A steam turbine system comprising: a rotor rotatively arranged within a high pressure section, an intermediate pressure section and a low pressure section, wherein the rotor is a drum rotor; the HP section having a casing (212, 214) arranged between the rotor and the exterior of the turbine; and the IP section having a casing and being fluidly connected to the HP section; wherein the HP section and the IP section each include a plurality of nozzle ring assemblies positioned such that each nozzle ring assembly surrounds the rotor, characterized in that the casing of the HP section is a double shell casing including an outer wall and an inner wall, the casing of the IP section is a single shell casing having only one wall between the rotor and the exterior of the turbine and the LP section is fluidly connected to the IP section by a crossover pipe, wherein the LP section is also connected to a condenser, wherein the plurality of nozzle ring assemblies of the IP section is encased by the casing of the IP section and axially spaced along the casing of the IP section, and wherein each nozzle ring assembly of the IP section includes: a supporting ring which is fitted into a groove in the casing of the IP section; and at least one set of individual nozzles coupled to the supporting ring and circumferentially positioned around the rotor; wherein each nozzle ring assembly includes one supporting ring supporting two sets of nozzles, wherein each set of nozzles comprises individual nozzles circumferentially positioned around the rotor, wherein the two sets of individual nozzles form two rows of nozzle vanes which are axially spaced with a row of rotor blades arranged axially between the two rows of nozzle vanes, wherein the nozzles are configured to be slid into grooves in the supporting ring, and wherein the blades are fitted into a groove in the rotor and circumferentially positioned around the rotor. a rotor rotatively arranged within a high pressure section, an intermediate pressure section and a low pressure section, wherein the rotor is a drum rotor; the HP section having a casing (212, 214) arranged between the rotor and the exterior of the turbine; and the IP section having a casing and being fluidly connected to the HP section; wherein the HP section and the IP section each include a plurality of nozzle ring assemblies positioned such that each nozzle ring assembly surrounds the rotor, characterized in that the casing of the HP section is a double shell casing including an outer wall and an inner wall, the casing of the IP section is a single shell casing having only one wall between the rotor and the exterior of the turbine and the LP section is fluidly connected to the IP section by a crossover pipe, wherein the LP section is also connected to a condenser, wherein the plurality of nozzle ring assemblies of the IP section is encased by the casing of the IP section and axially spaced along the casing of the IP section, and wherein each nozzle ring assembly of the IP section includes: a supporting ring which is fitted into a groove in the casing of the IP section; and at least one set of individual nozzles coupled to the supporting ring and circumferentially positioned around the rotor; a supporting ring which is fitted into a groove in the casing of the IP section; and at least one set of individual nozzles coupled to the supporting ring and circumferentially positioned around the rotor; wherein each nozzle ring assembly includes one supporting ring supporting two sets of nozzles, wherein each set of nozzles comprises individual nozzles circumferentially positioned around the rotor, wherein the two sets of individual nozzles form two rows of nozzle vanes which are axially spaced with a row of rotor blades arranged axially between the two rows of nozzle vanes, wherein the nozzles are configured to be slid into grooves in the supporting ring, and wherein the blades are fitted into a groove in the rotor and circumferentially positioned around the rotor.