Radioactive releases from conventional power plants

Field studies were made at two modern thermal (bituminous coal) large-scale power plants with an electric power of 320 and 600 MW respectively. In each case samples were taken for several days running at different places of the total fuel and ash cycle including the released off-gas. The natural nuclides contained in the coal evaporate or sublime in the combustion chamber similar to some elements or oxides and, on the further flue gas path via the dust separator to the purified gas, adhere again to the particulate dusts. These concentration phenomena are particularly pronounced for 210Pb and 210Po if bituminous coal from the Ruhr district is burned. Especially these two easily volatile nuclides are to a higher degree adsorbed by dust particles having got a large surface, which in particular is the case in the range of the finest particles. The assumption of radioactive equilibrium being often found in literature has been confined within the scope of these investigations only for 238U and 234U as well as between 232Th and 228Th. Thereby 234Th and 228Ra or 224Ra could be additionally counted in this category. The releases of nuclides measured in a power plant fired with Rhenish brown coal are lower by about an order of magnitude (a factor 4 to 20) in average. With the nuclide-specific releases model calculations of the environmental impact according to the SSK guidelines were made for the bituminous-coal power plant of 320 Mn under investigation and fictively also for today's usual power plant size of 750 MW. For this dispersion model also parameters of the Refinery Guideline of Northrhine Westphalia were alternatively applied. (orig./HP)