Then of course there is the old fashioned way of taking down the electricity grid using small quantities of C4 on each leg of an unguarded pylon on the transmission line interconnectors a few miles from all the Nuclear Generation Stations in a timed coordinated attack around the country. A Nuclear station at near maximum output (esp Pressuried Water Reactors) may have trouble coping with an instantaneous no load situation leading to a potential thermal runaway. Reacting to this type of catastrophic nuclear power station emergency such as another Chernobyl or 3 mile island with the nation without an electricity power grid would be extremely difficult especially if in the midst of a very cold winter where transportation network may be affected due to winter storms.