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

在加拿大，新不伦瑞克、安大略省、萨斯喀彻温省，甚至艾伯塔省(到目前为止都是一个“无核”省份)都考虑在能源组合中增加核能能力。然而，对于政府和公用事业公司采取的任何核能政策来说，旧核燃料管理和处置问题的解决对于公众接受该政策是至关重要的。 根据加拿大核废料管理组织(NWMO)的研究，目前沉积岩和结晶岩都被认为是深层地质库的潜在宿主。地下水的一个独特特征是盐水(总溶解固体&gt；100g/L)，许多市政当局都表示有兴趣在那里建立废核燃料处置库。 在废旧核燃料处置的安全评价中，Np(Np)-237将是长期的放射性风险的主导因素，定量了解Np-237在工程屏障(膨润土)上的吸附是提高安全评价可靠性的关键因素。然而，在盐水中，膨润土对NP(好氧条件下的Np(V)和厌氧条件下的Np(IV))的吸附还没有被研究过。 我们将(1)研究Np(V)和Np(IV)在合成卤水中在膨润土上的吸附行为，(2)将吸附反应形式化，(3)计算吸附反应的平衡常数。盐水中的平衡常数和评估平衡常数的方法对于建立一种在技术上、物理上、化学上和数学上可靠的安全评估方法是必不可少的，这是我研究计划的长期目标。 首先，采用间歇吸附的方法，在不同pH、离子强度、钠钙比和NP浓度不同的条件下，测定了Np(V)和Np(IV)在MX-80上的吸附。通过结合恒电容表面络合模型、密度泛函理论(DFT)计算和扩展X射线吸收精细结构(EXAFS)测量，Np(V)和Np(IV)在MX-80上的吸附反应将被识别和形式化。测定了吸附反应的平衡常数，并用Pitzer模型外推求出了零离子强度时的平衡常数。 每年将有两到三名全日制硕士和博士生和一名本科生暑期学生参加这项拟议的研究。HQP的培训将通过以研究为基础发展他们在未密封的鳗系元素处理、表面络合模型、DFT和EXAFS方面的技能，以及他们在鳗系元素化学、放射化学和界面化学方面的知识。 这项研究的成果对加拿大的核工业，特别是NWMO、安大略省发电和监管当局至关重要。我们建议的研究将在麦克马斯特大学建立一个关于使用过的核燃料管理的鳗系元素化学和安全评估研究的尖端研究和教育核心。本研究将有助于建立卤水中氧化还原敏感型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中的基本参数，本研究将有助于加拿大和其他正在考虑盐水处置的国家的旧核燃料管理的安全性。这些成就将提高放射性废物处置安全评估的可靠性，因此，将有助于加拿大和全世界可持续使用核能和放射性同位素的安全。

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.