# fast reactor

> English word · Noun

## Definitions
1. A nuclear reactor with no moderator, using fast neutrons directly in a controlled fission chain reaction without slowing them down, allowing for a much more compact reactor which uses fissile material much more efficiently and generates larger quantities of high-energy neutrons which can be used for breeding more fissile material or producing other useful radioactive nuclides, but requiring the use of highly-enriched uranium (at least 20% uranium-235) or other fuel containing a similarly high concentration of fissile material.

## Etymology
Clipping of fast-neutron reactor.

## Source
Compiled from Wiktionary via kaikki.org (CC BY-SA). Data vintage: 2026-05-06.
Canonical page: https://plainspell.com/en/word/fast-reactor