Behavior Comparison And Kinetics Simulation Of Nuclear Graphite Corroded By Oxygen And Vapor

As the moderator, reflector and structural material in High TemperatureGas-cooled Reactor （HTGR）, nuclear graphite is one of the key materials to maintainnormal reactor operation. However, graphite can be easily oxidized by oxidizing gasesunder high temperature, which may threaten reactor safety. The issue of nucleargraphite corrosion has been discussed widely, but the mechanism of graphite corrosionstill remains unclear. Here in our work, gas concentration measurement is applied tostudy the oxygen and vapor corrosion behavior of IG-110, a brand of nuclear graphitewhich will be applied in HTGR. A set of high temperature gas corrosion facility is setup, and gas chromatography is used to detect its outlet gas concentration data. Testshave been carried out to ensure the reliability of the whole set of facility.Both for graphite powder and balls corroded by oxygen, not all oxygen reacts withgraphite below600°C; but above600°C, oxygen all reacts, and the corrosion productchanges from CO₂to CO as temperature goes up.For vapor corrosion, corrosion doesnot happen below800°C, but becomes severe at1242°C. Corrosion product is H2andCO. The danger of vapor corrosion is much less than that of oxygen corrosion, becauseit happen at a higher temperature, and vapor consumes less graphitewhen same moles ofvapor and oxygen reacts with graphite.The change in inlet oxygen concentration does not alter corrosion mechanism bothfor graphite powder and balls. The outlet concentration of each product gas just riseslinearly as inlet oxygen concentration goes up.A thorough comparison between powder and ball corrosion shows that the6mmgraphite balls has better corrosion resistance than powder, because it has less productgas than powder under same temperature. It can be inferred that the actual ball used inHTGR, which is6cm in diameter, may have even better corrosion resistance.Chemical reaction software Chemkin is also used, and Perfectly-Stirred Reactormodel is applied to simulate the reaction mechanism of graphite powder corrosion. Thesimulation result under different temperature and inlet oxygen concentration suits wellwith experiment data. Simulation shows that at low temperatureregion,the main reactioncontrolling corrosion rate is C（S）+O₂<=> O+CO, with activation energy of250kJ/mol, and at high temperature region the main rate controlling reaction becomes C（S） +CO₂<=>2CO, with activation energy of340kJ/mol. This simulation result ofactivation energy matches previous results.