# Experimental Investigation of Uranium and Iron Condensation from High-Temperature Plasma Conditions

## TL;DR

This study uses a plasma reactor to create and analyze uranium and iron nanoparticle fallout, revealing new insights into their condensation and chemical speciation.

## Contribution

The paper demonstrates the first synthetic generation of uranium and iron fallout mixtures in a plasma flow reactor, identifying new ternary oxide formations.

## Key findings

- Uranium oxides (UO2 and α-UO3) and a ternary oxide (UFeO4) were observed in the condensation process.
- Iron-rich cores surrounded by uranium-rich regions suggest coagulation or nucleation pathways influenced by iron concentration.
- Variations in temperature and flow patterns affect the speciation and distribution of metal oxides in the fallout.

## Abstract

We used a plasma flow reactor (PFR) to generate synthetic
fallout
nanoparticles from vapor-phase condensation of two different input
concentrations of uranium and iron analytes (U/Fe = 1:1 and 1:2).
Synthetic fallout from complex chemical matrices (e.g., mixtures of
U and Fe) has not been generated in this setup before and allows for
the observation of relative condensation and fractionation of nuclear
debris. Experiments were conducted under two different temperature
histories with variations in particle flow patterns along the PFR.
Transmission electron microscopy (TEM) observation and analysis of
the nanoparticles revealed variations in speciation of uranium oxides
(UO2 and α-UO3) depending on the competition
between flow mixing and oxygen sequestration by iron. A ternary metal
oxide, UFeO4, was observed in addition to iron oxides (e.g.,
FeO and Fe3O4), which suggests that fallout
models should account for chemical speciation of ternary metal oxides
(i.e., UFeO4) and their relative condensation behaviors
in addition to those of singular metal oxides (e.g., FeO and UO2). X-ray Energy Dispersive Spectroscopy (EDS) elemental maps
showed that some particles had Fe-rich cores surrounded by U-rich
regions. This suggests that either condensed U oxides coagulate onto
molten Fe oxides or that the increase in iron analyte concentration
might drive the system toward a higher degree of supersaturation,
leading to earlier formation of iron oxide particles and providing
an energetically favored pathway for nucleation of uranium oxides
around iron oxide particles.