Re: How do you build a Nucular Reactor?

Basically, you need a fuel, something capable of fissioning, a moderator 
and a means of control.  Fuel means Uranium-235, Plutonium-239, or Thorium-
232, and reactors have been built in this country using all of these fuels.

Moderator means water, heavy water, graphite, and some other materials 
capable of slowing neutrons by absorbing their energy in collisions 
without undue capturing a lot of those neutrons because some will be 
needed to cause further fissioning.

Control, in most cases means rods containing material that can easily 
absorb those neutrons.

Put these three components together in the right proportions and you have 
a nuclear reactor.  The simplest of which was a spherical metal tank about 
the size of a basketball where water and finely ground U-235 were mixed.  
One round Cadmium rod was inserted in a pipe that ran all the way through 
the sphere.  When it was inserted, it absorbed so many neutrons that the 
reactor shutdown.

When it was slowly withdrawn, eventually, the number of neutrons produced 
by the fissioning of the fuel equaled that absorbed and leaked from the 
surface of the sphere.  At that point, the reactor was said to be 
"Critical."  Further withdrawal of the rod caused an exponential increase 
in the number of fissions until the rod was reinserted to the just 
critical position.  Since this was one of the early experimental reactors, 
the fission rate or power level was not allowed to get very high.

And, obviously, some sort of instrumentation is helpful to determine what 
the neutrons are doing.  That is done in the real world, but is not a 
necessary component to building a basic nuclear reactor.