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8 Environmental impact associated with pulverized fuel ash: Radioactive Aspects
The earth’s crust contains natural radionuclides. These radionuclides are naturally radioactive substances present since the formation of the earth, which have a very long half-life and are consequently still in existence. The three main natural radioactive substances are uranium, thorium and potassium-40 (40K). Each of the first two substances is associated with numerous radionuclides forming a decay series: radioactive daughter products formed by the decay of uranium 238U and thorium 232Th. These radioactive daughters include radium (226Ra) and the radioactive inert gases radon (222Rn) and thoron (220Rn). Because radioactive substances are found throughout the earth’s crust, a certain amount of radioactive radiation occurs naturally. This is known as background radiation. Substances extracted from the earth’s crust, including sand, clay, flint, marble, granite and coal, also contain certain amounts of radioactive material. The use of such substances – in construction, for example, or in power generation – can result in the concentration of radiation, so that levels exceed natural background radiation levels. When coal is burnt, the radioactive materials in it are left behind in the ash, which consequently has a raised concentration of radioactivity per unit weight. Working with such ash can therefore increase one’s background radiation level. Every year, everyone in the Netherlandsis exposed to an average of 2 mSv of radiation from natural sources. Various human activities increase the level of exposure to roughly 2.5 mSv.
KEMA-report 50030086-KPS/MEC 00-6048.
External reviewer:
Dr A.S. Keverling Buisman, scientist at ECN (Dutch Energy Foundation)
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