Aqueous Actinide Speciation and Redox Behavior in the Presence of Organic Ligands, Calcium, and Elevated Temperature

The mobility of actinides is of primary concern when considering the safety of a deep geologic repository for permanently disposing of nuclear or transuranic waste. The first portion of this dissertation addresses the risk of plutonium mobility in the context of a repository environment by exploring Pu interactions with citrate—an organic ligand that could mobilize Pu through complex formation or redox transformation. The second focal point of this dissertation explores curium(III) behavior (a plutonium(III) and americium(III) analog) in the presence of citrate and calcium—a ubiquitous cation in cementitious systems and present in many host rocks in which a repository may be situated. Lastly, we discuss the speciation of neodymium(III) and praseodymium(III) (An(III) analogs) in the presence of the nuclear waste-relevant organic ligand ethylenediaminetetraacetic acid (edta). The impact of ligand concentration, pH, and elevated temperature are key focal points of this third project. The aqueous species described herein can influence the mobility of trivalent actinides and radioactive lanthanides in the context of nuclear waste disposal and spent nuclear fuel, and the behavior and thermodynamic and kinetics parameters determined in this work may be used in subsequent predictive models for repository performance assessments.

在考量用于永久处置核废料或超铀废物的深层地质处置库安全性时，锕系元素的迁移性是首要关注点。本论文的第一部分通过探究钚（Pu）与柠檬酸根的相互作用，探讨处置库环境下钚迁移的风险——柠檬酸根是一种有机配体，可通过络合物形成或氧化还原转化来迁移钚。论文的第二部分重点探究在柠檬酸根和钙存在下的锔(III)行为（锔(III)是钚(III)和镅(III)的类似物）——钙是胶凝体系中普遍存在的阳离子，且存在于处置库可能选址的许多主岩中。最后，我们讨论在与核废料相关的有机配体乙二胺四乙酸（EDTA）存在下，钕(III)和镨(III)（锕系元素(III)类似物）的形态。配体浓度、pH值和高温的影响是该第三部分研究的核心关注点。本文所述的水相物种会影响核废料处置和乏核燃料场景下三价锕系元素和放射性镧系元素的迁移性，且本研究中确定的行为及热力学、动力学参数可用于后续处置库性能评估的预测模型。