First-principles study of helium incorporation in Pu-La2Zr2O7 pyrochlore

Helium (He) exerts significant influence on the physicochemical, structural, and electronic properties of pyrochlores. This paper reviews recent advancements in computer simulations aimed at stabilizing nuclear waste, focusing on disordered structures of pyrochlores, zirconate pyrochlores, and high-entropy pyrochlores. Using Pu-La₂Zr₂O₇ as a case study, we demonstrate how a first-principles approach facilitates the understanding of how He modifies the structural and electronic properties of this system. The incorporation of He interstitials in Pu-La₂Zr₂O₇ typically leads to an expansion in lattice constant and volume swelling. Analysis of the formation energies in this system reveals that octahedral interstitial sites or zirconium (Zr) vacancy sites are favored for He occupation, resulting in the formation of substitutional He atoms. The low concentration of He atoms in Pu-La₂Zr₂O₇ reduces the formation energy of cation antisite defects. Bader charge analysis indicates that the < Zr-O > bond exerts a greater influence on the irradiation resistance of the He-Pu-La₂Zr₂O₇ system compared to the < La-O > bond. Moreover, the capacity for He interstitials increases with higher Pu concentration in the octahedrons.