Measurement of Sources of Iodine-131 Releases to the Atmosphere from Nuclear Power Plants

Measurements of iodine-131 at operating BWR\´s recently reported by the AEC are evaluated in terms of proposed "as-low-as-practicable" regulations. Comparisons are made between measured releases and those calculated using a mathematical model developed by ORNL and used by the AEC in licensing nuclear power plants. It is concluded that iodine-131 releases in ventilation exhaust air are significant with respect to proposed regulations. Using methods given in Regulatory Guide 1.42, it is shown that releases may be 10 times higher than those which would give a potential dose of 15 mRem/year at the site boundary. It is shown that about one-half of the iodine-131 in ventilation air was elemental during power operation. During a refueling shutdown at one plant the average release rate of iodine-131 was 3 times that during power operation, but only a small fraction was elemental. It is concluded that the ORNL model did not represent the processes leading to the appearance of iodine-131 in ventilation exhaust air, although in the aggregate the agreement between calculated and measured releases was very good.