Scientific American, December 13, 2007
Coal Ash Is More Radioactive than Nuclear Waste
By burning away all the pesky carbon and other impurities, coal power plants
produce heaps of radiation
By Mara Hvistendahl
The popular conception of nuclear power is straight out of The Simpsons:
Springfield abounds with signs of radioactivity, from the strange glow
surrounding Mr. Burn's nuclear power plant workers to Homer's low sperm count.
Then there's the local superhero, Radioactive Man, who fires beams of "nuclear
heat" from his eyes. Nuclear power, many people think, is inseparable from a
volatile, invariably lime-green, mutant-making radioactivity.
Coal, meanwhile, is believed responsible for a host of more quotidian
problems, such as mining accidents, acid rain and greenhouse gas emissions. But
it isn't supposed to
spawn three-eyed fish like Blinky.
Over the past few decades, however, a series of studies has called these
stereotypes into question. Among the surprising conclusions: the waste produced
by coal plants is actually more radioactive than that generated by their
nuclear
counterparts. In fact, fly asha by-product from burning coal for
powercontains
up to 100 times more radiation than nuclear waste.
At issue is coal's content of uranium and thorium, both radioactive elements.
They occur in such trace amounts in natural, or "whole," coal that they aren't
a
problem. But when coal is burned into fly ash, uranium and thorium are
concentrated at up to 10 times their original levels.
Fly ash uranium sometimes leaches into the soil and water surrounding a coal
plant, affecting cropland and, in turn, food. People living within a "stack
shadow"the area within a half- to one-mile (0.8- to 1.6-kilometer) radius of a
coal plant's smokestacksmight then ingest small amounts of radiation. Fly ash
is also disposed of in landfills and abandoned mines and quarries, posing a
potential risk to people living around those areas.
In a 1978 paper for Science, J. P. McBride at Oak Ridge National Laboratory
(ORNL) and his colleagues looked at the uranium and thorium content of fly ash
from coal-fired power plants in Tennessee and Alabama. To answer the question
of
just how harmful leaching could be, the scientists estimated radiation exposure
around the coal plants and compared it with exposure levels around
boiling-water
reactor and pressurized- water nuclear power plants.
The result: estimated radiation doses ingested by people living near the coal
plants were equal to or higher than doses for people living around the nuclear
facilities. At one extreme, the scientists estimated fly ash radiation in
individuals' bones at around 18 millirems (thousandths of a rem, a unit for
measuring doses of ionizing radiation) a year. Doses for the two nuclear
plants,
by contrast, ranged from between three and six millirems for the same period.
And when all food was grown in the area, radiation doses were 50 to 200 percent
higher around the coal plants.
McBride and his co-authors estimated that individuals living near coal-fired
installations are exposed to a maximum of 1.9 millirems of fly ash radiation
yearly. To put these numbers in perspective, the average person encounters 360
millirems of annual "background radiation" from natural and man-made sources,
including substances in Earth's crust, cosmic rays, residue from nuclear tests
and smoke detectors.
Dana Christensen, associate lab director for energy and engineering at ORNL,
says that health risks from radiation in coal by-products are low. "Other risks
like being hit by lightning," he adds, "are three or four times greater than
radiation-induced health effects from coal plants." And McBride and his
co-authors emphasize that other products of coal power, like emissions of acid
rainproducing sulfur dioxide and smog-forming nitrous oxide, pose greater
health risks than radiation.
The U.S. Geological Survey (USGS) maintains an online database of fly
ashbased uranium content for sites across the U.S. In most areas, the ash
contains less uranium than some common rocks. In Tennessee's Chattanooga shale,
for example, there is more uranium in phosphate rock.
Robert Finkelman, a former USGS coordinator of coal quality who oversaw
research on uranium in fly ash in the 1990s, estimates that for the average
person the by-product accounts for less than 0.1 percent of total background
radiation exposure. According to USGS calculations, buying a house in a stack
shadowin this case within 0.6 mile [one kilometer] of a coal plantincreases
the annual amount of radiation you're exposed to by a maximum of 5 percent. But
that's still less than the radiation encountered in normal yearly exposure to
X-rays.
So why does coal waste appear so radioactive? It's a matter of comparison:
The chances of experiencing adverse health effects from radiation are slim for
both nuclear and coal-fired power plantsthey're just somewhat higher for the
coal ones. "You're talking about one chance in a billion for nuclear power
plants," Christensen says. "And it's one in 10 million to one in a hundred
million for coal plants."
Radiation from uranium in coal might only form a genuine health risk to
miners, Finkelman explains. "It's more of an occupational hazard than a general
environmental hazard," he says. "The miners are surrounded by rocks and
sloshing
through ground water that is exuding radon."
Developing countries like India and China continue to unveil new coal-fired
plantsat the rate of one every seven to
10 days in the latter nation. And the U.S. still draws around half of its
electricity from coal. But coal plants have an additional strike against them:
they emit harmful greenhouse gases.
With the world now focused on addressing climate change, nuclear power is
gaining favor in some circles. China
aims to quadruple nuclear capacity to 40,000 megawatts by 2020, and the U.S.
may
build as many as 30 new reactors in the next several decades.
But, although the risk of a nuclear core meltdown is very low, the impact of
such an event creates a stigma around the noncarbon power source.
The question boils down to the accumulating impacts of
daily incremental pollution from burning coal or the small risk but
catastrophic consequences of even one nuclear meltdown.
"I suspect we'll hear more about this rivalry," Finkelman says. "More coal will
be mined in the future. And those ignorant of the issues, or those who have a
vested interest in other forms of energy, may be tempted to raise these issues
again."
[Non-text portions of this message have been removed]
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