A steam turbine rotor assembly comprising: a rotor body having a slot extending entirely circumferentially about a primary axis of the rotor body, the slot including: a primary slot extending an entire circumferential distance about the rotor body; and a secondary slot extending axially from the primary slot and spanning only a portion of the circumferential distance about the rotor body; a circumferential seal within the primary slot spanning the entire circumferential distance about the rotor body, the circumferential seal including at least one circumferentially extending slot, the slot comprising circumferentially facing walls; the circumferential seal further comprising an axial face; and a rotor key member having: a main body sized to contact the axial face of the circumferential seal; and a locking member extending from the main body in a direction axially toward the circumferential seal, the locking member having at least one circumferential edge sized to complement the circumferentially extending slot in the circumferential seal to restrict movement of the circumferential seal relative to the rotor body, wherein the circumferential seal further includes a protrusion extending axially from the axial face of the circumferential seal the steam turbine rotor assembly being characterised in that the protrusion is located radially inward of the circumferentially extending slot, and wherein the rotor key member is sized to pass radially into the secondary slot, and when the rotor key member rotates with the rotor body, the locking member slides within the circumferentially extending slot to engage one of the circumferentially facing walls. a primary slot extending an entire circumferential distance about the rotor body; and a secondary slot extending axially from the primary slot and spanning only a portion of the circumferential distance about the rotor body; a circumferential seal within the primary slot spanning the entire circumferential distance about the rotor body, the circumferential seal including at least one circumferentially extending slot, the slot comprising circumferentially facing walls; the circumferential seal further comprising an axial face; and a rotor key member having: a main body sized to contact the axial face of the circumferential seal; and a locking member extending from the main body in a direction axially toward the circumferential seal, the locking member having at least one circumferential edge sized to complement the circumferentially extending slot in the circumferential seal to restrict movement of the circumferential seal relative to the rotor body, wherein the circumferential seal further includes a protrusion extending axially from the axial face of the circumferential seal the steam turbine rotor assembly being characterised in that the protrusion is located radially inward of the circumferentially extending slot, and wherein the rotor key member is sized to pass radially into the secondary slot, and when the rotor key member rotates with the rotor body, the locking member slides within the circumferentially extending slot to engage one of the circumferentially facing walls. a main body sized to contact the axial face of the circumferential seal; and a locking member extending from the main body in a direction axially toward the circumferential seal, the locking member having at least one circumferential edge sized to complement the circumferentially extending slot in the circumferential seal to restrict movement of the circumferential seal relative to the rotor body, wherein the circumferential seal further includes a protrusion extending axially from the axial face of the circumferential seal the steam turbine rotor assembly being characterised in that the protrusion is located radially inward of the circumferentially extending slot, and wherein the rotor key member is sized to pass radially into the secondary slot, and when the rotor key member rotates with the rotor body, the locking member slides within the circumferentially extending slot to engage one of the circumferentially facing walls.