DOE OSTI2012
The National Center for Nuclear Security (NCNS), established by the U.S. Department of Energy, National Nuclear Security Administration, is conducting a series of explosive tests at the Nevada National Security Site (NNSS; formerly the Nevada Test Site) that are designed to increase the understanding of certain basic physical phenomena associated with underground explosions. These tests will aid in developing technologies that might be used to detect underground nuclear explosions in support of verification activities for the Comprehensive Nuclear-Test-Ban Treaty (CTBT). The initial NCNS project is a series of explosive tests, known collectively as the Source Physics Experiment at the NNSS (SPE-N), being conducted in granitic rocks at the Climax stock in northern Yucca Flat. The SPE-N test series is designed to study the generation and propagation of seismic waves. The data will be used to improve the predictive capability of calculational models for detecting and characterizing underground explosions. The first SPE-N test (SPE-N-1) was a “calibration” shot conducted in May 2011, using 100 kilograms (kg) of explosives at the depth of 54.9 meters (m) (180 feet [ft]) in the U-15n source hole. SPE-N-2 was conducted in October 2011, using 1,000 kg of explosives at the depth of 45.7 m (150 ft) in the same source hole. Following the SPE-N-2 test, the core hole U-15n#10 was drilled at an angle from the surface to intercept the SPE-N-2 shot point location to obtain information necessary to characterize the damage zone. The desire was to determine the position of the damage zone near the shot point, at least on the northeast side, where the core hole penetrated it. The three-dimensional shape and symmetry of the damage zone are unknown at this time. Rather than spherical in shape, the dimensions of the damage zone could be influenced by the natural fracture sets in the vicinity. Geologic characterization of the borehole included geophysical logging, a directional survey, and geologic description of the core to document visual evidence of damage. Selected core samples were provided to Sandia National Laboratories (SNL) for laboratory tests (to be reported by SNL). A significant natural fault zone was encountered in the U-15n#10 angle core hole between the drilled depths of 149 and 155 ft (straight-line distance or range station [RS] from the shot point of 7.5 to 5.7 m). However, several of the fractures observed in the U-15n#10 hole are interpreted as having been caused by the explosion. These fractures are characterized by a “fresh,” mechanically broken look, with uncoated and very irregular surfaces. They tend to terminate against natural fractures and have orientations that differ from the previously defined natural fracture sets. The most distant fracture from the shot point that could be interpreted as having been caused by the explosion was seen at approximately RS 10.0 m. No other possibly explosion-induced fractures are apparent above the fault, but are common starting at RS 5.4 m, which is below the fault. It is unknown how the fault zone might have affected the propagation of seismic waves or how the materials in the fault zone (altered granite, breccia, gouge) were affected by the explosion. From RS 3.3 m to the end of the recovered core at RS 1.6 m, some of the core samples are softer and lighter in color, but do not appear to be weathered. It is thought this could be indicative of the presence of distributed microfracturing.