  Nuclear reactors are a source of electron antineutrinos due to the presence
of unstable fission products that undergo $\beta^-$ decay. They will be
exploited by the JUNO experiment to determine the neutrino mass ordering and to
get very precise measurements of the neutrino oscillation parameters. This
requires the reactor antineutrino spectrum to be characterized as precisely as
possible both through high resolution measurements, as foreseen by the TAO
experiment, and detailed simulation models. In this paper we present a
benchmark analysis utilizing Serpent Monte Carlo simulations in comparison with
real pressurized water reactor spent fuel data. Our objective is to study the
accuracy of fission fraction predictions as a function of different reactor
simulation approximations. Then, utilizing the BetaShape software, we construct
fissile antineutrino spectra using the summation method, thereby assessing the
influence of simulation uncertainties on reactor antineutrino spectrum.
