Technical progress on the research and development program being performed in connection with the design of the Pathfinder Atomic Power Plant is reported. Studies on fuel material cladding, bonding, and irradiation testing, heat transfer and fluid flow, fuel element manufacturing research and development, nuclear handling tools, lowenrichment superheater fuel element, vessel and structures, recirculatibn system, control rods, guide tube, control rod drives, reactor physics, reactor and system dynamics, critical experiments, and initial stability and performance tests are discussed.