Migration of u and Th series radionuclides in soils and Sediments from a coal mining catchment

In this work we present preliminary results about the disequilibrium of U- and Th- Decay series radionuclides in a fluvial catchment at Palencia (Spain) where several coal Mines and a coal-fired power plant are placed. The activities of several radionuclides (238U, 226Ra, 228Ra, 228Th, and 210Pb) have been determined in soil and sediments by Ray spectrometry with a n-type hp ge detector. Those measurements allow to quantify The radiological impact of the two main radionuclide sources in the catchment: - Mining drainage and migration of radionuclides from the waste piles next to the coal Mines, and; - Radon release from coal combustion at the power plant and from the ash and coal piles Stored there over long periods of time. The peculiar conditions of such environment explain the strong radionuclide Disequilibrium found in soils. Due to the high content of carbonate minerals in the Region the acid mine drainage is neutralize originating alkaline water. Both high ph Values, at least up to 8.8, and presence of carbonates in the soil solution highly increases The solubility of U. Alkaline ph favors, as well, the solubility of amphoteric Radionuclides, as radon descendants, Po, Bi and Pb, while Th and Ra associated with Carbonates behave as insoluble (Ivannovich, 1992). The above mentioned soluble elements will preferentially migrate from soil to drainage Water. The fate of the radionuclides in the river is followed by the analysis of the Sediment activities. Measurements are performed over four fractions of the sediment Sieved by grain-size, which allow to take into account the influence of the river Transport and sorting of the sediments in the radioactivity redistribution along the basin