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The Phebus FP project is an international collaboration led by the French Institut de Protection et de Surete Nucleaire (IPSN) at Cadarache in which severe nuclear accidents of various types are simulated.

The degraded FPT1 test bundle of irradiated fuel and debris was examined at ITU Karlsruhe. Metallographic and microprobe analysis of the degraded fuel pieces from the upper bundle as well as fuel from the outer edge from the central cavity was carried out. The fuel from the upper bundle and cavity edge are porous and had remnants of thick oxidised cladding adhering to them. Electron microprobe analysis (EPMA) revealed noticeable amounts of Zr (5-17 wt%) in the UO2 fuel that appeared to have diffused in during attack from the melted cladding or corium. Line scans across the cladding-fuel interface show inter-diffusion of U and Zr, with U diffusing down the grain boundaries of the oxidised cladding. Oxygen measurements on the heavy metal oxide were also carried out and revealed in the upper part of the bundle a superstoichiometry of x=0.3-0.4 in UO(2+x), so that fuel fragments in this position had undergone considerable oxidation. X-ray diffraction analysis of the degraded fuel from the upper bundle will be performed to confirm the structure and stoichiometry deduced from these analyses.

The fuel from the edge of the cavity showed elongated porosity oriented towards the inner melted edge indicating a weakened fuel undergoing corium attack at high temperatures. This outer degraded fuel remained solid because of insufficient Zr to liquefy it. it.

Additional information

Authors: BOTTOMLEY P.D.W, EC-JRC, Institute for Transuranium Elements, Karlsruhe (DE);BREMIER S, EC-JRC, Institute for Transuranium Elements, Karlsruhe (DE);PAPAIOANNOU D, EC-JRC, Institute for Transuranium Elements, Karlsruhe (DE);WALKER C.T, EC-JRC, Institute for Transuranium Elements, Karlsruhe (DE)
Bibliographic Reference: An oral report given at: 7th European Workshop on Modern Developments and Applications in Microbeam Analysis. Held in: Tampere (FI), 6-10 May (2001)
Record Number: 200013763 / Last updated on: 2001-09-18
Original language: en
Available languages: en
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