Characterization of the influence of fission product doping on the anodic reactivity of uranium dioxide

Abstract

The influence of fission product doping on the structure, composition, and electrochemical reactivity of uranium dioxide has been studied using X-ray diffractometry (XRD), scanning electron microscopy (SEM/EDX), Raman spectroscopy, and X-ray photoelectron spectroscopy (XPS). Experiments were conducted on SIMFUEL specimens with simulated burn-ups (increasing doping levels) of 1.5, 3.0, and 6.0 atom%. As the dopant level increased, the lattice contracted, suggesting the dominant formation of dopant-oxygen vacancy clusters. The smaller than expected lattice contraction can be attributed to the segregation of Zr (one of eleven added dopants) to ABO3 perovskite-type phases that SEM/EDX shows also contain Ba, Ce, and possibly some U. Raman spectroscopy shows that doping leads to a loss of cubic symmetry, possibly associated with tetragonal distortions. Raman mapping confirms this loss of cubic symmetry and suggests the specimen is not uniformly doped. Electrochemical experiments show that these distortions lead to a decrease in the oxidative dissolution rate of the UO2 with increased doping density.Key words: UO2, X-ray diffraction, electrochemistry, Raman spectroscopy, nuclear fission products.

Computational study of the energetics and defect clustering tendencies for Y- and La-doped UO2

“…The current results thus support the suggestion from Ref. [14] that the effect of increased burnup (leading to higher concentrations of soluble trivalent fission products) on oxidative corrosion rates in spent nuclear fuel can be attributed to lower oxygen mobility due to defect association.…”

“…Specifically, recent studies have attributed rare earth (i.e. trivalent) fission product dopant-oxygen vacancy clusters to the decreased rate of oxidative dissolution with increasing burnup in spent fuel [14]. The defect clusters are believed to reduce the concentration of mobile oxygen vacancies which facilitate oxidation and eventual dissolution of the fuel, in a manner similar to that by which rare earth doping impedes air oxidation of the cubic fluorite structure to orthorhombic U 3 O 8 [15][16][17][18].…”

The effect of Y2O3 on the dynamics of oxidative dissolution of UO2

“…X-ray photoelectron spectroscopic data on SIMFUEL suggest an increase in U(V) at the expense of U(IV) with increasing trivalent doping [21]. Furthermore, at doping levels up to 3 at.%, the electrical conductivity increases with increasing rare earth content.…”

“…Spent nuclear fuel [16][17][18][19], SIMFUEL [20,21], UO 2 pellets with palladium (as a model substance for metallic e-phase particles) [2,3], a-doped [4,19] and pure UO 2 [2,3,22] have been studied in dissolution and electrochemical experiments. From experiments under H 2 atmosphere, it has been shown that spent nuclear fuel, a-and Pd-doped UO 2 show lower U(VI) dissolution [2][3][4]19,23,24], and that the corrosion potential of SIMFUEL is significantly reduced [20].…”

Factors influencing the rate of radiation-induced dissolution of spent nuclear fuel

“…for U(IV) contributes to increased electrical conductivity [25]. However, recent results, presented by He et al [26], indicate that the structural changes occurring from the incorporation of fission products decrease the UO 2 dissolution rate. Noble metal fission products present in the spent nuclear fuel are known to congregate to nanometersized particles (e-particles) [27].…”