepartments. These departments, under the
responsibility of the licensee, are responsible for carrying
out inspections to ensure the safety of pressure equipment.
2.5 The containments
The containments undergo inspections and tests to check
their compliance with the safety requirements. Their
mechanical performance in particular must guarantee
a good degree of reactor building tightness in the event
of its internal pressure exceeding atmospheric pressure,
which can happen in certain types of accidents. This is
why, at the end of construction and then during the ten-
yearly inspections, these tests include an inner containment
pressure build-upwith leak ratemeasurement, as specified
inArticle8.1.1of the amendedOrder of 7thFebruary2012.
2.6 Protection against natural
events, fire and explosions
2.6.1 Prevention of seismic risks
Although the probability of a strong earthquake is low
in France, EDF’s consideration of this risk is nonetheless
closely monitored by ASN. Seismic protection measures
are taken into account in the design of the facilities. They
are periodically reviewed in linewith changing knowledge
and changes to the regulations, on the occasion of the
periodic safety reviews.
Design rules
Basic SafetyRule (RFS) 2001-01 of 31stMay 2001defines
themethodology for determining the seismic risk for surface
BNIs (except for radioactivewaste long-termrepositories).
This RFS is supplemented by a 2006 ASN guide which
defines acceptable calculationmethods for a study of the
seismic behaviour of buildings and particular structures
such as embankments, tunnels and underground pipes,
supports or tanks.
Buildings and equipment important for the safety of NPPs
are designed to withstand earthquakes of an intensity
greater than the most severe earthquakes that have ever
occurred in the region of the site.
Seismic reassessment
Aspartoftheperiodicsafetyreviews,theseismicreassessment
consists of verifying the adequacy of the seismic design of
the facility, taking account of advances inknowledge about
seismic activity in the region of the site or in the methods
for assessing the seismic behaviour of elements of the
facility. The lessons learned from international experience
feedback concerning earthquakes are also analysed and
integrated into this framework.
The studies carried out for the periodic safety review
associatedwith the third ten-yearlyoutages of the900 MWe
reactors (VD3-900) led to the definition of equipment or
structural reinforcements, which are implemented on the
occasion of the ten-yearly outage inspections.
Changes in the availableknowledgehave ledEDF to reassess
the seismic hazard for the periodic safety reviewassociated
with the third ten-yearlyoutages for the1,300MWe reactors
(VD3-1,300). ASN considers that EDF’s seismic hazards
assessment is acceptable, with the exception of that of
Saint-Alban, which is inadequate given the current state
of knowledge. ASN therefore asked EDF:
•
to reassess the seismic spectrum for the Saint-Alban
site to take account of uncertainties;
•
to define a working programme to verify the strength
of the equipment and civil engineering structures and
make any necessary seismic reinforcements for the
VD3-1,300 periodic safety review.
Extreme earthquakes
Following theFukushimaDaiichi accident, ASNaskedEDF
to define and install a “hardened safety core” of material
and organisational measures to control the fundamental
safety functions in extreme situationswhich, in the French
context, are comparable to thosewhich occurred in Japan
on 11th March 2011. This hardened safety core shall
notably be designed to withstand an earthquake of an
exceptional level, exceeding those adopted in the design
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CHAPTER 12:
EDF NUCLEAR POWER PLANTS (NPPs)
ASN report on the state of nuclear safety and radiation protection in France in 2015