Turbine with a shroud ring around rotor blades and method of limiting leakage of working fluid in a turbine

A gas (or steam) turbine (200) is disclosed including: a rotor with at least one array of rotor blades (213-1), a stator with a casing (261) and a shroud ring (250); the shroud ring (250) extends around the array of blades rotor (213-1) and the casing (261) extends around the shroud ring (250). The shroud ring (250) has radial size independent from temperature thanks to its material, and is movably coupled with the casing (261) so to allow the casing (261) of the stator to thermally expand and contract during operation of the turbine while maintaining the shroud ring radial size. Also the rotor thermally expands and contracts during operation of the turbine, and, at working temperature, tip regions of the rotor blades (213-1) are in close proximity to an inner region of the shroud ring (250) so that clearance is small or even zero at working condition.