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International Heat Transfer Conference 12

ISSN: 2377-424X (online)
ISSN: 2377-4371 (flashdrive)

Improvements in reactor code RELAP5/MOD2 to predict void distribution and flow instability for low-pressure subcooled boiling flows

Guan Heng Yeoh
School of Mechanical and Manufacturing Engineering University of New South Wales, NSW 2052, Australia; Australian Nuclear Science and Technology Organisation (ANSTO), PMB 1, Menai, NSW 2234, Australia

Jiyuan Tu
School of Engineering, RMIT University, Bundoora, VIC 3083, Australia; Key Laboratory of Ministry of Education for Advanced Reactor Engineering and Safety, Institute of Nuclear and New Energy Technology, Tsinghua University, 30 Shuang Qing Rd. Haidian District, Beijing 100086, China

DOI: 10.1615/IHTC12.4310
6 pages


This paper demonstrates that the empirical models developed for subcooled flow boiling in RELAP5/MOD2 at high pressure are not valid for applications at low pressures. Modifications carried out in RELAP5/MOD2 to include better correlations of the mean bubble diameter and more importantly, the wall heat flux partition model have shown to yield substantial improvements in the model predictions. When compared against experimental data covering a wide range of experimental data, predicted axial void fraction and onset of flow instability profiles follow closely to the measured data. Numerical predictions made through the default subcooled boiling model showed, however, unacceptable margin of error with the experimental data.

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