FISSION-PRODUCT RELEASE FROM URANIUM-ALUMINUM ALLOY FUEL IN SLOWPOKE-2 REACTORS

Increasing, but still low, radiation fields due to a release of fissio n products have been observed in the light-water-filled reactor contai ner of SLOWPOKE-2 reactors fueled with a highly enriched uranium alloy . To investigate this phenomenon, samples of water coolant and headspa ce gas from the reactor container have been examined by gamma spectros copy methods for several reactors with various burnup. A model has bee n developed to describe the kinetic behavior of the activity concentra tions of the short-lived iodine and noble gas species in the reactor c ontainer water, and the noble gas concentrations in the reactor contai ner headspace. The most likely source of the fission product release i s an area of uranium-bearing material exposed to the coolant at the en d weld line of the fuel elements that originated al the time of fuel f abrication. The fission product release analysis is consistent with ob servations from an underwater visual examination of a high-burnup core and a metallographic examination of archived fuel elements.