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Countercurrent gas liquid flow in a PWR hot leg during reflux condensation MURASE Michio1, MINAMI Noritoshi2, NAGAE Takashi2, and TOMIYAMA Akio3   1. Institute of Nuclear Safety System, Inc., 64 Sata, Mihama-cho, Mikata-gun, Fukui 919-1205, Japan (murase@inss.co.jp) 2. The Kansai Electric Power Company, Inc., 13 Yokota 8, Goichi, Mihama-cho, Mikata-gun, Fukui 919-1141, Japan(minami.noritoshi@c4.kepco.co.jp, nagae.takashi@a5.kepco.co.jp) 3. Department of Mechanical Engineering, Kobe University, Rokkodai-cho 1-1, Nada, Kobe, Hyogo 657-8501, Japan (tomiyama@mech.kobe-u.ac.jp) Abstract:The loss-of-RHR (residual heat removal systems) during mid-loop operation is one of the relatively high-risk events in pressurized water reactors. In order to increase reliability of transient analyses, the code scaling, applicability, and uncertainty methodology has been applied to evaluate the loss-of-RHR event, and a PIRT (phenomena identification and ranking table) for the event was developed. Based on the PIRT, important thermal-hydraulic behaviors during a loss-of-RHR eventhave been evaluated, and major results are summarized in thisreport. Reflux condensation by a steam generator is expectedto be one of substitute methods of RHR cooling. In that case, countercurrent gas-liquid flow in the hot leg, which consists of horizontal, elbow and inclined sections, affectsthe reactor cooling systempressure and coolant level in the core.In order to evaluate flow patterns and CCFL (countercurrent flow limitation) characteristicsin the hot leg, therefore, air-water experiments using small-scale models were carried out, and numerical simulations were conducted using a two-fluid modelin FLUENT6.3.26. The calculated flow patterns and CCFL characteristics agreed well with the data. Flow patterns in the hot leg, which were split by the CCFL curve, were stratified flow without CCFL and wavy mist flow under CCFL conditions.   Keyword:loss-of-RHR; reflux condensation; countercurrent flow; PWR hot leg
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