[en] The objective of the Sedimentary Rock Program at the Oak Ridge National Laboratory is to conduct investigations to assess the potential for shale to serve as a host medium for the isolation of high-level nuclear wastes. The emphasis on shale is a result of screening major sedimentary rock types (shale, sandstone, carbonate , anhydrite, and chalk) for a variety of attributes that affect the performance of repositories. The retardation of radionuclides was recognized as one of the potentially favorable features of shale. Because shale contains both clay minerals and organic matter, phases that may provide significant sorption of radioelement, the characterization of these phases is essential. In addition, the organic matter in shale has been identified as a critical area for study because of its potential to play either a favorable (reductant) or deleterious (organic ligands) role in the performance of a repository sited in shale. 36 refs., 36 figs., 10 tabs