Removable inner turbine shell with bucket tip clearance control

A method of operating a turbine having a rotor including axially spaced buckets carried thereby forming parts of first and second turbine stages, an outer containment shell, an inner shell about the rotor including nozzles carried thereby forming other parts of said first and second turbine stages and shrouds about the tips of said first and second-stage buckets, respectively, and a passage formed in said inner shell for flow of a thermal medium to control thermal growth of said inner shell, comprising the steps of:

• forming portions of said passage at least partially circumferentially about the inner shell at each axial location of the buckets of the first and second stages, respectively, and connecting the passage portions of said first and second stages in series;
• connecting said inner shell and said outer shell to one another to preclude radial and circumferential movement of said inner shell relative to said structural outer shell and enable thermal radial expansion and contraction of said inner shell relative to said structural outer shell;
• and
• flowing the thermal medium serially through said first and second passage portions to control the temperature and thermal radial expansion and contraction of said inner shell thereby to control the clearance between the bucket tips and the shroud, the step of flowing including flowing a cooling thermal medium through said passage during a steady-state operating condition of the turbine to cool the inner shell and cause thermal contraction of the inner shell about the rotor to minimize the clearance between the bucket tips and the shroud.