Can You Really “Shut Down” a Nuclear Power Plant before a Hurricane?

by Leonard Hyman and Willian Tilles, Wolf Street:

Soothing words before the storm: “Our nuclear plants are now shut down.”

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.

Let’s get something straight. If the zombie apocalypse occurred tomorrow, really bad things would happen at nuclear plants. And perhaps in the surrounding area of say a few thousand square miles. But what would not happen is a nuclear explosion.

This is not to deny the potential for explosion. But a hydrogen explosion, a steam explosion and a nuclear bomb type explosion are three very different things. Only the first two have been experienced at commercial nuclear plants. Fukushima Daichi was an unfortunate case of the former (Three Mile Island may have come close) while Chernobyl experienced the latter.

Nuclear plants, thus, need considerable amounts of electricity to maintain safe operations around both the reactor and spent fuel pool. Most of the time, the power comes from another electric generating station nearby.

But when a hurricane knocks down the electric transmission lines, nuclear power plants rely on large, on-site diesel engines to provide electricity for continued operation.

During Hurricane Andrew, a category 4 hurricane which passed over the Turkey Point nuclear power station about twenty five years ago, all the units lost offsite power and relied solely on electricity from diesel generators for more than five days — until electrical connection with the grid was restored. Some variant of this scenario could be occurring, as we write.

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