Xenon adsorption on geological media and implications for radionuclide signatures

Abstract

The detection of radioactive noble gases is a primary technology for verifying compliance with the pending Comprehensive Nuclear-Test-Ban Treaty. A fundamental challenge in applying this technology for detecting underground nuclear explosions is estimating the timing and magnitude of the radionuclide signatures. While the primary mechanism for transport is advective transport, either through barometric pumping or thermally driven advection, diffusive transport in the surrounding matrix also plays a secondary role. From the study of primordial noble gas signatures, it is known that xenon has a strong physical adsorption affinity in shale formations. Given the unselective nature of physical adsorption, isotherm measurements reported here show that non-trivial amounts of xenon adsorb on a variety of media, in addition to shale. A dual-porosity model is then discussed demonstrating that sorption amplifies the diffusive uptake of an adsorbing matrix from a fracture. This effect may reduce the radioxenon signature down to approximately one-tenth, similar to primordial xenon isotopic signatures.

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

“…When gas concentration is very low, , the Langmuir adsorption ( 2 ) behaves as Henry’s absorption where [m kg ] is the constant of the Langmuir linear portion. For this reason, Paul et al 21 fitted sorption experimental data using Henry’s linear function (Eq. 1 ).…”

“…We will use the atmospheric-pressure-fluctuation history at the Barnwell site covering the period of the NGME experiment as well as over-pressuring of the chimney initiated 99 days after injection of the three tracers. Gas sorption in crushed rock powder and intact core samples has been modeled as an interaction between gas and solid phases in a batch mode under dry conditions using Henry’s type and Langmuir isotherm models 20 , 21 . Recently, Neil et al 22 studied the combined effect of gas sorption and dissolution in partially saturated zeolites.…”

Using SF6 and Xe to Monitor Gas Migration Through Explosion‐Generated Fracture Networks

“…A laboratory study by Kilgallon et al () shows similar breakthrough times for both xenon and SF 6 mixed with CO 2 carrier gas passing through sandstone samples. However, a recent laboratory study involving adsorption of both xenon and SF 6 gases on rock surfaces under near‐vacuum conditions suggests that xenon has higher adsorption while moving through the rock mass (e.g., Paul, ; Paul et al, ) causing its breakthrough (i.e., reaching a sampling station) to be retarded at a given concentration compared to SF 6 . Therefore, the suitability of SF 6 as a surrogate for xenon has been called into question.…”

“…RNG are rare in Earth's atmosphere except for a low-level background generally associated with medical isotope production and nuclear reactor operations (e.g., Achim, 2016;Kalinowski et al, 2014); therefore, noble gas signatures can be used to confirm the nuclear nature of a seismic event (Kalinowski et al, 2010). Several studies have been conducted in the past to investigate RNG migration through rock, including field-scale experiments (e.g., Carrigan et al, 2016;Olsen et al, 2016), laboratory experiments (e.g., Broome et al 2016;Paul et al, 2018;Vandergraaf, 1995), and numerical studies (e.g., Jordan et al, 2014Jordan et al, , 2015Lowrey et al, 2013). However, in situ gas transport through fractured rock, especially near the ground surface, is not fully understood with predictions complicated by ill-constrained uncertainties.…”

“…• Table S1 • Table S2 • Table S3 • Table S4 adsorption of both xenon and SF 6 gases on rock surfaces under near-vacuum conditions suggests that xenon has higher adsorption while moving through the rock mass (e.g., Paul, 2017;Paul et al, 2018) causing its breakthrough (i.e., reaching a sampling station) to be retarded at a given concentration compared to SF 6 . Therefore, the suitability of SF 6 as a surrogate for xenon has been called into question.…”