Review of the potential sources of organic iodides in a NPP containment during a severe accident and remaining uncertainties

Abstract

In case of a severe accident in a nuclear power plant, organic iodides (RI) are one of the volatile iodine species that can be released in the environment thus possibly contributing to the radiotoxicity by inhalation. The formation and decomposition reactions of organic iodides have been studied through various experimental programs whose objectives were to understand their behavior and develop phenomenological models able to predict their volatility. Four potential sources of RI formation have been reviewed: (1) the reactor coolant system (RCS), (2) the containment sump, (3) the paints in the containment and (4) the containment gaseous phase. A review of the knowledge, chemical mechanisms leading to RI formation and decomposition and the remaining uncertainties is performed in order to recommend remaining needed experimental investigations. It has been identified that significant uncertainties remain on RI formation in the gaseous phase through reaction of iodine with volatile organic compounds (VOC, like methane) and that additional data should be obtained to improve its modeling as it can be a significant RI source during days after the beginning of the accident.