Bristling with weapons and tactical gear, a guard stands ready to defend steel and concrete casks holding spent fuel from a reactor in eastern Washington. The 103 power—generating nuclear reactors in the U.S. annually produce tons of radioactive debris that must be stored—and secured from terrorists—for millennia. A government plan to collect all the nation's nuclear waste in a massive storage vault built within Yucca Mountain, about 80 miles (130 kilometers) northwest of Las Vegas, has encountered vehement opposition from Nevada residents and politicians. New technology may help address the waste problem, allowing future reactors to burn nuclear fuel more efficiently, and leaving waste that is toxic for a shorter period of time.

Nukes again? Maybe. The United States operates 103 nuclear power reactors—that's a quarter of the world's total—even if the most famous U.S. nuke isn't even real. That would be the Springfield plant, where doofus TV cartoon hero Homer Simpson is a safety inspector. "They're cash cows," says James Tulenko, a nuclear fuel specialist, University of Florida professor, and immediate past president of the American Nuclear Society. With hefty construction bills paid off at many plants, "you just deal with the operating costs. All those plants run flat out day and night," he says. And they deliver electricity more cheaply than gas or coal plants.

That's not the whole story, of course. The hopes of a burgeoning nuclear industry imploded 27 years ago after the partial meltdown at one of the Three Mile Island reactors in Pennsylvania, followed by the horror of Chernobyl seven years after that. Plus, decisions made by utility regulators in the 1970s and '80s left companies barely able to pay off billion-dollar nuclear construction bills. Now the U.S. produces half its electricity with cheaper coal-burning plants. The trouble with that is the two billion tons (1.8 billion metric tons) of climate-warming carbon dioxide spewing skyward every year. Industrializing nations, such as India and China, hungry for every megawatt of power they can produce, are also building new coal plants at a rapid clip.

Still, for nearly a decade, with no new plants, nukes' 20 percent share of U.S. electricity production has held steady, keeping pace as overall electricity output has risen 15 percent. In the 1970s and 80s unscheduled shutdowns for repairs or other problems limited U.S. plants to less than 65 percent of their potential output. Today, with experience and improved operating practices, output exceeds 90 percent.

So is it time to embrace the atom again? There's a "nuclear renaissance" buzz emitting from engineers who design and operate reactors, think-tank academics who worry about long-range energy and environmental strategies, utility company executives, top members of the Bush Administration, and members of Congress. Proponents say atomic energy is a proven technology for a 21st-century civilization desperate to swear off fossil fuels and not to go broke doing it. Nuclear fission emits none of the greenhouse gases that are warming the climate. The Nuclear Energy Institute estimates that without nuclear power playing its current role in the generation of electricity, the U.S. would spew 29 percent—190 million metric tons (210 million tons)—more carbon than it does now.

Scratch a nuclear engineer these days, and you'll likely find, under the buttoned-down exterior, a raving green activist. Even among the ranks of environmentalists who a decade ago could barely tolerate the mention of nukes, the possibility is getting an occasional thumbs-up. Climate change, for many, trumps any fear of nuclear energy. Its overwhelming advantage is that it's atmospherically clean, writes Stewart Brand, founder of the 1970s Whole Earth Catalog.

Yet, Brand points out: "Nuclear certainly has problems—accidents, waste storage, high construction costs, and the possible use of nuclear fuel for weapons." Most experts agree that such problems are no small drawback to forging ahead with new nukes. So despite shifting attitudes, atomic allergy has eased only slightly if at all among the bulk of prominent environmental leaders. Analysts also point to other problems, such as unresolved waste questions and limited public input on the whole issue of nuclear power. The current strategy, predicts Gus Speth, co-founder of the Natural Resources Defense Council and Dean of Forestry and Environmental Studies at Yale University, will just replay the battles of the 1970s.

Other nations are watching the U.S., but not waiting. France gets 78 percent of its electricity from nuclear power and is considering replacing its older plants with new ones. And the industry is expected to burgeon in Asia in the next quarter century. China, on top of its headlong rush to build coal-burning plants, also has ambitious plans for new reactors: It can get 6,600 mega­watts of power now from nine reactors. It's aiming for 40,000 megawatts.

India, a nation of 1.1 billion people—and one beset both by crushing poverty and a tumultuously expanding economy—has 15 nuclear power reactors already at work. Eight more are under construction, more than in any other nation. The Department of Atomic Energy lauds the greenhouse benefits of nukes, but the main impetus is sheer gigawatt lust. "Our energy policy is simple," says Baldev Raj, director of the Indira Gandhi Centre for Atomic Research near the Bay of Bengal city of Chennai. "If you have a way to make electricity, then we say, make as much as you can."