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Insight into the Am-O Phase Equilibria: A Thermodynamic Study Coupling High-Temperature XRD and CALPHAD Modeling
Enrica Epifano1, Christine Guéneau2, Renaud C Belin3
1CEA, Nuclear Energy Division, Research Department on Mining and Fuel Recycling Processes, SFMA, LCC , F-30207 Bagnols-sur-Cèze, France.
Inorganic Chemistry
|June 17, 2017
Summary
This study reveals new details about the americium-oxygen system, crucial for nuclear fuel. Researchers clarified phase relationships and structural properties of americium oxide phases under varying temperatures.
Area of Science:
- Nuclear Materials Science
- Thermodynamics
- Actinide Chemistry
Background:
- Americium (Am) is a minor actinide relevant for transmutation in fast reactors.
- Understanding the americium-oxygen (Am-O) system, particularly the AmO2-x phase, is essential for predicting its behavior in nuclear fuels.
- Existing knowledge of the Am-O phase diagram requires refinement for accurate in-reactor performance predictions.
Purpose of the Study:
- To investigate the structural properties and phase equilibria of the AmO2-x-AmO1.61+x-Am2O3 domain.
- To establish the relationships between temperature, lattice parameter, and hypostoichiometry in the fcc AmO2-x phase.
- To develop an improved thermodynamic model and phase diagram for the Am-O system.
Main Methods:
- Coupling of high-temperature X-ray diffraction (HT-XRD) experiments.
- Application of CALPHAD (Calculation of Phase Diagrams) thermodynamic modeling.
- Experimental determination of phase boundaries and structural parameters.
Main Results:
- First-time assessment of temperature, lattice parameter, and hypostoichiometry for fcc AmO2-x.
- Identification of a hyperstoichiometric existence domain for the bcc AmO1.61+x phase.
- Demonstrated absence of a miscibility gap in the fcc AmO2-x phase, contradicting previous models.
Conclusions:
- The study provides crucial fundamental data on the Am-O binary system.
- A new CALPHAD thermodynamic model for Am-O has been developed based on new experimental data.
- An improved Am-O phase diagram is presented, enhancing the understanding of americium behavior in nuclear fuels.
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