An integral turbine rotor comprising: a forward hub section; an aft hub section, wherein the forward hub section and the aft hub section are coupled to one another along an annular interface that resides within a plane generally orthogonal to a rotational axis of the integral turbine; an airfoil blade ring, which comprises a plurality of integral blades, which are circumferentially spaced around and extend radially outward of the coupled forward and after hub sections (56, 60), coupled to a radial outer surface of the coupled forward and aft hub sections (56, 60); and an impingement cavity (68b, 70b) formed within an interior portion of the coupled forward and aft hub sections (56, 60), wherein the impingement cavity (68b, 70b) comprises an interior surface that is positioned proximate to the radial outer surface of the coupled forward and aft hub sections (56, 60); an impingement air flow channel in fluid communication with the impingement cavity (68b, 70b), wherein cooling air is accelerated and narrowed as it flows through the impingement air flow channel to produce the impingement cooling air flow; an internal hub cavity (68a, 70a) formed within an interior portion of the coupled forward and aft hub sections (56, 60) that is in fluid communication with the impingement air flow channel, wherein cooling air flows from the internal hub cavity (68a, 70a) into the impingement air flow channel, wherein the internal hub cavity (68a, 70a) is positioned radially-inward from the impingement cavity (68b, 70b) within the interior portion of the coupled forward and aft hub section (56, 60), wherein the impingement air flow channel has an axial width that is less than a greatest axial width of both the impingement cavity (68b, 70b) and the internal hub cavity (68a, 70a), and wherein the impingement air flow channel provides fluid connection between the internal hub cavity (68a, 70a) and the impingement cavity (68b, 70b), wherein an impingement cooling air flow impinges against the interior surface of the impingement cavity (68b, 70b) to provide convective and conductive cooling to the radial outer surface of the coupled forward and aft hub sections; and a central opening (64, 66) located radially inward from the internal hub cavity, and a hub cooling air passage, wherein the hub cooling air passage has an axial width that is less than a greatest axial width of both the impingement cavity (68b, 70b) and the internal hub cavity (68a, 70a), and wherein the hub cooling air passage provides fluid connection between the central opening (64, 66) and the internal hub cavity (68a, 70a). a forward hub section; an aft hub section, wherein the forward hub section and the aft hub section are coupled to one another along an annular interface that resides within a plane generally orthogonal to a rotational axis of the integral turbine; an airfoil blade ring, which comprises a plurality of integral blades, which are circumferentially spaced around and extend radially outward of the coupled forward and after hub sections (56, 60), coupled to a radial outer surface of the coupled forward and aft hub sections (56, 60); and an impingement cavity (68b, 70b) formed within an interior portion of the coupled forward and aft hub sections (56, 60), wherein the impingement cavity (68b, 70b) comprises an interior surface that is positioned proximate to the radial outer surface of the coupled forward and aft hub sections (56, 60); an impingement air flow channel in fluid communication with the impingement cavity (68b, 70b), wherein cooling air is accelerated and narrowed as it flows through the impingement air flow channel to produce the impingement cooling air flow; an internal hub cavity (68a, 70a) formed within an interior portion of the coupled forward and aft hub sections (56, 60) that is in fluid communication with the impingement air flow channel, wherein cooling air flows from the internal hub cavity (68a, 70a) into the impingement air flow channel, wherein the internal hub cavity (68a, 70a) is positioned radially-inward from the impingement cavity (68b, 70b) within the interior portion of the coupled forward and aft hub section (56, 60), wherein the impingement air flow channel has an axial width that is less than a greatest axial width of both the impingement cavity (68b, 70b) and the internal hub cavity (68a, 70a), and wherein the impingement air flow channel provides fluid connection between the internal hub cavity (68a, 70a) and the impingement cavity (68b, 70b), wherein an impingement cooling air flow impinges against the interior surface of the impingement cavity (68b, 70b) to provide convective and conductive cooling to the radial outer surface of the coupled forward and aft hub sections; and a central opening (64, 66) located radially inward from the internal hub cavity, and a hub cooling air passage, wherein the hub cooling air passage has an axial width that is less than a greatest axial width of both the impingement cavity (68b, 70b) and the internal hub cavity (68a, 70a), and wherein the hub cooling air passage provides fluid connection between the central opening (64, 66) and the internal hub cavity (68a, 70a).