Experimental and computational studies of the gamma-ray energy deposition rate in the Fast Breeder Blanket Facility (FBBF) were performed with thermoluminescent dosimeters (TLDs). Various corrections including the TLD neutron sensitivities and the f factors (general cavity-ionization theory) were applied to the TLD measurements. Comparisons were made with results of three computer codes — 1DX, 2DB, and ANISN — and two nuclear libraries — LIB-IV and EPR. Both neutron and gamma-ray calculations were performed. The previously reported deviations between the gamma-ray energy deposition calculated-toexperiment (C/E) ratios for lead and for stainless steel were resolved. It is believed that the remaining C/E discrepancy comes primarily from the inaccuracies in the neutronics part of the calculations, because similar dropoffs are also reported in the FBBF reaction rate C/E comparisons. Detailed analysis of the deviation between transport (Sn) and diffusion calculations in the FBBF were performed. It was found that the deviation is built up in the blanket region and is largely independent of the curvature of the “independent” source region. Comparisons between Sn and diffusion calculations (on a one-dimensional basis) for neutron fluxes and reaction rates indicated that the use of transport calculations should reduce the discrepancies of C/E comparisons.