Abstract

Exposure to air can cause amine solutions in CANada Deuterium Uranium (CANDU) reactor secondary coolant circuit feed tanks to absorb carbon dioxide (CO2). Likewise, carbon dioxide can be absorbed directly into the amine-containing secondary coolant by air ingress during shutdown, lay-up, and startup. Sampling operations, including transferring the sample to the laboratory and subsequent analyses, can also provide opportunities for CO₂ contamination. This paper reports the results of laboratory and chemical modeling studies to examine the effects of CO₂ contamination on aqueous morpholine solutions.

The chemistry of CO₂ uptake by feed tanks containing up to 50 wt% (11.5 mol·kg⁻¹) morpholine at 25°C was modeled using the OLI Studio 9.5.2 chemical equilibrium model, and the speciation was confirmed by ¹³C nuclear magnetic resonance spectroscopy (NMR) measurements. The effects of CO₂ contamination on the pH of the secondary coolant containing 60 ppm (0.006 wt%, 7.00 × 10⁻⁴ mol·kg⁻¹) morpholine and the resulting effects on the solubility of magnetite and nickel oxide from 25°C and 250°C at steam saturation were modeled as a function of CO₂ loading using the Electrical Power Research Institute chemical modeling software MULTEQ v.8.

The chemical modeling calculations show that concentrated alkaline morpholine solutions at room temperature and pressure would be expected to have a strong tendency to absorb CO₂ and have additional uptake abilities due to the formation of morpholine carbamates. For dilute morpholine solutions at room temperature and pressure, the solutions are still sufficiently alkaline to absorb enough CO₂ to cause a measurable change in the pH of the secondary coolant. This effect was shown to be negligible under reactor operating conditions. The absorption of CO₂ would potentially have the most effect on either unprotected feed tanks or during lay-up conditions in the steam generators, as it could depress the pH of the lay-up solution and adversely affect the rate of corrosion in the internal components of the steam generators (e.g., carbon steel materials).

The ¹³C NMR measurements on samples of 50 wt% aqueous morpholine solutions from feed tanks at the Ontario Power Generation’s Pickering Nuclear Generating Station found that CO₂ was below the 0.02 wt% detection limit, and suggest that the procedures used to avoid CO₂ contamination in feed tanks are effective. The ¹³C NMR was shown to be an effective tool for monitoring CO₂ uptake by morpholine solution in the feed tanks under conditions in which they may have undergone abnormal exposure to air.

摘要

暴露在空气中会导致加拿大氘铀 (CANDU) 反应堆二次冷却剂回路进料罐中的胺溶液吸收二氧化碳 (CO2)。同样，二氧化碳可以通过停机、搁置和启动期间的空气进入直接吸收到含胺的二次冷却剂中。采样操作，包括将样品转移到实验室和随后的分析，也可能为 CO ₂污染提供机会。本文报告了实验室和化学模型研究的结果，以检查 CO ₂污染对吗啉水溶液的影响。

使用 OLI Studio 9.5.2 化学平衡模型模拟了在 25°C 下含有高达 50 wt% (11.5 mol·kg ^-1 ) 吗啉的进料罐吸收CO ₂的化学反应，并通过¹³ C 核确认了物种形成磁共振波谱 (NMR) 测量。CO ₂污染对含有 60 ppm (0.006 wt%, 7.00 × 10 ^-4  mol·kg ^-1 ) 吗啉的二次冷却剂 pH 值的影响，以及由此产生的对磁铁矿和氧化镍在 25°C 和使用电力研究所化学建模软件 MULTEQ v.8 将蒸汽饱和度下的 250°C 建模为 CO ₂负载的函数。

化学模型计算表明，在室温和压力下，浓缩的碱性吗啉溶液将具有很强的吸收 CO _{2 的}趋势，并且由于吗啉氨基甲酸酯的形成而具有额外的吸收能力。对于在室温和压力下稀释的吗啉溶液，该溶液仍然具有足够的碱性以吸收足够的 CO ₂从而导致二次冷却剂的 pH 值发生可测量的变化。在反应器操作条件下，这种影响可以忽略不计。CO ₂的吸收可能对未受保护的进料罐或蒸汽发生器中的搁置条件产生最大影响，因为它可能降低搁置溶液的 pH 值并对蒸汽发生器内部组件的腐蚀速率产生不利影响（例如，碳钢材料）。

对来自安大略发电公司皮克林核电站进料罐的 50 wt% 吗啉水溶液样品的¹³ C NMR 测量发现 CO ₂低于 0.02 wt% 检测限，并建议用于避免 CO ₂污染的程序在饲料罐中是有效的。的¹³ C NMR被证明是用于监测CO的有效工具₂中，他们可能已经经历异常暴露于空气的条件下摄取通过在进料罐吗啉溶液。