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Title: Chemical behaviour of a nuclear-grade magnesium alloy during storage
Author: Majchrowski, Tomasz P.
ISNI:       0000 0004 5366 6703
Awarding Body: University of Aberdeen
Current Institution: University of Aberdeen
Date of Award: 2015
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Magnox, a magnesium alloy, was specifically developed in early 1950s for use as a fuel cladding in the British first generation nuclear civilian reactors. Magnesium metal demonstrates outstanding properties for use as a nuclear fuel cladding; however, it has an intrinsic ability to undergo oxidation. This introduces significant limitations during aqueous storage required prior to reprocessing of the spent fuel. A possibility exists for a failure of the dated reprocessing facilities, and therefore this may require for the spent fuel to be kept in the aqueous storage for an extended period of time. In a most extreme case, the corrosion of the fuel cladding may lead to a contamination of the storage facilities with hazardous radioactive fission species and corrosion products. A comprehensive study of chemical behaviour of the Magnox alloy may allow a deeper understanding of the reactivity of the cladding and lead to improvements in management of storage of spent Magnox fuel, thus preventing corrosion induced leakage of hazardous products. The understanding of chemistry of the Magnox alloy during storage may be improved by the development of a novel approach to study corrosion reactions. Infrared spectroscopy and Raman spectroscopy are widely used to study properties of surfaces. In addition, electron microscopy provides with information on the structure and physical appearance of materials. The results show clear evidence for reactivity of the alloy to be greatly influenced by changes induced by nature of cooling processes upon simulated discharge of spent Magnox fuel from a reactor. It is evident that the fast cooling process using water introduces the most deleterious change to the properties of the material. It is understood that presence of water provides with favourable conditions for oxidation of the metal to take place. Opposite effect is observed with slow cooling under an atmosphere of carbon dioxide gas. Further studies using X-ray diffraction suggest that crystallinity of the alloy is increased during simulated reactor exposure and phase segregation takes place during cooling. The latter appears to be dependent on the nature of the cooling process, and thus as a result different strains are applied. Through the studies it is shown that the pond conditions also contribute to control of the behaviour of the fuel cladding. A series of experiments demonstrated that sodium carbonate offers paramount corrosion protection when compared to sodium hydroxide. Systematic investigations allowed for a complete corrosion mechanism of the Magnox cladding to be drawn. It is demonstrated that the effects of present as well past conditions should be assessed and taken into consideration when establishing chemical behaviour of a material.
Supervisor: Not available Sponsor: Engineering and Physical Sciences Research Council ; Nuclear Decommissioning Authority ; University of Aberdeen
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: Magnesium alloys