Dissolution kinetics and rate-controlling mechanism of sintered uranium nitride pellets in nitric acid

Dissolution kinetics and rate-controlling mechanism of sintered uranium nitride pellets in nitric acid
Journal article, 2026

Uranium nitride (UN) is a promising advanced nuclear fuel material because of its high thermal conductivity and high

melting point. Efficient reprocessing of UN is essential for minimizing uranium consumption and reducing the volume and

radiotoxicity of nuclear waste. Dissolution is a key step in the reprocessing process. This work investigates the dissolution

kinetics of sintered UN pellets in nitric acid. UN powder was synthesized from UO2 powder by carbothermic nitridation and

characterized by X-ray diffraction (XRD). Pellets with densities of 90–92.5% of the theoretical density were produced by

spark plasma sintering (SPS) at 1923 K and 75 MPa. Dissolution experiments were conducted in 4, 6, and 8 M nitric acid

at 323, 343, and 363 K. A dissolution extent of 100% was achieved under several of the investigated conditions. Increasing

the nitric acid concentration from 4 to 8 M and the temperature from 323 to 363 K resulted in an increased dissolution rate.

Kinetic analysis using the shrinking-core model showed that surface chemical reaction control described the dissolution

behavior better than diffusional transport. The apparent activation energies obtained from Arrhenius plots ranged from 22.9

to 35.3 kJ/mol, further indicating that the dissolution process is predominantly controlled by a surface chemical reaction.