Speaker
Description
The breeding blanket First Wall is the first boundary separating the fusion plasma and its energetic particles from the rest of the Tokamak. In DEMO reactor, the First Wall integrated in the blanket is in charge of 1) removing the surface heat load connected with the charged particles and the volumetric power density arising from plasma; 2) ensuring the structural integrity of the blanket, thus maintaining the physical boundary of the radioactive breeder material in operating and accident conditions; 3) delivering the coolant to the First Wall Primary Heat Transfer System at design temperature for an efficient power conversion into electricity. In the frame of EUROFUSION Work Package Breeding Blanket, the cooling performances of Water Coolant Lithium Lead Breeding Blanket First Wall are investigated using a CFD approach. The heat load specifications are reviewed and different poloidal positions have been studied, i.e. the poloidal position characterized by the maximum heat load (surface radiation and charged particles), the outboard and inboard equatorial positions. In the analyses the reference geometry is compared with a different cooling scheme, with a different channel geometry and with different radial positions. The configuration with two passes has better cooling performances and still some margin, being the coolant velocity lower than the limit (i.e. 7m/s). Compared with the square channels, the circular ones penalize the temperature field in the Eurofer, but the presence of steam in the subcooled nucleate boiling region is more limited. Moreover, circular channels may imply enhanced reliability of the system and manufacturing advantages, because the absence of joints in direct contact with the fluid domain. The results have demonstrated that the water-cooled First Wall is effective in keeping the maximum temperature of the solid structure below the Eurofer limit, as well as ensuring the design coolant temperature at the channel outlet (i.e. 328°C).
