An improved gas circulatorfor a gas-cooled nuclear reactor system is disclosed which includes a stator, a rotor having a rotor shaft, and an impeller attached to one end thereof. A radial active magnetic bearing and a radial backup bearing are positioned proximate each end of the rotor shaft. An axial active magnetic bearing is also located between the ends of the rotor shaft, as is an axial backup bearing, with two of the backup bearings enclosed within a sealed chamber that may contain a lubricant, for example, a solid lubricant or a liquid lubricant. Preferably, the gas circulator is installed in a nuclear reactor system with the rotor shaft in a substantially vertical orientation and the sealed chamber near the bottom of the rotor shaft. The lower radial backup bearing and the axial backup bearing are advantageously located within the sealed chamber. The lower radial backup bearing and the axial backup bearing may be spaced apart sufficiently to permit the lower radial backup bearing to provide substantially all radial support for the rotor when the radial active magnetic bearings are deenergized.