Hello folks. My DS graduated and commissioned into the Navy last week and his first assignment (not sure what you call it) is at the Nuclear Power Command school in Charleston, SC. I was never in the military so I know nothing about this. Can anyone give or point me to any advice on that would help him? From talking to the NROTC leaders I got the feeling he is getting into something very difficult.
I went through nuke school both enlisted and as an officer.
My short advice is "buckle up."

Nuke school is very difficult and I once heard it described as the academic version of BUD/S (SEAL training). Students juggle three subjects at time, starting with Reactor Plant Systems (RPS), Math, and Physics. RPS is an overview and one week long, then switches out for chemistry. Math is three weeks if I recall correctly and then switches out for thermodynamics. This process continues for six months. Students stay in the same classroom and instructors rotate through, ~8-4pm, with mandatory evening study hours predicated on how the individual is performing. The material is classified so there's no studying at home. Tests occur frequently, typically 1-2/week and part of the challenge is the limited time the student has for an individual exam (very rare to finish early). Scores are posted by name, best to worst, with the failures highlighted (talk about peer pressure!).
Now, I've always been the "dumb smart kid" -- smart enough to get into the smart kid programs but then struggle. Nuke school, particularly as an officer was brutal for me. I averaged around 70-80 hours/week total in the schoolhouse for a 3.1 GPA. Comparatively, when enlisted I averaged 55-60 and had a 3.6. I bring this up because I hope your DS is similar to peers who had minds capable of far fewer hours and better grades than myself.
What if DS is more akin to myself in aptitude? I'll say this: once upon a time NNPTC had a mentality of failing as many people as possible. However, in the modern era the Navy knows that's an inefficient business practice. Significant screening goes into the officer applicants that are sent and the staff, which is generally phenomenal, works hard to get individuals across the line. I only saw a few people who legitimately could not make it. The others didn't want to put in the necessary effort to succeed in my opinion: yes, they logged 30 extra hours per week with evening / weekend study, but that time was spent feeling bad for themselves and whining, not hustling.
The six months end with the "comp", short for comprehensive exam, which is an eight hour test on
everything. It's a lot of fun...
As others have mentioned, after comp the student then attends NPTU (prototype) either in South Carolina or up in New York. I did NY both times and enjoyed prototype
much more. What I perhaps lacked in raw book smarts compared to my peers I made up for in practicality and application when actually operating a power plant. NPTU is shift work and a grind, don't get me wrong. Still very academic but also different.
My final comment is this advice: if you DS is offered attending SOBC (sub school) between nuke school (NNPTC) and prototype (NPTU)
do not do it. Several peers took that route and while SOBC is a much better quality of life, those individuals regretted falling out of sync with their classmates and arrived to NPTU feeling that they had forgotten too much. None of them were glad they took that option. Anecdotal, but my observation.
Good luck!
Edit: Clearly, nuke school is hard. It's also worth it and I don't mean because of the large financial incentives. All of the successes I've had during my unique career I attribute to the individual I became via Admiral Rickover's legacy.