United States Nuclear Regulatory Commission - Protecting People and the Environment

RELAP5/MOD3 Horizontal Off-Take Model for Application to Reactor Headers of CANDU Type Reactors (NUREG/IA-0238)

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Publication Information

Manuscript Completed: May 2010
Date Published: June 2010

Prepared by:
Bub Dong Chung, Won Jae Lee, and Moonkyu Hwang /KAERI
Young Seok Bang, In Goo Kim, and Seung Hoon Ahn /KINS

Korea Atomic Energy Research Institute (KAERI)
150-1 Dukjin-Dong, Yuseong-Gu
Daejeon, 305-353, Korea

Korea Institute of Nuclear Safety (KINS)
19 Gusung-Dong, Yuseong-Gu
Daejeon, 305-338, Korea

Antony Calvo, NRC Project Manager

Prepared for:
Division of Systems Analysis
Office of Nuclear Regulatory Research
U.S. Nuclear Regulatory Commission
Washington, DC 20555-0001

Availability Notice


The RELAP5 liquid entrainment and vapor pull-through models of horizontal pipe have been extended for the better prediction of thermal hydraulics in reactor header of CANDU plant. The model of RELAP5 accounts for the phase separation phenomena and computes the flux of mass and energy through an off-take attached to a horizontal pipe when stratified conditions occur in the horizontal pipe. This model is sometimes referred to as the off-take model. The importance of predicting the fluid conditions through an off-take in a small-break LOCA has been well known. In CANDU reactor, off-take model becomes so important that it controls the coolant flow of 95 feeders connected to the reactor header component where the horizontal stratification occurs. The current RELAP5 model is able to treat the only 3 directions junctions; vertical upward, downward, and side oriented junctions, thus improvements for the off-take model is needed for modeling the exact angles. The RELAP5 off-take model has been modified and generalized by considering the geometric effect of branching angles. Verification calculations have been performed for a conceptual blowdown problem in a pipe with different connected angles of branch. The calculated void fraction and mass flow rate of different location of branches shows the validity of implemented model. Experimental works have been also suggested for the further verification and improvement of models.

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