The kinetics and mechanism of H₂O₂ decomposition at the U₃O₈ surface in bicarbonate solution

Abstract

A transition from catalytic to oxidative H2O2 decomposition on U3O8 was observed with NaHCO3 with significant implications for uranium dissolution.

UO2 dissolution in bicarbonate solution with H2O2: the effect of temperature

“…The calculated values of k were in the range 0.5 to 63 × 10 −3 s −1 m −2 . A previous study by the authors 12 investigating U dissolution from U 3 O 8 in bicarbonate solution at 25 °C showed measured k values between 0.7 and 2.7 × 10 −4 s −1 m −2 , indicating that H 2 O 2 decomposition is slower on more oxidised forms of U. This effect is likely to be due to the abundance of U IV in UO 2 relative to U 3 O 8 facilitating the oxidative decomposition of H 2 O 2 at the surface via eqn (4) and (5 ).…”

“…The structure of the UO 2 powder was confirmed by XRD according to the procedure previously described in ref. 12 . An average crystallite size of 62 nm was obtained, with a cubic lattice constant of 5.46 Å which is consistent with published data for UO 2 .…”

“…Due to the importance of understanding U dissolution for the development of predictive models for radionuclide release, previous studies have investigated the dissolution of U under simulated groundwater conditions. Such studies on the oxidative dissolution of U include the effects of: the form of U, 11,12 the radiolytic oxidant, 3,[13][14][15][16][17] groundwater bicarbonate concentrations, [18][19][20] and redox conditions. 5,[21][22][23] Radionuclide release into the local environment via groundwater requires damage to the storage canister in order for groundwater to contact the spent fuel.…”