Mechanistic modeling of water radiolysis in supercritical water-cooled small modular reactors.

核能和水电是唯一可以取代化石燃料的低碳能源。在核反应堆中使用超临界水作为冷却剂是当前亚临界水冷堆（wcr）发展的必然趋势。在当前wcr（~250-330℃，10 MPa）和正在开发的小型模块化SCW-SMR（~280-500℃，25 MPa）的运行条件下，水的辐射诱导化学仍然知之甚少。对于所有SCW-SMR概念来说，最重要的水化学挑战之一是预测水辐射分解对材料性能的影响，并制定化学控制策略来减轻这些影响。这是因为在超临界水堆的高温下，放射性溶解过程中形成的化学物质与大多数金属合金高度反应，增加了腐蚀和应力腐蚀开裂（SCC）的速率，并导致燃料包层失效。水化学的直接测量是困难的（如果不是不可能的话），因为这些水在通过反应堆堆芯时受到强烈的混合辐射场的影响。因此，理论建模和计算机模拟提供了一个重要的研究途径，以帮助阐明辐射与SCW相互作用的机制及其对材料的影响。从理论上讲，我们的长期目标是开发基于计算机的SCW- smr辐射分解模型，使用耦合分子动力学和蒙特卡罗多轨道化学模拟，基于对辐射分解产量及其对温度、密度、SCW结构和其他参数（如LET和pH）的依赖的详细了解。我们的研究活动预计将产生可开发的结果，为scw - smr的水化学提供新的见解，从而通过支持计划目标为加拿大带来利益。此外，他们将向核管理机构提供有关关键化学参数的建议，这些参数必须进行监测，以确保SCW-SMR安全运行。

Together with hydropower, nuclear is the only low-carbon source of energy that can replace fossil fuels. The use of supercritical water (SCW) as the coolant in a nuclear reactor is the logical evolution of the current generation of subcritical water-cooled reactors (WCRs). The radiation-induced chemistry of water under the operating conditions of both current WCRs (~250-330 oC, 10 MPa) and small modular SCW-cooled reactor (SCW-SMR) concepts now under development (~280-500 oC, 25 MPa) remains poorly understood. One of the most significant water chemistry challenges for all SCW-SMR concepts is to predict the effects of water radiolysis on materials performance and develop a chemistry control strategy to mitigate these effects. This is because chemical species formed during radiolysis are highly reactive with most metal alloys at the elevated temperatures proposed for SCW reactors, increasing the rates of corrosion and stress corrosion cracking (SCC) and leading to fuel cladding failure. Direct measurements of the water chemistry are difficult (if not impossible) to perform due to the fact that this water is subjected to an intense mixed radiation field as it passes through the reactor core. As a result, theoretical modeling and computer simulations provide an important route of investigation to help elucidate mechanisms by which radiation interacts with SCW and the consequences for materials. Of a theoretical nature, our long-term goal is to develop a computer-based SCW-SMR radiolysis model using coupled molecular dynamics and Monte Carlo multi-track chemistry simulations, based on a detailed knowledge of radiolytic yields and their dependence on temperature, density, SCW structure and other parameters such as LET and pH of the solution. Our research activities are expected to generate exploitable results that will provide new insights into water chemistry in SCW-SMRs and thus provide benefits to Canada by supporting the program objectives. In addition, they will provide recommendations to nuclear regulatory agencies on key chemistry parameters that must be monitored to ensure that an SCW-SMR is operated safely.