4.1 Composite materials consist by definition of a reinforcement phase in a matrix phase. In addition, carbon-carbon composites often contain measurable porosity which interacts with the reinforcement and matrix. The composition and structure of the C-C composite are commonly tailored for a specific application with detailed performance requirements. The tailoring involves the selection of the reinforcement fibers (composition, properties, morphology, etc), the matrix (composition, properties, and morphology), the composite structure (component fractions, reinforcement architecture, porosity structure, microstructure, etc.), and the fabrication conditions (forming, assembly, forming, densification, finishing, etc.). The final engineering properties (physical, mechanical, thermal, electrical, etc.) can be tailored across a broad range with major directional anisotropy in the properties.

4.2 Specifications for specific C-C composite components covering materials, material processing, and fabrication procedures are developed to provide a basis for fabricating reproducible and reliable structures. Designer/users/producers have to write C-C composite specifications for specific applications with well-defined composition, structure, properties and processing requirements. But with the extensive breadth of selection in composition, structure, and properties in C-C composites, it is virtually impossible to write a "generic" composite specification applicable to any and all C-C composite applications that has the same type of structure and details of the commonly-used specifications for metal alloys. This guide is written to assist the designer/user/producer in developing a comprehensive and detailed material specification for a specific CMC application/component with a particular focus on nuclear applications.

4.3 The purpose of this guide is to provide guidance on how to specify the constituents, the structure, the desired engineering properties (physical, chemical, mechanical, durability, etc), methods of testing, manufacturing process requirements, the quality assurance requirements, and traceability for C-C composites for nuclear reactor applications. The resulting specification may be used for the design, production, evaluation, and qualification of C-C composites for structures in nuclear reactors.

4.4 The guide is applicable to C-C composites with flat plate, rectangular bar, round rod, and round tube geometries.

4.5 This guide may also be applicable to the development of specifications for C-C composites used for other structural applications, discounting the nuclear-specific chemical purity and irradiation behavior requirements.