Migration of plutonium and americium in the lithosphere

When radionuclides are stored as wastes either in permanent repositories or in waste storage areas, the possibility of escape into the environment must be considered. Surface contamination and the transport and migration of radionuclides into the lithosphere through the agency of water are discussed. Water in the form of rain will inevitably wash contaminants into soils and thence into conducting rocks. The migration of radionuclides must follow widely varying paths. In porous rocks, water percolates easily under a slight pressure gradient and rapid movement of large volumes of water can result with concommitant transport of large amounts of contaminating materials. In relatively non-porous rocks such as Niagara limestones the transport meets much more resistance and the volumes of water conducted are correspondingly reduced. In such situations much of the migration of water and its solutes may be through cracks and fissures in the rock. Certain strata of rock or rock products may be almost impervious to flow of water and by this token may be considered to be an especially suitable container for long term safe storage of nuclear wastes, particularly if these strata are quiescent. A series of investigations was undertaken to examine the properties of rocks in acting as a retarding agent in the migration of radionuclides. The rocks that are discussed are Niagara limestone (chosen for its density and fine porosity), basalt from the National Reactor Test site, and Los Alamos tuff