This paper describes the use principle and application fields of vortex diodes. Unfortunately, all the published studies have not taken into account the restrictions on the coolant flow rate in the vortex diode when used in a nuclear reactor. The diodicity declined significantly due to the limitation of the average flow velocity in the throttle, which does not exceed 12 m/s, while a parallel arrangement of vortex diodes could increase the maximum flow rate through it. In this paper a parameter E that describes the effectiveness of the vortex diode is proposed and the related factors are studied. The work presented in this paper will be useful in offering a better understanding of flows in vortex diodes and provides guidance for optimizing the vortex diode in fast neutron reactors.