Inducing the resumption of alteration in UK radioactive waste glasses

在与水接触的前1 - 28天内，放射性废玻璃的溶解速率降低约一千倍。这种溶解速率降低到所谓的残余速率，与溶解的热力学驱动力的降低有关（因为某些玻璃组分的溶解度接近极限，并且不再有玻璃可以溶解），并且与形成改变的层对玻璃表面的保护作用有关，所述改变的层抑制了向未改变的玻璃表面的运输和从未改变的玻璃表面的运输。在国际（和组成不同的）玻璃配方中，在长时间尺度上偶尔观察到的现象是玻璃溶解以接近初始溶解速率的速率恢复。这种现象被称为恢复蚀变，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。该研究项目将调查英国放射性废物玻璃的蚀变方案恢复的适用性，并确定其与国际放射性废物玻璃的成分差异方面的任何恢复的主要控制。恢复被认为是当溶解的热力学驱动力恢复时发生的，因为溶液成分在玻璃表面形成第二相。这种次生相的形成也可能导致地表保护性质的变化。该项目的两个主要目标是：>区分被认为会导致恢复蚀变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通过与回填或ILW拱顶中的胶结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。将部署固态核磁共振光谱技术，该技术可以量化改变层的程度（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重新沉淀的结晶和非晶组分的结构。同位素技术（柱分离和详细的质谱法），以确定作为时间的函数在溶液中的同位素比率提供了补充的意见，在恢复过程中的溶液和表面的演变。

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.