Post-irradiation Examination of the Lower Part of the Phébus FPT2 Degraded Bundle

The Phébus PF project is an international programme examining the release behaviour of fission products from irradiated fuel. It is led and being carried out by the French Institut de Radioprotection et de Sûreté Nucléaire (IRSN) at Cadarache in collaboration with the European Commission, EU national research institutes as well as USA, Canada, Korea, Japan and Switzerland. The FPT1 test examined bundle degradation and release under steam atmosphere while FPT2 was carried out under steam-limited conditions. After an initial campaign of macrophotography and examination of the major features of the degraded bundle at ITU, the PIE (Post Irradiation Examinations) continued with the extraction of six selected sites from different levels to perform microscopic examination and analysis of the structures found there. This paper reports on the initial findings in the lower part of the bundle. The macroscopy confirmed the state of the bundle determined by the immediate post-test X-ray and ¿ tomographies carried out at Cadarache. The bundle, as in previous tests, had a characteristic central cavity and a corium pool at one-third height of the bundle, while the upper part showed substantial oxidation, damage and distortion. The corium pool extended the full width of the bundle and appeared to be deeper than that of FPT1. The corium appears to be fully oxidic and has similar amounts of uranium and zirconium with traces of fission products, structural materials and shroud material. Beneath the pool, the cladding was still substantially oxidized and distorted with some fuel-cladding interaction. There was considerable debris beneath the bundle including zones of corium as well as melted metallic structures that probably originated from cladding and reactor structural materials. The extent of damage indicated that the most extreme temperatures were not achieved at this level.JRC.E.2-Hot cell