Critical power of boiling water flows in 33 rod bundle simulating BWR subchannels at elevated pressure conditions

高圧条件下におけるBWRサブチャネルを模擬した33ロッドバンドルにおける沸騰水流の限界出力

和田 裕貴   ; 柴本 泰照 ; 日引 俊詞*

Wada, Yuki; Shibamoto, Yasuteru; Hibiki, Takashi*

An experiment was conducted to measure critical power (CP) for steam-water flows in a short-length 33 rod bundle simulating boiling water reactor (BWR) subchannels at elevated pressure conditions. Two inlet conditions were considered: water single-phase flow and steam-water two-phase flow. The test conditions covered pressures from 2 to 7 MPa, mass fluxes from 250 to 1500 kg/ms, and inlet thermal equilibrium qualities (inlet quality) from 0.0 to 0.6. The measured CP data were compared with existing correlations: the CISE-GE, Biasi, and two types of Bowring correlations for single-phase and two-phase inlet conditions. For single-phase inlet conditions, these correlations somewhat overpredicted the CP data at lower pressure conditions. For two-phase inlet conditions, the Bowring correlation significantly underpredicted the CP data at higher inlet quality or higher mass flux conditions. The Bowring correlation for two-phase inlet conditions was modified using a correction factor formulated by the inlet vapor Reynolds number. The modified Bowring correlation predicted the CP with a mean absolute percentage error of 10.3%. The rod location of the first dryout was also investigated. The first dryout occurred on the center rod at higher mass flux conditions (500 kg/ms) and on the peripheral rod at lower mass flux conditions (500 kg/ms). This dependence on mass flux was influenced by steam-water distributions resulting from entrainment, deposition, and crossflow effects across subchannels. The experimental observations provide useful insights for developing mechanistic models to correlate CP or critical quality with local parameters at the CP location, independent of inlet flow conditions.