“One capsule of atomic fuel would power the engine and its human carrier for as long as two years.”
“50 Years Ago: Plans fizzled for nuclear-powered artificial heart”
It seems to me that one partial solution to the problem of plutonium-238 shortage, which makes ambitious space missions more difficult, is to promote the use of 238-Pu-powered pacemakers. Create a market for something, & it will get produced.
http://www.orau.org/ptp/collection/Miscellaneous/pacemaker.htm