The NRC contracted with LLNL to compile this supplement to NUREG-1617 to incorporate additional information specific to mixed uranium-plutonium oxide (MOX) fuel. This supplement provides details on package review guidance resulting from significant differences between spent nuclear fuel from irradiated LEU fuel and that from irradiated MOX fuel. The information presented is not to be construed as having the force and effect of NRC regulations (except where regulations are cited), or as indicating that applications supported by safety analyses and prepared in accordance with Regulatory Guide 7.9 will necessarily be approved, or as relieving anyone from the requirements of any pertinent regulations. The principal purpose of this supplement is to ensure the quality and uniformity of staff reviews of packagings intended for transport of MOX fuel assemblies irradiated in thermal reactors only. It is also the intent of this plan to make information about regulatory matters widely available, and improve communications between NRC, interested members of the public, and the nuclear industry, thereby increasing the understanding of the NRC staff review process. In particular, this supplemental guidance, together with NUREG-1617, assists potential applicants by indicating one or more acceptable means of demonstrating compliance with the applicable regulations.