ABSTRACT

A mechanistic model for dryout and rewetting in boiling water reactors, is necessary in safety evaluations since it could be commonly applicable to various fuel assemblies and wider ranges of thermal-hydraulic conditions. A dryout and rewetting mechanistic model based on the three-field model in the COolant Boiling in Rod Arrays-Three Field (COBRA-TF) code was validated in this study. The dryout and rewetting criteria were introduced into COBRA-TF with the critical liquid film thickness correlation proposed by Chun et al., taking into account the disappearance and reformation of a liquid film. The calculated results were compared with not only the experimental results on critical powers and rewetting velocities measured in single-tube experiments, but also those calculated with the original model in COBRA-TF. It was shown that the model had a good predictive capability for the dryout. Although the dependencies of the calculated rewetting velocities on wall surface temperatures were qualitatively consistent with the experimental results, there were quantitatively significant differences between the experimental and calculated results. The sensitivity analyses on the rewetting predictive capability showed a critical liquid film thickness model for the rewetting, which would consider the rewetting front behaviors, is necessary for an improvement of the rewetting prediction.

摘要

沸水反应堆干燥和再润湿的机械模型在安全评估中是必要的，因为它通常适用于各种燃料组件和更广泛的热工水力条件。本研究验证了基于棒阵列三场冷却液沸腾 (COBRA-TF) 代码中的三场模型的干燥和再润湿机理模型。将干燥和再润湿标准引入到 COBRA-TF 中，其中包含 Chun 等人提出的临界液膜厚度相关性，同时考虑了液膜的消失和重新形成。计算结果不仅与单管实验中测量的临界功率和再润湿速度的实验结果进行了比较，而且还与 COBRA-TF 中原始模型计算的结果进行了比较。结果表明，该模型对干涸具有良好的预测能力。尽管计算出的再润湿速度对壁面温度的依赖性与实验结果在性质上是一致的，但在实验和计算结果之间存在数量上的显着差异。对再润湿预测能力的敏感性分析表明，考虑再润湿前沿行为的再润湿临界液膜厚度模型对于改进再润湿预测是必要的。实验结果和计算结果之间存在数量上的显着差异。对再润湿预测能力的敏感性分析表明，考虑再润湿前沿行为的再润湿临界液膜厚度模型对于改进再润湿预测是必要的。实验结果和计算结果之间存在数量上的显着差异。对再润湿预测能力的敏感性分析表明，考虑再润湿前沿行为的再润湿临界液膜厚度模型对于改进再润湿预测是必要的。