PUBLICATION: CARBON

AUTHORS: Zhang, MJ; Wu, XJ; Yang, G; Qian, N; Wei, F; Zhao, C; Liu, JY; Deng, K; Liu, W

 

The removal of tritium from irradiated nuclear graphite is one of the key targets of nuclear graphite decontamination. Here, we employ first principle density functional theory (DFT) to study its adsorption and molecular desorption on the most common edges and their reconstructions. The calculated adsorption energy ranges from -2.6 to - 5 eV, depending on the edge structure and the hydrogenation level, and are much larger than on the bulk of graphite. The hydrogenation level increases with the increase of hydrogen partial pressure, and drops rapidly at high temperature. The pathways to fully saturated edges are then determined for each edge variant and the activation energy (E-ac) for molecular desorption computed by properly accounting for vibrational zero-point energy corrections (Delta E-ZPE). Our results showed that, there are three different stages for the desorption of hydrogen isotopes from nuclear graphite, namely stage 1 (200-300 degrees C), stage 2 (500-700 degrees C), stage 3 (1000-1100 degrees C). Our results can provide a theoretical basis for the tritium removal experiment from nuclear graphite. (C) 2020 Elsevier Ltd. All rights reserved.

 

LINKS: http://dx.doi.org/10.1016/j.carbon.2020.11.014