A model of early formation of uranium molecular oxides in laser-ablated plasmas

Abstract

In this work, we present a newly constructed UxOy reaction mechanism that consists of 30 reaction channels (21 of which are reversible channels) for 11 uranium molecular species (including ions). 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 supplemented by a detailed description of oxygen plasma chemistry (19 species and 142 reaction channels) and is used to model an atmospheric laser ablated uranium plume via a 0D (global) model. The global model is used to analyze the evolution of key uranium molecular species predicted by the reaction mechanism, and the initial stage of formation of uranium oxide species.

Description of nucleation, growth and coagulation processes in the modeling of debris formation after a nuclear burst

“…In addition to nucleation, condensation, and agglomeration, it is necessary to have a good representation of the chemistry of the fireball, especially in the gas phase. At early time, chemical kinetics can be expected to be fast because of the high temperatures, but there is still substantial uncertainty about the reaction rates and species involved (Koroglu et al [2018], Finko et al [2017]). In the past, oxides were assumed to be the dominant species (Miller [1960]), but recently researchers have suggested the possibility of reducing conditions (Giuli et al [2010], Cassata et al [2014]).…”

Ab initio calculations of material properties for modeling debris (FY2021 Progress Report)

“…To implement the chemical kinetics for the transformation between gas species, we use a selection of the chemical kinetic equations described by Finko for the system [50]. This set of chemical kinetic equations heavily assumes the mechanism of the uranium-oxygen transformations parallels the aluminum-oxygen system and fits constants to the uranium transformations accordingly.…”

“…This known issue will be examined in future work. For this current report, we continue with both the NASA polynomials and the Arrhenius assumption, and we refit those equations presented by Finko [50] that are not in the Arrhenius form for use with the code. The kinetic equations, their original rate constants, and their refitted values appear in APPENDIX B.…”

Laser-produced uranium plasma characterization and Stark broadening measurements

“…Spectral simulation may aid toward deeper understanding and deconvolution of underlying oxide spectral features from ionic or atomic emission in the plasma, for example, for U plasmas in which U oxide emission is significant and makes the plasma diagnostics more challenging. 11,22,33 In this work, we assess the validity of equilibrium assumptions in the U LIP under reduced pressure conditions in order to determine the plasma properties, namely, T e and N e and report the Stark broadening parameters of U II 500.82 nm and U I 499.01 nm transitions.…”