Uranium is recovered as an aqueous solution of uranyl nitrate and nitric acid in both the tributyl phosphate metal recovery process and the Redox separation process. The streams are designated as RCU and IIIEU in the respective processes. For metal recovery these streams are combined. The purpose of the nitric removal operation is to minimize equipment corrosion and to restrict contamination of the final uranium oxide with corrosion products which might be formed in the elevated temperature reactor employed for the decomposition of uranyl nitrate to the oxide. Because of the large quantities of uranium being processed it is desirable to conduct the concentration of the combined RCU and IIIEU streams in a continuous type process to reduce the operating and fixed charges. Determination of the physical and chemical properties of the dilute aqueous uranyl nitrate -- nitric acid system, as it progresses toward an essentially nitric acid free concentrated state, is necessary to define the optimum operating conditions.

The purpose of this memorandum is to present and analyze, in terms of the current status of knowledge of radiation damage to graphite, the data available at the present time on the expansion status of the graphite in the piles, and suggest, in terms of this analysis, several possibly feasible curative and preventive measures. The portion of the data to be covered in this memorandum consists of that obtained during the last four years from pile motion measurements and from tube bowing measurements, and particularly that from graphite mining operations during the last six months. The objective to be attained is twofold: (1) the information developed here should permit a better understanding of the need for and development of future corrective measures to be applied to the present piles, and (2) this summary will serve as a basis for further experimental work necessary to place the conclusions on a more firm foundation. This memorandum is being issued at this time, although present ideas and conclusions are in a somewhat uncertain state, in the hope that the currently most feasible preventive measure might be applied to the DR Pile before startup.