Thermohydraulic design of the KSTAR vacuum vessel

The KSTAR vacuum vessel is designed as a racetrack-shaped double wall configuration with major ports, reinforcing ribs, bellows and a leaf spring style support structure. The vessel will be baked out by hot nitrogen gas and cooled with shielding water during normal operation. The baking/cooling medium will be fed into the double wall through the manifold to bake the vessel at 250 °C within 24 h. The heat-transfer mechanism used for the design is introduced. The heat loads on the non-symmetric vessel during the bakeout produce a non-symmetric thermal expansion that can create high thermal stresses on the support structure and the vacuum vessel interface area with the ports. The 3D temperature distribution and the resulting thermal loads in the vacuum vessel during bakeout are calculated. It is found that the vacuum vessel and its supports are structurally robust based on the thermal stress analyses.