David Meyer comments

Fox, every nuclear powerplant is unique. Even reactors that use the same nuclear technology are different from one another. Power plants generally have large engineering staffs because they are continually improving powerplant efficiency and ginding ways to make them last longer. However large powerplants recieve comissions that are not to be tempered with. In the case of nuclear power plants they are usually built and designed to operate for a period of 40-70 years. That means after the designed operational period and comission have expired they will be dismantled and never used again. Prematurely shutting down a nuclear power plant is a huge deal because simply opening a nuclear power plant is a massive commitment. Technology is always advancing so it was decided that insted of building new powerplants every time new technology is developed they would wait until current powerplants reach the end of their designed lifecycle before committing to new powerplants. You can bet that the next round of nuclear power plants will definitely be leaps and bounds safer and more efficient than what we currently have