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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 producemechanical energy,
which they then transform into electricity. Conventional
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 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.
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 systems
are also associated with these elements: primary effluent
treatment, boron 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 on
the VVP) as well as the building housing the Fuel Storage
pool (BK). This building, which adjoins the reactor
building, is used to store new and spent fuel assemblies
(one third or one quarter of the fuel is replaced every
12 to 18 months depending on the reactor operating
modes). 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 barrier.
The conventional island equipment includes the turbine,
the AC generator and the condenser. Some components of
R
egulation of NPPs
is a traditional duty of ASN. Nuclear 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 the operation of the French nuclear power
generating reactors, it does entail an increased risk in the event a design or maintenance fault
is 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.
ASN requires the highest level of safety standards for regulatingNPPs and adapts the standards
continuously in the light of new knowledge. 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) and the Nuclear Pressure
Equipment Department (DEP), and of the staff of the regional divisions. It also requires
the support of some 200 experts from the Institute for Radiation Protection and Nuclear
Safety (IRSN).
ASN is developing an integrated approach to regulation that covers not only the design of new
facilities, their construction, modification, integration of feedback on events or maintenance
problems but also the fields of human and organisational factors, radiation protection,
environmental protection, worker safety and the application of labour legislation. This
integrated approach allows ASN to develop a finer appreciation and decide on its position
each year with regard to the current status of nuclear safety, radiation protection and the
environment with respect to NPPs.
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CHAPTER 12:
EDF NUCLEAR POWER PLANTS (NPPs)
ASN report on the state of nuclear safety and radiation protection in France in 2015