Olsson Daniel, Aydogan Hazal, Jonsson Mats
Department of Chemistry, KTH Royal Institute of Technology Stockholm SE-100 44 Sweden
RSC Adv. 2024 May 20;14(23):16248-16254. doi: 10.1039/d4ra02281e. eCollection 2024 May 15.
HO produced from water radiolysis is expected to play a significant role in radiation induced oxidative dissolution of spent nuclear fuel under the anoxic conditions of a deep geological repository if the safety-barriers fail and ground water reaches the fuel. It was recently found that the coordination chemistry between U(vi), HCO and HO can significantly suppress HO induced dissolution of UO in 10 mM bicarbonate. This was attributed to the much lower reactivity of the U(vi)O-coordinated O as compared to free HO. We have extended the study to lower bicarbonate concentrations and explored the impact of ionic strength to elucidate the rationale for the low reactivity of complexed HO. The experimental results clearly show that dissolution of U(vi) becomes suppressed at [HCO] < 10 mM. Furthermore, we found that the reactivity of the peroxide in solutions containing U(vi) becomes increasingly more suppressed at lower carbonate concentration. The suppression is not influenced by the ionic strength, which implies that the low reactivity of O in ternary uranyl-peroxo-carbonato complexes is not caused by electrostatic repulsion between the negatively charged complex and the negatively charged UO-surface as we previously hypothesized. Instead, the suppressed reactivity is suggested to be attributed to inherently higher stability of the peroxide functionality as a ligand to UO compared to as free HO.
如果安全屏障失效且地下水接触到乏核燃料，那么在深部地质贮存库的缺氧条件下，由水辐射分解产生的羟基自由基（HO）预计会在辐射诱导的乏核燃料氧化溶解过程中发挥重要作用。最近发现，在10 mM碳酸氢盐溶液中，U(vi)、HCO₃⁻和HO之间的配位化学能够显著抑制HO诱导的UO₂溶解。这归因于与游离HO相比，U(vi)O₂配位的O的反应活性要低得多。我们将研究扩展到更低的碳酸氢盐浓度，并探讨了离子强度的影响，以阐明络合HO反应活性低的原因。实验结果清楚地表明，当[HCO₃⁻]<10 mM时，U(vi)的溶解受到抑制。此外，我们发现，在较低的碳酸盐浓度下，含U(vi)溶液中过氧化物的反应活性受到的抑制作用越来越大。这种抑制不受离子强度的影响，这意味着三元铀酰-过氧-碳酸根络合物中O₂⁻的低反应活性并非如我们之前所假设的那样，是由带负电荷的络合物与带负电荷的UO₂表面之间的静电排斥引起的。相反，反应活性受到抑制被认为是由于过氧化物官能团作为UO₂配体时，其固有稳定性高于作为游离HO时的稳定性。
