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DEVELOPMENT OF JET IMPINGEMENT MODEL TO IMPROVE MARS FOR MIXING BEHAVIOR IN A DOWNCOMER

DOI: 10.1615/ICHMT.2017.CHT-7.530
pages 529-544

Keo Hyoung Lee
Energy System Engineering Department, Seoul National University, Seoul, Korea

Goon Cherl Park
Department of Nuclear Engineering, Seoul National University, Shillim-Dong, Gwanak-Gu, Seoul 151-742, Korea

Résumé

Korea Atomic Energy Research Institute (KAERI) has carried out experiments by utilizing Advanced Thermal-hydraulic Test Loop for Accident Simulation (ATLAS), an integral test facility. Among the experiments, a 50% Direct Vessel Injection (DVI) line break accident was selected for International Standard Problem (ISP) No. 50 exercise. In this exercise, multidimensional phenomena such as Emergency Core Cooling (ECC) water mixing in the upper downcomer observed were highlighted in terms of the prediction capability of the system analysis codes. According to the synthesis on this benchmark problem, it was found that the code's prediction capability of threedimensional downcomer mixing phenomena was not satisfactory in most calculations. In the experiment, the cold ECC water was vigorously mixed with the hot inventory in the downcomer. However, this vigorous and instant mixing was not reproduced appropriately by the system analysis codes including a system analysis code, Multi-dimensional Analysis Reactor Safety (MARS). In the MARS calculation, the momentum flux terms are set to zero for the junction between one-dimensional volume and three-dimensional cell of the MultiD component because the axial and radial velocity are small in the large three-dimensional region. However, if the nozzles are attached to the downcomer with a thin gap, the axial and radial velocity are not small when the incoming orthogonal flow through the nozzles impinges against the downcomer wall. It was required to consider the momentum flux terms induced by the impinging flow, and for that, an appropriate jet impingement model to be incorporated in the system analysis code, MARS, was developed in this study. To develop the jet impingement model, Computational Fluid Dynamics (CFD) calculations were carried out, and the jet impingement model was formulated based on the CFD calculations with various conditions. The momentum flux term by the jet impingement phenomena was correlated with the diameter of the nozzle, downcomer gap size, and the incoming flow velocity. This model was applied to MARS by considering the momentum flux term for the junctions connected to the cell of the MultiD component. The modified MARS incorporating the jet impingement model was validated with the test result from ATLAS, and the analysis result showed good agreements with test data.

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