In a comment to a post below, Paul Gunter of the extremist antinuclear organization NIRS, completely mischaracterized the reasons behind and the effects of shutting down plants prior to a hurricane. A very knowledgeable colleague of mine, Howard Shaffer, who spent many years working as a systems engineer and who has tangled with Gunter previously, sent me this explanation:
If the grid is lost suddenly, a plant will scram and go on to the diesel generators, as designed and tested. Emergancy Core Cooling is not needed, since there is no leak. This feature is by design choice. It is possible to design nuclear power plants, even the large ones, to have a loss of the grid, and keep running to restart the grid. This makes for a more complicated and expensive design, since when the grid is lost, and the plant is at full load, and the plant is to keep running, the 4.5 million horsepower must go somewhere for a few seconds until reactor power is cut back. A design like this is not optimum in the whole grid system, since other types of plants can be and obviously are designed for black start and reenergizing the grid. Hydro plants are ideal for this. I started up Ludington Pumped storage in Michigan, which was designed to do this. We tested it to prove it could, and it was made an annual drill for the Operators.Technorati tags: Nuclear Energy, Energy, Electricity, NIRS
As I recall, Vermont Yankee was originally designed and built to take a loss of the grid at full power, (full load reject) but this capability was dropped, I think based on upgraded reactor analytical results. The steam hardware was not removed, but of course the Reactor Protection system was made to scram on full load reject.
Plants are shut down in advance of anticipated grid loss (as from a hurricane) because of the conservative operational philosophy of never depending on Safety Systems to do a function that can be done without them.
The statement is completely mixed up when Gunter talks about operating off the grid for "Backup and Safety Systems" When Safety Systems are needed, the reactor is shut down, so it won't be making electric power. Conservative design assumes loss of the grid at the same time - i.e. the scram of the reactor and subsequent trip of the generator CAUSED the loss of the grid. Thus there is an emergency power supply with 100% backup, at least.