  The theoretical predictions of big bang nucleosynthesis (BBN) are dominated
by uncertainties in the input nuclear reaction cross sections. In this paper,
we examine the impact on BBN of the recent compilation of nuclear data and
thermonuclear reactions rates by the NACRE collaboration. We confirm that the
adopted rates do not make large overall changes in central values of
predictions, but do affect the magnitude of the uncertainties in these
predictions. Therefore, we then examine in detail the uncertainties in the
individual reaction rates considered by NACRE. When the error estimates by
NACRE are treated as 1\sigma limits, the resulting BBN error budget is similar
to those of previous tabulations. We propose two new procedures for deriving
reaction rate uncertainties from the nuclear data: one which sets lower limits
to the error, and one which we believe is a reasonable description of the
present error budget. We propagate these uncertainty estimates through the BBN
code, and find that when the nuclear data errors are described most accurately,
the resulting light element uncertainties are notably smaller than in some
previous tabulations, but larger than others. Using these results, we derive
limits on the cosmic baryon-to-photon ratio $\eta$, and compare this to
independent limits on $\eta$ from recent balloon-borne measurements of the
cosmic microwave background radiation (CMB). We discuss means to improve the
BBN results via key nuclear reaction measurements and light element
observations.
