Radial turbomachine, comprising: a fixed casing; at least one rotor disc (2,2') installed in the casing and rotatable in the casing around a respective rotation axis (X-X); a plurality of annular rotor elements (3,22,23,24; 22,23) coaxial with the rotation axis (X-X), axially projecting from a front face (4,4') of the rotor disc (2,2') and/or from a rear face (9,9') of the rotor disc (2,2'); a plurality of annular fixed elements (13,25,27; 34) coaxial with the rotation axis (X-X), axially projecting from the casing and each positioned in a radially external position with respect to a respective annular rotor element (3,22,23,24; 22,23); wherein the annular rotor elements (3,23,22,24) comprise rotor blades mounted on the front face of the rotor disc and the annular fixed elements (13,25,27) comprise stator blades facing the front face of the rotor disc; and/or wherein the annular rotor elements (22,23) are rotor sealing walls mounted on the rear face (9,9') of the rotor disc (2,2') and the annular fixed elements are fixed sealing walls facing the rear face (9,9') of the rotor disc (2,2'); a plurality of sealing devices (28,29; 29,31; 32,33) radially interposed between at least some of said annular rotor elements (3,22,23,24; 22,23) and the respective annular fixed elements (13,25,27; 34); characterised in that the annular rotor elements (3,22,23,24; 22,23) are radially movable between a first radially contracted configuration, when the turbomachine is in a non-operative condition, in which said sealing devices (28,29; 29,31; 32,33) of said annular rotor elements (3,22,23,24; 22,23) are radially spaced from the sealing devices (28,29;29,31;32,33) of the respective annular fixed elements (13,25,27; 34), and a second radially expanded configuration under the action of the centrifugal force and/or of the heat, when the turbomachine is operating, in which, at the sealing devices (28,29; 29,31; 32,33), said annular rotor elements (3,22,23,24; 22,23) are close to the respective annular fixed elements (13,25,27; 34); wherein in the second configuration, the sealing devices (28,29; 29,31; 32,33) substantially prevent the passage of a working fluid between the annular rotor elements (3,22,23,24; 22,23) and the annular fixed elements (13,25,27; 34). a fixed casing; at least one rotor disc (2,2') installed in the casing and rotatable in the casing around a respective rotation axis (X-X); a plurality of annular rotor elements (3,22,23,24; 22,23) coaxial with the rotation axis (X-X), axially projecting from a front face (4,4') of the rotor disc (2,2') and/or from a rear face (9,9') of the rotor disc (2,2'); a plurality of annular fixed elements (13,25,27; 34) coaxial with the rotation axis (X-X), axially projecting from the casing and each positioned in a radially external position with respect to a respective annular rotor element (3,22,23,24; 22,23); wherein the annular rotor elements (3,23,22,24) comprise rotor blades mounted on the front face of the rotor disc and the annular fixed elements (13,25,27) comprise stator blades facing the front face of the rotor disc; and/or wherein the annular rotor elements (22,23) are rotor sealing walls mounted on the rear face (9,9') of the rotor disc (2,2') and the annular fixed elements are fixed sealing walls facing the rear face (9,9') of the rotor disc (2,2'); a plurality of sealing devices (28,29; 29,31; 32,33) radially interposed between at least some of said annular rotor elements (3,22,23,24; 22,23) and the respective annular fixed elements (13,25,27; 34); characterised in that the annular rotor elements (3,22,23,24; 22,23) are radially movable between a first radially contracted configuration, when the turbomachine is in a non-operative condition, in which said sealing devices (28,29; 29,31; 32,33) of said annular rotor elements (3,22,23,24; 22,23) are radially spaced from the sealing devices (28,29;29,31;32,33) of the respective annular fixed elements (13,25,27; 34), and a second radially expanded configuration under the action of the centrifugal force and/or of the heat, when the turbomachine is operating, in which, at the sealing devices (28,29; 29,31; 32,33), said annular rotor elements (3,22,23,24; 22,23) are close to the respective annular fixed elements (13,25,27; 34); wherein in the second configuration, the sealing devices (28,29; 29,31; 32,33) substantially prevent the passage of a working fluid between the annular rotor elements (3,22,23,24; 22,23) and the annular fixed elements (13,25,27; 34).