This would not be a problem if
All countries agreed with a neutral third party to put beyond use their nuclear capability.
This may actually work if the weaponized materials are physically removed from the planet or converted into a form no longer useless for weapons.
Extra bonus points if they then do something interesting like superconduct at room temperature or convert solar energy into electrical energy at >80% efficiency.
Note: may need some near Magitech (tm) but in principle the impact of converting all the uranium, radium, plutonium and other "nasty" materials into something less dangerous yet retaining things like medical isotopes assuming fusion still works is actually a minor problem.
Even the top 1.8km of the planet feasibly within range of a quantum electrophoretic transmutation field may be enough.
Biting the hand that feeds IT
