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Mechanically blended powder of UO,, PuO, and graphite and its compact were heated in a vacuum to have some informations on the formation of mixed carbide (U,Pu)C. It was experimentally confirmed that PuO, was reduced to sesquicarbide without forming a solid solution with UO, in the reduction process. Larger quantity of sesquicarbide was formed in the compacted sample than in the powder one in the intermediate products. Compacts of UO,, PuO, and graphite were also heated a t 1,665-1,920K in He, in order to investigate the effects of reduction temperature, He flow rate and blending time on the rate constant of reduction. The reaction proceeded from the surface toward the center of the compact. I t was inferred that the rate-determining step was the reaction at the interfacial boundary between the reacted layer and the unreacted zone. The activation energy for the reduction was determined to be 375k20 kJ/mol. T h e Pu loss due to vaporization could be sufficiently suppressed, when compacted samples were reduced in He.

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