Existing nuclear, not new. Those facilities will eventually be decommissioned, as they’re nearing end of life, but it of course makes sense to extend their operating licenses if safe to do so (to be replaced last after fossil generators).
If you break ground on a new reactor this moment, it won’t generate its first kw for years. Historically, over a decade, but folks handwave that cutting regulation and red tape would speed up the process, so I say years to be generous.