Radionuclides in peat bogs and energy peat

The study was aimed at improving the general view on radionuclides contents in energy peat produced in Finland. The annual harvest of fuel peat in 1994 was studied extensively. Also thirteen peat bogs used for peat production and one bog in natural condition were analysed for vertical distributions of several radionuclides. These distributions demonstrate the future change in radioactivity of energy peat. Both natural nuclides emitting gamma radiation (238U, 235U, 232Th, 226Ra, 40K) and radiocaesium (137Cs, 134Cs) origin in fallout from a nuclear power plant accident (1986) and in atmospheric nuclear weapon tests were analysed. The beta and alpha active natural nuclides of lead and polonium (210Pb, 210Po) were determined on a set of peat samples. These nuclides potentially contribute to radiation exposure through inhalation when partially released to atmosphere during combustion of peat. The activity concentrations of natural radionuclides often increased towards the deepest peat bog layers whereas the radioactive caesium deposited from atmosphere was missing in the deep layers. In undisturbed surface layers of a natural bog and peat production bogs the contents of 210Pb and 210Po exceeded those of the deeper peat layers. The nuclides of the uranium series in the samples were generally not in radioactive equilibrium, as different environmental processes change their activity ratios in peat. Radiation exposure from handling and utilisation of peat ash was estimated with activity indices derived from the data for energy peat harvested in 1994. Intervention doses were exceeded in a minor selection of samples due to 137Cs, whereas natural radionuclides contributed very little to the doses. (orig.)