BIOGEOCHEMICAL BEHAVIOR OF PLUTONIUM AND AMERICIUM AND GEOCHEMICAL MODELING OF THE SOIL SOLUTION

Field observations suggest that plutonium and americium in the environ ment are present in different chemical forms in the interstitial water s of an intertidal sediment Thermodynamic modelling using the PHREEQE code predicts that plutonium is present entirely in oxidation state (V ) as the PuO2CO3- ion, whereas americium is present entirely in oxidat ion state (III), largely as the uncharged Am(OH)CO3 species, but with significant concentrations of the Am3+ and the AmSO4+ ions. There are, however, differences between these predictions and others published f or a very similar system which apparently arise from uncertainties in the thermodynamic data. Field data cannot resolve these differences un ambiguously.