Chemical Mechanism Of Graphite Dusts Migration In The Primary Loop Of HTGRS

Graphite material is used as neutron moderator and structure material in High Temperature Gas-cooled Reactors（HTGRs） because of its excellent neutron moderation performance and irradiation properties. Meanwhile during the operation of HTGRs, except that some graphite dusts are produced due to collision between the fuel elements, the graphite dusts produced due to the reactions between graphite with impurities in the helium coolant in the primary loop can’t be ignored. And the graphite dusts have an important effect on the save operation of HTGRs.Considering the chemical reaction between impurities in helium coolant and the graphite in the reactor core under high temperature and the possible reverse reaction in the steam generator under relatively low temperature, graphite dusts may be migrated from the high temperature region to the low temperature region in the reactor. And the article created an ideal model to research the migration of the graphite dusts based on the chemical thermodynamics theory and the chemical kinetics theory.According to the chemical thermodynamics theory, it is proved that in the ideal model, the graphite would react with H 2O, O2 and other impurities in the reactor core under high temperature and then the reverse reactions happen under relatively low temperature in the steam generator to produce graphite dusts. Also, the effect of the temperature in the reactor core, the initial amount of H₂ CO and H₂ O is investigated. The results show that more graphite dusts are migrated from the reactor core to the steam generator under higher temperature in the reactor core and given more amount of CO. And more graphite dusts are produced in the steam generator given more amount of H 2 or H. The results also prove that the migration of carbon mainly comes from the reaction of H 2O and graphite.Considering the effect of reaction time and reaction velocity on the equilibrium of reaction, the paper investigated chemical reaction process in the ideal model of the primary loop based on the principle of chemical dynamics. And the migration of graphite dusts was calculated mainly based on the reaction of H₂ O and graphite. The result after 2 seconds of reaction under 1000℃ in the reactor core and then 1 seconds of reaction under 750℃ in the steam generator was got. And the effect of the temperature in the reactor core, the initial amount of H₂, CO and H₂ O on the production of graphite dusts in the steam generator was investigated. Meanwhile, the calculations present that the temperature in the steam generator and the reaction time in the reactor has s ome effect of on the production of graphite dusts.As the research object of this paper is ideal model of the primary loop, the results about the amount of the migration of graphite dusts may be larger than the real results. More research on simulation analysis is needed to take the temperature field and the specific surface chemical reaction of H 2O and graphite in account.