Thermally driven advection for radioxenon transport from an underground nuclear explosion

Abstract

Barometric pumping is a ubiquitous process resulting in migration of gases in the subsurface that has been studied as the primary mechanism for noble gas transport from an underground nuclear explosion (UNE). However, at early times following a UNE, advection driven by explosion residual heat is relevant to noble gas transport. A rigorous measure is needed for demonstrating how, when, and where advection is important. In this paper three physical processes of uncertain magnitude (oscillatory advection, matrix diffusion, and thermally driven advection) are parameterized by using boundary conditions, system properties, and source term strength. Sobol' sensitivity analysis is conducted to evaluate the importance of all physical processes influencing the xenon signals. This study indicates that thermally driven advection plays a more important role in producing xenon signals than oscillatory advection and matrix diffusion at early times following a UNE, and xenon isotopic ratios are observed to have both time and spatial dependence.

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

“…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.…”

Evaluation of subsurface transport processes of delayed gas signatures applicable to underground nuclear explosions

“…In this section, we describe physical processes that can affect gas signatures from UNEs. Nonisothermal multiphase reactive transport in a fractured rock system has been modeled for water, air, and gas components in liquid, gas, and nondeformable solid phases 12 using the NUFT program 31 , 32 . Water and air are the major components in the liquid and gas phases, while other gas components are minor components with relatively low mass fractions in these two phases.…”

“…Different combinations of physical transport processes relevant to delayed signatures (e.g., barometric pumping and dissolution of gases in groundwater in a fractured regime) have been studied at different levels of detail (e.g., 3 , 5 – 7 , 9 , 10 , 27 – 31 ) to evaluate the effects on migration of noble gases from a UNE. However, UNE gas migration processes are complex, interdependent, and temporally and spatially dependent 6 , 11 , 12 . Increasing model fidelity of noble gas transport in complex and uncertain geological systems typically requires a large increase in computational and experimental resources necessary for model development, model validation, and parameter calibration.…”

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

“…When all precursors are included, the simulation becomes computationally expensive. For example, to simulate 131m Xe, 133m Xe, 133 Xe, and 135 Xe, at least 22 species have to be considered in multiphase flow and transport models (Sun and Carrigan 2016;Sloan et al 2016). To couple all six series with transport, 43 species must be considered.…”