[en] The Hybla Fair underground nuclear event was conducted by the Defense Nuclear Agency (DNA) to assess the feasibility of using low yield devices to reduce the expense of nuclear weapons effects testing. The economy of low yield tests was facilitated by placing of the test bed chamber closer to the source, thereby allowing the use of a shorter horizontal line-of-sight (HLOS) tunnel than used for higher yield testing. One main design concern for the Hybla Fair event centered around the desire for the radiation environment in the test chamber to be equivalent to that of higher yield tests. This concern imposed a severe constraint on the stemming column design. Studies of the required Hybla Fair stemming configuration, of the phenomenology of ground shock-induced stemming plug formation for low-yield events, of the effects of baffles on the stemming process, and of the integrity of the stemming closure region for the containment of the cavity gases are reported

[en] Containment evaluation of some underground nuclear events has become strongly dependent on the use of calculations to help define important phenomenology. This results from the increasing necessity to test in sites having a geology that precludes acceptance based solely on experience. This paper discusses the rationale of a suite of TENSOR code calculations undertaken in support of the containment evaluation for a recent event and highlights the results of these calculations. The calculations illustrate containment phenomena in a layered geology of alluvium and tuff with a working point in the proximity of the Paleozoic surface. They show that reflected disturbances from surfaces above and/or below the working point can significantly hinder the development of the residual stress field if their arrival in the residual stress region coincides with the rebound phase of cavity growth. In addition, the results demonstrate a need for the development of a criterion for the probability of successful containment in complex geology other than the historical concept of a strong, sufficiently thick residual stress field. 15 refs., 13 figs., 4 tabs

[en] The craters from high-yield nuclear tests at the Pacific Proving Grounds are very broad and shallow in comparison with the bowl-shaped craters formed in continental rock at the Nevada Test Site and elsewhere. Attempts to account for the differences quantitatively have been generally unsatisfactory. We have for the first time successfully modeled the Koa Event, a representative coral-atoll test. On the basis of plausible assumptions about the geology and about the constitutive relations for coral, we have shown that the size and shape of the Koa crater can be accounted for by subsidence and liquefaction phenomena. If future studies confirm these assumptions, it will mean that some scaling formulas based on data from the Pacific will have to be revised to avoid overestimating weapons effects in continental geology. 9 refs., 5 figs

[en] The On Site Seismic Yield experiment, OSSY, was performed to investigate the viability of a high-explosive technique to help estimate the yield of nuclear explosions. We have analyzed recorded data and conducted numerical simulations of the 100-pound OSSY experiments performed in hole UE-10 ITS No. 3 at the Nevada Test Site. Particle velocity wave forms from these experiments show a distinct dual-pulse structure in the close-in and far-field regions, with the amplitude of the second pulse being as large as or larger than the first pulse. To gain some insight into the cause of the dual-pulse feature, we examine how the explosion-induced close-in response is affected by (1) certain features of inelastic rock/soil constitutive models applied in the near-field region, (2) the large length-to-diameter charge ratio of 8, (3) the charge and gauge package emplacement, and (4) geology (e.g., layering) in the vicinity of the explosion. Our results from 1-D and 2-D simulations show the following: (a) the response, measured by accelerometers located above the charges, is significantly influenced by the charge length-to-diameter ratio out to a distance of 8 m. (b) the grout emplacement of the charge has very little effect on the response. (c) the geologic layering serves mainly to phase the arrival of the pulses. (d) the second pulse can be best accounted for by applying a dilatant feature that allows for pore recovery during unloading. Other material property variations do not provide any contribution to the formation of a second pulse

[en] Voitenko compressors are used to generate 43 mm/μs air shocks in both a steel and a grout outlet pipe containing ambient atmospheric air. Fiber-optic ports provide diaphragm burst times, time-of-arrival (TOA) data, and velocities for the shock front along the 20-mm-ID exit pipes. Pressure profiles are obtained at higher enthalpy shock propagation than ever before and at many locations along the exit pipes. Numerous other electronic sensors and postshot observations are described, as well as experimental results. The primary objectives of the experiments are as follows: (1) provide a data base for normalization/improvement of existing finite-difference codes that describe high-energy air shocks and gas propagation; (2) obtain quantitative results on the relative attenuation effects of two very different wall materials for high-energy air shocks and gas flows. The extensive experimental results satisfy both objectives

[en] A molecular beam source incorporating a dc discharge is used to study the emission spectrum of helium excimers near 600 A and of argon excimers near 1070 A. It is shown that under certain conditions the strength of the excimer radiation approaches that due to the helium resonance lines. The new source is expected to be useful for studying other excimers in the vacuum ultraviolet region of the spectrum