For nearly half the 20th century the atom's power has been harnessed to generate electricity on a large scale, yet high costs and chilling accidents have limited its expansion in recent years. Another issue looms into the indefinite future: What to do with tons of radioactive waste?
In 1955, England fired up the first full-scale nuclear power plant. The next year, the first U.S. plant began generating electricity in Shippingport, Pa.
By 1975, hundreds of nuclear power plants were built to produce billions of kilowatt-hours of electricity by the fission of unstable isotopes of heavy metals, most commonly uranium-235.
Here's how nuclear power works: Pellets of enriched uranium isotopes are sealed into fuel rods inside the reactor. Bombarding neutrons split the uranium atoms, creating two smaller atoms and liberating heat and more neutrons. A chain reaction develops, repeating this process.
Excess heat is absorbed by a coolant fluid, usually water. It transfers the heat energy from the reactor core to drive sets of turbines that generate electricity.
The process was promoted as an inexpensive, bountiful and -- with safeguards -- benign source of electricity.
But nuclear plants were not fail-safe. In 1979, a series of mechanical failures and operator mistakes at Three Mile Island in Pennsylvania led to a coolant pump malfunctioning and fuel rods partially melting.
Only the concrete shield surrounding TMI's containment vessel prevented a reactor meltdown and catastrophic radiation release known as the China Syndrome.
But TMI was nothing compared with April 26, 1986.
In the Ukraine, an explosion and fire during a careless overnight experiment caused a meltdown at the No. 4 reactor at Chernobyl.
Chernobyl had no concrete shield. The explosion blew the 1,000-ton steel lid off the reactor.
By some estimates, as many as 20,000 Ukrainian and Russian cleanup workers have died from radiation exposure. Most of Europe was shadowed by the accident's radioactive cloud. A concrete sarcophagus that now entombs the glowing debris is leaking, even as other reactors at Chernobyl still operate.
Worldwide, there are more than 430 nuclear plants, with 45 under construction, mostly in Asia. The United States has 103 nuclear power plants on-line. France relies on nuclear for 77 percent of its power.
Are there alternatives on the horizon?
Some utilities are trying solar, wind and other clean "renewables" to boost peak power generation during hot summer days. More abundant sources such as hydrogen power won't be commercially viable for decades. Ditto for fusion power, which seeks to harness the same properties that spark the nuclear furnace in sun.
Finally, there's the problem of waste.
Nuclear power plants typically store their used, radioactive fuel rods underwater inside their reactors. By some estimates, the industry has accumulated some 170 tons of spare plutonium.
Waste in the nuclear weapons industry is also a problem. At the former Rocky Flats plant in the Denver suburbs, tons of plutonium leftover from the fabrication of thermonuclear triggers remains guarded in a sealed, nitrogen-filled chamber.
The Department of Energy has nowhere to ship the stuff, even as thousands of workers dismantle the factory as part of a $7.3 billion cleanup at Rocky Flats.
In Washington State, the nation's largest military radioactive stockpile is buried in leaky tanks perilously near the Columbia River at the Hanford nuclear reservation.
Washington Gov. Gary Locke warns it's "an underground Chernobyl waiting to happen."
A plan to recycle waste plutonium into a more potent reactor fuel is being considered. But opponents are circling. Some experts believe it would increase the potential for theft of plutonium and for nuclear terrorism.
So what's left to do? Bury the stuff.
In the past 15 years, DOE has spent $2.2 billion to test a repository design at Yucca Mountain, a desert ridge two hours northwest of Las Vegas. Some 80,000 tons of used reactor fuel would be entombed 1,000 feet below the surface. Total construction and operating costs: $18 billion.
DOE's latest assessment: geological studies show there is "reasonable assurance" that Yucca Mountain won't be breached for thousands of years.
Some scientists want transform the wastes so they are less harmful and would decay faster -- perhaps within a few hundred years. That would help to protect the environment, and the federal budget.
At Los Alamos National Laboratory, where the atomic bomb was invented, a mile-long experimental particle beam accelerator bombards radioactive and toxic wastes with highly charged particles. The process would create a smaller amount of more stable wastes, as well as a form of recycled nuclear fuel.
But to the uninitiated, the accelerator process sounds suspiciously like modern-day alchemy.
"We can change lead to gold," agreed Gregory Van Tuyle, who conducts the accelerator tests. "But it's a matter of cost. It wouldn't be worth it."
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