Thermofluid Magnetohydrodynamic Issues for Liquid Breeders

This paper provides a description of the most promising liquid breeder blankets currently proposed for testing in ITER. The critical MHD issues for selfcooled and dual coolant LM systems are the MHD pressure drop and flow distribution with ideal and imperfect insulator barriers/coatings, ideal and imperfect flow channel inserts, and complex geometry flow elements like expansions, contraction, manifolds, etc.  Separately cooled LM systems still must circulate the LM for tritium removal, and similar MHD issues may limit flow velocity and influence tritium permeation due to creation of stagnant regions and other nonideal flow distribution effects. Molten salt breeder/coolants have significantly reduced electrical conductivity as compared to LMs, and MHD pressure drop is not considered a serious issue. However, MS also has much lower thermal conductivity, and the heat transfer to/from the structure depends on turbulent convection. The degradation of convective heat transfer by MHD turbulence modification/suppression is of great interest for both selfcooled MS systems where first wall cooling may need to be enhanced, and dual coolant MS systems where heat transfer from the hot breeder to the cooler wall needs to be suppressed. These issues are discussed in detail and development plans specifically for the dualcoolant PbLi concept, up to and including integrated testing in ITER, are presented.