MAGNETOHYDRODYNAMIC INVESTIGATIONS OF A SELF-COOLED PB-17LI BLANKET WITH POLOIDAL-RADIAL-TOROIDAL DUCTS

For self-cooled liquid metal blankets, the magnetohydrodynamic (MHD) p ressure drop and velocity distributions are considered as critical iss ues. This paper summarizes MHD work performed for a DEMO-related Pb-17 Li blanket, where the coolant flows downwards in rear poloidal ducts; turns around by 180 degrees at the blanket bottom; is diverted from po loidal ducts into short radial channels which feed to toroidal First w all coolant ducts; flows through the subsequent radial channels; is co llected again in poloidal channels and leaves the blanket segment at t he blanket top. To reduce the pressure drop and to decouple electrical ly parallel channels, flow channel inserts are used for all the ducts except the first wall ducts. A previous pressure drop assessment resul ted in significant values for duct geometries with flow distribution o r collection, and multichannel effects for the system of U-bends. As a result of the uncertainty of these assessments, corresponding investi gations were carried out recently. Characteristic results are presente d in this paper. It is shown that, for both geometries, the pressure d rops are considerably lower than those previously assessed. First resu lts from experiments on the velocity distribution in a radial-toroidal -radial U-bend are also presented. Here, it is shown that, with an inc reasing interaction parameter, the liquid preferentially flows close t o the First wall. Additionally, a pair of strong vortices was observed in a toroidal duct. Both effects are supposed very favourable for hea t transfer.