  We report new calculations of reactor antineutrino spectra including the
latest information from nuclear databases and a detailed error budget. The
first part of this work is the so-called ab initio approach where the total
antineutrino spectrum is built from the sum of all beta-branches of all fission
products predicted by an evolution code. Systematic effects and missing
information in nuclear databases lead to final relative uncertainties in the 10
to 20% range. A prediction of the antineutrino spectrum associated with the
fission of 238U is given based on this ab initio method. For the dominant
isotopes 235U and 239Pu, we developed a more accurate approach combining
information from nuclear databases and reference electron spectra associated
with the fission of 235U, 239Pu and 241Pu, measured at ILL in the 80's. We show
how the anchor point of the measured total beta-spectra can be used to suppress
the uncertainty in nuclear databases while taking advantage of all the
information they contain. We provide new reference antineutrino spectra for
235U, 239Pu and 241Pu isotopes in the 2-8 MeV range. While the shapes of the
spectra and their uncertainties are comparable to that of the previous analysis
of the ILL data, the normalization is shifted by about +3% on average. In the
perspective of the re-analysis of past experiments and direct use of these
results by upcoming oscillation experiments, we discuss the various sources of
errors and their correlations as well as the corrections induced by off
equilibrium effects.
