Exposure of actinide bearing solid phases to environmental conditions may result in a myriad of chemical or physical modifications including dissolution/precipitation, oxidation/reduction, and/or recrystallization/amorphization. Each of these reactions may have an impact on the fate and transport of the actinides in the envionment. To better understand such processes, a series of field lysimeter experiments have been used to monitor the changes in chemical and physical properties of a variety of U, Np, and Pu bearing solid phases including Pu(V)NH4CO3(s), Pu(IV)(C2O4)2(s), Pu(III)2(C2O4)3(s), Pu(IV)O2(s), Np(IV)O2(s) and Np(V)O2NO3(s). Formation of dissordered PuO2 type phases from reduction of Pu(V)NH4CO3 was observed under both field and laboratory conditions but accelerated under field conditions. Similarly, the oxidation of Np(IV)O2(s) under field conditions leads to formation of a much more disordered solid phase with a significantly altered morphology than the initial Np(IV)O2(s). Migration of Np and Pu from initially NpO2(s) and PuO2(s) was significantly retarded relative the to migration of oxidized sources. However, a small fraction of Np and Pu released from the source is proposed to be due to transport of colloidal species thought to be NpO2(s) and PuO2(s) type nanoparticles. The results of these experiments will be discussed in terms of evaluating the history of the sample through analysis of the microcrystalline structure and the influences of aging under various environments.

Aging of actinide solid sources during multi-year exposure to environmental conditions

255th National Meeting (2018)

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