ASN Report 2017

342 ASN report on the state of nuclear safety and radiation protection in France in 2017 Chapter 12  - EDF Nuclear Power Plants 2.3.2 Assessment of the condition of the containments Overall management of the containment function The organisation adopted by EDF for monitoring the activities and systems liable to have an impact on the static and dynamic containment of the facilities remains on the whole satisfactory. However, improvements are still expected with regard to the condition of the containment, of the third barrier and its components, in particular concerning maintenance of the floor drains and the doors participating in static containment. 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 associated with 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 (see box). For the other 900 MWe reactors, the results of the ten-year tests of the reactor containments during the third ten yearly-outage inspections have hitherto shown leak rates in compliance with the regulatory criteria. To date, this test has been performed on 30 reactors and should be carried out for all the 34 900 MWe reactors in 2020. Double-wall containments The test results for the double-wall containments performed during the first ten-yearly outages of the 1,300 MWe reactors detected a rise in the leak rate from the inner wall of some of them, under the combined effect of concrete deformation 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 1,450 MWe reactors. The tests performed since this work, during the second and the third ten-yearly outages of the 1,300 MWe reactors and the first ten-yearly outages of the 1,450 MWe reactors, showed that they all complied with the regulation leak rate criteria. In order to ensure that compliance with these criteria will be maintained on a lasting basis, EDF decided to supplement these inner surface sealants with a sealant of the same type on the outer surface of the inner containments of the reactor buildings. 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 effectiveness of the containment function of the double-wall reactors was thus examined by the Advisory Committee for Nuclear Reactors (GPR) on 26th June 2013, in preparation for the third ten-yearly inspections of the 1,300 MWe reactors. ASN issued a ruling on this subject in June 2014 and remains attentive to compliance with the undertakings that EDF made on this occasion. ASN’s main conclusions are: ཛྷ ཛྷ 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. ཛྷ ཛྷ EDF must reinforce in-service monitoring and visual inspection of certain containment singularities (sleeves, equipment hatch). ཛྷ ཛྷ ASN considers that EDF must 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. 2.4 Risk prevention and management 2.4.1 Monitoring the drafting and application of the general operating rules The General Operating Rules (RGE) cover the operation of nuclear power reactors. These are drafted by the licensee and are the operational implementation of the hypotheses and conclusions of the safety assessments constituting the nuclear safety case. They set the limits and conditions for operation of the installation. Normal and degraded operation Operating Technical Specifications The Operating Technical Specifications (STE), which constitute Chapter III of the general operating rules, define the normal operating conditions based on the design and sizing hypotheses and require the systems necessary for maintaining the safety functions, in particular the integrity FOCUS Leaktightness measurements for the Bugey NPP reactor 5 containment During the third ten-yearly outage inspection of the Bugey NPP reactor 5 carried out in 2011, an abnormal trend in the containment leaktightness measurement results was observed by comparison with those made in 2001. In order to control this change and ensure compliance with the safety requirements, ASN required the performance of an additional test, which was carried out in 2015. Its results revealed a deterioration in the leaktightness of the containment and situated the leaks in the lower part of the reactor building. The reactor remained shut down for the time it took EDF to define and implement a repair method, which ASN authorised on 28th March 2017. Following the repair, further checks and tests enabled EDF to demonstrate compliance with the safety requirements for the coming cycles. ASN gave its consent for restart of the Bugey NPP reactor 5 on 18th July 2017.