Frequency and Consequences Associated with a Steam Generator Tube Rupture Event

The results of a study into the frequency of steam generator tube rupture (SGTR) events are presented, including estimates on the upper and lower bound frequencies for U-tube and once-through steam generator plants and single- and multiple-tube ruptures. In addition, commercial pressurized water reactor operational data have been researched and iodine spiking data used to develop data bases of maximum resultant iodine concentrations and release rates. The frequencies and iodine spiking magnitudes are compared with other studies, and conclusions are drawn regarding current guidelines for analysis of this design-basis transient. The frequency of SGTR events, based on past occurrences, is high enough to warrant continued inclusion of this transient as a design-basis accident. An analysis of historical iodine spikes indicates that the current guidelines are overly conservative regarding the magnitude of iodine released to the reactor coolant system and could be relaxed while maintaining adequate protection for the public.