An axial flow turbine comprising: • a casing , • a rotor having a rotational axis (Z) and rotatably mounted into said casing , • at least one set of a plurality of moving blades supported by said rotor , and • at least one diaphragm having an outer ring , an inner ring , concentric to the outer ring , and a plurality of static blades mounted therebetween, wherein said at least one diaphragm being split in an upper half and a lower half along a horizontal joint plane (P), characterized in that said at least one diaphragm comprises an assembly system for assembling the upper half to the lower half while allowing the upper half and the lower half to move axially relative to each other, wherein the assembly system comprises: • a guiding element for axially guiding the upper half and the lower half , and • at least one fastening element for fastening the upper and lower halves together while allowing a relative axial movement of the halves relative to each other, wherein said fastening element being perpendicular to the horizontal joint plane (P), and wherein said at least one fastening element has: • a screw head , • a smooth shrank portion , and • a threaded portion , and wherein the upper half of said at least one diaphragm is formed with a drilling , made along the vertical axis (Y), and having a diameter bigger than the diameter of the smooth shrank portion , and wherein the lower half is formed with a threaded bolt hole coaxial with the drilling of the upper half and adapted to receive the threaded portion of said at least one fastening element . • a casing , • a rotor having a rotational axis (Z) and rotatably mounted into said casing , • at least one set of a plurality of moving blades supported by said rotor , and • at least one diaphragm having an outer ring , an inner ring , concentric to the outer ring , and a plurality of static blades mounted therebetween, wherein said at least one diaphragm being split in an upper half and a lower half along a horizontal joint plane (P), said at least one diaphragm comprises an assembly system for assembling the upper half to the lower half while allowing the upper half and the lower half to move axially relative to each other, wherein the assembly system comprises: • a guiding element for axially guiding the upper half and the lower half , and • at least one fastening element for fastening the upper and lower halves together while allowing a relative axial movement of the halves relative to each other, wherein said fastening element being perpendicular to the horizontal joint plane (P), and • a guiding element for axially guiding the upper half and the lower half , and • at least one fastening element for fastening the upper and lower halves together while allowing a relative axial movement of the halves relative to each other, wherein said fastening element being perpendicular to the horizontal joint plane (P), and wherein said at least one fastening element has: • a screw head , • a smooth shrank portion , and • a threaded portion , and • a screw head , • a smooth shrank portion , and • a threaded portion , and wherein the upper half of said at least one diaphragm is formed with a drilling , made along the vertical axis (Y), and having a diameter bigger than the diameter of the smooth shrank portion , and wherein the lower half is formed with a threaded bolt hole coaxial with the drilling of the upper half and adapted to receive the threaded portion of said at least one fastening element . <EOS>