United States Nuclear Regulatory Commission - Protecting People and the Environment

Dispersed Flow Film Boiling: An Investigation of the Possibility to Improve the Models Implemented in the NRC Computer Codes for the Reflooding Phase of the LOCA (NUREG/IA-0042)

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Publication Information

Date Published: August 1992

Prepared by:
M. Andreani1, G. Yadigaroglu1,2

Paul Scherrer Institute
Swiss Federal Institute of Technology (ETH)
CH-8092 Zuerich

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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1 Swiss Federal Institute of Technology (ETH), CH-8092 Zuerich, Switzerland
2 Thermal-Hydraulics Laboratory, CH-5232 Villigen PSI, Switzerland


Dispersed Flow Film Boiling is the heat transfer regime that occurs at high void fractions in a heated channel. The way this heat transfer mode is modelled in the NRC computer codes (RELAP5 and TRAC) and the validity of the assumptions and empirical correlations used is discussed. An extensive review of the theoretical and experimental work related with heat transfer to highly dispersed mixtures reveals the basic deficiencies of these models: the investigation refers mostly to the typical conditions of low rate bottom reflooding, since the simulation of this physical situation by the computer codes has often showed poor results. The alternative models that are available in the literature are reviewed, and their merits and limits are highlighted. The modifications that could improve the physics of the models implemented in the codes are identified.

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