Assessment of RELAP5/MOD3.2 for Steam Condensation Experiments in the Presence of Noncondensibles in a Vertical Tube of PCCS (NUREG/IA-0147)

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Publication Information

Date Published: September 1998

Prepared by:
H. S. Park, H. C. No/KAIST
Y. S. Bang, K. W. Seul, H. J. Kim/KINS

Korea Advanced Institute of Science & Technology 373-1 Kuseong-Dong, Yusong-Ku Taejon, Korea

Korea Institute of Nuclear Safety P.O. Box 114 Yusong, Taejon Korea 305–600

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

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

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Abstract

This report deals with the application of RELAP5/MOD3.2 to condensation experiments in the presence of noncondensable gases in a vertical tube of Passive Containment Cooling System. When steam-noncondensable gas mixture was injected into the vertical tube, steam was condensed on the inner surface of the condensing tube but the noncondensable gas greatly inhibited the condensation of the steam. As the scattering of previous experimental data was large, the present experimental apparatus was set up to get a reliable data on the condensation heat transfer coefficient of the steam-noncondensable gas mixture in a vertical tube. The experimental results show that the condensation heat transfer coefficient increases as the inlet steam-air mixture flow rate increases, the inlet air mass fraction decreases, and the inlet saturated steam temperature decreases. There are two wall film condensation models, the default model and the alternative model, in RELAP5/MOD3.2. After a condensation database was constructed, two models were assessed directly with the data of the database. The experimental apparatus was also modeled with RELAP5/MOD3.2, and simulations were performed for several sub-tests to be compared with the experimental results. The simulation results show that in overall sense the default model of RELAP5/MOD3.2 under-predicts the heat transfer coefficients, but that the alternative model of RELAP5/MOD3.2 over-predicts them throughout the condensing tube. Different from the modeling results of RELAP5/MOD3.1, the change in the number of the nodes for condensing tube has little influence on the simulation results of RELAP5/MOD3.2 both with the default and with the alternative model. From the sensitivity study of input parameters it is also shown that the effects of the coolant flow rate, the inlet coolant temperature and the vented mixture temperature are negligible, but that the effects of the inlet mixture flow rate, the inlet saturated steam temperature and the inlet air mass fraction are significant. Run statistics show that the grind time of the default model is always about 23% higher than that of the alternative model.