Studies on formation and transport of volatile iodine species in radiation field

In a late stage of a severe LWR accident, volatile iodine species are mainly formed by radiation-induced reactions in the water pool of reactor containment, and will be transported by natural and/or forced convection through gas/liquid interface into the gas phase, and then to the environment. The prediction of formation and transport models are examined in a late stage of a severe LWR accident. In order to direct our efforts to elucidate physical effects of natural and/or forced convection conditions on formation and transport of volatile iodine species, the test programs with a dynamic flow type VITA (Volatile Iodine Test Apparatus) system are in progress in JAERI. The transfer model described may be verified through the phase one tests. In which combination between chemical and physical effects will enable the estimation of volatile iodine release in a severe accident. Especially, the transfer model will clarify a long term release in a late stage of the accident. Lots of hydrogen gas are produced in a severe accident of LWR plant. Hydrogen gas reacts easily with OH radical by which iodide ion species is oxidized to form volatile iodine species. Therefore existence of hydrogen gas will suppresses the formations of volatile iodine species. Wall paints are a source of organic compounds following a severe accident. The mechanism of organic iodide formations may be clarified through the phase 3 tests. (authors)