Laboratory Investigation of Containment in Underground Nuclear Tests.

In support of the overall DNA program for stemming and containment of underground nuclear tests, existing laboratory techniques were further developed and applied to investigate the effects of a dynamically generated residual stress field on the containment of gases in exploded-device cavities. Laboratory experiments were performed on externally pressurized grout spheres containing a small explosive charge cast at the center. Immediately after detonation, water is pumped into the exploded cavity at a constant flow rate until the sphere is fractured to the outer surface. The fracture initiation pressures determined from the hydrofracture records are found to be substantially higher than those obtained in corresponding unexploded cavity experiments. This result provides a measure of the benefit to containment of the residual stress field created by the explosion. Relaxation of the residual stress field ws investigated by using a wide range of pumping rates, maintaining a constant cavity pressure for a time before hydrofracture, and by strain and stress gage measurements. An attempt was made to obtain hydrofracture records for uncoupled exploded cavities air space around the charge. Although not successful, it was found that only a minor modification to the technique is required to provide the results. Author