Revolatilization of iodine by bubbly flow in the suppression pool during an accident

Nanjo, Kotaro; Ishikawa, Jun ; Sugiyama, Tomoyuki ; Pellegrini, M.*; Okamoto, Koji*

To appropriately evaluate the amount of radioactive iodine released into the environment, we extended the current pool scrubbing model to consider revolatilization at bubble surfaces due to bubbly flow generated in the suppression pool, and the effect of revolatilization by bubbly flow was quantitatively evaluated using a station black out sequence in this work. Gaseous iodine species are produced in the suppression pool in an accident. They are gradually released from the pool surface, but when a large amount of gas flows from the drywell into the suppression pool, the revolatilization of gaseous iodine dissolved in the pool water is promoted by bubbly flow. The results of this study indicated that the release amount of iodine immediately after suppression chamber (S/C) vent operation increased by up to 134 times when considering the revolatilization effect associated with bubbly flow. These results were due to the increase in the gas-liquid interfacial area at bubble surfaces and the overall mass transfer coefficients under two-phase flow conditions due to bubbly flow. It was shown that caution is required for early S/C vent operation.