∙ the Reactor Cavity and Spent Fuel Pit Cooling and Treatment System (PTR), which in particular removes residual heat from the fuel elements stored in the fuel building pool. The design of the ultimate water source installed in the wake of the Fukushima Daiichi NPP accident, can also – in an extreme situation – inject water into the fuel building pool, if the PTR system and the water make-up systems are lost; ∙ the ventilation systems, which ensure containment of radioactive materials by creating negative pressure in the rooms and by filtering discharges; ∙ the fire-fighting water systems; ∙ the I&C system, which processes the information received from all the sensors in the NPP. It uses transmission networks and sends orders to the actuators from the control room, through the programmable logic controllers or operator actions. Its main role with regard to reactor safety is to monitor reactivity, control the removal of residual heat to the heatsink and take part in the containment of radioactive substances; ∙ the electrical systems, which comprise sources and electricity distribution. The French nuclear power reactors have two external electrical sources: the step-down transformer and the auxiliary transformer. These two external sources are supplemented by two internal electrical sources: the backup diesel generators. In the event of total loss of these external and internal sources, each reactor has another electricity generating set comprising a turbine generator and each NPP has an ultimate backup source, the nature of which varies according to the plant in question. Finally, following the Fukushima Daiichi NPP accident, these resources were supplemented by an “Ultimate back-up” Diesel generator set (DUS) for each reactor. 2 Monitoring the nuclear safety of the reactors in operation 2.1 FUEL 2.1.1 Fuel in the reactor The leaktightness of the cladding of the fuel rods, tens of thousands of which are present in each core and which constitute the first containment barrier, receives particularly close attention. In normal operation, leaktightness is monitored by EDF through permanent measurement of the activity of the radionuclides contained in the primary system. Any significant increase in this activity is a sign of a loss of leaktightness in the fuel assemblies. If the activity of the primary system exceeds a predetermined threshold, the General Operating Rules (RGEs) require shutdown of the reactor before the end of its normal cycle. At each outage, EDF is required to search for and identify the assemblies containing leaking rods: reloading of fuel assemblies containing leaking rods is not authorised. EDF conducts examinations of leaking rods in order to determine the origin of the failures and prevent them from reoccurring. The preventive and corrective measures may concern the design of the rods and assemblies, their manufacture or the reactor operating conditions. The conditions of fuel assembly handling, of core loading and unloading, as well as prevention of the presence of foreign objects in the systems and pools are also covered by operating specifications, in order to prevent the risks of fuel rods leaking. 2.1.2 Assessment of the condition of the fuel in the reactor In 2023, all the NPPs satisfactorily managed the integrity of the first barrier, consisting of the fuel rod cladding. There were fuel leaktightness defects in three reactors. This figure is very low, notably as a result of the gradual incorporation of fuel assemblies fabricated by Framatome, for which the mixing grid springs have been heat treated, thereby increasing their strength. The technical discussions held with EDF on the subject of the generalised corrosion of certain M5 alloy fuel cladding, enabled the compensatory operational measures implemented over the past few years to be lifted for all the reactors following justification. Pending the generalised use in all the reactor cores of cladding with an increased iron content, which could prevent this type of corrosion, EDF is maintaining measures to monitor the fuel at each unloading and each selection of assemblies for the next cycles. In addition, errors with calibration or parameter settings in the IT applications monitoring the core were brought to light in 2023. Most of these errors were down to human factors (forgetfulness, use of incorrect procedure). They had no consequences for either humans or the environment. 2.2 NUCLEAR PRESSURE EQUIPMENT 2.2.1 Design and manufacturing of Nuclear Pressure Equipment The manufacturer of the Nuclear Pressure Equipment (NPE) is responsible for the conformity of this equipment with the applicable safety requirements in order to guarantee that there will be no failures during its operation. These requirements are defined by a European Pressure Equipment (PE) Directive and are supplemented by specific NPE requirements, which take account of their importance for the safety of the installation. The manufacturer must define and apply the provisions that enable it to demonstrate compliance with these requirements. The industrial firms, EDF and Framatome in particular, initiated major changes to their industrial processes in 2015 to bring them into line with the regulatory requirements. Most of these actions were carried out within the framework of the “NPE programme” of the French Association for NSSS Design, Construction and Monitoring Rules (AFCEN), which involves the majority of the profession. The work done led to the AFCEN publishing methodology guides and several revisions of the RCC-M code (design and construction rules for mechanical equipment of PWR nuclear islands), on which ASN issued a position statement. ASN in particular recognised that the 2018 edition of the RCC‑M code was on the whole appropriate. This position statement will soon be updated and supplemented by a position statement on the 2020 edition. AFCEN’s work also led to the definition of a process to incorporate OEF into the RCC-M, and this is currently being reviewed by ASN. This is an essential area of work for the profession, in that this code is to be used as the basis for the design and manufacture of all the NPE for the EPR 2 programme. 294 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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