  We present a compositional compressible two-phase, liquid and gas, flow model
for numerical simulations of hydrogen migration in deep geological radioactive
waste repository. This model includes capillary effects and the gas
diffusivity. The choice of the main variables in this model, Total or Dissolved
Hydrogen Mass Concentration and Liquid Pressure, leads to a unique and
consistent formulation of the gas phase appearance and disappearance. After
introducing this model, we show computational evidences of its adequacy to
simulate gas phase appearance and disappearance in different situations typical
of underground radioactive waste repository.
