压力容器环形下降段内含硼溶液流动混合特性的数值模拟分析

发生堆芯应急冷却安注时，外部注入的含硼冷却剂与稀释水团将在环形下降段内发生混合，含硼冷却剂与稀释水团混合不均匀可能导致堆芯重返临界。本文基于Fluent 18.0对环形下降段内的流动混合特性进行分析。横截面的速度分布显示，入口截面的水平方向速度随周向位置的增加而显著衰减，而环形下降段下部区域横截面的速度分布趋于平缓；三维流线图显示，流体进入压力容器后在环腔内壁发生剧烈碰撞，随后绕环形下降段呈放射状流动。通过自定义硼酸溶液，并模拟其与稀释水团之间混合，数值结果与相关的实验研究结果较为一致；三维浓度分布显示，雷诺数较低时入口硼酸溶液将停滞在环形下降段上部空间，增加入口雷诺数有利于搅混均匀。

Numerical Simulation of Flow and Mixing Characteristics between Borated Coolant and De-borated Slug in Reactor Annular Down-comer

In the emergency core cooling situation, the mixing between external borated coolant and the de-borated slug occurred in the reactor annular down-comer is concerned, as heterogeneous mixing may lead re-critical. In this paper, the flow and mixing characteristics in the reactor annular down-comer was analyzed using Fluent 18.0. At the entrance cross section, velocity decreases as azimuthal angle increases due to the collision against the wall. At lower cross section, the velocity gradient becomes subdued. The three-dimensional streamline indicates that the entrance fluid spreads around the cylinder radially. The mixing between the boric solution and the water was conducted and the concentration distributions at cross sections in the experimental measurement and the CFD (computational fluid dynamics) simulation are consistent. From the time evolution of three-dimensional concentration, the boric acid solution stagnates in the upper space of the annular down-comer when inlet Reynolds number is low. Increasing inlet Reynolds number is favorable to uniform mixing.