Fission product release tests with uranium dioxide fuel and lead under conditions related to reactor accidents for lead-cooled reactors

Abstract

Tests of fission product release under accident conditions were performed on three samples of irradiated UO2 fuel fragments immersed in molten Pb. Two tests of bare irradiated UO2 fragment samples were conducted under similar conditions for direct comparison. The irradiated fuel samples had been cooled for several years, then encapsulated and trace-reirradiated to populate limited inventories of short-lived fission products (such as 133Xe and 131I). The tests were conducted with sample temperatures between 1570 and 1590 K. The releases from Pb-covered samples under inert conditions were similar to those from bare UO2 under inert conditions. Greater 133Xe releases were observed from Pb-covered samples in oxidizing environments. Release of 140Ba was detected for the Pb-covered sample exposed to air. Under oxidizing conditions, Pb-covered samples retained more 137Cs and 103Ru (delayed onset of release in air and complete retention in steam) as well as 131I.