A kinetic transport model of uranium molecular species formation in a laser ablated plasma plume

laser ablation;uranium fractionation;plasma chemistry;atmospheric pressure plasma

Finko, Mikhail ; Allain, Jean Paul ; Curreli ; Davide

关键词: laser ablation;    uranium fractionation;    plasma chemistry;    atmospheric pressure plasma;   

Others  :  https://www.ideals.illinois.edu/bitstream/handle/2142/101045/FINKO-THESIS-2018.pdf?sequence=1&isAllowed=y

美国|英语

来源: The Illinois Digital Environment for Access to Learning and Scholarship

【 摘 要 】

Nuclear forensics is a technical field of study concerned with the characterization and interpretation of nuclear materials. A central issue in nuclear forensics is the attribution of nuclear devices based on analysis of post-detonation nuclear debris. The issue is complicated by fractionation processes that result in the formation of nuclear debris whose composition does not directly reflect that of the source weapon. Furthermore, the volatility of uranium in atmospheric environments results in complex fractionation patterns that are currently not well understood. Therefore, there is a need to understand uranium chemical fractionation in terms of both the early-stage formation of uranium molecular species and the later-stage debris condensation. In this work, we focus on tackling only the former problem by developing a plasma-chemistry model of uranium molecular species formation during the early stages of nuclear fireball expansion. The model features a newly constructed U$_x$O$_y$ reaction mechanism that consists of 30 reaction channels for 11 uranium molecular species, supplemented by a detailed description of oxygen plasma chemistry. Both the selection of reaction channels and calculation of corresponding rate coefficients is accomplished via a comprehensive literature review and application of basic reaction rate theory. The reaction mechanism is used to model an atmospheric laser ablated uranium plume via both a 0D (global) model and a 2D compressible, reactive multi-species fluid model. The global model is mainly used to provide a detailed kinetic analysis of the early stages of plume evolution, showing both the dissociation and ionization of molecular oxygen and uranium during the pulse heating stage, as well as the sequential formation of increasingly larger uranium molecular oxides that follows in the aftermath of the laser pulse. The 2D fluid model is used to analyze both the kinetics and dynamics of a uranium laser ablation plume during the initial highly reactive stages of expansion, providing a detailed picture of both the complex evolution of internal shocks in the wake of the supersonic shock front expansion and the stratification of the ablation plume into regions of varying reactivity and molecular composition due to multi-species transport. The fluid model also shows that strong reactive heating takes place within the ablation plume, with a high flame temperature of around 8000 K, and that turbulent transport at the plume-material interface plays an important role in cooling the plume down towards ambient conditions.