Enhancing detection of underground nuclear tests with unconventional tracers

Underground nuclear explosions (UNEs) can generate significant air flow that carry, in addition to the radionuclides produced by the explosion, naturally occurring tracers initially present in the surrounding rock or the overlying soil layer. Here we show that these tracers, observed not only at the monitoring sites but also at the test site, could be used to improve the monitoring of the radionuclides used to detect UNEs, which can be hampered by several factors. We first developed a model for non-isothermal single-phase flow, heat and mass transfer, and tracer transport through fractured porous media. Using the conditions relevant for the Punggye-ri site in North Korea as an example, we provide estimates for the emission of water vapor and \(\hbox {CO}_2\) ${\text{CO}}_2$ at the test site, and for the emission of radon and radioxenon at the test site and at the Takasaki monitoring site in Japan. The influence of geological conditions is investigated. For a given monitoring station, it is possible to improve the detection of radioxenon from an underground nuclear explosion by detecting, shortly in advance, the emission of water vapor at the nuclear test site using satellite imagery. If \(\hbox {CO}_2\) ${\text{CO}}_2$ is contributed only from the soil layer and is then scavenged by the gas seeping from a UNE, it cannot be detected by satellite imagery. Radon cannot be detected at the monitoring site, although this gas species is contributed from everywhere by the rock medium, including the rock vaporized to form the cavity.