Power ramp testing of fresh fuel rods with added iodine

In order to study the relationship between the power ramp failure, which has been mainly an issue of BWR fuel integrity, and the out-pile iodine stress corrosion (SCC) experiments, a series of power ramp experiments was performed using fresh fuel rods enriched with iodine. By adopting narrow fuel-clad gap and other measures, cladding stress condition was set to a level somewhat lower than the prototypic condition in irradiated fuels. Iodine atmosphere was adjusted by mixing UO2+x or MoO3 with CsI powder. Three rods were ramp-tested one by one, in which conditions leading to SCC failure were gradually strengthened. No fuel failure occurred, however, even under iodine partial pressure as high as about 1 atm.. From this result and a survey of past in-pile stress corrosion experiments, it was concluded that contribution of iodine to power ramp failure is actually small, vast number of iodine SCC experiments not simulating the actual fuel conditions. (author)