[escepticos] re: Resumen sobre la jornada de Cambio Climático (II)

[Ramón Ordiales]

 Para echar más leña al fuego:

 http://www.ornl.gov/info/ornlreview/rev26-34/text/colmain.html



> Una central térmica es más radiactiva que una nuclear... (o eso 
> afirman... )
>
> ----------
>
>
>
>
> ver 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 fly ash.
>
> 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 produces.
>
>
>
> 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.
>
> Conclusions
>
> 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 constraints?
>
>
>
> 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 power.
>
> 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,
> 1987, 90-128.
>
> National Council on Radiation Protection, Radiation Exposure of the U.S.
> Population from Consumer Products and Miscellaneous Sources, Report No. 
> 95,
> 1987, 32-36 and 62-64.
>
> 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.
>
>
>
>