  We derive a compositional compressible two-phase, liquid and gas, flow model
for numerical simulations of hydrogen migration in deep geological repository
for radioactive waste. This model includes capillary effects and the gas high
diffusivity. Moreover, it is written in variables (total hydrogen mass density
and liquid pressure) chosen in order to be consistent with gas appearance or
disappearance. We discuss the well possedness of this model and give some
computational evidences of its adequacy to simulate gas generation in a water
saturated repository.
