Improvements of RELAP5/MOD3.2.2 Models for the CANDU Plant Analysis (NUREG/IA-0189)

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Publication Information

Date Published: October 2000

Prepared by:
B.D. Chung, W.J. Lee, KAERI
Y.S. Bang, KINS

Korea Atomic Energy Research Institute
P.O. Box 105
Yusung, Daejon, 305-600

Korea Institute of Nuclear Safety
P.O. Box 114
Yuseong-Gu, Taejon, 305-600

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

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

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The main purpose of this study is to develop a thermal hydraulic auditing analysis code For CANDU reactor by extending the model of current RELAP5/MOD3, which have been used for a long time as an auditing analysis tool of Light Water Reactors (LWR). The major thermal hydraulic phenomena for the key CANDU events and the modeling limitation of the current RELAP5/MOD3 for CANDU applications are based on the previous study oil the applicability of RELAP5 code to the CANDU-type plants. The seven models are improved: the CANDU fuel channel heat transfer model; the horizontal flow regime model; the digital control model; ANS94-4 decay heat model; Moody critical model; motor operative valve model; and pressurizer spray model. The models are improved and developed on generic base, thus, they also could be applicable to PWR. Especially, the plutonium contribution to decay heat can be considered by the ANS94-4 decay heat model. The Moody critical flow model using a heavy water property can provide an additional capability to evaluate the conservative break flow in CANDU system. Simulation of different rate of opening and closing the motor valve is now possible when calculating the liquid relief vale behavior during transient. And the new pressurizer spray model can be used for evaluating the droplet size effect on the condensation. All of those improvements are verified through some assessments with simple conceptual problems and Marviken critical flow test. The new code is based on the RELAP5/MOD3.2.2 gamma version, and written in FORTRAN90 language.

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