  The inclusion of massive neutrinos affects the cross sections involved in the
formation of heavy nuclei, modifying their abundances. Rapid neutron capture
processes (r-process) are often associated with explosive events such as
core-collapse supernovae. In this work we study the effects of active and
sterile neutrino oscillations and interactions, upon the calculation of
neutrino fluxes, the baryonic density and the electron fraction of the
material. We have considered two different initial distribution functions of
the neutrinos and different combinations of mixing parameters (including
{\theta} 34 = 0). We use the formalism of density matrices for the calculations
and included the effects of neutrino oscillations, interactions with matter and
self-neutrino interactions. We found that the interactions of the neutrinos
with matter and with themselves change the electron fraction, affecting the
onset of the r-process.
