Affects of Hydrogen Peroxide on the Stability of Becquerelite
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0893-JJ05-19.1
Affects of Hydrogen Peroxide on the Stability of Becquerelite Karrie-Ann Kubatko1, Daniel Unruh1, Peter C. Burns1 1
Department of Civil Engineering and Geological Sciences, University of Notre Dame, Notre Dame IN 46556 ABSTRACT While the majority of studies of alteration of UO2 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[(UO2)6O4(OH)6](H2O)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. INTRODUCTION Uranyl oxide hydrates, such as schoepite, dehydrated schoepite, becquerelite, and compreignacite, are significant constituents of the oxidized portions of uranium deposits [1]. These minerals can occur in soils contaminated by actinides [2] and are likely to be important in the oxidative alteration of nuclear waste in a geological repository [3-8]. Laboratory experiments have demonstrated that schoepite and meta-schoepite rapidly alter to becquerelite in Ca-bearing solutions [9-11]. Becquerelite is expected to be the most stable phase in the UO3(H2O)2-CaOH2O system under normal geochemical conditions. While the majority of studies of oxidative alteration of UO2 and commercial spent nuclear fuel under simulated repository conditions have emphasized the importance of uranyl oxide hydrates [4,8], the potential influence of peroxide on repository performance has been largely overlooked. Recently, McNamara et al. [12] found extensive formation of the peroxide mineral studtite, (UO2)(O2)(H2O)4, on the surface of spent nuclear fuel reacted at 25 ºC with deionized water for 1.5 years under ambient conditions. Sattonnay et al. [13] observed the formation of metastudtite, (UO2)(O2)(H2O)2, on the surface of UO2 irradiated with an α-particle beam, and concluded the peroxide was provided by alpha-radiolysis of water. Burakov et al. [14] reported that uranyl peroxides formed on the surface of fuel-containing material following the Chernobyl Nuclear Plant accident. Thus, there is considerable evidence that uranyl peroxides will be important alteration phases of nuclear waste, and that these minerals may impact the long-term performance of a geologic repository.
0893-JJ05-19.2
The long-term alpha radiation associated with spent nuclea
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