What are the main types of nuclear reactor?

Reactors are grouped by what they use as coolant and moderator. Light-water reactors (PWR and BWR) run on ordinary water and make up about 90% of the proven global fleet. Beyond them sits a rich menu of advanced designs: heavy-water reactors that need no enrichment, hot gas-cooled reactors, sodium fast reactors that can recycle their own fuel, and molten-salt reactors.

A second axis is size — from large Generation III plants down to small modular reactors and tiny microreactors. The headline is encouraging: today's fleet is built on decades of proven light-water experience, and a new generation of designs is moving from the lab toward deployment.