1.1 ,The purpose of this Guide is to provide methodologic information specific to highly graphitized, low surface area materials used in the nuclear industry. It applies to nitrogen adsorption measurements at 77 ,K for the characterization of graphite pore structure, such as: (1) specific surface area, (2) cumulative volume of open pores (for pore sizes less than about 300 ,nm), and (3) distribution of pore volumes as a function of pore sizes (for pore sizes less than about 30 ,nm). These properties are related to graphite’,s reactivity in oxidative environments, graphite’,s ability to retain fission products, and gas transport through graphite’,s pore system.