Experimental and Numerical Investigation of Boron Dilution Transients in Pressurized Water Reactors
Experimental and Numerical Investigation of Boron Dilution Transients in Pressurized Water Reactors
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DOI：
10.13182/nt03-a3353
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发表时间：
2003-01
影响因子：
1.5
通讯作者：
R. Hertlein;K. Umminger;S. Kliem;H. Prasser;T. Höhne;F. Weiss
中科院分区：
文献类型：
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作者：
R. Hertlein;K. Umminger;S. Kliem;H. Prasser;T. Höhne;F. Weiss
摘要近年来，在压水反应堆（PWR）安全分析中，人们越来越关注可能导致反应性瞬变的硼稀释事件。在低硼水进入堆芯之前，将低硼水与硼含量较高的环境冷却剂混合提供了重要的缓解机制。需要实验的支持，以验证计算工具，以分析低硼水的混合。实验是在德国的三个试验设施中进行的，即上集气室试验设施（UPTF）、Primärkreislauf（PKL）和Rossendorf冷却剂混合模型（ROCOM）。相关的PKL和UPTF试验集中在回流冷凝器模式和自然循环重启的小破口冷却剂损失事故（SBLOCA）场景。这两个试验设施代表了典型的西方式压水堆，由西门子/KWU（现为德国的法马通ANP）运营。在PKL系统试验设施（体积1：145，高度1：1）中研究自然循环的再启动时，UPTF试验涉及冷管段、反应堆压力容器（RPV）下降管和下部压力通风系统（所有这些部件均为全尺寸模型）中不同硼浓度的水流混合。来自PKL试验设施的结果表明，在假设的SBLOCA具有回流冷凝相的情况下，自然循环不会在所有回路中同时启动。这意味着，在回流冷凝器运行模式下，可能积聚在泵密封中的冷凝液团将在不同的时间点到达RPV。UPTF试验表明，在RPV下降管中，具有不同硼浓度的水流几乎是理想的混合。ROCOM试验设备是按1：5的线性比例建造的，用于研究德国KONVOI型压水堆反应堆压力容器中各种流动条件下的冷却剂混合现象。试验结果集中在第一台反应堆冷却剂泵启动过程中脱硼水段塞的混合。基于实验确定的脉冲响应，半解析模型描述的KONVOI RPV内的冷却剂混合已经开发。在第一反应堆冷却剂泵启动过程中，假定硼稀释事件的计算已经通过半解析模型和计算流体动力学代码CFX-4独立进行。半解析模型能够描述与时间相关的行为，在每个燃料元件的位置在一个很好的协议与实验。所有主要的混合效应，在实验中观察到的，也重现CFX计算。
Abstract Within the pressurized water reactor (PWR) safety analyses, attention has increasingly focused in recent years on boron dilution events that could potentially lead to reactivity transients. Mixing of the low-boron water with the ambient coolant of higher boron content provides an important mitigation mechanism before the low-boron water enters the core. Experimental support is needed to validate the computational tools to be applied to analyze the mixing of the low-boron water. Experiments were performed in the three test facilities—the Upper Plenum Test Facility (UPTF), the Primärkreislauf (PKL), and the Rossendorf coolant mixing model (ROCOM)—in Germany. The relevant PKL and UPTF tests were focused on small-break loss-of-coolant accident (SBLOCA) scenarios with reflux-condenser mode and restart of natural circulation. The two test facilities represent a typical western-type PWR and are/were operated by Siemens/KWU now Framatome ANP in Germany. While the restart of natural circulation was investigated in the PKL system test facility (volume 1:145, height 1:1), the UPTF experiments dealt with the mixing of water flows with different boron concentration in the cold legs, reactor pressure vessel (RPV) downcomer, and the lower plenum (all these components were full-scale models). The results from the PKL test facility demonstrate that in case of a postulated SBLOCA with reflux condensation phase, natural circulation does not start up simultaneously in all loops. This means that slugs of condensate, which might have accumulated in the pump seal during reflux-condenser mode of operation, would reach the RPV at different points in time. The UPTF tests showed an almost ideal mixing of water flows with different boron concentration in the RPV downcomer. The ROCOM test facility has been built in a linear scale of 1:5 for the investigation of coolant mixing phenomena in a wide range of flow conditions in the RPV of the German KONVOI-type PWR. The test results presented are focused on the mixing of a slug of deborated water during the startup of the first reactor coolant pump. Based on experimentally determined pulse responses, a semianalytical model for the description of coolant mixing inside the KONVOI RPV has been developed. Calculations for a presumed boron dilution event during the startup of the first reactor coolant pump have been carried out by means of the semianalytical model and independently by means of the computational fluid dynamics code CFX-4. The semianalytical model is able to describe the time dependent behavior of the deboration front at each fuel element position in a good agreement with the experiment. All main mixing effects, observed in the experiment, are also reproduced by the CFX calculation.