From the Nucleus to Electricity: Anatomy of a Nuclear Power Plant

Nuclear reactor — *Diagram of a pressurized water nuclear reactor (PWR). Image source: public domain (new window).*

Understanding Nuclear Fission

The basic principle of a nuclear power plant is based on the fission of heavy atoms, particularly uranium-235. When a uranium-235 nucleus absorbs a neutron, it becomes unstable and splits into two lighter nuclei, releasing a large amount of energy (about 200 MeV) as well as several additional neutrons. These neutrons can, in turn, cause further fissions: this is the chain reaction.

Structure of a Nuclear Power Plant

A nuclear power plant mainly consists of:

The reactor: the core of the plant, where fission occurs.
The primary circuit: transports heat from the core to a steam generator.
The steam generator: converts water from the secondary circuit into steam.
The turbine: driven by steam, it drives an alternator.
The alternator: converts mechanical energy into electricity.
The condenser: cools the steam to liquefy it and restart the cycle.

Managing the Reaction and Safety

Control of the chain reaction is ensured by control rods, made of materials that absorb neutrons (boron, cadmium). By inserting or removing these rods from the reactor core, the number of fissions is modulated. In an emergency, an automatic shutdown (scram) allows these rods to be inserted instantly to stop the reaction. The containment structure, often made of prestressed concrete, prevents radioactive releases in case of an accident.

Comparative Table of Reactor Types

Comparison of Common Nuclear Reactors
Reactor Type	Moderator	Cooling	Fuel	Example
PWR (Pressurized Water Reactor)	Light Water	Pressurized Water	Enriched UO₂ (~3-5% U-235)	PWR – France (EDF)
BWR (Boiling Water Reactor)	Light Water	Boiling Water	Enriched UO₂	BWR – Japan, USA
RBMK	Graphite	Light Water	Natural Uranium	Chernobyl – USSR
PHWR (CANDU)	Heavy Water	Heavy Water	Natural Uranium	Canada

Sources: International Atomic Energy Agency (IAEA) (new window), World Nuclear Association (new window)

Advantages and Limitations of Nuclear Energy

Nuclear energy has many advantages: continuous production, low CO₂ emissions, high energy density. However, it raises issues of safety, radioactive waste management, and proliferation. The lifespan of waste (up to several hundred thousand years for some isotopes like plutonium-239) implies intergenerational responsibility.

Towards Future Reactors

Fourth-generation reactors are under development (fast breeders, molten salts, high temperature) to improve safety, reduce waste, and optimize resources. At the same time, nuclear fusion – particularly via the ITER project – promises abundant energy, without long-lived waste, but remains at the experimental stage.

Nuclear Electricity Production by Country in 2023
Country	Nuclear Production (TWh)	Share of Nuclear in the Country	Share of Global Nuclear Production
United States	≈ 775 TWh	18.5%	≈ 30.5%
China	≈ 433 TWh	4.9%	≈ 17.0%
France	≈ 324 TWh	64.8%	≈ 12.6%
Russia	≈ 217 TWh	18.4%	≈ 8.5%
South Korea	≈ 180 TWh	30.7%	≈ 7.1%
Ukraine	≈ 86 TWh	≈ 55%	≈ 3.4%
Canada	≈ 85 TWh	≈ 13.7%	≈ 3.3%
Japan	≈ 77 TWh	≈ 5.5%	≈ 2.2%
Spain	≈ 54 TWh	≈ 20.3%	≈ 2.1%
India	≈ 48 TWh	≈ 3.1%	≈ 1.9%
Sweden	≈ 47 TWh	≈ 28.6%	≈ 1.8%
United Kingdom	≈ 37 TWh	≈ 12.5%	≈ 1.5%
United Arab Emirates	≈ 33 TWh	≈ 19.7%	≈ 1.3%
Finland	≈ 33 TWh	≈ 42%	≈ 1.3%
Belgium	≈ 31 TWh	≈ 41.2%	≈ 1.2%
Czech Republic	≈ 30 TWh	≈ 40%	≈ 1.2%
Pakistan	≈ 24 TWh	≈ 17.4%	≈ 0.9%
Switzerland	≈ 23 TWh	≈ 32.4%	≈ 0.9%
Slovakia	≈ 18 TWh	≈ 61.3%	≈ 0.7%
Taiwan	≈ 17.8 TWh	≈ 6.3%	≈ 0.7%
Brazil	≈ 14.5 TWh	≈ 2.2%	≈ 0.6%
Hungary	≈ 15 TWh	≈ 48.8%	≈ 0.6%

Sources: IAEA PRIS "Operating Experience 2023" and World Nuclear Association "World Nuclear Industry Performance Report 2024"