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The world's largest nuclear energy producer, the United States, Tuesday aired its first detailed public examination of whether stronger safety standards are needed in light of Japan's Fukushima Daiichi nuclear disaster.
Although the U.S. Nuclear Regulatory Commission (NRC) task force concluded that the sequence of events that caused Japan's crisis was unlikely to recur in the United States, the panel has urged a new focus on preparing for the unexpected.
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Especially at issue is how to deal with "beyond design-basis" risks, events considered too unlikely to be factored in when the plants were being designed. The U.S. task force recommended that a framework of "extended design-basis" requirements be established for the 104 reactors in the United States. This is especially important, task force member Gary Holahan said, in light of the fact that "many of the older plants might have less robust seismic, flooding, and other features."
"Part of the concept of the framework is for the NRC to articulate” expected safety requirements, and to test all plants, no matter their age or design, against that same standard, said Holahan, deputy director of NRC's office of new reactors.
The post-Fukushima inspection reports that NRC ordered for all U.S. nuclear power plants provide a window into risks that the task force says the agency should address.
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For instance, in their April visit to the oldest U.S. nuclear power plant, Exelon's Oyster Creek, near Toms River, New Jersey, close to the shore, the inspectors noted that if power were lost, emergency venting procedures "could result in hydrogen accumulation in the reactor building." Such a build-up is believed to have caused the explosions at Fukushima Daiichi, which, like Oyster Creek, had boiling water reactors with Mark 1 containment systems. Among the NRC task force's recommendations is that reliable hardened vent designs be required in such reactors. (Fukushima and most of the 31 U.S. boiling water reactors have hardened vent designs; the task force is urging steps to make them more reliable.)
Here's a look at some of the other post-Fukushima concerns raised by inspectors at the ten oldest U.S. nuclear power plants.
-- Marianne Lavelle and Christina Nunez