Nuclear Fuel Research, Fuel Cycle Development Program: Quarterly Progress Report for April 1 to June 30, 1960

Technical Report · Tue Jul 26 20:00:00 EDT 1960

DOI:https://doi.org/10.2172/4127841· OSTI ID:4127841

Kalish, Herbert S. ^[1]; Holden, Robert B. ^[1]

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1. Olin Mathieson Chemical Corporation, New Haven, CT (United States). Metallurgical Laboratories

Work was continued on a UO₂ pellet fabrication process based on inert atmosphere sintering at 1250 to 1300 deg C. The development of a two-stage sintering method, consisting of a nitrogen soak to densify the nonstoichiometric oxide followed by a hydrogen soak to remove excess oxygen, was iritiated. With Davison ADU oxide Lot O, uniform stoichiometric pellets were obtained having a density of 98% of theoretical after 3 hr in nitrogen and 1 hr in hydrogen at 1250 deg C. Further progress on this sintering technique, however, was hampered by the fact that the other ADU oxide lots employed in the investigation exhibited relatively poor sinterability. Among these was a small batch ordered for a pilot run prior to the procurement of enriched oxide which was to he prepared under similar conditions for the irradiation testing program. A study of the physical and chemical characteristics of the ADU oxide lots on hand was then begun with the objective of establishing a specification based on the correlation of low-temperature sinterability in nitrogen with pertinent properties. With the aim of producing reactive UO₂ sinterable to high densities, small quantities of nonstoichiometric ADU oxide were prepared. Compacts fabricated from this material were sintered at 1300 deg C to densities as high as 10.3 gr/cc by the two-stage method. A cost study was prepared comparing the low-temperature nitrogen sintering process with a conventional high-temperature hydrogen sintering process. Based on producing UO₂ pellets of the size used in the Yankee Reactor, the low-temperature nitrogen sintering process is estimated to permit cost savings of 025 per pellet. Uranium monocarbide was made in a vertical retort in the following manner. Cleaned and pickled bulk uranium was reacted at 3 psig pressure with deoxidized and dried hydrogen at 250 deg C in a closed system. The retort temperature was then increased to between 750 and 800 deg C and the uranium powder carburized in a purified hydrogen-methane mixture. Variables affecting the carbon content were reaction time and temperature and the amount of carburizing gas that flowed through the retort. The carbide powders were processed under argon to avoid contamination and burning in air. After compressing at 35 tons per sq in. pressure and vacuum sintering for 1/2 hr at 1700 deg C, the densities varied from 11.30 to 11.71 g/cm³. Further work is in progress to determine the effect of sintering temperatures between 1700 deg C and the melting point; the addition of uranium, uranium nitride, and uranium oxide; and the addition of selected binding elements, such as nobium and zirconium, on the sintered density of stoichiometric methane produced carbide. The skull furnace was operated systematically to the capacity of the rectifiers to determine design weaknesses and the limitation of the furnace. The preferred charge material was preformed uranium carbide made either by melting uranium with graphite in a button furnace or by reacting uranium powder with graphite in the solid state to form a pellet. It was found that mold preheat minimized surface imperfections. Castings 5/8 in. in diameter by 6 in. long were made in the skull furnace. (For preceding period see NYO-2687.)

• Research Organization: Olin Mathieson Chemical Corporation, New Haven, CT (United States). Metallurgical Laboratories
• Sponsoring Organization: US Atomic Energy Commission (AEC)
• NSA Number: NSA-15-000529
• OSTI ID: 4127841
• Report Number(s): NYO--2689
• Country of Publication: United States
• Language: English

Related Subjects

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS
AIR
ARGON
BINDERS
CARBIDES
CARBON
CARBURIZATION
COMBUSTION
COMPACTS
DENSITY
ECONOMICS
FABRICATION
GRAPHITE
HIGH TEMPERATURE
HYDROGEN
MELTING
METALS, CERAMICS, AND OTHER MATERIALS
METHANE
NIOBIUM
NITRIDES
NITROGEN
OXIDES
OXYGEN
PELLETS
POWDERS
PRESSURE
PRODUCTION
SINTERING
TEMPERATURE
URANIUM
URANIUM COMPOUNDS
URANIUM DIOXIDE
VACUUM
ZIRCONIUM