S>Progress is reported on the research and development program being performed in connection with the design of the Pathfinder Atomic Power Plant. The topics covered include: fuel material cladding, bonding, and irradiation testing; heat transfer and fluid flow; fuel element manufacturing research and development; low-enrichment superheater fuel element design; mechanical studies of control rods, guide tubes, and control rod drives; reactor physics; and reactor and system dynamics. (C.H.)

Foreword: This report describes the results of a series of engineering evaluation studies conducted between July 1, 1961 and June 30, 1962, related to heavy water moderated power reactor plants.

"A series of high urania-content glasses were fiberized and examined for high-temperature strength properties. One glass, RX360 containing 60% U/sub 3/O/ sub 8/ by weight, had better high-temperature tensile properties than any glass previously reported. It was observed that many of the glasses studied separated into immiscible phases and that the fiberizable glass phase had lower U/sub 3/O/ sub 8/ content than the base compositions. A physical analysis of crystal structures of the devitrification products from the nuclear fuel glasses indicated that most of the crystals consisted of uranium oxide in a reduced state. By adding O/sub 2/ to molten glass, it was possible to eliminate most of this devitrification. By elimination of crystals, the fiberizing of the glass was more uniform and the glasses produced had more consistent physical properties."