Comparison of Possible Flow Distribution Systems for PbLi Self-Cooled Blankets With Respect to MHD, Fabrication, and Maintenance

Previous conceptual design studies for liquid-metal (LM) cooled blankets of a fusion power plant often omit details of the complete flow distribution network required to bring the coolant into and out of the blanket, and especially the manifolding required for the transition from a small number of feed pipes to sometimes a large number of parallel channels within the actively heated part of the power core. Manifolding can induce large 3-D magnetohydrodynamics (MHD) currents and therefore dominate the pressure and flow distributions within the entire blanket, which is especially problematic for designs with electrically insulated channels. Especially risky are those elements that require bends which redirect the flow from parallel to perpendicular to the magnetic field and vice versa, because in those cases a bulk of the liquid metal can act as a short circuit. A fully developed flow in insulated ducts normally retains well-balanced electric potentials, preventing large 3-D currents; internal flows parallel to the magnetic field can easily disrupt this delicate balance. Within the ARIES-ACT1 power plant study several design concepts for flow distribution networks have been analyzed. Each system provides pros and cons. MHD effects as well as fabrication and maintenance issues were considered. Using SiCf/SiC as a structural material for blanket and manifolding, and a complex structure for these parts with an inner and outer pipe separated by ribs required a more detailed consideration of manufacturing as well as joining and cutting possibilities. Available technologies have been considered for a possible solution. Tradeoffs associated with the vacuum vessel and structural ring penetrations as well as pipe connections required for maintenance are discussed for the preferred solution. A maintenance scenario and fabrication steps for the latest ARIES-ACT1 manifold design are shown.