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

坎杜核反应堆是加拿大独有的技术，因为它们的设计是基于使用闭合回路中的重水将热量从反应堆核心传递到蒸汽发生器。这个“一次冷却剂系统”中重水的酸碱度受到严格控制，以最大限度地减少腐蚀和放射性输送的影响。优化初级冷却剂化学需要使用在轻水系统中测定的数据，对温度高达300°C的金属氧化物、溶解气体和pH控制添加剂的化学行为建立详细的模型。现在用来修正轻水和重水系统之间差异的这些模型的方法完全基于室温研究。这项建议是为最终实验室研究的最后阶段提供基本数据和了解在核反应堆中遇到的极端温度和压力(250至300℃和10兆帕)下单酸和碱的水和D2O之间的电离常数的差异。前两个阶段发展了高精度的交流电导、密度测量和紫外可见方法来测量氚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，可以承受高温水中存在的腐蚀条件，使我们能够直接测量相同条件下H2O和D2O中的化学平衡常数的差异。最后一阶段将使用这些仪器和定制的拉曼光谱系统，测量一些模型系统的数据，并开发一个改进的、实用的模型，以估计在CANDU操作条件下D2O同位素对金属水解和金属氧化物溶解度的影响程度。该项目将为旨在延长现有反应堆寿命的研究做出贡献，提供优化一回路pH的标准，以减少馈线管变薄。它将通过提供对极端温度和压力条件下D2O同位素对化学平衡的影响的基本了解，为加拿大在重水技术方面的领先地位做出长期贡献。

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.