Hjelm Publishes Work on Gas Diffusion in Journal of Environmental Radioactivity
Hjelm Publishes Work on Gas Diffusion in Journal of Environmental Radioactivity
New Mexico Consortium scientist, Rex P. Hjelm, recently published a new article, Gas diffusion through variably-water-saturated zeolitic tuff: Implications for transport following a subsurface nuclear event, in the Journal of Environmental Radioactivity.
Understanding noble gas transport through geologic media is essential for studying and interpreting underground nuclear explosions (UNEs). Accurate computer models of noble gas movement are critical because, without them, it can be difficult—if not impossible—to distinguish xenon signatures produced by civilian nuclear facilities from those associated with underground nuclear events.
In this study, Hjelm and his colleagues worked to improve understanding of noble gas transport in geologic materials. One important focus of the research was xenon transport time, a key parameter for interpreting measured xenon isotopic ratios. Another challenge in modeling gas transport is accounting for the effects of variable water saturation within geologic media, which can significantly influence how gases move through rock.
To investigate these effects, the researchers conducted bench-scale laboratory experiments to characterize the diffusion of krypton, xenon, and sulfur hexafluoride (SF₆) through intact zeolitic tuff under different water saturation conditions.
The results showed that water in rock cores with low partial saturation can dramatically affect xenon transport time compared with krypton and SF₆. This occurs because water blocks sites in zeolitic tuff that preferentially adsorb xenon, leading to breakthrough trends that are strongly influenced by the degree of rock saturation. Xenon was found to be especially sensitive to this effect, making the finding particularly important for gas transport models used in nuclear event identification.
The study also found that the breakthrough behavior of SF₆ separates significantly from that of the noble gases, highlighting the importance of evaluating how different gases interact with specific geologic materials.
These findings demonstrate the critical need to consider the relationship between rock saturation and fission product absorption or adsorption when developing transport models. They also emphasize the importance of assessing the specific interactions between geomedia and the gases of interest, as these interactions may differ substantially from those observed with chemical tracers.
To read more see: Gas diffusion through variably-water-saturated zeolitic tuff: Implications for transport following a subsurface nuclear event