The microstructural modelling of nuclear grade graphite

Hall, Graham; Marsden, Barry; Fok, S L

doi:10.1016/j.jnucmat.2006.02.082

Cited by 51 publications

(19 citation statements)

References 18 publications

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“…Hopefully the techniques described in this review will provide a useful tool to obtain further understanding. In addition further development of the use of finite element techniques used to model irradiation-induced microstructural changes pioneered by Hall et al 66,88 and more recently by Delannay et al 89 using a modified crystal plasticity model may further enhance mechanistic understanding of these complex processes in respect to the properties investigated here as well as others such as modulus and thermal conductivity.…”

Section: Discussionmentioning

confidence: 93%

Dimensional change, irradiation creep and thermal/mechanical property changes in nuclear graphite

Marsden

Haverty

Bodel

et al. 2016

International Materials Reviews

110

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Since the start of the 'nuclear age' graphite has been employed as a moderator in around 100 nuclear reactors, and today there are still some 30 graphite-moderated reactors operating and there are plans for new Generation IV high-temperature reactors. Many of the graphite moderator reactors now producing power are operating beyond their original design life. Therefore in some cases, to aid the reactor operators and designers, the existing graphite irradiation databases need to be extended either to a higher temperature or higher neutron fluence. Furthermore, data are needed for the different grades of graphite that are available at present. This can either be achieved by expensive, time consuming irradiation programmes or by improving the understanding of the mechanisms and processes which lead to irradiationinduced dimensional and property changes in the graphite core components. This review looks at three of the most important graphite properties which change with exposure to irradiation, namely dimensional change, irradiation creep and thermal expansion. The behaviour of UK AGR, Magnox and an experimental grade of German reactor graphite are explored in some detail. First graphite reactor core design is briefly discussed, giving examples of typical graphite components and core arrangements. Issues related to aging graphite component and core behaviour are illustrated through examples of component internal and thermal stress generation, and issues related to whole core behaviour are also outlined. Second the manufacture and microstructure of different nuclear graphite grades are discussed, highlighting how the choice of raw materials and manufacturing technique influences the graphite properties. Third the coefficient of thermal expansion, dimensional change and irradiation creep are analysed using microstructural and averaging methods which are used to relate crystal to bulk properties by accounting for graphite crystal orientation and porosity. These techniques, which were first applied to nuclear graphite in the 1960s, are extended and discussed with the aim of trying to lend some understanding to the role the microstructural crystallite and porosity distributions play in defining the dimensional stability and properties of virgin graphite, irradiated graphite and stressed graphite.

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Section: Discussionmentioning

confidence: 93%

Dimensional change, irradiation creep and thermal/mechanical property changes in nuclear graphite

Marsden

Haverty

Bodel

et al. 2016

International Materials Reviews

110

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“…Upon further irradiation and once the cracks and pores are fully closed, irreversible net macroscopic expansion occurs. The transition between contraction and expansion is referred to as 'turnaround' [24,25].…”

Section: Irradiation Of Nuclear Graphitementioning

confidence: 99%

Electron irradiation of nuclear graphite studied by transmission electron microscopy and electron energy loss spectroscopy

Mironov

Freeman

Brown

et al. 2015

Carbon

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Structural and chemical bonding changes in nuclear graphite have been investigated during in-situ electron irradiation in a transmission electron microscope (TEM); electron beam irradiation has been employed as a surrogate for neutron irradiation of nuclear grade graphite in nuclear reactors. This paper aims to set out a methodology for analysing the microstructure of electron-irradiated graphite which can then be extended to the analysis of neutron-irradiated graphites. The damage produced by exposure to 200 keV electrons was examined up to a total dose of approximately 0.5 dpa (equivalent to an electron fluence of 5.6x 10 21 electrons cm -2 ). During electron exposure, high resolution TEM images and electron energy loss spectra (EELS) were acquired periodically in order to record changes in structural (dis)order and chemical bonding, by quantitatively analysing the variation in phase contrast images and EEL spectra.

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“…6.5 dpa for an irradiation temperature of 600 C and ca. 8.5 dpa for an irradiation temperature of 430 C [16]. From this, we can postulate that specimen PCEA6.8 is approximately at the turnaround point and specimen PCEA1.5 is before the turnaround point, i.e.…”

Section: Methodsmentioning

confidence: 79%

“…Both irradiation temperature and received dose influence the structure of graphite; this is demonstrated with the varying doses at which turnaround (the point at which irradiation induced net shrinkage stops, and net expansion towards the original dimensions begins) is reached for differing irradiation temperatures [16,25]. With decreasing temperature, the point of turnaround occurs at higher doses.…”

Section: Methodsmentioning

confidence: 95%

“…The displacement of carbon atoms under irradiation leads to the clustering of interstitials between basal planes resulting in c-direction expansion and a-direction contraction [1,13e15]. With increasing dose during reactor operation, the rate of contraction in the a-direction reduces, and eventually the graphite starts to experience net expansion; the critical point at which this reversal occurs is known as "turnaround" which varies with operating temperature [16].…”

Section: Introductionmentioning

confidence: 99%

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Micro to nanostructural observations in neutron irradiated nuclear graphites PCEA and PCIB

Freeman

Mironov

Windes

et al. 2017

Journal of Nuclear Materials

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a b s t r a c tThe neutron irradiation-induced structural changes in nuclear grade graphites PCEA and PCIB were investigated using scanning electron microscopy (SEM), X-ray diffraction (XRD), Raman spectroscopy, transmission electron microscopy (TEM), selected area electron diffraction (SAED) and electron energy loss spectroscopy (EELS). The graphite samples were irradiated at the Advanced Test Reactor at the Idaho National Laboratory. Received doses ranged from 1.5 to 6.8 displacements per atom and irradiation temperatures varied between 350 C and 670 C.XRD and Raman measurements provided evidence for irradiation induced crystallite fragmentation, with crystallite sizes reduced by 39e55%. Analysis of TEM images was used to quantify fringe length, tortuosity, and relative misorientation of planes, and indicated that neutron irradiation induced basal plane fragmentation and curvature. EELS was used to quantify the proportion of sp 2 bonding and specimen density; a slight reduction in planar-sp 2 content (due to the buckling basal planes and the introduction of non-six-membered rings) agreed with the observations from TEM.

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The microstructural modelling of nuclear grade graphite

Cited by 51 publications

References 18 publications

Dimensional change, irradiation creep and thermal/mechanical property changes in nuclear graphite

Dimensional change, irradiation creep and thermal/mechanical property changes in nuclear graphite

Electron irradiation of nuclear graphite studied by transmission electron microscopy and electron energy loss spectroscopy

Micro to nanostructural observations in neutron irradiated nuclear graphites PCEA and PCIB

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