Out-containment mitigation of gaseous iodine by alkaline spray in severe accident situation

• Fukushima nuclear accident has shown the need for accident mitigation.
• Preventing the dispersion of radioactive material in atmosphere after severe accident through spray application is suggested.
• The removal efficiency for gaseous iodine by alkaline spray is experimentally studied.
• Removal efficiency is higher at high spray flow rate and pH and lower at high gaseous iodine release rate.
• Iodine volatility is decreased by increasing the sprayed solution temperature.

Radioactive iodine is one of the major constituents among fission products released into the atmosphere from damaged/leaked containment during severe core melt accident. This type of release can create significant impact on human health through thyroid cancer. To prevent the dispersion of such hazardous radionuclide, an emergency response spray system can be deployed outside the conventional physical barrier-the reactor containment. The purpose of this study is to examine the use of spray technology to mitigate the consequence of severe accidents outside the containment. The efficiency of spray method in the removal of the released fission products, in particular, gaseous iodine, was investigated under the hypothetical accident situation. Effects of different parameters such as spray flow rate, spray solution pH and gas release rate were investigated as part of the study. A laboratory-scale experimental system combining spray chamber with a nozzle and gaseous iodine release port was setup to examine the performance of the proposed system. The alkaline (aqueous NaOH.Na2S2O3) solutions of varying pH combined with water were used in the spray chamber to examine capture efficiency for gaseous iodine. The captured and un-captured fractions were determined by the UV–Visible spectroscopy and ion selective electrode method. Experimental results showed that use of proper spray solution pH and flow rate is important in determining iodine removal efficiency. The removal efficiency was also affected by the release rate of gaseous iodine. Temperature variation was also found to have effect on the volatility of the captured iodine in the sprayed solution.