Predictive models for D20 isotope effects on ionization and metal hydrolysis under CANDU reactor coolant conditions

CANDU核反应堆是加拿大的一项独特技术，其设计是基于在一个闭环中使用重水将热量从反应堆堆芯传递到蒸汽发生器。这个“一次冷却剂系统”中重水的pH值受到严格控制，以尽量减少腐蚀和放射性迁移的影响。优化一回路冷却剂化学特性需要使用轻水系统中确定的数据，建立温度高达300 °C时金属氧化物、溶解气体和pH控制添加剂化学行为的详细模型。现在用来修正这些模型的方法完全是基于室温研究的。该提案是一项确定性实验室研究的最后阶段，旨在为核反应堆中遇到的极端温度和压力（250至300 °C和10 MPa）下简单酸和碱的H2O和D2 O之间电离常数的差异提供基本数据和理解。前两个阶段发展了高精度的交流电导、密度计和紫外-可见光方法来测量氘同位素对酸碱电离的影响。这些最先进的仪器由惰性材料制成，可承受高温水中存在的腐蚀性条件，使我们能够直接测量相同条件下H2O和D2 O的化学平衡常数差异。最后阶段将使用这些仪器和一个定制的拉曼光谱测定系统来测量一些模型系统的数据，并开发一个改进的实用模型，用于估计在CANDU运行条件下D2 O同位素对金属水解和金属氧化物溶解度的影响程度。该项目将通过提供优化一回路pH值以减少进料管变薄的标准，为旨在延长现有反应堆寿命的研究做出贡献。它将通过提供对极端温度和压力条件下D2 O同位素对化学平衡的影响的基本理解，为加拿大在重水技术方面的领导作用做出长期贡献。

CANDU nuclear reactors are a uniquely Canadian technology in that their design is based on the use of heavy water in a closed loop to transfer heat from the reactor core to the steam generator. The pH of the heavy water in this "primary coolant system" is tightly controlled to minimize the effects of corrosion and radioactive transport. Optimizing primary coolant chemistry requires detailed models for the chemical behaviour of metal oxides, dissolved gases and pH-control additives at temperatures as high as 300 °C, using data determined in light-water systems. The methods now used to correct these models for the differences between light-water and heavy-water systems are based entirely on room temperature studies. This proposal is for the final phase of a definitive laboratory study to provide fundamental data and understanding for the difference in ionization constants between H2O and D2O, for simple acids and bases at the extreme temperatures and pressures encountered in nuclear reactors (250 to 300 °C and 10 MPa). The first two phases developed high precision AC conductance, densimetry, and UV-visible methods to measure the deuterium isotope effect on acid-base ionization. These state-of-the-art instruments, constructed of inert materials to withstand the corrosive conditions that exist in high temperature water, allow us to measure differences in the chemical equilibrium constants in H2O and D2O under identical conditions, directly. The final phase will use these instruments, and a custom-made Raman spectrometry system, to measure data for a number of model systems and to develop an improved, practical model for estimating the magnitude of D2O isotope effects on metal hydrolysis and metal oxide solubility, under CANDU operating conditions. The project will contribute to research aimed at extending the lifetime of existing reactors by providing criteria for optimizing primary circuit pH to reduce feeder tube thinning. It will make a long term contribution to Canada's leadership role in heavy water technology by providing a fundamental understanding of D2O isotope effects on chemical equilibria under extreme conditions of temperature and pressure.