"Critics Challenge Safety of New Reactor Design"

"As Southern Company and its partners, armed with federal loan guarantees of $8.3 billion, move toward construction of two new reactors at a site near Augusta, Ga., opponents are taking aim at the design details.

The reactor, the Westinghouse AP 1000, is also planned for several other locations, but has not yet been fully approved by the Nuclear Regulatory Commission. It is intended to be far safer than existing plants, ensuring that there will be no fuel melting in an accident by relying for its cooling on forces like gravity and natural heat flow instead of pumps, pipes and valves. That concept gives the AP 1000 its name, for Advanced Passive. (The 1,000 refers to the power rating in megawatts, although the actual power output is a less picturesque 1,154.)

A critical feature of the design is an unusual containment structure. One part is a free-standing steel dome, 130 feet high, surrounded by a concrete shield building and topped with a tank of emergency water.
The commission has raised concerns about whether a shield building would be strong enough to survive an earthquake. Westinghouse submitted a detailed report last month and plans another in May to demonstrate that the building is adequate.

But on Wednesday, Arnie Gundersen, a nuclear engineer commissioned by several anti-nuclear groups, released a report suggesting a different hazard.

In existing plants, he pointed out, the containment consists of a steel liner and a concrete dome, but sometimes the steel liner has rusted through.

In the new Westinghouse design, the liner and the concrete are now separated, to allow air to flow between them, so the temperature inside the steel structure will be kept down by natural forces. But if the steel rusts through, “there is no backup containment behind it,’’ Mr. Gundersen said."

Matthew L. Wald reports for the New York Times April 21, 2010.