The diffusion-bonded heat exchanger is a compact design being considered by several energy sectors to improve the economics and thermal performance of high-temperature power conversion systems. This dissertation examines the pressure loss and heat transfer characteristics of two commercially produced diffusion bonded heat exchangers (DBHE) with supercritical carbon dioxide, sodium nitrate/potassium nitrate molten salt, and liquid sodium. An 800H recuperator is examined in conjunction with a 316L primary heat exchanger which cooled the molten salt or sodium streams with carbon dioxide at pressure between 10 and 16 MPa. The recuperator is one of the first 800H DBHE built and preheats the cold stream to prevent freezing the hot fluid in the primary heat exchanger. Friction factor and Nusselt number correlations have been proposed for each of these three fluids. Comparison of these correlations with existing design information emphasizes the need to study salt and sodium performance in straight microchannels to complement this zig-zag channel work. A few important transients are discussed along with suggestions for further modeling and validation efforts with less challenging working fluids. This work also addresses several technical gaps associated with a draft addendum (Code Case) to Section III, Division 5 of the Boiler and Pressure Vessel Code, which addresses high-temperature nuclear components. The results of several hydrostatic rupture tests are discussed and the results of non-destructive examination trials on lab-scale components are discussed along with implications regarding post-fabrication and in-service inspection techniques for compact heat exchangers. Finally, a list of potential operational challenges voiced by industrial stakeholders are discussed to identify topics for future research. Conservative filtration and oxide concentration techniques were used for the molten salt and sodium tests performed here. Less aggressive techniques should be examined to reduce pressure losses or parasitic heat loads. The acceptable ramp rate of these components is still an open question which should be addressed by additional transient studies using simple fluids. The DBHE is a robust and attractive option for high-temperature molten salt and sodium heat transfer systems. Future work at University of Wisconsin – Madison will help to further this technology towards commercialization.