The paper aims at developing a validated model that can accurately predict the flow of a particulate material. This model will serve as a virtual design tool for the design of a novel passive safety system for nuclear reactors. Therefore an experimental setup consisting of a vertical glass tube is filled with 500±30 μm spherical glass particles. The experiment is then placed in a vacuum and the particles are released by opening a valve. The velocity of the particles is recorded during their fall at three different heights using a non invasive optical tracking technique with an original implementation. The same experiment is then simulated using the Discrete Element Method and results are compared. A good agreement between the simulation and the experiment was found. The sensitivity of the simulation to a change in the contact stiffness, dynamic Coulomb coefficient of friction and tangential contact force model was investigated. The influence of the initial position of the simulated particles on the packing factor was shown to be very important. Finally the experiment proved to be extremely sensitive to a perturbation of the outflow section of the tube, something that was predicted by the simulations.