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

A gas (or steam) turbine is disclosed including: a rotor with at least one array of rotor blades, a stator with a casing and a shroud ring; the shroud ring extends around the array of blades rotor and the casing extends around the shroud ring. The shroud ring has radial size independent from temperature due to its material and is movably coupled with the casing so to allow the casing 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 are in close proximity to an inner region of the shroud ring so that clearance is small or zero at working condition.