Simulation of gaseous phase, liquid phase, and mass transfer reactions of iodine species in the containment under severe accident conditions

Iodine is considered to be released during Beyond Design Basis Accident as well as postulated Design basis accident (DBA) like Loss of Coolant Accident. The extent of release depends on the fuel heat up under these scenarios. The released iodine subsequently will get released into the environment through containment leakage paths. Iodine radionuclide species are considered to cause thyroid damage and their concentration in the environment determines short term emergency planning for NPPs undergoing a severe accident. Iodine is highly reactive and undergo many reactions in the containment. A module named RASAYAN is developed for studying the chemical behavior of iodine within the containment. The RASAYAN module models various mass transfer processes between sump and gas, mass transfer of iodine species on dry and wet surfaces of the containment, chemical reactions in the gas phase, and chemical reactions in the liquid phase. The models are tested for a sample case having a total volume of 0.3 m³ and a sump volume of 0.00332 m³. The interfacial surface area between gas-sump is s 0.0051 m². The initial masses of various iodine species present in the sump and gas volume are specified. The various chemical reactions as mentioned earlier are simulated. The various iodine species namely elemental/molecular iodine, iodide ion, organic iodine, organic compound, and iodate in the containment are as shown in the article