Not that I ever sat through one but, I always had the impression it was more about getting a feel for who you are as a person. The fact you are there means you have the grades/knowledge background to be there, thus no need to aks you to draw a 3-D diagram showing an actual fission event or how to design circuit card that count the number of ions in a cubic foot of vacuum

What they want to know is why you want to be nuc? What make you ticks? Can you handle the pressure? Old timers tell tale of Rickover used to try and piss guys off just to see how they react! I have heard he did all kinds of crap to people to see how they reacted. I would guess if you look hard enough you will find stories saying same.
Two of my faviortes:
Once told pilot Lt who wanted to convert that he would not take him because while they were eating lunch together the pilot but pepper on his food with out tasting it! Meant was to set in his way to change (not open minded enough to become nuke)
Once faced an interviewe who told him he was wise to his game and that he could try and piss him off but that it would not work! Rickover said fine then you piss me off or you do not get in! Story is kid picked up model of Natulis of table in the office and stomped on it

. Rickover cused him out and told him he was in and to get the ____ out of his office now.
(are they true?? I am not sure but they sound cool)
Rob