ASN Report 2017

332 ASN report on the state of nuclear safety and radiation protection in France in 2017 Chapter 12  - EDF Nuclear Power Plants 1. Overview of nuclear power plants 1.1 General presentation of a pressurised water reactor In routing heat from a heat source to a heat sink, all thermal electric power plants produce mechanical energy, which they then transform into electricity. Conventional thermal power plants use the heat given off by the combustion of fossil fuels (fuel oil, coal, gas). Nuclear plants use the heat resulting from the fission of uranium or plutonium atoms. The heat produced in the reactor is used to vaporise water. The steam is then expanded in a turbine which drives a generator producing a 3-phase electric current with a voltage of 400,000 V. After expansion, the steam passes through a condenser where it is cooled on contact with tubes circulating cold water from the sea, a river or an atmospheric cooling circuit. The condensed water is reused in the steam production cycle. Each reactor comprises a nuclear island, a conventional island, water intake and discharge infrastructures and possibly a cooling tower. The nuclear island mainly consists of the reactor vessel, the reactor coolant system, the steam generators and the N uclear power reactors are at the heart of the nuclear industry in France. Many other installations described in the other chapters of this report produce the fuel intended for NPPs or reprocess it, are used for disposal of the waste produced by NPPs, or are used to study the physical phenomena related to the operation and safety of these reactors. The French reactors are technologically similar to each other and form a standardised fleet operated by Électricité de France (EDF). Although this standardisation enables the licensee and ASN to acquire extensive experience of their operation, it does entail an increased risk in the event of a generic design, manufacturing, or maintenance fault being detected on one of these facilities. ASN thus requires a high degree of responsiveness on the part of EDF when analysing the generic nature of these faults and their consequences for the protection of people and the environment. 2017, marked by several major generic events, once again illustrated the implications and the risks entailed by this standardisation. ASN demands a high level of stringency in the monitoring of the NPPs and continuously adapts it, in particular in the light of experience feedback from the design, manufacturing, operation and maintenance of NPP reactor components. Monitoring the safety of the reactors in service, under construction and planned for the future, is the daily task of around 200 members of ASN staff working in the Nuclear Power Plant Department (DCN), the Nuclear Pressure Equipment Department (DEP) and the regional divisions. It also calls on the services of some 200 experts from the Institute for Radiation Protection and Nuclear Safety (IRSN). ASN is developing an integrated approach to facilities monitoring. ASN intervenes at all stages in the life of the NPP reactors, from design up to decommissioning and delicensing. Through its expanded scope of intervention it examines the fields of nuclear safety, organisational and human factors, environmental protection, radiation protection, occupational safety and the application of labour laws, at all stages in the life of the NPP reactors. For each of these fields, it monitors all aspects, whether technical, organisational, or human. This approach requires that it take account of the interaction between these fields and that it adjust its actions accordingly. The resulting integrated view allows ASN to develop a finer appreciation and decide on its position each year with regard to the status of nuclear safety, radiation protection and the environment with respect to NPPs. circuits and systems ensuring reactor operation and safety: the chemical and volume control, residual heat removal, safety injection, containment spray, steam generator feedwater, electrical, I&C and reactor protection systems. Various support function systems are also associated with these elements: primary effluent treatment, boric acid recovery, feedwater, ventilation and air-conditioning, and backup electrical power (diesel generating sets). The nuclear island also comprises the systems removing steam to the conventional island (Steam Shutoff Valve (VVP)) as well as the building housing the Fuel Storage pool (BK). This building, adjacent to the reactor building, is used for storage of new and spent fuel assemblies. The fuel is kept submerged in cells in the pool. The pool water, mixed with boric acid, on the one hand absorbs the neutrons emitted by the nuclei of the fissile elements to avoid sustaining a nuclear fission reaction and, on the other, acts as a radiological shield. The conventional island equipment includes the turbine, the AC generator and the condenser. Some components of this equipment contribute to reactor safety. The secondary systems belong partly to the nuclear island and partly to the conventional island.