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Fast reactor

Photo related to the term with caption below

The reactor block of the Superphenix nuclear reactor in Creys-Malville. The Superphenix is a fast breeder reactor developed in France in the Isere department.

(Source: IAEA)

A reactor that, unlike thermal reactors, operates mainly with fast neutrons (neutrons in the energy range above 0.1 MeV) and does not need a moderator. Fast reactors are generally designed to use plutonium fuels and can produce, through transmutation of 238U, more plutonium than they consume, i.e., they can be operated as breeder reactors with a conversion ratio greater than unity.