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

目前的压水堆系统(~320°C，10 Mpa)和未来的超临界水(SCW)反应堆(~430~625°C，25 Mpa)的运行条件下，水的辐射化学仍很大程度上是未知的。在这么高的温度和压力下，特别是在水的临界点(H2O：374°C，22.1兆帕)之外，直接测量是困难的，而计算机模拟是一条重要的研究途径。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)对反应堆堆芯水体系的影响的可靠理解，以便制定一种化学控制策略，将因.oh、H2O2、O2和HO2/O2等氧化产物的辐射分解而导致的反应堆部件的腐蚀和退化降至最低。我们的长期目标是利用联合分子动力学(MD)和蒙特卡罗(MC)计算机模拟开发一个基准的SCW反应堆辐射分解模型。这个项目是基于初步结果(在我们实验室获得的)，这些结果表明SCW的非均相(被类似气体的区域包围的类似液体的团簇)分子结构可能是更好地理解374°C以上的水辐射分解的关键。这里建议使用MD计算来生成在从非常稀薄的蒸汽到密集的SCW的广泛密度范围内选定温度下的SCW的分子详细构型，与MC模拟相结合，(I)描述这些特定配置下超临界水的辐射分解，(Ii)定量确定温度高达625°C的辐射分解物种的产量。我们的模型计算还将进行激动人心的发展，包括pH的影响，添加的溶质(如H2和其他.oh清除剂，溶解O2)及其浓度，剂量率，以及高LET照射下水分子多次电离和碎裂的影响。这个项目将受益于我们在水的辐射化学方面的长期经验，以及在各种实验条件下应用于液态水辐射分解的随机MC技术。

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.