Liquid-Fluoride Thorium Reactors can be started and stopped without incident, in a few hours. I believe their output can also be adjusted in operation. They're safe and efficient enough to build one into a 40-foot trailer that can be started, stopped, and moved on a moment's notice.
My favorite idea for this sort of thing is to put a LFTR on a barge (or, better, in a submarine), using seawater for cooling, and ship them out to any coastal area where they're needed. Build them in factories, assemble them in shipyards where such things are relatively easy, and handle the periodic maintenance and refueling in a centralized location.
Here's where it gets really fun: you can use the waste heat for desalination. There are a lot of places that sit next to a coastline but are short on electricity and fresh water. Russia is trying to make a lot of money from this, using a variant of the reactors they've been using on their nuclear ice-breaker ships.
And if you're using something like a LFTR that's compact enough to fit in a submarine, the water will protect you from hurricanes, earthquakes, aerial attack, and so on. It's a pretty clever scheme. Here's a thread on the Energy From Thorium forums discussing it:
Liquid-Fluoride Thorium Reactors can be started and stopped without incident, in a few hours. I believe their output can also be adjusted in operation. They're safe and efficient enough to build one into a 40-foot trailer that can be started, stopped, and moved on a moment's notice.