What is a suitable geologic environment to safely isolate nuclear waste in the Deep Isolation solution?
Nuclear waste disposal is a global challenge and we are developing a solution that can be adapted to work in a number of different geologic settings.
Directional drilling technology allows Deep Isolation to precisely place nuclear waste 1-3 kilometers beneath the surface in carefully selected geologic formations. The target geologic media for our repositories are in or below formations that have been out of contact with surface waters for millions of years. This is a robust predictor of future isolation that can be determined by a number of isotopic age dating methods.
In addition to having demonstrated past isolation, it is important to consider fundamental rock properties and the regional seismic and hydrologic setting. In general, we seek rock types that have low permeability and hydraulic conductivity, a capacity for self-healing fractures, and which have the ability to adsorb radionuclides and inhibit their mobility. The primary formations which demonstrate these traits are deep sedimentary strata, such as clays, mudstones, and shales as well as salt formations.
In regions that lack these lithologies, other non-sedimentary rock types such as granite or crystalline basement are promising options for repositories if they demonstrate long term isolation capacity. In many regions of the world very old crystalline basement rocks have waters at depths between 1-3 kilometers that have remained isolated for tens to hundreds of millions of years. This is determined by measuring the accumulation of noble gases such as helium, argon, or neon which are produced within the rock deep underground.
We believe that there can be many good options for disposal, and a reasonably thorough search in most countries will reveal several satisfactory options. These options can be explored and evaluated through detailed geologic, hydrologic, and seismic studies, as well as through isotopic testing and repository modeling to help clarify which sites and formations are most suitable.