SOURCE TERM OF IODINE AND NOBLE-GAS FISSION-PRODUCTS IN THE FUEL-TO-SHEATH GAP OF INTACT OPERATING NUCLEAR-FUEL ELEMENTS

To support "source-term" studies, a series of in-reactor tests have been performed at the Chalk River Nuclear Laboratories to determine the behaviour of short-lived fission products (Xe, Kr, I) in operating UO2 fuel elements. In this paper, a methodology has been developed to present the noble gas activity available for release in the fuel-to-sheath gap of intact fuel during normal reactor operation, including reactor shutdown and startup. Although iodine was not directly observed in these experiments, a model is described to estimate the available gap activity of the short-lived iodine species based on the release kinetics of noble gas. The model is shown to be in excellent agreement with indirectly measured values of 133I and 135I. The fission gas measurements are used to assess the standard ANS 5.4 fission product release model. © 1990.