Immediately after a nuclear explosion, all surrounding materials are vaporized from the intense release of energy via temperature and pressure. A strong blast wave emanates from the detonation point, leaving behind it a luminous fireball consisting of a heterogeneous vapor-plasma mixture. As the fireball mixture interacts with air, anisotropic combustion reactions produce oxides from the various fission fragments, actinide fuel, local sediment, and other ubiquitous materials. Once the fireball starts to rapidly cool, within the first second, the vaporized constituents condensate and mix to form fallout debris particles. Therefore, there is a strong connection between the early fireball vapor chemistry and the chemical composition of subsequent fallout debris. Recently, laser ablation plasma plumes have been presented as high fidelity, lab-scale surrogates for studying the early nuclear fireball chemistry. In this work, a pure uranium LA plume expanding into air is simulated as a compressible, reactive flow. The uranium vapor combustion chemistry is modeled according to a robust chemical kinetic system and set of thermodynamic equations derived for this work. The spatial concentrations of UxOy are updated with respect to time and displayed in high-resolution 2D colormaps. A custom optical emission spectrum code was applied to the simulated uranium plumes to further characterize the system in a way that can be evaluated with respect to experimental laser-induced breakdown spectroscopy (LIBS) figures. Understanding the evolution of the uranium vapor chemistry and emission spectrum may also bolster the applicability of LIBS for environmental sampling in both nuclear forensics and safeguards inspection regimes.
Year
2022
Abstract