Study of oxidation effects on HTGR graphite in air ingress accidents condition

Abstract

The high temperature gas cooled reactor (HTGR) uses helium as a cooler. Graphite is used as a core component material. Graphite is widely used in fuel matrices and structural materials such as moderators and reflectors in the HTGR core. One of the accidents that occur in HTGR reactors is the entry of into the main circuit, which is called the ingress accident. However, at the operating temperature and accident at the core following D-LOFC, the ingress can cause significant oxidation. The level of incoming flow and the oxygen content of air (gas) available depend on the type of reactor feature and the cavity design. Chemical attack by moisture causes oxidation of the graphite material. Air ingress into the primary system is a safety concern. The purpose of this research is to study the effects of oxidation on graphite HTGR during normal operating conditions and ingress accidents. Problem solving using computational simulation methods with the help of the GRSAC code and estimated mechanical strength of graphite using analytic method. The simulation results show that the weight loss of graphite in the depressurized loss of forced circulation (D-LOFC) condition is higher than the pressurized loss of forced circulation (P-LOFC) condition. The total weight loss of HTGR graphite was 0.48%, graphite support was 2.49% at fuel temperature of 1651 °C with a delay of 2500 minutes and a pressurized time of 200 minutes (Weight loss of graphite in one component greater than Idaho National Laboratory results experiment of 0.647%) and oxidation effects on the mechanical strength of graphite (S/So) of 0.625. From the simulation results, it was concluded that material degradation occurs depending on the length of the oxidation and depressurization process. Moreover the simulation results showed that the graphite material used is degraded (damaged).