Abstract Four grades of nuclear graphite were oxidized in helium with traces of moisture and hydrogen in order to evaluate the effects of slow oxidation by moisture on graphite components in high temperature gas cooled reactors. Kinetic analysis showed that the Langmuir-Hinshelwood (LH) model cannot consistently reproduce all results. In particular, at high temperatures and water partial pressures, oxidation was always faster than the LH model predicts. It was also found empirically that the apparent reaction order for water has a sigmoid-type variation with temperature which follows the integral Boltzmann distribution function. This suggests deviations from the LH model are apparently caused by activation with temperature of graphite reactive sites, which is probably rooted in specific structural and electronic properties of graphite. A semi-global kinetic model was proposed, whereby the classical LH model was modified with a temperature-dependent reaction order for water. This new Boltzmann-enhanced Langmuir-Hinshelwood (BLH) model consistently predicts oxidation rates over large ranges of temperature (800–1100 °C) and partial pressures of water (3–1200 Pa) and hydrogen (0–300 Pa). The BLH model can be used for modeling chronic oxidation of graphite components during life-time operation in high- and very high temperature advanced nuclear reactors.

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超越高温气冷反应堆中水分对石墨慢性氧化的经典动力学模型

摘要 为了评估湿气缓慢氧化对高温气冷堆石墨部件的影响，在氦气中氧化四种等级的核石墨，并加入微量水分和氢气。动力学分析表明，Langmuir-Hinshelwood (LH) 模型无法始终如一地重现所有结果。特别是在高温和水分压下，氧化总是比 LH 模型预测的要快。还凭经验发现，水的表观反应级次随温度呈 sigmoid 型变化，其遵循积分玻尔兹曼分布函数。这表明与 LH 模型的偏差显然是由石墨反应位点的温度激活引起的，这可能源于石墨的特定结构和电子特性。提出了一个半全局动力学模型，其中经典的 LH 模型被修改为水的温度相关反应顺序。这种新的 Boltzmann 增强的 Langmuir-Hinshelwood (BLH) 模型在大范围的温度 (800–1100 °C) 和水分压 (3–1200 Pa) 和氢 (0–300 Pa) 内一致地预测氧化率。BLH 模型可用于模拟高温和超高温先进核反应堆寿命周期运行期间石墨部件的慢性氧化。这种新的 Boltzmann 增强的 Langmuir-Hinshelwood (BLH) 模型在大范围的温度 (800–1100 °C) 和水分压 (3–1200 Pa) 和氢 (0–300 Pa) 内一致地预测氧化率。BLH 模型可用于模拟高温和超高温先进核反应堆寿命周期运行期间石墨部件的慢性氧化。这种新的 Boltzmann 增强的 Langmuir-Hinshelwood (BLH) 模型在大范围的温度 (800–1100 °C) 和水分压 (3–1200 Pa) 和氢 (0–300 Pa) 内一致地预测氧化率。BLH 模型可用于模拟高温和超高温先进核反应堆寿命周期运行期间石墨部件的慢性氧化。