Exploring the Local Structure of Molten NaF-ZrF₄ through In Situ XANES/EXAFS and Molecular Dynamics

Area of Science:

• Materials Science
• Nuclear Engineering
• Physical Chemistry

Background:

• Molten salts are crucial for advanced energy systems, especially molten salt reactors (MSRs).
• Understanding the atomic structure of fluoride-based salts with high zirconium concentrations is limited.
• Detailed knowledge of molten salt atomic structures is essential for optimizing their performance.

Purpose of the Study:

• To investigate the atomic structure and thermophysical properties of NaF-ZrF4 salt mixtures.
• To elucidate the local environment and coordination states of Zr atoms at elevated temperatures.
• To develop reliable models for molten salt behavior in advanced energy applications.

Main Methods:

• Integrated experimental and computational approach.
• X-ray absorption near edge structure (XANES) and extended X-ray absorption fine structure (EXAFS) spectroscopy.
• Ab initio molecular dynamics (AIMD) and neural network-based molecular dynamics (NNMD) simulations.

Main Results:

• Observed temperature-driven transition toward lower Zr coordination numbers (530-700 °C).
• Revealed increased structural distortion with increasing temperature.
• Validated simulation data against experimental XANES/EXAFS results.

Conclusions:

• The atomic structure of NaF-ZrF4 salts is sensitive to temperature changes.
• Structural insights provide understanding of fluoroacidity and potential corrosiveness.
• This research aids the development of advanced molten salts for next-generation nuclear reactors.