Subsurface mass transport affects the radioxenon signatures that are used to identify clandestine nuclear tests

Abstract

[1] The ratios of noble gas radioisotopes can provide critical information with which to verify that a belowground nuclear test has taken place. The relative abundance of anthropogenic isotopes is typically assumed to rely solely on their fission yield and decay rate. The xenon signature of a nuclear test is then bounded by the signal from directly produced fission xenon, and by the signal that would come from the addition of xenon from iodine precursors. Here we show that this signal range is too narrowly defined. Transport simulations were done to span the range of geological conditions within the Nevada Test Site. The simulations assume a 1 kt test and the barometric history following the nuclear test at Pahute Mesa in March 1992. Predicted xenon ratios fall outside of the typically assumed range 20% of the time and situations can arise where the ground level signal comes entirely from the decay of iodine precursors. Citation: Lowrey, J. D., S. R. Biegalski, A. G. Osborne, and M. R. Deinert (2013), Subsurface mass transport affects the radioxenon signatures that are used to identify clandestine nuclear tests, Geophys.

Uncertainty in Prediction of Radionuclide Gas Migration from Underground Nuclear Explosions

“…Background concentrations of the gases in the subsurface and atmospheric boundary were assumed to be zero, although SF 6 , 3 He, and 133 Xe all have low background concentrations in air (Carrigan et al, 1996; Geller et al, 1997; Hebel, 2010). Our current work did not address other Xe isotopes or the contribution from 133 Xe precursors (radioiodine) to the original 133 Xe source term (Lowrey et al, 2013).…”

“…Carrigan et al (1996) and Sun and Carrigan (2014) have developed numerical models for vadose zone transport of radionuclide gases from UNEs in fractured rock with barometric pumping. Double‐porosity modeling of subsurface transport of Xe isotopes from UNEs has also been used to show the effects of uncertain geologic properties on the fractionation of various Xe isotopes ( 133 Xe, metastable 133 Xe and 131 Xe, and 135 Xe) (Lowrey et al, 2013).…”

Detection in subsurface air of radioxenon released from medical isotope production

“…Measurement of radioxenon during an OSI is heavily dependent on underground transport processes and the geology through which transport occurs (Carrigan et al, 1996;Carrigan and Sun, 2014;Lowrey et al, 2013Lowrey et al, , 2012.While transport in homogenous media may be dominated by diffusion at small scales, in fractured geologies barometric pumping is predicted to dominate the bulk movement of air (Nilson et al, 1991). Barometric pumping involves changes in atmospheric pressure acting to impress or withdraw gas from the subsurface, with it generally resulting in an increase in the rate of vertical mixing of air in the subsurface (Carrigan and Sun, 2011;Lowrey, 2013).…”

Noble gas migration experiment to support the detection of underground nuclear explosions

“…Immediately following the blast, the initial heat and pressure drives bulk movement of explosion gases. In the days and months following the blast, longer-term gas diffusion and weatherdriven advection take over in a process called barometric pumping to more slowly drive noble gases to the surface [2,3]. The Noble Gas Migration Experiment (NGME) reported here focused on a typical OSI scenario in which the primary mode of transport of the noble gases to the surface was by barometric pumping.…”