01
U
Fission
Uranium nuclei split and release energy.
NUCLEAR ENERGY
Inside a Nuclear Reactor
Discover how a nuclear reactor works, how uranium atoms release energy through nuclear fission, and how this energy is used to generate electricity.
Nuclear
Energy
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Thermal
Energy
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Mechanical
Energy
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Electrical
Energy
REACTOR COMPONENTS
Explore the reactor
Select a component to learn what it does inside the reactor.
Interactive model
Reactor core
Select a component
Control rods
Absorb neutrons
Uranium rods
Nuclear fuel
Reactor vessel
Thick steel
Containment wall
Reinforced concrete
Coolant
Removes heat
Graphite moderator
Slows neutrons
REACTOR SIMULATION
Operate the reactor
Control the chain reaction, coolant flow and electrical output while keeping the reactor within a safe operating temperature.
Ready
CHAIN REACTION
Reactor controls
Withdrawn
Inserted
Coolant pump
Circulates coolant through the reactor.
Simulation speed
Reactor power
0%
Fission rate
Core temperature
25 °C
Reactor core
Coolant flow
0%
Primary coolant
Steam output
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Steam production
Turbine speed
0 RPM
Mechanical energy
Electrical output
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Generator output
INSIDE THE ATOM
How Nuclear Fission Works
Discover what happens when a neutron strikes a uranium-235 nucleus and starts a nuclear chain reaction.
Simplified illustration — not to scale
STEP 1 OF 4
A neutron approaches uranium
A neutron is absorbed by a uranium-235 nucleus, making it unstable.
In a nuclear reactor, the chain reaction is controlled so energy is released steadily as heat.
CONNECTED SIMULATION
From Fission to Electricity
Follow heat from the reactor through the steam generator, turbine and electrical generator. This diagram responds to the reactor controls above.
Reactor heat
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Steam output
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Turbine speed
0 RPM
Electricity generated
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Educational schematic. The primary coolant transfers heat through the steam generator without mixing with the secondary steam circuit. Values follow the simplified reactor model above.
HOW IT WORKS
From fission to electricity
Follow the energy released inside the reactor.
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02
Heating
Energy from fission heats the coolant.
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03
Turbine
Steam turns the turbine.
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04
⚡
Electricity
The generator produces electrical energy.
NUCLEAR TECHNOLOGY
Types of Nuclear Reactors
Discover how nuclear reactors have evolved, and how different designs use coolants, moderators and steam-generation systems.
A brief history of nuclear power
Important milestones in the development of nuclear electricity generation.
First nuclear electricity
EBR-I in the United States generates usable electricity using a fast reactor.
Obninsk power station
The Soviet Obninsk reactor begins supplying nuclear-generated electricity to the grid.
Calder Hall
Britain's Calder Hall begins operation, marking the development of gas-cooled commercial nuclear power.
Shippingport PWR
The Shippingport demonstration plant introduces PWR technology to civilian electricity generation in the US.
Dresden BWR
Dresden Unit 1 begins commercial operation, helping establish boiling water reactors.
Canadian heavy-water reactor
Canada's NPD reactor supplies electricity, demonstrating technology that leads to CANDU reactors.
RBMK development
Leningrad Unit 1 connects to the grid, marking an early Soviet RBMK power reactor.
Advanced gas-cooled reactors
Britain's AGR fleet begins operating at stations including Hinkley Point B and Hunterston B.
Explore reactor designs
Select a reactor type to learn how it works and what makes it different.
PWR Pressurized Water Reactor Light-water reactor ⌄
A PWR uses water under high pressure to remove heat from the reactor core without allowing the primary coolant to boil.
How it works
Hot primary coolant transfers heat through a steam generator to a separate water circuit. Steam from that second circuit drives the turbine.
History
Developed from early US naval reactor technology. Shippingport began operating in 1957 as a pioneering civilian demonstration PWR.
Coolant: Light water
Moderator: Light water
Separate steam generator
BWR Boiling Water Reactor Light-water reactor ⌄
A BWR allows water to boil directly inside the reactor vessel.
How it works
Nuclear fission heats water into steam. After moisture separation, the steam travels directly to the turbine and is later condensed and returned to the reactor.
History
Developed through experimental boiling-water reactor programmes in the 1950s. Dresden Unit 1 began commercial operation in 1960.
Coolant: Light water
Moderator: Light water
Direct steam production
PHWR Pressurized Heavy Water Reactor CANDU is a major example ⌄
A PHWR uses heavy water containing deuterium, rather than ordinary light water, as its moderator. Many designs also use it as coolant.
How it works
Heavy water slows neutrons while absorbing relatively few of them. CANDU designs can use natural uranium fuel and allow refuelling during reactor operation.
History
Developed prominently in Canada. The NPD prototype generated electricity in 1962 and helped establish CANDU technology.
Coolant: Heavy water
Moderator: Heavy water
Natural uranium possible
AGR Advanced Gas-cooled Reactor Graphite-moderated reactor ⌄
An AGR uses carbon dioxide gas as coolant and graphite to slow down neutrons.
How it works
Hot carbon dioxide carries energy from the reactor core to steam generators. These produce steam to turn the turbine.
History
Developed in the United Kingdom as a successor to Magnox gas-cooled reactors. The commercial AGR fleet began operating in 1976.
Coolant: Carbon dioxide
Moderator: Graphite
Separate steam generation
RBMK High-Power Channel Reactor Light-water-cooled, graphite-moderated ⌄
An RBMK uses graphite to moderate neutrons and ordinary water to cool fuel inside pressure channels.
How it works
Water boils inside the fuel channels. Steam is separated from the water and directed to turbines to generate electricity.
History
Developed in the Soviet Union. Leningrad Unit 1 connected to the grid in 1973. An RBMK reactor was involved in the 1986 Chernobyl disaster, leading to major safety modifications to remaining units.
Coolant: Light water
Moderator: Graphite
Boiling pressure channels
FAST Fast Neutron Reactor Fast-spectrum reactor family ⌄
Fast reactors use high-energy neutrons without deliberately slowing them with a moderator.
How it works
Many fast reactors use liquid metal coolants such as sodium, allowing heat to be transferred without moderating neutrons. Some can be designed to breed additional fissile material.
History
EBR-I, an experimental liquid-metal fast reactor, produced the first usable nuclear-generated electricity in December 1951.
Coolant: Often liquid sodium
Moderator: None
Fast neutrons
How do they differ?
Compare the main technical characteristics of these reactor families.
| Type | Coolant | Moderator | Steam generation |
|---|---|---|---|
| PWR | Light water | Light water | Separate steam generator |
| BWR | Light water | Light water | Directly in reactor vessel |
| PHWR / CANDU | Heavy water | Heavy water | Separate steam generator |
| AGR | Carbon dioxide | Graphite | Separate steam generator |
| RBMK | Light water | Graphite | Steam separated after boiling in channels |
| Fast reactor | Often liquid sodium | None | Typically through heat exchangers |
These are representative reactor families. Actual designs vary. A Small Modular Reactor (SMR) is a size and construction approach, not a separate coolant or moderator category. The interactive reactor above is an educational model rather than an exact commercial design.