5×5全长棒束组件通道过冷沸腾工况下均匀与非均匀轴向功率分布对比分析

Comparison of Subcooled Flow Boiling in a Full-Length 5×5 Rod Bundle between Uniform and Non-Uniform-Axial Power Distribution

压水堆燃料组件结构采用正方形排列的棒束形式,本文采用计算流体力学(CFD)方法对5×5全长棒束中过冷沸腾传条件下的均匀轴向功率分布(U-APD)和非均匀轴向功率分布(Non-U-APD)工况进行了热工水力性能对比分析。分析结果表明,所采用的壁面沸腾模型、相间作用力界面力模型和气泡尺寸分布模型能够较好地预测5×5全长棒束组件通道过冷沸腾工况的传热过程。通过对比发现Non-U-APD工况下,棒束通道内平均空泡份额起始点较均匀加热工况提前,增长速度较U-APD工况更快。在子通道平均值方面,Non-U-APD工况下角通道末端平均空泡份额要高于U-APD工况,而中心通道基本相同。Non-U-APD工况下,在第5个和第6个搅混格架(MVG)下游,文中所分析的角通道和中心通道的液相质量流速逐渐低于U-APD工况。

The structure of PWR fuel assembly is in form of square rod bundle.In this study,Computational Fluid Dynamics(CFD)method is verified to compare thermal-hydraulic(T-H)characteristics between Uniform-Axial Power Distribution(U-APD)and Non-Uniform-Axial Power Distribution(Non-U-APD)under subcooled flow boiling condition.It is shown that CFD method has the ability to achieve a goog agreement on the void fraction prediction while reasonalbe wall boiling model,interface force model and bubble size distribution model are implemented.The comparison shows that the onset of significant void point of Non-U-APD bundle appear in advance and the averaged void of Non-U-APD along the axial direction has a more higher increasing rate rather than that of the U-APD.At the end of the heated length,the corner channel-avereged void of Non-U-APD is higher than that of the U-APD while the central channels are nearly the same,although the same inlet condition and heated power is applied in both the simulation.At the downstream of 5th and 6th Mixing Vane Grid(MVG),the liquid mass flux of corner and central channel in Non-U-APD are lower than that of U-APD due to the phase change.