A post-irradiation study of deposits in the streaming stabilizer of the KEMA suspension test reactor

During critical operation of the KEMA Suspension Test Reactor (KSTR) deposition of fuel particles occurred onto the wall of the stabilizer, situated in the reactor core. After stopping of the KSTR operation the weight of the recovered fuel from the stabilizer amounted to nearly two kilograms. The thickness of the deposition layer varied from 17 to 20 mm. Post-irradiation examination revealed that during critical operation there had been a radial temperature gradient similar to that in some LWR fuel. At the centre the operation temperature was about 30000C, leading to partial fuel melting. In addition migration of uranium, thorium, iron and chromium was found, which can be explained by an evaporation-condensation process. It was noticed further that drifting of the pores was dependent on their position in the fuel layer. (orig.)