Investigation of nuclide inventory of cladding material irradiated in the Goesgen PWR core

Abstract

A characterization of the spent nuclear fuel (SNF) for its radionuclide (RN) inventory is vital for various back-end stages of the nuclear fuel cycle. It concerns both the fuel and the metallic (i.e., cladding and structural material) components of the spent fuel assemblies, where different calculation approaches and methods should be deployed for their characterization. This study concentrates on fuel traces and other impurities within the cladding. During the operating cycles, the Zircaloy cladding is exposed to a considerable amount of irradiation. The impact of the exposure should be checked to assure the integrity of the cladding and thus the safety of the stored spent fuel. Within the work package “Spent Nuclear Fuel Characterization and Evolution until Disposal” (SFC) of the EURAD project, dedicated samples were produced, irradiated and the radionuclide inventory of the cladding was analysed and compared. In parallel a blind test was performed, in which different partners used different codes to simulate the irradiation quantity. The blind test showed good agreement between most of the codes, in particular in view of the small amount of the evolved fuel traces. Furthermore, the presence of actinides, caused by precipitation of uranium on the inner surface of the cladding during manufacturing, was found to be negligible in comparison to precipitation of traces of fuel pellets on the cladding during operation. The good agreement between the simulating codes enables to depict further the initial amount of alloying elements of the cladding material itself in a better manner. In particular specific isotopes of cobalt, nickel and iron, which are directly connected to the unique properties of each cladding material can be better identified based on the accurate measuring techniques used in this study.