Deliverable 8.10: Chemical and structural / crystallographic properties of simulated fuel pellets and irradiated fuel pellets at the cladding / fuel interface; Work Package 8 SFC

The European Joint Programme on Radioactive Waste Management (EURAD) focusses on the European wide collaboration towards the safe and robust radioactive waste management. In EURAD, the work package (WP) “Spent Fuel Characterisation and Evolution until Disposal” (SFC) foresees to develop and document an experimentally verified procedure to accurately determine the source term of irradiated spent nuclear fuels (SNF), in order to establish a profound scientific database to understand the physicochemical evolution of SNF compounds, i.e., pellets and claddings.
Subtask 3.3 within the EURAD SFC WP contributes to the knowledge increase on pellet-cladding interaction under conditions of extended storage, transport and handling of SNF rods. The aim is to get deeper insights in particularly chemical effects of activation and fission products on the cladding integrity, as well as activity release considerations under dry storage and subsequent transportation conditions.
This final report summarises the experimental results gained within subtask 3.3 until the 48th month of the project. The research groups contributing with experiments are Centro de Investigaciones Energétic, Medioambientales y Tecnológicas (CIEMAT), Karlsruher Institut für Technologie – Institut für Nukleare Entsorgung (KIT-INE), HUN-REN Energiatudományi Kutatóközpont (HUN-REN EK) and Paul Scherrer Institut (PSI). ... mehrAnalyses of pellet-cladding interactions were performed using non-irradiated UO2 fuel, as well as high burn-up UO2 and mixed oxide (MOX) fuel, irradiated in commercial pressurised water reactors (PWR). The morphological and chemical/spectroscopic analyses of fuel-cladding interfaces and claddings were performed by means of X-ray photoelectron spectroscopy (XPS), X-ray diffractometry (XRD), Raman spectroscopy, scanning electron microscopy in conjunction with energy dispersive X-ray spectroscopy (SEM-EDX) as well as X-ray absorption spectroscopy (XAS) to elucidate the pellet-cladding chemical interaction mechanisms and chemical speciation.
The outcomes and insights of the work performed within this report, help to gain a deeper understanding of the processes occurring during interim storage of spent nuclear fuel rods by using state-of-the-art methods in different laboratories. It is demonstrated, that the effect of hydrogen loading, oxygen ingress and temperature affect the integrity of fuel rod claddings during non-accident scenarios. Furthermore, spectroscopic analyses performed on actual SNF specimens, elucidate the importance of research on irradiated specimens in order to describe the different processes occurring during irradiation and subsequent storage of SNF assemblies, which may affect the later handling and conditioning of the fuel rods for disposal in a geological disposal facility.
Altogether, the results obtained within subtask 3.3 of the EURAD SFC WP help to understand the physicochemical parameters and properties of SNF claddings throughout the nuclear fuel cycle. Maintaining the integrity of the cladding tube during the interim storage period until relocation into a geological disposal facility is of utter importance in order to prevent the release of radionuclides into the biosphere.