Development of a radiolysis model for Generation-IV supercritical water-cooled reactors

在目前的加压水冷反应堆系统（~320 °C，10 MPa）和未来的超临界水反应堆（~430-625 °C，25 MPa）的运行条件下，辐射诱导的水化学在很大程度上仍然是未知的。在如此高的温度和压力下，特别是超过水的临界点（H2O：374 °C，22.1 MPa），直接测量是困难的，计算机模拟是一个重要的研究途径。我们的目标是提高对辐射（高能中子、伽马射线、反冲质子和q = 1-8的Oq+离子）对反应堆堆芯含水系统影响的可靠认识，以便制定化学控制策略，最大限度地减少因辐射分解形成氧化产物（如.OH、H2 O2、O2和HO 2）而导致的反应堆组件腐蚀和降解。/氧气我们的长期目标是开发一个基准的SCW反应堆辐解模型结合分子动力学（MD）和蒙特卡罗（MC）的计算机模拟。该项目基于初步结果（在我们的实验室中获得），该结果表明SCW的异质（“液体”状簇被“气体”状区域包围）分子结构可能是更好地理解374 °C以上水辐解的关键。本文建议使用分子动力学计算在选定的温度下在从非常稀的蒸汽到致密的SCW的广泛密度范围内生成SCW的分子详细构型，结合MC模拟（i）描述SCW在这些特定构型下的辐解，以及（ii）定量确定温度高达625 °C时辐解物质的产率。令人兴奋的发展，也将与我们的模型计算包括pH值的影响，添加溶质（如H2和其他.OH清除剂，溶解O2）和它们的浓度，剂量率，以及多电离和高LET照射下的水分子的碎片化的影响。 该项目将受益于我们在水的辐射化学和随机MC技术应用于液态水辐解在各种实验条件下的使用的长期经验。

The radiation-induced chemistry of water under the operating conditions of both current pressurized water-cooled reactor systems (~320 °C, 10 MPa) and supercritical water (SCW) reactors in the future (~430-625 °C, 25 MPa) remains largely unknown. Direct measurements at such high temperatures and pressures, and especially beyond the critical point of water (H2O: 374 °C, 22.1 MPa), are difficult, and computer simulations are an important route of investigation. Our objective is to develop an enhanced, reliable understanding of the effects of radiation (energetic neutrons, gamma-rays, recoil protons and Oq+ ions with q = 1-8) on aqueous systems in the reactor cores, in order to develop a chemistry control strategy that minimizes corrosion and degradation of reactor components resulting from the radiolytic formation of oxidizing products such as .OH, H2O2, O2, and HO2./O2.-. Our long-term goal is to develop a benchmark SCW reactor radiolysis model using combined molecular dynamics (MD) and Monte Carlo (MC) computer simulations. This project is based on preliminary results (obtained in our laboratory) that suggest that the heterogeneous ("liquid"-like clusters surrounded by "gas"-like regions) molecular structure of SCW might be a key to better understand water radiolysis above 374 °C. It is proposed here to use MD calculations to generate molecularly detailed configurations of SCW at selected temperatures over a wide range of densities from very dilute vapor to dense SCW, in combination with MC simulations (i) to describe the radiolysis of SCW under these specific configurations and (ii) to quantitatively determine the yields of radiolytic species for temperatures up to 625 °C. Exciting developments that will also be made with our model calculations include the effects of pH, added solutes (such as H2 and other .OH scavengers, dissolved O2) and their concentrations, dose rate, as well as the effects of multiple ionization and fragmentation of water molecules under high-LET irradiation. This project will benefit from our long experience in the radiation chemistry of water and in the use of stochastic MC techniques applied to liquid water radiolysis under a variety of experimental conditions.