Source physics experiments at the Nevada Test Site.

Abstract

The U. S. capability to monitor foreign underground nuclear test activities relies heavily on measurement of explosion phenomena, including characteristic seismic, infrasound, radionuclide, and acoustic signals. Despite recent advances in each of these fields, empirical, rather than physics-based, approaches are used to predict and explain observations. Seismologists rely on prior knowledge of the variations of teleseismic and regional seismic parameters such as p- and s-wave arrivals from simple one-dimensional models for the teleseismic case to somewhat more complicated enhanced two-dimensional models for the regional case. Likewise, radionuclide experts rely on empirical results from a handful of limited experiments to determine the radiological source terms present at the surface after an underground test. To make the next step in the advancement of the science of monitoring we need to transform these fields to enable predictive, physics-based modeling and analysis. The Nevada Test Site Source Physics Experiments (N-SPE) provide a unique opportunity to gather precise data from well-designed experiments to improve physics-based modeling capability. In the seismic experiments, data collection will include time domain reflectometry to measure explosive performance and yield, free-field accelerometers, extensive seismic arrays, and infrasound and acoustic measurements. The improved modeling capability that we will develop using this data should enable important advances in our ability to monitor worldwide for nuclear testing. The first of a series of source physics experiments will be conducted in the granite of Climax Stock at the NTS, near the locations of the HARD HAT and PILE DRIVER nuclear tests. This site not only provides a fairly homogeneous and well-documented geology, but also an opportunity to improve our understanding of how fractures, joints, and faults affect seismic wave generation and propagation. The Climax Stock experiments will consist of a 220 lb (TNT equivalent) calibration shot and a 2200 lb (TNT equivalent) over-buried shot conducted in the same emplacement hole. An identical 2200 lb shot at the same location will follow to investigate the effects of pre-conditioning. These experiments also provide an opportunity to advance capabilities for near-field monitoring, and on-site inspections (OSIs) of suspected testing sites. In particular, geologic, physical, and cultural signatures of underground testing can be evaluated using the N-SPE activities as case studies. Furthermore, experiments to measure the migration of radioactive noble gases to the surface from underground explosions will enable development of higher fidelity radiological source term models that can predict migration through a variety of geologic conditions. Because the detection of short-lived radionuclides is essential to determining if an explosion was nuclear or conventional, a better understanding of the gaseous and particulate radionuclide source terms that reach the surface from underground testing is critical to development of OSI capability.