An approach is developed to study the stability of mixed convection in the poloidal flows of the DCLL blanket. Modified Orr-Sommerfeld equations are derived and then solved using a numerical code based on a pseudo-spectral method. The stability analysis has been performed for the flows in the front blanket ducts, where the forced flow is upwards; showing that in the DCLL blanket conditions, all disturbances associated with the buoyant flows in the front ducts will likely be damped by a strong toroidal magnetic field.