Four years ago this month, James Lovelock upset a lot of his fans. Lovelock was revered in the green movement for developing the Gaia hypothesis, which links everything on earth to a dynamic, organic whole. Writing in the British newspaper The Independent, Lovelock stated in an op-ed: “We have no time to experiment with visionary energy sources; civilisation is in imminent danger and has to use nuclear—the one safe, available energy source—now or suffer the pain soon to be inflicted by our outraged planet.”

Lovelock explained that his decision to endorse nuclear power was motivated by his fear of the consequences of global warming and by reports of increasing fossil-fuel emissions that drive the warming. Jesse Ausubel, head of the Program for the Human Environment at Rockefeller University, recently echoed Lovelock’s sentiment. “As a green, I care intensely about land-sparing, about leaving land for nature,” he wrote. “To reach the scale at which they would contribute importantly to meeting global energy demand, renewable sources of energy such as wind, water, and biomass cause serious environmental harm. Measuring renewables in watts per square meter, nuclear has astronomical advantages over its competitors.” All of this has led several other prominent environmentalists to publicly favor new nuclear plants. I had a similar change of heart. For years I opposed nuclear power, but while I was researching my book Power to Save the World: The Truth About Nuclear Energy, my views completely turned around.

According to the Department of Energy, just to maintain nuclear’s 20 percent share of the energy supply, the United States would need to add three or four new nuclear power plants a year starting in 2015. (There are 104 nuclear power plants currently in operation in the United States.) But no new nuclear power plants have been built here in 30 years, partly because of the public’s aversion to nuclear power after the Three Mile Island accident in 1979 and the Chernobyl disaster in 1986. Now NRG Energy, based in Princeton, New Jersey, is sticking its neck out with plans to build two new nuclear reactors at the South Texas Project facility near Bay City. The new reactors will be able to steadily generate a total of 2,700 megawatts—enough to light up 2 million households.

The United States alone pumped the equivalent of nearly 7 billion tons of carbon dioxide into the atmosphere in 2005. More than 2 billion tons of that came from electricity generation—not surprising, considering that we burn fossil fuels for 70 percent of our electricity. About half of all our electricity comes from more than 500 coal-fired plants. Besides contributing to global warming, their pollution has a serious health impact. Burning coal releases fine particulates that kill 24,000 Americans annually and cause hundreds of thousands of cases of lung and heart problems.

America’s electricity demand is expected to increase by almost 50 percent by 2030, according to the Department of Energy. Unfortunately, renewable energy sources, such as the wind and sun, are highly unlikely to meet that need. Wind and solar installations today supply less than 1 percent of electricity in the United States, do so intermittently, and are decades away from providing more than a small boost to the electric grid. “To meet the 2005 U.S. electricity demand of about 4 million megawatt-hours with around-the-clock wind would have required wind farms covering over 780,000 square kilometers,” Ausubel notes. For context, 780,000 square kilometers (301,000 square miles) is greater than the area of Texas. Solar power fares badly too, in Ausubel’s analysis: “The amount of energy generated in [one quart] of the core of a nuclear reactor requires [2.5 acres] of solar cells.” Geothermal power also is decades away from making a significant contribution to America’s electricity budget.

“Nuclear has the power to move the needle in the fight against global warming,” says NRG’s president and CEO, David Crane. “While the up-front costs of building new nuclear generation are not cheap, in the long run it’s one of the most economical ways to make electricity.” NRG is already the target of vocal opposition. National environmental groups, and some in Texas like the Sierra Club and Public Citizen, do not want new electrical demand met by nuclear power. “We’re all very much in opposition,” says Karen Hadden, director of the Sustainable Energy and Economic Development Coalition, which has rallied other groups to the battle. “We’ll fight the reactors.” She, like other opponents, insists that nuclear power is unsafe and costly and diverts dollars from conservation, energy efficiency, wind, solar, and energy-storage technologies.

Public concerns about nuclear power have traditionally centered on two issues: the risk of widespread radioactive fallout from an accident and the hazards of nuclear waste. (Since 9/11, security risk has emerged as a third major worry.) My research shows such fears are unfounded. A Chernobyl cannot happen here—a survey by the Nuclear Regulatory Commission (NRC) established that our reactors are free of the design flaws that permitted Chernobyl to explode, and in the United States a typical reactor core is surrounded by multiple enclosures to block the escape of radioactive material even in the event of an accident. Chernobyl had no such containment.

Our worst commercial reactor accident, at Three Mile Island 2, was said to be successfully contained despite a partial meltdown, according to the NRC’s investigation. A minute quantity of radioactive gas was intentionally vented from the reactor building, but several independent, peer-reviewed studies have not ascertained any health effects attributable to exposure. Since then, U.S. regulations have instituted many additional safety measures. The reactors that will be used by NRG in the South Texas Project are of a type dubbed the Advanced Boiling Water Reactor (pdf), the latest iteration of a thoroughly vetted design that has been safely used for a decades, the light water reactor. These reactors have the intriguing feature that the water used to cool the core and run the generating turbine is also essential to maintaining a nuclear chain reaction. Briefly, fissioning atoms in the nuclear reactor’s fuel emit neutrons that are traveling too fast to efficiently cause other atoms to fission. The water slows the neutrons, allowing the chain reaction to continue at a steady pace. In case of an accident, multiple systems would keep cooling water flowing to the core, and control rods would quickly drop, automatically shutting down the nuclear reactions.

What about the waste? Uranium is an extremely dense source of energy, and the volume of waste is therefore small. According to David Bradish, a data analyst at the Nuclear Energy Institute, a nuclear fuel pellet measures 0.07 cubic inch (about the size of your fingertip) and contains the energy equivalent of 1,780 pounds of coal. The nation’s 104 reactors generate roughly 800 billion kilowatt-hours a year and contribute about 2,000 tons of spent nuclear fuel a year. By contrast, U.S. coal combustion produces some 100 million tons of toxic material annually.

At nuclear plants, spent fuel is currently being transferred from pools to robust concrete casks, where it can be secured for about a century. But this spent fuel, which retains more than 95 percent of its energy, can be reprocessed to make new fuel, reducing the ultimate volume of waste by more than 60 percent. The National Academy of Sciences has given the nod to long-term disposal of spent fuel in canisters that will be sealed deep inside a mountain near the vast, remote Nevada Test Site, where hundreds of atomic bombs were once exploded.

NRG is currently waiting for a go-ahead from the NRC to construct and operate its new pair of reactors, scheduled to come online in 2014 and 2015. Several other companies are now lining up to submit their own new reactor plans. NRG’s approval is expected no sooner than 2011, but should it come, it could signal the start of a nuclear renaissance and of substantial reductions in America’s carbon footprint.