Coal radioactivity release

About one-fifth of our annual exposure to radiation comes from nonnatural sources, primarily medical procedures. Television sets, fallout from nuclear testing, and the coal and nuclear power industries are minor but significant nonnatural sources. Interestingly, the coal industry far outranks the nuclear power industry as a source of radiation. The global combustion of coal annually releases into the atmosphere about 13,000 tons ol radioactive thorium and uranium. Worldwide, the nuclear power industries generate about 10,000 tons of radioactive waste each year. Most of this waste is contained, however, and is not released into the environment. As we explore in Chapter 19, where to bury this contained radioactive waste is a heated issue yet to be resolved. 

During recent years, radioactivity released into the environment by coal power stations has received a great deal of attention from the public, as well as from governments and their agencies. Some of the reports have received much attention and have been published in journals and newspapers. 

Mishra, U.C., Lalit, B.Y. and Ramachandran, T.V., Radioactivity release to the environment by thermal power stations using coal as a fuel. Sci. Total Environ. 14 (1980) 77-83. 

Concerns have often been expressed about coal utilization as a source of toxic and also of radioactive materials since coals contain uranium and thorium at concentration levels of one to four parts per million (ppm), with uranium at levels of 20 ppm rare and thorium as high as 20 ppm veiy rare (USGS, 1997). Coal combustion releases bothU and Th from the coal matrix. As a result, more than 99.5% of these elements ends up in the 10% of solid ash which is formed on the average, i.e., the concentrations of radioac-... 

The two most common objections to nuclear energy are easily disposed of. The radioactivity released by most nuclear plants is smaller than the radioactivity released by a coal fired plant with the same energy output. The amounts of radioactive materials contained in coal are very small but 2.5 million times more coal has to be burned than uranium consumed to produce the same amount of energy. The sulphur dioxide problem of coal-fired plants was mentioned before. The second often heard objection is that nuclear plants may explode as bombs do. The enrichment in the uranium used in our plants is far too small to render an explosion possible. 

Nuclear reactors, however, do generate highly radioactive waste. This waste, which consists primarily of the fission fragments and their radioactive-decay products, must be stored for many years before its radioactivity decays to a reasonable level, and the safe long-term storage of this waste is a matter of great concern and debate. Fortunately, the volume of waste that is created is only about 20 cubic meters annually from a reactor, compared with 200,000 cubic meters of waste ash from a coal-fired plant. When nuclear weapions were tested in the atmosphere, the radioactive products from the nuclear explosions were released into the air and fell to Earth as radioactive fallout. 

Radon-222, a decay product of the naturally occuring radioactive element uranium-238, emanates from soil and masonry materials and is released from coal-fired power plants. Even though Rn-222 is an inert gas, its decay products are chemically active. Rn-222 has a a half-life of 3.825 days and undergoes four succesive alpha and/or beta decays to Po-218 (RaA), Pb-214 (RaB), Bi-214 (RaC), and Po-214 (RaC ). These four decay products have short half-lifes and thus decay to 22.3 year Pb-210 (RaD). The radioactive decays products of Rn-222 have a tendency to attach to ambient aerosol particles. The size of the resulting radioactive particle depends on the available aerosol. The attachment of these radionuclides to small, respirable particles is an important mechanism for the retention of activity in air and the transport to people. 

Fossil fuel electrical power plants can be more hazardous to humans than nuclear power plants because of the pollutants. A 1,000 megawatt (MW) coal-fired power plant releases about 100 times as much radioactivity into the environment as a comparable nuclear plant. A 1,000-MW power plant will use 2,000 railroad cars of coal or 10 supertankers of oil but only 12 cubic meters of natural uranium every year. Fossil fuel... 

Thus it becomes apparent that, for the very high projected coal consumption in this region, the discharge of trace constituents is important, and potential environmental interaction and effects warrant immediate attention. There has been some attention given to radioactive elements in coal and their release during combustion (7, 8, 9). However, the stable element trace constituents are permanent pollutants of the environment, and their immediate and potential long-term effects should be investigated. 

Radioactive materials such as uranium, thorium, and radon gas are released to the environment during coal combustion (51, 52). The amounts of radioactivity are often in excess of that released by many modern nuclear power plants but, nevertheless, are well below established radiation standards (52). 

Worldwide, the amount of energy available from coal is estimated to be about ten times greater than the amount available from all petroleum and natural gas reserves combined. Coal is also the filthiest fossil fuel because it contains large amounts of such impurities as sulfur, toxic heavy metals, and radioactive isotopes. Burning coal is therefore one of the quickest ways to introduce a variety of pollutants into the air. More than half of the sulfur dioxide and about 30 percent of the nitrogen oxides released into the atmosphere by humans come from the combustion of coal. As with other fossil fuels, the combustion of coal also produces large amounts of carbon dioxide. 

In the United States, however, the public perception of nuclear energy is less than favorable. There are formidable disadvantages, including the creation of radioactive wastes and the possibility of an accident that releases radioactive substances into the environment. In rebuttal, advocates point out that we cannot insist that nuclear fission energy be absolutely safe while at the same time accept tanker spills, global warming, acid rain, and coal-miner diseases. 

Because radium is present, usually at very low levels, in the surrounding environment, you are always exposed to it and to the small amounts of radiation that it releases to its surroundings. You may be exposed to higher levels of radium if you live in an area where it is released into the air from the burning of coal or other fuels, or if your drinking water is taken from a source that is high in natural radium, such as a deep well, or from a source near a radioactive waste disposal site. 

Combustion of coal is a significant source of enhanced natural radioactivity (especially combustion of coal from the western United States, which contains significantly more uranium than coal from the eastern United States). When coal is burned, some of the radioactivity is released directly to the atmosphere, but a significant fraction is retained in the bottom ash. Enhanced concentrations of uranium have been found on the ground around coal-fired power plants (UNSCEAR 1982). 

Mastinu, G.G., Natural radioactivity levels in releases from coal-fired power plants in Italy. In Seminar on the radiological burden of man from natural radioactivity in the countries of the European Communities, pp. 429-436. CEC report V/2408/80, 1980. 

The benefit of this type of process is that all potential emissions could be handled at once. However, burning coal releases not just small molecule emissions but sulfur and heavy metals in addition to carbon formation and radioactive emissions. Therefore, it is necessary to perform in situ diagnostics to receive feedback on transient concentrations in order to maintain the most efficient coal burning. 

As compared to power plants based on fossil fuel, in nuclear power plants, the amount of harmful emissions is very low, producing no CO2, SO2, NO, CO or fly a.sh. The amounts of radioactive substances released into the atmosphere by nuclear power plants are also less than those emitted by plants operating with fossil fuel. Surprisingly the local low exposure of the environment surrounding the power plant to radioactivity may be higher by a factor of 400 in the case of power plants burning coal than that in the case of nuclear power plants, since coal contains natural radioactive elements. 

Radionuclides are created for matty other industrial rrses. Some scientific instmments use radioactive sources as part of the measmement process. For example, tritium is often used as an electron sonrce to measure gases in airsticams, and Am (half-life = 432 yr) is nsed as a neutron sorrrce to measme soil moisture. Luminescerrt sigrrs, especially for aircraft runways, are made with tritium. These apph-cations tend to nse only small amormts of radionuclides, and their distribntion is limited, so they do rrot contribute much to the overall level of environmental radioactivity. The use of coal and phosphates (e.g., agricultural fertilizers) also releases uranium- and thorium-series radionuclides and " °K. 

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