COSINE多相场子通道程序格架模型开发与评估

Development and Assessment of Spacer Grid Model in COSINE Multiphase Subchannel Code

格架模型作为子通道程序中的重要模块,对大破口事故中再淹没工况下热工水力学参数的计算具有重要意义,COSINE多相场子通道程序包括格架的压降模型、壁面传热增强模型、相间传热增强模型、液滴破裂模型、格架再湿模型、格架温度模型等。本研究选取棒束传热实验装置(RBHT)典型再淹没工况进行建模分析,评估格架模型对再淹没工况下热工水力学参数计算的影响。计算结果表明:采用格架模型后,程序计算的通道换热能力显著增强,格架模型可提高计算的骤冷前沿速度,加快包壳冷却及蒸汽温度的下降,并显著降低燃料包壳峰值温度(PCT),程序计算结果与实验数据符合良好;程序计算的格架温度变化趋势与实验值符合良好;程序中采用的液滴破裂模型可模拟格架前后的液滴尺寸变化,可精准预测液滴直径散射比;程序预测的格架附近液滴速度随时间的变化与实验趋势符合良好。COSINE多相场子通道程序中采用的格架模型可有效提高程序对再淹没工况下热工水力学参数的预测能力,程序中采用的格架模型是有效且合理可靠的。

The spacer grid models are important models for simulating the thermal-hydraulics phenomena during reflooding process.The spacer grid pressure drop model,wall heat transfer enhancement model,interfacial heat transfer enhancement model,droplet breakup model,spacer grid re-wet model and grid temperature model are integrated in COSINE multiphase sub-channel code.In this paper,the typical rod bundle heat transfer(RBHT)reflooding tests were selected to assess the spacer grid model in the code.The calculation results show that the spacer grid models can significantly enhance the code predicted heat transfer capacity,accelerate the quench rate and reduce the peak cladding temperature(PCT)during the reflooding process,and the calculated results are in good agreement with the experimental measurements.In addition,the deviation of the PCT predicted by the code is reduced from 10%to 7%due to the adoption of the spacer grid models.The spacer grid models have the ability to enhance the interfacial heat transfer between vapor and droplet,therefore the calculated results with the spacer grid models show a significantly faster decrease in vapor temperature than that without the spacer grid models.And the calculated vapor temperatures with spacer grid models are in good agreement with the experimental measurements.The trend of the code predicted spacer grid temperature agrees well with the experimental results,but the code predicted spacer grid temperature is slightly higher than the experimental measurements.Furthermore,the early wetting of the temperature probe located on the spacer grid in the experiment results in a rapid decrease in the spacer grid temperature,however,the code predicted spacer grid temperature does not show as sharp a decrease as the experimental results due to the interpolation method in the calculation of the spacer grid temperature.The spacer grid models adopted in the code can simulate the breakup of droplets across the spacer grid,the diameter ratio of the shattered droplets predicted by the code is in good agreement with the experimental measurements,and the calculation results of the Cheung model are more accurate than those of the Paik model in the test case 7151.In addition to this,the code can predict the trend of droplet velocity near the spacer grid during reflooding process,but the calculated droplet velocity decreases significantly faster than the experimental measurements,and it needs more work in future.In general,the calculated results with the spacer grid models are in good agreement with the experimental results,and the spacer grid models adopted in the code are reasonable and reliable.