March 12, 2011

Japan Quake Reveals US Nuclear Vulnerabilities

The devastating earthquake that forced the closure of four nuclear power plants in Japan demonstrates the serious risk of inadequate back-up generators at U.S. facilities, said experts with the Union of Concerned Scientists on Friday.

Although U.S. regulators insist the nation's nuclear fleet can withstand such a massive quake, the scientists said more work is needed to ensure that future quakes don't result in the reactor impact now being experienced in Japan.

"We do not believe the safety standards for U.S. nuclear reactors are enough to protect the public today," Edwin Lyman, senior scientist for global security programs at the Union of Concerned Scientists, told Reuters.

The organization supports nuclear power as a way to combat global warming, but wants better safety measures.

The magnitude 8.9 quake that hit Japan on Friday knocked out power to the backup cooling systems of a reactor in Fukushima prefecture, north of Tokyo.  Thousands of residents were evacuated due to the elevated risk of a radiation leak.

Lyman said U.S. reactors are also without adequate backup power to ensure a safe shutdown during an emergency.  If reactors lose both off-site power and backup generators, a core meltdown could result in a short period of time, since the plants rely on power to keep water flowing over the fuel rods to prevent overheating.

The latest news of widespread shutdowns across Japan's nuclear sector raised concerns about how the United States' 104 reactors might respond in a similar disaster.

"There have been tremblers felt at U.S. plants over the past several years, but nothing approaching the need for emergency action," Scott Burnell, a Nuclear Regulatory Commission spokesman, told Reuters.

Burnell said the reactors are designed to safely shut down in the event of an earthquake as large as the one that hit Japan.

Before any reactor can be built in the United States, owners must conduct geologic seismic studies to determine the largest earthquake to have occurred in that area going back thousands of years.

As in Japan, U.S. reactors are designed to safely shut down in the event of an earthquake.  If a larger quake were to occur, the plant safety systems would continue to provide the level of safety needed to shut the plant, Burnell said. 

Although there would likely be some degradation, it would not be more than the plant was designed for, he added.

There are numerous and redundant safety systems at a nuclear plant used to shut the reactor and prevent the release of radiation during such a disaster.  These systems include an air tight steel or reinforced concrete containment building with walls 4 to 8 feet thick -- strong enough to withstand the impact of a fully loaded passenger airliner without rupture.  The plants also include a reactor vessel made of high tensile steel four to eight inches thick that contain the uranium fuel rods.

Two nuclear plants along the California coast -- built by PG&E Corp. and Edison International -- made preparations for a potential tsunami on Friday, but continued normal operations.


Image Caption: Diablo Canyon Power Plant, on the coast of California. Credit: Doc Searls/Wikipedia (CC BY-SA 2.0)  


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