I would have to believe that the spent fuel pools are supplied by the safety-related busses. Can someone verify this for me?
That would be the busses that were being supplied by the diesel generators at Fukushima until the tsunami hit and knocked them offline.
In my plant, the service water system provides cooling to the spent fuel pool heat exchangers.. the SW pumps and spent fuel pool pumps are safeguards equipment, and on protected busses, powered by the diesels like you said. edit: However, i believe the SFP pumps are initially "stripped" off the safeguards busses, as it typically takes a number of days before SFP heat is a pressing issue. That gives the Ops team time to restore offsite power, or re-fuel the diesel tanks, etc.. Of course, having an entire core offloaded into your SFP for refueling or inspection changes that a little (like in one of the Fukushima units).
I wonder if the tsunami physically took out both trains of the diesel generators themselves at fukushima (if they even have separate trains??), or if the wave simply took out the fuel tanks, effectively disabling both? (or all of the above?).. In any case, losing emergency backup power is bad.. No SI, no aux feed (pwr of course), no spent fuel cooling, no RHR for RCS cooling... Everything was going well after the earthquake. The other plant (Daichi?), which was only a few miles from the epicenter (much closer than the fukushima plants) shut itself down just fine.. It was definitely the wave that did fukushima in. It will be interesting to see what new system enhancements/recommendations/requirements come out of this event for U.S. plants.