In the present work the CFD modeling of cryogenic hydrogen releases in quiescent environment is presented. Two tests from the series of experiments performed in the ICESAFE facility at KIT (Karlsruhe Institute for Technology) have been simulated within the SUSANA project. During these tests hydrogen at temperature of 37K and 36K and at pressure of 19 and 29 bars, respectively, is released horizontally. The release at the nozzle is sonic and the modeling of the under-expanded jet was performed using two different approaches: the Ewan and Moodie approach and a modification of the Ewan and Moodie approach (modified Ewan and Moodie) that is introduced here and employs the momentum balance to calculate the velocity in the under-expanded jet. Using these approaches a pseudo-diameter is calculated and this diameter is set as source boundary in the simulation. Predictions are consistent with measurements for both experiments with both approaches. However, the Ewan and Moodie approach seems to perform better.