1.1 ,This guide covers the preparation and characterization of working reference materials (WRM) that are produced by a laboratory for its own use in the analysis of nuclear fuel cycle materials. Guidance is provided for proper preparation, packaging, and storage, requirements for characterization, homogeneity and stability considerations, and establishing traceability of WRMs to certified reference materials by a defined, statistically sound characterization process. While the guidance provided is generic for nuclear fuel cycle materials, detailed examples for some materials are provided in the appendixes.