Extensive numerical simulations of isothermal air/water flow in an idealised model of the header/feeder system of a CANDU nuclear reactor were performed under conditions that are relevant to postulated loss-of-flow accidents (LOFA) and small-break loss-of-coolant accidents (SBLOCA). Following our recent work, in which the present CFD methodology was validated against in–house experimental results, we used the volume of fluid method to solve the system of multi-phase flow governing equations and the detached eddy simulation model to close this system in turbulent flow. We computed the steady-state liquid flow distribution to the different feeders for different combinations of inlet water and air mass flow rates and different mass extraction rates, namely, values of the ratio of the leak liquid mass flow rate and the inlet liquid mass flow rate, and found that, in general, this distribution tends to become more uniform as the inlet flow rate of either the liquid or the gas increases. A “free surface” separating air above from an air–water mixture below was observed in many cases, generally moving downward with decreasing inlet flow rates and increasing mass extraction ratio. The liquid distribution to non-leaking feeders was not affected significantly by a change in the location of the leak. Time histories of flow properties following a step change in boundary conditions showed that the change of flow rate through each feeder can be represented by a first-order model with a time constant of roughly 1 s. As part of the validation of the present CFD analysis, the computed local pressure loss coefficient for a leaking feeder was found to be in excellent agreement with previously published experimental results. The static pressure loss across the header, estimated from available semi-empirical two-phase flows models was, in most cases, found to be within 10% of the CFD solution.

在与假定的流量损失事故（LOFA）和小断裂流量损失有关的条件下，对CANDU核反应堆的集管/进料系统的理想模型进行了等温空气/水流的广泛数值模拟。冷却液事故（SBLOCA）。继我们最近的工作（其中针对内部实验结果验证了当前的CFD方法）之后，我们使用了流体体积法来求解多相流控制方程组，并采用了独立的涡流仿真模型来在湍流中封闭该系统流动。对于进水和空气质量流量的不同组合以及不同的质量提取率，我们计算了到不同进料器的稳态液体流量分布，即泄漏液体质量流量与入口液体质量流量之比的值，并且发现，通常，随着液体或气体的入口流速增加，该分布趋于变得更均匀。在许多情况下，观察到“自由表面”将上方的空气与下方的空气-水混合物分隔开，通常随着入口流速的降低和质量提取比的增加而向下移动。泄漏位置的变化不会显着影响分配给非泄漏进料器的液体。边界条件发生阶跃变化后，流动特性的时间历史表明，通过每个进料器的流量变化可以用时间常数约为1 s的一阶模型表示。作为当前CFD分析验证的一部分，计算得出的泄漏给料机的局部压力损失系数与先前发表的实验结果非常吻合。在大多数情况下，根据可用的半经验两相流模型估算的集管两端的静压损失在CFD解决方案的10％以内。