A bench-top type ultracentrifuge to secure the reliability of safety assessment of used nuclear fuel disposal

在这项NSERC RTI赠款中，需要一个台式超离心机。这是衡量决定使用过的核燃料处置长期风险的元素的吸附分配系数(Kd)值的关键工具。*由于储存库、地球圈和生物圈中元素的迁移是根据其Kd值来评估的，因此可靠地测量这些值的能力在处置安全评估中至关重要。此外，对核废料管理组织(NWMO)、日本原子能机构等机构进行的安全评估敏感性分析表明，Kd值的不确定性直接影响安全评估结果。*安大略省的五个城市正在接受NWMO对废核燃料储存库选址的审查。三种为结晶岩介质，两种为沉积岩介质。这些地区地下水的独特之处在于离子强度高(盐水和盐水)。即使当岩石和膨润土(加拿大工程屏障的候选材料)接触盐水和盐水时，小颗粒(大约2.5纳米到几十纳米)被释放到溶液中。测量可靠的Kd值最关键的因素之一是我们能将液体与固体(包括小颗粒)完全分离。超速离心法是将这些小颗粒从液体中分离出来的唯一方法，也是测量可靠Kd值的全球标准方法。小颗粒的不完全分离导致Kd值存在很大的不确定性。*NWMO计划在2023年选择一个直辖市作为储存库的所在地，并在2028年向联邦政府提交环境评估和许可证申请。这意味着必须尽快测量可靠的Kd值，这对于保护我们的健康和环境以及提高我们对加拿大使用过的核燃料处置的信心至关重要。*这笔赠款中要求的台式超速离心机将用于由NWMO资助的研究。由于台式，它可以安装在手套箱中，其中的大气受到严格控制，以达到相当于安大略省深部地质介质的实验条件。将测量还原和氧化条件下加拿大盐岩和卤水中Se、Tc和Np的Kd值，并将其汇编到NWMO吸附数据库中。此外，NWMO列出了在安全评估中重要的19种感兴趣的元素，并且只进行了几项关于它们在还原条件下在盐水和盐水中的吸附的工作。麦克马斯特大学是加拿大唯一可以研究重要元素吸附行为的机构，因此使用超离心机的机会肯定会在未来的工作中扩大，包括目前申请的NSERC发现拨款。

In this NSERC RTI Grant, a bench-top type ultracentrifuge is required. This is a critical tool to measure the values of sorption distribution coefficient (Kd) of elements which dominate the long-term risk of used nuclear fuel disposal.*** Since the migration of elements in the repository, the geosphere and the biosphere is assessed by their Kd values, the ability to reliably measure these values is critical in the safety assessment of disposal. Furthermore, the sensitivity analysis on the safety assessment by the Nuclear Waste Management Organization (NWMO), the Japan Atomic Energy Agency and other institutes shows that the uncertainty of the Kd value significantly and directly affects the result of safety assessment. *** Five municipalities in Ontario are under review for the site selection of used nuclear fuel repository by the NWMO. Three are the crystalline rock media and two are the sedimentary rock media. The unique feature of groundwater in these areas is the high ionic strength (saline and brine). Even when the rocks and the bentonite (a candidate material for engineered barrier in Canada) contact saline and brine, small particles (about 2.5 nm to several tens nm) are released into the solution. One of the most critical factors to measure the reliable Kd values is how completely we can separate the liquid from the solid including the small particles. The ultracentrifugation is the only way to separate such small particles from liquid phase, and is a global standard method to measure the reliable Kd values. Incomplete separation of small particles leads to large uncertainties of Kd values.*** The NWMO plans to select one municipality to host the repository in 2023, and to submit the Environmental Assessment and Licence application to the Federal Government in 2028. This means that the reliable Kd values have to be measured as soon as possible, and are essential to protect our health and environment and to improve our confidence in the used nuclear fuel disposal in Canada.*** The bench-top type ultracentrifuge requested in this grant will be used in the research funded by the NWMO. Because of the bench-top type, it can be installed in a glove box in which the atmosphere is strictly controlled to achieve the experimental conditions equivalent to deep geological media in Ontario. The Kd values of Se, Tc and Np on Canadian rocks in saline and brine under the reducing and oxidizing conditions will be measured, and will be compiled in the NWMO Sorption Database. Furthermore, the NWMO lists 19 elements of interest which are important in the safety assessment, and only few works on their sorption in saline and brine under the reducing conditions have been conducted. McMaster University is the only institute in Canada where the sorption behaviours of the important elements can be studied, and so the opportunity to use the ultracentrifuge will certainly be expanded in future works including NSERC Discovery Grant applied for now.