Let me try some napkin math with nuclear. France is usually taken as a positive example for nuclear. They have 56 reactors on a population of 67 million. For the whole world to get to that level we are talking about 6k-7k in reactors. There are a couple hundred in the world already so let's make it 6k. The costs depend on a lot of things, but 10 billion a pop is a nice round number and for the majority of the world a low estimate. So roughly 60 trillion in construction costs only. Then we need to run them and eventually decommission and store the waste, which even with much smaller scale nuclear programs today will cost hundreds of billions.

Not a realistic solution. We can do more, faster and cheaper with renewables. If you can't get to 100% with renewables, nuclear should anyway be the last option.