McGrady John, Kumagai Yuta, Watanabe Masayuki, Kirishima Akira, Akiyama Daisuke, Kitamura Akira, Kimuro Shingo
Nuclear Science and Engineering Center, Japan Atomic Energy Agency (JAEA) Tokai Ibaraki 319-1195 Japan
Institute of Multidisciplinary Research for Advanced Materials, Tohoku University 1-1 Katahira, 2-chome, Aoba-ku Sendai 980-8577 Japan.
RSC Adv. 2021 Aug 31;11(46):28940-28948. doi: 10.1039/d1ra05580a. eCollection 2021 Aug 23.
In the event of nuclear waste canister failure in a deep geological repository, groundwater interaction with spent fuel will lead to dissolution of uranium (U) into the environment. The rate of U dissolution is affected by bicarbonate (HCO ) concentrations in the groundwater, as well as HO produced by water radiolysis. To understand the dissolution of UO by HO in bicarbonate solution (0.1-50 mM), dissolved U concentrations were measured upon HO addition (300 μM) to UO/bicarbonate mixtures. As the HO decomposition mechanism is integral to the dissolution of UO, the kinetics and mechanism of HO decomposition at the UO surface was investigated. The dissolution of UO increased with bicarbonate concentration which was attributed to a change in the HO decomposition mechanism from catalytic at low bicarbonate (≤5 mM HCO ) to oxidative at high bicarbonate (≥10 mM HCO ). Catalytic decomposition of HO at low bicarbonate was attributed to the formation of an oxidised surface layer. Second-order rate constants for the catalytic and oxidative decomposition of HO at the UO surface were 4.24 × 10 m s and 7.66 × 10 m s respectively. A pathway to explain both the observed UO dissolution behaviour and HO decomposition as a function of bicarbonate concentration was proposed.
如果深部地质处置库中的核废料罐发生故障，地下水与乏燃料的相互作用将导致铀（U）溶解到环境中。铀的溶解速率受地下水中碳酸氢根（HCO₃⁻）浓度以及水辐射分解产生的过氧化氢（H₂O₂）的影响。为了了解在碳酸氢盐溶液（0.1 - 50 mM）中过氧化氢对二氧化铀（UO₂）的溶解作用，在向UO₂/碳酸氢盐混合物中添加过氧化氢（300 μM）后测量了溶解铀的浓度。由于过氧化氢分解机制是二氧化铀溶解过程中不可或缺的一部分，因此研究了UO₂表面过氧化氢分解的动力学和机制。二氧化铀的溶解随着碳酸氢盐浓度的增加而增加，这归因于过氧化氢分解机制从低碳酸氢盐浓度（≤5 mM HCO₃⁻）时的催化分解转变为高碳酸氢盐浓度（≥10 mM HCO₃⁻）时的氧化分解。低碳酸氢盐浓度下过氧化氢的催化分解归因于形成了一个氧化表面层。UO₂表面过氧化氢催化分解和氧化分解的二级速率常数分别为4.24×10⁻⁴ m³ s⁻¹和7.66×10⁻⁵ m³ s⁻¹。提出了一种途径来解释观察到的二氧化铀溶解行为以及过氧化氢分解随碳酸氢盐浓度变化的情况。
