The US needs to finalize waste processing/storage. Congress' inability to do this has held the industry back. There are 70 reactor sites with waste stored in the parking lot, about a 1/3 of them no longer have active reactors.
Forced obsolescence. One of the advantages is to get everyone using the same design and then set mandatory retirement dates to get folks to move to newer standards. Our constant extending nuclear reactors beyond their planned life span just creates unnecessary risk.