Abstract
The transport of noble gas radionuclides in porous media is relevant to the detection of underground nuclear detonations as well as the sequestration of reprocessing off-gases. However, in field tests releasing radioxenon underground, the quantity of radioxenon observed at the surface has fallen well below expectations.[Formula: see text] This study examined the diffusivity of noble gases (Kr and Xe) and the inert molecular gas sulfur hexafluoride (SF[Formula: see text] in porous media to observe any unexpected behavior. To replicate the transport of radiogenic noble gases in underground media, a two-bulb gaseous diffusion apparatus was constructed. The two bulbs were connected with a column of 10–30 Ottawa sand and ordinary atmosphere filled both the bulbs and pore spaces. The tracer gases were diluted in an isolated bulb to approximately 1000 ppm. Once released, the gases were allowed to diffuse through the column. Aliquots were withdrawn at regular time intervals from both bulbs and concentrations were quantified using a Shimadzu QP2010 SE gas chromatograph-mass spectrometer. The effective diffusivity was then calculated using a maximum likelihood estimate on the quasi-steady state model. The effective diffusivity of Xe in the silica sand was observed to be 135.2% that of SF[Formula: see text] whereas the effective diffusivity of Kr was observed to be 161.4% that of sulfur hexafluoride. These findings are consistent with the binary diffusivities in N[Formula: see text]: 132.6% and 161.7%, respectively. However, the apparent volume of the system was inconsistent amongst the species, with Xe converging at slightly lower gas-phase concentrations than Kr or SF[Formula: see text]. This apparent reduction in gas-phase concentration occurred within the first few measurements and is consistent with transient accumulation of an adsorbed phase. As the effective diffusivities in the silica sand were shown to be consistent with the binary diffusivities in N[Formula: see text], a porosity-tortuosity model appears to be sufficient when considering similar geological materials. However, with the observation of significant gas adsorption, consideration of adsorbed-phase accumulation is necessary when scaling to larger geological systems.
Highlights
During an underground nuclear explosion, numerous radioactive fission products will form as a direct result of fission within the event
Transport processes including barometric pumping and diffusion affect the quantity of these species detectable at the surface. While these noble gas radionuclides are of importance to underground nuclear explosion detection, relatively few field tests have been conducted using noble gases in underground transport
Three trials were conducted on the dry silica sand using Kr, Xe, and SF6 as tracer gases, and CF4 as a spiked internal standard
Summary
During an underground nuclear explosion, numerous radioactive fission products will form as a direct result of fission within the event. This is an Open Access article published by World Scientific Publishing Company. Radioisotopes of Xe and Ar have been identified to be of interest for detection of clandestine nuclear activities.[1] transport processes including barometric pumping and diffusion affect the quantity of these species detectable at the surface. While these noble gas radionuclides are of importance to underground nuclear explosion detection, relatively few field tests have been conducted using noble gases in underground transport
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
