title: Delayed signatures of underground nuclear explosions.
abstract: Radionuclide signals from underground nuclear explosions (UNEs) are strongly influenced by the surrounding hydrogeologic regime. One effect of containment is delay of detonation-produced radioxenon reaching the surface as well as lengthening of its period of detectability compared to uncontained explosions. Using a field-scale tracer experiment, we evaluate important transport properties of a former UNE site. We observe the character of signals at the surface due to the migration of gases from the post-detonation chimney under realistic transport conditions. Background radon signals are found to be highly responsive to cavity pressurization suggesting that large local radon anomalies may be an indicator of a clandestine UNE. Computer simulations, using transport properties obtained from the experiment, track radioxenon isotopes in the chimney and their migration to the surface. They show that the chimney surrounded by a fractured containment regime behaves as a leaky chemical reactor regarding its effect on isotopic evolution introducing a dependence on nuclear yield not previously considered. This evolutionary model for radioxenon isotopes is validated by atmospheric observations of radioxenon from a 2013 UNE in the Democratic People's Republic of Korea (DPRK). Our model produces results similar to isotopic observations with nuclear yields being comparable to seismic estimates.
authors.affiliation: Lawrence Livermore National Laboratory, Livermore, California, USA.
authors.forename: Charles R
authors.initials: CR
authors.lastname: Carrigan
authors.affiliation: Lawrence Livermore National Laboratory, Livermore, California, USA.
authors.forename: Yunwei
authors.initials: Y
authors.lastname: Sun
authors.affiliation: Lawrence Livermore National Laboratory, Livermore, California, USA.
authors.forename: Steven L
authors.initials: SL
authors.lastname: Hunter
authors.affiliation: Lawrence Livermore National Laboratory, Livermore, California, USA.
authors.forename: David G
authors.initials: DG
authors.lastname: Ruddle
authors.affiliation: Lawrence Livermore National Laboratory, Livermore, California, USA.
authors.forename: Jeffrey L
authors.initials: JL
authors.lastname: Wagoner
authors.affiliation: Lawrence Livermore National Laboratory, Livermore, California, USA.
authors.forename: Katherine B L
authors.initials: KB
authors.lastname: Myers
authors.affiliation: National Security Technologies, Las Vegas, Nevada, USA.
authors.forename: Dudley F
authors.initials: DF
authors.lastname: Emer
authors.affiliation: National Security Technologies, Las Vegas, Nevada, USA.
authors.forename: Sigmund L
authors.initials: SL
authors.lastname: Drellack
authors.affiliation: National Security Technologies, Las Vegas, Nevada, USA.
authors.forename: Veraun D
authors.initials: VD
authors.lastname: Chipman