Hot Isostatic Pressing (HIP): A novel method to prepare Cr-doped UO 2 nuclear fuel
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MRS Advances © 2020 Materials Research Society DOI: 10.1557/adv.2020.62
Hot Isostatic Pressing (HIP): A novel method to prepare Cr-doped UO2 nuclear fuel Theo Cordara, Hannah Smith, Ritesh Mohun, Laura J. Gardner, Martin C. Stennett, Neil C. Hyatt and Claire L. Corkhill* NucleUS Immobilisation Science Laboratory, Department of Materials Science and Engineering, University of Sheffield, Sheffield, S1 3JD, United Kingdom
ABSTRACT
The addition of Cr2O3 to modern UO2 fuel modifies the microstructure so that, through the generation of larger grains during fission, a higher proportion of fission gases can be accommodated. This reduces the pellet-cladding mechanical interaction of the fuel rods, allowing the fuels to be “burned” for longer than traditional UO2 fuel, thus maximising the energy obtained. We here describe the preparation of UO2 and Cr-doped UO2 using Hot Isostatic Pressing (HIP), as a potential method for fuel fabrication, and for development of analogue materials for spent nuclear fuel research. Characterization of the synthesised materials confirmed that high density UO2 was successfully formed, and that Cr was present as particles at grain boundaries and also within the UO2 matrix, possibly in a reduced form due to the processing conditions. In contrast to studies of Cr-doped UO2 synthesised by other methods, no significant changes to the grain size were observed in the presence of Cr.
INTRODUCTION Recent media coverage of the Hinkley Point C nuclear power station in the UK has highlighted the extreme costs of generating energy through nuclear fission in light water reactors (LWR). One way that power producers have sought to lower the cost is by developing new fuels that are capable for being “burnt” for longer within the reactor, maximising the amount of energy obtained from each fuel pellet and increasing the flexibility and reliability of LWR fuel [1]. One of the main limitations for how long fuel can remain in the reactor is the ability of the fuel to accommodate fission products, especially fission gases such as Kr, Xe, He, etc. The build-up of these gases at grain boundaries of the UO2, and in the gap between the cladding and the fuel once the grain boundaries have become saturated, results in swelling of the fuel. If the volume of the 45
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fuel exceeds that of the cladding, or the cladding experiences excessive strain from the swollen fuel, the cladding may rupture, resulting in reactor downtime. The solution to this issue is to improve the UO 2 fuel by promoting the growth of larger grains and lengthening the diffusion pathway of fission products to the grain boundaries during fission [2]. This is achieved by doping UO2 with additives; the most extensively applied are Cr2O3 [1,3,4], Al2O3 [5] and a mixture thereof [1,6]. This study aimed to investigate the synthesis of UO
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