Energy Encyclopedia

Nuclear Energy · 8 min read · Energy Atlas Editorial

Coolant and Moderator

The coolant removes heat. The moderator slows neutrons. Sometimes they are the same fluid.

  • reactors

In PWRs and BWRs, ordinary water is both moderator and coolant. In CANDU reactors, heavy water moderates (and usually cools). In AGRs, graphite moderates and carbon dioxide cools. Fast reactors avoid moderation so neutrons stay energetic; they use liquid metals or other coolants that do not slow neutrons much.

A good moderator slows neutrons in few collisions and absorbs few of them. A good coolant carries heat, remains chemically compatible, and does not create unmanageable activation products.

Technology

Pressurized Water Reactor Plant

The world's most common power-reactor type: water under high pressure cools the core and transfers heat to a secondary steam cycle.

Keep reading

Articles

Pressurized Water Reactor (PWR)

The pressurized water reactor (PWR) uses light water at a pressure of 15.7 MPa as a coolant. Steam in the secondary circuit propels the turbine.

3 min read

Heavy Water Reactor (PHWR)

The pressurized heavy water reactor (PHWR) uses natural uranium as fuel and heavy water as coolant and moderator. Most of them are of the CANDU type.

3 min read

Fission Chain Reaction

When a neutron splits the 235U nucleus, 2-3 neutrons are released. The fission chain reaction occurs when they split other nuclei, releasing more neutrons.

3 min read

Glossary

C

Coolant

Fluid that removes heat from a reactor or plant.

M

Moderator

Material that slows neutrons.

H

Heavy water

Water with deuterium instead of ordinary hydrogen.

T

Thermal neutron

Neutron in thermal equilibrium with the moderator.