SG replacement operations are scheduled at the rate of one reactor per year over the coming years, starting in 2024. Main Primary System auxiliary lines Numerous stress corrosion cracks have been discovered, in particular on the SIS and RRA lines of the 1,450 MWe and 1,300 MWe type P’4 reactors, in the immediate vicinity of certain welds. They led to a very large number of destructive assessments and repairs (see box previous page). 2.3 THE CONTAINMENTS 2.3.1 The containments The containments, which constitute the third containment barrier, undergo inspection and testing to check their compliance with the safety requirements. More specifically, their mechanical behaviour must guarantee good tightness of the reactor building if the pressure inside it were to exceed atmospheric pressure, which can happen in certain types of accidents. This is why, at the end of construction and then during the ten-yearly outages, these tests include an inner containment pressure rise with leak rate measurement. These tests are required by the Order of 7 February 2012, setting the general rules concerning Basic Nuclear Installations (BNIs). Other equipment takes part in the containment function, such as the systems for accessing the interior of the containment (airlocks and equipment hatch), the circuit depressurising the annulus between the double-wall containments or the control room ventilation system. 2.3.2 Assessment of the containments Overall management of the containment function EDF’s management of the containment function is on the whole relatively satisfactory. ASN however still observes occasional but recurring unavailabilities affecting certain equipment participating in the containment function. These unavailabilities notably concern the containment penetrations pressurisation system and leak monitoring system, as well as the control room ventilation system. Since 2014, EDF has also been carrying out an action plan with the aim of guaranteeing that the flowrates in the ventilation systems meet the safety requirements both for the containment and for thermal conditioning of the installations, in the light of the changes made to the reactors since they were built. The action plan is being deployed, reactor by reactor, on all the ventilation systems concerned, and includes an inventory of the equipment and ducts. As necessary, EDF carries out repairs and improvements and adjusts the ventilation flow rates. The final phase of this national action plan includes a programme to ensure the lasting nature of the adjustments made. ASN will issue a position statement in 2024 on the pertinence of this programme. Single-wall containments with an internal metal sealing liner The ten-yearly tests on the 900 MWe reactor containments carried out since 2019 as part of their fourth ten-yearly outages did not bring to light any generic problems liable to compromise their operation. In 2023, five single-wall containment reactors carried out their containment tests and the results were satisfactory. Double-wall containments The tests on 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 a loss of prestressing of certain tendons, that was greater than anticipated at the design stage. EDF then initiated major work consisting in locally applying a resin sealing coating to the interior and exterior surfaces of the inner wall of the containments of the most severely affected 1,300 MWe reactors, as well as to the 1,450 MWe reactors. For all the reactors on which it was carried out, this work enabled the leak rate criteria to be met during the containment pressure tests. On Civaux NPP reactor 1, a sealing coating was applied to a large part of the inner containment. Despite this work, the leak rate found during the second ten-yearly outage test remained high, although lower than the specified criterion to be met. This is why ASN will remain vigilant with regard to changes in the situation of this containment and, more broadly, to changes in the leaktightness of all the containments and to maintaining the long-term effectiveness of the coatings. 2.4 ORGANISATION FOR REACTOR OPERATIONS 2.4.1 Reactor operations The Order of 7 February 2012 stipulates that the licensee must have the technical skills needed to manage the activities involved in operation. Furthermore, this Order requires that the licensee define and implement an Integrated Management System (IMS) to ensure that the requirements concerning nuclear safety and protection of the environment are systematically considered in any decision concerning the facility. This IMS must specify the steps taken with regard to organisation and to resources of all kinds, in particular those adopted to control the activities important for the protection of persons and the environment. Normal operation The EDF NPPs are permanently monitored from a control room by a control team which is also in charge of controlling the installations. The operating limits within which the teams must keep the installation are defined in the RGEs. The licensee ensures that this is done using normal operation documentation, in particular the operating instructions and alarm data sheets. The licensee is regularly required to modify the installation’s configuration to allow intervention by the maintenance crews, to test the availability of a system or to change the status of the reactor. Tests are regularly performed to check the correct working of the systems which could be required in an incident or accident situation and to check the correct behaviour of the reactor’s core. Some tests are performed with the reactor operating, while others can only be carried out during reactor outages. The control teams perform some of these tests themselves, while others require intervention by specialised teams. Operation in the event of an incident or accident The operating strategies and practices to be implemented in an incident or accident situation are developed in various documents (operating rules and instructions) placed at their disposal. They specify what action is to be taken by the control team. To manage these situations, the organisation of the control team changes and each person has a specific role. The control teams are regularly trained in the implementation of these control strategies. 298 ASN Report on the state of nuclear safety and radiation protection in France in 2023 • 10 • The EDF Nuclear Power Plants
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