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It's not just a matter of red tape. Nukes are best used as "base load" capacity, they don't take kindly to having their power level set up and down, especially down. Has to do with daughter products poising the reaction. I forget the specifics from my Nuclear Engineering course, it's been a long time and I never used the stuff, but I do remember that much, partly because my master's thesis adviser had another grad student working on "optimum dispatch", which means figuring out which generators to use for any given set of conditions of load and generator availability.

I wasn't referring to loading characteristics of nukes so much as the difficulty in dealing with restarts after a shutdown due to an "unusual event". A controlled shutdown for a pending hurricane is classified as such by the government and there is a series of permissions that are required to get back on line.

You're right about baseloading - It isn't just that the units can't be regulated up and down, but they are at their most efficient at full output. Essentially, the fuel rods give up the same amount of useful life whether the unit is generating at full output or half-load (probably due to the "poisoning effect" that you mention). It used to nearly take an act of congress to get a nuke to reduce load on a cool, mild weekend when we had minimum load problems. Often, the choice was to remove some coal units from service on Fridays and return them on Monday morning. Of course, the heating/cooling cycle isn't good for boiler tubes in fossil units either, but it's the lesser of evils.

Optimum dispatch is right up my alley, though things have changed a bit in the last few years. It used to be a lot simpler and a bit less critical, but deregulation has brought out the need for greater precision in order to squeeze every bit of economy out of the available generation that can possibly be had (within the constraints of transmission contingencies and such). It's still part art and part science, but the tools available offer much better cost data with which to work.

In the situation that is the basis of this thread, it isn't clear as to the exact reason of the rolling blackouts, but I suspect it is very localized. Obviously, available power is insufficient to meet the area's requirements, but the exact reason isn't mentioned. Could be a transmission shortage, a generation shortage, a lack of voltage support, or any combination thereof in the area affected.

I did a little more looking, at the Entergy web site. They haven't said much about nuclear operations, but it's very possible that they shut down Waterford and River Bend in anticipation of Rita (as they did for Katrina). It's a precautionary move, but a necessary one. While a direct hit isn't likely to damage the vital parts of the plant, the switchyard and lines leading out of the plant are vulnerable as is offsite power.

Anyway, as to the rolling blackouts, the are local in nature and are probably based on the fact that many, many transmission lines have been damaged in the area. It would seem that the power simply cannot get to the area north of Houston in adequate quantities so the rolling blackout serves to ration power equally until things can be repaired.