Abstract: A granular fill material is disclosed for use in a storage module for the storing of nuclear and hazardous waste materials. The waste materials are packaged in a waste container which is in turn deposited within the storage module, thereby creating a void space between the waste package or packages and the interior sidewalls of the module. The filler material is reintroduced within the module to fill within this void space, to immobilize the waste containers within the module, and to provide a physical and chemical barrier around the waste containers. The granular filler material comprises a sand filler, an absorbent clay such as Wyoming bentonite, and an organic liquid absorbent material such as Fuller's earth. Other constituents that can be mixed in the granular fill material are an acid neutralizing material such as quicklime or slaked lime, and a getter material for absorbing radionuclides.