Atomistic simulation of helium diffusion and clustering in plutonium dioxide.

Area of Science:

• Materials Science
• Nuclear Engineering
• Computational Physics

Background:

• Radiogenic helium from plutonium alpha decay can impact spent nuclear fuel safety.
• Understanding helium behavior in plutonium dioxide (PuO2) is crucial for secure fuel storage.

Purpose of the Study:

• Investigate helium diffusion and clustering mechanisms in PuO2.
• Determine the influence of temperature, vacancies, and defects on helium mobility.

Main Methods:

• Molecular dynamics simulations
• Barrier searching techniques
• Static calculations

Main Results:

• Helium diffusion in pristine PuO2 is negligible below 1500 K (barrier: 2.4 eV).
• Oxygen vacancies drastically reduce the helium diffusion barrier to 0.6 eV, facilitating vacancy-assisted hopping.
• Plutonium vacancies trap helium, while Schottky defects promote helium cluster formation.

Conclusions:

• Oxygen vacancies are key to helium diffusion in PuO2 at elevated temperatures.
• Helium clustering is influenced by vacancy concentrations and defect structures.
• The maximum stable helium-to-vacancy ratio in clusters is approximately 3.5:1.