The massive earthquake that forced the closure of four nuclear power plants in Japan has highlighted the grave risk of inadequate back-up generators at U.S. facilities, a leading U.S. scientist group said.
While the U.S. regulator made clear that the national nuclear fleet is built to withstand the biggest earthquakes in history, scientists said they needed to do more to ensure that future quakes don't risk the kind of reactor impact that Japan is now grappling with.
"We do not believe the safety standards for U.S. nuclear reactors are enough to protect the public today," Edwin Lyman, senior scientist, global security programs, at the Union of Concerned Scientists, told Reuters. The group supports nuclear power as a means to combat global warming, but wants tougher safety measures.
Meanwhile, an explosion at the Fukushima Dai-ichi nuclear power station Saturday in Japan destroyed a building housing the reactor, but a radiation leak was decreasing despite fears of a meltdown from damage caused by a powerful earthquake and tsunami, officials said.
Japanese officials reportedly issued evacuation orders for at least 45,000 people living near Dai-ichi and a second nuclear power plant where cooling systems broke down as a result of the earthquake. The Daiichi and Daini plants, operated by Tokyo Electric Power, are 10 miles apart in Fukushima Prefecture, about 160 miles north of Tokyo and close to the magnitude 8.9 quake’s epicenter off the coast.
About 24 percent of electricity in Japan is produced by 55 nuclear power units in 17 plants.
US PLANTS LACK BACKUP POWER
Lyman said U.S. reactors also do not have enough backup power to ensure a safe shutdown during an emergency. If reactors could lose both off-site power and backup generators it could lead to a core meltdown in a short period of time.
Nuclear plants need power to keep water flowing over the fuel rods to prevent overheating.
BUILT TO STAND
But news of widespread shutdowns across the nuclear sector in Japan raised questions about how the United States' 104 reactors would respond in the event of a similar quake, one of the five biggest of the past century.
"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 spokesman at the Nuclear Regulatory Commission told Reuters.
Before any reactor is built in the United States, owners are required to conduct geologic seismic studies to determine the biggest earthquake to have occurred in that area going back thousands of years. As in Japan, U.S. reactors are designed to safely shut in the event of an earthquake.
If a bigger earthquake were to occur, Burnell said the plant safety systems would continue to provide the level of safety needed to shut the plant but there would likely be some degradation, though not more than the plant was designed for.
Two U.S. nuclear plants along the California coast made preparations for a potential Pacific Ocean tsunami on Friday, but continued to operate normally.
The reactors — built by companies including PG&E Corp. and Edison International — are designed to safely shut in the event of an earthquake that big, Burnell said.
There are multiple and redundant safety systems at a nuclear plant used to shut the reactor and prevent the release of radiation during an accident.
These systems include an air tight steel or reinforced concrete containment building with walls between 4 to 8 feet thick that is strong enough to withstand the impact of a fully loaded passenger airliner without rupture, and a reactor vessel containing the uranium fuel rods that is made of high tensile steel four to eight inches thick.
The two biggest nuclear operators in the United States are Exelon Corp and Entergy Corp.
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