[en] One of the major concerns with the continued growth of the nuclear power industry is the production of the high level radioactive wastes which are by-products of the fission process. The risks associated with the disposal of high level wastes derive from the potential for release of radioactive materials into the environment. The assessment of these risks requires a methodology for risk analysis, an identification of the radioactive sources, and a method by which to express the relative hazard of the various radio nuclides that comprise the high level waste. Radioactive wastes are either contained or discharged. Contained wastes are either stored or disposed of in trenches, caverns, or deep mines. On the other hand, some gaseous and liquid wastes are discharged from chimney stacks or sea pipelines directly into the environment. Contained wastes either decay before escaping from their disposal site or are arranged to leak at such a low rate as not to raise appreciably the level of radiation in the environment. In the multiple barrier approach, each containment is a reliable barrier to migration-the packaging material (glass or concrete), the vault and backfill, and the geology. (author)