Chemical fractionation of Sr-90, Ru-106, Cs-137 and Ce-144 in Chernobyl-contaminated soils: an evolution in the course of time

The sequential extraction procedure was used for the evaluation of the chemical species of Sr-90, Ru-106, (CS)-C-134, Cs-137 and Ce-144 nuclides in highly contaminated soils inside a 30-km restricted zone around the Chernobyl nuclear power plant. Chemical leaching and weathering of fuel particles have resulted in a rapid increase in the relative contents in soil exchangeable Sr-90 and amount of Ce-144 easily extracted by diluted hydrochloric acid, whereas the ageing effect has helped to make caesium gradually more strongly fixed. In all cares, the behaviour of Cs-134 and Cs-137 in soils was identical. The fact that only partial extraction of Ru-106 by diluted and strong acid has occurred reflects the low solubility of ruthenium, probably included in fuel particles as an intermetallic impurity. The variations in radionuclides speciation with time have been used for estimating the rate of their release from fuel particles and fixation in soil. Average leaching rate constants for Sr-90, Ce-144 and Ru-106 are 1.1 x 10(-3), 6.9 x 10(-4) and 9.4 x 10(-5) day(-1), respectively, and the rate constant for caesium fixation is about 7.3 x 10(-4) day(-1). (C) 1997 Elsevier Science Ltd.