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The lifetime of non-replaceable items
Non-replaceable items such as the reactor vessel (see
point 2.4.4) and the containment (see point 2.5)
are closely monitored in order to ensure that they
are ageing as anticipated and that their mechanical
properties remain within limits that guarantee their
correct performance.
Equipment or component obsolescence
Before it is installed in theNPPs, some equipment undergoes
a “qualification” process designed to ensure that it is able
to perform its functions in the stress and atmosphere
conditions corresponding to the accident situations in
which it would be required. The availability of spares for
this equipment is heavily dependent on the development
of the industrial network of suppliers and the cessation
of manufacture of certain components or the closure of
the manufacturing company, which can lead to supply
difficulties. Prior to installing these parts, EDFmust check
that the newspares that are different fromthe original parts
donot compromise the “qualification” of the equipment on
which they are to be installed. Given the incompressible
lengthof this procedure, the licenseemust anticipate these
needs well in advance.
2.9.3 How EDF manages equipment ageing
The approach adopted by EDF to control the ageing of its
facilities is based on three key points:
•
Anticipate ageing in the design: during the design and
manufacture of components, the choice ofmaterials and
the installation arrangements must be tailored to the
intendedoperating conditions and take into account the
kinetics of knownor presumeddeteriorationprocesses.
•
Monitor the actual condition of the facility: during
operation, degradation phenomena other than those
considered in the design canbe discovered. The periodic
monitoring and preventive maintenance programmes,
the additional investigation programmes as well as
examination of operating experience feedback (see
points 2.7.1, 2.8.2 and 2.8.3) are all designed to detect
these phenomena sufficiently early.
•
Repair, renovateor replace equipment: given theoperating
constraints liable to be generated by such routine or
exceptional maintenance operations, especially when
they can only be performed during reactor outages,
EDFmust seek to anticipate them, in particular to take
account of the time needed toprocure newcomponents,
the time required to prepare for and carry out thework,
the risk of obsolescence of certain components and the
loss of technical skills on the part of the workforce.
EDF has established a methodology for controlling
the ageing of its reactors after 30 years of operation.
Its aim is to demonstrate their ability to continue to
function until their fourth ten-yearly outage inspection
in satisfactory conditions of safety, on the one hand, in
light of the condition of the facilities during their third
ten-yearly outage inspections and, on the other, given
the knowledge and experience of the mechanisms and
kinetics of deterioration linked to ageing.
This methodology comprises a first generic phase,
which aims to take account of ageing for an identical
reactor series, in order to pool and share the studies.
Subsequently, on the occasion of the third ten-yearly
outage inspection (VD3) on each reactor, a summary
file specific to each reactor is produced in order to
demonstrate control of the ageing of the equipment
and the reactor’s ability to continue to operate for the
ten-year period following its VD3. It is drawn up on
the basis of the generic file and aims to take account of
any specific features of each of these reactors.
Given EDF’s envisaged goal of continued reactor
operations beyond forty years, the satisfactory control of
ageing and the management of equipment obsolescence
constitute key safety issues (see point 3.2). ASN considers
that the approach adopted by EDF, both generic and for
each individual reactor, is on the whole satisfactory but
needs to be supplemented with respect to a few points:
•
identify the possible vulnerabilities in the components
industrial replacement processes, including in the case
of an unforeseen operational event on the reactors,
and propose steps to improve the robustness of these
processes;
•
provide a robust demonstration of the mechanical
resistance of the vessels beyond their fourth ten-yearly
outage inspection.
2.9.4 The periodic safety review
In accordance with the provisions of Article L. 593-18 of
the Environment Code, EDF must carry out a periodic
safety review of its reactors every ten years, comprising
of the following two parts:
•
A check on the condition and conformity of the facility:
this step aims to verify the situation of the facility
with respect to the rules applicable to it. It is based
on a range of inspections and tests in addition to
those performed in real-time. These verifications can
concern checks on the initial design studies as well
as field inspections of equipment not addressed by
maintenance programmes, or tests conducted every
ten years such as the containment pressure tests.
Any deviations detected during these investigations
are then restored to conformity within a time-frame
commensurate with their potential consequences.
•
The safety reassessment: this step aims to improve
the level of safety in the light of the experience
acquired during operation, changing knowledge, the
requirements applicable to the more recent facilities
and international best practices. Following these
reassessments, EDF identifies the modifications it
intends to make to its facilities in order to reinforce
their safety.
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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