Improvement of RELAP5/MOD3.3 Reflood Model Based on the Assessments against FLECHT-SEASET Tests (NUREG/IA-0251)

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Publication Information

Date Published: February 2011

Prepared by:
Tong-Soo Choi, Chang-Hwan Ban
KEPCO Nuclear Fuel
Daejeon, Korea

Dong-Gu Kang, Seung-Hoon Ahn
Korea Institute of Nuclear Safety
Daejeon, Korea

A. Calvo, NRC Project Manager

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

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

Published by:
U.S. Nuclear Regulatory Commission

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Abstract

The reflood model of RELAP5/MOD3.3 was assessed against eight selected FLECHT-SEASET tests. Comparisons of predicted and measured peak cladding temperatures and quench times indicated that the code predicts peak cladding temperatures relatively well. However, rod quenches were predicted to occur too early. To improve the predictability for quench times, we carefully reviewed and modified the wall-to-fluid heat transfer models for the film boiling regime. After the modifications, the same set of eight FLECHT-SEASET tests was simulated again to show that the modifications made in this study improve the code’s predictability not only for quench times but also for peak clad temperatures. The modifications reduced the RMS error in the prediction of peak clad temperatures and quench times from 48.3 to 36.7 K and 85.9 to 32.1 seconds, respectively.