A particularly difficult problem for first-generation fusion power reactor systems is the recovery of tritium at very low concentration levels from the reactor blanket when lithium metal is the principal tritium breeding medium. On the basis of recent data and reasonable extrapolations, we show that it is likely that yttrium metal can be used to extract tritium from lithium at concentrations as low as 10−6 atom fraction tritium in lithium under conditions that are practicable for commercial power machines.