[InclinedPlane]

Weapons grade HEU is typically 80% or above, though strictly speaking anything above about 20% is pretty easy to make a nuke out of provided you have enough material.

Also, back in the day it was quite normal for such small research reactors to use HEU (specifically, about 93% enrichment), and such reactors were pretty commonplace at the time. See: http://en.wikipedia.org/wiki/Research_reactor