Reaction Kinetics In Supercritical Water as Probed with Muonium

我们建议对超临界水中的钚反应速率进行测量，以便为发展超临界水冷却核反应堆提供独特的数据。钼(Mu)是氢原子(H)的一种轻同位素。不列颠哥伦比亚省温哥华的TRIUMF是世界上仅有的四个地点之一，那里有适合于此类工作的高强度介子束。我们已经进行了高达470°C的测量，但对于这个新项目，需要设计能够承受更高温度的新设备，理想情况下最高可达650°C。到目前为止，我们测量的一个共同特征是，Muonium速率常数最初随温度增加(预期行为)，但随后达到最大值。对于一个反应(Mu+甲醇)，速度常数在临界点(374°C)附近有一个极小值，然后又上升。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。最近其他作者关于H、OH和水合电子的工作显示了类似的行为，从而支持了我们的模型。因此，Mu反应数据可以用来模拟在这种条件下H和其他辐解瞬变的行为，或者至少提供可以用来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Muon自旋光谱只对研究中的瞬变物种敏感，不受环境影响。有可能产生一束具有足够能量穿透压力容器的厚金属窗口的µ子束，从而避免与竞争方法所需的光学窗口相关的问题。Muon自旋光谱在微秒时间尺度上工作，因此，对于预期的快速率常数，反应物浓度为0.01-100 mm时，可以获得最佳的Mu衰减率。将在AECL科学家的指导下选择要研究的反应，将包括水(氢和氧)辐射分解的关键产物以及作为pH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.