This is true of course, but the power plant is very very simple. Its a fission powered tea kettle. All the 'complicated' bits, the steam turbines the engines, operate outside the tea-kettle part and have been maintained and kept up to date. I don't know if they have done any long term radiological studies on metal fatigue but there aren't a lot of moving parts to go wrong. No reason to think you couldn't continue to use it for another 100 years. And since it goes about 20 years on a single fill up, you'd probably get 50 years out of a refueling if it basically stayed in one place.