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needs to improve its control of the operational processes
which help to maintain the conformity of the facilities
with their design, construction and operating baseline
requirements.
In accordancewith theASNresolutiononPWR shutdowns
and restarts (ASN resolution 2014-DC-0444 of 15th July
2014), EDF performs an analysis of the combination of
these deviations for each reactor. ASNconsiders that these
analyses need to be carried out in greater depth.
Finally, in accordancewith theASNresolutiononphysical
modifications to BNIs (ASNresolution2014-DC-0420 of
13th February 2014), ASN observed that EDF has made
progress in demonstrating the qualification of the new
equipment installed, whenever necessary.
The first containment barrier
ASN considers that in 2015 the condition of the first
containment barrier, which is the fuel cladding, progressed
on the whole, despite a few points still to be improved. It
in particular noted that the organisation set up to avoid
foreign material entering the primary system once again
made progress this year.
The number of significant events linked to fuel handling
was down. However, during a number of reactor refuelling
outages, loosepartswere once againdetected in theprimary
system, for example:
•
In Golfech 2, 31 pieces of fuel assembly grid springs
were removed.
•
In Cruas 3, numerous metal brush hairs fell into the
pressuriser during amaintenance operation. Theywere
subsequently recovered.
At the end of 2015, the number of reactors with leaking
fuel claddingwas significantly down, involving only four
reactors, instead of the seven one year earlier.
In 2014, the Nogent reactor had been stopped before the
normal end of its operating cycle owing to the significant
rise in control rod drop time, caused by deformation of
fuel assemblies. Dropping the control rod assemblies
under the effects of gravity enables the reactor to be
shut down in an emergency. In 2015, owing to the
significant rise in the drop time of a control rod cluster,
EDF interrupted the operating cycle in order to repair
two rod assemblies close to this cluster, thus improving
the cluster drop time.
In2014, following anASNrequest, EDF adoptedmeasures
to reduce the risks of excessive oxidisationof the zircaloy-4
alloy fuel cladding (excessive oxidisation could reduce the
strength of the cladding in certain accident situations).
Thesemeasures limit the oxidisationof the zircaloy-4 alloy
cladding and keep control rod movements to the strict
minimumnecessary once the calculated oxide thickness
reaches 80 µm. The number of reactors using assemblies
with zircaloy-4 cladding has been reduced from 49 in
July 2014 to 31 in July 2015.
Second containment barrier
The requirements of the Order of 10th November 1999,
more particularly with regard to maintenance, defect
handling, inspections and periodic requalification of
the main primary and secondary systems, were on
the whole met. Preparation for the hydrotesting of
these systems was however inadequate in at least three
plants (lack of appropriate tooling, steam generator
saturation, etc.).
Compliance with the provisions regarding restart
of the reactors after a maintenance outage was also
improved in 2015. ASNhowever observed the persistence
of shortcomings in the drafting of the significant
maintenance summary files and delays in transmission
of the reactor outage results summary documents. A
number of the regulation checks required following
replacement of main primary and secondary system
components had not been performed on several reactors.
Corrective measures were taken on this point in 2015.
The absence of these checks indicates a lack of stringency
in implementation of the requirements applicable to
the second barrier.
Similarly, management of the procurement of main
primary and secondary systemequipment manufactured
in accordance with the Order of 12th December 2005 is
improving but still requires particular vigilance.
The most sensitive equipment constituting the second
containment barrier includes the SGs andmore particularly
their tube bundles.
ASN considers that the condition of the SG tube bundles
has improved owing to the replacement of the last SGs
equipped with 600 MA alloy tube bundles (susceptible
to external corrosion). The SG replacement campaign
will continue in 2016 on the tube bundles made of heat
treated Inconel (600 TT). This will be the case of the
Gravelines 5 and Paluel 2 reactors in 2016.
ASN considers that EDF’s operating and maintenance
strategy with regard to SG tube support plate clogging
(use of high pH conditioning, monitoring of chemical
parameters and preventive SG cleaning) is appropriate.
This approach aims to keep the secondary system at an
acceptable level of cleanness at all times.
Third containment barrier
Overall management of the containment function
The organisation adopted by the NPPs for monitoring
the activities and systems liable to have an impact on the
static and dynamic containment of the facilities remains
on thewhole satisfactory. However, improvements are still
expectedwith regard to the condition of the containment,
of the third barrier and its components, in particular
concerningmaintenance of the floor drains and the doors
participating in static containment.
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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