Radioiodine in gaseous effluents from nuclear power plants

Understanding more about the appearance and behaviour of iodine-131 in nuclear power plants is essential for developing the capability of effectively controlling it and accurately determining its potential dose impact. Based on the above concerns, a multi-faceted programme studying the emanation and transport of radioiodine both in-plant and in the environment has been sponsored by the Electric Power Research Institute (EPRI). Objectives addressed specific areas where information is needed such as: identifying important in-plant sources, determining annual average releases, establishing the chemical forms of the iodine and determining their persistence in the environment, and determining the long-term efficiency of charcoal filters, surface interaction, spiking during estimating typical releases from plants currently operating and for experience in making similar evaluations of future plants. These studies have provided the following information concerning iodine-131: (i) Releases during routine operations from unplanned pathways are relatively small. (ii) The majority of in-plant sources are locally treatable. (iii) This study found the magnitude of power and pressure transient induced iodine spikes to be roughly a factor of ten. (iv) Charcoal adsorbers remain efficient over a relatively long period of time for elemental and inorganic forms of iodine but may not necessarily remain so for organic forms. (v) Surfaces can effect iodine releases significantly. (vi) In the environment iodine tends to convert to organic forms. (author)