Thermal convection loop experiments and analysis of mass-transport processes in lithium/Fe-12Cr-1MoVW systems

Lithium is an attractive coolant and breeder material for first-generation fusion-reactor blankets. The compatibility of lithium with structural alloys, in the form of mass transport and deposition, may impose restrictions on blanket operating parameters such as temperature and lithium purity. A ferritic steel, such as Fe-12Cr1MoVW, is a candidate for use as a structural alloy in a self-cooled lithium blanket design. Experimental data on mass transport in lithium/Fe-12Cr1MoVW were obtained from two thermal convection loops that spanned the fusion-relevant temperature range; one operated from 360 to 505 degree C for 3040 hours and the other from 525 to 655 degree C for 2510 hours. Analyses of mass transport and deposition, as measured by specimen weight change, were not simple functions of temperature for the entire temperature range investigated. The mass-transfer behavior and surface morphology at low temperatures were dominated by impurity reactions of nitrogen and carbon in the lithium with the steel. In the experiment between 360 and 505 degree C nitrogen levels were sufficient below 450 degree C to allow the formation of the adherent, protective corrosion product Li9CrN5