The oxidative dissolution mechanism of uranium dioxide.: I.: The effect of temperature in hydrogen carbonate medium

被引:117
作者
De Pablo, J [1 ]
Casas, I [1 ]
Giménez, J [1 ]
Molera, M [1 ]
Rovira, M [1 ]
Duro, L [1 ]
Bruno, J [1 ]
机构
[1] Univ Politecn Cataluna, ETSEIB, Dept Chem Engn, E-08028 Barcelona, Spain
关键词
D O I
10.1016/S0016-7037(99)00237-9
中图分类号
P3 [地球物理学]; P59 [地球化学];
学科分类号
0708 ; 070902 ;
摘要
The oxidative dissolution of uranium (IV) dioxide has been experimentally investigated as a function of hydrogen carbonate concentration at 4 different temperatures (10, 25, 45, and 60 degrees C) by using a continuous thin-layer flow-through reactor. The experimental results have been interpreted as evidence for a bicarbonate-promoted oxidative dissolution mechanism which can be differentiated in to 3 steps: 1) initial oxidation of I:he uranium dioxide solid surface; 2) binding of HCO3- at the U(VI) sites of the oxidized layer; and 3) detachment of the U(VI)-carbonato surface complex. From this mechanism a general rate equation has been derived: r= k(1)k(2){>UO2}(tot)[O-2][HCO3-] divided by k(-1) + k(2)[HCO3-] + k(1)[O-2] Which allows to rationalization of some of the discrepancies found in the literature concerning the dependence of the dissolution rate of uranium dioxide on the hydrogen carbonate concentration. The application of this bicarbonate-promoted oxidative dissolution mechanism allows us to predict unirradiated UO2 and spent nuclear fuel dissolution rates which are in satisfactory agreement with rates determined experimentally. Some differences observed in spent fuel dissolution rates have been attributed to radiolysis effects. Copyright (C) 1999 Elsevier Science Ltd.
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页码:3097 / 3103
页数:7
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