First-principle Study on Adsorption and Corrosion Behavior of O, Pb and Bi Atoms on SiC Surface

Lead-cooled fast reactor (LFR) is one of the most promising fourth-generation nuclear reactors. However, when the liquid metal coolant, lead-bismuth eutectic (LBE) is in contact with the structural materials in the reactor core, liquid metal atoms and oxygen atoms can cause oxidative corrosion and dissolution of the structural materials. The corrosion process is closely related to the composition, microstructure and operational environment of the materials. Therefore, compatibility between LBE and structural materials is critical for the safe operation of lead-cooled fast reactors. Cubic silicon carbide (3C-SiC) exhibits excellent properties such as low neutron activation, resistance to high-temperature creep, high-temperature oxidation, and high thermal conductivity, therefore was taken as a promising candidate material for key structural components in next-generation advanced nuclear energy systems. As in contact with LBE, SiC generally demonstrates better corrosion resistance than steel under certain experimental conditions, such as in oxygen controlled LBE or low temperature. However, SiC still exhibits different corrosion behaviors under saturated oxygen and irradiation. The adsorption and corrosion behaviors of oxygen (O), lead (Pb), and bismuth (Bi) atoms on the surface of SiC in a lead-cooled fast reactor environment using first-principles calculations were investigated in this study, and the effects of oxygen on the adsorption of Pb and Bi as well as the corrosion of SiC surface were also examined. The stability of several typical low-index crystal surfaces was firstly evaluated based on their surface energy, revealing that the order of crystal surface stability is as follows: (100)^Si＜(100)^C＜(111)^Si＜(111)^C＜(110). The most stable SiC surface for further analysis was determined to be the (110) surface. Adsorption behaviors of O, Pb, and Bi atoms on this surface were then investigated. Results indicate that Pb and Bi atoms preferentially adsorb at carbon hollow sites (H_C), while O atoms favor adsorption at silicon-carbon bridge sites (B_SiC). Furthermore, O atoms exhibit stronger adsorption tendencies compared to Pb and Bi. The oxygen adsorbed on the SiC surface was found to enhance the adsorption of nearby Pb and Bi atoms. Additionally, all three elements, O, Pb and Bi promote the dissolution of carbon and silicon atoms at the surface. Importantly, C atoms are more prone to dissolution than silicon atoms, and the presence of oxygen significantly enhances the dissolution corrosion caused by Pb and Bi on the SiC surface. These findings provide fundamental insights into the mechanisms underlying the interaction between LBE and SiC, offering valuable guidance for the development of advanced nuclear energy systems with enhanced safety and reliability.