Oxygen Isotope Fractionation in U3O8 during Thermal Processing in Humid Atmospheres
Michael R Klosterman1, Erik J Oerter2, Michael J Singleton2
1Department of Civil & Environmental Engineering, Nuclear Engineering Program, University of Utah, 201 President's Circle, Salt Lake City, Utah 84112, United States.
ACS Omega
|February 7, 2022
Summary
Uranium oxides can reveal their origin by incorporating oxygen isotopes from water during industrial processing. This study shows how oxygen isotopes from humidity and O2 are incorporated into uranium oxides at different temperatures.
Area of Science:
- Geochemistry
- Materials Science
- Forensic Science
Background:
- Uranium oxides can incorporate oxygen isotopes from atmospheric water vapor.
- This process can be used to determine the geographical origin of uranium materials.
- Understanding oxygen isotope exchange in uranium oxides is crucial for forensic applications.
Purpose of the Study:
- To investigate the kinetics and equilibrium fractionation of oxygen isotopes in uranium oxide (U3O8) with water vapor.
- To determine how temperature and atmospheric composition (water vapor, O2) affect oxygen isotope incorporation.
- To elucidate the mechanism of oxygen isotope exchange for forensic signature development.
Main Methods:
- Uranium oxide (U3O8) was processed at 400, 600, and 800 °C in controlled atmospheres.
- Atmospheres included water vapor (50-55% relative humidity) diluted in N2, and mixed atmospheres with O2.
- Oxygen isotope exchange and fractionation factors were measured.
Main Results:
- Oxygen isotope equilibration in U3O8 with water vapor occurred rapidly (within 12h at 400°C, 2h at 600-800°C).
- Fractionation factors (1000lnα, U3O8-H2O) were -12.1, -11.0, and -8.0 at 400, 600, and 800°C, respectively.
- In mixed atmospheres, isotope incorporation depended on temperature: preferentially from water vapor at 400°C and O2 at 600-800°C.
Conclusions:
- Uranium oxides inherit oxygen isotopes from humidity during thermal processing.
- The exchange mechanism is temperature and species-dependent, impacting forensic signature reliability.
- This confirms a viable pathway for determining the geographical origin of uranium materials.
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