Abstract
Radiation damage in nuclear grade graphite has been investigated using transmission electron microscopy (TEM) and electron energy loss spectroscopy (EELS). Changes in the structure on the atomic scale and chemical bonding, and the relationship between each were of particular interest. TEM was used to study damage in nuclear grade graphite on the atomic scale following 1.92×108 electrons nm−2 of electron beam exposure. During these experiments EELS spectra were also collected periodically to record changes in chemical bonding and structural disorder, by analysing the changes of the carbon K-edge. Image analysis software from the 'PyroMaN' research group provides further information, based on (002) fringe analysis. The software was applied to the micrographs of electron irradiated virgin 'Pile Grade A' (PGA) graphite to quantify the extent of damage from electron beam exposure.
Highlights
Around 90% of the UK’s current nuclear reactors are graphite-moderated generation II Advanced Gas Cooled Reactors
3.1 transmission electron microscopy (TEM) Pile Grade A’ (PGA) graphite was exposed to the electron beam for 600 seconds, corresponding to a flux of 1.92x108 electrons nm-2
The use of image analysis software revealed that 600 seconds of beam exposure broke up fringes; reducing fringe length by approximately 68%
Summary
Around 90% of the UK’s current nuclear reactors are graphite-moderated generation II Advanced Gas Cooled Reactors. As well as moderating the energies of fission neutrons, the graphite core provides structural support, contains the fuel and control rods and allows for coolant flow. Graphite blocks in these reactors are subject to high levels of radiation and as a result they experience chemical and physical property changes which can affect other reactor components. The bulk properties of damage features have been thoroughly experimented upon and theoretical models have been derived This has allowed behavioural changes in the irradiated bulk to be accounted for to some extent, in current and future graphite -based reactor designs, the mechanisms of such processes on the nanoscale still remain uncertain. This work investigates the effect of electron irradiation on nuclear grade graphites to understand the fundamental processes involved in radiation damage
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