Experience of Graphite Crucibles during the Pyrometallurgical Processing of Uranium

Conference · Mon May 01 04:00:00 EDT 2017

OSTI ID:1411593

Westphal, B. R.; Price, J. C.; Marsden, K. C.; Patterson, M. N.

Throughout the history of processing molten uranium, various materials have been investigated and utilized for the containment of uranium at temperatures greater than 1135oC. Of these, graphite is the most prevalent material due to its ease of fabrication, expense, compatibility with induction systems, and robust characteristics. Graphite in contact with molten uranium will react to form uranium carbide species, thus a coating or mold is needed to prevent reaction of the uranium and the subsequent adherence of the solidified metal. During the pyrometallurgical treatment of used nuclear fuel for uranium recovery at the Idaho National Laboratory, two operational steps utilize graphite crucibles for containment of molten uranium. The cathode processor step separates molten salt from the uranium while the casting step blends uranium for de-enrichment and allows molten sampling of the uranium. Zirconia and yttria based materials on graphite are employed for the cathode processor and casting steps, respectively. For the cathode processor, zirconia coatings were applied initially to graphite crucibles but more recently a zirconia castable material has been molded into the graphite. Although not perfect, zirconia has been found to be compatible with both molten salt and uranium whereas yttria will react with molten salts if carried over to the casting operation. With development, the uranium losses associated with the reaction of uranium and zirconia have been reduced to approximately 1 wt. % of the total uranium throughput. Losses from yttria coating reaction during casting are typically an order of magnitude less than zirconia. The real benefit of these materials is their cost effectiveness given the multiple number of times the graphite crucibles can be reused and/or recoated. Nearly thirty uses have been recorded for graphite crucibles at both the cathode processor and casting operations. The amount of impurity pickup to the uranium products from the graphite crucibles has been minimal (<300 ppm) in terms of carbon, oxygen, zirconium, and yttrium content. Based on the promising results with the zirconia castable at the cathode processor, zirconia material has been cast into a graphite casting crucible and will be tested for comparison in the absence of salt.

• Research Organization: Idaho National Laboratory, Idaho Falls, ID (United States)
• Sponsoring Organization: USDOE Office of Nuclear Energy (NE)
• DOE Contract Number: AC07-05ID14517
• OSTI ID: 1411593
• Report Number(s): INL/CON-17-41015
• Country of Publication: United States
• Language: English

Related Subjects

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS
pyroprocessing
uranium melting
used nuclear fuel