  A simple model for nuclear structure functions in the region of small $x$ and
small and moderate $Q^2$, is presented. It is a parameter-free extension, in
the Glauber-Gribov approach to nuclear collisions, of a saturation model for
the nucleon. A reasonable agreement with experimental data on ratios of nuclear
structure functions is obtained. The unintegrated gluon distribution and the
behavior of the saturation scale which result from this model are discussed.
