H. (Bill) Wattenburg
TECHNICAL REPORTS ON MAJOR ISSUES -- IN LAYMAN'S TERMS
Oak Ridge Lab Coal Combustion Report
Over the past few decades, the American public has become
increasingly wary of nuclear power because of concern about radiation
releases from normal plant operations, plant accidents, and nuclear
waste. Except for Chernobyl and other nuclear accidents, releases have
been found to be almost undetectable in comparison with natural
background radiation. Another concern has been the cost of producing
electricity at nuclear plants. It has increased largely for two
reasons: compliance with stringent government regulations that restrict
releases of radioactive substances from nuclear facilities into the
environment and construction delays as a result of public opposition.
Partly because of these concerns about radioactivity and the cost of
containing it, the American public and electric utilities have
preferred coal combustion as a power source. Today 52% of the capacity
for generating electricity in the United States is fueled by coal,
compared with 14.8% for nuclear energy. Although there are economic
justifications for this preference, it is surprising for two reasons.
First, coal combustion produces carbon dioxide and other greenhouse
gases that are suspected to cause climatic warming, and it is a source
of sulfur oxides and nitrogen oxides, which are harmful to human health
and may be largely responsible for acid rain. Second, although not as
well known, releases from coal combustion contain naturally occurring
radioactive materials--mainly, uranium and thorium.
Former ORNL researchers J. P. McBride, R. E. Moore, J. P. Witherspoon,
and R. E. Blanco made this point in their article "Radiological Impact
of Airborne Effluents of Coal and Nuclear Plants" in the December 8,
1978, issue of Science magazine. They concluded that Americans living
near coal-fired power plants are exposed to higher radiation doses than
those living near nuclear power plants that meet government
regulations. This ironic situation remains true today and is addressed
in this article.
The fact that coal-fired power plants throughout the world are the
major sources of radioactive materials released to the environment has
several implications. It suggests that coal combustion is more
hazardous to health than nuclear power and that it adds to the
background radiation burden even more than does nuclear power. It also
suggests that if radiation emissions from coal plants were regulated,
their capital and operating costs would increase, making coal-fired
power less economically competitive.
Finally, radioactive elements released in coal ash and exhaust produced
by coal combustion contain fissionable fuels and much larger quantities
of fertile materials that can be bred into fuels by absorption of
neutrons, including those generated in the air by bombardment of
oxygen, nitrogen, and other nuclei with cosmic rays; such fissionable
and fertile materials can be recovered from coal ash using known
technologies. These nuclear materials have growing value to private
concerns and governments that may want to market them for fueling
nuclear power plants. However, they are also available to those
interested in accumulating material for nuclear weapons. A solution to
this potential problem may be to encourage electric utilities to
process coal ash and use new trapping technologies on coal combustion
exhaust to isolate and collect valuable metals, such as iron and
aluminum, and available nuclear fuels.
Makeup of Coal and Ash
Coal is one of the most impure of fuels. Its impurities range from
trace quantities of many metals, including uranium and thorium, to much
larger quantities of aluminum and iron to still larger quantities of
impurities such as sulfur. Products of coal combustion include the
oxides of carbon, nitrogen, and sulfur; carcinogenic and mutagenic
substances; and recoverable minerals of commercial value, including
nuclear fuels naturally occurring in coal.
Coal ash is composed primarily of oxides of silicon, aluminum, iron,
calcium, magnesium, titanium, sodium, potassium, arsenic, mercury, and
sulfur plus small quantities of uranium and thorium. Fly ash is
primarily composed of non-combustible silicon compounds (glass) melted
during combustion. Tiny glass spheres form the bulk of the fly ash.
Since the 1960s particulate precipitators have been used by U.S.
coal-fired power plants to retain significant amounts of fly ash rather
than letting it escape to the atmosphere. When functioning properly,
these precipitators are approximately 99.5% efficient. Utilities also
collect furnace ash, cinders, and slag, which are kept in cinder piles
or deposited in ash ponds on coal-plant sites along with the captured
Trace quantities of uranium in coal range from less than 1 part per
million (ppm) in some samples to around 10 ppm in others. Generally,
the amount of thorium contained in coal is about 2.5 times greater than
the amount of uranium. For a large number of coal samples, according to
Environmental Protection Agency figures released in 1984, average
values of uranium and thorium content have been determined to be 1.3
ppm and 3.2 ppm, respectively. Using these values along with reported
consumption and projected consumption of coal by utilities provides a
means of calculating the amounts of potentially recoverable breedable
and fissionable elements (see sidebar). The concentration of
fissionable uranium-235 (the current fuel for nuclear power plants) has
been established to be 0.71% of uranium content.
Uranium and Thorium in Coal and Coal Ash
As population increases worldwide, coal combustion continues to be the
dominant fuel source for electricity. Fossil fuels' share has decreased
from 76.5% in 1970 to 66.3% in 1990, while nuclear energy's share in
the worldwide electricity pie has climbed from 1.6% in 1970 to 17.4% in
1990. Although U.S. population growth is slower than worldwide growth,
per capita consumption of energy in this country is among the world's
highest. To meet the growing demand for electricity, the U.S. utility
industry has continually expanded generating capacity. Thirty years
ago, nuclear power appeared to be a viable replacement for fossil
power, but today it represents less than 15% of U.S. generating
capacity. However, as a result of low public support during recent
decades and a reduction in the rate of expected power demand, no
increase in nuclear power generation is expected in the foreseeable
future. As current nuclear power plants age, many plants may be retired
during the first quarter of the 21st century, although some may have
their operation extended through license renewal. As a result, many
nuclear plants are likely to be replaced with coal-fired plants unless
it is considered feasible to replace them with fuel sources such as
natural gas and solar energy.
As the world's population increases, the demands for all resources,
particularly fuel for electricity, is expected to increase. To meet the
demand for electric power, the world population is expected to rely
increasingly on combustion of fossil fuels, primarily coal. The world
has about 1500 years of known coal resources at the current use rate.
The graph above shows the growth in U.S. and world coal combustion for
the 50 years preceding 1988, along with projections beyond the year
2040. Using the concentration of uranium and thorium indicated above,
the graph below illustrates the historical release quantities of these
elements and the releases that can be expected during the first half of
the next century, given the predicted growth trends. Using these data,
both U.S. and worldwide fissionable uranium-235 and fertile nuclear
material releases from coal combustion can be calculated.
Because existing coal-fired power plants vary in size and electrical
output, to calculate the annual coal consumption of these facilities,
assume that the typical plant has an electrical output of 1000
megawatts. Existing coal-fired plants of this capacity annually burn
about 4 million tons of coal each year. Further, considering that in
1982 about 616 million short tons (2000 pounds per ton) of coal was
burned in the United States (from 833 million short tons mined, or
74%), the number of typical coal-fired plants necessary to consume this
quantity of coal is 154.
Using these data, the releases of radioactive materials per typical
plant can be calculated for any year. For the year 1982, assuming coal
contains uranium and thorium concentrations of 1.3 ppm and 3.2 ppm,
respectively, each typical plant released 5.2 tons of uranium
(containing 74 pounds of uranium-235) and 12.8 tons of thorium that
year. Total U.S. releases in 1982 (from 154 typical plants) amounted to
801 tons of uranium (containing 11,371 pounds of uranium-235) and 1971
tons of thorium. These figures account for only 74% of releases from
combustion of coal from all sources. Releases in 1982 from worldwide
combustion of 2800 million tons of coal totaled 3640 tons of uranium
(containing 51,700 pounds of uranium-235) and 8960 tons of thorium.
Based on the predicted combustion of 2516 million tons of coal in the
United States and 12,580 million tons worldwide during the year 2040,
cumulative releases for the 100 years of coal combustion following 1937
are predicted to be:
U.S. release (from combustion of 111,716 million tons):
Uranium: 145,230 tons (containing 1031 tons of uranium-235)
Thorium: 357,491 tons
Worldwide release (from combustion of 637,409 million tons):
Uranium: 828,632 tons (containing 5883 tons of uranium-235)
Thorium: 2,039,709 tons
Radioactivity from Coal Combustion
The main sources of radiation released from coal combustion include not
only uranium and thorium but also daughter products produced by the
decay of these isotopes, such as radium, radon, polonium, bismuth, and
lead. Although not a decay product, naturally occurring radioactive
potassium-40 is also a significant contributor.
According to the National Council on Radiation Protection and
Measurements (NCRP), the average radioactivity per short ton of coal is
17,100 millicuries/4,000,000 tons, or 0.00427 millicuries/ton. This
figure can be used to calculate the average expected radioactivity
release from coal combustion. For 1982 the total release of
radioactivity from 154 typical coal plants in the United States was,
therefore, 2,630,230 millicuries.
Thus, by combining U.S. coal combustion from 1937 (440 million tons)
through 1987 (661 million tons) with an estimated total in the year
2040 (2516 million tons), the total expected U.S. radioactivity release
to the environment by 2040 can be determined. That total comes from the
expected combustion of 111,716 million tons of coal with the release of
477,027,320 millicuries in the United States. Global releases of
radioactivity from the predicted combustion of 637,409 million tons of
coal would be 2,721,736,430 millicuries.
For comparison, according to NCRP Reports No. 92 and No. 95, population
exposure from operation of 1000-MWe nuclear and coal-fired power plants
amounts to 490 person-rem/year for coal plants and 4.8 person-rem/year
for nuclear plants. Thus, the population effective dose equivalent from
coal plants is 100 times that from nuclear plants. For the complete
nuclear fuel cycle, from mining to reactor operation to waste disposal,
the radiation dose is cited as 136 person-rem/year; the equivalent dose
for coal use, from mining to power plant operation to waste disposal,
is not listed in this report and is probably unknown.
During combustion, the volume of coal is reduced by over 85%, which
increases the concentration of the metals originally in the coal.
Although significant quantities of ash are retained by precipitators,
heavy metals such as uranium tend to concentrate on the tiny glass
spheres that make up the bulk of fly ash. This uranium is released to
the atmosphere with the escaping fly ash, at about 1.0% of the original
amount, according to NCRP data. The retained ash is enriched in uranium
several times over the original uranium concentration in the coal
because the uranium, and thorium, content is not decreased as the
volume of coal is reduced.
All studies of potential health hazards associated with the release of
radioactive elements from coal combustion conclude that the
perturbation of natural background dose levels is almost negligible.
However, because the half-lives of radioactive potassium-40, uranium,
and thorium are practically infinite in terms of human lifetimes, the
accumulation of these species in the biosphere is directly proportional
to the length of time that a quantity of coal is burned.
Although trace quantities of radioactive heavy metals are not nearly as
likely to produce adverse health effects as the vast array of chemical
by-products from coal combustion, the accumulated quantities of these
isotopes over 150 or 250 years could pose a significant future
ecological burden and potentially produce adverse health effects,
especially if they are locally accumulated. Because coal is predicted
to be the primary energy source for electric power production in the
foreseeable future, the potential impact of long-term accumulation of
by-products in the biosphere should be considered.
Energy Content: Coal vs Nuclear
An average value for the thermal energy of coal is approximately 6150
kilowatt-hours(kWh)/ton. Thus, the expected cumulative thermal energy
release from U.S. coal combustion over this period totals about 6.87 x
10E14 kilowatt-hours. The thermal energy released in nuclear fission
produces about 2 x 10E9 kWh/ton. Consequently, the thermal energy from
fission of uranium-235 released in coal combustion amounts to 2.1 x
10E12 kWh. If uranium-238 is bred to plutonium-239, using these data
and assuming a "use factor" of 10%, the thermal energy from fission of
this isotope alone constitutes about 2.9 x 10E14 kWh, or about half the
anticipated energy of all the utility coal burned in this country
through the year 2040. If the thorium-232 is bred to uranium-233 and
fissioned with a similar "use factor", the thermal energy capacity of
this isotope is approximately 7.2 x 10E14 kWh, or 105% of the thermal
energy released from U.S. coal combustion for a century. Assuming 10%
usage, the total of the thermal energy capacities from each of these
three fissionable isotopes is about 10.1 x 10E14 kWh, 1.5 times more
than the total from coal. World combustion of coal has the same ratio,
similarly indicating that coal combustion wastes more energy than it
Consequently, the energy content of nuclear fuel released in coal
combustion is more than that of the coal consumed! Clearly, coal-fired
power plants are not only generating electricity but are also releasing
nuclear fuels whose commercial value for electricity production by
nuclear power plants is over $7 trillion, more than the U.S. national
debt. This figure is based on current nuclear utility fuel costs of 7
mils per kWh, which is about half the cost for coal. Consequently,
significant quantities of nuclear materials are being treated as coal
waste, which might become the cleanup nightmare of the future, and
their value is hardly recognized at all.
How does the amount of nuclear material released by coal combustion
compare to the amount consumed as fuel by the U.S. nuclear power
industry? According to 1982 figures, 111 American nuclear plants
consumed about 540 tons of nuclear fuel, generating almost 1.1 x 10E12
kWh of electricity. During the same year, about 801 tons of uranium
alone were released from American coal-fired plants. Add 1971 tons of
thorium, and the release of nuclear components from coal combustion far
exceeds the entire U.S. consumption of nuclear fuels. The same
conclusion applies for worldwide nuclear fuel and coal combustion.
Another unrecognized problem is the gradual production of plutonium-239
through the exposure of uranium-238 in coal waste to neutrons from the
air. These neutrons are produced primarily by bombardment of oxygen and
nitrogen nuclei in the atmosphere by cosmic rays and from spontaneous
fission of natural isotopes in soil. Because plutonium-239 is
reportedly toxic in minute quantities, this process, however slow, is
potentially worrisome. The radiotoxicity of plutonium-239 is 3.4 x
10E11 times that of uranium-238. Consequently, for 801 tons of uranium
released in 1982, only 2.2 milligrams of plutonium-239 bred by natural
processes, if those processes exist, is necessary to double the
radiotoxicity estimated to be released into the biosphere that year.
Only 0.075 times that amount in plutonium-240 doubles the
radiotoxicity. Natural processes to produce both plutonium-239 and
plutonium-240 appear to exist.
For the 100 years following 1937, U.S. and world use of coal as a heat
source for electric power generation will result in the distribution of
a variety of radioactive elements into the environment. This prospect
raises several questions about the risks and benefits of coal
combustion, the leading source of electricity production.
First, the potential health effects of released naturally occurring
radioactive elements are a long-term issue that has not been fully
addressed. Even with improved efficiency in retaining stack emissions,
the removal of coal from its shielding overburden in the earth and
subsequent combustion releases large quantities of radioactive
materials to the surface of the earth. The emissions by coal-fired
power plants of greenhouse gases, a vast array of chemical by-products,
and naturally occurring radioactive elements make coal much less
desirable as an energy source than is generally accepted.
Second, coal ash is rich in minerals, including large quantities of
aluminum and iron. These and other products of commercial value have
not been exploited.
Third, large quantities of uranium and thorium and other radioactive
species in coal ash are not being treated as radioactive waste. These
products emit low-level radiation, but because of regulatory
differences, coal-fired power plants are allowed to release quantities
of radioactive material that would provoke enormous public outcry if
such amounts were released from nuclear facilities. Nuclear waste
products from coal combustion are allowed to be dispersed throughout
the biosphere in an unregulated manner. Collected nuclear wastes that
accumulate on electric utility sites are not protected from weathering,
thus exposing people to increasing quantities of radioactive isotopes
through air and water movement and the food chain.
Fourth, by collecting the uranium residue from coal combustion,
significant quantities of fissionable material can be accumulated. In a
few year's time, the recovery of the uranium-235 released by coal
combustion from a typical utility anywhere in the world could provide
the equivalent of several World War II-type uranium-fueled weapons.
Consequently, fissionable nuclear fuel is available to any country that
either buys coal from outside sources or has its own reserves. The
material is potentially employable as weapon fuel by any organization
so inclined. Although technically complex, purification and enrichment
technologies can provide high-purity, weapons-grade uranium-235.
Fortunately, even though the technology is well known, the enrichment
of uranium is an expensive and time-consuming process.
Because electric utilities are not high-profile facilities, collection
and processing of coal ash for recovery of minerals, including uranium
for weapons or reactor fuel, can proceed without attracting outside
attention, concern, or intervention. Any country with coal-fired plants
could collect combustion by-products and amass sufficient nuclear
weapons material to build up a very powerful arsenal, if it has or
develops the technology to do so. Of far greater potential are the much
larger quantities of thorium-232 and uranium-238 from coal combustion
that can be used to breed fissionable isotopes. Chemical separation and
purification of uranium-233 from thorium and plutonium-239 from uranium
require far less effort than enrichment of isotopes. Only small
fractions of these fertile elements in coal combustion residue are
needed for clandestine breeding of fissionable fuels and weapons
material by those nations that have nuclear reactor technology and the
inclination to carry out this difficult task.
Fifth, the fact that large quantities of uranium and thorium are
released from coal-fired plants without restriction raises a
paradoxical question. Considering that the U.S. nuclear power industry
has been required to invest in expensive measures to greatly reduce
releases of radioactivity from nuclear fuel and fission products to the
environment, should coal-fired power plants be allowed to do so without
This question has significant economic repercussions. Today nuclear
power plants are not as economical to construct as coal-fired plants,
largely because of the high cost of complying with regulations to
restrict emissions of radioactivity. If coal-fired power plants were
regulated in a similar manner, the added cost of handling nuclear waste
from coal combustion would be significant and would, perhaps, make it
difficult for coal-burning plants to compete economically with nuclear
Because of increasing public concern about nuclear power and
radioactivity in the environment, reduction of releases of nuclear
materials from all sources has become a national priority known as "as
low as reasonably achievable" (ALARA). If increased regulation of
nuclear power plants is demanded, can we expect a significant
redirection of national policy so that radioactive emissions from coal
combustion are also regulated?
Although adverse health effects from increased natural background
radioactivity may seem unlikely for the near term, long-term
accumulation of radioactive materials from continued worldwide
combustion of coal could pose serious health hazards. Because coal
combustion is projected to increase throughout the world during the
next century, the increasing accumulation of coal combustion
by-products, including radioactive components, should be discussed in
the formulation of energy policy and plans for future energy use.
One potential solution is improved technology for trapping the exhaust
(gaseous emissions up the stack) from coal combustion. If and when such
technology is developed, electric utilities may then be able both to
recover useful elements, such as nuclear fuels, iron, and aluminum, and
to trap greenhouse gas emissions. Encouraging utilities to enter
mineral markets that have been previously unavailable may or may not be
desirable, but doing so appears to have the potential of expanding
their economic base, thus offsetting some portion of their operating
costs, which ultimately could reduce consumer costs for electricity.
Both the benefits and hazards of coal combustion are more far-reaching
than are generally recognized. Technologies exist to remove, store, and
generate energy from the radioactive isotopes released to the
environment by coal combustion. When considering the nuclear
consequences of coal combustion, policymakers should look at the data
and recognize that the amount of uranium-235 alone dispersed by coal
combustion is the equivalent of dozens of nuclear reactor fuel
loadings. They should also recognize that the nuclear fuel potential of
the fertile isotopes of thorium-232 and uranium-238, which can be
converted in reactors to fissionable elements by breeding, yields a
virtually unlimited source of nuclear energy that is frequently
overlooked as a natural resource.
In short, naturally occurring radioactive species released by coal
combustion are accumulating in the environment along with minerals such
as mercury, arsenic, silicon, calcium, chlorine, and lead, sodium, as
well as metals such as aluminum, iron, lead, magnesium, titanium,
boron, chromium, and others that are continually dispersed in millions
of tons of coal combustion by-products. The potential benefits and
threats of these released materials will someday be of such
significance that they should not now be ignored.--Alex Gabbard of the
Metals and Ceramics Division
References and Suggested Reading
- J. F. Ahearne, "The Future of Nuclear Power," American Scientist, Jan.-Feb 1993: 24-35.
- E. Brown and R. B. Firestone, Table of Radioactive Isotopes, Wiley Interscience, 1986.
- J. O. Corbett,
"The Radiation Dose From Coal Burning: A Review of Pathways and Data,"
Radiation Protection Dosimetry, 4 (1): 5-19.
- R. R. Judkins and W. Fulkerson, "The Dilemma of Fossil Fuel Use and Global Climate Change," Energy & Fuels, 7 (1993) 14-22.
- National Council
on Radiation Protection, Public Radiation Exposure From Nuclear Power
Generation in the U.S., Report No. 92, 1987, 72-112.
- National Council
on Radiation Protection, Exposure of the Population in the United
States and Canada from Natural Background Radiation, Report No. 94,
- National Council
on Radiation Protection, Radiation Exposure of the U.S. Population from
Consumer Products and Miscellaneous Sources, Report No. 95, 1987, 32-36
- Serge A. Korff,
"Fast Cosmic Ray Neutrons in the Atmosphere," Proceedings of
International Conference on Cosmic Rays, Volume 5: High Energy
Interactions, Jaipur, December 1963.
- C. B. A. McCusker,
"Extensive Air Shower Studies in Australia," Proceedings of
International Conference on Cosmic Rays, Volume 4: Extensive Air
Showers, Jaipur, December 1963.
- T. L. Thoem, et
al., Coal Fired Power Plant Trace Element Study, Volume 1: A Three
Station Comparison, Radian Corp. for USEPA, Sept. 1975.
- W. Torrey, "Coal Ash Utilization: Fly Ash, Bottom Ash and Slag," Pollution Technology Review, 48 (1978) 136.