Analysis of coupled nuclear/thermal instabilities of two-phase flows in parallel boiling channels

Book · Sat Jun 01 04:00:00 EDT 1996

OSTI ID:234300

Uehiro, M; Rao, Y F; Fukuda, K ^[1]

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1. Kyushu Univ., Fukuoka (Japan). Dept. of Nuclear Engineering

An analytical model is proposed to study the two-phase flow instabilities of in-phase and out-of-phase modes in boiling water reactors. This model, developed for parallel boiling channels with the void-reactivity feedback loop, takes into consideration the interaction between channels with different void fraction variations by modeling the diffusion of neutron. Linear stability analysis in the frequency domain is performed to reveal the mechanisms of the instability. Stability boundaries and flow oscillation modes for the system are obtained. In the case of parallel two channels, two types of stability boundaries are found to exist on the stability map; one for the instability of the in-phase mode and the other for that of the out-of-phase mode respectively. For a certain range of the void-reactivity coefficient, the void-reactivity feedback loop is found to be unstable in a certain region on the stability map, which has an effect on the stability of the in-phase mode. Froude number is important to the stability of the system, especially to the instability of the in-phase mode. The interaction between channels affects the instability of the out-of-phase mode. The results are also obtained for the case of three and four channels. The channels having stronger interaction between them are more likely to oscillate in-phase with each other, while those having weaker interaction are more likely to oscillate out-of-phase with each other.

• OSTI ID: 234300
• Report Number(s): CONF-960306--; ISBN 0-7918-1226-X
• Country of Publication: United States
• Language: English

Related Subjects

21 SPECIFIC NUCLEAR REACTORS AND ASSOCIATED PLANTS
BWR TYPE REACTORS
HEAT TRANSFER
HYDRAULICS
MATHEMATICAL MODELS
REACTOR CHANNELS
REACTOR STABILITY
THEORETICAL DATA
TWO-PHASE FLOW