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Vol.9 No.2previous AASP17 (125-126-127-128-129-130-131-132-133-134-135-136-137-138-139-140-141-142) NT85

Academic Articles
Regular Paper Vol.9 No.2 (2017) p.138 - p.144
 

Why graphite ? A Structural Study from the Atomic to the Macrocsopic scales.

 
Zhou ZHOU1,*, Wim BOUWMAN1, Henk SCHUT1, Catherine PAPPAS1
 

1 Department of Radiation Science and Technology, Delft University of Technology, Mekelweg 15, 2629 JB Delft, The Netherlands

 
Abstract
Graphite is an important moderator material in nuclear reactors, which has a complex structure, where complexity refers to two main respects: defects and disorder within the crystallites, and porosity including cracks and pores with lengths varying over six orders of magnitude, from nanometers to millimeters. A comprehensive characterization of the structure, needed e.g. to predict structural changes for long-term safe operation of nuclear reactors, requires the complementary input from several techniques to cover the relevant length scale range. In this work X-ray/neutron diffraction, small angle neutron scattering (SANS), spin echo SANS (SESANS) and neutron imaging have been applied to investigate the structure of nuclear graphite from atomic to macroscopic length scales: from nm to mm. The results provide a key to model and quantify disorder at the atomic level. At the meso- and macro-scopic levels a fractal structure is found that spans over an extraordinary large scale of lengths of 6 orders of magnitude and has fractal dimensions close to 2.5, a case where surface and mass fractal dimensions coincide.
 
Keywords
graphite, diffraction, neutron irradiation, structure characterization, neutron scattering, neutron radiography, stacking fault, fractal
 
Full Paper: PDF
Article Information
Article history:
Received 6 November 2016
Accepted 27 April 2017