The eventual entrainment of gas bubbles in the reactor core of a Light Metal Fast Breeder Reactors (LMFBR) may cause an effective increase in reactivity as in the current state of the art LMFBRs have usually a positive void coefficient. Since this may have a negative effect on safety and operation, the possibility of gas entrainment needs to be evaluated in the thermal-hydraulics design. Several studies on the gas entrainment in a LMFBR system have been conducted over the years (Eguchi et al, 199410). The most common situations that may lead to gas entrainment have been classified into vortex dimple, concave free surface and breaking wave. Among these, the vortex-induced gas entrainment phenomenon is considered in the present work, because more likely to be present in operating or accidental conditions. The focus is on the issue of turbulence modeling for the simulation of gas-entraining vortexes, and in particular for the case of Moriya13. We will propose two different approaches: a large eddy simulation and a detached eddy simulation. Results are in excellent agreement with the experiment for the radial velocity even if no surface model has been employed.