Progress in Out-Of-Pile Study of Low Enriched UMo/AlSi Fuel
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1043-T09-10
Progress in Out-Of-Pile Study of Low Enriched UMo/AlSi Fuel Marilyne Cornen1, Xavière Iltis1, Fabrice Mazaudier1, Sylvie Dubois1, and Patrick Lemoine2 1 DEN/DEC, CEA Cadarache, Saint Paul Lez Durance, 13108, France 2 DEN/DSOE, CEA Saclay, Gif sur Yvette, 91191, France
ABSTRACT The main problem we have to face in order to improve the in-pile behaviour of the UMo/Al dispersed fuel, is the instability of the interaction zone, that is formed between the UMo particles and their surrounding Al matrix during irradiation. As the latest irradiations (e.g. IRIS 3 or RERTR 6) tend to prove, addition of Si into the Al matrix seems to be beneficial for the interaction rate decrease. To further understand the role of silicon, a wide out-of-pile interdiffusion study has been launched in CEA-France in 2006 and is still under progress. It has given promising preliminary results by showing a real effect of Si addition upon the interaction zone. The first results related to the physico-chemical aspects of the modified UMo/Al interaction as well as the kinetics aspects of the interaction layer (IL) formation are described in this paper. On a wide range of annealed couples made of UMo7 or UMo10 and Al-Si matrix (Si content ranging from 0.11 wt % to 12 wt %), the IL thicknesses have been systematically measured. Microstructures have been fully characterized by means of optical and scanning electron microscopy and the elementary compositions have been evaluated through EDX analyses. Finally, XRD characterizations and micro-hardness tests have also been performed on a few samples. On the basis of these different results, we discuss first clues about the role played by silicon on slowing down the UMo/Al interaction process. INTRODUCTION UMo/Al dispersed fuel is developed as high-uranium-density fuel in order to convert Materials Testing Reactors (MTR) cores, currently working with U3Si2 or UAlx fuel. This conversion is foreseen to fulfill requirements of nuclear treaty of non-proliferation limiting the use of 235U in fuel to 20% in weight. In operating conditions, the reaction between UMo particles and the Al matrix results in a large interaction zone [1][2] that surrounds the particles and that sometimes leads to the failure of the fuel element because of its poor irradiation behaviour (large porosities development, leading to pillowing and sometimes failure). That is the reason why studies, aimed to stabilize and minimize (or avoid) the interaction zone between fuel particles and the matrix, are performed by several teams. One remedy consists in modifying the interaction layer (IL) composition [3][4] and thickness by adding a new element in the matrix. Based on thermodynamic calculations, on previous out-of-pile diffusion studies and on latest irradiation tests, addition of Si into the Al matrix seems to be a promising solution. Main trends are as follows : - thermodynamic calculations [5][6] : Si has a large affinity for U and not for Al (no intermetallics between Al and Si on the binary phase diagram). U-Si binary compound
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