Department of Civil and Environmental Engineering, Massachusetts Institute of Technology , Cambridge, Massachusetts 02139, United States.
MultiScale Material Science for Energy and Environment, UMI 3466 CNRS-MIT, 77 Massachusetts Avenue, Cambridge, Massachusetts 02139, United States.
Environ Sci Technol. 2015 Nov 17;49(22):13676-83. doi: 10.1021/acs.est.5b02609. Epub 2015 Oct 29.
One of the main challenges faced by the nuclear industry is the long-term confinement of nuclear waste. Because it is inexpensive and easy to manufacture, cement is the material of choice to store large volumes of radioactive materials, in particular the low-level medium-lived fission products. It is therefore of utmost importance to assess the chemical and structural stability of cement containing radioactive species. Here, we use ab initio calculations based on density functional theory (DFT) to study the effects of (90)Sr insertion and decay in C-S-H (calcium-silicate-hydrate) in order to test the ability of cement to trap and hold this radioactive fission product and to investigate the consequences of its β-decay on the cement paste structure. We show that (90)Sr is stable when it substitutes the Ca(2+) ions in C-S-H, and so is its daughter nucleus (90)Y after β-decay. Interestingly, (90)Zr, daughter of (90)Y and final product in the decay sequence, is found to be unstable compared to the bulk phase of the element at zero K but stable when compared to the solvated ion in water. Therefore, cement appears as a suitable waste form for (90)Sr storage.
核工业面临的主要挑战之一是核废料的长期封存。由于水泥价格低廉且易于制造，因此它是存储大量放射性物质的首选材料，特别是低水平中寿命裂变产物。因此，评估含有放射性物质的水泥的化学和结构稳定性至关重要。在这里，我们使用基于密度泛函理论 (DFT) 的从头算计算来研究 (90)Sr 插入和在 C-S-H（钙-硅-水合物）中衰变的影响，以测试水泥捕获和保持这种放射性裂变产物的能力，并研究其β衰变对水泥浆结构的后果。我们表明，(90)Sr 在取代 C-S-H 中的 Ca(2+) 离子时是稳定的，其β衰变后的子核 (90)Y 也是稳定的。有趣的是，与零 K 时元素的体相相比，(90)Y 的子核 (90)Zr 以及衰变序列中的最终产物被发现是不稳定的，但与水中的溶剂化离子相比是稳定的。因此，水泥似乎是 (90)Sr 存储的合适废物形式。
