About 20% of United States' and 12% of Canadian electrical generation comes from nuclear power plants. Nuclear plants can operate a long time between refuelings ? 500 days is a typical quoted figure, and some plants (Brunswick 1 and Pickering 7) are notable for having gone more than 700 days between refuelings. Nuclear plants tend to be more stable in operation than coal plants, and generally have more advanced control systems that can correct for minor problems or routine fluctuations. Two nuclear plant operators I asked about this wondered what I had been drinking, then said that a modern North American nuclear plant would likely run unattended for quite a bit longer than a coal power plant barring a mandated operator response ? perhaps as long as a few days to a week. This could vary considerably depending on the plant.