Abstract
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.