United States Nuclear Regulatory Commission - Protecting People and the Environment

TRACE5 Assessment of 100% Direct Vessel Injection Line Break in ATLAS Facility (NUREG/IA-0425)

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Publication Information

Manuscript Completed: October 2013
Date Published: March 2013

Prepared by:
Byung-Gil Huh, Dong-Gu Kang, Chae-Yong Yang, Seung Hoon Ahn
Korea Institute of Nuclear Safety
Daejeon, Korea

Ki-Yong Choi
Korea Atomic Energy Research Institute
Daejeon, Korea

A. Calvo, NRC Project Manager

Prepared as part of:
The Agreement on Research Participation and Technical Exchange
Under the Thermal-Hydraulic Code Applications and Maintenance Program (CAMP)

Published by:
Office of Nuclear Regulatory Research
U.S. Nuclear Regulatory Commission
Washington, DC 20555-0001

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The calculations using TRACE V5.0 patch2 code were conducted for 100% DVI line break test of ATLAS which is the first domestic standard problem (DSP-01). In the steady state conditions, the errors between the calculated and measured values are acceptable for most primary/secondary system parameters. From the transient calculations, the predicted sequence of events occurred some seconds later than that of experiment due to slow depressurization of the primary side after break. Before the LSC, the code could not predict well the behavior of downcomer and core collapsed water levels due to the under-prediction of the discharged mass and high flow rate returned to core from hot leg. After the LSC, the downcomer and core collapsed water levels drop rapidly and the code predicts relatively well the trend of downcomer and core water level. All RCPs suction legs or loop seals are cleared completely and suddenly. The predicted cladding temperature generally agrees well with the experiment except the peaking behavior. In the sensitivity studies, if the discharging mass increases arbitrarily, the downcomer and core water level before SIP injection shows better prediction result than that of base case. However, except for this, the overall behavior for main parameters shows the bad prediction results. For the effect of flow restriction from hot leg using the CCFL model, the predicted core water level was not significantly decreased compared to the base case. In conclusions, TRACE code has good capabilities to simulate the 100% DVI line break test of ATLAS. However, TRACE code including the choked flow and CCFL models needs to be improved and more detailed modeling is needed to predict more accurate results.

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