  Perturbative quantum gravity formalism is applied to compute the lowest order
corrections to the classical spatially flat cosmological FLRW solution (for the
radiation). The presented approach is analogous to the approach applied to
compute quantum corrections to the Coulomb potential in electrodynamics, or
rather to the approach applied to compute quantum corrections to the
Schwarzschild solution in gravity. In the framework of the standard
perturbative quantum gravity, it is shown that the corrections to the classical
deceleration, coming from the one-loop graviton vacuum polarization
(self-energy), have (UV cutoff free) opposite to the classical repulsive
properties which are not negligible in the very early Universe. The repulsive
"quantum forces" resemble those known from loop quantum cosmology.
