Krypton and Helium Irradiation Damage in Yttria-stabilised Zirconia
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Krypton and Helium Irradiation Damage in Yttria-stabilised Zirconia M. Gilbert1, C. Davoisne2, M. C. Stennett3, N. C. Hyatt3, N. Peng4, C. Jeynes4, W. E. Lee1 1
Centre for Advanced Structural Ceramics, Department of Materials, Imperial College London, Exhibition Road, London, SW7 2AZ, UK. 2 Laboratoire de Réactivité et Chimie des Solides, CNRS-UMR 6007, Université de Picardie Jules Verne, 33 rue Saint-Leu, 80039 Amiens, France. 3 Immobilisation Science Laboratory, University of Sheffield, Sir Robert Hadfield Building, Mappin Street, Sheffield, S1 3JD, UK. 4 Surrey Ion Beam Centre, Nodus Laboratory, University of Surrey, Guildford, Surrey, GU2 7XH, UK. ABSTRACT A candidate matrix material for inert matrix fuel (IMF), yttria-stabilised zirconia (YSZ) has been doped with Nd3+ as a surrogate for Pu3+. To simulate and assess the effects of fission gas accommodation and alpha decay on the microstructure, samples of (Y0.1425,Nd0.05,Zr0.8075)O1.904 have been irradiated with 2 MeV 36Kr+ ions, at fluences of 1×1014 and 5×1015 cm-2, and 200 keV 4He+ ions at fluences of 1×1014, 5×1015 and 1×1017 cm-2. Analysis by transmission electron microscopy (TEM) of thin sections prepared by focussed ion beam (FIB) milling revealed damage was only observed at the highest 36Kr+ and 4He+ fluences. Monte Carlo simulations using the TRIM code showed that it is only at these fluences that the level of atomic displacements was sufficient to result in observable defect cluster formation within the material. INTRODUCTION The use of inert matrix fuel (IMF) in either thermal or fast reactors has emerged as the most promising method of maximising plutonium burn-up within a reactor, and so gaining better control over waste stockpiles. IMF is certainly more competitive than mixed-oxide fuel (MOX), which will only produce sufficient plutonium burn-up in fast reactors [1], and although increased plutonium burn-up will result in increased production of minor actinides the overall radiotoxicity of the spent fuel cores would be significantly less than for UO2 or MOX [2]. In such a fuel system, the plutonium carrier is an ‘inert matrix,’ that is, a neutron-inactive or neutron-transparent compound [3]. Candidate IMFs can be divided broadly into two categories: heterogeneous particle fuels, where the plutonium is embedded in the inert matrix, such as with molybdenum, ferritic steels and spinels; and homogeneous fuels, where the plutonium forms a solid solution with the inert matrix, such as with zirconium oxides and yttriastabilised zirconia (YSZ) [4]. The inert matrix must give the fuel stable mechanical behaviour under irradiation and as such must display high thermal conductivity and good pile performance for swelling, fission gas release and pellet-cladding interaction. Although development of such fuel is still at an early stage, LWR tests of Pu-IMFs have shown marked increases in the burn-up of plutonium compared to MOX. Zirconia-based PuIMFs have achieved plutonium consumption rates of up to 142 kg/TWhe, although the thermal
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conductivity of zirc
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