Re: Not always joking, it seems

One often speaks of critical masses for nuclear explosives.  That is,
fewer neutrons leak out of a system than is generate by the system, so
power levels grow exponentially over time, until all the material is
consumed in the reaction.

One also speaks of criticality - which is important in self-sustaining
nuclear reactions.

An interesting feature of neutron mirror reactors - is that with a
perfectly efficient mirror thre is no lower limit on critical mass.
So, one can imagine lightbulb filament sized rods that get quite hot,
when coated by such mirrors.

Perfect mirrors are not known to exist, but damn good ones do.  A rod
coated in such material can be rather small.  The ends of the rod can
be covered or uncovoered to leak neutrons into an absorber to control
power level.  The whole thing sits in a vacuum tube and solid state PV
cells tuned to the colors the filament produces convert the light to
electricity with no moving parts.  The whole thing is encased in a
neutron sheilded container.

Neutron reflectors and neutron sheilds of high efficiency are not
presently known to exist - especially on a small scale - but this sort
of thing might concievably work at some level - vastly reducing the
size and cost and complexity of nuclear energy.