1. A rotor key member (20) for radially retaining a circumferential seal (24, 124)
in a steam turbine rotor body (46), the rotor key member (20, 120) comprising:
a main body (26) sized to contact an axial face (56) of the circumferential seal (24, 124); and
a hook (28) extending from the main body (26) in a direction axially away from the circumferential seal (24, 124), the hook (28, 34) sized to substantially complement a corresponding shelf (30) in the steam turbine rotor body (46) to restrict movement of the circumferential seal (24, 124) relative to the steam turbine (2) rotor body (46).
2. The rotor key member (20, 120) as claimed in claim 1, wherein the hook (28, 34) includes a first portion (130) extending from the main body (26) in the direction axially away from the circumferential seal (24, 124), and a second portion (132) extending radially inward from the first portion (130).
3. The rotor key member (20, 120) as claimed in claim 2, wherein the main body (26) and the second portion (132) form a ledge (136) sized to complement a corresponding shelf (30, 134) in the circumferential seal (24, 124).
4. The rotor key member (20, 120) as claimed in claim 1, wherein the main body (26) and the hook (28, 34) are substantially unitary and formed of a common material.
5. The rotor key member (20, 120) as claimed in claim 4, wherein the common material includes steel.

6. The rotor key member (20, 120) as claimed in claim 1, wherein the hook (28) has a first surface (32) sized to contact the shelf (30) in the steam turbin rotor body (46), the rotor key member (20, 120) further comprising a fillet, bevel or chamfer edge (36) extending between the main body (26) and the hook (28) at a second surface (34) of the hook (28) distinct from the first surface (32).
7. A steam turbine rotor assembly (22, 122) comprising:
a rotor body (46) having a slot (48) extending substantially entirely circumferentially about a primary axis of the rotor body (46), the slot (48) including:
a primary slot (50) extending substantially an entire circumferential distance about the rotor body (46); and
a secondary slot (52) extending axially from the primary slot (50) and spanning only a portion of the circumferential distance about the rotor body (46);
a circumferential seal (24, 124) within the primary slot (50) spanning substantially the entire circumferential distance about the rotor body (46);
a set of seal retaining members (54) within the primary slot (50) contacting an axial face (56) of the circumferential seal (24, 124); and
a first rotor key member (20, 120) having:
a main body (26) sized to contact an axial face (56) of the circumferential seal (24, 124); and
a hook (28, 34) extending from the main body (26) in a direction axially away from the circumferential seal (24, 124), the hook (28, 34) sized to substantially complement a corresponding shelf (30, 134) in the primary slot (50).
8. A steam turbine (2) comprising:

a casing (7); and
a rotor assembly (22, 122) at least partially contained within the casing (7), the rotor assembly (22, 122) having:
a rotor body (46) having a slot (48) extending substantially entirely circumferentially about a primary axis of the rotor body (46), the slot (48) including:
a primary slot (50) extending substantially an entire circumferential distance about the rotor body (46); and
a secondary slot (52) extending axially from the primary slot (50) and spanning only a portion of the circumferential distance about the rotor body (46);
a circumferential seal (24, 124) within the primary slot (50) spanning substantially the entire circumferential distance about the rotor body (46);
a set of seal retaining members (54) within the primary slot (50) contacting an axial face (56) of the circumferential seal (24, 124); and
a first rotor key member (20, 120) having:
a main body (26) sized to contact an axial face (56) of the circumferential seal (24, 124); and
a hook (28, 34) extending from the main body (26) in a direction axially away from the circumferential seal (24, 124), the hook (28, 34) sized to substantially complement a corresponding shelf (30, 134) in the primary slot (50).
9. The steam turbine (2) as claimed in claim 8, wherein the first rotor key member (20, 120) is sized to pass radially through the secondary slot (52) and circumferentially into the primary slot (50) to engage the shelf (30, 134) in the primary slot (50) and contact the circumferential seal (24, 124).

10. The steam turbine (2) as claimed in claim 8, r comprising a second rotor key member (20, 120) for retaining the first rotor key member (20, 120) in the primary slot (50), the second rotor key member (20, 120) sized to substantially fill the secondary slot (52) and restrict circumferential movement of the circumferential seal (24, 124).