  Precision on primordial abundances, deduced from observations, have now
reached the percent level for 4He and deuterium. Precision on big bang
nucleosynthesis (BBN) predictions should, hence, reach the same level. The
uncertainty on the 4He mass fraction is strongly affected by theoretical
uncertainties on the weak reaction rates that interconvert neutrons with
protons. All these corrections have been calculated in a self-consistent manner
and implemented in a new, and public, Mathematica code PRIMAT, together with an
extensive data base of reaction rates. Both can be obtained at
http://www2.iap.fr/users/pitrou/primat.htm.
