As far as I know he didn't do well in math. I suspect what might have helped most is to have less enablers.
He didn't seem to have ambition to aquire the kind of knowledge that makes a difference. Math. Safety protocols. The politics of working with others and creating a sense of absolute trust.
He may have had a lot of domain knowledge, but was any of it at all relevant to a supercomputer simulation of a reactor?
This isn't something you learn as you go. If you try something, and aren't already 99% sure what is going to happen before you try it, then you may be learning lots of random nuclear facts, but you aren't learning what the professionals do.
99.99% of nuclear engineers have probably never done even one DIY experiment past the very safe "Let's measure bananas" stuff.
The best way to steer him towards a real career would be to make him understand why you do not build backyard reactors, and why you learn your math, go to college, and do things professionally or not at all.