Low-alloy ferritic steel (16MND5) is used for pressure vessels in French nuclear reactors, where radiationinduced defects are continuously nucleated during their operational lifetime. More specifically, such defects have a major influence on the collective behavior of dislocations, leading to a significant hardening and embrittlement. A multiscale modeling approach based on a combination of molecular dynamics and dislocation dynamics simulations is therefore adopted. Interactions of edge dislocations with radiation-induced defects have been widely studied compared to those of screw dislocations. The later are nevertheless of great interest as their specific mobility has a significant impact on the mechanical properties of steels at low and moderate temperatures. Furthermore, prior molecular dynamics(MD) studies[1, 2] have shown that their interactions with irradiation loopslead to significant hardening. In this study, a systematic investigation is made of the interactions between screw dislocations with [100] and [111] loops using a three-dimensional nodal dislocation dynamics (DD) code NUMODIS. The same configurations that were previously simulated with MD are successfully reproduced. This allows for a direct comparison between atomic scale and DD simulations to validate our multiscale strategy. Ultimately, the modeling of the collective behavior of dislocations properties controlling irradiation strengthening will be undertaken in order to identify and incorporate the relevant parameters in a crystal plasticity simulation.