Reactions During the Processing of U3O8—Al Cermet Fuels

The cermet fuel (U₃O₈ dispersed in Al) being considered for use in the Savannah River Site Reactors is thermodynamically unstable because of the potential for an exothermic metallothermic reduction reaction. This paper describes work performed to quantify the extent of reaction during powder metallurgy (P/M) processing of the U₃O₈—Al cermet fuel, and to determine the effect of partial reduction to U₄O₉ on the metallothermic reduction reaction. During the fabrication of the U₃O₈—Al cermet fuel by the P/M technique, a significant portion of the U₃O₈ is reduced to U₄O₉. The reaction between U₄O₉ and Al is also exothermic; however, the maximum heat released by the reaction is substantially less than that released for the U₃O₈—Al reaction, approximately 335 J (80 cal) per gram of oxide reacted compared to 940 J (225 cal). Metallothermic reduction reactions for U₃O₈/U₄O₉/Al mixtures do not occur at the normal reactor operating temperature, ∼ 370 K (∼ 100°C) or at temperatures below the melting point of aluminum, 930 K (660°C).