  We present and discuss results of a density functional theory (DFT) study of
a perfect UO2 crystals and He atoms in octahedral interstitial positions. We
have calculated basic bulk crystal properties and He incorporation energies
into the low temperature anti-ferromagnetic UO2 phase using several
exchange-correlation functionals within the spin-polarized local density (LDA)
and generalized gradient (GGA) approximations. In all these DFT calculations we
included the on-site correlation corrections using the Hubbard model (DFT+U
approach). We analysed a potential crystalline symmetry reduction and confirmed
the presence of the Jahn-Teller effect in a perfect UO2. We discuss also the
problem of a conducting electronic state arising when He is placed into a
tetragonal antiferromagnetic phase of UO2. Consequently, we found a specific
lattice distortion which allows us to restore the semiconducting state and
properly estimate He incorporation energies. Unlike the bulk properties, the He
incorporation energy strongly depends on several factors, including the
supercell size, the use of spin polarization, the exchange-correlation
functionals and on-site correlation corrections. We compare our results for the
He incorporation with the previous shell model and ab initio DFT calculations.
