An axial flow turbine comprising a casing, a rotor having an axial rotational axis and rotatably mounted into the casing, at least one set of a plurality of moving blades supported by the 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, at least the outer ring being split in an upper half and a lower half along a vertical joint plane. The turbine 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.