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Using Intercalation to Simulate Irradiation Damage of Nuclear Graphite

Luyken, Lewis

[Thesis]. Manchester, UK: The University of Manchester; 2012.

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Abstract

This thesis investigates the use of bromine intercalation of graphite as a method to simulate and investigate irradiation damage. In particular this study investigates the effects of intercalation on dimensional change on the macro and micro scales and how these changes combine to affect Young’s modulus.Highly Orientated Pyrolytic Graphite has been used to gather data as a close approximation to single crystal graphite. Three different grades of polycrystalline nuclear graphite have been used to investigate the effect of different microstructure on intercalation and subsequent property changes. The graphites have been characterized by optical microscopy, pycnometry and x-ray powder diffraction and texture measurements. A number of bespoke rigs were designed and manufactured to carry out sorption, tomography and laser vibrometry experiments.The results indicate that the rate of dimensional change for polycrystalline graphites is significantly lower than for single crystal graphites. Modelling of dimensional change suggests that the difference in expansion is due to closure of porosity. Closer investigation of the dimensional change within the microstructure shows that the majority of the dimensional change is driven by expansion of filler particles.The young’s modulus results show an initial increase in modulus followed by a decrease, which corresponds with empirical evidence for irradiated samples. It is postulated that the initial increase in modulus is due to crystal expansion and that the subsequent decrease is due to crack growth. After experimentation some samples show significant cracking which would appear to support this assertion.

Layman's Abstract

This thesis uses a simulation technique to replicate certain aspects of the damage processes experienced by graphite moderators in nuclear reactors. The work investigates how changes to the structure of graphite crystals affect the properties of large polycrystalline components. A number of analytical techniques are used to develop a model to gain further insight into the changes in dimensions and strength experienced by graphitic components in a nuclear reactor.