On Dec. 22, a deluge of coal-ash slurry broke through a retaining wall near the Kingston Fossil Plant, a power plant in eastern Tennessee.

Black sludge inundated a valley and destroyed houses as it surged down to the Emory River, where hundreds of fish soon lay dead on fouled banks. Helicopter video footage showed a landscape resembling the moon's surface, with more than a billion gallons of sludge covering 300 acres.

The disaster also temporarily halted an incoming train loaded with coal.

This presumably came from other industrially ravaged landscapes to the east, where entire Appalachian mountaintops are routinely bulldozed into valleys to access seams of Paleozoic carbon.

Tests of river water near the spill found high levels of arsenic, lead, cadmium, thallium and other toxic heavy metals. One sample tested by the Environmental Protection Agency on Dec. 23 had an arsenic concentration 149 times the federal safety standard.

Local folk were caught off-guard.

"The disaster carries a hint of irony for longtime residents," reported the Los Angeles Times. "If there was a concern about ecological threats, it came from a few miles south, where TVA (Tennessee Valley Authority) operates a nuclear plant." Indeed, the Watts Bar Nuclear Generating Station, about 20 miles downstream from the Kingston plant, has been a focus of intense protest and litigation by environmental groups ever since it was licensed for construction in 1973. Yet it is the Kingston plant, never really on green radar, that is suddenly in the news. These sister TVA plants produce almost the same amount of electricity, but their waste streams are very different. About 96 percent (by weight) of the Kingston plant's waste can't be seen from any helicopter, since it has vanished into the air through tall, twin 334-yard-tall smokestacks.

In 2007, Kingston emitted 11 million tons of carbon dioxide (the principal "greenhouse gas" driving climate change), 51,000 tons of sulfur dioxide (which causes acid rain), 12,500 tons of nitrogen oxides (300 times more potent than carbon dioxide for global warming, and a source of acid rain plus low-lying ozone), 1,700 tons of hydrochloric acid aerosol, 330 tons of sulfuric acid aerosol, 230 tons of hydrogen fluoride, 11 tons of ammonia and 30 tons of toxic heavy metals — arsenic, barium, mercury, selenium, etc. — in airborne particulates (smoke).

Except for the carbon dioxide, all these substances harm the respiratory systems of people and animals. However, the power plant's emissions could have been worse. Because Kingston uses "clean coal" technology (in one of its dirtiest incarnations), most of the particulate emissions that darken raw coal smoke never go up the smokestacks. Particles of smoke and ash, mostly in the 10-micron range, are captured and hauled off to storage. In 2007, Kingston impounded about 400,000 tons (dry) of this "fly ash," with a total volume of about half a million cubic yards, which contained 1,100 tons of toxic heavy metal compounds, including 24 tons of arsenic, 720 tons of barium, 25 tons of lead, 90 tons of vanadium, and roughly 10 tons of radioactive thorium and uranium. Unfortunately, water seeping through fly ash readily dissolves heavy metals and washes them into rivers, groundwater and drinking supplies.

It was this poison-leaching, cancer-causing fly ash slurry that recently surprised the Kingston plant's neighbors. Just a half-day's float down the once-pristine river is Watts Bar.

This, not Kingston, is the TVA power plant that environmentalists have been denouncing for decades as a public menace because of its unmanageable wastes. In 2007, the Watts Bar nuclear reactor produced 26 tons of waste, with a total volume of 3.5 cubic yards. This is in the form of dense metal-oxide pellets, stored (for now) in long metal tubes or "fuel rods," that are mounted in metal racks and immersed in water.

In a well-guarded building, somewhere on the 5-square-mile grounds of the Watts Bar plant, there is a concrete-lined pool smaller in area than an Olympic-size swimming pool that now holds all the used fuel rods from the plant's history of providing electricity to 650,000 Tennessee homes, with enough room to keep future spent fuel for at least an additional decade. These rods are very radioactive, especially for the first few years, until their shorter-lived components decay.

The water around them serves as an absorbing shield. The Watts Bar plant managers expect the spent fuel to eventually be placed in a dry, underground repository for safe, long-term storage. However, anti-nuclear activists, unconvinced by the analyses of Energy Department scientists, think that some of the waste will contaminate a patch of desert, raising its level of radioactivity measurably above the background after perhaps 10,000 to 1 million years. With the planet now being ravaged wholesale by the burning of fossil fuels, such speculative concerns seem oddly misdirected. Moreover, the issue is very likely moot because of technologies on the horizon.

In particular, 95 percent of nuclear "waste" can be burned as fuel in advanced fast-neutron reactors after suitable reprocessing. This promises to wring about 20 times more energy out of "spent" fuel rods than they have produced so far. The ultimate waste of nuclear power generation will likely consist only of fission products (split atoms), which decay to a level of radioactivity equal to that of the uranium ore from which the fuel originally came after only 400 years. Even if this advanced technology is never developed (which is unlikely since all parts of it already have been demonstrated in labs and pilot projects), the contrast between the Kingston and Watts Bar waste streams should be clear.

Kingston produces 400,000 times more waste, with vast toxic, radioactive and climate-destroying components, all released into the environment. Watts Bar's waste stream is fully contained, and so minuscule in volume that its management poses no substantial economic or logistical burdens. It never has hurt anyone, and there's no good reason to think that it ever will.

One last note: The anti-nuclear organization Greenpeace has called Watts Bar "a lemon" and "a clear and present danger," but Watts Bar has never had an operational accident in its entire working life. In 2006-08, it ran for 437 days straight at nearly full capacity without a glitch, stopping only for scheduled refueling.

Nuclear energy provides about 20 percent of our nation's electricity, but not a single person ever has been killed in a U.S. commercial nuclear power plant accident, not in the industry's whole 51-year history. (The 1979 Three Mile Island incident harmed equipment, but not people. Some radioactive steam was vented up a stack, but so little that there's only a small chance that it caused a single case of human cancer.)

Many Americans still learn to fear nuclear power from groups like Greenpeace, or from "The Simpsons" on television. This would be funny if the environmental devastation of fossil-fuel burning was not so tragic and so unnecessary.

Robert C. Duncan is a research scientist at the University of Texas in Austin. He wrote this for the Fort Worth (Texas) Star-Telegram.