Oxidative Stability of Carbon by Thermal Gravimetric Analysis

The Pebble Bed Modular Reactor (PBMR) is a High Temperature Gas Cooled nuclear Reactor (HTGR) with numerous inherent passive safety features. Graphite is the most important material of construction for the reactor core and the fuel pebbles. PBMR accident scenarios include uncontrolled air ingress into the reactor. Understanding the high temperature behavior of the graphite materials under such conditions is vital for design and accident modeling purposes [1]. Graphitic materials have a very high thermal stability compared to ordinary organics. The high degradation temperatures are beyond the capability of Differential Scanning Calorimetry (DSC) and thus necessitate the use of Differential Thermal Analysis (DTA) or Thermogravimetric Analysis (TG). The oxidative stability of two graphite samples was investigated using temperature scanning TG. It was found that air oxidation of a natural graphite sample commenced at temperatures that were significantly lower than those observed for a synthetic graphite sample. The natural graphite also showed peculiar bimodal mass loss rates.