Title: Demonstration of Minor Actinide Recycling with Metal Fuel (II): Post-Irradiation Examination Data of Minor Actinide-Bearing Metal Fuel
Publisher: SFEN
Publication Year: 2015
JRC N°: JRC95275
URI: http://global2015papers.com/program.index.html
Type: Articles in periodicals and books
Abstract: The METAPHIX project is a collaboration between CRIEPI and JRC-ITU investigating safety and performance of a closed fuel cycle option based on fast reactor metal alloy fuels containing Minor Actinides (MA: Np, Am, Cm). The aim of the project is to investigate the behaviour of this type of fuel and demonstrate the burning of MA under irradiation. Four U-Pu-Zr-based fuel alloy compounds were fabricated in ITU: base U71Pu19Zr10 fuel; two fuel alloys containing 2 and 5 wt.% MA and Rare Earths (RE: Y, Ce, Nd, Gd); fuel containing 5 wt.% MA. RE were added to reproduce the output of pyrometallurgical reprocessing of LWR spent fuel. The fuels were irradiated in the PHÉNIX reactor with support of CEA, achieving burnups of ~2.5at.%, ~6.0at.% and ~10.0at.%. Post-Irradiation Examination (PIE) is performed at ITU. Pyro-metallurgy separation is also performed, thus covering (at a laboratory scale) all steps of a closed fuel cycle. Non-destructive PIE has been completed on all the irradiated pins, showing no dramatic degradation of the performance for MA-bearing fuel pins. Destructive examinations currently focus on ~2.5at.% and ~6.0at.% burnup fuels; so far they included morphology and structure analysis by optical and scanning electron microscopy, and elemental and phase distribution by electron probe microanalysis (EPMA). Chemical analysis was also performed. Additional techniques are applied in the ongoing campaigns. Microscopy and microanalysis characterization of irradiated METAPHIX fuel revealed the presence of a variety of phases and structural features. A central region, typically separated from the rest of the fuel by a circumferential gap, is evident in most cross sections examined. Radial relocation of base fuel constituents and depletion of Zr from the central region is observed. The outer regions are generally porous, especially at the radial periphery of the fuel. EPMA analysis on ~6.0at.% base alloy fuel allowed identifying numerous phases and morphologies, and quantifying the redistribution of the main constituents and of some fission products and RE. The redistribution of the main elements consists of strong depletion of Zr from the central region and specular redistribution profiles for U and Pu. Concentric rings of repeating morphologies and compositions were found in the central region, bound, at mid-radius, by a dense ζ phase "crust" layer, Zr-depleted and essentially RE-free. A porous phase characterized the outer radial region. Zr-rich secondary phases, in some cases associated with Ru and other noble metals, were identified. RE-rich phases were observed at different radial locations, in some cases including Pd and Rh. New examinations on MA-bearing compounds are assessing the possible association of Am with RE phases and their distribution, in particular at the radial periphery of the fuel. The results of the PIE obtained so far indicate that the presence of MA in the fuel did not cause significant deviations in terms of fuel behavior during low-, medium- or high-burnup irradiation compared with conventional U-Pu-Zr fuels. Ongoing work will extend the base of data and contribute to the full understanding of the irradiation effects on this type of fuel.
JRC Directorate:Nuclear Safety and Security

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