b'Figure 2. Gamma scanning profile of Cs-137 along the fuel pin. Neutron radiography of the pin is also shown as reference.beginning of change in bulk densityPreliminary destructive examinations in the central region of the pin or aas optical microscopy are underway. change in composition. Figure 3 shows a metallography The gamma spectrometry techniqueimage taken from the center of the reveals the behavior of gamma emitterfuel stack. The fuel has swelled to isotopes within the fuel stack. Typicalcontact the cladding for the major isotopes important to understandextent (it is possible to notice some the performance of a metallic fuelpart of circumferential gap not system are Ru-106, Cs-137, Co-60closed) and re-structuring of the and Eu-154. In this specific case allmicrostructure has already begun at isotopes have decayed, due to thethis low burn-up. Rounded porosity long time pass between irradiationin the center of the fuel are visible and exam, apart from Cs-137 whichand from them the existence of is often dissolved in the Na bonda cubic structure can be inferred. between the fuel and the cladding.From the central region towards the The Cs-137 migrates with the Naperiphery various degrees of porosity above the fuel column producingcan be noticed. Close to the cladding a Cs activity spike above the fuel aslarge and swirled porosity are under observed in Figure 2.218 2019|AFC ACCOMPLISHMENTS'