| Summary: | Diplôme : Dr. Ing. For the safety assessment of underground radioactive waste disposal conducted by Andra, it is required to estimate the behaviour of radionuclides in soils for the next ten thousand years. Within this time scale, soils would probably evolve from their actual status, according to climate changes. It is then necessary to assess these changes in order to predict the behaviour of the radiochemicals that would enter the soils. We present a pedological forecast method for the assessment of a specific case (i.e. limestone plateau), undergoing periglacial conditions. Then we study the retention of mobile radionuclides, iodine (I) and technetium (Tc) on the forecast periglacial soils. The method relies on the study of analogous soils, sampled in regions with similar geochemical (calcareous) and topographical contexts but undergoing a cold climate which mimics future periglacial conditions of the reference region (steppe-tundra or boreal forest biomes). We have added to the cold and dry climatic series a cold and humid biome (montane strata). The organic matter compartment (OM), considered as an indicator of the effects of the climate on the soils, was thoroughly characterised and taken into account. The analogous soils sampled have developed under boreal forest, cold steppe and subalpine conditions from limestone or calcareous parent materials. The observed soils were eutric Leptosols under boreal forest, and Chernozems under cold steppe. In both biomes, under hydromorphic conditions, OM accumulated in the soil and was high in aromatic molecules in the humified fraction. In the montane strata, the leaching of carbonates was strong enough to allow a diversification of soil genesis: from humic Leptosols to dystric Luvisols. The OM of these soils was different from that of the soils from dry biomes. This study has confirmed that the main differences between soils were observed between the humid and cold climate (montane) on one side and the dry and cold (cold steppe and boreal) on the other. Evolution ...
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