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See Inside May 2011

The Newest Nuclear Plants Sprout in the U.S. South

As always, safety is a balancing act

The first new nuclear reactor in the U.S. in nearly three decades is taking shape outside Augusta, Ga. Southern Company has dug up a patch of red clay down to bedrock for the foundation of a new AP-1000—a new generation of reactor with passive safety features that keep working even when the power goes out. Southern plans to build two such AP-1000s in the next six years, and other utilities have plans for 12 more, along with another six new reactors of various designs, all of them with passive safety features.

Safety features that operate in the absence of electricity or human intervention were lacking at the Fukushima Daiichi nuclear power plant in Japan, which was built in the 1970s. The March earthquake knocked out the plant’s connection to the grid, and the subsequent tsunami damaged backup generators and electrical equipment, crippling cooling systems and allowing reactor cores to heat up. Each AP-1000, in contrast, has a giant tank of water that sits above the reactor core. In the event of a potential meltdown, the heat buildup would trigger a valve, allowing the water to flow into the reactor.

The AP-1000 also has an open-sky design that, in a pinch, uses air currents to cool the reactor. In a departure from standard designs, the outer concrete building that encloses the reactor’s primary concrete and steel shell has vents near the roof. In a meltdown, natural convection would pull in air.

Convection would also spread radioactive particles out through the roofline vents, critics point out. Engineers counter that eliminating all risk is impossible; the best they can do is strike an acceptable balance between safety and cost. “With earthquakes, there are limits to what you can do,” says Michael Golay, a nuclear engineer at M.I.T. “What risk are you willing to tolerate?”

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