It's an idea that may be catching on. At least 11 new nuclear plants are in the design stage in nine states, including Virginia, Texas, and Florida, according to the Nuclear Energy Institute website.
But that carbon-free pitch has researchers asking anew: How carbon-free is nuclear power? And how cost-effective is it in the fight to slow global warming?
"Saying nuclear is carbon-free is not true," says Uwe Fritsche, a researcher at the Öko Institut in Darmstadt, Germany, who has conducted a life-cycle analysis of the plants. "It's less carbon-intensive than fossil fuel. But if you are honest, scientifically speaking, the truth is: There is no carbon-free energy. There's no free lunch.
Nuclear power has more than just a little greenhouse gas attached to it, when mining uranium ore, refining and enriching fuel, building the plant, and operating it are included. A big 1,250 megawatt plant produces the equivalent of 250,000 tons of carbon dioxide a year during its life, Dr. Fritsche says.
That's still much less than coal-fired power plants and natural-gas turbines. It even does better than solar power and small-scale hydro projects. However, the gap with solar is closing and emissions from manufacturing photovoltaic panels are now on par with nuclear, a new study funded by the U.S. Energy Department finds.
Officials in the nuclear power industry say references to carbon-free energy in their promotions refer only to the power-plant operation and are not intended to describe carbon emissions during the entire nuclear life cycle.
"Yes, absolutely there's carbon," says Paul Genoa, director of policy development for the Nuclear Energy Institute, which represents the nuclear power industry in the U.S. "Most studies have found life-cycle emissions of nuclear to be comparable with renewable. Some show nuclear to be extremely high, but we do not find those credible."
Neither do many researchers. A 2003 Massachusetts Institute of Technology study recommended vast expansion of nuclear power to make a dent in the climate-change problem. Princeton researchers also cited it as an option, although they acknowledged concerns about terror threats and potential accidents.
One University of Wisconsin life-cycle emissions study in 2003 found even lower carbon emissions for nuclear than for most renewables. "We found wind and nuclear fission to have the lowest greenhouse-gas emissions over their life-cycle," says Paul Meier, director of the energy institute at the university. "We didn't include biomass and some of the others now available."
Yet it's not so much nuclear's carbon emissions, which are still relatively modest, but its cost-effectiveness in reducing carbon-dioxide emissions globally that's the key question, researchers say. Few studies have addressed that question.
According to one study that has studied the question, nuclear power may not fare as well when its life-cycle cost of reducing CO2 emissions is compared with other energy alternatives. An Öko Institut study last year found that countries would get more bang for their buck by moving to other forms of energy such as biomass and even some natural-gas power plants rather than nuclear power.
Wind surprisingly has about the same carbon footprint as nuclear when manufacturing and load factors are included. But wind power also doesn't produce long-lived nuclear waste storage of which includes an energy cost that's unknown and is not factored into the Öko or most other analyses yet.
Just improving a nation's energy efficiency would produce far less CO2 than a new nuclear plant (5 grams vs. 32 grams per kilowatt-hour), the study found. And it would do so at lower cost (4.8 cents vs. 5.2 cents per kilowatt-hour).
A handful of other studies show far higher life-cycle CO2 emissions for nuclear than the Öko study. One Dutch researcher, for instance, finds that a vast expansion of nuclear powerr could deplete ore reserves and lead to a far higher level of energy use and carbon emissions from extracting uranium and refining it.
Mr. Genoa of the Nuclear Energy Institute dismisses the claim.
"The bottom line is that society needs to figure out how to get the energy it needs at the lowest possible social and environmental costs," he says. "Any reasonable researcher would recognize that renewable energy has a significant and increasing role to play. But by 2050, these will not supply even a small percentage of the worldwide electricity need. You have to get real about what is needed massive amounts of energy on a massive scale."
But for those energy experts who have done life-cycle analysis of nuclear power, the big concern is that policymakers may be misled into believing that just because nuclear CO2 emissions are low, the cost of nuclear as an option to address climate change would be a bargain. Better, they say, to take the huge amounts of money needed for nuclear plants and use it to build lower-cost solutions that will displace more coal.
"It's easy to show that building more reactors makes climate change worse than it should have been," says Amory Lovins, chairman of the Rocky Mountain Institute, an energy think tank in Snowmass, Colorado. "That's because a dollar put into new reactors gives two to 10 times less climate solution for the amount of coal-power displaced than if you had bought cheaper solutions with the same dollars."
Environmental groups, too, are well aware of the conundrum surrounding the claim of carbon-free energy. Most of them maintain that nuclear is not the answer to climate change.
But their antinuclear arguments have centered on environmental damage from nuclear waste, potential accidents, and terror threats.
"First, nuclear was supposed to be too cheap to meter; now, they're framing it as a solution to climate change," says Erich Pica, director of economic policy for Friends of the Earth, an environmental group. "We hope this Democratic Congress will be skeptical of that claim."