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