An atomistic computational study was made of He accommodation and diffusion in

Pu4+- and U4+-doped zircon. The He–cation potentials derived for this work gave

results which were of comparable accuracy to DFT calculations. Structural features

of doped lattices were calculated, as well as He solution energies in the interstitial

sites of perfect and doped zircon and its diffusion in these lattices. The mode of He

accommodation in the perfect zircon was influenced mainly by the topological

features of the lattice; promoting the site preference of He towards accommodation

in interstitial sites in the middle of c cylinder channels, whereas the presence of

Pu4+ and U4+ dopants in the zircon lattice significantly affected the energetics of He

accommodation and diffusion in the lattice. Doping caused strong local structural

distortions, extending to next-nearest neighbour atoms of the dopants up to a radius

of some 4Å; in agreement with experimental results. The presence of dopants in the

vicinity of He enhanced the solubility of He in the lattice compared to the perfect lattice. The mechanism of diffusion was also affected, where the dopants could

create a He trap along the most energetically favourable pathway in the (001)

direction. This could slow down the movement of He along the c-direction. The

dopants also lowered the energy barriers by about 50% in the octahedral sites.

A Computer Simulation Study of the Accommodation and Diffusion of He in

Uranium- and Plutonium-Doped Zircon (ZrSiO4). I.Saadoune, N.H.de Leeuw:

Geochimica et Cosmochimica Acta, 2009, 73[13], 3880-893