Coolant mixing in a pressurized water reactor:: Deboration transients, steam-line breaks, and emergency core cooling injection
Coolant mixing in a pressurized water reactor:: Deboration transients, steam-line breaks, and emergency core cooling injection
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DOI：
10.13182/nt03-a3396
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发表时间：
2003-07-01
影响因子：
1.5
通讯作者：
Weiss, FP
中科院分区：
文献类型：
--
作者：
Prasser, HM;Grunwald, G;Weiss, FP
压水堆入口硼浓度或冷却剂温度扰动引起的反应堆瞬态取决于反应堆压力容器内的混合。通过与未受影响回路冷却剂和RPV水存量的湍流混合，初始陡梯度部分减小。然而，假设反应堆下降管和下部增压室中存在理想混合，导致反应性插件不切实际地变小。理想混合和完全不混合之间的不确定性太大，无法接受安全分析。实际上，发生部分混合。为了进行实际的预测，有必要研究PWR复杂几何结构中三维流场的混合。为此，建立了德国PWR KONVOI的1：5比例模型[Rossendorf混合模型（ROCOM）设施]。与其他实验相比，重点是广泛的测量仪器和设施的最大灵活性，以涵盖尽可能多的不同测试场景。使用特殊的电极-网格传感器与盐示踪技术一起提供了在空间和时间上具有高分辨率的降液管和堆芯入口内的扰动分布。特别是降液管的测量获得了有关混合现象的详细信息。获得的数据用于支持代码开发和验证。调查的设想如下：（a）在多个冷却剂回路中的稳态流动，其中一个运行回路中具有温度或硼浓度扰动，（B）在一个或多个回路中具有随时间变化的流率的瞬态流动情况，例如在其中一个回路中具有脱硼段塞的泵启动情况或在沸腾冷凝器模式操作之后自然循环的开始，以及（c）由大密度梯度引起的重力驱动流动，例如，通过ECC注入冷段，混合进入RPV的冷应急堆芯冷却（ECC）水。实验结果表明，在堆芯入口处存在典型的浓度和温度分布的不完全混合，这强烈地依赖于边界条件。计算流体动力学计算结果与实验结果吻合较好。
The reactor transient caused by a perturbation of boron concentration or coolant temperature at the inlet of a pressurized water reactor (PWR) depends on the mixing inside the reactor pressure vessel (RPV). Initial steep gradients are partially lessened by turbulent mixing with coolant from the unaffected loops and with the water inventory of the RPV Nevertheless the assumption of an ideal mixing in the downcomer and the lower plenum of the reactor leads to unrealistically small reactivity inserts. The uncertainties between ideal mixing and total absence of mixing are too large to be acceptable for safety, analyses. In reality, a partial mixing takes place. For realistic predictions it is necessary to study the mixing within the three-dimensional flow field in the complicated geometry of a PWR. For this purpose a 1:5 scaled model [the Rossendorf Coolant Mixing Model (ROCOM) facility] of the German PWR KONVOI was built. Compared to other experiments, the emphasis was put on extensive measuring instrumentation and a maximum of flexibility of the facility to cover as much as possible different test scenarios. The use of special electrode-mesh sensors together with a salt tracer technique provided distributions of the disturbance within downcomer and core entrance with a high resolution in space and time. Especially, the instrumentation of the downcomer gained valuable information about the mixing phenomena in detail. The obtained data were used to support code development and validation. Scenarios investigated are the following: (a) steady-state flow in multiple coolant loops with a temperature or boron concentration perturbation in one of the running loops, (b) transient flow situations with flow rates changing with time in one or more loops, such as pump startup scenarios with deborated slugs in one of the loops or onset of natural circulation after boiling-condenser-mode operation, and (c) gravity-driven flow caused by large density gradients, e.g., mixing of cold emergency core cooling (ECC) water entering the RPV through the ECC injection into the cold leg. The experimental results show an incomplete mixing with typical concentration and temperature distributions at the core inlet, which strongly depend on the boundary conditions. Computational fluid dynamics calculations were found to be in good agreement with the experiments.