Boiling heat transfer problems in a tokamak

A prime incentive to employ a potassium or cesium boiler submerged in a recirculating lithium blanket is that this arrangement gives the most uniform temperature distribution through the blanket and hence the lowest thermal stresses of any configuration that has been proposed. The principal problems currently envisioned are associated with the MHD effects on the liquid feed flow to the boiler tubes and a possibly unsatisfactory boiler feed flow distribution because of the differences in pressure drop in the feed lines from one region to another as a consequence of differences in magnetic field strength and line lengths. Various ways of coping with these problems have been considered and their relative merits have been appraised. The two most promising appear to be the use of a set of EM pumps in a series-parallel arrangement with the EM pumps used to circulate the lithium, and the use of a liner inside the pipes traversing the magnetic field. This liner would consist of a thin layer of electrical insulation covered by a thin layer of the structural material. The principal uncertainty associated with this approach is the extent to which pin holes in the metallic coating over the oxide (zirconia, yttria, thoria, or alumina) cause blistering of the coating