He basically got a bunch of radioactive stuff and put it together. He wasn't anywhere close to making a nuclear reactor let alone a nuclear weapon. For a weapon you need isotopes which he didn't have access to.
Thankfully, that complete failure seems to have been the end of either of their mad scientist careers, as they are now twenty and twenty-three, and both well-adjusted, peaceful members of the community.
A real nuclear engineer with the knowledge he needed would also have said "no, don't do that and I won't help you." We are programming the knowledge into the ai agent. Giving ai a little discretion makes sense too.
https://en.wikipedia.org/wiki/Natural_nuclear_fission_reacto...