For the old obsolete light water reactors
Smaller Thorium reactors do not have to be built on site can can be built in a factory and shipped by rail. They don't require huge concrete and steel containment domes because they don't run at high pressure, they don't need to be built near large bodies of water they can be installed in series which will provide redundancy and allow regular maintenance to be performed without interruption in power generation.
And they can use the nuclear waste we already have an abundance of for fuel.