Inducing the resumption of alteration in UK radioactive waste glasses

促使英国放射性废玻璃恢复改造

• 批准号: 2622056
• 金额: --
• 依托单位: University of Cambridge
• 依托单位国家: 英国
• 项目类别: Studentship
• 财政年份: 2021
• 资助国家: 英国
• 起止时间: 2021 至 无数据
• 项目状态: 未结题
• 来源: https://gtr.ukri.org/projects?ref=studentship-2622056
• 关键词: Inducing; resumption; alteration; UK; radioactive

The dissolution rate of radioactive waste glasses reduces by approximately a factor of one thousand over the first 1 - 28 days of contact with water. This reduction in dissolution rate, to what is known as the residual rate, is associated with a reduction in the thermodynamic driving force for dissolution (as solubility limits of certain glass components are approached and no more glass can be dissolved) and the protective effect on the glass surface of the formation of an altered layer that inhibits transport to and from the unaltered glass surface. A phenomenon that is occasionally observed at long time scales in international (and compositionally different) glass formulations is that glass dissolution resumes at rates approaching the initial dissolution rate. This phenomenon is known as resumption of alteration and remains as a potential uncertainty in the long-term performance of radioactive waste glasses in a geological disposal facility. This research project will investigate the applicability of a resumption of alteration scenario for UK radioactive waste glasses and determine the primary controls on any resumption with respect to their compositional differences from international radioactive waste glasses.The resumption is thought to occur when the thermodynamic driving force for the dissolution resumes as solution components form secondary phases on the surface of the glass. This secondary phase formation may also cause changes to the protective nature of the surface.The two main objectives of the project will be:> Distinguish between the relative importance of the two effects thought to cause resumption of alteration.> Determine the mechanism of the resumption of dissolution and its rate with respect to the initial rate and the rate-drop.> Determine the sensitivity of the process to pH. This is to cover potential scenarios where groundwaters have become highly alkaline through contact with cementitious material in back-fill or ILW vaults.In addition to conventional measurements of solution concentrations, detailed analysis of the surface material will be undertaken using scanning electron microscopy, EDX and microprobe analysis. Solid-state nuclear magnetic resonance spectroscopy techniques will be deployed that can quantify the extent of the altered layer (by 1H NMR) and selectively probe and identify the structure of both crystalline and amorphous components present or re-precipitated on the glass surface by 1H- cross polarisation techniques. Isotope techniques (column separation and detailed mass spectrometry) to determine the isotopic ratios in solution as a function of time provide the complementary views of the evolution of both solution and surface during the resumption process.

在与水接触的最初 1 - 28 天内，放射性废玻璃的溶解率降低了大约一千倍。溶解速率的降低（即所谓的残留速率）与溶解热力学驱动力的降低（当接近某些玻璃组分的溶解度极限并且不再有玻璃可以溶解）以及对玻璃表面形成的变质层的保护作用有关，变质层抑制了与未改变的玻璃表面之间的传输。在国际（且成分不同）玻璃配方中，在长时间尺度上偶尔观察到的一个现象是，玻璃溶解以接近初始溶解速率的速率恢复。这种现象被称为蚀变恢复，并且仍然是地质处置设施中放射性废玻璃长期性能的潜在不确定性。该研究项目将研究英国放射性废玻璃恢复变化情景的适用性，并确定其与国际放射性废玻璃的成分差异方面的恢复的主要控制措施。当溶液成分在玻璃表面形成第二相时，溶解的热力学驱动力恢复时，就会发生恢复。这种二次相的形成也可能导致表面保护性质的变化。该项目的两个主要目标是： > 区分被认为导致蚀变恢复的两种效应的相对重要性。 > 确定溶解恢复的机制及其相对于初始速率和速率下降的速率。 > 确定过程对 pH 值的敏感性。这是为了涵盖地下水因与回填或 ILW 拱顶中的胶凝材料接触而变得高度碱性的潜在情况。除了溶液浓度的常规测量之外，还将使用扫描电子显微镜、EDX 和微探针分析对表面材料进行详细分析。将采用固态核磁共振波谱技术，可以量化改变层的范围（通过 1H NMR），并通过 1H 交叉极化技术选择性地探测和识别玻璃表面上存在或再沉淀的结晶和非晶成分的结构。用于确定溶液中同位素比率随时间变化的同位素技术（柱分离和详细质谱分析）提供了恢复过程中溶液和表面演变的互补视图。