Determination of dissolution rates of spent fuel in carbonate solutions under different redox conditions with a flow-through experiment

Dissolution rates of spent UO2 fuel have been investigated using flow-throu gh experiments under oxidizing, anoxic and reducing conditions. For oxidizi ng conditions, approximately congruent dissolution rates were obtained in t he pH range 3-9.3 for U, Np, Ba, Tc, Cs, Sr and Rb. For these elements, ste ady-state conditions were obtained in the flow rate range 0.02-0.3 ml min(- 1). The dissolution rates were about 3 mg d(-1) m(-2) for pH > 6. For pH < 6, dissolution rates were strongly increasing for decreasing pH. Incongruen t dissolution was found for Zr, Mo, Ru, Rh, Pd, Am and the lanthanides. The dissolution rates with H-2(g) saturated solutions dropped by up to four or ders of magnitude as compared to oxidizing conditions. Because of the very low concentrations, only U, Pu, Am, Mo, Te and Cs could be measured. For an oxic conditions, both the redox potential and dissolution rates increased a pproaching the same values as under oxidizing conditions. (C) 2001 Elsevier Science B.V. All rights reserved.