Thermal protection shield for a rotating shaft
A thermal protection shield for a rotating shaft of a primary coolant pump shaft of a nuclear power station includes, in the thermal transition region between the hot fluid and the cold fluid, a ring of nickel alloy shrunk onto the shaft. An external ring of austenitic stainless steel is shrunk at each of its ends onto the ring of nickel alloy. Between the two shrunk-on ends, a cylindrical cavity forms a clearance with the external surface of the nickel alloy ring.
1. A thermal protection shield for a rotating shaft of a primary coolant pump shaft of a nuclear power station, wherein the shield comprises, in the thermal transition region between the hot fluid and the cold fluid:
a ring of nickel alloy shrunk onto said shaft;
an external ring of austenitic stainless steel surrounding the nickel alloy ring, the external ring shrunk at each of its ends onto the ring of nickel alloy; and
a cylindrical cavity between the two shrunk on ends for forming a clearance with the external surface of said ring of nickel alloy.
2. A shield according to claim 1 , wherein a wall of the cylindrical cavity of the external ring has projecting annular portions for reducing the clearance between said wall and the external face of the ring of nickel alloy.
3. A shield according to claim 1 , wherein the total length of the shrunk-on ends of the external ring represents about 20% of an overall length of the external ring.
4. A shield according to claim 1 , further comprising:
a transverse pin of austenitic stainless steel for linking the ring of nickel alloy and the external ring of austenitic stainless steel with the shaft;
the pin being mounted in an orifice provided in the shaft and both rings; and
the free end of the pin being welded to the external ring.
5. A shield according to claim 1 , wherein the shaft has, in the lower part of the ring of nickel alloy, a cavity in which a split ring is mounted.
6. A shield according to claim 5 , wherein the split ring is made of a material whose expansion coefficient is identical to the material of the shaft.