  We discuss the problem of ultra high energy nuclei propagation in
astrophysical backgrounds. We present a new analytical computation scheme based
on the hypothesis of continuos energy losses in a kinetic formulation of the
particles propagation. This scheme enables the computation of the fluxes of
ultra high energy nuclei as well as the fluxes of secondaries (nuclei and
nucleons) produced by the process of photo-disintegration suffered by nuclei.
