Experimental study on boiling transition under flow-power oscillating condition for hyper ABWR

In the envisioned high-power density core plant, the degradation of stability is concerned that is attributed to the shortening of rod heat conduction time constant upon the dense fuel grid and the increment of pressure drop caused by the wall friction. Under power and flow oscillating conditions, the two-phase flow behavior might be different from that under the steady conditions. Therefore, the thermal-hydraulic test using the rod bundle under oscillating conditions were performed to obtain the verification data for the analysis code. In this paper, the test results were described. It was found that the critical power decreased under flow oscillating conditions compared with under steady conditions, and the power oscillation had a little effect on the critical power. (author)