Fission product chemistry and transport in reactor accidents

Radioactive iodine has been recognized, since the inception of nuclear power programs, to be radiologically the most hazardous of the radionuclides that could be released from nuclear fuel in the event of an accident affecting the core of a reactor. Therefore, reactor design, licensing, operation, and emergency planning procedures have been dominated by conservative assumptions regarding the fraction of the radioiodine inventory that could be released in a postulated reactor accident. Experimental and theoretical results show, however, that such assumptions are too conservative and that potential radioiodine releases from water-cooled power reactors will be far less than previously assumed, because of the inherent chemical behavior of iodine. Thus, the Canadian Reactor Safety Program includes a comprehensive study of the chemistry of iodine and its precursors in the reactor coolant system (RCS) and in the containment building of the Canada deuterium uranium (CANDU trademark) reactor under accident conditions. On the basis of this work, as well as literature data, the authors have developed the LIRIC (library of iodine reactions in containment) model and data base, which can be used to predict the concentrations and chemical forms of radioiodine in the containment building after an accident. Current effort is focused on developing and validating LIRIC against data obtained in intermediate-scale integrated tests in the Radioiodine Test Facility