Affects of Hydrogen Peroxide on the Stability of Becquerelite

摘要

While the majority of studies of alteration of UO_2 and commercial spent nuclear fuel under simulated geological repository conditions have emphasized the importance of uranyl oxide hydrates and uranyl silicates, the potential influence of peroxide on repository performance has been largely overlooked. There is considerable evidence that uranyl peroxides may be important alteration phases of nuclear waste, and that these phases may impact the long-term performance of a geologic repository. Here we report the thermodynamics and kinetics of becquerelite, Ca[(UO_2)_6O_4(OH)_6](H_2O)_8, in the presence of solutions containing hydrogen peroxide. Thermodynamic calculations reveal that in solutions containing 3.5 x 10~(-6) M hydrogen peroxide, studtite formation is thermodynamically favorable over becquerelite at 298 K. To access the kinetics of this reaction, batch experiments were conducted by the reaction of becquerelite and solutions containing hydrogen peroxide. In the presence of 0.1 M hydrogen peroxide, becquerelite altered to studtite within eight hours.