Mechanistic modeling and simulation of water radiolysis for controling the chemistry in Generation-IV supercritical water-cooled reactors

目前的压水堆（~250 ~ 330℃，10 MPa）和未来的第四代SCW堆（~430 ~ 625℃，25 MPa）在运行条件下，水的辐射分解情况仍不得而知。在如此高的温度和压力下，特别是超过水的临界点（H2O: tc ~ 373.95 oC, pc ~ 22.06 MPa）的直接测量是困难的，计算机模拟是研究的重要途径。这项工作的目的是增强对辐射（快中子、伽马射线、反冲质子/Oq+离子，q = 1-8）对反应堆堆芯水系统的影响的理解，以便指定一种化学控制策略，以最大限度地减少由氧化物质（如氧化物质）的辐射分解形成的反应堆组件的腐蚀和降解。OH, H2O2， O2和O2.-/HO2..我们的长期目标是利用耦合分子动力学（MD）和蒙特卡罗（MC）模拟开发一个基准的SCW反应堆辐射分解模型。这个项目是基于我们实验室获得的初步结果，这些结果表明，SCW的非均匀分子结构（高密度的“液体”状区域被低密度的“气体”状区域包围）可能是更好地理解tc附近或以上水辐射分解的关键因素。本文建议使用MD模拟来生成在不同选择温度下从极稀蒸汽到致密SCW的密度范围内的SCW的分子详细构型，并结合MC模拟来描述这些特定构型下SCW的辐射分解，以及ii)定量确定温度高达625℃时所有辐射分解物种的产率。将对正在开发的代码进行一些有效性测试，包括关键参数的影响：LET、pH、添加的溶质（H2和其他）。OH清除剂，溶解O2)，高剂量率等)。结果数据将成为加拿大SCW反应堆水化学控制策略开发的关键输入，确定堆芯不同位置冷却剂的氧化能力。这些数据对于解释即将在捷克共和国使用芯内SCW循环进行的测试结果也具有重要价值。

The radiolysis of water under operating conditions of both current pressurized water-cooled reactors (~250-330 oC, 10 MPa) and 4th-generation SCW reactors in the future (~430-625 oC, 25 MPa) remains largely unknown. Direct measurements at such high temperatures and pressures, and especially beyond the critical point of water (H2O: tc ~ 373.95 oC, pc ~ 22.06 MPa) are difficult, and computer simulations are an important route of investigation. The objective of this work is to obtain an enhanced understanding of the effects of radiation (fast neutrons, gamma-rays, recoil protons/Oq+ ions, q = 1-8) on aqueous systems in the reactor cores, in order to specify a chemistry control strategy that minimizes corrosion and degradation of reactor components resulting from the radiolytic formation of oxidizing species such as .OH, H2O2, O2, and O2.-/HO2.. Our long-term goal is to develop a benchmark SCW reactor radiolysis model using coupled molecular dynamics (MD) and Monte-Carlo (MC) simulations. This project is based on preliminary results (obtained in our laboratory) that suggest that the heterogeneous molecular structure of SCW (high-density, "liquid"-like regions surrounded by low-density, "gas"-like regions) might be a key factor to better understand water radiolysis near or above tc. It is proposed here to use MD simulations to generate molecularly detailed configurations of SCW at different 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 all radiolytic species for temperatures up to 625 oC. A number of tests of validity of the codes that are being developed will be carried out, including the influence of key parameters: LET, pH, added solutes (H2 and other .OH scavengers, dissolved O2), high dose rate, etc.). The resulting data will be key inputs into the development of a water chemistry control strategy for the Canadian SCW reactor, defining the oxidizing power of the coolant at various locations in the core. These data will also be of great value for the interpretation of the results of upcoming tests using in-core SCW loops in the Czech Republic.