Steam Oxidation Kinetics and Oxygen Diffusion in UOz at High Temperatures

Abstract

APPENDIX Equation (4) must be changed to accommodate Hillert's analysis. Instead of normalizing D with respect to D, 9/86 (the critical grain size) is used; and a new parameter u = 8/9(D/D) is defined as the relative grain size. Making these alterations to Eq. (4), P U " ,

FASTGRASS: A mechanistic model for the prediction of Xe, I, Cs, Te, Ba, and Sr release from nuclear fuel under normal and severe-accident conditions

“…However, the successful interpretation of the HI 1-4 test series (Figs. [28][29][30][31][32][33] Emd of the trends of the PBF test fission-gas-retease-rate data (e.g.. Fig. 34), and the reasonable agreement between the predicted integral releases Table 12), support the hypothesis set forth in this report.…”

Novel insights in the study of water penetration into polycrystalline UO2 by secondary ion mass spectrometry

“…For oxygen, several attempts to estimate the coefficients for both chemical diffusion and self-diffusion (i.e., diffusion in presence or absence of a concentration gradient, respectively) have been made, mostly with indirect approaches, e.g., measurements of electrical conductivity after reduction of oxidised samples [4], thermogravimetry following steam oxidation [5], or gas-solid isotopic exchange coupled with sample sectioning [6]. As well as the problem of the inconsistency in the reported values, the applicability of these data to the prediction of oxidation kinetics in final disposal scenarios is further constrained by the fact that all experiments have been performed in temperature ranges between 600 and 1800 K, whereas in a final repository the temperature can be expected to be in the range 290-370 K [7].…”

Thermodynamic Evaluation of Equilibrium Oxygen Composition of UO2-Mo Nuclear Fuel Pellet Under High Temperature Steam

“…While several experimental datasets on the equilibrium O/U ratio exist for steam oxidation of UO 2 pellets above 1273 K, few data are available for steam oxidation below 1273 K owing to the slow oxidation of UO 2 at low temperatures and the challenges related to controlling the steam-hydrogen composition. Kuhlman (Kuhlman, 1948) found no significant weight change in UO 2 after exposure to oxygen-free steam at 873 K for 6 h. Bittel et al (Bittel et al, 1969) reported that the final average O/U ratio of pellets annealed at 1158 K for 290 min in steam was 2.039, which is far below the calculated value. On the contrary, Dumitrescu et al (Dumitrescu et al, 2015) reported that UO 2 pellets pulverize to U 3 O 8 after annealing in 873 K steam for 10 h. Recently, Jung et al (Jung et al, 2020) have also shown the formation of U 3 O 8 particles on the UO 2 pellet annealed for 1,000 min in steam maintained at a temperature range of 673-733 K. This discrepancy between the experimental results appears to be due to the very slow oxidation reaction in low-temperature steam and the strong influence of the oxygen and hydrogen contents on the equilibrium oxygen potential of the steam.…”

“…Therefore, oxygen diffusion inside the UO 2 matrix is an important parameter that needs to be considered to better understand the influence of Mo on oxidation behavior. Considering the diffusion distance for oxygen to reach the Mo surface via the dense UO 2 and the low lattice diffusion rate owing to the low pellet temperature of less than 1093 K (Bittel et al, 1969), relatively long incubation time seems to be required for the Mo inside the pellet fragment to meet with oxygen and start the oxidation reaction. The MoO 2 layer is known to adhere to the Mo surface and act as an anti-corrosion layer, so the formation of a MoO 2 surface layer is expected to further delay the oxidation rate.…”