Steam cooling a turbine rotor

An axial bore tube assembly (48) for a turbine is provided to supply cooling steam to hot gas components of the turbine wheels and return the spent cooling steam. A pair of inner and outer tubes (52, 50) define a steam supply passage (54) concentric about an inner return passage (56). The forward ends of the tubes communicate with an end cap assembly (80) having sets of peripheral holes (88) communicating with first and second sets of radial tubes (92) whereby cooling steam from the concentric passage (54) is supplied through the end cap holes (88) to radial tubes (93) for cooling the buckets and return steam from the buckets is provided through the second set of radial tubes (95) through a second set of openings (90) of the end cap (80) into the coaxial return passage (56). A radial-to-axial flow transitioning device, including anti-swirling vanes (112), is provided in the end cap (81). A strut ring adjacent the aft end of the bore tube assembly permits axial and radial thermal expansion of the inner tube (52) relative to the outer tube (50).