End-to-End HPC Numerical Simulations of Underground Explosions, Cavity Formation and Circulation Processes, Subsurface Gas Transport, and Prompt Atmospheric Releases

Radionuclide monitoring is complementary to seismic, hydroacoustic, and infrasound wave monitoring technologies used in verification, and it is the only one that can discriminate and confirm whether an explosion detected and located is indicative of a military nuclear explosion. Therefore, to understand radioactive particles and noble gas prompt releases from underground nuclear explosions, their transport in the atmosphere to radionuclide monitoring stations, and to discriminate nuclear explosion generated radioisotopes from artificially produced ones, generated and released by nuclear reactors, particle accelerators, or radionuclide generators, one must accurately and numerically simulate the explosion phase, the interaction of the explosive energy released with the fractured hosting rock, and cavity formation, the radionuclide generation and their circulation within the cavity, and the eventual prompt release or seepage of the radionuclide gases to the atmosphere. To support this daunting task, LLNL has developed an HPC-based comprehensive numerical framework to simulate, from source-to-atmosphere, the radioisotope gas releases by coupling a non-linear explosion hydrocode to a geomechanical code that converts explosion-induced damage to rock permeability, which is a key parameter to subsurface and surface coupled gas transport codes. The resulting gas releases source to the atmosphere is then used as an input to a global atmospheric circulation code to reach the monitoring stations. We illustrate the onset of the different regimes and their combined effect of flow, heat and mass transport of different gas species, the fraction of molten rock and their impact on the noble gas fractionation. We also present a sensitivity analysis of the effect of the outer cavity boundary condition on the heat loss and cooling to the adjacent rock formation and its eventual release to the atmosphere. We demonstrate several scenarios of underground prompt releases to the atmosphere using a first-ever fully coupled prompt subsurface-to-atmospheric transport without ad-hoc boundary conditions between physics-based domains, or handshakes between different numerical codes. We also demonstrate using HPC-empowered numerical hypothetical explosion scenarios, the benefits of the proposed technology versus the common approaches. We will conclude by exploring physics informed ML schemes for developing surface responses of the end-to-end simulation framework to anthropogenic explosions. This work performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344.