form is certainly questionable » since there are so many serious unknowns to be resolved. It is probably best classified along with the Fast Breeder as a promising "long-shot", Sodium-Graphite Reactor North American Aviation's program was described by Chauncey Starr and associates at the Oak Ridge meeting. NAA's Nuclear Division initially worked on nuclear propulsion for missiles for the Air Force but is now concentrating on industrial reactors for AEC, with a team of about 250 professionals. Their sodium-graphite reactor experiment (SRE) at Santa Susana is expected to go critical in December 1955. $10 million has been allocated, of which $2.5 million is being supplied by NAA itself. Dr. Starr emphasized that this total does not provide for getting all the requisite data for potential manufacturers to design a plant whose performance can be guaranteed eee nt ee “nor fordesirablework on the general reactor program, e.g., effects of irradiation on materials, new moderators such as organics and zirconium hydride, new methods of fuel reprocessing by "compact chemistry", and new safety devices, The SRE, rated at 20 MW, will use uranium at 2.75% enrichment, although less enrichment would ‘be required in larger sizes. It is expected that thorium would later be used as a uranium-thorium alloy. The design embodies a reactor tank 11 ft. in diameter and 21 ft. high containing a 6 ft. by 6 ft. core. The core is composed of zirconium-sheathed graphite hexagons on 11 inch centers, immersed in sodiun, with stainless-jacketed fuel rods installed vertically in central holes of the graphite hexagons. hung in holes provided at the corners of the hexagons. Control elements are Sodium coolant passes 5a} ote so : ‘s at one . po Ne ov