Electronic structure calculations of positron lifetimes in nuclear materials: SiC and UO2

We present first-principles calculations of positron lifetimes of vacancy-type defects in two nuclear materials: SiC and UO2. We use a self-consistent positron lifetime calculation scheme based on the two-component density functional theory. Full defect relaxation due to both the creation of the vacancy and the presence of the positron was taken into account. Our results for SiC differ strongly from those published in literature up to now [G. Brauer et al. Phys. Rev. B 54, 2512 (1996)]. This is mostly due to the effect of the relaxation, that was not taken into account before. We also present the first calculated positron lifetimes obtained for UO2 in the DFT+U approach. Results are compared with the experimental data.