Coherence of accelerated water bulk induced by rapid air injection

Experiment of pressurized air injection into water-filled vessel with inner diameter 2 m was examined, to evaluate magnitude of water hammer induced by strike of accelerated water bulk due to steam explosion in ex-vessel coolant pool. And correlation of the bulk movement observed in past and this experiment, predicted water hammer pressure in the vessel. And, index to investigate degree of coherence, which affects the magnitude, was suggested and applied to two-dimensional analysis with two components. Two conclusions are highlighted. (1) Experiment of pressurized air injection into water filled vessel with inner diameter, 2 m, declared scale independent factor and scale effect of water bulk acceleration, compared with past experiments by smaller vessel. And expected water hammer pressure in the vessel was estimated based on the experiments. (2) Relative difference between velocity of bulk and that of bulk unit as vector was suggested as index to evaluate coherence of water bulk movement quantitatively. And application of the index to result of analysis with RELAP5-3D indicated this index was available and influence of growing bubble shape to the coherence was evidenced. (authors)