Observations of Nuclear Explosive Melt Glass Textures and Surface Areas

This memo report summarizes our current knowledge of the appearance of melt glass formed and subsequently deposited in the subsurface after an underground nuclear test. We have collected archived pictures and melt glass samples from a variety of underground nuclear tests that were conducted at the Nevada Test Site (NTS) during the U.S. nuclear testing program. The purpose of our work is to better determine the actual variation in texture and surface area of the melt glass material. This study is motivated by our need to better determine the rate at which the radionuclides incorporated in the melt glass are released into the subsurface under saturated and partially saturated conditions. The rate at which radionuclides are released from the glass is controlled by the dissolution rate of the glass. Glass dissolution, in turn, is a strong function of surface area, glass composition, water temperature and water chemistry (Bourcier, 1994). This work feeds into an ongoing experimental effort to measure the change in surface area of analog glasses as a function of dissolution rate. The conclusions drawn from this study help bound the variation in the textures of analog glass samples needed for the experimental studies. The experimental work is a collaboration between Desert Research Institute (DRI) and Earth and Environmental Sciences-Lawrence Livermore National Laboratory (EES-LLNL). On March 4, 1999 we hosted a meeting at LLNL to present and discuss our findings. The names of the attendees appear at the end of this memo. This memo report further serves to outline and summarize the conclusions drawn from our meeting. The United States detonated over 800 underground nuclear tests at the NTS between 1951 and 1992. In an effort to evaluate the performance of the nuclear tests, drill-back operations were carried out to retrieve samples of rock in the vicinity of the nuclear test. Drill-back samples were sent to Los Alamos National Laboratory (LANL) and Lawrence Livermore National Laboratory (LLNL) and analyzed for diagnostic purposes. As a result of these activities, a body of knowledge consisting of personal accounts, photos, reports and archived solid samples was gained regarding the physical nature of the melt glass that formed during an underground nuclear test. In this memo report, we summarize previously published reports, compile archived photos, document and describe melt glass samples and summarized discussions from former field engineers and radiochemists who had direct knowledge of drill-back samples. All the information presented in the report was gathered from unclassified sources. We have included as wide a variation of samples as we could document. Unfortunately, as part of the drill-back and diagnostic efforts, it was not common practice to photograph or physically describe the material returned to the surface