Tritium adsorption and desorption on/from nuclear graphite edge by a first-principles study. (March 2021)

• Record Type: Journal Article
• Authors: Zhang, Mingjun; Wu, Xijun; Yang, Guo; Qian, Nan; Wei, Fei; Zhao, Chao; Liu, Jiayu; Deng, Ke; Liu, Wei
• Is Part Of: Carbon. Volume 173(2021)
• Page Start: 676
• Page End: 686
• Publication Date: 2021-03
• Subjects: Tritium -- Hydrogen -- Adsorption and desorption -- Nuclear graphite edge -- First-principles study; Carbon -- Periodicals; Carbone -- Périodiques; Koolstof; Toepassingen; Electronic journals; 546.681
• DOI: 10.1016/j.carbon.2020.11.014
• Languages: English
• ISSNs: 0008-6223

Abstract

Abstract: 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 (Eac ) for molecular desorption computed by properly accounting for vibrational zero-point energy corrections (ΔEZPE ). Our results showed that, there are three different stages for the desorption of hydrogen isotopes from nuclear graphite, namely stage 1 (200–300 °C), stage 2 (500–700 °C), stage 3 (1000–1100 °C). Our results can provide a theoretical basis for the tritium removal experiment from nuclear graphite. Graphical abstract: Image 1 Highlights: The adsorption of hydrogen on the graphite edge is energetically favored compare to the perfect graphite surface. The best adsorption pathways of hydrogen are found based on simulation. At reasonable temperature and hydrogen pressure, AC+8H is the most stable edge. The activation energy and desorption temperature of hydrogen isotopes desorb from graphite edges are calculated. There are three different stages for hydrogen isotopes desorb from nuclear graphite.