ASN Report 2018

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 a pressurised water reactor leads to the creation of steam, which does not come into contact with the nuclear fuel. 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 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 circuits and systems are also associated with these elements: primary effluent treatment, feedwater, ventilation and air-conditioning, and backup electrical power (diesel generating sets). CHAPTER 10 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, which could affect all the reactors. ASN thus requires a high degree of responsiveness on the part of EDF and considerable rigorousness when analysing the generic nature of these faults and their consequences for the protection of people and the environment, as well as when processing them. ASN exercises particularly strict oversight of nuclear safety, environmental protection measures and radiation protection in the NPPs and adapts it continuously, more particularly on the basis of operating experience feedback relating to the design, manufacture, operation and maintenance of the nuclear power 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. It intervenes at all stages in the life of the nuclear power 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 interactions between these fields and that it define its regulation and oversight actions accordingly. The resulting integrated view allows ASN to develop a finer appreciation of the state of nuclear safety, radiation protection, environmental protection and the protection of NPP workers. EDF Nuclear Power Plants 276  ASN report on the state of nuclear safety and radiation protection in France in 2018