Study of oxidation effects on HTGR Graphite in air ingress accidents condition (Elfrida Saragi1,a), Roziq Himawan2

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 air into the main circuit, which is called
the air ingress accident. However, at the operating temperature and accident at the core following D-LOFC, the air
ingress can cause significant oxidation. The level of incoming air 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 air 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 oC 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).