Uranium-235 is the isotope that can sustain a chain reaction in a nuclear reactor.

Materials which can sustain a chain reaction are called fissile.

The fuel is not supposed to be able to sustain a chain reaction outside the reactor.

The containers were kept small to limit the possibility of assembling a critical mass of nuclear material that would sustain a chain reaction.

Such fuel has been used in the reactor and can no longer sustain a chain reaction.

Not all fissionable isotopes can sustain a chain reaction.

Nuclear power relies on fissionable material that can sustain a chain reaction with neutrons.

In principle, berkelium-249 can sustain a nuclear chain reaction in a fast breeder reactor.

That reduced the ability of the core to sustain a chain reaction.

By definition, fissile materials can sustain a chain reaction with neutrons of any energy.