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Single wall containments with an internal metal liner
The ageing of the 900 MWe reactor containments was
examined in 2005 during the periodic safety review
associatedwith their third ten-yearly outage inspection,
in order to assess their leaktightness and mechanical
strength. The reactor containment tests performed during
the ten-yearly outage inspections on these reactors since
2009 have brought to light no particular problems liable
to compromise their operation for a further ten years,
with the exception of Bugey reactor 5. Even though its
results were in conformity with the test criteria, a test
carried out in 2011 showed an unfavourable trend in the
tightness of the containment. In prescription [BNI 89-36]
of its resolution 2014-DC-0474 of 23rd December
2014, ASN asked the Bugey NPP to schedule a further
test no later than September 2016. Pressure testing
performed during the partial inspection of reactor 5,
which began on 27th August 2015, showed that this
containment needs to be repaired. For the rest of the
900 MWe reactor containments, the results of the ten-
yearly reactor containment tests have hitherto shown
leak rates in compliance with the regulatory criteria
(27 of the 34 reactors have undergone this test).
Double-wall containments
The test results for thedouble-wall containments performed
during the first ten-yearlyoutages of the1,300MWe reactors
detected a rise in the leak rate from the inner wall of some
of them, under the combinedeffect of concretedeformation
and loss of pre-stressing of certain cables that was higher
than expected in the design.
EDF then initiated significant work consisting in using
a resin sealant locally to cover the interior surface of
the inner wall of the most severely affected 1,300 MWe
reactors, but also reactors of theN4 plant series. The tests
performed since this work, during the second ten-yearly
outages of the 1,300 MWe reactors and the first ten-yearly
outages on the N4 series of reactors, showed that they
all complied with their regulation leak rate criteria. In
order to guarantee that these criteria are met during the
next ten-yearly outage inspections, EDF is considering
supplementing these inner wall sealant coatings with a
coating of the same type applied to the outer surface of
the reactor building inner containments.
ASN is remaining vigilant with regard to the development
of the leaktightness of these containments for which the
design makes no provision for an integral metal liner.
The issues linked to the double-wall reactor containments
were thus analysed by the GPR on 26th June 2013, in the
run-up to the third ten-yearly outage inspections for the
1,300 MWe reactors. ASN issued a ruling on this subject
in June 2014 andwill be attentive to compliancewith the
undertakings that EDF made on this occasion.
ASN’s main conclusions are:
•
In addition to EDF’s satisfactory monitoring of the
condition of the concrete, additional measures to
prevent or mitigate the ingress of water from outside
must also be envisaged because, given the current state
of knowledge, this is the primary means of protecting
containments from concrete swelling pathologies.
•
EDF must reinforce in-service monitoring and visual
inspection of certain containment singularities (sleeves,
equipment hatch).
•
ASN considers that EDFmust give a safety classification
to the instrumentation system providing continuous
monitoring of the containment leak rate (Sexten) along
with in-service monitoring of its correct operation.
4.1.2 Evaluating human and organisational
measures
The steps taken by the NPPs and the stakeholders to
take account of organisational and human factors
It is considered that the organisation of the NPPs designed
to take account of Organisational and Human Factors
(OHF) could be improved.
EDF has Human Factors (HF) consultants, who contribute
to operating experience feedback and personnel training.
Their roles could be extended to other OHF fields, such
as taking account of the organisation and the needs
of the personnel when making changes to systems or
modifications to certain equipment. In 2015, ASN found
that several HF consultant positions on several sites
were vacant. However, some sites are now beginning to
deploy a network of local HF correspondents within the
technical departments, coordinated by the HF consultant.
The managers are on the whole strengthening their
presence in the field, even if the purpose of these
field visits is sometimes lacking in clarity; they can be
performed to check behavioural nonconformities by
the workers or indeed the condition of the facilities,
rather than to observe working situations which would
allow the detection of possible improvements or areas
in which worker training might be needed.
Major efforts are being made by EDF to develop the
use of error reduction practices. ASN considers that
this might be insufficient and site-specific measures to
improve organisation, safety management or working
conditions must also be developed.
Organisation of work and working conditions
In 2015, ASN still observed numerous shortcomings with
regard toworking conditions. ASN thus noted equipment
inappropriate for the tasks in question, owing to its
unavailability or poor design, cramped or inaccessible
work spaces, errors in signage, or instructions that are
hard to read.
On all the sites, documents placed at the disposal of the
workers by EDF are sometimesmissing and are regularly
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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