A MRFZone is created using topoSet dictionary topoSetDict.mrf:

actions
(
  {
        name    rotor_mrf_set;
        type    cellSet;
        action  new;
        source  cylinderToCell;
        sourceInfo
        {
            radius 0.2;
            p1 (0 0 0);
            p2 (0 0 0.110);
        }
    }
    {
        name rotor_mrf_zone;
        type cellZoneSet;
        action new;
        source setToCellZone;
        sourceInfo
        {
            set  rotor_mrf_set;
        }
    }
);

Run the topoSet utility:

# topoSet -dict system/topoSetDict.mrf