Irradiation of Plutonium Tributyl Phosphate Complexes by Ionizing Alpha Particles: A Computational Study

Area of Science:

• Nuclear Chemistry
• Materials Science
• Computational Chemistry

Background:

• The PUREX process uses tributyl phosphate (TBP) for nuclear fuel reprocessing.
• Alpha particle emission from plutonium degrades TBP.
• Understanding TBP degradation is vital for nuclear industry safety and efficiency.

Purpose of the Study:

• To investigate the ultrashort time alpha irradiation effects on tributyl phosphate (TBP) and its plutonium complex.
• To analyze electron dynamics and secondary electron emission during irradiation.
• To understand the influence of ligands and irradiation sites on TBP degradation.

Main Methods:

• Real-Time-Dependent Auxiliary Density Functional Theory (RT-TD-ADFT) for electron dynamics.
• Absorption Boundary Conditions (ABC) in molecular orbital space to model secondary electron emission.
• Systematic analysis of basis set, exchange-correlation functional, and ABC parameter effects.

Main Results:

• Preliminary studies on water and TBP show the necessity of system-specific ABC parameterization.
• Irradiation of TBP and its plutonium complex reveals ligand influence on atomic charge variations on femtosecond timescales.
• Charge accumulation in TBP alkyl chains observed during nitrate group irradiation; plutonium rapidly regains charge, utilizing its coordination sphere.

Conclusions:

• The study provides insights into the fundamental mechanisms of TBP degradation under alpha irradiation.
• Accurate modeling of secondary electron emission requires careful ABC parameter selection.
• This research contributes to understanding and mitigating the degradation of organic extractants in nuclear applications.