The problem is neutron embrittlement of the containment vessel. There comes a time where it must be replaced and at that point all that's left is the steam infrastructure.
I would mod you up if I had the points.
The neutron bombardment literally causes hydrolysis, and the hydrogen actually penetrates hardened nickel steel! When this steel expands and contracts with thermal changes the steel literally has sections that pop out, sometimes resulting in cracks at joints or even along the entire plumbing -- including the pressure vessel itself.
There is a Swiss reactor that we literally refer to as the Swiss cheese reactor for this reason. The cracks there are not just in the plumbing, but the pressure vessel itself, and the pictures are truly frightening if you think about the age of that reactor and the proposed age of reactors here.
There is another issue though, its the actual concrete that surrounds the plant that is also subject to embrittlement; sometimes this is caused by things like salt water (concrete is porous), but its being seen now that areas near the reactor itself the concrete is breaking down in unexpected ways due to low level neutron bombardment. This is your containment vessel.