Sorption of Np(V) and Np(IV) on bentonite in brine groundwater

咸水地下水中膨润土对 Np(V) 和 Np(IV) 的吸附

• 批准号: RGPIN-2014-05732
• 负责人: Nagasaki, Shinya
• 金额: $ 2.19万
• 依托单位: McMaster University
• 依托单位国家: 加拿大
• 项目类别: Discovery Grants Program - Individual
• 财政年份: 2016
• 资助国家: 加拿大
• 起止时间: 2016-01-01 至 2017-12-31
• 项目状态: 已结题
• 来源: https://www.nserc-crsng.gc.ca/ase-oro/Details-Detailles_eng.asp?id=611813
• 关键词: Sorption; Np; IV; bentonite; brine

In Canada, New Brunswick, Ontario, Saskatchewan, and even Alberta (heretofore a “non-nuclear” province) have considered adding nuclear capacity to their energy mix. However, for any nuclear energy policy taken by the government and utilities, a solution to the problem of used nuclear fuel management and disposal is essential for public acceptance of the policy. According to the research of the Nuclear Waste Management Organization (NWMO) in Canada, currently both sedimentary and crystalline rocks are considered as potential hosts for a deep geological repository. One of the unique characteristics of groundwaters, where many municipalities are expressing their interest to host the used nuclear fuel disposal repository, is brine (total dissolved solids > 100 g/L). In the safety assessment of used nuclear fuel disposal, neptunium (Np)-237 will dominate the long-term radiological risk, and the quantitative understanding of sorption of Np-237 on the engineered barrier (bentonite) is a key factor to improve the reliability of safety assessment. However, the sorption of Np (Np(V) in aerobic condition and Np(IV) in anaerobic condition) on bentonite in brine has not been studied at all. We will (1) investigate the sorption behaviour of Np(V) and Np(IV) on bentonite in synthesized brine, (2) formalize the sorption reactions and (3) evaluate the equilibrium constants of the sorption reactions. The equilibrium constants and the methodology to evaluate the equilibrium constants in brine are essential to establish a technologically, physically, chemically and mathematically robust safety assessment methodology which is the long-term goal of my research program. First, the sorption of Np(V) and Np(IV) on the MX-80, which is a promising candidate material of bentonite used as engineered barrier in Canada, will be measured at varying pH, ionic strength, Na+/Ca2+ ratio at constant ionic strength and Np concentration by batch sorption method. By integrating constant capacitance surface complexation model, Density Functional Theory (DFT) calculations and extended X-ray absorption fine structure (EXAFS) measurement, the sorption reactions of Np(V) and Np(IV) on the MX-80 will be identified and formalized. The equilibrium constants of the sorption reactions will be determined and the constant at zero ionic strength will be evaluated by extrapolation using Pitzer model. Two to three full time Master’s and Ph.D. students and one undergraduate summer student will participate in this proposed research every year. Training of HQP will be accomplished through the research-based development of their skills on unsealed actinide handling, surface complexation model, DFT and EXAFS, and of their knowledge on actinide chemistry, radiochemistry and interface chemistry. The achievements of this research are critical to nuclear industries in Canada, especially the NWMO, Ontario Power Generation and the regulation authorities. Our proposed research will establish a cutting-edge research and education core in actinide chemistry and safety assessment research on used nuclear fuel management at McMaster University. This research will contribute to establishing the research methodology on sorption of redox sensitive radionuclides in brine. Furthermore, since the equilibrium constants of sorption reactions are essential parameters in safety assessment, this research will contribute to the safety of used nuclear fuel management in Canada and other countries where the disposal in brine is considering. These achievements will improve the reliability of safety assessment of radioactive waste disposal, and therefore, will contribute to the safety of the sustainable use of nuclear energy and radioisotopes in Canada and throughout the world.

在加拿大，新不伦瑞克省、安大略省、萨斯喀彻温省，甚至阿尔伯塔省（迄今为止是“非核”省份）都考虑在其能源结构中增加核电容量。然而，对于政府和公用事业公司采取的任何核能政策，解决方案都是废旧核燃料的管理和处置问题对于公众接受该政策至关重要。 根据加拿大核废物管理组织（NWMO）的研究，目前沉积岩和结晶岩都被认为是地下水的独特特征之一，许多城市都表示有兴趣建立深层地质储存库。使用过的核燃料处置库是盐水（总溶解固体> 100 g/L）。 在废旧核燃料处置的安全评估中，镎（Np）-237将主导长期放射性风险，了解Np-237在工程屏障（膨润土）上的吸附是提高处置可靠性的关键因素。然而，尚未研究盐水中膨润土对 Np（需氧条件下的 Np(V) 和厌氧条件下的 Np(IV)）的吸附作用。 我们将 (1) 研究 Np(V) 和 Np(IV) 在合成盐水中膨润土上的吸附行为，(2) 形式化吸附反应，以及 (3) 评估吸附反应的平衡常数以评估平衡。盐水中的常数对于建立技术、物理、化学和数学上稳健的安全评估方法至关重要，这是我的研究计划的长期目标。 首先，MX-80 是一种很有前途的膨润土候选材料，在加拿大用作工程屏障，Np(V) 和 Np(IV) 在 MX-80 上的吸附将在不同的 pH、离子强度、Na+/Ca2+ 比率下进行测量通过批量吸附法恒定离子强度和 Np 浓度通过集成恒定电容表面复杂性模型、密度泛函理论 (DFT) 计算和扩展 X 射线吸收精细结构 (EXAFS) 测量， MX-80 上的 Np(V) 和 Np(IV) 吸附反应将被确定并形式化。吸附反应的平衡常数将被确定，并且零离子强度下的常数将通过使用 Pitzer 模型外推来评估。 每年将有两到三名全日制硕士和博士生以及一名本科生暑期学生参与这项拟议的研究，将通过基于研究的非密封锕系元素处理、表面络合模型等方面的技能发展来完成。 DFT 和 EXAFS，以及他们在锕系化学、放射化学和界面化学方面的知识。 这项研究的成果对于加拿大的核工业，特别是 NWMO、安大略发电公司和监管机构至关重要。我们提出的研究将在锕系化学和废核燃料管理的安全评估研究方面建立尖端的研究和教育核心。这项研究将有助于建立盐水中氧化还原敏感放射性核素吸附的研究方法。此外，由于吸附反应的平衡常数是安全评估的重要参数，这项研究将有助于废旧核燃料管理的安全。在加拿大和其他国家这些成就将提高放射性废物处置安全评估的可靠性，从而有助于加拿大和全世界核能和放射性同位素的可持续利用的安全。