Comparative migration behaviour of 137Cs, 90Sr, 241Am and 239+240Pu in soils: examples of forest soil of Vosges and wetland of Mercantour areas (France)
N. SOLOVITCH-VELLA, L. POURCELOT, P. FROIDEVAUX, F. GAUTHIER-LAFAYE, P. STILLE, D. AUBERT
15th Goldschmidt Conference, may 2005, Moscow USA
Geochimica et Cosmochimica Acta, Volume 69, Issue 10, Supplement 1, A479.
The aim of the present work is to compare the behaviour of RNs (137Cs, 90Sr, 241Am and 239+240Pu) in two soils (acidic forest soil in Vosges and organic wetland of Mercantour Mountains). The inventories, vertical distribution of the RNs and their ratios were calculated for each soil. A compartment model has been developed in order to estimate the migration rate of the RNs in the horizons. The results show that the inventory of 241Am and 239+240Pu is 2-3 times higher in soil of Vosges (74±3.5 Bq.m-2 and 207±7.6 Bq.m-2) than in soil of Mercantour (25±1.1 Bq.m-2 and 86±3.0 Bq.m-2 respectively); it is lower for 90Sr in Vosges soil (530±130 Bq.m-2) compared to Mercantour soil (2300±60 Bq.m-2) and similar for 137Cs (16500±2000 Bq.m-2 and 11400±650 Bq.m-2 respectively). In the first 10 cm, the retention of 241Am was more important in wetland of Mercantour (93 % of the inventory) than in forest soil of Vosges (only 68 %). For 239+240Pu, retention in surface layer was less important in Mercantour soil (65 %) with respect to Vosges soil (75 %) whereas comparable values were observed for Cs (80 %) and Sr (60 -65 %). The migration rate of 239+240Pu in Mercantour wetland, calculated with the compartment model, was more important compared to 241Am while it was less important in mineral forest soil of Vosges. In both studied cases estimated migration rates of RNs could explain the different evolution of 241Am/239+240Pu ratio with the depth. The results are discussed in term of the different affinity of the components of two types of soils to the RNs. Further geochemical modelling is planed to understand the interactions occurring between RNs and solid/liquid phases in both studied soils.