Cho Sangki, Kim Hee-Kyung, Kim Tae-Hyeong, Cha Wansik, Cho Hye-Ryun
Nuclear Chemistry Research Team, Korea Atomic Energy Research Institute, Daejeon 34057, Republic of Korea.
Department of Radiochemistry and Nuclear Nonproliferation, University of Science and Technology (UST), Daejeon 34113, Republic of Korea.
Inorg Chem. 2022 Aug 15;61(32):12643-12651. doi: 10.1021/acs.inorgchem.2c01590. Epub 2022 Aug 3.
The temperature-dependent reaction properties of actinide elements are of particular interest in the safety assessment of high-level radioactive waste (HLRW) disposal systems. In this study, the hydrolysis of Pu(III) and the solubility of Pu(OH)(am) were investigated at various temperatures (10-40 °C) in 0.1 M NaClO. A strong reducing condition for maintaining the oxidation state of Pu(III) while slowly increasing the pH of the solution was realized by electrolysis. The formation constants of the first hydrolysis species, log β, and the solubility products of Pu(OH)(am), log , at 10, 17, and 40 °C were experimentally determined using spectrophotometry, laser-induced breakdown detection, and radiometry. The enthalpy and entropy changes for these reactions were estimated using the van't Hoff equation. The first hydrolysis of Pu(III) is endothermic (Δ = 34.10 ± 4.48 kJ mol), and the dissolution of Pu(OH)(am) is exothermic (Δ = -294.29 ± 23.05 kJ mol) with negative entropy changes. These thermodynamic data will contribute to improving the reliability of the safety assessment of HLRW disposal facilities and understanding the geochemical behavior of Pu under reducing or anoxic aqueous conditions at elevated temperatures.
锕系元素的温度依赖性反应特性在高放废物（HLRW）处置系统的安全评估中尤为重要。在本研究中，研究了在0.1 M NaClO中不同温度（10 - 40°C）下Pu(III)的水解以及Pu(OH)(am)的溶解度。通过电解实现了在维持Pu(III)氧化态的同时缓慢提高溶液pH值的强还原条件。使用分光光度法、激光诱导击穿检测和放射测量法，实验测定了10、17和40°C下第一个水解物种的形成常数log β以及Pu(OH)(am)的溶度积log 。利用范特霍夫方程估算了这些反应的焓变和熵变。Pu(III)的首次水解是吸热的（Δ = 34.10 ± 4.48 kJ mol），而Pu(OH)(am)的溶解是放热的（Δ = -294.29 ± 23.05 kJ mol），且熵变为负。这些热力学数据将有助于提高高放废物处置设施安全评估的可靠性，并有助于理解高温下还原或缺氧水条件下Pu的地球化学行为。
