The work performed at Irstea investigates the use of CO2 hydrates slurries as phase change materials. A tank with a pilot loop is used to form slurries by subcooling. Several studies (thermal, rheological) were carried out to evaluate slurries characteristics useful for a complete energy study of the system. The aim of this paper is to present the modelling of a device for hydrate slurries formation including a tank reactor and a loop. Finite volume method with implicit time discretization scheme is used. This model allows predicting the slurry temperature evolution; it is validated by experimental data on a hydrate formation during a cooling process. The energy balance is performed to evaluate the storage efficiency and the heat losses through the reactor wall.