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

A method of limiting leakage of working fluid between a rotor and a stator in a turbine during working operation of the turbine, the turbine comprising at least one rotor wheel with an array of rotor blades and a stator casing extending around the array of rotor blades, wherein the stator casing has radial size dependent from its temperature, wherein the rotor wheel has radial size dependent from its temperature, the method comprising the steps of:

• arranging a shroud ring having a radial size substantially independent from its temperature,
• positioning the shroud ring concentrically about the rotor wheel, between the array of rotor blades and the stator casing, and
• mechanically coupling the shroud ring with the casing so that coupling is maintained independently from a temperature of the shroud ring and from a temperature of the casing;
• wherein at working temperature of turbine, tip regions of the blades of said array are in close proximity to or in contact with an inner region of the shroud ring.