MULTIPLE OPTIONS FOR GEOLOGIC DISPOSAL OF HIGH-LEVEL RADIOACTIVE WASTE

Deep geologic disposal has been identified for more than fifty years as the preferred approach for permanently isolating highly radioactive wastes from the human environment, but no repositories for spent nuclear fuel or high-level reprocessing wastes are operating anywhere in the world. A lack of geologically suitable sites, however, does not appear to be the limiting factor. Although there are significant technical challenges associated with identifying suitable sites, designing a repository, and understanding the complex interactions between the waste, its packaging, and the geologic environment, decades of experience in the US and other nations indicates that there are multiple geologic options that have the potential to provide excellent long-term isolation.

Extensive site characterization programs and modeling studies in multiple countries confirm that many rock types, including granitic crystalline rocks, argillites, salt, volcanic tuffs, and carbonates all could host a mined repository with the potential to meet protective long-term regulatory requirements. Deep boreholes drilled into crystalline basement rock also have the potential to provide exceptionally robust isolation. Different disposal concepts rely on different approaches to achieve isolation, with some relying primarily on the extremely low permeability of the host rock and the seal system (e.g., mined repositories in salt and deep boreholes), and others placing more emphasis on the long-term stability of the engineered barriers (e.g., the waste form itself, the waste packages, and backfill) in the specific environment anticipated in the host rock (e.g., mined repositories in granite). Regardless of the chosen geologic media, repository designs must take into account the specific needs and attributes of the national program they serve. Specifically, repositories must be designed to work with the host geology to provide long-term isolation while also meeting stringent operational safety requirements and providing a cost-effective solution to managing existing and future wastes.

Sandia National Laboratories is a multiprogram laboratory operated by Sandia Corporation, a Lockheed Martin Company, for the United States Department of Energy’s National Nuclear Security Administration under contract DE-AC04-94AL85000.