Nuclear Fuel Research Fuel Cycle Development Program (Quarterly Progress Report, July 1 to September 30, 1960)

Technical Report · Thu Nov 10 19:00:00 EST 1960

DOI:https://doi.org/10.2172/4068871· OSTI ID:4068871

Work was continued on the development of a UO₂ pellet fabrication process based on low temperature sintering in an inert atmosphere. A study of the chemical and physical characteristics of several ADU oxides on band was carried out to determine the cause of poor sinterability as compared with Davison Lot 0. The latter has consistently sintered to densities exceeding 95% of theoretical in this process. The properties investigated included (1) particle size distribution, (2) surface area, (3) microscopic appearance, (4) hydrogen sinterability. and (5) chemical analysis. No clear distinguishing difference among the various oxides lots has yet been found which accounts for the observed variation in sinterability. A program aimed at improving sinterability by activation techniques was initiated and, of the methods employed, oxidation-reduction cycling was by far the most effective. After only one cycle, consisting of oxidation to U₃O₈ at 500°C and reduction to UO₂ at 525°C, all production lot oxides could be densified to at least 95% of theoretical at temperatures not exceeding 1300°C. The enhancement of sinterability is so pronounced that such densities have been achieved after sintering at as low as 1100°C for only one hour in nitrogen. High temperature hydrogen sinterability has been similarly improved. Under Task II, extensive chemical analyses of uranium carbide prepared by the methane reaction indicated that improvements are necessary in the control of heating rate and time at temperature for the carburizing step to achieve adequate carbon compositional control. It was observed that the analyses of the uranium carbide product was not affected by increasing the carburizing gas flow rate in the retort from about 1-1/2 to 16 times the amount required to achieve stoichiometry. Thus, gas flow in excess of the minimum required, based on approximately a 60% to 70% efficiency, has no effect. Using methane, it appears that the average of nitrogen, oxygen and free carbon contents are 0.43%, 0.77% and 0.25%, respectively. A preliminary study was made of the use of propane for carburizing uranium. The results indicated that the free carbon was slightly higher than that obtained with methane, but that the nitrogen and oxygen contents were significantly lower, viz., 0.06% nitrogen and 0.22% oxygen. Further work is planned, using propane as the carburizing gas. Further work on the cold pressing and 1800°C vacuum sintering of uranium carbide produced by the methane reaction indicated that the best densities that could be achieved by this method with essentially stoichiometric uranium monocarbide was 11.2 to 12.2 g/cm³. Nitrogen and oxygen appear to form an isomorphous solid solution in the uranium monocarbide structure and do not appear to enhance the sinterability. It was found that the presence of free uranium is essential and that approximately 51 a/o or more of uranium must be present in the composition in order to achieve a high sintered density. Densities approaching the theoretical were obtained when an adequate quantity of free uranium was present, either because of the composition of the product as produced from the methane-uranium reaction or when adjusted in composition by the addition of uranium in the form of uranium hydride to the powder mixture prior to cold pressing and sintering. Significant improvements were made in the skull arc melting and casting technique by utilizing a ten-turn water-cooled coil inserted beneath the crucible in the skull furnace. This provided sufficient magnetic field at 400 amperes to prevent arc deflection during melting uranium carbide at 2,500 amperes melting current. Good melting and pouring were achieved consistently, by utilizing this method. Although crack-free castings were obtained, surface quality must be further improved by optimizing the graphite mold temperature. Encouraging results were obtained by arc melting uranium oxide graphite mixtures, blended to yield, after reaction, uranium monocarbide. Pelletized charge material was reacted and melted in the arc furnace which yielded a product containing 4.71% carbon, 0.084% oxygen and 0.06% nitrogen. Work was carried out, also, on the use of pre-reacted uranium oxide graphite mixtures to form a consumable electrode. An electrode, pre-reacted by vacuum induction heating at 2000°C, was consumably arc melted successfully.

• Research Organization: Olin Mathieson Chemical Corp., Baltimore, MD (United States)
• Sponsoring Organization: US Atomic Energy Commission (AEC)
• NSA Number: NSA-15-013431
• OSTI ID: 4068871
• Report Number(s): NYO--2690
• Country of Publication: United States
• Language: English

Related Subjects

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS
AMMONIUM COMPOUNDS
CARBON
CARBURIZATION
CHEMICAL REACTIONS
COILS
COLD WORKING
COMPACTING
CONTROL
COOLING
CRUCIBLES
CURRENTS
DENSITY
DISTRIBUTION
EFFICIENCY
ELECTRIC ARCS
ELECTRODES
FABRICATION
FUELS
FURNACES
GAS FLOW
GRAIN SIZE
GRAPHITE
HEATING
HIGH TEMPERATURE
HYDROGEN
INDUCTION
INERT GASES
LATTICES
LOW TEMPERATURE
MAGNETIC FIELDS
MELTING
METALS, CERAMICS, AND OTHER MATERIALS
METHANE
MIXING
NITROGEN
OSCILLATIONS
OXIDATION
OXYGEN
PELLETS
POWDERS
PROPANE
QUALITATIVE ANALYSIS
QUANTITY RATIO
REDUCTION
SINTERING
SOLID SOLUTIONS
SURFACES
U3O8
URANATES
URANIUM
URANIUM CARBIDES
URANIUM DIOXIDE
URANIUM HYDRIDES
URANIUM OXIDES
VACUUM
W