Found elsewhere - it would appear the loge of the current reactors is designed around the life of the boat - not the other way round…
“Sub vet here, currently work for the Navy maintaining them. A submarine life is calculated based on its number of dives. Very much like airplanes. When they design the reactor for a submarine and its expected life they calculate how many dives they think they need to get out of it and design a reactor life based on this. For the los angeles class this meant an expected once in a lifetime refuel. For the newer virginia class, better fuel loading technology means they expect to go the entire submarine life without refueling. But the hull and expected number of missions stayed about the same.
There are examples of ships that had to be retired with a lot of fuel left, because the hull was evaluated to be done. And it’s possible to use that reactor still. But once a ship is scheduled for decommissioning, the first thing they do is start cannibalizing components for use elsewhere in the fleet. So keeping high performance reactors and their high performance components operating just to make power would not make good sense. Something like 60 percent of the entire us navy maintenance budget is for submarines alone.
In a perfect world reactor life would be managed to match the hull life exactly. And most of the time it does come very close, because as the boat gets old they start managing it tighter and tighter. But failing that, our next priority is to manage our resources to keep the other boats ready to go and repaired quickly. And that means getting the old ones decommisioned.”
Also interesting is this paper, particularly concerning testing, which explains the issues with aging Life of Ship reactors.
https://uploads.fas.org/media/Life-o...ed-Testing.pdf