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

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Dissolution behavior of irradiated fuels in nitric acid and characteristics of insoluble residue F. Liu1   · T. H. Yan1 · B. Li1 · G. A. Ye1 Received: 14 April 2020 / Published online: 14 September 2020 © Akadémiai Kiadó, Budapest, Hungary 2020

Abstract 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 U ­ O2 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. Keywords  Spent fuel · Dissolution · Insoluble residue · Platinum group metals

Introduction Dissolution behaviors of ­UO2 pellets were investigated about the mechanism and dynamics by many researchers [1–11], but an elaborate research of real spent fuel was rarely reported. There are many differences between the U ­ O2 pellets and real spent fuel can not be predicted which will influence the dissolution behavior dramatically, such as the random split in shearing, the change of components caused by irradiation. So integrated dissolution data of spent fuel dissolution is very useful for the equipment and technology design. Dissolution of irradiated fuel prior to extraction reprocessing is always accompanied by information of insoluble residues. The formation of the residues complicates the solution clarification prior to extraction and in the first extraction cycle. High specific activity of the insoluble precipitates and the presence of fissile materials in them give rise to certain problems in disposal. It is quite obvious that the problems of insoluble residues will be more serious wile reprocessing fast reactor spent fuel with more burn-up. The interest shown * F. Liu [email protected] 1



Radiochemistry, China Institute of Atomic Energy, Yong‑chi Road Fang‑shan District, Beijing 102413, China

by the researchers in insoluble residues is determined by two following reasons. In the first place the amount and the constitution of residues determine the choice of the equipment and operational mode at the stage of solution clarification. The fission products insoluble residue thus formed sometimes causes problems in the clarification and/or extraction process in the nuclear reprocessing plants [12–14]. For the smooth operation of the dissolver and the pulsed filter, it was important to estimate the insoluble particles and follow up their behav