How a nuclear energy plant works

How a nuclear energy works in 4 key stages

To generate electricity, nuclear power plants function using the phenomenon of nuclear fission, based on the energy released when heavy atoms, such as uranium 235, split. It occurs when a neutron strikes an atom, causing it to split and triggering a chain reaction that releases additional neutrons. This multiplication of atoms generates a large amount of energy in the form of heat. Once cooled, this heat creates steam, which turns turbines connected to alternators to generate electricity!

Getting into more detail, nuclear power plants operate across 4 stages:

1. The primary circuit: at the core of the reactor, small pellets of enriched uranium are placed in metal tubes known as rods. These tubes are immersed in a tank of water, thereby forming the primary circuit. Under the effect of fission in uranium atoms, the water in this circuit heats up to 320°C. The water is kept under pressure to maintain its liquid state.
   
   
2. The secondary circuit: hot water from the primary circuit is used to heat water in the secondary circuit via a steam generator. The steam produced drives steam turbines, which in turn operate an alternator to generate electricity.
   
   
3. Voltage boosting: the resulting electric current is then boosted in voltage via a transformer, reaching levels of 225,000 to 400,000 volts. This enables electricity to be transported more efficiently over the power grid.
   
   
4. The cooling circuit: steam from the secondary circuit is cooled to be transformed back into water. This is achieved by means of a condenser, which can be fed either by cold water taken from the sea or a river, or by air cooled in air-cooled towers.
   

The operating stages of a nuclear energy plant explained in just 2 minutes and 30 seconds

A nuclear power plant can be broken down into 4 different sections:

1. The building housing the reactor, where the nuclear fission reaction takes place (there are 2 to 6 reactors per power plant in France).
   
   
2. The machine room, where electricity is generated from this reaction.
   
   
3. The outlet power lines that transport and remove the electricity that has been generated.
   
   
4. The cooling towers, which will always be located next to a body of water, used for cooling the system.

The 5 main types of nuclear reactors and their specific features

Although nuclear energy plants all use nuclear fuel to generate electricity, they do have different features and benefits that depend on their design. Here is an overview of the main types of reactor and their general features. These will especially depend on the type of fuel used.

1. Pressurized Water Reactors (PWR)  

The 56 reactors currently in operation in France are all PWRs and this reactor family represents more than 80% of the world's operating nuclear fleet. These reactors feature the following characteristics:

• Proven safety: PWRs are widely used around the world due to their excellent safety record.
  
• Cooling system efficiency: they use pressurized water to cool the reactor, which helps maintain thermal stability.

2. Boiling Water Reactors (BWR) 

Boiling water reactors are less commonly used in France and they account for 22% of reactors installed worldwide. But they do have their own particular features:

• Smaller secondary circuit: unlike PWRs, BWRs have no secondary cooling circuit. The steam produced in the reactor is fed directly to the turbines, thereby simplifying the system.
  
• Savings: BWRs are more efficient in their use of water, which can be an advantage in some regions where water is less abundant.

3. Heavy Water Reactors 

Heavy water is both the pressurized heat transfer fluid and the moderator material. It is made up of water molecules containing a heavy hydrogen isotope known as deuterium. Natural uranium is used as fuel.

4. Fast Neutron Reactors (FNR) 

France also uses fast-neutron reactors, such as the Phénix reactor at Marcoule. This type of reactor works differently from PWRs and BWRs:

• Closed fuel cycle: fast-neutron reactors are able to burn plutonium and other fissile materials, reducing the amount of long-lived radioactive waste.
• Plutonium production: they can be used to produce plutonium for reprocessing.

5. Gas-cooled reactors (GCR) 

These reactors use helium to transport heat and can be brought up to high temperature to power the turbine directly, dispensing with any intermediate steps.
GCRs can be used for small power plants (from 100 to 300 MW) and can also operate with fast neutrons.

New reactor technologies under study 

France is exploring the development of new-generation reactors, such as the SMR (Small Modular Reactors), the molten salt reactor (MSR) and the high-temperature reactor (HTR). These reactors feature benefits including:

• Improved nuclear safety: emerging technologies aim to make reactors even safer and more resistant to nuclear accidents.
• Better use of resources: some of these reactors can use fuel more efficiently, reducing the amount of radioactive waste.

TRUE OF FALSE? Smoke from power plants pollutes the atmosphere! 

FALSE Power plants are often depicted with gigantic plumes of smoke rising from their towers. These are not CO₂ discharges but merely water vapor from the air-cooling towers and not from the reactors.
It is harmless to both humans and the environment. Nuclear energy plants do not emit fine particles, nitrogen dioxide or sulfur dioxide into the atmosphere.