Abstract
This report discusses potential design concepts for facilities to qualify existing dual-purpose canisters (DPCs) that are already filled with spent nuclear fuel (SNF) for direct repository disposal using filler materials as a mitigation strategy against criticality after repository closure. . It also briefly describes technical acceptance criteria for filled canisters to be qualified for direct disposal. Acceptable filler materials are being investigated for use in DPCs to ensure that the probability of criticality in DPCs during the disposal time frame is below the probability threshold for inclusion in a repository performance assessment, thereby abating the need to repackage the DPCs into smaller multipurpose canisters for the sole purpose of avoiding postclosure criticality. The effort at Oak Ridge National Laboratory and Sandia National Laboratories includes material property evaluations, fill and verification concepts, and experimentation that will ultimately result in full-scale demonstrations. Filler material selection will be based on specific performance criteria for material properties related to mechanical, nuclear, chemical, and repository performance. This report also describes several types of proposed filler materials for criticality control in DPCs and methods for their introduction.
