Thermal and hydraulic assessments of the cooling system for ITER vacuum vessel

A 1/6 sub-scale partial model of ITER vacuum vessel corresponding to the outboard section of 9° sector has been fabricated to examine the flow distribution and the possibility of flow stagnation in the cooling passages under the forced convection flow condition. Flow network analyses for the subscale model were performed to confirm validity of the calculation model employed for the vessel design. The result indicates that the mass flow rate distribution has a large difference among the coolant passages, with the smallest flow rate in the passage around divertor port and horizontal port. Natural convection analysis was also conducted for the thermal-hydraulic assessment of the vessel cooling system in the off-normal operating condition. Analytical results show that natural convection flow occurs at the coolant with the exit temperature rise of 37°C, and the vacuum vessel temperatures are found to be sufficiently below the design limit of 250°C