Multiscale diffusion model of NpO2+ through compacted bentonite in saline solution

NpO2 在盐溶液中通过压实膨润土的多尺度扩散模型

• 批准号: RGPIN-2019-05396
• 负责人: Nagasaki, Shinya
• 金额: $ 2.04万
• 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: 2021
• 资助国家: 加拿大
• 起止时间: 2021-01-01 至 2022-12-31
• 项目状态: 已结题
• 来源: https://www.nserc-crsng.gc.ca/ase-oro/Details-Detailles_eng.asp?id=738247
• 关键词: Multiscale; diffusion; model; NpO2+; through

Approximately 16% and 60% of electricity generation are covered by nuclear energy in Canada and Ontario, respectively. The safe management of used nuclear fuel is essential to protect our health and environment, and critical to increasing the public confidence of Canadians in the use of nuclear energy. The result of safety assessment for used nuclear fuel disposal is sensitive to the values of sorption and diffusion coefficients of important radionuclides (RI) such as Np-237. Since Np-237 is an alpha-emitter with a long half-life (2.14 million years) and diffuses slowly under reducing conditions, but diffuses moderately under oxidizing conditions, Np is one of key RI which dominate the long-term risk in the safety assessment of used nuclear fuel.    Saline solution is a typical feature of porewaters in deep rocks in Southern Ontario (e.g. ionic strength of saline is up to about 6 mol/kgw). However, little data on sorption and diffusion of RI in compacted bentonite and host rocks in saline solution is available. The diffusion of RI in compacted bentonite is generally discussed by the sorption distribution coefficient (Kd) obtained by batch test. However, there is frequently a large discrepancy between the actual diffusivity of RI and their diffusivity predicted by Kd value. We do not completely understand why this discrepancy takes place and do not have a diffusion model which is applicable in compacted bentonite.    Our research program will study the diffusion of Np(V) and HTO (tritiated water) in compacted bentonite as a function of porewater salinity, develop a diffusion model in compacted bentonite, and elucidate the mechanisms on this discrepancy.    The diffusion behaviours of Np(V) and HTO through compacted bentonite will be measured by a through-diffusion method. A diffusion model will be developed by combining with the sorption model developed in the current NSERC Discovery Grant research (2014-2019) and by considering electrostatic double layer theory, water movement by molecular dynamic simulation (MDS), surface charge density by density functional theory (DFT), and electro viscose effect. By discussing the validity of measured diffusion coefficient values and by comparing those with MDS results, the diffusion model will be validated and the reasons for the discrepancy will be studied.     Six Master, two Ph.D. and five undergraduate students will participate in this research. One Postdoctoral fellow will also participate in this research, with expertise in material sciences. Training of HQP will be accomplished through the research-based development of their skills in unsealed actinide handling, diffusion theory, MDS and DFT, and of their knowledge of radiochemistry and interface chemistry.     With uncertainties and incomplete public deliberations on the nuclear energy development, the results of this research will advance the methods of safety assessment and enhance the training of individuals in radioactive waste management.

加拿大和安大略省分别约有 16% 和 60% 的发电量由核能提供。对废核燃料的安全管理对于保护我们的健康和环境至关重要，对于提高加拿大公众对使用核燃料的信心也至关重要。核能。废核燃料处置的安全评估结果对重要放射性核素（RI）（例如 Np-237）的吸附和扩散系数值敏感，因为 Np-237 是一种具有Np 半衰期长（214 万年），在还原条件下扩散缓慢，但在氧化条件下扩散适度，是废旧核燃料安全评估中主导长期风险的关键 RI 之一。安大略省南部深层岩石孔隙水的典型特征（例如盐水的离子强度高达约 6 mol/kgw）。然而，关于 RI 在压实中的吸附和扩散的数据很少。膨润土和围岩在盐溶液中的扩散通常通过批量试验获得的吸附分配系数（Kd）来讨论，但RI的实际扩散率与其扩散率之间经常存在较大差异。我们不完全理解为什么会出现这种差异，并且没有适用于压实膨润土的扩散模型。压实膨润土中的 Np(V) 和 HTO（氚化水）作为孔隙水盐度的函数，建立了压实膨润土中的扩散模型，并阐明了这种差异的机制 Np(V) 和 HTO 通过压实的扩散行为。膨润土将通过扩散法进行测量，并结合当前 NSERC 发现资助研究中开发的吸附模型来开发扩散模型。 （2014-2019）并通过考虑静电双层理论、分子动力学模拟（MDS）的水运动、密度泛函理论（DFT）的表面电荷密度以及电粘胶效应，讨论了测量的扩散系数值的有效性。通过与MDS结果的比较，验证扩散模型并研究差异的原因。本研究还将有6名硕士生、2名博士生和5名本科生参与。 HQP 的培训将通过基于研究的非密封锕系元素处理、扩散理论、MDS 和 DFT 以及放射化学和界面化学知识的发展来完成。公众对核能发展的审议，这项研究的结果将改进安全评估方法并加强放射性废物管理方面的个人培训。