If Leavenworth is anything like the military prison in Mannheim, Germany, there's not much to worry about. It's like basic training, only much harder and with more discipline and none of outdoors fun. Prisoners are still in the military and are expected to conduct themselves properly as soldiers.
No, I wasn't in there, just worked with a guard.
That may be true of Mannheim, but Graner has been sentenced to a dishonorable discharge. He will be a civilian at Leavenworth or where ever it is he goes.