Worldwide, a consensus is developing among countries using nuclear power that deep, geologic disposal of spent nuclear fuel and high-level radioactive waste is the safest long-term option (National Research Council, 1990, 2001; EPA, 2001). The geologic medium acts as a component of a multiple barrier system (including the waste form and engineering components) designed to isolate the waste from the biosphere. Regulations in many countries, therefore, require repository developers to consider various natural hazards when evaluating repository performance. Among the hazards considered is the potential for igneous activity at the site and surrounding area (Long and Ewing, 2004). For example, in the United States, regulations governing the geologic disposal of high-level radioactive waste at the potential Yucca Mountain, Nevada, repository require inclusion of risk (i.e. probability and consequence) in assessments of the safety of the repository system. Based on probabilities estimated for repository disruption by future basaltic volcanism (e.g. 1.8 × 10-8: Bechtel SAIC Company, LLC, 2007; 1.0 × 10-6: Smith and Keenan, 2005) and the potential risks for this natural hazard, performance assessments should evaluate the consequences of a basaltic volcano intersecting the drifts and tunnels of the potential repository, which might damage the emplaced waste packages and waste form, and could transport radioactive material to the biosphere (NRC, 2005).

There is almost no precedent for a volcanic eruption interacting with an underground storage facility of the kind envisaged for radioactive waste repositories. These facilities generally consist of a network of tunnels or drifts.