With an almost unlimited heat-sink available right next to the reactor, plus, nuclear technician training in the Navy is very, very difficult to pass.
Rigorous, yes, but not "very, very difficult to pass". The Navy needs a consistent stream of replacement operators, and their preferred way of getting them is to take reasonably capable volunteers and tutor/coach/remediate as many people as needed once they're in that group.
My experience too. Do you remember the "skyhook"? We'd return to the barracks after class and find that the guy next to you had vanished without a trace.