Geothermal Systems Created by Underground Nuclear Testing

Abstract

The detonation of nuclear bombs in deep drillholes is associated with the sudden release of heat energy which vaporizes and fuses rocks in the immediate vicinity of the explosion, creating a "cavity". Surrounding rocks around the cavity are intensely shattered, and collapse in to the cavity creating a vertical "chimney" structure. Significant fracturing also extends upwards beyond the chimney. In saturated, permeable rocks, condensation of hot gases takes place and the temperature of the fluids seeping in to the backfilled cavity is raised. After equilibration, the volume of shattered rocks filled by heated pore waters constitutes a geothermal reservoir . Simple two-dimensional models for hypothetical explosion chambers beneath Mururoa Atoll are presented which show the role of thermal convection if the reservoir cools by convective heat transfer. These models indicate that high permeabilities of the order of 10. to 50 Da can be created by such explosions. Computed mass flow rates point to flow velocities of the order of 25 to 150m/yr with in the inner and outer fracture zones surrounding the explosion chamber.