Experience in treatment and conditioning of gas cooled reactor metallic degraded spent fuels: the star project

摘要

STAR, namely "Station de Traitement, d'Assainissement et de Reconditionnement" (Treatment, Cleansing and Reconditioning Facility), was created to solve a spent nuclear fuel problem in the Research center of Cadarache (France). About 30 years ago, some 2000 spent irradiated fuel cartridges from GCR French reactors, once examined for R/D purposes, were stored in waterpools. Unfortunately, the sotrage conditions allowed the water of the pool to soak through canisters and to react with the fuel elements, i.e. metallic uranium wrapped by magnesium cladding. Water chemical reactions with metallic uranium formed several compounds among which uranium hydrides and hydrogen. Uranium hydride (UH_3) is well known to readily ignite when in contact with air and additionally, the large quantity of gases released during sotrage leads to the pressurization of containers. This behavior thus prevents a safe transportation of the degraded fuels to reprocessing plants or a safe storage.