Kinetics of the degradation of type 316 stainless steel by liquid lithium

A forced convection loop is used to study the corrosion of type 316 stainless steel by liquid lithium at temperatures relevant to fusion reactors. Weight loss data are reported for tubular samples located in the hot zone of the loop. Temperatures of 440C and 490C have been used in the hot zone with temperature differences of 100C to 200C between the hot and cold zones. The effect of lithium velocity on local mass transfer rates is examined by simultaneously exposing stainless steel samples to parallel streams of lithium at velocities ranging from 40 to 130 cm/s. The loss rates become essentially steady after one month of exposure. The rates agree substantially with rates reported by previous workers, but are one to two orders of magnitude smaller than the rates predicted by boundary layer theory, using an extrapolation of the available solubility data for iron in lithium. It is presumed that particles of iron circulate in the lithium and by their dissolution and precipitation act as a buffer to reduce the wall fluxes. The loss rate increases with lithium velocity in a manner suggestive of liquid-phase controlled mass transfer. The velocity dependence is weaker than expected for flows in the range of Reynolds numbers studied. This may reflect a significant interfacial resistance to the dissolution. The mass loss rates at 440C are reduced when the temperature difference between the hot and cold zones is reduced. The rates during the first 1000 hours are three to four times higher at 490C than at 440C. The dissolution rate at 490C decreases markedly after 1000 hours. The transformation of the steel surface to a ferritic phase may cause the reduction in the rate