Reaction Kinetics In Supercritical Water as Probed with Muonium

我们建议在超临界水中测量μ 鎓反应速率，以提供发展超临界水冷却核反应堆所需的独特数据。Muonium（Mu）是氢原子（H）的轻同位素。位于不列颠哥伦比亚省温哥华的TRIUMF是世界上仅有的四个拥有适合此类工作的强μ子束的地点之一。我们已经进行了高达470 °C的测量，但对于这个新项目，有必要设计能够承受更高温度的新设备，理想情况下高达650 °C。迄今为止，我们测量的一个共同特征是，μ 鎓速率常数最初随温度增加（预期的行为），但随后经历一个最大值。对于一个反应（Mu +甲醇），发现速率常数在接近临界点（374 °C）时达到最小值，然后再次上升。我们认为，关键因素是溶剂驱动的动力学，特别是一对反应物每次相遇的碰撞次数。最近的工作H，OH和水合电子的其他作者显示了类似的行为，从而支持我们的模型。因此，Mu反应数据可用于模拟在这种条件下H和其他辐解瞬态的行为，或至少提供可用于模拟溶剂行为的数据。在极端条件下对样品进行Mu动力学实验相对容易。这是因为μ子自旋光谱仅对所研究的瞬态物种敏感，不受环境影响。有可能产生具有足够能量的μ子束，以穿透压力容器的厚金属窗口，避免与竞争方法所需的光学窗口相关的问题。μ子自旋光谱在微秒时间尺度上操作，因此对于预期的快速速率常数，可以用0.01-100 mM的反应物浓度实现最佳μ衰变速率。要研究的反应的选择将在AECL科学家的指导下进行，并将包括水（氢和氧）辐解的关键产物以及作为pH值和离子强度函数的研究。

We propose to make measurements of muonium reaction rates in supercritical water to provide unique data necessary for the development of a supercritical-water-cooled nuclear reactor. Muonium (Mu) behaves as a light isotope of atomic hydrogen (H). TRIUMF, in Vancouver, B.C. is one of only four locations in the world with intense muon beams suitable for such work. We have already made measurements as high as 470°C, but for this new project it will be necessary to engineer new apparatus capable of higher temperatures, ideally up to 650°C. A common feature of our measurements to date is that muonium rate constants initially increase with temperature (the expected behaviour) but then go through a maximum. For one reaction (Mu + methanol) the rate constant was found to go through a minimum close to the critical point (374°C) and then rise again. It is our belief that the key factor is the solvent-driven dynamics, in particular the number of collisions per encounter of a pair of reactants. Recent work on H, OH and hydrated electrons by other authors shows similar behaviour, thus supporting our model. Therefore Mu reaction data can be used to simulate the behaviour of H and other radiolysis transients under such conditions, or at the very least provide data which can be used to model the behaviour of the solvent. It is relatively easy to carry out Mu kinetics experiments on samples under extreme conditions. This is because muon spin spectroscopy is sensitive only to the transient species under study and is unaffected by environmental effects. It is possible to produce a beam of muons with sufficient energy to penetrate a thick metal window of a pressure vessel, avoiding the problems associated with optical windows needed for competing methods. Muon spin spectroscopy operates on the microsecond timescale, so optimal Mu decay rates can be achieved with reactant concentrations of 0.01-100 mM for the fast rate constants expected. The choice of reactions to be studied will be made with the guidance of AECL scientists and will include key products of the radiolysis of water (hydrogen and oxygen) as well as studies as a function of pH and ionic strength.