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ASN ensures that EDF looks for and analyses the causes
of the loss of leaktightness observed, in particular by
examining the leaking rods in order to determine the
origin of the failures and prevent them from reoccurring.
Preventive and remedial actions may therefore affect
the design of rods or assemblies, their manufacture,
or the reactor operating conditions. Furthermore, the
conditions of assembly handling, of core loading and
unloading, and the measures taken to exclude foreign
material from the systems and pools are also the subject
of operating requirements, some of which contribute
to the safety case and for which EDF’s compliance is
verified by ASN. ASN also conducts inspections to
ensure that EDF carries out adequate monitoring of
its fuel assembly suppliers in order to guarantee that
fuel design and manufacture comply with the rules
established. Finally, ASN periodically consults the GPR
with regard to the lessons learned from fuel operating
experience feedback.
2.4 Pressure equipment
2.4.1 Monitoring the manufacture of Nuclear
Pressure Equipment (ESPN)
ASN assesses the conformity with the regulatory
requirements of the nuclear pressure equipment most
important for safety, known as “level N1”. This conformity
assessment concerns the equipment intended for the
new nuclear facilities (EPR Flamanville 3) and the
equipment spares intended for nuclear facilities already
in operation (replacement steamgenerators in particular).
For the performance of these duties, ASN can rely on
the organisations that it approves, which can be tasked
by ASNwith performing some of the inspections on the
level N1 equipment and are responsible for assessing
conformity with the regulatory requirements applicable
to nuclear pressure equipment that is less important
for safety, referred to as “level N2 or N3”. Oversight by
ASN and its approved organisations comes into play at
different stages of design and manufacture of nuclear
pressure equipment. It takes the formof examination of
the technical documentation for each itemof equipment
and of inspections in themanufacturers’ facilities as well
as in those of their suppliers and subcontractors. Five
inspection organisations or bodies are currently approved
by ASN to assess ESPN conformity: Apave SA, Asap,
Bureau Veritas, AIB Vinçotte International and the EDF
users inspection entity.
In2015, ASNand the approvedorganisations carriedout:
•
4,483 inspections to check the manufacture of nuclear
pressure equipment intended for the Flamanville 3
EPR reactor, representing 10,133 man-days in the
manufacturers’ plants, aswell as those of their suppliers
and subcontractors,
•
1,063 inspections to check the manufacture of the
spare steam generators intended for the NPP reactors
in operation, which represented 3,936man-days in the
manufacturer’s plants, aswell as those of their suppliers
and subcontractors.
Most of these inspectionswere performedby the approved
organisations, under the supervision of ASN.
2.4.2 Monitoring the main primary
and secondary systems
The reactorMainPrimary andSecondarySystems (MPS and
MSS) operate at high temperature and high pressure and
contribute to the containment of radioactive substances,
to cooling and to controlling reactivity.
The monitoring of the operation of these systems is
regulated by the Order of 10th November 1999 relative
to the monitoring of operation of the main primary and
themain secondary systems of nuclear pressurisedwater
reactorsmentioned inpoint 3.6of chapter 3. These systems
are thus monitored and periodically maintained by EDF.
This monitoring is itself checked by ASN.
These systems are subject to periodic re-qualification
every ten years, which comprises a complete inspection
of the systems involving non-destructive examinations,
pressurised hydrotesting and verification of the good
condition and proper operation of the over-pressure
protection accessories.
2.4.3 Monitoring of nickel-based alloy areas
Several parts of pressurised water reactors are made
with nickel-based alloy. The use of this type of alloy is
justifiedby its resistance to generalised or pitting corrosion.
However, in reactor operating conditions, one of the
alloys adopted, Inconel 600, proved to be susceptible
to stress corrosion. This particular phenomenon occurs
when there are high levels of mechanical stress. It can
lead to the appearance of cracks, as observed on the
SG tubes in the early 1980s or, more recently in 2011,
on a vessel bottom head penetration in the Gravelines
reactor 1. These cracks require that the licensee repair
the zones concerned or isolate them from the rest of the
system to prevent any undue risk.
At the request of ASN, EDF adopted anoverallmonitoring
andmaintenance approach for the areas concerned. Several
parts of the main primary system made of Inconel 600
alloy are thus subject to special monitoring. For each of
them, the in-servicemonitoring programme, defined and
updated annually by the licensee, is submitted to ASN,
which checks that the performance and frequency of the
checks carried out are satisfactory and able to detect the
deteriorations in question.
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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