Gas transport across the low-permeability containment zone of an underground nuclear explosion

Abstract

Understanding the nature of gas transport from an underground nuclear explosion (Une) is required for evaluating the ability to detect and interpret either on-site or atmospheric signatures of noble gas radionuclides resulting from the event. We performed a pressure and chemical tracer monitoring experiment at the site of an underground nuclear test that occurred in a tunnel in nevada to evaluate the possible modes of gas transport to the surface. the site represents a very well-contained, low gaspermeability end member for past Unes at the nevada national Security Site. However, there is very strong evidence that gases detected at the surface during a period of low atmospheric pressure resulted from fractures of extremely small aperture that are essentially invisible. our analyses also suggest that gases would have easily migrated to the top of the high-permeability collapse zone following the detonation minimizing the final distance required for migration along these narrow fractures to the surface. this indicates that on-site detection of gases emanating from such low-permeability sites is feasible while standoff detection of atmospheric plumes may also be possible at local distances for sufficiently high fracture densities. Finally, our results show that gas leakage into the atmosphere also occurred directly from the tunnel portal and should be monitored in future tunnel gas sampling experiments for the purpose of better understanding relative contributions to detection of radioxenon releases via both fracture network and tunnel transport.

Heterogeneous multiphase flow properties of volcanic rocks and implications for noble gas transport from underground nuclear explosions

“…Concerning natural and induced fracture continua, although the style and relative amount of fracturing are documented in the lithologic‐stratigraphic units of interest, the current imaging logs from the UNESE program have not been used to generated fracture networks and continuum properties for permeability, relative permeability, or capillary pressure to the best of our knowledge (Carrigan et al., 2020; Prothro, 2018). Log‐based fracture measurements with location, orientation, and degree of opening or potential to transmit fluids are potentially useful data, but the limited extent of the fractures intersecting any borehole may preclude understanding fracture connections to each other and their full geometries, and thus generation of fracture network models would require many assumptions.…”

“…The cores include ash‐flow tuffs and lava flows from the Timber Mountain Group, the Calico Hills Formation, the Paintbrush Group, and the Crater Flat Group. Due to their location near or overlying past UNEs, these lithostratigraphic intervals are of interest in the modeling of gas transport or field‐scale tracer gas release studies in the context of UNESE to advance capabilities to detect, locate, and discriminate signatures of UNEs (Bourret et al., 2019; Carrigan et al., 2020; Prothro, 2018).…”

“…Carrigan et al. (2020) performed parameter variational studies on dual‐permeability properties to best fit measured barometric pressure and Freon tracer movement to the surface at Aqueduct Mesa; however, the effect of water saturation was not explicitly addressed. Inasmuch as the previous work does not use direct measurement of multiphase flow properties from UNE sites, the assumption of immobile water is by itself not justified by these studies.…”

“…A signature of interest for explosion monitoring is timing and patterns of explosion-generated noble gases that reach or "break through" to the land surface. Current conceptual and numerical models of gas breakthrough on the timescale of hours to weeks and months after an explosion incorporate the following: temperature effects (e.g., phase changes and thermally-driven advection; Sun & Carrigan, 2016) and barometric pumping as driving forces, and single-phase gas flow in the presence of immobile water (Bourret et al, 2020;Carrigan et al, 2020;Harp et al, 2018Harp et al, , 2019Jordan et al, 2014Jordan et al, , 2015. Important hydrologic and radionuclide parameters of the previous studies are fracture aperture size, matrix (i.e., intact rock) permeability, matrix porosity, water saturation, and radioactive decay constants.…”

A Closed-form Solution for Source-term Emission of Xenon Isotopes from Underground Nuclear Explosions

“…Similarly, the analytical models developed here do not depend on the batch-mode or closed-system assumptions by following the model development of Carrigan et al (2020b). In the cavity-melt partitioning model of Carrigan et al (2020b), xenon production and transport from a UNE are described using partial differential equations (PDEs) governing multiphase flow and transport and ordinary differential equations (ODEs) governing radioactive decay and ingrowth (Carrigan and Sun 2014;Carrigan 2014, 2016;Lowrey et al 2015;Sun et al 2015;Jordan et al 2015;Sloan et al 2016;Bourret et al 2019;Harp et al 2019;Carrigan et al 2020a). To mitigate the difficulty and high computational expense of solving the coupled PDEs and ODEs of transport and the complex decay/ingrowth networks necessary in evaluating details of the linkage between the physical and chemical evolution of the cavity, closedform solutions may be developed.…”