Analysis of the conditions required for producing highly purified carbide fuel by reducing oxides with carbon, and study of the behavior of oxygen and carbon impurities in the presence of fission products

Conclusions

• 1. We have made a thermodynamic analysis of the U−C−O system by the Pourbaix method, and on the basis of the resultant diagram have determined the minimum temperatures required to produce uranium carbides and metallic uranium from uranium dioxide.

• 2. We have analyzed the various possible mechanisms for the mass transfer of the reagents in the production of carbides from oxides. The main contribution to mass transfer in the UO₂−C system at temperatures up to 1800°C arises from the diffusion of the components through the layer of reaction products. The contribution of uranium dioxide evaporation to the mass-transfer mechanism becomes appreciable at temperatures above 2000°C.

• 3. We have studied the phase composition of hyperstoichiometrical uranium carbide samples containing fission-element simulators (Zr, Mo, Y, Pd, Ce, La, Nd, Pr, Sm, Ba, Sr, Ru) in quantities corresponding to 10% burn-up.

• 4. On the basis of the chemical reactions between the fragments under consideration we have estimated the changes taking place in the amounts of oxygen (dissolved in the monocarbide) and carbon (in the form of the dicarbide) during irradiation.

• 5. The calculated solid swelling of the carbide fuel was 0.4% swelling for 1% burn-up.