Anxiety over Japan's quake-crippled nuclear reactors has triggered calls from lawmakers and activists for review of U.S. energy policy and for brakes on expansion of domestic nuclear power.

President Barack Obama has urged expansion of nuclear power to help meet the country's energy demands, lower its dependence on imported fossil fuels and reduce its climate-warming greenhouse gas emissions.

But as engineers in Japan tried yesterday to avert a meltdown at three nuclear reactors following Friday's massive earthquake, some U.S. policy makers were re-evaluating their take on nuclear energy even as the industry itself offered assurances about the safety of new and existing plants.

"I don't want to stop the building of nuclear power plants," independent Senator Joe Lieberman, chairman of the Senate Homeland Security and Governmental Affairs Committee, said on the CBS television's "Face the Nation."

The Fukushima Daiichi nuclear power plant.

"But I think we've got to kind of quietly put, quickly put, the brakes on until we can absorb what has happened in Japan as a result of the earthquake and the tsunami and then see what more, if anything, we can demand of the new power plants that are coming on line," Lieberman added.

Since the 1979 accident at the Three Mile Island nuclear plant in Pennsylvania, many Americans have harbored concerns about nuclear power's safety. Controversy has also dogged the nuclear power industry due to its radioactive waste, which is now stored on site at reactor locations around the country.

The Nuclear Energy Institute, which represents the industry in Washington, said regulators already are reviewing license applications for 20 reactors that would be built over the next 15 to 20 years. Four to eight new reactors are slated to begin operating between 2016 to 2020, spokesman Steven Kerekes said.

"It is a fairly measured build-out program," he said. "We feel it would be premature at this point to draw any conclusions from the tragic events in Japan relative to the U.S. program."

In February 2010, Obama announced $8.3 billion in loan guarantees to build the first U.S. nuclear power plant in nearly three decades. The backing helps Southern Co build two reactors at a plant in the U.S. state of Georgia.

The White House said it was watching the events in Japan for lessons about nuclear safety but indicated that no major policy changes were imminent.

"Information is still coming in about the events unfolding in Japan, but the administration is committed to learning from them and ensuring that nuclear energy is produced safely and responsibly here in the U.S.," White House spokesman Clark Stevens said.

"The president believes that meeting our energy needs means relying on a diverse set of energy sources that includes renewables like wind and solar, natural gas, clean coal and nuclear power."

Environmentalists said Japan's example should be a wake-up call for Obama to reconsider his policies.

"Obama's request for additional loan guarantees for new nuclear reactor projects is now revealed to be a questionable approach given the inherent safety risks of nuclear reactors and resulting radioactive waste," said Tom Clements of environmental group Friends of the Earth.

"Congress should deny any additional funding," he said. The group was opposed to the expansion of nuclear power even before the Japan disaster.

Both Democrats and Republicans have embraced expanding nuclear power as a way to generate electricity and jobs. The recent spike in gasoline prices as well as the Gulf of Mexico oil spill have put a renewed focus on revamping U.S. energy policies to find more sources of fuel.

Senate Republican leader Mitch McConnell, speaking on "Fox News Sunday," urged a cautious approach.

"I don't think right after a major environmental catastrophe is a very good time to be making American domestic policy. I think we ought to just concentrate on helping the Japanese in any way that we can," McConnell said.

Lieberman noted there are 104 nuclear power plants in the United States, and that about 23 of them are built according to designs similar to the nuclear power plants in Japan that are now the focus of the world's concern.

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