Thermal disadvantage factor measurements in cells of seed-blanket assemblies containing highly enriched 235U and 233U fuel rods as well as in cells containing slightly enriched 233U fuel rods are in agreement within experimental uncertainties with calculations for all but a very tightly packed blanket lattice. The measurements  were corrected for flux perturbations in the fuel rod and the moderator channel caused by the detecting foils. MARC calculations using the Radkowsky scattering kernel yield results approximately 8% higher than similar calculations using the Nelkin kernel. While THERMOS calculations for the tightly packed blanket cells appear to be in agreement with measurement (possibly fortuitous), MARC results are significantly above the measured values. The source of the discrepancy is not known at this time. Higher order scattering as well as angular energy effects in the source-to-thermal neutron energy treatment have been investigated  using a newly developed full energy range (0 to 10 MeV) Monte Carlo program RECAP-4C.