Stability analysis of SiO_2/SiC coatings on matrix graphite for HTR-10 fuel elements

摘要

The stability behaviours of SiC coatings and SiO_2/SiC coatings in helium with little impurities are studied by HSC Chemistry 4.1. It is found that in helium with a low partial pressure of oxidative impurities, the critical stable temperature of SiC (T_(cp)) increases with the partial pressure of oxidative impurities; but the critical stable temperature of SiO_2 (T_(cs_) depends on both the partial pressure of impurities and the ratio of the amount of impurities to the amount of SiO_2, and T_(cs_) of SiO_2 increases with the partial pressure of oxidative impurities while it decreases with the ratio of the amount of impurities to the amount of SiO_2. The influence of other impurities on T_(cs_) of SiC in He-O_2 is further studied and it is found that the introduction of CO_2, H_2O and N_2 increases T_(cp_ of SiC in He-O_2 while the introduction of H_2, CO and CH_4 decreases T_(cp) of SiC He-O_2. When there exist both oxidative impurities and reductive impurities, their effect of a kind of impurities on T_(cs) of SiO_2 can be suppressed by the other kind of impurities. In HTR-10 operation atmosphere, SiO_2/SiC coatings could keep stable at higher temperature than SiC coatings, so SiO_2/SiC coatings should be more suitable to improve the oxidation resistance of graphite in HTR-10 operation atmosphere compared with SiC coatings.