  The propagation of uncertainties in reaction cross sections and rates of
neutron-, proton-, and alpha-induced reactions into the final isotopic
abundances obtained in nucleosynthesis models is an important issue in studies
of nucleosynthesis and Galactic Chemical Evolution. We developed a Monte Carlo
method to allow large-scale postprocessing studies of the impact of nuclear
uncertainties on nucleosynthesis. Temperature-dependent rate uncertainties
combining realistic experimental and theoretical uncertainties are used. From
detailed statistical analyses uncertainties in the final abundances are derived
as probability density distributions. Furthermore, based on rate and abundance
correlations an automated procedure identifies the most important reactions in
complex flow patterns from superposition of many zones or tracers. The method
so far was already applied to a number of nucleosynthesis processes. Here we
focus on the production of p-nuclei in white dwarfs exploding as thermonuclear
(type Ia) supernovae. We find generally small uncertainties in the final
abundances despite of the dominance of theoretical nuclear uncertainties. A
separate analysis of low- and high-density regions indicates that the total
uncertainties are dominated by the high-density regions.
