DELAYED MOBILISATION OF Sr-90 ASSOCIATED WITH FUEL PARTICLES

Following accidental releases from nuclear installations, information on the source terms, and processes influencing radionuclidc mobility and biological uptake within the affected ecosystem is needed for assessing long-term consequences. Information on source terms (composition, activity level, physico-chemical forms) is usually restricted to the list of inventory, or total activities of radionuciides released or deposited, while consideration with respect to radionudide speciation are rarely taken into account. Following the Chernobyl accident released radionuciides were present in different physico-chemical forms, i.e. volatilcs, and associated with condensed and fuel panicles. Close to the source, i.e. within the 30 km zone, the deposition of fuel particles were high and the biological uptake in vegetation of fallout 1}7Cs was low (Bondar et al, 1992). With increasing distance from Chernobyl, a decrease was observed, not only in the total activity level and in the relative contribution from "Sr, transurarrics and refractory fission products, but also in the size and number of deposited fuel particles. However, small fuel particles were identified even in far distant areas i.e. Scandinavia (Devell et al., 1986, Salbu, 1988). Fuel panicles collected from inside and outside the Chernobyl reactor, and contaminated soil