There are those who believe the answers to life’s most pressing questions can be found in one of two movies: “The Godfather” (part one) or “The Princess Bride.” In the latter movie, think of the Spaniard’s vaguely taunting response: “You keep using that word. I do not think it means what you think it means.” Which might also be the reply to: “Our nuclear plants are now shut down.”
Right now we are thinking about the Turkey Point and St. Lucie nuclear power stations in South Florida, in the aftermath of hurricane Irma. But we could have been referring to the South Texas Nuclear Project south of Houston, just a week or two earlier.
Those Westinghouse pressurized water reactors have six modes of operation, sort of like gears in a car. The highest level of performance, mode 1 includes power operations all the way up to 100% power. Mode 6, the lowest level of operation, describes a plant in the state of being refueled.
Senior management at NextEra’s utility subsidiary, Florida Power & Light, placed their nuclear reactors in mode 4, “hot shutdown,” as the hurricane advanced towards the plants. (Mode 5 is cold shutdown with far lower internal reactor temperatures.)
In so-called hot shutdown, a nuclear plant has one primary requirement for ongoing safe operation — a reliable supply of electricity (assuming competent staff of course).
Even though nuclear plants produce electricity for the grid, they also require large amounts of electricity to maintain their own operations particularly in this instance for: 1) cooling the fuel in the recently operating nuclear reactor core and 2) cooling the spent fuel pools where used fuel rods are placed after removal from the reactor. These activities are known as residual heat removal.
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