Nuclear reactors are regularly maintained, tested and checked. When possible, old plants are upgraded to new safety standards.
You can upgrade certain components, and safety systems. However things like the containment structure or pressure vessel can't be changed. You for example can't retrofit a core catcher, but you could improve the turbines, I think Steam Generators as well, replace PLC's, Tsunami proof your site by building a larger tsunami wall / making your backup generators flood proof...
You can upgrade certain components, and safety systems. However things like the containment structure or pressure vessel can't be changed. You for example can't retrofit a core catcher, but you could improve the turbines, I think Steam Generators as well, replace PLC's, Tsunami proof your site by building a larger tsunami wall / making your backup generators flood proof...