Americium incorporation into studtite: a theoretical and experimental study

Area of Science:

• Nuclear Chemistry
• Materials Science
• Geochemistry

Background:

• Studtite and metastudtite are key alteration phases of uranium dioxide (UO2) in spent nuclear fuel repositories.
• These minerals are known to interact with actinides like Neptunium (Np(v)).

Purpose of the Study:

• To investigate the interaction of Americium (Am(v)) with studtite on a tracer scale.
• To elucidate the incorporation mechanisms and energetics of Am and Np in studtite and metastudtite.
• To assess the leachability of incorporated Am from studtite.

Main Methods:

• Spectroscopic analysis to confirm Am incorporation and oxidation state.
• Computational modeling to study reaction mechanisms and calculate incorporation energies.
• Leaching experiments to evaluate Am mobility.

Main Results:

• Spectroscopic evidence confirms Am incorporation into studtite as Am(iii).
• Computational studies indicate protonation of the -yl oxygen as the favored incorporation mechanism for both Np and Am.
• Am incorporation into metastudtite is energetically more favorable than into studtite, and Np incorporation is favored over Am.

Conclusions:

• Americium(iii) can be incorporated into studtite, but the process is energetically less favorable than for Neptunium.
• Metastudtite presents a more favorable energetic landscape for the incorporation of both actinides compared to studtite.
• Incorporated Am exhibits significant leachability from studtite, with subtle structural changes observed.