- 學位論文
LOFT設施L2-5測試之RELAP5-3D/K爐心與降流區多維度模擬結果與分析
Phenomenal Investigations of the Thermal-hydraulic Responses of Multi-Dimensional simulation and Modeling in Core and Downcomer during the L2-5 Test of LOFT Using RELAP5-3D/K
摘要
本研究利用 RELAP5-3D/K 模擬 LOFT (Loss of Fluid Test) 設施 L2-5 冷卻水流失事故 (Loss of Coolant Accident, LOCA) 測試。分析時，爐心和降流區 (Downcomer) 元件立體化的模擬採用程式之多維度元件 (Multi-Dimensional Component)。期望量化以多維度元件模擬爐心和降流區，可以增加冷卻水流失事故分析的安全餘裕 (Safety Margin)，以利於提升核電廠的功率。分析結果顯示，採用 RELAP5-3D立體化多維度元件模擬爐心與降流區所預測之燃料護套溫度較原先一維度案例低約 180℉。爐心立體化會造成沖放期 (Blowdown) 之燃料護套尖峰溫度較未立體化的分析結果為高。立體化的爐心可以觀測到煙囪效應，即冷卻水會自較冷的區域進入溫度較高的熱通道，有效地降低事故中的護套最高溫度。多維度降流區模擬所預測之降流區橫向流動 (Cross Flow) 情形較一維度降流區模擬結果低，亦即有較多之注入的緊急冷卻水可以由降流區進入壓力槽底部區間，而提早進入再泛水階段 (Reflood);提早進入再泛水階段亦可降低冷卻水流失事故之燃料棒護套尖峰溫度。
並列摘要
In this study, RELAP5-3D/K code is used to simulate the L2-5 test of Loss of Fluid Test (LOFT) facility. RELAP5-3D is a multi-dimensional reactor system thermal-hydraulic analysis code. In the present simulation, the core and downcomer are modeled as inconnected three dimensional components. The results of the simulation are compared with the results of the RELAP5-3D/K one-dimensional analysis. The purpose of this study is to qualify the margin of the safety analysis relatd to the design criteria of loss of coolant accident. The results show that the peak cladding temperatures (PCT) as predicted by the 3-D model of core and downcomer is about 180℉ lower than that of the 1-D model of the corresponding components. The results show that the predicted rise of cladding temperature in the blowdown phase of accident is higher in the case that core is simulated three-dimensionally. It is also demonstrated that the chimney effect in the 3-D core simulation is stronger than the case of 1-D simulation of core, which tends to lower the PCT in LOCA analysis. Chimney effect is referred as the coolant flow rate in a hot channel will increase by sucking in the coolant from nearby colder region. Modeling the downocmer three-dimensionally has a tendency to reduce the predicted crossflow in the annular region surrounded the core barrel. It implies that large amount of injected emergency cooling water will flow downward into the lower plenum. The initiation of core reflooding will be earlier for the core with three-dimensional simulation of downcomer.