  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. Nuclear effects in the
longitudinal-to-transverse cross section ratios are found to be small.
Predictions of the model for values of $x$ smaller than those available to
present experiments are given. The unintegrated gluon distribution and the
behaviour of the saturation scale which result from this model are shown and
discussed.
