National Science Center
Kharkov Institute of Physics and Technology

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Microstructural researches of candidate HTGR graphites for nuclear power systems generation IV in the initial state and irradiated in the oxygen environment by electrons at the ELIAS accelerator

Analytical methods of metallography and electron microscopy obtained experimental data on post-radiation tests for the microstructure determination and porosity analysis of reactor graphites of ARV, MPG, and GSP grades irradiated at the ELIAS electron accelerator NSC KIPT in oxygen at the temperatures of the nominal and hypothetical emergency operation of the HTGR for the fourth generation nuclear power systems.

 As a result of the systematization of the obtained data, it is set:

 changes in the graphites microstructure induced by irradiation are due to considerable porosity, open pore surface and the presence or absence of amorphous carbon in the pores of the samples in the initial state;

 pores have a high reactivity in high-temperature oxidation due to the activation of the surface under electron irradiation, which entails a 6-8-fold increase in the graphite oxidation rate;

Graphite microstructure after oxidation in oxygen environment for 30 min. when irradiated with electrons   Graphite microstructure after oxidation in oxygen environment for 30 min. when irradiated with electrons   Graphite microstructure after oxidation in oxygen environment for 30 min. when irradiated with electrons
a)   b)   c)

Fig. 1 - Graphite microstructure after oxidation in oxygen environment for 30 min. when irradiated with electrons with an energy of ~ 2.5 MeV at 800 °C (increase × 1000): a) ARV; b) MPG; c) GSP

 a lower reaction capacity in case of oxidation in the oxygen environment and a greater corrosion resistance of GSP graphite in comparison with graphites of the ARV and MPG grades both without radiation, and in case of radiation by electrons, is caused by existence in it pyrocarbonic globules and carbonic tubes

The received results, first of all, are important for implementation of the systems approach to the selection of graphite materials which can be used in heat-generating and absorbing of nuclear reactors core and also in constructional components of nuclear power systems generation IV.
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