Polonium, an alpha-emitting sulfur-like element, is formed by neutron irradiation of lead or bismuth impurity in lead. Design studies of both the Pulse*Star inertial confinement fusion (ICF) reactor and the MARS mirror fusion reactor postulated use of 83Pb-17Li melt as the tritium breeding blanket and coolant- Comparison of the amounts of polonium in the melt at plant shutdown indicated that Pulse*Star would have a far higher level of polonium in the melt. Neutronic considerations and the polonium distribution between the vacuum cleanup system and 83Pb-17Li melt for the two reactors are explored in this paper. Sample neutronics runs showed that the codes used by each design team were not the source of the difference in polonium content.