ASN Report 2020

During the 2013 examination on the effectiveness of the double-wall reactor containment function, ASN noted that the characteristics of some containments were liable to create internal swelling of the concrete prejudicial to its tightness in the long-term. Since this examination, EDF has initiated measures to characterise and monitor the phenomena which could affect the concrete of the containments. The analyses carried out by EDF notably showed that the kinetics of the development of these phenomena are very slow and that the containments concerned suffer from no structural damage. ASN remains vigilant with regard to the medium to long-term development of the phenomena involved. Modelling of the containments of the 1,300 MWe and 1,450 MWe reactors in a severe accident situation show particular behaviour, which leads to a risk of cracking in part of the thickness of the dome, in certain accident scenarios. In 2019, EDF transmitted data concerning this behaviour, and they are currently being examined by ASN. 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 generating 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 mode operation Operating Technical Specifications The Operating Technical Specifications (STE), which constitute Chapter III of the RGE, define the normal operating conditions based on the facility’s design and sizing hypotheses and require the systems needed for maintaining the safety functions, in particular the integrity of the radioactive substance containment barriers and the monitoring of these functions in the event of an incident or accident. They also stipulate the action to be taken in the event of temporary failure of a required system or if a limit is exceeded, situations which constitute “degraded mode” operation. The STEs evolve to integrate the lessons learned from their applic­ ation and the modifications made to the reactors. The licensee can also modify them temporarily if need be, for example to carry out an operation in conditions that differ from those initially considered in the nuclear safety case. It must then demonstrate the relevance of this temporary modification and define adequate compensatory measures to control the associated risks. Depending on their significance, STE modifications that could affect safety require either submittal of an authorisation application to ASN or notification to ASN before they are implemented. During NPP inspections, ASN verifies that the licensee complies with the STE and, as necessary, the compensatory measures associated with any temporary modifications. It also checks the consistency between the modifications made to the facilities and the normal operating documents, such as operational control instructions and alarm sheets, and the training of the persons responsible for applying them. Periodic tests The Protection Important Component (PIC) of persons and the environment undergo qualification to guarantee their ability to perform their assigned functions in the situations where they are needed. The periodic tests of these equipment items help check their continued qualification and regularly verify that they will be available when required. The periodic test rules for equipment important for safety are incorporated into the general operating rules of the reactors. They set the nature of the technical checks to be performed, their frequency and the criteria for determining the satisfactory nature of these checks. ASN ensures that the periodic tests on the equipment important for safety are pertinent and are continuously improved. It carries out this verification when examining the reactor commissioning authorisation application and then the applications for authorisation to modify the RGE. During inspections, it also verifies that these periodic tests are carried out in accordance with the test programmes stipulated in the RGE. Core physics tests The core physics tests contribute to the first two levels of Defence in Depth. Their purpose is, on the one hand to confirm that the core in operation is compliant with the design baseline requirements and the safety case and, on the other, to calibrate the automatic control and protection systems. These tests, prescribed in the RGE, are performed periodically. The physics tests at restart are comparable to requalification tests following reloading of the core. The physics tests during the cycle and for the cycle extension guarantee the availability and representativeness of the instrumentation as well as the performance of the core in operation. The modifications to the RGE concerning core physics tests are made using a process similar to that for STE modifications and generally require ASN authorisation. During the on site inspections, ASN checks the conformity of the tests performed (compliance with procedures and criteria to be verified) and EDF’s organisation during these particular operating phases. Operating rules in the event of an incident or accident Operation in the event of an incident or accident The strategies and reactor operating rules for an incident or accident situation are defined in the RGE. These evolve notably to take account of experience feedback from incidents and accidents, to correct the anomalies detected during their application or to take account of modifications made to the facilities, in particular those resulting from the periodic safety reviews. Most of these modifications require ASN authorisation. ASN regularly checks the processes to draft and validate the incident or accident operating rules, their pertinence and how they are implemented. To do this, ASN can place the facility’s control teams in a simulated situation to check how they apply the above-mentioned rules and manage the specific equipment used in accident operating situations. It in particular ensures correct application of the emergency teams organisation principles described in the EDF baseline requirements validated by ASN. This organisation more particularly requires that each emergency team member take part in an exercise at least once a year. Operation in a severe accident situation Following an incident or accident, if the safety functions (control of reactivity, cooling and containment) are not guaranteed owing to a series of failures, the situation is liable to develop into a severe accident following severe fuel damage. When faced with such unlikely situations, the installation control strategies place emphasis on preserving the containment in order to minimise releases into the environment. The implementation of these strategies mobilised the expertise of the local and national emergency teams. These teams draw on the On site Emergency Plan (PUI) plus the severe accident intervention guide and the emergency teams action guides in particular. ASN Report on the state of nuclear safety and radiation protection in France in 2020 295 10 – THE EDF NUCLEAR POWER PLANTS 10