LBB泄漏率计算与热力学非平衡效应影响评估

裂纹泄漏率计算是破前漏（LBB）在核电站管道和设备上应用的基础。在Fauske模型基础上，整个裂纹内流体流动假设为等焓过程且充分考虑摩擦效应对裂纹临界泄漏率的影响，利用Mathcad计算得到了管道裂纹两相泄漏率，与已有文献中实验数据进行对比，将其发展成为可准确计算裂纹泄漏率的计算机程序。同时根据两相流动不平衡理论，对模型进行热力学不平衡参数影响修正。结果表明：随裂纹长径比(L/D)增大，两相泄漏率减小；随裂纹入口滞止压力增大，两相泄漏率增大；裂纹入口流体过冷度增大，两相泄漏率增大，数学模型计算结果与实验结果趋势一致，但忽略热力学非平衡效应，数学模型计算得到的临界流量小于实验流量。对于热力学不平衡参数修正后模型，模型计算得到的结果均与实验数据符合很好，故由修正后模型编制的Mathcad程序可完成裂纹泄漏率的准确计算，为LBB在核电站管道上的应用提供基础。

LBB Leak Rate Calculation and Thermodynamic Non-equilibrium Effect Evaluation

Crack leak rate calculation is the foundation of leak before break (LBB) technology application in nuclear power plant pipe system. The crack leak rate calculation results were obtained with isenthalpic flow assumption based on Fauske two-phase critical model with considering the friction effect. A Mathcad code was developed to calculate crack leak rate. According to non-equilibrium two-phase flow theory, the modification of the model taken into account thermodynamic non-equilibrium effect on the crack leak rate was also implemented. All the calculation results were compared with experimental data. The results show that the two-phase crack leak rate decreases with the increase of crack length to diameter ratio L/D, but increases with either the stagnation pressure or the fluid sub-cooling at the crack entrance. The mathematical model can predict consistent trends with experimental data, but the calculated critical flow rates with the model omitting thermodynamic non-equilibrium effect are lower than experimental data. While considering crack flow as thermodynamic non-equilibrium, the agreement between the calculated results and experimental data is very good, showing that the Mathcad code with modified model made in the paper can be used to calculate the crack leak rate accurately and provide application foundation of LBB in nuclear plant pipe system.