Graphitic matrix material encapsulates tristructural isotropic (TRISO) coated fuel particles and is a structural component for both pebble and cylindrical fuel compacts in high temperature gas reactor (HTGR) designs. In an off-normal event involving steam exposure, the matrix material is exposed to oxidants, leading to degradation of the fuel compact and subsequent exposure of the TRISO particle fuel to oxidizing species. This study presents microstructural characterization of matrix material after exposure to high temperature (1200°C), 48 kPa steam in which the evolved microstructure demonstrated nonuniform degradation. Subsequent Raman spectroscopy determined the nature of the remaining material post-exposure. The electron microscopy characterization suggests and Raman spectroscopic analysis confirms, under off-normal conditions, the carbonized phenolic resin binder is preferentially oxidized ahead of the graphite flake filler and is responsible for the nonuniform degradation and enhanced depth of attack.

石墨基质材料封装了三结构各向同性（TRISO）涂层的燃料颗粒，并且是高温气体反应堆（HTGR）设计中卵石和圆柱形燃料压块的结构组件。在涉及蒸汽暴露的异常情况下，基质材料暴露于氧化剂，导致燃料压块降解，随后TRISO颗粒燃料暴露于氧化性物质。这项研究介绍了暴露于高温（1200°C），48 kPa蒸汽后基体材料的微观结构特征，其中演化出的微观结构显示出不均匀的降解。随后的拉曼光谱法确定了暴露后剩余材料的性质。电子显微镜表征表明，拉曼光谱分析证实，在非正常条件下，