The anodic dissolution of SIMFUEL (UO2) in slightly alkaline sodium carbonate/bicarbonate solutions

2014

J. Electrochem. Soc.

The anodic behavior of simulated nuclear fuel (SIMFUEL) in solutions containing H 2 O 2 and HCO 3 − /CO 3 2− has been studied electrochemically and using surface analytical techniques, in particular X-ray photoelectron spectroscopy. Two anodic reactions are possible, the oxidative dissolution of UO 2 and H 2 O 2 oxidation. The rates of both reactions are controlled by the chemical release of U VI surface species, and can both be increased by the addition of HCO 3 − /CO 3 2−. Under anodic conditions the dominant reaction is H 2 O 2 oxidation, although UO 2 dissolution may also be accelerated by the formation of a uranyl peroxocarbonate complex. Similarly, under open circuit (corrosion) conditions both UO 2 corrosion and H 2 O 2 decomposition are also controlled by the rate of release of U VI surface species which blocks access of H 2 O 2 to the underlying conductive U IV 1-2x U V 2x O 2+x surface. Presently, the balance between these two reactions is not known.

Section: Resultssupporting

confidence: 72%

mentioning

confidence: 94%

The Anodic Reactions on Simulated Spent Fuel (SIMFUEL) in H₂O₂Solutions: Effect of Carbonate/Bicarbonate

Goldik

2014

J. Electrochem. Soc.

“…A similar set of data previously obtained for 1.5 at% SIMFUEL in the presence of carbonate is included. 30 In the presence of carbonate, the anodic currents for Gd-UO 2 are considerably lower than those recorded on SIMFUEL. The Tafel slopes at lower potentials (≤0.3 V) are in the range 120 to 150 mV indicating the mechanism of anodic oxidation/dissolution does not change, only the overall reactivity of the matrix.…”

Section: Resultsmentioning

confidence: 90%

“…The disappearance of this reduction peak on SIMFUEL was attributed to the enhanced dissolution of U VI (as U VI O 2 (CO 3 ) x (2−2x)+ ) on the forward scan. 30 -1. No carbonate The presence of this reduction peak in Fig.…”

Section: Resultsmentioning

confidence: 99%

The Electrochemical Reactivity of 6.0 wt% Gd-Doped UO₂in Aqueous Carbonate/Bicarbonate Solutions

Razdan

2014

J. Electrochem. Soc.

The effect of gadolinium doping on the anodic reactivity of UO 2 in aqueous carbonate solutions has been investigated voltammetrically, potentiostatically, by Raman spectroscopy and X-ray photoelectron spectroscopy. The mechanism of oxidation/dissolution is the same as on undoped UO 2 and lightly doped SIMFUEL (doped UO 2) but the reactivity is significantly reduced. This is attributed to the formation of Gd III-Oxygen vacancy (O V) clusters which limits the availability of these vacancies required to accommodate excess O 2− during matrix oxidation to U IV 1−2x U V 2x O 2+x. The subsequent reaction of this oxidized surface layer to U VI O 3 .yH 2 O/U VI O 2 (CO 3) x (2−2x)+ is also suppressed by Gd-doping. The overall oxidation/alteration (dissolution) reaction appears to be kinetically controlled by the creation of U VI surface species prior to dissolution.

“…Since, the anticipated ground water pH will be between 6 and 9 (when U VI is at a solubility minimum), corrosion product lms would be expected to form and to inuence the corrosion rate. [7][8][9] In Canadian groundwater, the key constituent likely to inuence fuel dissolution is HCO 3 À /CO 3 2À (10 À4 to 10 À3 mol L À1 ), 10 which increases the solubility of U VI O 2 2+ by complexation 11 and buffers the pH. In the presence of HCO ] $ 10 À3 mol L À1 , both electrochemical 6,12,13 and chemical studies [14][15][16] show not only is U VI O 3 $yH 2 O formation prevented but the formation of the underlying U IV 1À2x U V 2x O 2+x layer is retarded 14,15 and oxidative dissolution becomes strongly promoted.…”

Section: Introductionmentioning

confidence: 99%

The influence of hydrogen peroxide and hydrogen on the corrosion of simulated spent nuclear fuel

Razdan

2015

Faraday Discuss.

The synergistic influence between H(2)O(2) and H(2) on the corrosion of SIMFUEL (simulated spent nuclear fuel) has been studied in solutions with and without added HCO(3)(-)/CO(3)(2-). The response of the surface to increasing concentrations of added H(2)O(2) was monitored by measuring the corrosion potential in either Ar or Ar/H(2)-purged solutions. Using X-ray photoelectron spectroscopy it was shown that the extent of surface oxidation (U(V) + U(VI) content) was directly related to the corrosion potential. Variations in corrosion potential with time, redox conditions, HCO(3)(-)/CO(3)(2-) concentration, and convective conditions showed that surface oxidation induced by H(2)O(2) could be reversed by reaction with H(2), the latter reaction occurring dominantly on the noble metal particles in the SIMFUEL. For sufficiently large H(2)O(2) concentrations, the influence of H(2) was overwhelmed and irreversible oxidation of the surface to U(VI) occurred. Subsequently, corrosion was controlled by the chemical dissolution rate of this U(VI) layer.