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Science and Technology of Nuclear Installations
Volume 2017, Article ID 8296387, 8 pages
https://doi.org/10.1155/2017/8296387
Research Article

Adsorption Behaviors of Cobalt on the Graphite and SiC Surface: A First-Principles Study

Wenyi Wang,1,2,3 Chuan Li,1,2,3 Jianzhu Cao,1,2,3 and Chao Fang1,2,3

1Institute of Nuclear and New Energy Technology, Tsinghua University, Beijing 100084, China
2Collaborative Innovation Center of Advanced Nuclear Energy Technology, Beijing 100084, China
3The Key Laboratory of Advanced Reactor Engineering and Safety, Ministry of Education, Beijing 100084, China

Correspondence should be addressed to Chao Fang; nc.ude.auhgnist@oahcgnaf

Received 19 October 2016; Revised 13 February 2017; Accepted 12 March 2017; Published 20 March 2017

Academic Editor: Arkady Serikov

Copyright © 2017 Wenyi Wang et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Abstract

Graphite and silicon carbide (SiC) are important materials of fuel elements in High Temperature Reactor-Pebble-bed Modules (HTR-PM) and it is essential to analyze the source term about the radioactive products adsorbed on graphite and SiC surface in HTR-PM. In this article, the adsorption behaviors of activation product Cobalt (Co) on graphite and SiC surface have been studied with the first-principle calculation, including the adsorption energy, charge density difference, density of states, and adsorption ratios. It shows that the adsorption behaviors of Co on graphite and SiC both belong to chemisorption, with an adsorption energy 2.971 eV located at the Hollow site and 6.677 eV located at the hcp-Hollow site, respectively. Combining the charge density difference and density of states, it indicates that the interaction of Co-SiC system is stronger than Co-graphite system. Furthermore, the variation of adsorption ratios of Co on different substrate is obtained by a model of grand canonical ensemble, and it is found that when the temperature is close to 650 K and 1700 K for graphite surface and SiC surface, respectively, the Co adatom on the substrate will desorb dramatically. These results show that SiC layer in fuel element could obstruct the diffusion of Co effectively in normal and accidental operation conditions, but the graphite may become a carrier of Co radioactivity nuclide in the primary circuit of HTR-PM.