I'm afraid it isn't that easy. Shure you can build more modern and more save nuclear plants. The problem is what happens if something goes (terribly) wrong. If a gas plant fails terribly, you get a big explosion and a number of killed people. Tragic, but the consequences are limited in terms of regional spread and timeline. If a nuclear plant fails, the consequences are quite different. You can't just go, clean the place up and build a new plant. The contamination remains and will continue to be lethal for generations to come.
Just invest some time and money? Well, you certainly believe in software that has no bugs, do you?