Uranium metal by carbon reduction of oxide

Abstract

Uranium metal was prepared by reacting an oxide (UO₂ or U₃O₈) with graphite powder under vacuum conditions. U₃O₈ prepared from production grade UO₃ gave the highest uranium content per unit volume of charge compared to other uranium oxide sources.

The process consists of two separate vacuum induction heating steps. The first step involves heating a stoichiometric mixture of oxide and carbon in a graphite crucible to temperatures in the range 1550–1950°C to prepare an electrically conducting intermediate product. The final, or refining, step to obtain the metal consists of heating this intermediate product by self-induction at temperatures in the neighborhood of 2200°C in an urania crucible.

When a mixture of U₃O₈ and carbon is being heated, considerable reaction takes place at temperatures well below 1000°C and some CO₂ is evolved. About 7.2 moles of carbon per mole of U₃O₈ are required for complete reduction to metal. The carbon reduction of UO₂ yields practically no CO₂ and therefore requires a carbon to oxygen ratio of unity. The quality of the final metal is essentially the same regardless of whether UO₂ or U₃O₈ is used as the starting oxide. The total carbon, oxygen plus nitrogen content in the metal is in the range of 400 ppm with better than an 80% overall yield on a 200 g of metal scale.