External Gelation Conditions in Fabrication of Nitride Fuel for Transmutation of Minor Actinides

Toward the establishment of fabrication technology of nitride fuel for the transmutation of minor actinides, optimal external gelation condition was investigated by using dysprosium nitrate as surrogate for trivalent minor actinides nitrate.The external gelation tests were performed under the various viscosity and pressure conditions of solution as parameters to obtain the spherical gel particle less than 600 m in diameter.Smaller gel particles with higher sphericity were achieved at pressure above 300 kPa under 36 mPas condition and above 490 kPa under 54 mPas condition.The results indicates that higher viscosity required higher optimal pressure, and the range of optimal viscosity and pressure conditions was experimentally determined.For the carbothermic nitridation, carbon was added into the gel particles at the optimal condition, and it was observed that excessive carbon addition led to the formation of cracks on the particle surface and adhesion of fine powders including carbon.From these results, it was confirmed that gel particles with required specifications could be prepared by adding approximately 1.0 wt% polyvinyl alcohol to the drop solution, adjusting the viscosity of about 30 to 35 mPas, and maintaining a carbon to dysprosium atomic ratio to approximately 1.75, and a droplet formation pressure of 300 kPa.