United States Nuclear Regulatory Commission - Protecting People and the Environment

Assessment of RELAP5/MOD2 Using LOCE Large Break Loss-of-Coolant Experiment L2-5 (NUREG/IA-0045)

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Publication Information

Date Published: April 1992

Prepared by:
Lainsu Kao, Kuo-Shing Liang, Jeng-Lang Chiou,
Lih-Yih Liao, Song-Feng Wang, Yi-Bin Chen

Institute of Nuclear Energy Research
P.O. Box 3, Lung-Tan 32500
Taiwan, Republic of China

Prepared as part of:
The Agreement on Research Participation and Technical Exchange
under the International Thermal-Hydraulic Code Assessment
and Application Program (ICAP)

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

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Abstract

Comprehensive analysis with RELAP5/MOD2 is performed to predict the LOFT transient thermal-hydraulic responses for the LOCE L2-5 test. Experiment L2-5 is planned to simulate a hypothetical LOCA which results from a 200% double-ended offset shear break in a cold-leg of a typical pressurized water reactor. The test simulation begins with break initiation and subsequent blowdown, and continues through lower plenum refill, core reflood, and terminates with corewide quench. The nominal best estimate calculation results indicate that the cladding temperature continuously increases during blowdown phase without an early fuel-rod rewet (blowdown quench). A peak cladding temperature of 1,112 K, which is very close to the experimental data, is calculated at 7.0 s, and fuel rods are predicted to be quenched at 57 s after the break initiation. Sensitivity analyses of the test simulation with respect to various code input uncertainties, including broken loop initial temperature, cross-flow junction, discharge coefficient, accumulator condition, reflood fine mesh number, form loss coefficient, fuel gap dimension, and reflood option are performed to investigate their impacts on the calculation results. Scenario study on the pump behavior is analyzed to see whether the blowdown quench could be resulted from the RELAP5/MOD2 model. The effect of the uncertainty of Biasi CHF on the cladding temperature response is also studied.

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