Structure, properties and formation of PuCrO sub(3) and PuAlO sub(3) of relevance to doped nuclear fuels

We have employed a variety of computational methods to understand the behaviour of Pu, generated by neutron capture reactions in UO sub(2) fuel, with Cr sub(2)O sub(3) and Al sub(2)O sub(3), two common UO sub(2) fuel dopants. Structure search calculations using density functional theory and empirical potentials show that PuCrO sub(3) and PuAlO sub(3) are likely to form in these systems. The lowest energy structure adopted by both compounds is predicted to be the orthorhombic (Pnma) GdFeO sub(3)-type perovskite structure. Relative to UO sub(2), the thermal conductivity of PuCrO sub(3) was calculated to be approximately three times smaller over the explored temperature range and therefore the presence of this phase will impact the microstructure, fission product distribution and gas release properties of UO sub(2)-based fuels. In contrast, the PuAlO sub(3) phase had a similar thermal conductivity to UO sub(2). Calculated defect energies suggest that defects in both PuCrO sub(3) and PuAlO sub(3) will be dominated by antisite defects and that their radiation tolerances are similar to that of UO sub(2). Calculation of the solution and partition energies of a range of trivalent cations indicate that minor actinides are likely to substitute for Pu in the perovskite structure having an impact on the in-reactor behaviour of Cr-containing fuels and subsequently the waste reprocessing route.