Expander and thermodynamic cycle using the expander

An expander for a supercritical or transcritical carbon dioxide thermodynamic cycle, the expander comprising:

• an outer casing;
• at least one combustor combined with the outer casing, the at least one combustor being adapted to receive a flow of compressed oxidant and a fuel;
• a rotor with a rotation axis, housed for rotation in the outer casing;
• wherein the rotor comprises:
• a shaft;
• a plurality of rotor disks mounted on the intermediate shaft portion;
• wherein each rotor disk of said plurality of rotor disks comprises a respective annular row of rotor blades;
• and
• upstream of each annular row of rotor blades, a respective annular row of stationary vanes;
• wherein each annular row of stationary vanes and the respective annular row of rotor blades form an expander stage;
• at least one cooling duct extending along the shaft, the cooling duct having an inlet end adapted to be fluidly coupled to a high-pressure plenum of the turbomachine when the rotor is mounted in the turbomachine, and fluidly coupled to at least one intermediate annular space between a pair of sequentially arranged rotor disks;
• wherein each rotor disk of said plurality of rotor disks is mounted on the shaft by shrink-fitting.