Dissolution behavior of irradiated fuels in nitric acid and characteristics of insoluble residue

The dissolution behavior of spent fuel with high burn-up was investigated, and the insoluble residues were filtered and analyzed. The dissolution behavior was investigated by tracing the evolution of concentration of U, Pu, Kr and nitric acid. The results showed that UO₂ pellets in the irradiated fuel rods sliced to 20-30 mm in length were completely dissolved within 2 h in 6.5 mol/L nitric acid at about 95 °C. The amount and composition of insoluble residues formed in the course of dissolution of spent fuel with the burn-up 40,433 MWd/tU were examined. The weight of the insoluble precipitates was about 2.185 g/kgU. The major elements determining the composition of the precipitates were platinum group metals (Ru, Rh, Pd), Mo and Zr. Depending on the dissolution conditions, the U content was 2.4%, and the Pu content was 0.24% compared to the weight of insoluble residue. The micro-graphs of the residue were observed by SEM. (author)