"NASA has conducted tests of a nuclear reactor
intended to generate electricity in space for the
first time since 1965, offering hope that humanity
may now belatedly get serious about building
proper, powerful spaceships of the sort long
envisaged in science fiction.

The space agency has just announced the
tests, conducted by engineers from NASA's
Goddard centre in conjunction with Department
of Energy boffins from the Los Alamos national
lab. The effort made use of an experimental
reactor named "Flattop" and was inauspiciously
dubbed Demonstration Using Flattop Fissions
(DUFF)."

See:

http://www.theregister.co.uk/2012/11...engine_trials/