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

ABSTRACT

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 evaluated using a station blackout 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 dry well into the suppression pool, the revolatilization of the 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.

KEYWORDS:

• source term
• severe accident
• iodine
• pool scrubbing
• revolatilization
• iodine chemistry
• organic iodine
• containment vent
• mass transfer coefficient
• bubble surfaces

Acknowledgments

This study is a part of the collaborative research between the Nuclear Regulation Authority, Japan, and Japan Atomic Energy Agency.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Nomenclature

CsI Cesium iodide

SBO Station blackout

JAEA Japan Atomic Energy Agency

FP Fission product

DF Decontamination factor

S/C Suppression chamber

THALES-2 Severe accident analysis code

KICHE Iodine chemistry simulation code

HVRI High-volatility organic iodides

LVRI Low volatility organic iodides

CV Containment vessel

D/W Drywell

RCIC Reactor core isolation cooling system

RPV Reactor pressure vessel

SRV Safety relief valve

Pe Peclet number [−]