Thermal Effects of Underground Nuclear Explosions

Most of the energy of an underground nuclear explosion is deposited near the site of the explosion as heat. The heat remains localized for a long time because of the low thermal conductivity of rock. This heat plays a role in Plowshare applications by generating steam and, in the case of carbonate-bearing rocks, CO₂. Applications to stimulate natural-gas production are complicated by the production of tritiated steam and CO₂. The temperature of the rubble in the chimney fixes the steam partial pressure in the produced gas. Increasing chimney temperature, and thus steam pressure, is expected with increasing depth of explosion and also with decreasing spacing between detonations, in the case of multiple explosions. Laboratory experiments on shales that are mostly fine grain mixtures of quartz and carbonate show that CO₂ is released at temperatures as low as 500°C, even under a CO₂ pressure of 50 atm. In the future, the release of large amounts of CO₂ may be used to advantage in secondary oil recovery and in the recovery of heavy crude oils, because of the great reduction in viscosity that results as CO₂ dissolves in these oils. The nuclear chimney, with its large void volume, large surface area for catalysis, and high temperatures, is a potential high pressure vessel for chemical reaction.